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Terrestrial glacial records from the Patagonian Andes and New Zealand Alps document quasi-synchronous southern hemisphere-wide glacier advances during the late Quaternary. Although detailed, these records are inherently incomplete. Here, we provide a continuous marine record of Patagonian Ice Sheet (PIS) extent over a complete glacial/interglacial cycle back to the previous glacial (~140 ka). Sediment core MR16-09 PC03, located at 46° S and ~150 km offshore Chile, received high terrestrial sediment input when the PIS advanced westward. We use biomarkers, foraminiferal oxygen isotopes, and major element data for reconstructing terrestrial sediment and freshwater input related to PIS variations. Our sediment record documents four major intervals of general PIS advance, during Marine Isotope Stage (MIS) 6 (135 – 140 ka), late MIS 5 (~85 – 95 ka), MIS 4 (~60 – 70 ka) and late MIS 3 to MIS 2 (~18 – 40 ka). These higher terrigenous input intervals occur during sea-level low stands when the western PIS covered most of the Chilean fjords which today retain glaciofluvial sediments. Superimposed, high amplitude phases of enhanced sediment supply reoccur at millennial time scales and reflect marine-based phases of the PIS with direct sediment discharge to the continental slope. We assign the late MIS 3 to MIS 2 phases and, by inference, also older advances to Antarctic stadials, consistent with the terrestrial record. Concomitantly, we observe enhanced meltwater release and conclude that the temperature-controlled PIS advances during southern hemisphere cold phases were likely reinforced by higher precipitation through enhanced westerly winds at the northwestern margin of the PIS.

The short sediment core EMB201/7-4 retrieved from the East Gotland Basin, central Baltic Sea, is explored here as a candidate to host the stratigraphical basis for the Anthropocene series and its equivalent Anthropocene epoch, still to be formalized in the Geological Time Scale. The core has been accurately dated back to 1840 CE using a well-established event stratigraphy approach. A pronounced and significant change occurs at 26.5 cm (dated 1956 +/- 4 CE) for a range of geochemical markers including Pu239+240, Am-241, fly-ash particles, DDT (organochlorine insecticide), total organic carbon, and bulk organic carbon stable isotopes. This stratigraphic level, which corresponds to a change in both lithology and sediment colour related to early anthropogenic-triggered eutrophication of the central Baltic Sea, is proposed as a Global Boundary Stratotype Section and Point for the Anthropocene series., The Anthropocene Review, 10 (1), ISSN:2053-0196, ISSN:2053-020X

The Drake Passage, as the narrowest passage around Antarctica, exerts significant influences on the physical, chemical, and biological interactions between the Pacific and Atlantic Ocean. Here, we identify terrigenous sediment sources and transport pathways in the Drake Passage region over the past 140 ka BP (thousand years before present), based on grain size, clay mineral assemblages, geochemistry and mass-specific magnetic susceptibility records. Terrigenous sediment supply in the Drake Passage is mainly derived from the southeast Pacific, southern South America and the Antarctic Peninsula. Our results provide robust evidence that the Antarctic Circumpolar Current (ACC) has served as the key driver for sediment dispersal in the Drake Passage. High glacial mass accumulation rates indicate enhanced detrital input, which was closely linked to a large expansion of ice sheets in southern South America and on the Antarctic Peninsula during the glacial maximum, as significantly advanced glaciers eroded more glaciogenic sediments from the continental hinterlands into the Drake Passage. Moreover, lower glacial sea levels exposed large continental shelves, which together with weakened ACC strength likely amplified the efficiency of sediment supply and deposition in the deep ocean. In contrast, significant glaciers' shrinkage during interglacials, together with higher sea-level conditions and storage of sediment in nearby fjords reduced terrigenous sediment inputs. Furthermore, a stronger ACC may have induced winnowing effects and further lowered the mass accumulation rates. Evolution of ice sheets, sea level changes and climate related ACC dynamic have thus exerted critical influences on the terrigenous sediment supply and deposition in the Drake Passage region over the last glacial-interglacial cycle.

Alkenones and Glycerol Dialkyl Glycerol Tetraether lipids (GDGT) as remnants of living organisms are widely used biomarkers for determining past oceans’ water temperatures. The organisms these proxy carriers stem from, are influenced by a number of environmental parameters, such as water depth, nutrient availability, light conditions or seasonality, which all may significantly bias the calibration to ambient water temperatures. Reliable temperature determinations remain thus challenging, especially in higher latitudes and for under-sampled regions. We analyzed 33 sediment surface samples from the Southern Chilean continental margin and the Drake Passage for alkenones and GDGTs and compared the results with gridded instrumental reference data from the World Ocean Atlas 2005 (WOA05), as well as previously published data from an extended study area covering the Central and Western South Pacific towards the New Zealand continental margin. We show that for alkenone-derived SSTs, the widely-used global core-top calibration of Müller et al. (1998) yields the smallest residuals, whereas the calibration of Sikes et al. (1997), adapted to higher latitudes and supposed to show summer SSTs, overestimates modern WOA05-based (summer and annual mean) SSTs. Our alkenone SSTs show a slight seasonal shift of ~1 °C at the Southern Chilean Margin and up to ~2 °C in the Drake Passage towards austral summer SSTs, whereas samples in the Central South Pacific reflect an annual mean signal. We show that for GDGT-based temperatures, a more complex pattern emerges. In areas north of the Subantarctic Front (SAF) the subsurface calibration of Kim et al. (2012a) best reflects temperatures from the WOA05, largely within the margin error of ±2.2 °C. Temperatures south of the SAF instead are significantly overestimated by up to 14 °C, irrespective of the applied calibration. Based on a qualitative assessment of the GDGT [2] / [3]-ratios, which likely indicate water depth of origin, our samples reflect a subsurface (0 to 200 m water depth) rather than a surface (0–50 m water depth) signal. The overestimation of surface and subsurface temperatures south of the SAF highlights the need for a re-assessment of existing calibrations in the polar Southern Ocean, and leads to limitations in reliably both obtaining absolute values and assessing relative changes. Therefore, we suggest a modified Southern Ocean calibration for surface and subsurface GDGT-based temperatures, which shows a lower temperature sensitivity of the TEXL86 and yields principally lower absolute temperatures, which align more closely with WOA05-derived values.

End-member modelling of bulk grain-size distributions allows the unravelling of natural and anthropogenic depositional processes in salt marshes and quantification of their respective contribution to marsh accretion. The sedimentology of two marshes is presented: (1) a sheltered back-barrier marsh; and (2) an exposed, reinstated foreland marsh. Sedimentological data are supplemented by an age model based on lead-210 decay and caesium-137, as well as geochemical data. End-member modelling of grain-size data shows that marsh growth in back-barrier settings is primarily controlled by the settling of fines from suspension during marsh inundation. In addition, nearby active dunes deliver aeolian sediment (up to 77% of the total sediment accretion), potentially enhancing the capability of salt marshes to adapt to sea-level rise. Growth of exposed marshes, by contrast, primarily results from high-energy inundation and is attributed to two sediment-transport processes. On the seaward edge of the marsh, sedimentation is dominated by coarser-grained traction load, whereas further inland, settling of fine-grained suspension load prevails. In addition, a third, coarse-grained sediment sub-population is interpreted to derive from anthropogenic land-reclamation measures, that is material from drainage channels relocated onto the marsh surface. This process contributed up to 34% to the total marsh accretion and terminated synchronously with the end of land reclamation measures. Data suggest that natural sediment supply to marshes alone is sufficient to outpace contemporary sea-level rise in the study area. This underlines the resilience potential of salt marshes in times of rising sea levels. The comparison of grain-size sub-populations with observed climate variability implies that even managed marshes allow for the extraction of environmental signals if natural and anthropogenic sedimentary processes are determined and their relative contribution to bulk sediment composition is quantified. Data series based solely on bulk sediments, however, seem to be of limited use because it is difficult to exclude bias of natural signals by anthropogenic measures.

Knowledge about the timing, amplitude and spatial gradients of Holocene environmental variability in the circum-Baltic region is key to understanding its responses to ongoing climate change. Based on a multi-dating and proxy approach, we reconstruct changes in productivity using total organic carbon (TOC) contents in sediments of Lake Kälksjön (KKJ) from west–central Sweden spanning the last 9612 (+255/-114) years. An exception is the period from 1878 CE until today, in which sedimentation was dominated by anthropogenic lake level lowering and land use. In-lake productivity was higher during periods of warmer winters with shortened ice cover and prolonged growing seasons. A multi-millennial increase in productivity throughout the last ∼ 9600 years is associated with progressively warmer winters in northwestern Europe, likely triggered by the coinciding increase in Northern Hemisphere winter insolation. Decadal to centennial periods of higher productivity in KKJ tend to correspond to warmer winters during a more positive North Atlantic Oscillation (NAO) polarity, as reconstructed for the last 8000 years. In consequence, we assume our decadal to centennial productivity record from KKJ sediments for the complete ∼ 9600 years to provide a qualitative record of NAO polarity. A shift towards higher productivity variability at ∼ 5450 cal a BP is hypothesized to reflect a reinforcement of NAO-like atmospheric circulation variability, possibly driven by more vigorous changes in North Atlantic deep-water formation.

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.

Changes in Southern Ocean export production have broad biogeochemical and climatic implications. Specifically, iron fertilization likely increased subantarctic nutrient utilization and enhanced the efficiency of the biological pump during glacials. However, past export production in the subantarctic Southeast Pacific is poorly documented, and its connection to Fe fertilization, potentially related to Patagonian Ice Sheet dynamics is unknown. We report on biological productivity changes over the past 400 ka, based on a combination of 230Thxs-normalized and stratigraphy-based mass accumulation rates of biogenic barium, organic carbon, biogenic opal, and calcium carbonate as indicators of paleo-export production in a sediment core upstream of the Drake Passage. In addition, we use fluxes of iron and lithogenic material as proxies for terrigenous matter, and thus potential micronutrient supply. Stratigraphy-based mass accumulation rates are strongly influenced by bottom-current dynamics, which result in variable sediment focussing or winnowing at our site. Carbonate is virtually absent in the core, except during peak interglacial intervals of the Holocene, and Marine Isotope Stages (MIS) 5 and 11, likely caused by transient decreases in carbonate dissolution. All other proxies suggest that export production increased during most glacial periods, coinciding with high iron fluxes. Such augmented glacial iron fluxes at the core site were most likely derived from glaciogenic input from the Patagonian Ice Sheet promoting the growth of phytoplankton. Additionally, glacial export production peaks are also consistent with northward shifts of the Subantarctic and Polar Fronts, which positioned our site south of the Subantarctic Front and closer to silicic acid-rich waters of the Polar Frontal Zone, as well as a with a decrease in the diatom utilization of Si relative to nitrate under Fe-replete conditions. However, glacial export production near the Drake Passage was lower than in the Atlantic and Indian sectors of the Southern Ocean, which may relate to complete consumption of silicic acid in the study area. Our results underline the importance of micro-nutrient fertilization through lateral terrigenous input from South America rather than aeolian transport, and exemplify the role of frontal shifts and nutrient limitation for past productivity changes in the Pacific entrance to the Drake Passage.

International audience; Introduction 5 Sedimentology 11 Biostratigraphy 20 Paleomagnetism 22 Geochemistry 25 Physical properties 31 Downhole measurements 32 Stratigraphic correlation 34 References

Redox-sensitive trace metals are powerful tools for the reconstruction of modern and past redox conditions in aquatic ecosystems. The most prominent example is molybdenum (Mo), which behaves conservatively as soluble molybdate in the oxygenated ocean, but forms particle-reactive thiomolybdates at sufficiently high sulfide concentrations. Previous studies proposed that the redox behavior of tungsten (W), the geochemical twin of Mo, is also affected by sulfide, suggesting its potential as a promising new redox proxy. Here we present a comprehensive W dataset from the highly sulfidic Black Sea and the weakly sulfidic Landsort Deep (Baltic Sea), as the type localities of modern euxinic basins, that combines water column, pore water, and sediment records. A dataset from the Gotland Basin obtained following oxygenation of the formerly euxinic water column during the major Baltic inflow in 2014 is used as the hypoxic example. The even stronger adsorption of W than Mo on Mn and Fe oxides at pelagic redoxclines identified these particles as important carrier transferring W from the oxygenated surface ocean to euxinic bottom waters. This shuttling was most pronounced during the inflow event in the Gotland Basin causing substantial deposition of Mn oxides that were highly enriched in W. Compared to the oxygenated surface waters, dissolved Mo was severely depleted in the highly sulfidic water column of the Black Sea, whereas the bottom water levels of dissolved W were elevated. An additional W source derived from pore-water reflux, as indicated by the exceptionally high concentrations of W in highly sulfidic pore waters from the Landsort Deep sediments. In addition to the decoupling from Mn, the pore water W enrichments are compatible with the previously proposed greater solubility of thiotungsate species than of tungstate. Despite the absence of a substantial sedimentary accumulation of authigenic W in the sapropels of the Black Sea, the comparable patterns of S, Fe, and W in an Eemian record may suggest sorption of internally cycled (thio)tungstate onto pyrite. Unexpected W enrichments in modern and medieval sediments from the central Landsort Deep indicate a close relationship with Mn carbonate formation occurring during long-lasting bottom water hypoxia. In contrast to the highly variable Mo content, the near-background variation of W in the sapropels of euxinic basins questions the utility of W as a redox proxy in euxinic systems. However, given the strong affinity between W and the Mn/Fe cycle, this element may be a useful proxy in hypoxic systems, especially its isotopic signature.

In shallow lakes, increasing phosphorus (P) loading has often been accompanied by a shift from a clear-water, macrophyte-dominated state to a turbid state featuring phytoplankton dominance. The effect of a regime shift on P burial and P fractions in lake sediments, however, is poorly understood. We used sediment cores from a eutrophic hard-water lake (Lake Gollinsee, Germany) that had undergone a regime shift (in approximately 1917) to investigate the effect on the accumulation rate of P and on changes in P forms. The cores were dated using Hg contents and radioisotopes ( 210 Pb, 137 Cs, and 241 Am). A combination of total organic carbon to total nitrogen ratios (TOC:TN), δ 13 TOC values, X-ray fluorescence calcium (Ca) counts, and sediment colour clearly distinguished sediment layers that were deposited during periods of macrophyte or phytoplankton dominance. The accumulation rate of total P (TP) in the sediments was 1.8 times higher after the regime shift and was associated with changes in the distribution of P fractions. The proportions of loosely-(NH 4 Cl-extracted TP) and Ca-(HCl-extracted TP) bound P decreased significantly, whilst the proportions of biogenic P (NaOH-extracted NRP) and aluminium-bound P (NaOH-extracted SRP) increased significantly. A higher dry mass deposition rate, reduced burial of stable Ca-P complexes, and increased contents and proportions of the mobile iron-bound (BD-extracted TP) and biogenic P fractions in the near-surface sediment layers are assumed to have enhanced the internal cycling of P and hence to have helped to maintain a state of phytoplankton dominance.

The Antarctic Circumpolar Current is the world’s largest current system connecting all major ocean basins of the global ocean. Its flow, driven by strong westerly winds, is constricted to its narrowest extent in the Drake Passage, located between South America and the Antarctic Peninsula. Due to the remoteness of the area, harsh weather conditions and strong bottom currents, sediment recovery is difficult and data coverage is still inadequate. Here, we report on the composition of 51 surface sediments collected during the R/V Polarstern PS97 expedition (February–April 2016) across the western and central Drake Passage, from the Chilean/Argentinian continental margin to the South Shetland Islands and the Bransfield Strait (water depth: ∼100–4000 m). We studied microfossils (diatoms), bulk sediment composition and geochemical proxies (biogenic opal, organic carbon, calcium carbonate, carbon and nitrogen stable isotopes, sterols and photosynthetic pigments), and evaluated how they respond to, and reflect oceanic domains and polar to subpolar frontal systems in this region. Our multi-proxy approach shows a strong relationship between the composition of surface sediments and ocean productivity, terrigenous input, intensity of ocean currents, and ice proximity, clearly differentiating among 4 biogeographical zones. The Subantarctic Zone was characterized by warmer-water diatoms, high carbonate (>45%) and low organic carbon contents (avg. 0.26%), as well as low concentrations of pigments (avg. 1.75 μg/g) and sterols (avg. 0.90 μg/g). A general N-S transition from carbonate-rich to opal-rich sediment was observed at Drake Passage sites of the Polar Front and Permanently Open Ocean Zone. These sites were characterized by low organic carbon content (0.22%), high relative abundances of heavily silicified diatoms (≥60% Fragilariopsis kerguelensis), and abundant foraminifera at shallower stations. Approaching the Antarctic Peninsula in the Transitional Zone, an increase in the concentrations of pigments and sterols (avg. 2.57 μg/g and 1.44 μg/g, respectively) and a strong decrease in carbonate content was observed. The seasonal Sea-Ice Zone in the southern section of the study area, had the highest contents of biogenic opal (avg. 14.6%) and organic carbon (avg. 0.7%), low carbonate contents (avg. 2.4%), with the occurrence of sea-ice-related diatoms and sterols. In all zones, terrigenous input was detected, although carbon/nitrogen ratios and δ13Corg suggest a predominance of marine-derived organic matter; lower values of δ13Corg occurred south of the Polar Front. The new results presented here constitute a highly valuable reference dataset for the calibration of microfossil and geochemical proxies against observational data and provide a useful regional baseline for future paleo-research.

Salt-marsh sediments of the southeastern North Sea provide an archive to unravel the influences of coastal management and natural processes such as storm-tide deposition on salt-marsh development. We present a record of salt-marsh evolution during the past century from the Bay of Tumlau (northwestern Germany) based on fossil foraminiferal assemblages and sedimentological data. After diking the hinterland of the Bay of Tumlau in 1935 CE and commencing marsh management, the environment at the study site changed from a tidal flat to a salt marsh. Salt-marsh sediment accretion is influenced by recurrent dredging events, as indicated by layers rich in calcareous tidal-flat foraminifera, and redeposition of siliciclastic particles from the surrounding tidal flats during storm tides. The latter fostered the establishment of a typical salt-marsh foraminiferal fauna dominated by the agglutinating species Entzia macrescens. Storm-tide layers have a lighter sediment color and commonly a more negatively skewed grain-size distribution with variable sorting. The observed long-term coarsening of the salt-marsh sediment likely reflects the landward progression of the vertical erosional cliff and the depletion of fine-grained sediment particles in the tidal flats under the influence of sea-level rise. Supra-tidal conditions, resulting from natural protection measures and abandonment of dredging, are indicated by the occurrence of Balticammina pseudomacrescens around 2001 CE. This species is adapted to only occasional submergence during storm tides. The recent increase in elevation is accompanied by establishment of high-marsh vegetation and characterized by a present height of the marsh surface 50 cm above mean high water springs. During the past sixty years, average sediment accretion rates decreased from 18 to 11 mm yr−1 reflecting the maturing of the salt marsh. These rates clearly outpace the recent mean sea-level rise in the southern North Sea demonstrating that the regional salt marshes are still resilient to sea-level rise.

Isochrysidales species of the phylum Haptophyta are the exclusive producers of C37 to C42 long chain alkyl ketones, also called long chain alkenones (LCAs). While LCA distributions are known to vary with temperature and salinity, it is difficult to tease apart the direct effects of environmental parameters vs changes in the LCA-producing organisms. The Baltic Sea surface salinity gradient, which ranges from oligohaline (0.5–5 g/kg) to polyhaline (18–30 g/kg), represents a unique opportunity to study the relationships between salinity changes, species distribution and LCA biomarkers in a single ecosystem. LCA biomarkers revealed the presence of the three known Isochrysidales groups (Groups I, II and III) in Baltic Sea surface sediments, and the presence of Groups I and II were further confirmed with DNA sequencing. Group III Isochrysidales were present in the mixoeuhaline Skagerrak based on LCA signature alone. Groups I and II Isochrysidales were found for the first time in the Baltic Sea using a combination of LCAs and DNA biomarkers, solving an eighteen-year long mystery of Baltic Sea LCA-producing haptophyte identity. Group II Isochrysidales, which have a large salinity tolerance range, were spread over the Skagerrak and the complete Baltic Sea, but were characteristic for the central Baltic Sea. Oligohaline Group I Isochrysidales were representative for the northern Baltic Sea. However, evidence of Group I Isochrysidales in the central and southern Baltic Sea suggests a possible transport by surface currents since this group is typically confined to oligohaline conditions. Testing the recently developed ratio of isomeric C37 ketones (RIK37) against the Baltic Sea surface salinity gradient revealed a significant positive correlation. This may represent a salinity proxy reflecting the amount of Group I Isochrysidales relative to Group II Isochrysidales in oligohaline environments. The present study elucidates for the first time the identity and the spatial distribution of LCA producers thriving in a large and stable brackish environment.

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.

Volcanic ash layers are important markers for the chronostratigraphy of paleoclimate and paleoenvironmental archives at the southern tip of South America. However, this requires that tephras are well-dated. We report geochemical data from the MA1 stalagmite formed in a non-karst cave near Mt. Burney volcano in southernmost Patagonia (~53°S). High-resolution LA-ICP-MS analyses, SEM imagery, and NanoSIMS enable to identify volcanogenic signals during the last 4.5 kyrs BP from sub-annual trace element variations and tephra particles in distinct laminae. The new 230Th/U-chronology of MA1 provides precise dating of tephra from Mt. Burney (MB) and Aguilera (A) at 4216 +93/−193 yrs BP (MB2), 2291 ± 33 yrs BP (MB3), 853 +41/−60 yrs BP (MB4) and 2978 +91/−104 yrs BP (A1). This unique high-resolution record of MA1 holds potential to date further eruptions from Southern Andean volcanoes for the tephrochronology in this critical region, and potentially also large-volume explosive volcanism off South America.

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

The Black Sea experienced pronounced millennial-scale changes in temperature and rainfall during the last glacial coinciding with Dansgaard-Oeschger cycles. However, little is known regarding the amount and sources of freshwater reaching this inland basin. Here, we present detailed ostracod δ18O data from the glacial Black Sea showing subdued Dansgaard-Oeschger cyclicity and four prominent longer-term saw-tooth shaped Bond-like cycles. We propose that the δ18Oostracods signature primarily reflects changes in the atmospheric circulation in response to the waxing and waning Eurasian Ice Sheet. The millennial-scale ice sheet variations likely resulted not only in latitudinal migrations of atmospheric frontal systems but also in shifts of dominant moisture sources for the Black Sea. Heavier isotopic precipitation arrived from the North Atlantic-Mediterranean realm during the warmer interstadials and lighter isotopic precipitation from the Eurasian continental interior during the colder stadials. The subdued Dansgaard-Oeschger variability likely reflects an integrated precipitation signal additionally affected by the long mixing times of the large Black Sea volume up to 1,500 years as suggested from hydrologic-isotope-balance modelling. Moisture sources to the Black Sea changed in response to atmospheric frontal displacements driven by Eurasian Ice Sheet dynamics during the last glacial period, according to analyses of ostracod oxygen and strontium isotope data from Black Sea sediments.

Our understanding of glacial isostatic rebound across Patagonia is highly limited, despite its importance to constrain past ice volume estimates and better comprehend relative sea-level variations. With this in mind, our research objective is to reconstruct the magnitude and rate of Late Glacial to Holocene glacial isostatic adjustment near the center of the former Patagonian Ice Sheet. We focus on Larenas Bay (48°S; 1.26 km2), which is connected to Baker Channel through a shallow (ca. 7.4 m) and narrow (ca. 150 m across) inlet, and hence has the potential to record periods of basin isolation and marine ingression. The paleoenvironmental evolution of the bay was investigated through a sedimentological analysis of a 9.2 m long, radiocarbon-dated, sediment core covering the last 16.8 cal. kyr BP. Salinity indicators, including diatom paleoecology, alkenone concentrations and CaCO3 content, were used to reconstruct the bay’s connectivity to the fjord. Results indicate that Larenas Bay was a marine environment before 16.5 cal. kyr BP and after 9.1 cal. kyr BP, but that it was disconnected from Baker Channel in-between. We infer that glacial isostatic adjustment outpaced global sea-level rise between 16.5 – 9.1 cal. kyr BP. During the Late Glacial - Holocene transition, the center of the former Patagonian Ice Sheet rose ca. 96 m, at an average rate of 1.30 cm/year. During the remainder of the Holocene, glacial isostatic adjustment continued (ca. 19.5 m), but at a slower average pace of 0.21 cm/year. Comparisons between multi-centennial variations in the salinity indicators and existing records of global sea-level rise suggest that the glacial isostatic adjustment rate fluctuated during these time intervals, in agreement with local glacier dynamics. More specifically, most of the glacial isostatic adjustment registered between 16.5 – 9.1 cal. kyr BP seems to have occurred before meltwater pulse 1A (14.5 – 14.0 kyr BP). Likewise, it appears that the highest Holocene glacial isostatic rebound rates occurred during the last 1.4 kyr, most likely in response to glacier recession from Neoglacial maxima. This implies a relatively rapid response of the local solid earth to ice unloading, which agrees with independent modelling studies investigating contemporary uplift. We conclude that the center of the former Patagonian Ice Sheet experienced a glacial isostatic adjustment of ca. 115 m over the last 16.5 kyr, and that >80% occurred during the Late Glacial and early Holocene.

Intertidal coastal wetlands are regularly exposed to storm surges and associated flooding, resulting in the recurrent accretion of reworked sediments on the salt-marsh surfaces. In this context, well-stratified salt-marsh sediment sequences provide an exceptional archive to evaluate the response of coastal wetlands to past storm-climate variability. Hence, this study focusses on the investigation of two sedimentary salt-marsh sequences from the south-eastern German North Sea coast (Bay of Tumlau and Friedrichskoog) to understand how and to which extent changes in the storm-surge climate are transferred into the sediment archive. This objective is particularly challenging as German mainland salt marshes have been greatly altered by human activities over the last century. To overcome this problem, this study combines different sedimentological and geochemical proxy data, using mean grain sizes together with ln(Br/Cl), Br/Corg, and ln(Zr/Rb) ratios, to allow for the identification of storm-surge layers. Local changes in the sedimentary organic matter supply are reflected by the ln(Br/Cl) ratio. There, abrupt drops in the ln(Br/Cl) data coincide with relatively coarser textured sand layers, indicating impacts by regional storm surges during winter, while intervals of comparable higher ln(Br/Cl) values may represent deposition during spring to fall. The Br/Corg record reflects the marine versus terrestrial organic matter input and reveals a long-term increase starting during the first half of the 20th century towards recent times, resembling the observed amplification in North Sea storminess. A similar trend is reflected by the ln(Zr/Rb) ratio (since 1950 CE), which can be used as a proxy for the grain-size distribution. Periodic fluctuations in the ln(Zr/Rb) ratio at inter-decadal timescales (10–19 years) suggest a close linkage between local sediment accretion and large-scale atmosphere-ocean climate oscillations over the North Atlantic and Europe, and thus related storm-surge frequency and intensity. Periodic variability on decadal scales was also identified in the ln(Br/Cl) record at the less human-modified and more naturally developed salt marsh at the Bay of Tumlau (12–22 years), likewise indicating a relation between North Sea storminess and associated shifts in the seasonal signal of the primary production and sediment texture to oscillations in the atmosphere-ocean system. On the contrary, similar periodicities are lacking for the intense modified salt marsh at Friedrichskoog. Apparently, the salt-marsh depositional system in the Bay of Tumlau reacts more sensitively to super-regional climatic changes, respectively, the natural depositional processes in the salt marsh at Friedrichskoog are superimposed by the more intense local human activities.

The Antarctic Circumpolar Current (ACC), the world’s strongest zonal current system, connects all three major ocean basins of the global ocean and therefore integrates and responds to global climate variability. Its flow is largely driven by strong westerly winds and is constricted to its narrowest extent in the Drake Passage. Fresh and cold Pacific surface and intermediate water flowing through the Drake Passage (cold-water route) and warm Indian Ocean water masses flowing through the Agulhas region (warm-water route) are critical for the South Atlantic contribution to Meridional Overturning Circulation changes. Furthermore, physical and biological processes associated with the ACC affect the strength of the ocean carbon pump and therefore are critical to feedbacks linking atmospheric CO2 concentrations, ocean circulation, and climate/cryosphere on a global scale. In contrast to the Atlantic and Indian sectors of the ACC, and with the exception of drill cores from the Antarctic continental margin and off New Zealand, there are no deep-sea drilling paleoceanographic records from the Pacific sector of the ACC. To advance our understanding of Miocene to Holocene atmosphere-ocean-cryosphere dynamics in the Pacific and their implications for regional and global climate and atmospheric CO2, International Ocean Discovery Program Expedition 383 recovered sedimentary sequences at (1) three sites in the central South Pacific (CSP) (U1539, U1540, and U1541), (2) two sites at the Chilean margin (U1542 and U1544), and (3) one site from the pelagic eastern South Pacific (U1543) close to the entrance to the Drake Passage. Because of persistently stormy conditions and the resulting bad weather avoidance, we were not successful in recovering the originally planned Proposed Site CSP-3A in the Polar Frontal Zone of the CSP. The drilled sediments at Sites U1541 and U1543 reach back to the late Miocene, and those at Site U1540 reach back to the early Pliocene. High sedimentation rate sequences reaching back to the early Pleistocene (Site U1539) and the late Pleistocene (Sites U1542 and U1544) were recovered in both the CSP and at the Chilean margin. Taken together, the sites represent a depth transect from ~1100 m at Chilean margin Site U1542 to ~4070 m at CSP Site U1539 and allow investigation of changes in the vertical structure of the ACC, a key issue for understanding the role of the Southern Ocean in the global carbon cycle. The sites are located at latitudes and water depths where sediments will allow the application of a wide range of siliciclastic-, carbonate-, and opal-based proxies to address our objectives of reconstructing, with unprecedented stratigraphic detail, surface to deep-ocean variations and their relation to atmosphere and cryosphere changes.

The marine-terrestrial Baltic ecosystem is sensitive to a range of environmental forcing and thresholds. Multi-archive investigations of its evolution require a precise synchronization of the considered archives. Here, we apply globally common cosmogenic radionuclide production rate variations to synchronize 10Be records from brackish Western Gotland Basin (Baltic Sea) and terrestrial lake Tiefer See (NE Germany) sediments to the atmospheric 14C time-scale and investigate phase-relationships in proxy responses in the southern Baltic realm associated with the onset of a centennial Mid-Holocene climate oscillation ∼5800 a BP. Based on paired molybdenum and titanium records, we identify a 98 ± 81-year delay in Western Gotland Basin ventilation, compared to the terrestrial response at the onset of the recorded Mid-Holocene climate oscillation. Most plausible mechanism for this delay is strengthened stratification in response to enhanced freshwater input during the first decades of the oscillation.

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.

Understanding hemisphere-wide millennial-scale temperature variability during past glacials in response to ice sheet dynamics and orbital forcing is one of the key targets for Quaternary climate research. While an inland propagation of abrupt temperature changes into Eurasia from the North Atlantic realm during the last glacial (Weichselian) receives increasingly broad support, much less is known regarding the penultimate glacial (Saalian) temperature variability, especially from a continental interior perspective. Here, we present a TEX86-derived lake surface temperature (LST) record from the former Black Sea ���Lake��� covering nearly the entire Marine Isotope Stage (MIS) 6. While orbital-scale LST cooling likely relates to meltwater discharge from the retreating Eurasian Ice Sheet during insolation maxima, millennial-scale LST variability suggests interstadial warming in phase with Greenland and northern Mediterranean Sea temperature records during the first half of MIS 6. Although summer insolation reached an interglacial-like level during this period, we propose that the reduced extent of the Eurasian Ice Sheet associated with northward shifted atmospheric fronts was ultimately responsible for the inland propagation of Dansgaard-Oeschger-like temperature variability. During the second half of MIS 6, temperature patterns across the North Atlantic-Eurasian corridor were more variable and less comparable with each other, likely because of the larger continental ice sheet weakening northern hemisphere atmospheric teleconnections. Temperature records across the North Atlantic-Eurasian realm suggest a weaker atmospheric teleconnection during MIS 6 compared to MIS 3, likely related to a stronger imprint of the Eurasian Ice Sheet on the continental and regional climate.

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.

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.

Salt marshes are of substantial importance for the adaptation of coastal regions to present-day and predicted future climate changes, and accompanied sea-level fluctuations. This gives the motivation to investigate salt-marsh archives from the southern North Sea region, which provide an exceptional archive to understand the response of coastal systems to climate variability of the recent past. For this study, well-stratified sediment sequences from two different salt-marsh systems were analysed by scanning XRF spectroscopy. The study sites are affected by both natural processes and anthropogenic interventions on different time scales. To address the complex interplay between storm surges, human-induced coastal management, and coupled internally forced atmosphere-ocean mechanisms during the last century, this study focuses on the ln(Zr/Rb) ratio as proxy for the relative particle-size distribution, and the Br/Corg ratio as an indicator for the marine versus terrestrial organic matter input to the sediment. Additional information about local changes in the sedimentary organic matter quality is provided by the alteration of ln(Br/Cl) ratios. The ln(Zr/Rb) records reveal periodic fluctuations at inter-annual, inter-decadal to multi-decadal time scales, suggesting a close link of sediment accretion to the atmospheric-ocean climate oscillation over the North Atlantic and Europe, which is accompanied by variations in the wind field, precipitation and river runoff. By contrast, the Br/Corg ratios exhibit a long-term increase starting from the mid-twentieth century towards recent times, resembling the observed increasing trend in North Sea storminess. Abrupt drops in the ln(Br/Cl) records coincide with relatively coarser sand layers, indicating impacts by regional storm surges during winter, while intervals of comparable higher ln(Br/Cl) values represent times of generally calm weather conditions of periods with less frequent storm surges. Our results imply that past regional to super-regional climate changes have been transferred into the sedimentary salt-marsh archives of the southern North Sea region.

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.

Depositional processes in coastal wetlands respond to a changing climate as documented in the sediment sequences of salt marshes. In this context, robust chronologies are crucial for the reconstruction of salt-marsh depositional processes in the past. However, salt-marsh sediments from the highly dynamic North Sea coast often lack a reliable stratigraphy due to the combined influences of natural processes and human activities, causing a reworking and re-deposition of the sediments. Here, a combination of absolute and relative dating methods has been applied in order to establish an integrated stratigraphic framework for active foreland salt marshes along the south-eastern North Sea coast. This stratigraphic framework is based on radionuclides (210Pb, 137Cs, 241Am, 14C) and mercury (Hg) contaminations, together with ln(Zr/Rb) as a grain-size proxy for additional inter-correlation between the four studied sites. The studied salt marshes encompass different environmental settings concerning the inundation frequency and intensity, and anthropogenic influences. As a result, the reconstructed mean sediment-accretion rates range from 1.16 cm yr–1 in the anthropogenically modified and grazed coastal salt marsh at Friedrichskoog, to 1.31 cm yr–1 in the more sheltered and semi-enclosed salt marsh in the Bay of Tümlau, and up to 1.75 cm yr–1 in the dynamic open coastal salt-marsh at Kaiser-Wilhelm-Koog. Similar mean high accretion rates of 1.72 cm yr–1 are documented for the Eider estuary until AD 1965, before they dropped to 0.72 cm yr–1 after completion of the Eider tidal barrier in AD 1973. The results highlight the advantage of combining independent dating methods for the establishment of salt-marsh chronologies, which proves to be essential to compensate for absence or blurring of distinct stratigraphic signals in highly dynamic coastal depositional settings, such as the salt-marsh systems at the south-eastern North Sea coastal region. The reconstructed sediment-accretion rates suggest a high resilience of salt-marsh systems to ongoing sea-level rise as long as sediment availability and natural flooding dynamics are maintained.

Manganese (Mn) oxides preferentially adsorb isotopically light tungsten (W). The global deposition of Mn oxides in (hyp)oxic marine settings represents the most plausible reason for an open ocean stable W isotope composition ( δ 186 / 184 W = +0.543 ± 0.046‰) that is distinctly heavier than the main input source of marine W, the upper continental crust ( δ 186 / 184 W of +0.080 ± 0.053‰). If so, the seawater stable W isotope composition might be intimately linked to the areal extent of (hyp)oxic conditions, whereby earliest increases in the seawater δ 186 / 184 W might indicate earliest increases in marine oxygen concentrations in Earth history. However, stable W isotope data for sediments that might preserve the variability in the seawater δ 186 / 184 W are rare. We present the first stable W isotope data for a sedimentary record from the Landsort Deep, Baltic Sea, covering the last ∼1,700 years. Within this basin, distinct vertical stratification causes bottom water hypoxia or even euxinia that alternated with fully oxic conditions. Sediments deposited during long-lasting fully oxic periods such as the Little Ice Age are dominated by detrital W and Mn components and show crust-like δ 186 / 184 W values between -0.008 and +0.112‰. In contrast, during periods of pronounced bottom water hypoxia (e.g. modern warm period), sediments are authigenically enriched in Mn and W with δ 186 / 184 W values up to +0.226‰. Smooth depth trends in δ 186 / 184 W during hypoxic periods reflect temporal changes in the inflow intensity of O2 bearing Baltic seawater. Elevated inflow rates increase the sedimentary δ 186 / 184 W mainly because a slight O2 contribution fosters Mn oxide shuttling near the sediment-seawater interface and the preferential scavenging of isotopically light W. Consequently, the δ 186 / 184 W of the bottom water and subsequently deposited Mn oxides shift towards higher values. Thus, the variation in sedimentary δ 186 / 184 W values is related to the extent of Mn oxide formation that in turn depends on changing marine redox conditions. This emphasises the potential of stable W isotopes as a new tracer for early Earth redox reconstructions.

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.

The sediments of the Landsort Deep and Gotland Basin in the central Baltic Sea are strongly enriched in Mn carbonate. However, conceptual models attempting to explain the intense Mn carbonate precipitation in both basins are in part conflicting. In the Gotland Basin model, deposited Mn oxides are converted to Mn carbonate after the oxygenation of euxinic bottom waters enriched in dissolved Mn by major Baltic inflows (Huckriede and Meischner, 1996). By contrast, according to the Landsort Deep model, Mn carbonate precipitation occurs independent of oxygenation events below a euxinic water column (Lepland and Stevens, 1998; Lenz et al., 2015). In this study, we investigated Mn solid-phase signatures in recent/sub-recent well-dated sediments from the Landsort Deep and compared them to long-term observations to identify the hydrographic conditions favoring Mn carbonate formation. The comparisons of water column O2 and sulfide time series with sedimentary Mn carbonate enrichments identified long-lasting bottom water oxygenation as an important environmental factor in the enhancement of Mn carbonate precipitation (up to 32 wt% Mn) in the Landsort Deep. Thus, by preventing the escape of dissolved Mn from still reducing sediments into the open water column, these conditions allow the accumulation of large amounts of Mn-oxide particles at the sediment/water interface, with their subsequent conversion to Mn carbonate. The euxinic conditions that have prevailed almost continuously in the Landsort Deep since roughly AD 2000 do not favor Mn enrichment (maximum 0.9 wt% Mn), highlighting the importance of the recurring oxygenation of bottom water, most likely via medium-intensity inflows. The Mn abundances in seven sediment cores from water depths of 190–437 m together with Mn balance calculations indicated that the Mn inventory in the water column in response to porewater Mn reflux and detrital Mn input is sufficient for Mn carbonate enrichment only in the deepest part of the basin.

The Black Sea repeatedly experienced major hydrographic changes during glacial-interglacial transitions, with alternating limnic and brackish stages. While the redox conditions during the present Holocene brackish period (since ~ 9,000 yr BP) have been intensively studied, the redox evolution during the last interglacial, the Eemian (~ 128,000-120,000 yr BP), remains largely unexplored. With its at least 3 °C warmer climate and an up to 10 m higher global sea level, the Eemian could open a window into the future development of the Black Sea. This study provides a detailed comparison of the Black Sea redox evolution during Eemian and Holocene sapropel formation. We show that the redox conditions and associated geochemical processes in the Black Sea water column can strongly deviate from the Holocene when sea level and climate conditions are different. Mo/Al and Re/Mo as well as Mo and Fe isotope proxies record a comparatively uniform rise of the Eemian redoxcline culminating in pronounced euxinia. This scenario strongly contrasts with weaker euxinic conditions during the Holocene Unit II sapropel (~ 8,000-2,500 yr BP). Higher Mo/TOC ratios during the Eemian and Mo inventory considerations suggest a higher Eemian Mo availability, possibly due to an improved connection to the Mediterranean Sea. We conclude that higher temperatures, productivity, sea level-associated salinity changes, and corresponding higher sulphide levels were ultimately responsible for enhanced trace metal enrichment during the Eemian Black Sea sapropel stage.