Bulk components and ice rafted debris of five sediment cores of the Sophia Basin, Arctic Ocean

Periods of enhanced terrigenous input to the ocean's basins of the North Atlantic have been reported for the last glacial period. We present a set of new sediment cores recovered from the Sophia Basin north of Svalbard which exhibit wide spread IRD layers reflecting enhanced terrigenous input throughout the last ~200 kyr. BP. Their consistent stratigraphic position, sedimentological character, high sedimentation rate and geochemical characteristic point to synchronously deposited layers which we name terrigenous input events (TIEs). Due to their higher densities, they generate excellent reflectors for sediment penetrating acoustic devices and prominent acoustic layers in the imagery of sedimentary structures. Therefore TIEs can be used for regional acoustic stratigraphy. Each of the events can be linked to major glacial activity on Svalbard. However, the Early Weichselian glaciation is not recorded as a TIE and, in agreement with other work, might not have occurred on Svalbard as a major glacial advance to the shelf break. Non-synchronous timing of western and northern sources on Svalbard points against sea-level induced iceberg discharge events.

Chemistry and stable isotope record of sediment core GeoB4905-4

Evidence of rapid climatic oscillations like those observed in the Greenland ice cores and sediments from high latitudes of the northern Atlantic have been recognized in the pulses of terrigenous material to continental margin sediments off Cameroon. Fe/Ca ratios used as a parameter to quantify the relative proportions of terrigenous fluxes versus marine carbonate monitor the variability of the west African monsoon. They reveal the history of abrupt changes in precipitation over western and central Africa during the past 52 kyr. These rapid changes are particularly pronounced during the last glacial period and occur at timescales of a few thousand years. Stable oxygen isotope (delta18O) records of Globigerinoides ruber (pink) show high negative values reflecting periods of high monsoon precipitation. The Fe/Ca pattern is very similar to the Dansgaard-Oeschger cycles from the Greenland ice cores. The good correspondence between the warm interstadials of the Dansgaard-Oeschger cycles from the GISP2 ice core records and the high pulses of Fe/Ca sedimentation in our core suggest a strong teleconnection between the low-latitude African climate and the high-latitude northern hemisphere climate oscillations during the last glacial. This climatic link is probably vested in the west African monsoonal fluctuation that alters tropical sea surface temperatures, thermohaline circulations and in turn net export of heat from the south to the north Atlantic, coupled with the variability of the low-latitude southeast trade winds.

Radiocarbon dating and alkenone-based proxies of sediment core GeoB7702-3

In this study we utilize two organic geochemical proxies, the Uk'37 index and TEX86, to examine past sea surface temperatures (SST) from a site located near the Nile River Delta in the eastern Mediterranean (EM) Sea. The Uk'37 and TEX86 records generally are in agreement and indicate SST ranges of 14°C-26°C and 14°C-28°C, respectively, during the last 27 cal ka. During the Holocene, TEX86-based SST estimates are usually higher than Uk'37-based SST estimates, which is likely due to seasonal differences between the timing of the haptophyte and crenarchaeota blooms in the EM and is related to the onset of the modern flow regime of the Nile River. Both records show that SST varied on centennial to millennial timescales in response to global climate events, i.e., cooling during the Last Glacial Maximum (LGM), Heinrich event 1 (H1), and the Younger Dryas (YD) and warming during the Bølling-Allerød and in the early Holocene during deposition of sapropel S1. The H1 cooling was particularly severe and is marked by a drop in SST of ~4.5°C in comparison to pre-H1 SST, with temperatures >1°C cooler than during the LGM. In contrast to high-latitude and western Mediterranean records, which indicate both an abrupt onset and termination of the YD event, the transition from the YD to the Holocene was much more gradual in the EM.

Geochemistry and minerals at DSDP Legs 68-70 Holes

The compositions of natural glasses and phenocrysts in basalts from Deep Sea Drilling Project Sites 501, 504, and 505, near the Costa Rica Rift, constitute evidence for the existence of a periodically replenished axial magma chamber that repeatedly erupted lavas of remarkably uniform composition. Magma compositions were affected by three general components: (1) injected magmas carrying (in decreasing order of abundance) Plagioclase, olivine, and chrome-spinel phenocrysts (spinel assemblage); (2) injected magmas carrying Plagioclase, clinopyroxene, and olivine phenocrysts, but no spinel (clinopyroxene assemblage); and (3) moderately evolved hybrids in the magma chamber itself. The compositions of the injected phenocrysts and minerals in glomerocrysts are as follows: Plagioclase - An85-94; olivine - Fo87-89; clinopyroxene - high Cr2O3 (0.7-1.1%), endiopside (Wo42En51Fs7), and aluminous chromian spinel (Cr/Cr + Al = 0.3). These minerals resemble those thought to occur in upper mantle sources (9 kbars and less) of ocean-ridge basalts and to crystallize in magmas near those sources. In the magma chamber, more sodic Plagioclase (An79-85), less magnesian olivine (Fo81-86) and low-Cr2O3 (0.1-0.4%) clinopyroxene formed rims on these crystals, grew as other phenocrysts, and formed cumulus segregations on the walls and floors of the magma chamber. In the spinel-assemblage magmas, magnesiochromite (Cr/Cr + Al = 0.4-0.5) also formed. Some cumulus segregations were later entrained in lavas as xenoliths. The glass compositions define 16 internally homogeneous eruptive units, 13 of which are in stratigraphic order in a single hole, Hole 504B, which was drilled 561.5 meters into the ocean crust. These units are defined as differing from each other by more than analytical uncertainty in one or more oxides. However, many of the glass groups in Hole 504B show virtually no differences in TiO2 contents, Mg/Mg + Fe2+, or normative An/An + Ab, all of which are sensitive indicators of crystallization differentiation. The differences are so small that they are only apparent in the glass compositions; they are almost completely obscured in whole-rock samples by the presence of phenocrysts and the effects of alteration. Moreover, several of the glass units at different depths in Hole 504B are compositionally identical, with all oxides falling within the range of analytical uncertainty, with only small variations in the rest of the suite. The repetition of identical chemical types requires (1) very regular injection of magmas into the magma chamber, (2) extreme similarity of injected magmas, and (3) displacement of very nearly the same proportion of the magmas in the chamber at each injection. Numerical modeling and thermal considerations have led some workers to propose the existence of such conditions at certain types of spreading centers, but the lava and glass compositions at Hole 504B represent the first direct evidence revealed by drilling of the existence of a compositionally nearly steady-state magma chamber, and this chapter examines the processes acting in it in some detail. The glass groups that are most similar are from clinopyroxene-assemblage lavas, which have a range of Mg/Mg + Fe2"1" of 0.59 to 0.65. Spinel-assemblage basalts are less evolved, with Mg/Mg + Fe2+ of 0.65 to 0.69, but both types have nearly identical normative An/An + Ab (0.65-0.66). However, the two lava types contain megacrysts (olivine, Plagioclase, clinopyroxene) that crystallized from melts with Mg/Mg + Fe2+ values of 0.70 to 0.72. Projection of glass compositions into ternary normative systems suggests that spinel-assemblage magmas originated deeper in the mantle than clinopyroxene-assemblage magmas, and mineral data indicate that the two types followed different fractionation paths before reaching the magma chamber. The two magma types therefore represent neither a low- nor a high-pressure fractionation sequence. Some of the spinel-assemblage magmas may have had picritic parents, but were coprecipitating all of the spinel-assemblage phenocrysts before reaching the magma chamber. Clinopyroxene-assemblage magmas did not have picritic parents, but the compositions of phenocrysts suggest that they originated at about 9 kbars, near the transition between plagioclase peridotite and spinel peridotite in the mantle. Two glass groups have higher contents of alkalis, TiO2, and P2O5 than the others, evidently as a result of the compositions of mantle sources. Eruption of these lavas implies that conduits and chambers containing magmas from dissimilar sources were not completely interconnected on the Costa Rica Rift. The data are used to draw comparisons with the East Pacific Rise and to consider the mechanisms that may have prevented the eruption of ferrobasalts at these sites.

14C specific radiocarbon ages and bulk ages accompanied by geochemical proxys from surface sediment samples in the Black Sea

Transfer of organic carbon (OC) from the terrestrial to the oceanic carbon pool is largely driven by riverine and aeolian transport. Before transport, however, terrigenous organic matter can be retained in intermediate terrestrial reservoirs such as soils. Using compound-specific radiocarbon analysis of terrigenous biomarkers their average terrestrial residence time can be evaluated. Here we show compound-specific radiocarbon (14C) ages of terrigenous biomarkers and bulk 14C ages accompanied by geochemical proxy data from core top samples collected along transects in front of several river mouths in the Black Sea. 14C ages of long chain n-alkanes, long chain n-fatty acids and total organic carbon (TOC) are highest in front of the river mouths, correlating well with BIT (branched and isoprenoid tetraether) indices, which indicates contribution of pre-aged, soil-derived terrigenous organic matter. The radiocarbon ages decrease further offshore towards locations where organic matter is dominated by marine production and aeolian input potentially contributes terrigenous organic matter. Average terrestrial residence times of vascular plant biomarkers deduced from n-C29+31 alkanes and n-C28+30 fatty acids ages from stations directly in front of the river mouths range from 900 ± 70 years to 4400 ± 170 years. These average residence times correlate with size and topography in climatically similar catchments, whereas the climatic regime appears to control continental carbon turnover times in morphologically similar drainage areas of the Black Sea catchment. Along-transect data imply petrogenic contribution of n-C29+31 alkanes and input via different terrigenous biomarker transport modes, i.e., riverine and aeolian, resulting in aged biomarkers at offshore core locations. Because n-C29+31 alkanes show contributions from petrogenic sources, n-C28+30 fatty acids likely provide better estimates of average terrestrial residence times of vascular plant biomarkers. Moreover, sedimentary n-C28 and n-C30 fatty acids appear clearly much less influenced by autochthonous sources than n-C24 and n-C26 fatty acids as indicated by increasing radiocarbon ages with increasing chain-length and are, thus, more representative as vascular plant biomarkers.

Chemical composition of tephra from the Greenland-Iceland-Norwegian-Sea

Explosive ocean island volcanism in the Greenland-Iceland-Norwegian Sea (GIN Sea) is indicated by marine tephra layers at 10-300 ka. Peaks of explosive volcanism occurred in oxygen isotope stages 8, 7, 5 and 1. The depositional age of the tephra was estimated using the oxygen isotope stratigraphy and dating of marine records. Geochemical analyses of the tephra layers show that all originate from Iceland. Here we report the characteristics of tephra from these major Icelandic events in 30 deep-sea cores from the GIN Sea. Our findings provide constraints on the distribution of tephra from the eruption source. For the Vedde Ash (oxygen isotope stage 1) we estimate a minimum fallout area of 2*10**5 km**2, stretching from central Greenland in the west and southern Sweden in the east, to 71°N in the GIN Sea. The magnitude of the eruption and the regional wind conditions controlled the extent and concentrations of these ash fallout events. Oceanic circulation and differential settling may have affected the distribution and final deposition of ash particles such as bubble wall shards.

Age determinations on sediment cores from the North Atlantic

Sediments in the North Atlantic ocean contain as eries of layers that are rich in ice-rafted debris and unusally poor in foraminifera. Here we present evidence that the most recent six of the 'Heinrich layers', deposited between 14,000 and 70,000 years ago, record marked decreases in sea surface temperature and salinity, decreases in the flux of planktonic forminifera to the sediments, and short-lived, massive discharges of icebergs originating in eastern Canada. The path of the icebergs, clearly marked by the presence of ice-rafted detrital carbonate, can be traced for more than 3,000 km - a remarkable distance, attesting to extreme cooling of surface waters and enormous amounts of drifiting ice. The cause of these extreme events is puzzling. They may reflect repated rapid advances of the Laurentide ice sheet, perhaps associated with reductions in air temperatures, yet temperature records from Greenland ice cores appear to exhibit only a weak corresponding signal. Moreover, the 5-10,000-yr intervals between the events are inconsistent with Milankovitch orbital periodicities, raising the question of what the ultimate cause of the postulated cooling may have been.

Lake Tiefer See varve microfacies, bulk geochemistry, µ-XRF, vegetation openness and Cladocera record

The Holocene sediment record of Lake Tiefer See exhibits striking alternations between well-varved and non-varved intervals. Here we present a high resolution multi-proxy record for the past ~6000 years and discuss possible causes for the observed sediment variability. This approach comprises of microfacies, geochemical and microfossil analyses as well as of a multiple dating concept including varve counting, tephrochronology and radiocarbon dating. Four periods of predominantly well-varved sediment were identified at 6000-3950 cal. a BP, 3100-2850 cal. a BP, 2100-750 cal. a BP and AD 1924-present. Except of sub-recent varve formation, these periods are considered to reflect reduced lake circulation and consequently, stronger anoxic bottom water conditions. In contrast, intercalated intervals of poor varve preservation or even extensively mixed non-varved sediments indicate strengthened lake circulation. Sub-recent varve formation since AD 1924 is, in addition to natural forcing, influenced by enhanced lake productivity due to modern anthropogenic eutrophication. The general increase in periods of intensified lake circulation in Lake Tiefer See since ~4000 cal. a BP presumably is caused by gradual changes in Northern Hemisphere orbital forcing, leading to cooler and windier conditions in Central Europe. Superimposed decadal to centennial scale variability of the lake circulation regime likely is the result of additional human-induced changes of the catchment vegetation. The coincidence of major non-varved periods at Lake Tiefer See and intervals of bioturbated sediments in the Baltic Sea implies a broader regional significance of our findings.

Stable isotope record of foraminifera from the Barents Sea

We measured the oxygen isotopic composition of planktonic and benthic foraminifera in three cores collected at key positions to reconstruct the paleoceanography of the Barents Sea: core ASV 880 on the path of the northern branch of Atlantic water inflowing from the Arctic Ocean, core ASV 1200 in the central basin near the polar front, and core ASV 1157 in the main area of brine formation. Modern seawater d18O measurements show that far from the coast, d18O variations are linearly linked to the salinity changes associated with sea ice melting. The foraminifer d18O records are dated by 14C measurements performed on mollusk shells, and they provide a detailed reconstruction of the paleoceanographic evolution of the Barents Sea during the Holocene. Four main steps were recognized: the terminal phase of the deglaciation with melting of the main glaciers, which were located on the surrounding continent and islands, the short thermal optimum from 7.8 ka B.P. to 6.8 ka B.P., a cold mid-Holocene phase with a large reduction of the inflow of Atlantic water, and the inception of the modern hydrological pattern by 4.7 ka B.P. Brine water formation was active during the whole Holocene. The paleoclimatic evolution of the Barents Sea was driven by both high-latitude summer insolation and the intensity of the Atlantic water inflow.

340,000-year centennial-scale marine record of southern hemisphere climatic oscillation

In order to investigate rapid climatic changes at mid-southern latitudes, we have developed centennial-scale paleoceanographic records from the southwest Pacific that enable detailed comparison with Antarctic ice core records. These records suggest close coupling of mid-southern latitudes with Antarctic climate during deglacial and interglacial periods. Glacial sections display higher variability than is seen in Antarctic ice cores, which implies climatic decoupling between mid- and high southern latitudes due to enhanced circum-Antarctic circulation. Structural and temporal similarity with the Greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations.

Determination of Uranium, Thorium, and Ionium in sediment cores of the Caribbean and Ionian Sea

A rapid procedure for Io (Th230) dating of sediments with accumulation rates in the range of several cm/1000 years is described. Studying of large sample populations with very small Io-excess activity is possible as the counting time (around 1500 min/sample) are 2 to 5 times shorter than with the standard Io-excess method. Improved sensitivity of the Io-excess measurement is achieved by: 1) extraction ( ~90 %) of the authigenic Io-excess with EDTA, with minor leaching ( ~30 %) of the allogenic Th232 and Io-supported, 2) processing samples as large as 10 g or more. The procedure was applied to sediments from the Caribbean (V 12-122) and from the Ionian Sea (M22_48 and M17_17). In the case of the standard core V 12-122 our results are in good agreement with previous time-consuming Io determinations. The resulting average accumulation rates of 2.0 ± 0.3 cm/1000 years for the Ionian Sea cores are close to the average derived from magnetic reversal studies of a nearby core.

Age model and pollen analysis from site GIK16867 in the northern Angola Basin

Sporomorphs and dinoflagellate cysts from site GIK16867 in the northern Angola Basin record the vegetation history of the West African forest during the last 700 ka in relation to changes in salinity and productivity of the eastern Gulf of Guinea. During most cool and cold periods, the Afromontane forest, rather than the open grass-rich dry forest, expanded to lower altitudes partly replacing the lowland rain forest of the borderlands east of the Gulf of Guinea. Except in Stage 3, when oceanic productivity was high during a period of decreased atmospheric circulation, high oceanic productivity is correlated to strong winds. The response of marine productivity in the course of a climatic cycle, however, is earlier than that of wind vigour and makes wind-stress-induced oceanic upwelling in the area less likely. Monsoon variation is well illustrated by the pollen record of increased lowland rain forest that is paired to the dinoflagellate cyst record of decreased salinity forced by increased precipitation and run-off.

Sedimentology, age models and stable isotope ratios of sediment cores from the equatorial Pacific

Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic d13C record of CO2, which is dissolved in the deep ocean, strongly differed between the Last Glacial Maximum and the Holocene. With the onset of Termination I about 15,000 years ago, the new (export) production of low- and mid-latitude upwelling cells started to decline by more than 2-4 Gt carbon/year. This reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric CO2 as recorded in ice cores and, with a slight delay of more than 1000 years, to a large-scale gradual CO2 depletion of the deep ocean by about 650 Gt C. This estimate is based on an average increase in benthic d13C by 0.4-0.5 per mil. The decrease in new production also matches a clear 13C depletion of organic matter, possibly recording an end of extreme nutrient utilization in upwelling cells. As shown by Sarnthein et al., [1987], the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades, which in turn was linked via a shrinking extent of sea ice to a massive increase in high-latitude insolation, i.e., to orbital forcing as primary cause.

The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink, supplementary datasets

Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface-subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring-summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall-winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink.

Thyroid hormone and gland status of Greenland sledge dogs (Canis lupus familiaris) exposed to contaminated blubber

As a model of high trophic level carnivores, sledge dogs were fed from 2 to 18 months of age with minke whale blubber containing organohalogen compounds (OHC) corresponding to 128 µg PCB/day. Controls were fed uncontaminated porcine fat. Thyroid hormone levels were assessed in 7 exposed and 7 control sister bitches (sampled at age 6-18 months) and 4 exposed and 4 control pups, fed the same diet as their mothers (sampled age 3-12 months). Lower free and total T3 and T4 were seen in exposed vs. control bitches beyond 10 months of age, and total T3 was lower through 3-12 months of age in exposed pups. A negative correlation with thyroid gland weight was significant for SumDDT, as was a positive association with total T3 for dieldrin. This study therefore supports observational data that OHCs may adversely affect thyroid functions, and it suggests that OHC exposure duration of 10 months or more may be required for current OHC contamination levels to result in detectable adverse effects on thyroid hormone dynamics.