Search

SUMMARY A detailed palaeointensity study was performed using the modified Thellier method on 18 Quaternary and Neogene volcanic units, ages ranging from 0.08 to 5.98 Ma, in Central Anatolia, Turkey. Robust data, which were estimated from 12 lava units in the study area, significantly increase the database of palaeomagnetic data, directions and absolute palaeointensity for the Anatolian region covering the time window back to ∼6 Ma. Previous studies sensitively dated the samples, except for one site dated in this study. The palaeointensity (VDM) value from the upper Miocene site estimated as 48.6 ± 9.2 μT (10.1 × 1022 ± 1.9 Am2) fits well into the Neogene VDM range in the data archives. For Pliocene samples with an age of 4.7 Ma, the palaeointensity was calculated to be 21.0 ± 4.7 μT. For these samples, an inclination of +42.9° was determined, and together with the results of low palaeointensity and normal polarity, this corresponds to the Nunivak or Sidufjall subchrons. These are normal polarity chrons within the Gilbert Chron which predominantly has reversed polarity. Palaeodirectional data and field strength with age between 0.08 and 2.57 Ma clearly showed the Brunhes and Matuyama Chrons in the Pleistocene. Three new data with 25.0 ± 7.9 μT (age 1.84 Ma), 59.7 ± 8.2 μT (age 2.15 Ma) and 79.6 ± 19.3 μT (age 2.57 Ma) from the early Pleistocene period significantly contribute to global data archives, which lack palaeointensity data from similar latitude range. The average VDM values for nine Pleistocene sites were calculated to be 51.5 ± 16.4 μT (10.3 × 1022 ± 3.7 Am2). According to the comparison of our data with the palaeointensity database, field model record and previous studies of the Pleistocene, significantly high field strength obtained from Central Anatolia, located in the Northern Hemisphere, could have occurred due to asymmetry between the Northern and Southern Hemispheres during the Pleistocene.

In the Mesoamerican region, arid or hydrological variable conditions are commonly interpreted from 4 ka onwards. It is not well known how these changes modified the Mesoamerican monsoon system, which were the main atmospheric-oceanic forcings involved and their effect in the Pre-Classic Mesoamerican societies' history. Here, we study the possible link between paleoclimatic changes and decreased social development of societies in Mesoamerica during the Pre-Classic period (4.3 ka to 2.2 ka), which correspond to the Middle-Late Holocene transition. We also describe the principal oceanic-atmospheric mechanism related. We employed a partly laminated sediment sequence from La Alberca maar lake in the central Mexico highlands by means of environmental magnetism and comparing versus X-ray fluorescence (XRF), pollen, and δ18O analyses. Increased concentrations and preservation of ferrimagnetic minerals and enhanced detrital load as described by the XRF Ti counts reveal the occurrence of variable hydrological conditions between ~4.4 ka to 2.2 ka. These conditions coincide with the onset of high-frequency latitudinal variations of the Intertropical Convergence Zone (ITCZ) and the rise of ENSO and Pacific decadal oscillation activity. We suggest that variable hydrological conditions affected the development of Mesoamerican agrarian societies stressing agricultural production during the Pre-Classic period.

Continuous paleosecular variations reconstructed from sedimentary archives have remarkably deepened our insights into the dynamics of the Earth's magnetic field as well as the chronological purpose. Nevertheless, to construct reliable sedimentary paleomagnetic records in diagenetic reducing sediments is challenging generally due to the pervasive magnetic mineral diagenesis. The relict magnetic minerals are residuals after diagenesis and probably able to record a depositional remanent magnetization, thus it is worthy to explore their paleomagnetic potentials. For this study, two Black Sea sediment cores covering the past 8 ka were subjected to mineralogical and paleo- and rock magnetic analyses. Paramagnetic pyrite framboids are pervasive in the studied sediments deposited under anoxic bottom water conditions in the Black Sea. In addition, relict magnetic minerals of ferrous hemoilmenite, Fe-Mn and Fe-Cr spinels, and magnetite inclusions are also present in the studied cores. Compared to the previous published paleomagnetic results from the same cores over the last glacial period (20–30 ka) which are dominated by detrital (titano-)magnetite particles, the studied relict magnetic mineral samples exhibit a similar behavior in recording the depositional remanent magnetization. Furthermore, the obtained paleosecular variations spanning the past 8 ka reproduce the high intensity patterns observed in the regional archeomagnetic and volcanic datasets. Thus, the successful reconstruction of paleomagnetic secular variations from the anoxic Black Sea sediments greatly extend the application of paleomagnetism in sediments deposited in water with a reducing sub-surface environments from where paleomagnetic data are generally sparse.

Holocene history of the Indian monsoon reconstruction using environmental magnetism has emerged as an effective paleoclimate proxy with its fast, efficient, and repeatable measuring procedures. In this chapter, we have made an attempt to provide a broad synthesis of the available sediment magnetic records obtained from the loess-paleosols (central Himalaya), lake (western India), delta and lagoon sequences (eastern coast Godavari and Iskapalli). Variations in magnetomineralogical S-ratio values of sediment archives were combined and stacked as a surrogate for Holocene paleomonsoon change. High S-ratio results from low weathering rates were attributed to more wet conditions, while low S-ratios were related to dry conditions from intense low temperature oxidation. Combining the S-ratio data from diverse environments collectively revealed three broad climate phases with minor oscillations during the past 20 ka. These are (i) a step-wise intensification of the SW monsoon since the Last Glacial Maximum with its peak level at ∼9.0 ka, (ii) the prevalence of a prolonged dry spell along the eastern coast and western India at ∼3.5 ka that led to the collapse of the Harappan civilization, and (iii) reduction of monsoon rainfall during the period of global cooling events such as Last Glacial Maximum, Younger Dryas, and Little Ice Age. We observed that instead of the concentration-specific magnetic susceptibility (χ), the combined remanence S-ratio seems to be a more sensitive proxy responding to the monsoon variability both at centennial and millennial time scales.

Our study on the exact timing and the potential climatic, environmental, and evolutionary consequences of the Laschamps Geomagnetic Excursion has generated the hypothesis that geomagnetism represents an unrecognized driver in environmental and evolutionary change. It is important for this hypothesis to be tested with new data, and encouragingly, none of the studies presented by Picin et al . undermine our model.

The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage in vicinity of the modern Polar Front over a complete glacial-interglacial cycle (i.e., the past 140,000 years), based on sediment grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with weakened current strength during glacials and a stronger circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We infer that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations modulated Pacific-Atlantic water exchange via the “cold water route” and potentially affected the Atlantic Meridional Overturning Circulation and marine carbon storage., How the Antarctic Circumpolar Current (ACC) changed on glacial-interglacial time scales is not well known. Here, the authors present a 140,000 year long sediment record from the Drake passage and show both glacial-interglacial as well as millennial-scale variability which are linked to Atlantic variability and marine carbon storage.

A full‐vector paleosecular variation (PSV) record (inclination, declination, and relative paleointensity) from the pen‐ultimate glacial (130–180 ka) could be constructed from a total of 12 sediment cores recovered from the Arkhangelsky Ridge in the SE Black Sea. Stacking of the individual partly fragmented records was achieved by a detailed correlation using high‐resolution data records from X‐ray fluorescence scanning, Ca/Ti and K/Ti log‐ratios, as well as magnetic susceptibility. Age constraints are provided by a detailed composite oxygen isotope stratigraphy from three of the cores, correlated to U‐Th‐dated speleothem oxygen isotope records from Hungary and Turkey. The temporal resolution of the stacked paleomagnetic data records is 200 years. Practically, this data set is the first high‐resolution PSV record for SE Europe/SW Asia from marine isotope stage 6, comprising inclination, declination and relative paleointensity. Besides an easterly swing in declination at ∼159 ka and a pronounced intensity low together with low inclinations at ∼148 ka, both not reaching an excursional PSV index of >0.5, the obtained directional variations reflect only normal PSVs, with a PSV index of, Key Points: Reconstructed geomagnetic field variation record between 180 and 130 ka from Black Sea sediments. First full‐vector paleosecular variation record from marine isotope stage 6 for Southeast Europe/Southwest Asia. Intensity maxima occur at 166.5 ka and at 141.0 ka., Chinese Scholarship Council, Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/501100001659

Reconstructions of the geomagnetic field on long timescales are important to understand the geodynamo processes in the Earth’s core. The geomagnetic field exhibits a range of variations that vary from normal, dipole–dominated secular variation to geomagnetic excursions and reversals. These transitional events are associated with significant directional deviations and very low intensities. Here we present a new, global geomagnetic field model spanning the period 70–15 ka (GGFSS70) that includes three excursions: Norwegian–Greenland Sea, Laschamps, and Mono Lake/Auckland. The model is built from nine globally distributed, high–resolution, well–dated, sedimentary paleomagnetic records. The GGFSS70 indicates that the axial–dipole component changed sign for about 300 years in the middle of the Laschamps excursion (41.25–40.93 ka). The energy comparison at the Earth’s surface reveals that the axial–dipole energy is always higher than the non-axial-dipole except over the Laschamps. In the other two excursions, the axial-dipole is reduced by about one order of magnitude for the Norwegian–Greenland Sea excursion and less for the Mono Lake/Auckland. At the core–mantle boundary, the large–scale non-axial-dipole power is comparable to the axial-dipole power, except over the excursions when the axial-dipole decreases, though less clearly for the Mono Lake/Auckland excursion. The axial dipole moment over the 15–70 ka varies from 0 to 8 ×1022 Am2, with an average and standard deviation of 5.1±1.5 ×1022Am2. The Laschamps excursion is associated with growth and poleward movement of reversed flux patches and reversed field in the tangent cylinder at the excursion midpoint, which is not the case for the other two excursions. Plain Language Summary Earth possesses a magnetic field that is constantly changing in time and space. Its source is located in the outer core and the mechanism by which the geomagnetic field is generated is known as the geodynamo. Studying the field on long timescales contributes to a better understanding of the source processes. The geomagnetic field can be approximated as a dipole, except during reversals and excursions. The past 70,000 years period contains three geomagnetic excursions, the Norwegian--Greenland Sea (65,000 years ago), Laschamps (41,000), and Mono Lake/Auckland (34,000). During the excursions, the intensity is globally very low and the poles may or may not change polarity. However, they always recover to the original polarity in contrast to the reversals, when the North Pole becomes South and the South becomes North. To model the long--term field variations, we rely on geological archives, sediments and rocks, that record and preserve the geomagnetic field. We selected the best sedimentary records in terms of magnetic components and good age control. The Laschamps excursion is the most pronounced event in this period, has the lowest dipole moment, and is observed globally. The other two events occur at regional scales and have only a moderate dipole moment decrease.

SUMMARY Diluted slurry with an initial density of 1.30 g cm−3 prepared from natural glacial Black Sea sediments was deposited under controlled field conditions between 1.72 and 114.21 µT. Compaction was achieved by evaporation of a portion of the pore water from the open sample boxes over 4–7 d until a density of about 1.44–1.55 g cm−3 was reached. Magnetizations M acquired in a magnetic field B follow a slightly non-linear function with M ∼ B0.82. Similar relationships were also obtained for palaeointensity estimates for the artificial samples by using normalization by low-field susceptibility, anhysteretic remanent magnetization and saturation magnetization. All samples are characterized by a magnetic fabric typical for natural sediments as checked by determining the anisotropy of magnetic susceptibility. The sediments’ anisotropy is in the range of 6–7 per cent and it is characterized by an oblate anisotropy ellipsoid with its small axis perpendicular to the deposition plane. According to scanning electron microscope imaging low-Ti magnetite particles present in the used sediments are in the range of 1–30 µm with the majority of particles 2–5 µm in size. Obtained results confirm the conclusion from other magnetostratigraphic studies that the Laschamps geomagnetic polarity excursion in the Black Sea area exhibited field values as low as 2.8 µT in its transitional phase between normal and reversed polarity.

Reversing the field Do terrestrial geomagnetic field reversals have an effect on Earth's climate? Cooper et al. created a precisely dated radiocarbon record around the time of the Laschamps geomagnetic reversal about 41,000 years ago from the rings of New Zealand swamp kauri trees. This record reveals a substantial increase in the carbon-14 content of the atmosphere culminating during the period of weakening magnetic field strength preceding the polarity switch. The authors modeled the consequences of this event and concluded that the geomagnetic field minimum caused substantial changes in atmospheric ozone concentration that drove synchronous global climate and environmental shifts. Science , this issue p. 811

Northern Hemispheric high-latitude climate variations during the last glacial are expected to propagate globally in a complex way. Investigating the evolution of these variations requires a precise synchronization of the considered environmental archives. Aligning the globally common production rate variations of the cosmogenic radionuclide (10)Be in different archives provides a tool for such synchronizations. Here, we present a (10)Be record at

The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage over the past 140,000 years, based on grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with reduced ACC intensity during glacials and a more vigorous circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We hypothesize that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations regulated Pacific-Atlantic water exchange via the “cold water route” and affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

A full vector paleomagnetic record, comprising directional data and relative paleointensity (rPI), was derived from 16 sediment cores recovered from the southeastern Black Sea. The obtained data were used to create a stack covering the time window between 68.9 and 14.5 ka. Age models are based on radiocarbon dating and correlations of warming/cooling cycles monitored by high‐resolution X‐ray fluorescence (XRF) elementary ratios as well as by ice‐rafted debris (IRD) in Black Sea sediments to the sequence of ‘Dansgaard‐Oeschger’ (D‐O) events defined from the Greenland ice core oxygen isotope stratigraphy. The reconstructed prominent lows in paleointensity at about 64.5 ka, 41.2 ka and 34.5 ka are coeval with the Norwegian–Greenland Sea, the Laschamps, and the Mono Lake excursions, respectively. For a further analysis, the stacked Black Sea paleomagnetic record was converted into one component being parallel to the direction expected from a geocentric axial dipole (GAD) and two components perpendicular to it (EW, inclined NS), representing definitely only non‐GAD components of the geomagnetic field. Discussions of the field configurations at the Black Sea site are focused on the three excursional events. The Norwegian‐Greenland Sea excursion was dominated by a decaying axial dipole and persisting weak non‐dipole field, with directional variations still within the range of normal secular variations. The Laschamps excursion comprises two full polarity transitions and a short stable interval of reversed polarity in between. The Mono Lake excursion was mostly dominated by a non‐dipole field, though with a less pronounced weakening of the axial dipole component.

Lake Sihailongwan in Jilin province, NE China, provides the first continuous and almost entirely seasonally laminated sediment record on the East Asian mainland comprising the complete Holocene, the Late-glacial period, and large parts of the Last Glacial. Sediment and palynological proxy data provide a finely resolved regional environmental history of the East Asian monsoon. A varve-based chronology (shl-vc2) has been established for the last 65,000 years and allows a detailed comparison with other long regional and global palaeoclimate records. Vegetation density of the study area depends, on the long run, on precessionally forced insolation changes, with superimposed millennial-scale variability during the Last Glacial. Periodic increase of organic carbon content and thermophilous tree species like Ulmus and Fraxinus and contemporary decrease of shrub Alnus precisely mirror millennial-scale climatic variations primarily known from Greenland ice-cores as Dansgaard-Oeschger cycles, as well as Late-glacial period climate changes. Percentages of trees & shrubs pollen and in particular lake productivity-related data reveal substantial differences between interstadial intensities, with those between 50 and 60 ka BP being more pronounced than the following ones.

We report here on results of palaeo- and rock magnetic investigations of two sediment cores from the Upper Congo deep-sea fan. The sediments have a high organic content and contain a heterogeneous Fe-mineral assemblage with biogenic magnetite and detrital (Ti-)magnetite as the main magnetic carrier minerals. Pyrite, hematite, and Fe-oxyhydroxides were identified by comparing high-temperature magnetic susceptibility curves with those from Fe-minerals of known composition. According to AMS 14C dates, the 6.8 m-long profile spans the last 37 kyr. Sediments older than 20 ka are affected by reductive diagenesis that has led to a loss of the fine-grained magnetic mineral fraction. Sediments younger than 20 ka have stable magnetizations. Characteristic remanent magnetization records of inclination and declination were obtained for each core. There is a little agreement between these records, modelled curves, and other sediment records from Equatorial Africa, so no composite record could be established. The cores are not ideal relative palaeointensity recorders and estimates using different normalizers did not yield consistent signals from both cores. Normalization methods used for relative palaeointensity estimation were not developed for sediments that contain large amounts of ultra-fine-grained biogenic magnetite; therefore, the relative palaeointensity estimates should be considered with caution. However, in view of the incoherent picture given by the scarce available palaeointensity information from the region off South-West Africa, the GeoB6517-2 record may provide a tentative relative palaeointensity record for comparison, at least for the past 10 kyr.

Detailed magnetic analysis of the four sediment cores from Lake Van, Eastern Turkey dating back to 9.4 cal ka BP were carried out for discriminating and correlating tephras and laminated sediments in four different cores. Six tephra units (T0, T1, T2, T3, T4 and T5) with distinct magnetic properties were identified in the cores. The tephra units are characterized by ferrimagnetic material, with a grain size in the pseudo single domain (PSD) range. There is no significant correlation between magnetic susceptibility peaks of the different tephra units except for the tephra T1 and T2. On the contrary ARM profiles show significant correlations as remanent magnetization indicators. The tephra units T1 and T2, have a higher magnetic susceptibility and a higher intensity of remanent magnetization, and finer grain size than the other tephra units. The results suggest that there is a clear difference between the magnetic properties of the different tephra units and the lake sediments. Our findings show that also differential deposition of volcanic material including magnetic mineral occurs during the transport with distance from the volcanic source.

A comprehensive magnetostratigraphic investigation on sixteen sediment cores from the southeastern Black Sea yielded a very detailed high-quality paleosecular variation (PSV) record spanning from 20 to 15 ka. The age models are based on radiocarbon dating, stratigraphic correlation, and tephrochronology. Further age constraints were obtained by correlating four meltwater events, described from the western Black Sea, ranging in age from about 17 to 15 ka, with maxima in K/Ti ratios, obtained from X-ray fluorescence (XRF) scanning, and minima in S-ratios, reflecting increased hematite content, in the studied cores. Since the sedimentation rates in the investigated time window are up to 50 cm ka−1, the obtained PSVs records enabled a stacking using 50-yr bins. A directional anomaly at 18.5 ka, associated with pronounced swings in inclination and declination, as well as a low in relative paleointensity (rPI), is probably contemporaneous with the Hilina Pali excursion, originally reported from Hawaiian lava flows. However, virtual geomagnetic poles (VGPs) calculated from Black Sea sediments are not located at latitudes lower than 60°N, which denotes normal, though pronounced secular variations. During the postulated Hilina Pali excursion, the VGPs calculated from Black Sea data migrated clockwise only along the coasts of the Arctic Ocean from NE Canada (20.0 ka), via Alaska (18.6 ka) and NE Siberia (18.0 ka) to Svalbard (17.0 ka), then looping clockwise through the Eastern Arctic Ocean.

After a comprehensive geophysical prospecting the Quaternary Mýtina Maar, located on a line between the two Quaternary scoria cones Komorní hůrka/Kammerbühl and Železná hůrka/Eisenbühl, could be revealed by a scientific drilling at the German–Czech border in 2007. Further geophysical field investigations led to the discovery of another geological structure about 2.5 km ESE of the small town Neualbenreuth (NE-Bavaria, Germany), inferred to be also a maar structure, being the fourth volcanic feature aligned along the NW–SE trending Tachov fault zone. It is only faintly indicated as a partial circular rim in the digital elevation model. Though not expressed by a clear magnetic anomaly, geoelectric and refraction seismic tomography strongly indicates a bowl-shaped depression filled with low-resistivity and low-velocity material, correlating well with the well-defined negative gravity anomaly of − 2.5 mGal. Below ca. 15 m-thick debris layer, successions of mostly laminated sediments were recovered in a 100 m-long sediment core in 2015. Sections of finely laminated layers, likely varves, rich in organic matter and tree pollen, were recognized in the upper (22–30 m) and lower (70–86 m) part of the core, respectively, interpreted as interglacials, whereas mostly minerogenic laminated deposits, poor in organic matter, and (almost) barren of tree pollen are interpreted as clastic glacial deposits. According to a preliminary age model based on magnetostratigraphy, palynology, radiocarbon dating, and cyclostratigraphy, the recovered sediments span the time window from about 85 ka back to about 270 ka, covering marine isotope stages 5–8. Sedimentation rates are in the range of 10 cm ka−1 in interglacials and up to 100 cm ka−1 in glacial phases. The stratigraphic record resembles the one from Mýtina Maar, with its eruption date being derived from a nearby tephra deposit at 288 ± 17 ka, thus supporting the age model of the inferred Neualbenreuth Maar.

Varved lake sediments provide climatic records with seasonal to annual resolution and low associated age uncertainty. Robust and detailed comparison of well-dated and annually laminated sediment records is crucial for reconstructing abrupt and regionally time-transgressive changes as well as validation of spatial and temporal trajectories of past climatic changes. The VARved sediments DAtabase (VARDA) presented here is the first data compilation for varve chronologies and associated palaeoclimatic proxy records. The current version 1.0 allows detailed comparison of published varve records from 95 lakes. VARDA is freely accessible and was created to assess outputs from climate models with high-resolution terrestrial palaeoclimatic proxies. VARDA additionally provides a technical environment that enables us to explore the database of varved lake sediments using a connected data model and can generate a state-of-the-art graphic representation of a multisite comparison. This allows the reassessment of existing chronologies and tephra events to synchronize and compare even distant varved lake records. Furthermore, the present version of VARDA permits the exploration of varve thickness data. In this paper, we report in detail on the data-mining and compilation strategies for the identification of varved lakes and assimilation of high-resolution chronologies, as well as the technical infrastructure of the database. Additional palaeoclimatic proxy data will be provided in forthcoming updates. The VARDA graph database and user interface can be accessed online at https://varve.gfz-potsdam.de (last access: 15 September 2020), all datasets of version 1.0 are available at https://doi.org/10.5880/GFZ.4.3.2019.003 (Ramisch et al., 2019).

Paleomagnetic records reconstructed from globally distributed marine sediments have greatly improved our understanding of long-term paleosecular variations and geomagnetic excursions. Nevertheless, questions regarding to the development of the geomagnetic field anomaly in the Southern Atlantic Ocean and the asymmetric geomagnetic field between Northern and Southern Hemispheres are not yet satisfactorily resolved. Paleomagnetic data, particularly from the Southern Hemisphere, is needed to better define the global geomagnetic field configurations spanning paleosecular variations and excursions. In this study, three sediment cores (PS97-085, PS97-84, PS97-079) recovered from the Drake Passage, Southern Ocean were subjected to detailed rock magnetic and paleomagnetic investigations. Preliminary age models were obtained by correlating their magnetic susceptibility to the ẟ18O master record from Dome C, Antarctica. In addition, rock magnetic records of the studied PS97 cores were further correlated to that of core PS67/197-1 with AMS 14C age constraints. The results from PS97 cores are thus continuously covering the past about 110 ka. Rock magnetic results indicate titanomagnetite is the dominant magnetic carrier in the studied PS97 cores. Relative paleointensities (RPI) derived from these PS97 cores are comparable with the regional relative paleointensity records and the South Atlantic paleointensity stack (SAPIS). Additionally, anomalous inclinations at about 41 ka and 35 ka, observed in core PS97-085, are coeval with the Laschamps and the Mono Lake excursions, respectively. This study provides new paleomagnetic records from the Southern Ocean, though further age constrains are needed to consolidate the paleomagnetic interpretations. The up to now obtained paleomagnetic records, together with previous studies from the Southern Ocean, are aiming to clarify the asymmetric pattern of non-dipole geomagnetic field between Northern and Southern Hemispheres.

The Antarctic Circumpolar Current (ACC) is the largest current system in the world, linking the Pacific, Atlantic and Indian Ocean basins. However, the variability of the ACC, which plays a fundamental role on global ocean circulation and climate variability, is still poorly constrained. This information is crucial for understanding the role of the ACC on global ocean circulation in response to global warming. Here, we reconstruct changes in the ACC over the past 155,000 years based on sediment grain size variations recorded in a highly-resolved marine sedimentary record from the central Drake Passage near the Polar Front. Our results show significant changes in the ACC during the last glacial cycle and a remarkable boundary between the glacial and interglacial periods. Substantial decreases (~33% to ~47%) in the ACC flow speed from interglacial to glacial period, which corroborates and extends results of previous studies along the subantarctic northern limit of the ACC into the central Drake Passage. This strong variation of ACC likely plays a significant role in regulating Pacific-Atlantic water mass exchange via the “cold water route” and could significantly affect the Atlantic Meridional Overturning Circulation. Superimposed on these glacial-interglacial changes, we found strong millennial-scale variations in ACC current speed, increasing in amplitude close to full glacial conditions. We hypothesise that the central ACC increases its sensitivity to Southern Hemisphere millennial-scale climates oscillations, likely associated with westerlies’ wind stress and Antarctic sea ice extent once glacial conditions fully formed.

Reconstructing global patterns of past climate change requires large-scale networks of paleoclimatic archives. Generating paleoclimatic networks relies on precise synchronization of individual records with robust age control. The detailed age constrains of continuous varved lake sediments and the good preservation of isochrones from supra-regional extreme events make these records ideal for constructing large scale continental paleoclimatic networks. Yet, a global synthesis of varved lake archives is missing.Here we present the VARved sediments DAtabase 1.0 (VARDA 1.0), the first global data compilation for varve chronologies and associated palaeoclimatic proxy records. VARDA 1.0 uses a connected data model provided by a state-of-the-art graph database, enabling custom generations of synchronized paleoclimatic networks. We report on compilation strategies for the identification of varved lakes and assimilation of high-resolution chronologies. Existing chronologies have been re-assessed and harmonized using a novel approach that infers information on sedimentation rates enclosed in varve thickness records. This information provides detailed information on the priors required for Bayesian age-depth modelling and strongly improves these results. Additionally, a synthesis of tephra layers from volcanic eruptions provides supra-regional isochrones for synchronizing even distant varved lake records. The current version (VARDA 1.0) comprises 261 datasets from 95 varved lake archives, including chronological information from 14C dating and varve thickness measurements, but also palaeoclimatological proxy data. We further explore potential applications of such networks in paleoclimatic studies, such as identifying leads and lags of regional climate change, large-scale model-data comparisons or differentiated proxy responses between archives. The VARDA graph-database and user interface can be accessed online at https://varve.gfz-potsdam.de.

Available sea surface temperature (SST) records from the subantarctic SE Pacific reveal large amplitude changes at orbital time-scales. High sedimentation rates along the southern Chilean margin provided higher resolution records back to ~70 ka showing millennial-scale SST variations paralleling temperatures reconstructed in Antarctic ice-cores.Here we present high-resolution millennial-scale SST and subsurface temperature records based on core MR16-09 PC03 covering a complete glacial/interglacial cycle back to Marine Isotope Stage 6, including a high-resolution record of the Eemian. Located on the Chilean margin at the bifurcation of the Antarctic Circumpolar Current into the Peru-Chile Current to the North and the Cape Horn Current to the South, core MR16-09 PC03 is in an ideal position to study the continent-ocean interactions, including changes in water masses, ice sheet formation, precipitation and vegetation.We used alkenones and GDGTs to determine SST (UK’37) and subsurface temperatures (TEXH86; 0 - 200 m), and integrated these results with XRF core scanner and planktic δ18O data (G. bulloides). During the Eemian, SSTs and subsurface temperatures were ~2° C and ~4° C, higher than during the Holocene, respectively. The high Eemian temperatures at our site are roughly consistent with the few available subantarctic SST records. The large temperature difference in the subsurface water masses between the Eemian and the Holocene could be explained by a deeper thermocline during the Eemian. During the last glacial period, the strongly fluctuating temperatures averaged ~8° C at the surface and ~6° C in the subsurface. The relative amount of C37:4 alkenone (%C37:4) show a drastic increase during the glacial period, especially in Marine Isotope Stage 3 in concentration. High %C37:4 values suggest increased freshwater supply, which could be related to fluctuations of the Patagonian Ice sheet and/ or precipitation on the adjacent land. The sedimentation rate and other terrigenous proxies, e.g. Titanium, BIT, Iron and Alkanes, confirm such increased and highly variable terrestrial inputs.

Due to the meridional extension and prominent orography, the Central Andes of NW Argentina act as a topographic barrier to the moisture-bearing easterly winds. This result in contrasting climate conditions and a steep E-W rainfall gradient with high precipitation on the eastern flanks and increasing aridity westwards into the Puna plateau. Laguna Comedero is a shallow lake located in the subtropical forest of the Yungas in the eastern flank of the Argentine Eastern Cordillera (24°06'54.7" S - 65°29'7.2" W, 2,035 m a.s.l.). About 80% of the total annual precipitation (~1300 mm, Los Nogales station 1958-1989) occurs between November and March, controlled by the dynamics of the South American Monsoon System (SAMS). This region is considered sensitive to shifts in the SAMS, as well as the superposition of other large-scale phenomena (e.g. El Niño Southern Oscillation, Pacific Decadal Oscillation) but the timing and extent of precipitation changes prior to the instrumental period in this area are still largely unknown.Here we present a combination of XRF core scanning, CN elemental analyses and stable isotopes of an 11 m-long sediment record from this lake for reconstructing the regional late Holocene climate history in this region of South America. Our results reveal a prominent shift in sedimentation, from detrital brown event-triggered silt and clay deposition and sandy intervals in the lower part of the core to an alternation of gray clastic and black organic-rich intervals in the upper 3.5 m. Below this shift in sedimentation, low TOC values (mean 0.34%) and high values of elements indicative of detrital sediments (e.g. Ti) suggest a dominance of catchment erosion processes. High TOC values of up to 20.5% in the organic-rich intervals in the uppermost 3.5 m likely reflect substantial terrestrial organic matter influx as suggestd by C/N atomic ratios around 17. δ13COM values in these intervals (-28.8 to -22.2‰) reflect the contribution of the Yungas forest (-27.9 to -27.2‰) surrounding the lake, dominated by Alnus acuminata, Polypepis australis, Podocarpus parlatorei, among other subtropical tree species. Alnus forest is related to >1000 mm/yr rainfalls. The pronounced alternation of organic-rich and detrital sediments in the upper 3.5 m suggest highly variable lake conditions that might be either influenced by climate and/or catchment changes and is the focus of further investigations. Preliminary dating suggests that the increase in organic matter deposition in the lake occurred at the beginning of the last millennium (ca. AD 1,000). A more detailed chronological framework is in progress including a paleomagnetic reconstruction for this area.

Over the last 12 years, from magnetostratigraphic investigation of 16 sediment cores from the Southeastern Black Sea, a high-resolution paleo-secular variation record spanning from 64 to 14 ka could be compiled. Due to glacial erosion in the catchment sedimentation rates are in the range of 25 to 50 cm/kyr. Obtained relative paleointensity data reflect a highly dynamic geomagnetic field during that time. By comparison to absolute paleointensity data it could be estimated that the field intensity varied between about 3 µT and 60 µT (present day field intensity 48 µT). The lowest value is associated with the Laschamps polarity excursion centred at 41.0 ka. Its N-R and R-N transitions lasted just 200 and 270 years, respectively, with a 440 year long stable reversed phase (intensity max. 12 µT, VGP latitudes higher than 65°S) in between. The second deepest intensity minimum at 64.5 ka with about 8 µT is associated with fast directional changes but still in the range of normal secular variation (VGP latitudes above 45 °N). This is likely the mid-latitude expression of the postulated Norwegian-Greenland Sea excursion, as derived from Arctic marine sediments. In contrast to this, the Mono Lake excursion at 34.5 ka was characterized by intermediate field intensities of 20 µT, but clearly non-dipolar directional variations, indicating a multi-polar field configuration during the excursion. Another moderate field minimum of 25 µT at 18.5 ka is coeval with the postulated Hilina Pali excursion. But, despite high sedimentation rates (50 cm/kyr), only normal secular variation amplitudes were recorded in Black Sea sediments with VGP latitudes higher than 60°N. Ongoing re-sedimentation experiments with Black Sea mud indicate a very rapid lock-in of the paleomagnetic signal and a fairly linear relationship between field strength (1.8 to 110 µT) and acquired magnetization. Thus it can be concluded that data from Black Sea sediments reflect true geomagnetic field behaviour.

SUMMARY Magnetostratigraphic and geochemical analyses were performed on two sediment cores recovered from the Sea of Marmara to investigate geomagnetic field variations over the last 70 ka. A chronology for each of the two cores was developed from eight AMS 14C datings, tephrochronology, and tuning of Ca concentrations with stadials and interstadials observed in Greenland ice core oxygen isotope data. Based on the age models, cores MD01–2430 and MRS-CS19 reach back to 70 and 32 ka, respectively. High average sedimentation rates of 43 cm kyr–1 for core MD01–2430 and 68 cm kyr–1 for core MRS-CS19 allow high-resolution reconstruction of geomagnetic field variations for the Sea of Marmara. Mineral magnetic properties are sensitive to glacioeustatic sea level changes and palaeoclimate variations in this region, reflecting the variable palaeoenvironmental conditions of the Sea of Marmara during last 70 ka. Despite the impairment of the palaeomagnetic record in some stratigraphic intervals due to early diagenesis, relative palaeointensity variations in the Sea of Marmara sediments correlate well with similar records derived from other regions, such as the nearby Black Sea and the GLOPIS-75 stack. The directional record derived from the Sea of Marmara cores exhibits typical palaeosecular variation patterns, with directional anomalies at 41 and 18 ka, representing the Laschamps and postulated Hilina Pali excursions, respectively. Both directional anomalies are also associated with palaeointensity minima. A further palaeointensity minimum at 34.5 ka is likely related to the Mono Lake excursion, with no directional deviation documented in the Sea of Marmara palaeomagnetic record so far.

Mediterranean climates are characterized by strong seasonal contrasts between dry summers and wet winters. Changes in winter rainfall are critical for regional socioeconomic development, but are difficult to simulate accurately1 and reconstruct on Quaternary timescales. This is partly because regional hydroclimate records that cover multiple glacial–interglacial cycles2,3 with different orbital geometries, global ice volume and atmospheric greenhouse gas concentrations are scarce. Moreover, the underlying mechanisms of change and their persistence remain unexplored. Here we show that, over the past 1.36 million years, wet winters in the northcentral Mediterranean tend to occur with high contrasts in local, seasonal insolation and a vigorous African summer monsoon. Our proxy time series from Lake Ohrid on the Balkan Peninsula, together with a 784,000-year transient climate model hindcast, suggest that increased sea surface temperatures amplify local cyclone development and refuel North Atlantic low-pressure systems that enter the Mediterranean during phases of low continental ice volume and high concentrations of atmospheric greenhouse gases. A comparison with modern reanalysis data shows that current drivers of the amount of rainfall in the Mediterranean share some similarities to those that drive the reconstructed increases in precipitation. Our data cover multiple insolation maxima and are therefore an important benchmark for testing climate model performance.

The Saalian was one of the largest glaciations during the Quaternary with an ice sheet extending considerably wider into the Eurasian continent than during other glacials. Orbital variations caused the ice sheet to switch between growing and shrinking. The partial retreat of the ice sheet and meltwater discharge resulted in global sea-level rise and increased lake levels of inland seas with broader environmental implications. During Marine Isotope Stage 6 (MIS 6), meltwater entered the formerly enclosed Black Sea at least twice as documented in a δ18O record from Anatolian speleothems. Here we present a sedimentary record from the Black Sea “Lake” covering MIS 6 and provide evidence for three meltwater periods coinciding with insolation maxima (BSWP-6-1: 180-167 ka BP, BSWP-6-2: 160-145 ka BP, BSWP-II: 133-130 ka BP). While δ18Oostracods and Sr/Caostracods point to pronounced meltwater supply and decreasing salinity, 87Sr/86Srostracods shed light on meltwater sources and pathways. During all three periods, meltwater drained most likely via the Dnieper and Volga into the Black and Caspian Seas and connected both basins. Relatively low 87Sr/86Srostracods values during the oldest meltwater period suggest melting solely of the eastern Eurasian Ice Sheet. In contrast, during the younger meltwater periods, exceptional high 87Sr/86Srostracods values point towards additional meltwater from the western Eurasian Ice Sheet. A surplus from melting glaciers in the Tian Shan and Pamir Mountains that finally entered the Caspian Sea via the Amu Darya and Sry Darya probably amplified the input of high radiogenic Sr-isotope water. We also show that higher temperatures and productivity suggest Dansgaard-Oeschger-like climate variability during the first half of MIS 6.

The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial–interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before ∼ 320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe / Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high- to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial–interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial–interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes.

Palaeoecological evidence of intra-Saalian warm stages in Central Europe, which was strongly affected by glacial and periglacial processes during the major Middle and Late Pleistocene cold periods, is ambiguous so far. Recently, the first continuous sedimentary sequence of Central Europe containing the Saalian complex (MIS 8–6) with the Eemian interglacial in stratigraphic superposition was recovered from the newly discovered Neualbenreuth Maar (NE-Bavaria). Here we present palynological results from this record allowing us to critically discuss the available biostratigraphical evidence of alternating intra-Saalian warm-cold intervals from Central Europe. The new pollen record from the Neualbenreuth Maar comprises a continuous record of vegetation and climate changes encompassing four warm stages and five cold periods. The dominance of cold and dry tolerant herbs and the sparse representation of pioneer trees and shrubs during most parts of the sequence indicate open landscapes of steppe to woody-steppe character typical of late Middle and Late Pleistocene glacial periods in Central Europe. The pollen assemblages of the warm stage in the upper part of the core clearly support its correlation with the Eemian interglacial. The three pre-Eemian warm stages represent terrestrial analogues of the marine isotope stages (MIS) 7e, 7c, and 7a. During each of these intervals forests were established, but the reduced abundances and lower diversity of thermophilous and sub-oceanic elements in comparison to the Eemian attest to a weak interglacial character. Each of these interglacials shows a similar vegetation succession and only minor differences in the vegetation composition. The intervening stadial periods represent a strong (MIS 7d) and a moderate (MIS 7b) climate deterioration, respectively. The vegetation and climate succession during the Saalian glacial-interglacial complex of Neualbenreuth is broadly in line with the respective palynological signature from the Velay record (French Massif Central) and the Hoogeveen interstadial (The Netherlands). In contrast, there is only limited correspondence with most pollen records from northern and southern Central Europe, which were hitherto classified as MIS 7.

Paleofire reconstructions of past interglacials using molecular burning residues preserved in lake sediments compared to vegetation and climate reconstructions to understand future fire regime shifts

State‐of‐the‐art paleoclimate research strongly depends on the availability of time‐equivalent markers as chronological control to disentangle interrelationships in the climate system from regional to global scale. Geomagnetic reversals are regarded as excellent age constraints because they are global events and independent from climatic conditions. However, spatial variations of timing and internal dynamics of reversals may limit their precision. Our 1.2 Ma high‐resolution (~25 cm/kyr) sediment record from Lake Ohrid is promising to precisely depict the Matuyama‐Brunhes (MB) reversal and the Jaramillo subchron. Two generations of diagenetic ferrimagnetic minerals are present in glacial intervals of the Lake Ohrid record. Early diagenetic greigite acquired a quasi synsedimentary chemical magnetization, while a late diagenetic greigite formation, triggered by the upward diffusion of H2S‐rich waters, obscures the polarity record at the top of the Jaramillo. Interglacial intervals are unaffected by greigite formation, likely due to low iron concentrations. Based on an orbitally tuned age model with tephrostratigraphic markers, the base of Jaramillo can be precisely dated to 1072.4 ka, and the MB reversal to 778.5 ka. Both polarity reversals occurred very rapidly in our record, lasting 2.3 and 1 kyr, respectively. Our results reveal that the dipole component of the Earth's magnetic field fell below the nondipole components only for a short duration in the Mediterranean region. The comparison of the timing of the MB boundary across different archives implies that the onset of the reversal provides a more synchronous age marker compared to often used midpoint ages.

Marine and lacustrine sediments represent an important source of global paleomagnetic data. Although it is usually assumed that detrital iron oxides record most of the magnetic signal in sediments, iron sulfides—which form during bacterial sulfate reduction—can also represent a significant source of sedimentary magnetism. Knowing how sulfate reduction impacts sedimentary magnetism is critical to the interpretation of paleomagnetic records. Here, we show that three distinct types of magnetic particles can be produced by bacterial sulfate reduction, each of which impacts the bulk sediment magnetism in a distinct way. We combined magnetic force microscopy and electron probe microanalysis to image magnetic mineral extracts from Dead Sea sediments from a glacial period and an interglacial period. In sediments from the dry interglacial period, during which bacterial sulfate reduction was suppressed, we found greigite framboids (Fe3S4) with strong intergrain magnetic interactions. Contrastingly, in sediments from the wet glacial period, which experienced extensive sulfate reduction, pyrite (FeS2) is the dominant sulfide phase. High-resolution magnetic imaging of glacial pyrite reveals that greigite is present as single-domain particles within the pyrite. We also found that as titanomagnetite grains undergo bacterially mediated alteration to form pyrite, the original magnetic grains become divided into smaller regions, which potentially facilitates acquisition of secondary magnetization by the reorganization of these magnetic domains. Our results provide a previously undocumented mechanism by which bacterially mediated alteration can overwrite primary detrital magnetic records.

Historical events are sometimes expressed in destruction layers. We present here a study in which aspects of construction, destruction, and chronostratigraphy of fired mud bricks were explored using archaeomagnetism, infrared spectroscopy, and micromorphology. We measured 88 oriented samples mostly collected from one stratum, dated ca. 1000 B.C.E., representing a destroyed late Canaanite (late Iron Age I) city in Tel Megiddo, Israel. Firing temperatures, evaluated from infrared spectroscopy, micromorphology, and high‐temperature magnetic susceptibility cycles, range between 300°C and 800°C. Samples studied in one archaeomagnetic site yield a single stable magnetization vector in demagnetization experiments. Archaeomagnetic site means of three standing walls are grouped near the expected direction of the ancient geomagnetic field. We propose that walls in the destruction layer were constructed from sun‐dried mud bricks that later burned during the destruction. Collapsed bricks and tilted walls show variable directions, diagnostic for the relative timing of collapse and cooling of bricks, during and following the destruction event. In addition, we attempt to assign stratigraphic affiliation based on archaeomagnetic considerations to standing walls, which are spatially disconnected from the studied destruction layer. Altogether, this study demonstrates the usefulness of archaeomagnetism to understanding site formation processes related to fire and destruction.

Western Poland is located in the central European climatic transition zone, which separates the mild and humid Atlantic climate of Western Europe and the East European continental climate. This region is sensitive to lateral shifts of the European climate zones and is particularly suitable for reconstructing Holocene climate variability. This paper presents detailed analyses of the sedimentary record from Lake Strzeszynskie since the Late Pleistocene. These include smear-slide and thin-section observations, X-ray fluorescence core scanning, magnetic susceptibility measurements, pollen analyses, and radiocarbon dating. The sediment record reveals three distinct sedimentary units consisting of: (1) an alternation of sand layers and laminated silt and clay deposits accumulated prior to 14,600 cal yr BP; (2) faintly laminated calcareous sediments intercalated with organic matter-rich layers deposited between 14,600 and 10,200 cal yr BP; and (3) massive calcareous mud deposited after 10,200 cal yr BP. The Holocene period is marked by nine phases of organic-rich sedimentation and enhanced Fe deposition, which occurred at ca. 10.1, 9.3, 6.4–6.1, 5.5–5.1, 4.7–4.5, 2.7–2.4, 1.3–1.2, 0.8–0.6, 0.4–0.2 kyr cal BP. These phases are associated with high lake levels and correspond with wet periods recognized in several other records from Poland and central Europe. These phases partly coincide with North Atlantic cold periods, which may suggest that high lake levels are triggered by an ocean-continent linking mechanism.

Geophysical Journal International, 195 (1), ISSN:0956-540X, ISSN:1365-246X

High-resolution pollen and dinoflagellate cyst records from sediment core M72/5-25-GC1 were used to reconstruct vegetation dynamics in northern Anatolia and surface conditions of the Black Sea between 64 and 20 ka BP. During this period, the dominance of Artemisia in the pollen record indicates a steppe landscape and arid climate conditions. However, the concomitant presence of temperate arboreal pollen suggests the existence of glacial refugia in northern Anatolia. Long-term glacial vegetation dynamics reveal two major arid phases ~64–55 and 40–32 ka BP, and two major humid phases ~54–45 and 28–20 ka BP, correlating with higher and lower summer insolation, respectively. Dansgaard–Oeschger (D–O) cycles are clearly indicated by the 25-GC1 pollen record. Greenland interstadials are characterized by a marked increase in temperate tree pollen, indicating a spread of forests due to warm/wet conditions in northern Anatolia, whereas Greenland stadials reveal cold and arid conditions as indicated by spread of xerophytic biomes. There is evidence for a phase lag of ~500 to 1500 yr between initial warming and forest expansion, possibly due to successive changes in atmospheric circulation in the North Atlantic sector. The dominance of Pyxidinopsis psilata and Spiniferites cruciformis in the dinocyst record indicates brackish Black Sea conditions during the entire glacial period. The decrease of marine indicators (marine dinocysts, acritarchs) at ~54 ka BP and increase of freshwater algae (Pediastrum, Botryococcus) from 32 to 25 ka BP reveals freshening of the Black Sea surface water. This freshening is possibly related to humid phases in the region, to connection between Caspian Sea and Black Sea, to seasonal freshening by floating ice, and/or to closer position of river mouths due to low sea level. In the southern Black Sea, Greenland interstadials are clearly indicated by high dinocyst concentrations and calcium carbonate content, as a result of an increase in primary productivity. Heinrich events show a similar impact on the environment in the northern Anatolia/Black Sea region as Greenland stadials. Open-Access-Publikationsfonds 2013 peerReviewed

The relationship between climatic-environmental changes and its cultural implications in the Northern Mesoamerican Frontier is poorly understood, because of the lack of high-resolution well-dated records. In this work we present a high-resolution paleoclimate and paleoenvironmental reconstruction of the Northern Mesoamerican Frontier for the last 6700 yr BP, using laminated sediments from La Alberca maar lake, Guanajuato. For this purpose, we used different techniques such as X-ray fluorescence, microfacies analysis, magnetic parameters, bulk sedimentary δ18O, δ13C records and twelve AMS 14C ages. In Prehistory times, different climatic events are well defined. At around 5600 yr BP, our data indicate the end of Holocene Thermal Maximum and a subsequent decline of monsoon strength is observed. Variable hydrological conditions start to dominate around ∼4400 yr BP consistent with the rise of latitudinal variations of the Intertropical Convergence Zone. A rise in sedimentation rate and increase in Amaranthaceae pollen percent occurred between ∼225 CE- 600 CE are linked to the beginning of agricultural activities by the Chupicuaro Pre-Hispanic culture. In Historical times, during the Epiclassic period, we interpreted two drought events around ∼700–790 CE and ∼810–880, supporting the Armillas’ theory that drastic climate events motivated the social changes and shift in the geographic position of Northern Mesoamerican Frontier. In the final part of the Postclassic period a pluvial interval is associated with the rise of Tarascan culture in the area. We propose that droughts and pluvial periods between 600 and 1500 CE are connected with SSTs variability of the Atlantic Basin.

We report the results of our investigations on the catchment area, surface sediments, and hydrology of the monsoonal Lonar Lake, central India. Our results indicate that the lake is currently stratified with an anoxic bottom layer, and there is a spatial heterogeneity in the sensitivity of sediment parameters to different environmental processes. In the shallow (0-5 m) near shore oxic-suboxic environments the lithogenic and terrestrial organic content is high and spatially variable, and the organics show degradation in the oxic part. Due to aerial exposure resulting from lake level changes of at least 3m, the evaporitic carbonates are not completely preserved. In the deep water (>5 m) anoxic environment the lithogenics are uniformly distributed and the delta C-13 is an indicator not only for aquatic vs. terrestrial plants but also of lake pH and salinity. The isotopic composition of the evaporites is dependent not only on the isotopic composition of source water (monsoon rainfall and stream inflow) and evaporation, but is also influenced by proximity to the isotopically depleted stream inflow. We conclude that in the deep water environment lithogenic content, and isotopic composition of organic matter can be used for palaeoenvironmental reconstruction.

The recent and fossil pollen data obtained under the frame of the multi-disciplinary international El'gygytgyn Drilling Project represent a unique archive, which allows the testing of a range of pollen-based reconstruction approaches and the deciphering of changes in the regional vegetation and climate. In the current study we provide details of the biome reconstruction method applied to the late Pliocene and Quaternary pollen records from Lake El'gygytgyn. All terrestrial pollen taxa identified in the spectra from Lake El'gygytgyn were assigned to major vegetation types (biomes), which today occur near the lake and in the broader region of eastern and northern Asia and, thus, could be potentially present in this region during the past. When applied to the pollen spectra from the middle Pleistocene to present, the method suggests (1) a predominance of tundra during the Holocene, (2) a short interval during the marine isotope stage (MIS) 5.5 interglacial distinguished by cold deciduous forest, and (3) long phases of taiga dominance during MIS 31 and, particularly, MIS 11.3. These two latter interglacials seem to be some of the longest and warmest intervals in the study region within the past million years. During the late Pliocene–early Pleistocene interval (i.e., ~3.562–2.200 Ma), there is good correspondence between the millennial-scale vegetation changes documented in the Lake El'gygytgyn record and the alternation of cold and warm marine isotope stages, which reflect changes in the global ice volume and sea level. The biome reconstruction demonstrates changes in the regional vegetation from generally warmer/wetter environments of the earlier (i.e., Pliocene) interval towards colder/drier environments of the Pleistocene. The reconstruction indicates that the taxon-rich cool mixed and cool conifer forest biomes are mostly characteristic of the time prior to MIS G16, whereas the tundra biome becomes a prominent feature starting from MIS G6. These results consistently indicate that the study region supported significant tree populations during most of the interval prior to ~2.730 Ma. The cold- and drought-tolerant steppe biome first appears in the reconstruction ~3.298 Ma during the tundra-dominated MIS M2, whereas the tundra biome initially occurs between ~3.379 and ~3.378 Ma within MIS MG4. Prior to ~2.800 Ma, several other cold stages during this generally warm Pliocene interval were characterized by the tundra biome.

The Last Interglacial Period (LIP) is often regarded as a good analogue for potential climatic conditions under predicted global warming scenarios. Despite this, there is still debate over the nature, duration and frequency of climatic changes during this period. One particularly contentious issue has been the apparent evidence of climatic instability identified in many marine cores but seemingly lacking from many terrestrial archives, especially within the Arctic, a key region for global climate change research. In this paper, geochemical records from Lake El'gygytgyn, north-eastern Russia, are used to infer past climatic changes during the LIP from within the high Arctic. With a sampling resolution of ~ 20–~ 90 years, these records offer the potential for detailed, high-resolution palaeoclimate reconstruction. This study shows that the LIP commenced in central Chukotka ~ 129 thousand years ago (ka), with the warmest climatic conditions occurring between ~ 128 and 127 ka before being interrupted by a short-lived cold reversal. Mild climatic conditions then persisted until ~ 122 ka when a marked reduction in the sedimentation rate suggests a decrease in precipitation. A further climatic deterioration at ~ 118 ka marks the return to glacial conditions. This study highlights the value of incorporating several geochemical proxies when inferring past climatic conditions, thus providing the potential to identify signals related to environmental change within the catchment. We also demonstrate the importance of considering how changes in sedimentation rate influence proxy records, in order to develop robust palaeoenvironmental reconstructions.

This paper focuses on the characterization and genesis of mass movement deposits (MMDs) in the Quaternary and Pliocene sediments of Lake El'gygytgyn, Far East Russian Arctic. Three partly overlapping holes were drilled into the 320 m long sediment record at International Continental Scientific Drilling Program (ICDP) Site 5011-1 in the lake basin, recovering the Quaternary almost completely, and the Pliocene down to 3.6 Ma with 52% recovery. Mass movement deposits were investigated in all three cores, based on macroscopical core descriptions, radiographic images, high-resolution magnetic susceptibility and gamma-ray density. Five different types of MMDs were identified: turbidites, grain-flow deposits, debrites, slumps and slides. These are formed by transitional mass movement processes, and thus can be co-generic. An initial slope failure is thought to transform into a debris flow that deforms frontal sediments, partly disintegrates and dilutes into a turbidity flow. Turbidites are by far the most frequent MMD type in the lake center. They occur throughout the record in all pelagic sedimentary facies, but they are thinner in facies formed during cold climate conditions. All other MMDs, by contrast, incise exclusively the pelagic facies deposited during warm climates. In the 123 m thick Quaternary composite sediment record 230 mass movement events are identified, comprising 33% of the sediment length. Turbidites contribute 93% of the number of Quaternary MMDs, but only 35% of their thickness. In the Pliocene sediments between 123 and 320 m, 181 additional mass movement deposits are identified, which constitute ~33% of the recovered sediments. The mean recurrence interval for MMDs is 11 and 5 ka in the Quaternary and Pliocene, respectively.

The sedimentary sequence of Lake Stymphalia (NE-Peloponnese) for the first time sheds light on the palaeoclimate development of Southern Greece from 15 to 5 ka BP. New geochemical data based on high-resolution X-ray fluorescence scanning provide in-situ, and continuous analysis of predefined element suites on split-core surfaces. Variations of elements over time were assessed constructing correlation matrices based on the calculation of Pearson correlation coefficients. The element suite includes Al, Si, K, Ca, Ti, Mn, Fe, Zn, Rb, Sr, and Zr. A major result includes that changes in element behaviour are related to hydrological changes in the catchment (precipitation), lake level status, and evaporation (insolation/solar activity), and are ultimately driven by climate. Major trends/shifts in elemental ratios correspond to the climate development in the Eastern Mediterranean region. Based on correlation of Rb/Sr, reflecting wet/dry climates, with foraminiferal proxies of marine core LC21 from the Southern Aegean Sea, and the stable oxygen-isotope record of Soreq cave (Israel), the Bolling–Allerod, the Younger Dryas, and the 8.2 ka cold event were identified.

From Russia with Lovely Data Climate and the atmospheric concentration of CO 2 are closely linked. Brigham-Grette et al. (p. 1421 , published online 9 May) present data from Lake El'gygytgyn, in northeast Arctic Russia, that shows how climate varied between 3.6 and 2.2 million years ago, an important interval in the global cooling trend that accelerated rapidly at the end of the Miocene. Summer temperatures were about 10°C warmer than today, even though the concentration of atmospheric CO 2 was similar.

[1] This study presents paleomagnetic data from 59 independent lava flows from the trans-Mexican volcanic belt (TMVB) with ages from 6.4 Ma to recent, 52 being younger than 1 Ma, and 11 new 40Ar/39Ar age determinations. Most remanence carriers are Ti-poor titanomagnetite of pseudosingle-domain magnetic structure, nine lavas contain small amounts of titanomaghemite, and four lavas additional (titano-) hematite. Paleosecular variation of lava flows younger than 1.7 Ma is consistent with latitude-dependent Model G and also in agreement with other Pleistocene paleomagnetic data from the TMVB. The directional record of Brunhes and Matuyama Chrons lavas was correlated to the geomagnetic polarity timescale and there is evidence for at least four geomagnetic excursions. One lava flow dated at 592 ± 20 ka has a fully reversed paleodirection and most likely erupted during the Big Lost excursion. Another fully reversed flow, dated at 671 ± 12 ka, gives new volcanic evidence for the Delta/Stage 17 excursion. This excursion is supported by a reversed intermediate direction of another flow from a different volcanic field but of very close age of 673 ± 10 ka. From the Matuyama age lavas, one flow with normal polarity magnetization, dated at 949 ± 37 ka, could either be related to the Kamikatsura or the Santa Rosa excursion and a normal polarity flow, dated at 1628 ± 56 ka, could have been emplaced during the Gilsa excursion. The results presented here confirm in one case but disagree in four cases with results presented in two previous studies of the same lava flows and interpreted as geomagnetic excursions.

Four cores from the bottom sediments of Lake Esmeralda, Vega Island, Antarctica (60°48'S, 57°37'W) were studied. Analysis of rock magnetics indicates that the main carriers of magnetization are ferrimagnetic minerals, predominantly pseudo-single-domain (titano-) magnetite with a small proportion of paramagnetic and antiferromagnetic minerals. The magnetic grain size of the samples is in the range of 1-5 μm and the variation of the interparametric ratios is less than one order of magnitude. Demagnetization of the natural remanent magnetization shows a stable remanent magnetization in most of the samples. Thus, the samples fulfil the necessary conditions to calculate relative palaeointensity (RPI) and the curves obtained correlated with global models enabling dating of the cores. The 250 cm of sediment recovered spans the last 10 200 yr bp. Finally, some samples with high organic matter content were dated by accelerator mass spectrometry 14C. By comparison with the age defined by the RPI curves, a reservoir effect of c. 5200 years is suggested for this region of Vega Island. Fil: Irurzun, Maria Alicia. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentina Fil: Chaparro, Marcos Adrián Eduardo. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentina Fil: Sinito, Ana Maria. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentina Fil: Gogorza, Claudia Susana. Universidad Nacional del Centro de la Provincia de Buenos Aires. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tandil. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires. - Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones en Física e Ingeniería del Centro de la Provincia de Buenos Aires; Argentina Fil: Nuñez, H.. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Nowaczyk, N. R.. German Research Centre for Geosciences; Alemania Fil: Böhnel, H. N.. Universidad Nacional Autónoma de México. Centro de Geociencias; México

SUMMARY Magnetic extracts obtained from sediment cores recovered from Lake Kinneret, Israel, were subjected to comprehensive scanning electron microscope and in-line energy dispersive X-ray spectroscopy analyses. A variety of ferrimagnetic iron oxides and iron sulphide particles were identified, along with apparently non-magnetic iron sulphides. The majority of the iron oxides are titanomagnetites that have undergone pervasive dissolution, and in many cases were only preserved as skeletal, 3-D lattices of ilmenite lamellae. Often the spaces between the submicron ilmenite lamellae are empty. Also sponge-like dissolution features are observed in some residual titanomagnetite grains. Another group of titanomagnetite grains is characterized by superficial shrinkage-cracks, which indicate low-temperature maghemitization. In some cases, these cracks appear to be where dissolution started. Most titanomagnetites contain impurities of Al, Mg, Si and Mn on the order of 1 per cent. Chromium-magnetites, with minor Ti, Mg and Al content on the order of a few percent, but without Mn, were also found. Chromium-magnetites mostly occur as octahedra in a well-preserved state, which indicates that they are less prone to dissolution. Magnetite spherules of 40–60 μm in size, which were mostly hollow, were only found in material collected from the outer zone of the core section that was in contact with the steel core barrel. These spherules were not found in material collected from the centre of the core. They are therefore interpreted as contaminants that were produced during fabrication of the steel core barrel. Iron sulphides are present as pyrite, either as larger aggregates of cubic crystals, each of up to 20 μm in size, or as 5–10 μm framboidal aggregates, consisting mostly about 0.3 μm idiomorphic octahedra. The cubic pyrite crystals have heterogeneous compositions. Pure pyrite should be non-magnetic, but even aggregates of up to 150 μm in size were magnetically separated. They probably therefore contain a magnetic core of greigite or overgrown titanomagnetite. The latter possibility is supported by observations of residual titanomagnetites with individual pyrite crystals residing directly on their surfaces, or filling space between ilmenite lamellae. Irregular aggregates of flaky, submicron iron sulphides were also found, which are interpreted to be greigite. The greigite has a low degree of visible crystallization. Pyrite and/or greigite grains were found inside the aggregates, or in agglomerates with organic remnants. Together, visual observations and elemental analyses provide clear evidence of pervasive dissolution of primary titanomagnetite and concurrent sulphidization of sediments from Lake Kinneret.

Variations of the Earthfs magnetic field during the first millennium BC in western Europe remain poorly constrained, especially archaeointensity changes. Three salt-kilns (MOA, MOB and MOC) sampled in Moyenvic (Lorraine, eastern France) have been studied to provide new reference data. Each kiln has been dated by radiocarbon to originate from the Early Iron Age or Hallstatt period (between VIII and Vth Century BC). Rock magnetic experiments and hysteresis results suggest the predominance of pseudo-single domain (PSD) Ti-poor magnetite. Archaeomagnetic directions obtained by thermal and alternating field demagnetizations have high mean inclination (close to 70.) and declination (between 19 and 31.). A first set of classical Thellier.Thellier experiments was conducted on 46 samples with a laboratory field almost parallel to the direction of the characteristic remanent magnetization (ChRM). Only 24 of these specimens present a linear NRM.TRM plot. For other specimens, NRM.TRM plots are concave-up with positive pTRM checks. The very large dispersion observed between the determined palaeointensity values suggests some artefacts have not been fully recognized. A second set of Thellier experiments was conducted on 34 sister specimens with the laboratory field applied quasi-perpendicular to the ChRM. In these cases,mineralogical evolutions during heating and chemical remanent magnetization acquisitions have been clearly recognized, despite positive pTRM checks. The concave-up shapes of NRM.TRM plots appear mainly due to mineralogical alteration rather than to the presence of PSD.MD grains. For the entire set of samples the success rate of the palaeointensity determinations is very low with 80 per cent of the samples rejected. Nevertheless, reliable mean archaeointensities have been obtained for two of the three kilns (MOA, 80.1 } 14.5 ƒET and MOB, 86.6 } 6.9 ƒET at the latitude of Paris). The high field strength and the archaeomagnetic directions determined, combined with previous published data, provide further evidence for important changes of the Earth magnetic field in Europe during the first half of the first millennium BC. These large variations of the geomagnetic field during the Iron Ages indicate that archaeomagnetism is highly suitable for dating of structures from this period.