Search

Radiocarbon is an extremely useful carbon cycle tracer and radiometric dating tool. Here, we review the main principles and challenges involved in the use of radiocarbon in paleoceanography. First, we present a conceptual framework in which there are three possible uses of a radiocarbon measurement: (a) to obtain a calendar age interval, or a fossil entity's age; (b) to obtain an estimate of a carbon reservoir's past radiocarbon activity; or (c) to compare the relative radiocarbon activities of two contemporary carbon reservoirs. We discuss the analysis of marine fossil material, the generation of an atmospheric reference curve, and the interpretation of marine radiocarbon “ventilation metrics” in relation to this reference curve. It is emphasized that marine radiocarbon integrates the influences of: changing radiocarbon production; air-sea gas exchange effects at the sea surface; transport times within the ocean interior; and the mixing of water parcels with different transit times from the sea surface, and different sea-surface sources. These controls are what make radiocarbon such a powerful paleoceanographic tracer, though the difficulty of disentangling them is what makes marine radiocarbon dating and tracer studies so challenging. We discuss the implementation of radiocarbon in numerical models, and explore the theory linking ocean-atmosphere partitioning of radiocarbon and CO2. Finally, we review existing records of marine radiocarbon variability over the last ∼25,000 years, which highlight the influence of ocean-atmosphere carbon exchange on past atmospheric CO2 and climate, and point to emerging opportunities for resolving the global radiocarbon- and carbon budgets over the last glacial cycle. [ABSTRACT FROM AUTHOR]

We analyse phase lags between the 11-year variations of three records: the semi-annual oscillation of the length of day (LOD), the solar activity (SA) and the cosmic ray intensity (CRI). The analysis was done for solar cycles 20–23. Observed relationships between LOD, CRI and SA are discussed separately for even and odd solar cycles. Phase lags were calculated using different methods (comparison of maximal points of cycles, maximal correlation coefficient, line of synchronization of cross-recurrence plots). We have found different phase lags between SA and CRI for even and odd solar cycles, confirming previous studies. The evolution of phase lags between SA and LOD as well as between CRI and LOD shows a positive trend with additional variations of phase lag values. For solar cycle 20, phase lags between SA and CRI, between SA and LOD, and between CRI and LOD were found to be negative. Overall, our study suggests that, if anything, the length of day could be influenced by solar irradiance rather than by cosmic rays. [ABSTRACT FROM AUTHOR]

Abstract: The mismatch between the 100 and 400 k.y. components of Pleistocene climate and the relative power of those terms from the eccentricity of the Earth''s orbit remains a challenge to the Milankovitch hypothesis. Coccolithophores have the potential to respond to parameters of orbital forcing other than insolation, and, as a critical component of the ocean carbon cycle, can act to modify the climate response. The first direct comparison of coccolith fraction Sr/Ca, alkenone abundance and automated coccolithophore counts, shows that CF Sr/Ca is largely driven by changing production of bloom species, with unusually high Sr/Ca ratios. The periods of high CF Sr/Ca and high bloom production mark periods of high global coccolithophore production, which correlate inversely with the low amplitude 100 and higher amplitude 400 k.y. eccentricity orbital frequency. ∼400 k.y. cycles of coccolithophore bloom production correspond to periods of enhanced carbonate accumulation in some parts of the ocean, deep ocean dissolution in others, positive shifts in global ocean δ13C, and acmes of Gephyrocapsa caribbeanica and Emiliania huxleyi. The link between production of coccolithophore blooms and eccentricity may be due to orbital control of silica leakage from the Southern Ocean, to the orbitally defined inverse correlation between insolation and growing season length and the asymptotic growth response to these parameters, or to changes in nutrient input from weathering. During the Pleistocene, the eccentricity induced coccolithophore acmes have no apparent influence on atmospheric carbon dioxide (pCO2) due to the shift towards small bloom coccolithophores, or to coupling with increased diatom productivity, or the ballast effect of the calcium carbonate rain, such that Pleistocene climate has no significant variance at the largest amplitude eccentricity forcing of 400 k.y. Coccolithophores and their influence on the carbon cycle may act as a filter between the incident orbital forcing and resultant climate. [Copyright &y& Elsevier]

Investigates the nonspecific secretory immunity in HIV-infected patients with oral candidiasis. Concentrations of lysozyme and lactoferrin in serum and saliva; Concentrations of immunoglobulin in serum, saliva and stool specimens; Concentration of albumin in serum.

Several studies were carried out to characterize the humoral immune response on mucosal genital surfaces. However, the results obtained so far were particularly conflicting due to the absence of validation methods. The aim of this study was to develop and validate a quantitative ELISA method, which is sensitive and reproducible, to measure immunoglobulin and secretory immunoglobulin concentrations in various biological fluids. This quantitative, sensitive (detection limit = 1 µg/L) and reproducible (coefficient of variation < 15%) method could be of interest to study the effects of viral infections on mucosal non-specific immune response in genital tract. To explore the humoral response, serum, saliva, vaginal secretions, and cervicovaginal secretions from 18 women, 20-45 years old, were evaluated for total-IgA, secretory IgA, IgM, and IgG. Albumin level was also evaluated by immuno-nephelometry. The secretion rates of immunoglobulins were measured by calculating their relative coefficients of excretion by reference to albumin. Despite large individual variations, median immunoglobulin levels were higher in the endocervical secretions than in the cervicovaginal secretions. When we compared the rates of immunoglobulins in genital fluids, IgG prevalence was higher (80%) in cervicovaginal and endocervical secretions than IgA prevalence (12%). In contrast, digestive mucosal secretions, such as saliva, contained mostly IgA (80%). In cervicovaginal and endocervical secretions, IgG and IgM originated mainly from serum, whereas a local synthesis provided total-IgA and secretory IgA. These results allowed us to raise a possible hypothesis for the origin of immunoglobulins in the genital tract. They illustrated the peculiar feature of the female reproductive tract and the difficulty for this tissue to contribute in the mucosal associated lymphoid tissue. The low secretory-IgA and total-IgA levels could explain the particular sensitivity of the vagina and the cervix... [ABSTRACT FROM AUTHOR]

The article discusses the role of hydrocarbon as a diagnostic tracer throughout the Earth and climate system. Topics covered include the recognition of radiocarbon as providing an essential dating method for the past 55,000 years, the ability of radiocarbon to give insight into Earth's magnetic field, and the key challenges in harnessing the full potential of radiocarbon.

The article discusses when can listeners detect disfluency in spontaneous speech. Spontaneous speech contains many disfluencies: The speaker hesitates in midutterance to alter something in the preceding speech, to repeat, or just to consider how to continue. Although, strictly speaking, it is the reparandum which is the disfluency, in the sense that it would have to be edited out of a verbatim transcription to make fluent text, reparanda are often perfectly acceptable sequences. The psycholinguistic studies which deal directly with disfluent speech also suggest a role for prosody.

Presents an analysis of the prospects for and perils to the peace process in the Middle East. Dangers posed by Israeli and Palestinian rejectionism; Policy recommendations for the United States, Israel and the Palestinian National Authority.

Presents research focusing on the uranium-thorium/14C comparison of corals for the past 30,000 years. Methods; Results; Comparison with previous 14C calibration; Possible geochemical artifacts; Carbon cycle changes; Changes in the 14C production;Discussion.

Presents results bearing on the sea level record for the past 130,000 years. Concludes that the last deglaciation started 3,000 years earlier than previously thought, and confirms that there were two surges in meltwater at about 11 kyr and 14 kyrbefore present.

The Holocene colonisation of islands by humans has invariably led to deep-seated changes in landscape dynamics and ecology. In particular, burning was a management tool commonly used by prehistoric societies and it acted as a major driver of environmental change, particularly from the Neolithic onwards. To assess the role of early human impacts (e.g. livestock grazing, forest clearance and the cultivation of marginal land) in shaping "pristine" island landscapes, we here present a 350-year record of fire history and erosion from Malta, straddling the earliest peopling of the island. We show that recurrent anthropogenic burning related to Neolithic agro-pastoral practices began ∼7500 years ago, with well-defined fire-return intervals (FRI) of 15–20 years that engendered erosion and rapid environmental degradation. As early as the Neolithic, this study implies that, in sensitive insular contexts, just a few generations of human activities could rapidly degrade natural islandscapes. • We reconstruct fire history during the early Neolithic peopling of Malta. • Anthropogenic burning related to agro-pastoral practices began ∼7500 years ago. • Human-induced fire led to erosion and rapid environmental degradation. • A few generations of human activities could rapidly degrade natural islandscapes. [ABSTRACT FROM AUTHOR]

Abstract Background and purpose Physical activity provides substantial health benefits. Older adults are less physically active than the rest of the population, and interventions that promote physical activity are needed. In this meta-analysis, we investigate how different wearable activity trackers (pedometers and accelerometers) may impact physical activity levels in older adults. Methods We searched MEDLINE, Embase and CINAHL for randomized controlled trials including participants that were ≥65 years, using wearable activity trackers with the intent of increasing physical activity. Studies whose comparator groups were engaged in active or inactive interventions, such as continued a physical therapy program or goal-setting counseling, were not excluded simply for implementing co-interventions. We used random-effects models to produce standardized mean differences (SMDs) for physical activity outcomes. Heterogeneity was measured using I2. Results Nine studies met the eligibility criteria: Four using accelerometers, four using pedometers, and one comparing accelerometers and pedometers, for a total number of 939 participants. Using pooled data, we found a statistically significant effect of using accelerometers (SMD = 0.43 (95%CI 0.19–0.68), I2 = 1.6%, p = 0.298), but not by using pedometers (SMD = 0.17 (95%CI −0.08–0.43), I2 = 37.7%, p = 0.174) for increasing physical activity levels. Discussion and conclusions In this study, we found that accelerometers, alone or in combination with other co-interventions, increased physical activity in older adults however pedometers were not found to increase physical activity. The high risk of bias found in most studies limits these findings. High quality studies that isolate the effects of accelerometers on physical activity changes are needed. Highlights • Interventions that promote physical activity are needed for the less active older adult population. • Accelerometers, alone or in combination with co-interventions, increased physical activity in older adults. • High quality studies that isolate the effects of accelerometers on physical activity changes are needed. [ABSTRACT FROM AUTHOR]

Aims. The solar activity in the past millennia can only be reconstructed from cosmogenic radionuclide proxy records in terrestrial archives. However, because of the diversity of the proxy archives, it is difficult to build a homogeneous reconstruction. All previous studies were based on individual, sometimes statistically averaged, proxy datasets. Here we aim to provide a new consistent multi-proxy reconstruction of the solar activity over the last 9000 yr, using all available long-span datasets of 10Be and 14C in terrestrial archives. Methods. A new method, based on a Bayesian approach, was applied for the first time to solar activity reconstruction. A Monte Carlo search (using the χ2 statistic) for the most probable value of the modulation potential was performed to match data from different datasets for a given time. This provides a straightforward estimate of the related uncertainties. We used six 10Be series of different lengths (from 500–10 000 yr) from Greenland and Antarctica, and the global 14C production series. The 10Be series were resampled to match wiggles related to the grand minima in the 14C reference dataset. The stability of the long data series was tested. Results. The Greenland Ice-core Project (GRIP) and the Antarctic EDML (EPICA Dronning Maud Land) 10Be series diverge from each other during the second half of the Holocene, while the 14C series lies in between them. A likely reason for the discrepancy is the insufficiently precise beryllium transport and deposition model for Greenland, which leads to an undercorrection of the GRIP series for the geomagnetic shielding effect. A slow 6–7 millennia variability with lows at ca. 5500 BC and 1500 AD in the long-term evolution of solar activity is found. Two components of solar activity can be statistically distinguished: the main component, corresponding to the “normal” moderate level, and a component corresponding to grand minima. A possible existence of a component representing grand maxima is indicated, but it cannot be separated from the main component in a statistically significant manner. Conclusions. A new consistent reconstruction of solar activity over the last nine millennia is presented with the most probable values of decadal sunspot numbers and their realistic uncertainties. Independent components of solar activity corresponding to the main moderate activity and the grand-minimum state are identified; they may be related to different operation modes of the dynamo. [ABSTRACT FROM AUTHOR]

After 6 years of 36 Cl routine operation, more than 6000 unknown samples have been measured at the 5MV French accelerator mass spectrometry (AMS) national facility ASTER (CEREGE, Aix en Provence). This paper presents the long term behavior of ASTER through the analysis of the measurements of the most used chlorine standards and reference materials, KNSTD1600, SM-Cl-12 and SM-CL-13 over a 46 months’ time period. Comparison of measured chlorine concentrations (both 35 Cl and 36 Cl) from ice samples on two AMS facilities operating at 5MV (ASTER) and 6MV (DREAMS, Helmholtz-Zentrum Dresden-Rossendorf) and normalizing to two different reference materials agree within uncertainties making both reference materials (SM-Cl-12 and KNSTD1600) suitable for 36 Cl measurement at ASTER. [ABSTRACT FROM AUTHOR]

The Sea of Marmara is the connection between the vast Black Sea-Caspian Sea basin (Pontocaspian) and the Global Ocean via the Mediterranean Sea. Its water levels and water conditions has widely varied over times. Combining two cores in the Sea of Marmara (Turkey) and using organic-walled dinoflagellate cyst assemblages as the main proxy (combined with alkenones, diatoms and benthic foraminifera), allow qualitatively reconstructing water conditions during Marine Isotopic Stage (MIS) 6 and 5, such as salinity and oxygen level. A clear main marine phase is illustrated in MIS 5e. A minor marine incursion occurred during MIS 5c, mostly supported by alkenone data. The rest of the record indicates brackish Pontocaspian conditions, with more Spiniferites inaequalis in MIS 6 and more S. cruciformis in the non-marine parts of MIS 5. At the MIS 6/MIS 5 transition, an earlier initial marine flooding in the Sea of Marmara (dinocyst assemblages) in comparison to the Black Sea was highlighted. The marine reconnection occurred at different moments as seen in the terrestrial vegetation reconstructed from pollen analysis linking the two seas. The sapropels of the Sea of Marmara form when marine water penetrates at depth from the Aegean Sea beneath a layer of lower salinity water. Variations of the residence time of the marine deep water in a stratified Sea of Marmara are potentially an important factor underlying hypoxia/anoxia and sapropel deposition. When combining surface water proxies with benthic foraminifera (test assemblages and presence of inner organic lining), it appears that the successive MIS 5 sapropels formed under decreasing salinity and oxygen availability conditions as the marine inflow was increasingly restricted. Understanding the hydrologic evolution of the Sea of Marmara during MIS 5 implies taking into account that the Bosphorus and Dardanelle straits are hydrodynamically coupled and may not be simplified as on/off switches based on present day sill depths. • Dinocyst analyses of last interglacial and previous glacial in the Sea of Marmara on two long cores. • Marine phase in MIS5e (dinocysts, benthic foraminifera, alkenones) minor in MIS5c • BrackishPontocaspian conditions for rest of sequence although different in MIS6 & 5. • Earlier marine flooding at beginning of MIS5e in Sea of Marmara than in Black Sea. • Three sapropels highlight decreasing anoxic conditions over time. [ABSTRACT FROM AUTHOR]

The Marmara region (NW Turkey) has a transitional vegetation and climate between the Mediterranean one and the Euxinian one. For the last Interglacial period or Eemian and following the two Saint-Germain Interstadials (i.e. c. MIS 5), as well and the previous glacial, the Saalian, no vegetation or climate information is available yet. Here we provide the results of the pollen analysis of two sediment cores taken from the Sea of Marmara. We focus on the period below a major erosion horizon, i.e. the red-H1 seismic horizon, which corresponds to the last Interglacial and a large part of the previous glacial period. A palaeoclimatic reconstruction inferred from pollen assemblages is also proposed here. Based on geochemistry that allows inter-core comparison and on a succession of warm and cold phases derived by pollen analysis, a nearly complete sequence from the Saalian Glacial period (c. MIS 6) to the Saint-Germain II Interstadial (MIS 5a) was obtained, despite the occurrence of hiatuses corresponding often to lowstands. The Pterocarya extinction has been traced from MIS 7 in Italy to Saint-Germain I Interstadial (c. MIS 5c) in the eastern Sea of Marmara, showing a progressive retreat from west to east until the Black Sea region, where it is still present nowadays. The climatic changes reconstructed for the Eemian Interglacial (or c. MIS 5e) are characterised by warmer temperature and a slightly drier climate than at present, at its peak. This pattern is in agreement with the Ohrid climate pattern, in the Balkans. In the Marmara region, this is reflecting a shift of the Mediterranean climate towards the NE and a reduction of the Euxinian vegetation. • Pollen analyses of last Interglacial and previous Glacial in Sea of Marmara. • Progressive Pterocarya extinction from MIS7 in S. Europe to MIS5c in Sea of Marmara. • Reduction of Euxinian vegetation and extension of the Mediterranean one during Eemian. • Eemian warmer and slightly drier than present climate. [ABSTRACT FROM AUTHOR]

The Colônia Deep Drilling Project held its first International Continental Scientific Drilling Program (ICDP) workshop in September 2014 at the University of São Paulo (Brazil). Twenty-seven experts from six countries discussed the feasibility and the expectations of a deep drilling in the structure of Colônia located at the southwestern margin of the city of São Paulo. After presenting the studies performed at the site during the last decades, participants focused on the objectives, priorities and detailed planning for a full deep-drilling proposal. An excursion to the site and new auger coring showed the importance of the Colônia site for studying the evolution of a tropical rainforest and to evaluate the interplay between the South American summer monsoon, the Intertropical Convergence Zone (ITCZ) and the southern Westerlies belt during the last 5 million years. In addition, deep drilling will eventually solve the still unresolved issue of the origin of the structure of Colônia as a result of meteorite impact or endogenous processes. [ABSTRACT FROM AUTHOR]

During the last glaciation the Marmara Sea was isolated from the Mediterranean Sea because global sea level was below the depth of the Dardanelles sill. Prior to the postglacial reconnection to the Mediterranean Sea (∼14.7 cal kyr BP), the surface waters of the Marmara Sea were brackish (Marmara Lake). Freshening of a previously saline Marmara Sea could have happened via spill-out of brackish to fresh water from the surface water of the Black Sea through the Bosphorus Strait. This hypothesis has not been tested against alternative possibilities (salt flushing by river run-off and precipitation). Here we use the dissolved Cl − and stable isotope composition ( δ O 18 and δ D ) of Marmara Sea sediment pore water to estimate the salinity and stable isotope composition of Marmara Lake bottom water and to evaluate possible freshening scenarios. We use a transport model to simulate pore water Cl − , δ O 18 and δ D in Marmara Sea sediments in the past 130 kyr, which includes the last interglacial (130–75 cal kyr BP), the last glacial (75–14 cal kyr BP) and the current postglacial period. Our results show that the bottom waters of the Marmara Lake were brackish ( ∼ 4 ‰ salinity) and isotopically depleted ( δ O 18 ∼ − 10.2 ‰ and δ D ∼ − 70 ‰ , respectively) compared to modern seawater. Their salinity and stable isotope ratios show that they are a mixture of Mediterranean waters and Danube-like waters implying that the freshening took place via spill-out of freshwater through the Bosphorus. Our modelling approach indicates that the transit of fresh water from glacial Eurasia to the Mediterranean via the Marmara Sea started at least 50 cal kyr BP, was continuous throughout most of the last glaciation and persisted up to the post glacial reconnection to the Mediterranean through the Dardanelles sill (14.7 cal kyr BP). These results are consistent with previously published micropaleontological and geochemical investigations of sediment cores that indicate lacustrine conditions in the Marmara Sea from about 75 to 14.7 cal kyr BP. [ABSTRACT FROM AUTHOR]

Context. Abreu et al. (2012, A&A. 548, A88) have recently compared the periodicities in a 14C - 10Be proxy record of solar variability during the Holocene and found a strong similarity with the periodicities predicted on the basis of a model of the time-dependent torque exerted by the planets on the sun's tachocline. If verified, this effect would represent a dramatic advance not only in the basic understanding of the Sun's variable activity, but also in the potential influence of this variability on the Earth's climate. Cameron and Schussler (2013, A&A. 557, A83) have seriously criticized the statistical treatment used by Abreu et al. to test the significance of the coincidences between the periodicities of their model with the Holocene proxy record. Aims. If the Abreu et al. hypothesis is correct, it should be possible to find the same periodicities in the records of cosmogenic nuclides at earlier times. Methods. We present here a high-resolution record of 10Be in the EPICA Dome C (EDC) ice core from Antarctica during the Marine Interglacial Stage 9.3 (MIS 9.3), 325-336 kyr ago, and investigate its spectral properties. Results. We find very limited similarity with the periodicities seen in the proxy record of solar variability during the Holocene, or with that of the model of Abreu et al. Conclusions. We find no support for the hypothesis of a planetary influence on solar activity, and raise the question of whether the centennial periodicities of solar activity observed during the Holocene are representative of solar activity variability in general. [ABSTRACT FROM AUTHOR]

Abstract: A source-to-sink multi-proxy approach has been performed within Lake Paladru (492 m a.s.l., French Prealps) catchment and a 6-m long sediment sequence retrieved from the central lacustrine basin. The combination of minerogenic signal, specific organic markers of autochthonous and allochthonous supply and archaeological data allows the reconstruction of a continuous record of past human disturbances. Over the last 10,000 years, the lacustrine sedimentation was dominated by autochthonous carbonates and the watershed was mostly forest-covered. However, seven phases of higher accumulation rate, soil erosion, algal productivity and landscape disturbances have been identified and dated from 8400 to 7900, 6000 to 4800, 4500 to 3200, 2700 to 2050 cal BP as well as AD 350–850, AD 1250–1850 and after AD 1970. Before 5200 cal BP, soil erosion is interpreted as resulting from climatic deterioration phases towards cooler and wetter conditions. During the Mid-Late Holocene period, erosion fluxes and landscape disturbances are always associated with prehistorical and historical human activities and amplified by climatic oscillations. Such changes in human land-used led to increasing minerogenic supply and nutrients loading that affected lacustrine trophic levels, especially during the last 1600 years. In addition, organic and molecular markers document previously unknown human settlements around Lake Paladru during the Bronze and the Iron Ages. [Copyright &y& Elsevier]

The article presents a study which explores the use of climate forcing reconstructions in the Paleoclimate Model Intercomparison Project Phase III (PMIP3) simulations over the period 850 CE to 1850 CE. Assessments in the anthropogenic changes in Land Use/Land Cover (LULC) are outlined. A discussion on the calibration of solar activity and solar irradiance is provided.

The article discusses the Paleoclimate Model Intercomparison Project Phase III (PMIPP3) experiments on climate forcings. It offers updates on the reconstructions of the land use and the changes in land cover, and the solar activity calibration. It also discusses the radiative forcing used to estimate actual forcing in a climate model.

Abstract: During the last decade, a debate arose regarding the timing and pattern of the last reconnection of the Black Sea “Lake” with the global ocean. On a geochemical basis, the radiocarbon age of Black Sea “Lake” surface water, during the time of reconnection, was determined to be ∼8400 14C a. BP. Despite the potential bias induced by the hard water effect in lakes, the reconnection age was calibrated without any reservoir age correction, which led to an estimate of ∼9400 cal a. BP. Since knowledge for the actual calendar age has important hydrologic implications that would provide new insights regarding the mechanism of reconnection, determining the actual calendar age for the last reconnection remains important. Based upon modeling experiments and micropaleontological reconstructions, the Black Sea “Lake” reconnection occurred in two steps, as follows: 1) Initial Marine Inflow (IMI) followed by 2) a period of increasing basin salinity that led to the Disappearance of Lacustrine Species (DLS). In order to better define the actual calendar age for the last reconnection, a review of the sedimentary expressions of the IMI and DLS boundaries was performed in order to correlate them throughout the Black Sea sedimentary environments. This correlation reconciles the apparent inconsistency in the published radiocarbon dataset, and provides the atmospheric radiocarbon age of the last reconnection, which represents the reference for reservoir age calculations and which can be directly calibrated. We determine reservoir ages for the water column, as well as the reconnection calendar age to be 9000 cal a. BP. At the reconnection with the global ocean, Black Sea “Lake” reservoir ages were non-negligible and water-depth-dependent, consistent with a weak water column stratification during the Early Holocene. The calibrated age of Initial Marine Inflow (9000 cal a. BP) implies that the former Bosphorus sill was shallower by ∼10 m than is commonly assumed in the literature. Compared to the sedimentary context of the Sakarya coastal plain, this result suggests that the level of the isolated Black Sea was below the former Bosphorus sill depth at the time of the last reconnection. Furthermore, a lag of ∼900 yr between Initial Marine Inflow and the Disappearance of Lacustrine Species indicates that approximately ten centuries were needed to establish the currently observed two-way flow exchange with the global ocean. [Copyright &y& Elsevier]

The article discusses the utilization of climate forcing reconstructions for the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3) simulations over the last millennium (LM). It describes an approach taken in defining the scenarios in PMIP3 such as land use changes, variation in greenhouse levels and volcanic forcing of aerosols. It notes that the changes in global mean forcing related with orbital changes are little like the net forcing due to ozone-related changes.

Abstract: The circulation patterns of the deep glacial Pacific Ocean are still debated. Difficulties arise due to the scarcity of reliable paleoceanographic records that can document the past movements and properties of Pacific Ocean water masses. Here, we jointly use δ13C and δ18O measured on the epibenthic foraminifer Cibicidoides wuellerstorfi, from the MD02-2529 sediment core collected at 1619m water depth in the eastern equatorial Pacific, to monitor changes in water mass circulation spanning the past 150kyrBP. After the extraction of short-term (centennial to millennial-scale) δ13C and δ18O changes, which were ~1.0 and 0.5‰, respectively, we observed that these rapid δ13C and δ18O shifts were closely interrelated during the last 150kyrBP. A comparison of MD02-2529 with other benthic δ13C records localized to the north and south of the core location revealed that MD02-2529 was alternately bathed by a northern nutrient-rich and a southern nutrient-poor water mass. The comparison provided a diagnostic for the latitudinal movements of a sharp water mass front that was particularly evident during marine isotope stages 4 and 3 on the millennial timescale. By considering that δ13C is an indicator of the northern vs. southern origin of the water that bathed the MD02-2529 coring site in the past, we found that a North Pacific water mass, that occasionally spreads to the eastern Pacific Ocean as deep as 1600m and as far south as 8°N, was responsible for shifts toward the positive δ18O we observed in the past. We then used the δ13C/δ18O relationship to reconstruct latitudinal temperature and/or salinity gradients of the water mass that were linked to changes in the northern and/or the southern water mass end-members. Evolution of the δ13C/δ18O relationship spanning the past 150kyrBP has shed light on how hydrological processes occurring at northern and southern high latitudes are transmitted to the ocean''s interior through water mass advection. [Copyright &y& Elsevier]

Abstract: Chloride and δ 18O compositions of interstitial water extracted from a long sediment core retrieved from the NW coast of the Black Sea allowed us to constrain the main hydrologic changes of the Back Sea during the Late Pleistocene and Holocene. Prior to its reconnection with the Mediterranean Sea (through the Marmara Sea) at approximately 9000 calendar yr before present (9kacalBP), the Black Sea has evolved as a fresh to brackish water lake. At the time of reconnection, hydrologic changes were drastic. Bottom water salinities changed from a few psu (practical salinity unit) to ∼22psu. Since solutes in the interstitial water column within sediments are advected and diffused the measured concentrations do not reflect those of past bottom waters. In order to reconstruct these former concentrations, we used an advection/diffusion model. Different scenarios of bottom water chloride and δ 18O variations were accounted for in this model in order to simulate “present day” vertical profiles for concentrations of interstitial water in order to compare them to measured ones. The comparison suggests that the glacial Black Sea was a homogeneous freshwater lake (with a δ 18O of ∼−10‰ and a salinity of ∼1psu). Modern hydrologic conditions would only have been reached at ∼2kacalBP, concomitant with the onset of coccolith-rich thin layers that characterize modern basin sediments. Such delayed salinization (over ∼7000yr) in the basin may have been due to higher precipitation during the early Holocene. We also simulated the impact of a catastrophic reconnection and a smoother reconnection. Both salinity scenarios lead to undistinguishable modelled “present day” profiles, indicating that the precise impact of the last reconnection was lost due to the advection/diffusion processes. [Copyright &y& Elsevier]

The article discusses the approach taken in defining the scenarios used into the third phase of the Paleoclimate Modelling Intercomparison Project (PMIP3) over the last millennium (LM) along with the forcing reconstructions and implications. It presents the first-order forcing functions that are relevant for this period which had been chosen by the availability of data and state of knowledge. The functions include orbital variations, well-mixed greenhouse gases and land use/land cover (LULC).

Abstract: Chirp sub-bottom profiling, multibeam bathymetric mapping and a combination of faunal and isotopic analysis of molluscs and foraminifera in sediment cores on the northern shelf of the Sea of Marmara (SoM) provide evidence of sea-level excursions, water exchanges between the adjacent Mediterranean and Black Seas, and oscillating salinity over the last 160ka bp. During the marine isotope stages MIS-2, MIS-3, MIS-4 and MIS-6 the SoM disconnected from the Mediterranean Sea and evolved into a lake. During MIS-1, MIS-5 and MIS-7, the SoM reconnected and became salty once again. Sapropels formed shortly after each invasion of Mediterranean saltwater observed in our cores. Concurrent suboxic–dysoxic conditions prevailed over quite shallow substrates on the shelf. Ancient shorelines are pervasive at −85m on the northern shelf and in the region of Prince Islands coincident with the elevation of the modern bedrock sill in the Çanakkale (Dardanelles) Strait. At times when global (eustatic) sea level dropped below this sill, the surface of the SoM stabilized at its outlet and freshened. Thus this particular shoreline is interpreted as the edge of the most recent SoM lake that existed from about 75ka bp to 12ka bp. The freshening is observed in very light (−6‰) values of δ 18O measured on freshwater molluscs and the complete absence of foraminifera. Two brief lacustrine episodes during MIS-5 suggest that the level of the Çanakkale outlet might have been as shallow as −50m in the past, a likelihood supported by submerged terraces along its margins bounding the modern central channel and the presence of an euryhaline biofacies in Unit L4.1 corresponding to MIS-5b. δ 18O profiles and carbon-14 dating show that salinification of the SoM and the blossoming of bioherms evolved rapidly after the latest connection with the Mediterranean at 12ka bp. However, freshening proceeded more slowly once the connection was severed. [Copyright &y& Elsevier]

Abstract: The direct sea–land correlation applied to core MD99-2331 retrieved from the north-western Iberian margin shows a two-phase pattern within Heinrich events 4, 2 and 1 in the ocean and in the adjacent landmasses. Changes between wet/cold and dry/cool conditions in the Iberian Peninsula detected during these extreme events cannot be explained by a simple oceanographic mechanism related to changes in the strength of the Atlantic Meridional Overturning Circulation. Here we propose an additional atmospheric mechanism able to produce this scenario based on the comparison between the MD99-2331 record and other available palaeoclimate sequences from the North Atlantic region (18–75°N and 0–75°W). The climatic asymmetry observed between mid- and subtropical eastern North Atlantic latitudes (wet/dry) and the Blake Outer Ridge (dry/wet) during H4, H2 and H1 can be explained by changes in the position of the Atlantic jet-stream. During the first phase of H4, H2 and H1 the Atlantic jet-stream was located further south following the southward displacement of the oceanic thermal front as far south as 35°–37°N. On the contrary, during the second phase of H4, H2 and H1 the jet-stream was located further north following the northward displacement of this thermal front as far north as 42°N. From the atmospheric point of view, these two phases are reminiscent of the present-day negative and positive prevailing modes of the North Atlantic Oscillation (NAO), respectively, but high-resolution studies of additional North Atlantic key sites and climate simulations are needed to confirm the hypothesis of a NAO-like mechanism operating on millennial timescales. [Copyright &y& Elsevier]

Results from multiple model simulations are used to understand the tropical sea surface temperature (SST) response to the reduced greenhouse gas concentrations and large continental ice sheets of the last glacial maximum (LGM). We present LGM simulations from the Paleoclimate Modelling Intercomparison Project, Phase 2 (PMIP2) and compare these simulations to proxy data collated and harmonized within the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface Project (MARGO). Five atmosphere–ocean coupled climate models (AOGCMs) and one coupled model of intermediate complexity have PMIP2 ocean results available for LGM. The models give a range of tropical (defined for this paper as 15°S–15°N) SST cooling of 1.0–2.4°C, comparable to the MARGO estimate of annual cooling of 1.7 ± 1°C. The models simulate greater SST cooling in the tropical Atlantic than tropical Pacific, but interbasin and intrabasin variations of cooling are much smaller than those found in the MARGO reconstruction. The simulated tropical coolings are relatively insensitive to season, a feature also present in the MARGO transferred-based estimates calculated from planktonic foraminiferal assemblages for the Indian and Pacific Oceans. These assemblages indicate seasonality in cooling in the Atlantic basin, with greater cooling in northern summer than northern winter, not captured by the model simulations. Biases in the simulations of the tropical upwelling and thermocline found in the preindustrial control simulations remain for the LGM simulations and are partly responsible for the more homogeneous spatial and temporal LGM tropical cooling simulated by the models. The PMIP2 LGM simulations give estimates for the climate sensitivity parameter of 0.67°–0.83°C per Wm−2, which translates to equilibrium climate sensitivity for doubling of atmospheric CO2 of 2.6–3.1°C. [ABSTRACT FROM AUTHOR]

Abstract: In their comment Hiscott and co-authors adhere rigidly to ages and sources for sedimentary units in the subsurface of the Marmara shelf that they have previously reported in their publications from 2002 through 2007. This adherence is in spite of a superior age-depth model from our 13 m-long sediment core that penetrated deeply into the deposits under consideration and in disregard to the results of subsequent more-detailed and full-coverage mapping of the region under scrutiny. The age revisions are dismissed by the authors of the comment as representing sediments severely disturbed during coring. We rebut this criticism. The Bosporus source attributed by them to the sedimentary units sampled and dated by us appears to be driven by their conception that the Black Sea had a persistent outflow prior to its two-way connection with Marmara. Irrespective of whether the outflow was persistent, our reply shows that the drawing of the isopachs of the sedimentary units by Hiscott and co-authors was accomplished in a fashion to promote the Bosporus source hypothesis regardless of the geographic limits of their survey. The ages assigned to the units are equally indeterminate because the cores used by them have missing core tops of unknown lengths that are not discussed in their publications. Furthermore, the sub-bottom reflectors at the sites where the reflectors were calibrated to their only core without a missing top are actually hidden by the finite width of the bottom reflecting wavelet. [Copyright &y& Elsevier]

Abstract: High-resolution seismic reflection profiles and analyses of the sedimentary substrate at the Sea of Marmara (SoM) entrance to the Strait of İstanbul (SoI, Bosphorus) provide a detailed record of the transgression that took place after the SoM reconnected with the Mediterranean. The sediments progressively fill a paleo shelf valley that incised the margin from the SoI to the shelf break at the time of the pre-Holocene lowstand. We map seven seismic reflection units that can be confidently correlated to sediment cores by lithology and physical properties. Sediments in the cores are dated by radiocarbon methods. Early channel and levee deposits within the paleo valley belong to the Younger Dryas cold stage and record outflow from the Black Sea via the SoI. Small clinoform packages on the valley margin formed in proximity to climbing paleo shorelines. The elevations of these deposits conform to the sealevel history recorded in Barbados corals. The younger part of the succession includes a subaqueous prodelta sourced from the Kurbağalıdere River. Its relatively young age when the Holocene sea had almost reached its modern level suggests that the thick progradational and aggradational clinoform development was primarily a response to sediment supply rather than the filling of expanding accommodation space. Our findings refute the hypothesis of Aksu et al. (Aksu, A.E., Hiscott, R.N., Mudie., P.J., Rochon, A., Kaminski, M.A., Abrojano, T., Yaşar, D., 2002a. Persistent Holocene outflow fromn the Black Sea to the Eastern Mediterranean contradicts Noah''s Flood hypothesis, GSA Today 10,(6), 3–7., Aksu, A.E., Hiscott, R.N., Kaminski, M.A., Mudie, P.J., Gillespie, H., Abrojano, T., Yaşar, D., 2002b. Last glacial–Holocene paleoceanography of the Black Sea and Marmara Sea: stable isotopic, foraminiferal and coccolith evidence. Mar. Geol., 190, 119–149.) and Hiscott et al. (Hiscott, R.N., Aksu, A.E., Yaşar, D., Kaminski, M.A., Mudie, P.J., Kostylev, V.E., MacDonald, J.C. Isler, F.I., Lord, A.R., 2002. Deltas south of the Bosphorus Strait record persistent Black Sea outflow to the Marmara Sea since ∼10 ka, Mar. Geol., 190, 95–118., Hiscott, R.N., Aksu, A.E., Mudie., P.J., Kaminski, M.A., Abrajano, T., Yaşar, D., Rochon, A., 2007. The Marmara Sea gateway since ∼16 ky BP: non-catastrophic causes of paleoceanographic events in the Black Sea at 8.4 and 7.15 ky BP. In Yanko-Hombach,V., Gilbert, A.S., Dolukhanov, P.M. (Eds.), The Black Sea Flood Question, Springer, The Netherlands, 89–117.) that this deposit was supplied from the SoI and that its presence requires a persistent Black Sea outflow since 10 14C ka bp (not corrected from the reservoir age or calibrated). [Copyright &y& Elsevier]

Radiocarbon dating archaeological bone typically requires 300–1000 mg material using standard protocols. We report the results of reducing sample size at both the pretreatment and 14C measurement stages for eight archaeological bones spanning the radiocarbon timescale at different levels of preservation. We adapted our standard collagen extraction protocol specifically for <100 mg bone material. Collagen was extracted at least twice (from 37–100 mg material) from each bone. Collagen aliquots containing <100 μg carbon were measured in replicate using the gas ion source of the AixMICADAS. The effect of sample size reduction in the EA-GIS-AMS system was explored by measuring 14C of collagen containing either ca. 30 μg carbon or ca. 90 μg carbon. The gas dates were compared to standard-sized graphite dates extracted from large amounts (500–700 mg) of bone material pretreated with our standard protocol. The results reported here demonstrate that we are able to reproduce accurate radiocarbon dates from <100 mg archaeological bone material back to 40,000 BP. [ABSTRACT FROM AUTHOR]