Recent ostracods in surface sediment samples from Admiralty Bay, King George Island, West Antarctica

Ostracods from Admiralty Bay on King George Island (South Shetland Islands) represent 29 podocopid species, belonging to 19 genera, one cladocopid and six myodocopid species. They were recovered from Recent marine and/or glacio-marine sediment samples from water depths of up to 520 m. These ostracods constitute a variable assemblage, which is overall typical for the Antarctic environment. Shallow-water assemblages tend to be more variable in terms of frequencies and species richness than deep-water assemblages. The later are low in numbers and remain relatively high diversities. Overall, no linear relation between ostracod assemblage-composition and environmental features analyzed was recognized.

Mg/Ca variability in Globigerinoides ruber tests

Laser ablation inductively coupled plasma-mass spectrometry microanalysis of fossil and live Globigerinoides ruber from the eastern Indian Ocean reveals large variations of Mg/Ca composition both within and between individual tests from core top or plankton pump samples. Although the extent of intertest and intratest compositional variability exceeds that attributable to calcification temperature, the pooled mean Mg/Ca molar values obtained for core top samples between the equator and >30°S form a strong exponential correlation with mean annual sea surface temperature (Mg/Ca mmol/mol = 0.52 exp**0.076SST°C, r**2 = 0.99). The intertest Mg/Ca variability within these deep-sea core top samples is a source of significant uncertainty in Mg/Ca seawater temperature estimates and is notable for being site specific. Our results indicate that widely assumed uncertainties in Mg/Ca thermometry may be underestimated. We show that statistical power analysis can be used to evaluate the number of tests needed to achieve a target level of uncertainty on a sample by sample case. A varying bias also arises from the presence and varying mix of two morphotypes (G. ruber ruber and G. ruber pyramidalis), which have different mean Mg/Ca values. Estimated calcification temperature differences between these morphotypes range up to 5°C and are notable for correlating with the seasonal range in seawater temperature at different sites.

Planktonic foraminifera and stable isotope record of ODP Site 162-980

Detailed faunal, isotopic, and lithic marine records provide new insight into the stability and climate progression of the last interglacial period, Marine Isotope Stage (MIS) 5, which peaked approximately 125,000 years ago. In the eastern subpolar North Atlantic, at the latitude of Ireland, interglacial warmth of the ice volume minimum of substage 5e (MIS 5e) lasted ~10,000 years (10 ka) and its demise occurred in two cooling steps. The first cooling step marked the end of the climatic optimum, which was 2-3 ka long. Minor ice rafting accompanied each cooling step; the second, larger, step encompassing cold events C26 and C25 was previously identified in the northwestern Atlantic. Approximately 4 °C of cooling occurred between peak interglacial warmth and C25, and the region experienced an additional temporary cooling of at least 1-2 °C during C24, a cooling event associated with widespread ice rafting in the North Atlantic. Beginning with C24, MIS 5 was characterized by oscillations of at least 1-2 °C superimposed on a generally cool baseline. The results of this study imply that the marine climatic optimum of the last interglacial was shorter than previously thought. The finding that the eastern subpolar North Atlantic cooled significantly before C24 reconciles terrestrial evidence for progressive climate deterioration at similar and lower latitudes with marine conditions. Our results also demonstrate a close association between modest ice rafting, cooling, and deep ocean circulation even during the peak of MIS 5e and in the earliest stages of ice growth.

Age determination and planktonic foraminifera og ODP Site 159-958

Site 958 was drilled to monitor the late Neogene history of both continental aridity in northwestern Africa and the Canary Current distant from nearshore upwelling. Based on magnetostratigraphy, biostratigraphic datums, variations in carbonate, coarse fraction components, and the species composition of planktonic foraminifers, as well as using the d18O records of Globigerinoides ruber (white), we established a splice between Holes 958A and 958B and a stratigraphic age scale deciphering Milankovitch cycles. Over the last 630 k.y., sedimentation rates amount to 2.9 cm/k.y., and to 2.05-2.53 cm/k.y. back to the base of the Pleistocene. Extremely low rates of 0.4 cm/k.y. and a reworking of fossils mark the late Pliocene. The first continuous, long, sea-surface temperature (SST) record from the center of the Canary Current, which is based on foraminifer species census data, depicts a general temperature decrease in the late Pliocene, lower SST and high seasonalities of up to 6°C ~2.0-1.6 Ma, a warmer interval from 1.6 Ma to ~0.85 Ma, again lower SST and higher seasonalities until 0.33 or 0.26 Ma, and a final warmer interval, lasting until at least 50 ka, possibly reflecting the attenuated dynamics of the Canary Current. Especially over the last 400 k.y., since Stage 11, glacial stages are hardly reflected by cold SST cycles, except for various abrupt and extremely short cooling events amounting to D6°C, which possibly result from North Atlantic Heinrich events. Similar, but not necessarily synchronous, events of short-term, extremely high values occur in the paleoproductivity and (d13Cbased) paleonutrient records, which indicate a generally low primary production averaging to 180 g C m**-2 yr**-1 at 50-330 ka and about 300 g C m**-2 yr**-1 back to the base of the Pleistocene. Near 1.2-1.6 Ma, the grain-size and magnetic susceptibility records document a significant increase in the discharge of south Saharan/Sahelian dust, possibly linked to increasing aridity.

A multiproxy analysis of late MIS 6 to early MIS 5d OSP Site 161-975 sediments

A multiproxy analysis based on planktic foraminiferal abundances, derived SSTs, and stable planktic isotopes measurements together with alkenone abundances and Uk'37 SSTs was performed on late MIS 6 to early MIS 5d sediment recovered from Site 975 (ODP Leg 161) in the South Balearic Islands basin (Western Mediterranean) with emphasis on reconstructing the climate progression of the last interglacial period. A number of abrupt climate changes related to alternative influence of nutrient rich northern and oligotrophic southern water masses were revealed. Heinrich event 11 and cooling events C27, C26, C25, C24, C23, which have been previously described in the North Atlantic, were recognized. However, in comparison to the eastern North Atlantic mid-latitude region, events C27 and C26 at Site 975 seem to be significantly more pronounced. Together with evidence of a two-phase climate optimum with maximum SSTs reached during its later phase, this implies a close similarity in climate dynamics between the Western Mediterranean and the Nordic seas. We propose that postglacial effects in the Nordic seas had an influence on the western Mediterranean climate via atmospheric circulation and that these effects competed with the insolation force.

Foraminifera abundances and biostratigraphy of Cenozoic sediments from the Ontong Java Plateau

The Ontong Java Plateau in the western equatorial Pacific contains a deposition record of biserial planktonic foraminifers concentrated in the Paleogene, in which frequencies up to 67% of the planktonic foraminifers are reported, and in the late Neogene, in which a maximum frequency of 48% is reported. Biserial planktonic foraminifers are rare or absent in the latest Oligocene and early Miocene, an interval characterized by warm bottom water and low temperature gradients. These conditions supported a surface assemblage rather than the biserial planktonic foraminifers, whose Neogene species inhabited the oxygen minimum at intermediate depths in the upper water column. Biserial planktonic foraminifers tend to be of high frequency during high sea stands and low frequency during low sea level, presumably in response to the strengthening or weakening of the oxygen minimum. Species extinction and evolution events occur during low sea stands in the Neogene and sometimes correspond to strong reflection horizons of the plateau's seismic stratigraphy. The biserial species are useful biostratigraphic indexes in the plateau section. The last occurrence (LO) of Streptochilus martini corresponds with the Eocene/Oligocene boundary; S. subglobigerum without Neogloboquadrina acostaensis indicates Zone N15; S. latum occurs from the middle of Zone N16 to near the top of Zone N17; S. globigerum ranges from near the top of Zone N17 to the middle of Zone N19/N20; and the S. globulosum continuous range begins just before the first left-to-right coiling change of Pulleniatina, but the species becomes rare in the Pleistocene section.

Neogene silicoflaggelates in ODP Leg 104 holes

A quantative study was made of silicoflagellates recovered from Sites 642 (lower Miocene-upper Pliocene), 643 (lower Miocene-upper Miocene), and 644 (upper Pliocene-Quaternary) on the Voring Plateau. Although disconformities are present in these sequences, they represent a much more complete record of the Neogene than was recovered previously in the Norwegian Sea by DSDP Leg 38. Silicoflagellates are rare or absent for glacial sequences younger than 2.65 Ma, and generally sparse and poorly preserved in the lower upper Pliocene and upper Miocene. Lower and middle Miocene assemblages are diverse and generally well preserved. Temporal changes in the silicoflagellate assemblage are indicative of major paleoceanographic changes in the Norwegian Sea. A regional zonation for the Neogene of the Norwegian Sea is proposed, consisting of eleven zones: Naviculopsis lata Zone, N. quadrata Zone (emended), N. ponticula Zone (emended), Distephanus speculum hemisphaericus Zone (new), Caryocha ernestinae Zone (new), Bachmannocena circulus var. apiculata/Caryocha Zone (new), Distephanus crux scutulatus Zone (new), Bachmannocena diodon nodosa Zone (new), Distephanus boliviensis Zone (new), Ds. jimlingii Zone (elevated from subzonal to zonal status) with Subzones a and b (new), and Ds. speculum Zone (new). The ranges and abundances of over 100 species and morphotypes are tabulated.

IRD, benthic foraminifera and stable isotopic record of northern Sargasso Sea sediments

New geochemical proxy data from Bermuda Rise piston cores reveal ocean and climate conditions in the northern Sargasso Sea during marine isotope stage 3. Using ?18O on the planktonic foraminifer Globigerinoides ruber, we can correlate explicitly with every stadial/interstadial change in Greenland ice between ~32 and 58 ka. These data suggest repetitive changes of ~4°C in the annual average sea surface temperature (SST), with maximum cooling comparable to or greater than SST during glacial maximum conditions. The extent of SST depression is about the same for typical stadial events and for Heinrich events 4 and 5, which we have identified on the Bermuda Rise by traces of ice rafting. Benthic foraminiferal d13C decreases during every stadial event, consistent with reduced production of the deepest component of North Atlantic Deep Water and shoaling of its interface with Antarctic Bottom Water. This interpretation is supported by benthic Cd/Ca data from the climate cycle associated with interstadial 8.

Live benthic foraminifera in surface sediments of the Indo-Pakistan continental margin

The Indo-Pakistan Continental Margin represents an extreme habitat for benthic foraminifera since (1) high fluxes of organic matter offer a high food supply, (2) an intensified oxygen minimum Zone (OMZ) develops from the base of the euphotic Zone to water depths over 1000 m and (3) the monsoon causes seasonal oscillations within the biogeochemical cycle. At three stations from the uppermost (233 m), the central (658 m) and the deeper part (902 m) of the OMZ, living benthic foraminiferal assemblages were analyzed within the uppermost 10 cm of the sediment column. The ecologic structure of foraminiferal faunas is characterized by high abundances at the sediment surface and a rapid decrease within the uppermost 2 cm of the sediment column. Despite dysoxic to suboxic bottom-water conditions, stained benthic foraminifera occurred in all cores down to the base of the sampled interval. High surface abundances, a high dominance by few endobenthic calcareous taxa and a low diversity, which may result from specific physiological adaptations to almost anoxic conditions and the absence of predators, are recognized in the central part of the OMZ. The upper and lower margins of the OMZ are characterized by higher diversities and lower abundances. The shallowest part of the OMZ is dominated by calcareous foraminifera, whereas agglutinated species are the most common taxa in the deeper part. Comparisons with previous studies show that benthic foraminiferal assemblages, that are influenced by seasonal oscillations controlling food supply and/or the availability of oxygen, show variations in faunal density and species composition. Since there is strong evidence that oxygen is not a limiting factor for some taxa, it seems more likely that the distribution pattern of benthic foraminifera is preferentially controlled by trophic conditions.

Latest Miocene-Pleistocene benthic foraminiferal record of DSDP Hole 23-219

Knowledge of the biology of deep-sea benthic foraminifera was used to interpret the results of multivariate analyses (factor and cluster) on relative abundance data of benthic foraminifera at Deep Sea Drilling Project Site 219 (southeastern Arabian Sea; 1764 m depth) in combination with carbon and oxygen isotope data. Faunal data document major changes in deep-sea ventilation and productivity over the past 5.5 Ma, including the end of the Miocene-Pliocene Indo-Pacific 'biogenic bloom' period at ~4.0 Ma. Interestingly, there is no simple correlation between high productivity and low oxygenation. Productivity fluctuated but became overall more pulsed, whereas overall oxygenation increased. We interpret the records as a combination of local to regional fluctuations in productivity probably caused by changes in monsoonal development, particularly its seasonality, and changes in oxygenation of intermediate depth waters in the Indian Ocean caused by global changes in climate and ocean circulation.

Stable isotope record of planktonic foraminifera of the South Atlantic

The central problem of late Quaternary circulation in the South Atlantic is its role in transfer of heat to the North Atlantic, as this modifies amplitude, and perhaps phase, of glacialinterglacial fluctuations. Here we attempt to define the problem and establish ways to attack it. We identify several crucial elements in the dynamics of heat export: (1) warm-water pile-up (and lack thereof) in the Western equatorial Atlantic, (2) general spin-up (or spin-down) of central gyre, tied to SE trades, (3) opening and closing of Cape Valve (Agulhas retroflection), (4) deepwater E-W asymmetry. Means for reconstruction are biogeography, stable isotopes, and productivity proxies. Main results concern overall glacial-interglacial contrast (less pile-up, more spin-up, Cape Valve closed, less NADW during glacial time), dominance of precessional signal in tropics, phase shifts in precessional response. To generate working hypotheses about the dynamics of surface water circulation in the South Atlantic we employ Croll's paradigm that glacial - interglacial fluctuations are analogous to seasonal fluctuations. Our general picture for the last 300 kyrs is that, as concerns the South Atlantic, intensity of surface water (heat) transport depends on the strength of the SE trades. From various lines of evidence it appears that strenger SE trades appeared during glacials and cold substages during interglacials, analogous to conditions in southern winter (August).

Abundance of organic-walled dinoflagellate cysts and geochemical analysis of sediment core GeoB5546-2

NW African climate shows orbital and millenial-scale variations, which are tightly connected to changes in marine productivity. We present an organic-walled dinoflagellate cyst (dinocyst) record from a sediment core off Cape Yubi at about 27°N in the Canary Basin covering the time period from 47 to 3ka before present (BP). The dinocyst record reflects differences in upwelling intensity and seasonality as well as the influence of fluvial input. Sea-level changes play an important role for the upwelling pattern and productivity signals at the core site. Within the studied time interval, four main phases were distinguished. (1) From 45 to 24ka BP, when sea-level was mostly about 75m lower than today, high relative abundances of cysts of heterotrophic taxa point to enhanced upwelling activity, especially during Heinrich Events, while relatively low dinocyst accumulation rates indicate that filament activity at the core location was strongly reduced. (2) At sea-level lowstand during the LGM to H1, dinocyst accumulation rates suggest that local filament formation was even more inhibited. (3) From the early Holocene to about 8ka BP, extraordinary high accumulation rates of most dinocyst species, especially of Lingulodinium machaerophorum, suggest that nutrient supply via fluvial input increased and rising sea-level promoted filament formation. At the same time, the upwelling season prolongated. (4) A relative increase in cysts of photoautotrophic taxa from about 8ka BP on indicates more stratified conditions while fluvial input decreased. Our study shows that productivity records can be very sensitive to regional features. From the dinocyst data we infer that marine surface productivity off Cape Yubi during glacial times was within the scale of modern times but extremely enhanced during deglaciation.