Ages analysis, trace elements and relative frequencies of foraminifera snd diatoms from sediment cores AvH248260-2 and AvH248260-1, Ameralik Fjord, SW Greenland

A multiproxy record including benthic foraminifera, diatoms and XRF data of a marine sediment core from a SW Greenland fjord provides a detailed reconstruction of the oceanographic and climatic variations of the region during the last 4400 cal. years. The lower part of our record represents the final termination of the Holocene Thermal Maximum. After the onset of the 'Neoglaciation' at approximately 3.2 ka cal. BP, the fjord system was subject to a number of marked hydrographical changes that were closely linked to the general climatic and oceanographic development of the Labrador Sea and the North Atlantic region. Our data show that increased advection of Atlantic water (Irminger Sea Water) from the West Greenland Current into the Labrador Sea was a typical feature of Northeast Atlantic cooling episodes such as the 'Little Ice Age' and the 'European Dark Ages', while the advection of Irminger Sea Water decreased significantly during warm episodes such as the 'Mediaeval Warm Period' and the 'Roman Warm Period'.Whereas the 'Mediaeval Warm Period' was characterized by relatively cool climate as suggested by low meltwater production, the preceding 'Dark Ages' display higher meltwater runoff and consequently warmer climate. When compared with European climate, these regional climate anomalies indicate persisting patterns of advection of colder, respectively warmer air masses in the study region during these periods and thus a long-term seesaw climate pattern between West Greenland and Europe.

Organic d13C values, kerogen atomic C/N ratios and relative weights of some kerogen pyrolysis products of ODP Hole 112-682A (Table 1)

Carbon isotopic composition of predominantly marine kerogen in latest Oligocene mudstones of the Peru Margin ODP 682A Hole shows an about 3.5? increase with decreasing age. Py-GC and elemental (C=N ratio) analysis of the kerogen plus sulphur isotopic study together with earlier knowledge on geological setting and organic geochemistry results in a better understanding of depositionary environment and allows to separation of the influence of concentration of water dissolved carbon dioxide (ce) on kerogen delta13C from that of other factors (bacterial degradation, sea surface temperature, DIC delta13C, productivity, and admixture of land plant OM). Based on this analysis, the major part of the kerogen shift is considered as a result of the latest Oligocene decrease of marine photosynthetic carbon isotopic fractionation in the Peru Margin photic zone, which in turn possibly reflects a simultaneous drop in atmospheric CO2 level. Uncertainties in the evaluation of the factors affecting the marine photosynthetic carbon isotopic fractionation and the extent of ocean-atmosphere disequilibrium do not permit calculation of the decrease of the atmospheric CO2.

Eolian mass-accumulation rates and grain size at DSDP Sites 86-576 and 86-578

The mass-accumulation rate and grain size of the total eolian component of North Pacific pelagic clays at Deep Sea Drilling Project Sites 576 and 578 have been used to evaluate changes in eolian sedimentation and the intensity of atmospheric circulation that have occurred during the past 70 m.y. Eolian deposition, an indicator of source area aridity, was low in the Paleocene, Eocene, and Oligocene, apparently reflecting the humid environments of that time as well as the lack of glacial erosion products. A general increase in eoiian accumulation in the Miocene apparently reflects the relative increase in global aridity during the latter part of the Cenozoic. A dramatic increase in eolian accumulation rates in the Pliocene reflects the increased aridity and availability of glacial erosion products associated with Northern Hemisphere glaciation 2.5 m.y. ago. Eolian grain size, an indicator of wind intensity, suggests that Late Cretaceous wind strength was comparable to present-day wind strength. A sharp decrease in eolian grain size across the Paleocene/Eocene boundary is not readily interpreted, but may indicate a significant reduction in the intensity of atmospheric circulation at that time. Fine eolian grain size and low accumulation rates in the Eocene and early Oligocene are in agreement with low early Tertiary thermal gradients and less vigorous atmospheric circulation. Large increases in grain size during the Oligocene, mid-to-late Miocene, and Pliocene appear to be a response to steepening thermal gradients resulting from increasing polar isolation.

Dissolved organic carbon concentrations, amino sugar concentrations and highly significantly correlating FT-ICR mass peak magnitudes obtained from solid phase extracted marine dissolved organic matter during POLARSTERN cruise ANT-XXV/1

Dissolved organic matter (DOM) was extracted with solid phase extraction (SPE) from 137 water samples from different climate zones and different depths along an Eastern Atlantic Ocean transect. The extracts were analyzed with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) with electrospray ionization (ESI). D14C analyses were performed on subsamples of the SPE-DOM. In addition, the amount of dissolved organic carbon was determined for all water and SPE-DOM samples as well as the yield of amino sugars for selected samples. Linear correlations were observed between the magnitudes of 43% of the FT-ICR mass peaks and the extract D14C values. Decreasing SPE-DOM D14C values went along with a shift in the molecular composition to higher average masses (m/z) and lower hydrogen/carbon (H/C) ratios. The correlation was used to model the SPE-DOM D14C distribution for all 137 samples. Based on single mass peaks a degradation index was developed to compare the degradation state of marine SPE-DOM samples analyzed with FT-ICR MS. A correlation between D14C, degradation index, DOC values and amino sugar yield supports that SPE-DOM analyzed with FT-ICR MS reflects trends of bulk DOM. A relative mass peak magnitude ratio was used to compare aged SPE-DOM and fresh SPE-DOM regarding single mass peaks. The magnitude ratios show a continuum of different reactivities for the single compounds. Only few of the compounds present in the FT-ICR mass spectra are expected to be highly degraded in the oldest water masses of the Pacific Ocean. All other compounds should persist partly thermohaline circulation. Prokaryotic (bacterial) production, transformation and accumulation of this very stable DOM occurs probably primarily in the upper ocean. This DOM is an important contribution to very old DOM, showing that production and degradation are dynamic processes.

(Table 3) Relative depth and age, CaCO3, d18O, d13C and Sr/Ca analysis from ODP Leg 130, 154 and 138

Interpretations of calcite strontium/calcium records in terms of ocean history and calcite diagenesis require distinguishing the effects on deep-sea calcite sediments of changes in ocean chemistry, of different mixes of calcite-depositing organisms as sediment contributors through time and space, and of the loss of Sr during diagenetic calcite recrystallization. In this paper Sr/Ca and d18O values of bulk calcium carbonate sediments are used to estimate the relative extent of calcite recrystallization in samples from four time points (core tops, 5.6, 9.4, and 37.1 Ma) at eight Ocean Drilling Program sites in the equatorial Atlantic (Ceara Rise) and equatorial Pacific (Ontong Java Plateau and two eastern equatorial Pacific sites). The possibility that site-to-site differences in calcite Sr/Ca at a given time point originated from temporal variations in ocean chemistry was eliminated by careful age control of samples for each time point, with sample ages differing by less than the oceanic residence times of Sr and Ca. The Sr/Ca and d18O values of 5.6- and 9.4-Ma samples from the less-carbonate-rich eastern equatorial Pacific sites and Ceara Rise Site 929 appear to be less diagenetically altered than the Sr/Ca and d18O values of contemporaneous samples from the more carbonate-rich sites. It is evident from these data that both Sr/Ca and d18O in bulk calcite have been diagenetically altered in some samples 5.6 Ma and older. These data indicate that noncarbonate sedimentary components, like clay and biogenic silica, have partially suppressed recrystallization at the lower carbonate sites. Sr/Ca data from the less altered, carbonate-poor sites indicate higher oceanic Sr/Ca relative to today at 5.6 and 9.4 Ma.

Relative sea-level history of Marguerite Bay, Antarctic Peninsula derived from optically stimulated luminescence-dated beach cobbles

Calmette Bay within Marguerite Bay along the western side of the Antarctic Peninsula contains one of the most continuous flights of raised beaches described to date in Antarctica. Raised beaches extend to 40.8 m above sea level (masl) and are thought to reflect glacial isostatic adjustment due to the retreat of the Antarctic Peninsula Ice Sheet. Using optically stimulated luminescence (OSL), we dated quartz extracts from cobble surfaces buried in raised beaches at Calmette Bay. The beaches are separated into upper and lower beaches based on OSL ages, geomorphology, and sedimentary fabric. The two sets of beaches are separated by a prominent scarp. One of our OSL ages from the upper beaches dates to 9.3 thousand years ago (ka; as of 1950) consistent with previous extrapolation of sea-level data and the time of ice retreat from inner Marguerite Bay. However, four of the seven ages from the upper beaches date to the timing of glaciation. We interpret these ages to represent reworking of beaches deposited prior to the Last Glacial Maximum (LGM) by advancing and retreating LGM ice. Ages from the lower beaches record relative sea-level fall due to Holocene glacial-isostatic adjustment. We suggest a Holocene marine limit of 21.7 masl with an age of 5.5-7.3 ka based on OSL ages from Calmette Bay and other sea-level constraints in the area. A marine limit at 21.7 masl implies half as much relative sea-level change in Marguerite Bay during the Holocene as suggested by previous sea-level reconstructions. No evidence for a relative sea-level signature of neoglacial events, such as a decrease followed by an increase in RSL fall due to ice advance and retreat associated with the Little Ice Age, is found within Marguerite Bay indicating either: (1) no significant neoglacial advances occurred within Marguerite Bay; (2) rheological heterogeneity allows part of the Antarctic Peninsula (i.e. the South Shetland Islands) to respond to rapid ice mass changes while other regions are incapable of responding to short-lived ice advances; or (3) the magnitude of neoglacial events within Marguerite Bay is too small to resolve through relative sea-level reconstructions. Although the application of reconstructing sea-level histories using OSL-dated raised beach deposits provides a better understanding of the timing and nature of relative sea-level change in Marguerite Bay, we highlight possible problems associated with using raised beaches as sea-level indices due to post-depositional reworking by storm waves.

Relative contents of foraminifera species in bottom sediments of northern and southern seas

Correlation of paleoceanographic events in several key regions of the World Ocean: North Atlantic, Antarctic, West Arctic Seas, North Pacific and tropical Indo-Pacific has been carried out for the last 135 ka based on micropaleontological, stable isotope, geochronological (AMS-14C) and other data. It has been shown that the global thermohaline circulation controls remote climatic teleconnections on millennial-scale and partly on centennial-scale, while short-term climate changes are mainly transferred by the atmosphere. The basic information is given about the recent thermohaline circulation and stages of its development during Neogene.

Relative abundance of dinoflagellate cysts in surface sediments and dinoflagellate counts from three sediment cores from the Atlantic sector of the Southern Ocean

In this study we investigate the potential of organic-walled dinoflagellate cysts (dinocysts) as tools for quantifying past sea-surface temperatures (SST) in the Southern Ocean. For this purpose, a dinocyst reference dataset has been formed, based on 138 surface sediment samples from different circum-Antarctic environments. The dinocyst assemblages of these samples are composed of phototrophic (gonyaulacoid) and heterotrophic (protoperidinioid) species that provide a broad spectrum of palaeoenvironmental information. The relationship between the environmental parameters in the upper water column and the dinocyst distribution patterns of individual species has been established using the statistical method of Canonical Correspondence Analysis (CCA). Among the variables tested, summer SST appeared to correspond to the maximum variance represented in the dataset. To establish quantitative summer SST reconstructions, a Modern Analogue Technique (MAT) has been performed on data from three Late Quaternary dinocyst records recovered from locations adjacent to prominent oceanic fronts in the Atlantic sector of the Southern Ocean. These dinocyst time series exhibit periodic changes in the dinocyst assemblage during the last two glacial/interglacial-cycles. During glacial conditions the relative abundance of protoperidinioid cysts was highest, whereas interglacial conditions are characterised by generally lower cyst concentrations and increased relative abundance of gonyaulacoid cysts. The MAT palaeotemperature estimates show trends in summer SST changes following the global oxygen isotope signal and a strong correlation with past temperatures of the last 140,000 years based on other proxies. However, by comparing the dinocyst results to quantitative estimates of summer SSTs based on diatoms, radiolarians and foraminifer-derived stable isotope records it can be shown that in several core intervals the dinocyst-based summer SSTs appeared to be extremely high. In these intervals the dinocyst record seems to be highly influenced by selective degradation, leading to unusual temperature ranges and to unrealistic palaeotemperatures. We used the selective degradation index (kt-index) to determine those intervals that have been biased by selective degradation in order to correct the palaeotemperature estimates. We show that after correction the dinocyst based SSTs correspond reasonably well with other palaeotemperature estimates for this region, supporting the great potential of dinoflagellate cysts as a basis for quantitative palaeoenvironmental studies.

(Table T2) Relative signal intensity of intact polar lipids in sediments from ODP Sites 207-1257 and 207-1258

We report results from the analysis of intact polar lipids (IPLs) in sediments from Ocean Drilling Program Sites 1257 and 1258. IPLs, constituting the cell membranes of living organisms, were detected in organic-lean sediments but not in underlying organic-rich black shales. Microbial activity in organic-lean sediments is likely due to sulfate-dependent oxidation of methane whereas difficulties detecting IPLs in black shales are interpreted to result from unfavorable signal-to-noise ratios due to low cell concentrations in combination with extremely high analytical noise created by uncharacterized organic matrix. IPLs found are consistent with a low-diversity community of archaea and bacteria. The concentrations of IPLs are more than one order of magnitude lower than those in Neogene deep subsurface sediments at the Peruvian margin, suggestive of significantly lower cell concentrations in Demerara Rise. This finding is consistent with inferred low rates of subsurface microbial activity.

Stable oxygen isotope ratios of diatoms and relative species abundances in ODP Site 145-882

Recent research has increasingly advocated a role for the North Pacific Ocean in modulating global climatic changes over both the last glacial cycle and further back into the geological record. Here a diatom d18O record is presented from Ocean Drilling Program Site 882 over the Pliocene/Quaternary boundary from 2.73 Ma to 2.52 Ma (MIS G6-MIS 99). Large changes in d18Odiatom of c. 4 per mil from 2.73 Ma onwards are documented to occur on a timeframe broadly coinciding with glacial-interglacial cycles. These changes are primarily attributed to large scale inputs of meltwater from glacials surrounding the North Pacific Basin and the Bering Sea. Despite these inputs and associated change in surface water salinity, on the basis of existing opal and UK37 temperature data and new modelled water column densities, no evidence exists to suggests a removal of the halocline stratification or a resumption of the high productivity system similar to that which prevailed prior to 2.73 Ma. The permanence of the halocline suggests that the region played a key role in driving global climatic changes over the early glacial-interglacial cycles that followed the onset of major Northern Hemisphere Glaciation by inhibiting deep water upwelling and ventilation of CO2 to the atmosphere.

(Figure 4) Stable carbon isotopic values and relative contents of biphytanes and sugars from sediment sample from the Peru margin and from the Pakistan margin

Glycolipids are prominent constituents in the membranes of cells from all domains of life. For example, diglycosyl-glycerol dibiphytanyl glycerol tetraethers (2Gly-GDGTs) are associated with methanotrophic ANME-1 archaea and heterotrophic benthic archaea, two archaeal groups of global biogeochemical importance. The hydrophobic biphytane moieties of 2Gly-GDGTs from these two uncultivated archaeal groups exhibit distinct carbon isotopic compositions. To explore whether the isotopic compositions of the sugar headgroups provide additional information on the metabolism of their producers, we developed a procedure to analyze the d13C values of glycosidic headgroups. Successful determination was achieved by (1) monitoring the contamination from free sugars during lipid extraction and preparation, (2) optimizing the hydrolytic conditions for glycolipids, and (3) derivatizing the resulting sugars into aldononitrile acetate derivatives, which are stable enough to withstand a subsequent column purification step. First results of d13C values of sugars cleaved from 2Gly-GDGTs in two marine sediment samples, one containing predominantly ANME-1 archaea and the other benthic archaea, were obtained and compared with the d13C values of the corresponding biphytanes. In both samples the dominant sugar headgroups were enriched in 13C relative to the corresponding major biphytane. This 13C enrichment was significantly larger in the putative major glycolipids from ANME-1 archaea (~15 per mil) than in those from benthic archaea (<7 per mil). This method opens a new analytical window for the examination of carbon isotopic relationships between sugars and lipids in uncultivated organisms.