Determination of absolute coccolith abundances in deep-sea sediments by spiking with microbeads and spraying - SMS-method (Table 1)

A quick new method is described for the quantification of absolute nannofossil proportions in deep-sea sediments. This method (SMS) is the combination of Spiking a sample with Microbeads and Spraying it on a cover slide. It is suitable for scanning electron microscope (SEM) analyses and for light microscope (LM) analyses. Repeated preparation and counting of the same sample (30 times) revealed a standard deviation of 10.5%. The application of tracer microbeads with different diameters and densities revealed no statistically significant differences between counts. The SMS-method yielded coccolith numbers that are statistically not significantly different from values obtained from the filtration-method. However, coccolith counts obtained by the random settling method are three times higher than the values obtained by the SMS- and the filtration-method.

Paleogene benthic foraminifera from the Kerguelen Plateau

Benthic foraminifers were studied from lower Paleocene through upper Oligocene sections from Sites 747 and 748. The composition of the benthic foraminifer species suggests a middle to lower bathyal (600-2000 m) paleodepth during the Neogene and a probable upper abyssal (2000-3000 m) paleodepth during the Paleocene at Site 747. Site 748 is thought to have remained at middle to lower bathyal paleodepths throughout the Cenozoic. Principal component analysis distinguished four major benthic foraminifer assemblages: (1) a Paleocene Stensioina beccariiformis assemblage at Sites 747 and 748, (2) an early Eocene Nuttallides truempyi assemblage at lower bathyal Site 747, (3) an early through middle Eocene Stilostomella-Lenticulina assemblage at middle bathyal Site 748, and (4) a latest Eocene through Oligocene Cibicidoides-Astrononion pusillum assemblage at both sites. Major benthic foraminifer changes, as indicated by the principal components and first and last appearances, occurred at or close to the Paleocene/Eocene boundary, and in the late Eocene close to the middle/late Eocene boundary.

Micropaleontological and geochemical proxy studies of sediment core GeoB7926-2

[1] The low-latitude upwelling regime off the Mauritanian coast in the subtropical NE Atlantic accounts for a significant part of global export production. Although productivity variations in coastal upwelling areas are usually attributed to changes in wind stress and upwelling intensity, productivity dynamics off Mauritania are less straightforward because of the complex atmospheric and hydrographic setting. Here we integrate micropaleontological (diatoms) and geochemical (bulk biogenic sediment components, X-ray fluorescence, and alkenones) proxies to examine on submillennial-to-millennial changes in diatom production that occurred off Mauritania, NW Africa, for the last 25 ka. During the Last Glacial Maximum (LGM, 19.0-23.0 ka B.P.), moderate silicate content of upwelled waters coupled with weakened NE trade winds determined moderate diatom productivity. No significant cooling is observed during the LGM, suggesting that our alkenone-based SST reconstruction represents a local, upwelling-related signal rather than a global insolation related one. Extraordinary increases in diatom and opal concentrations during Heinrich event 1 (H1, 15.5-18.0 ka B.P.) and the Younger Dryas (YD, 13.5-11.5 ka B.P.) are attributed to enhanced upwelling of silica-rich waters and an enlarged upwelling filament, due to more intense NE trade winds. The synchronous increase of CaCO3 and K intensity and the decreased opal and diatoms values mark the occurrence of the Bølling/Allerød (BA, 13.5-15.5 ka B.P.) due to weakened eolian input and more humid conditions on land. Although the high export of diatoms is inextricably linked to upwelling intensity off Mauritania, variability in the nutrient content of the thermocline also plays a decisive role.

Oliogocene to Pleistocene benthic foraminifera in ODP Leg 121 sites

Oligocene to Pleistocene bathyal benthic foraminifers at Broken Ridge (Site 754) and Ninetyeast Ridge (Site 756), eastern Indian Ocean, were investigated for then- stratigraphic distribution and their response to paleoceanographic changes. Q-mode factor analysis was applied to relative abundance data of the most abundant benthic foraminifers. At Site 754, seven varimax assemblages were recognized from the upper Oligocene to the Pleistocene: the Gyroidina orbicularis-Rectuvigerina striata Assemblage in the uppermost Oligocene; the Lenticulina spp. Assemblage in the upper Oligocene to lower Miocene, and in lower Miocene to lowermost middle Miocene; the Burseolina cf. pacifica-Cibicidoides mundulus Assemblage in the lower Miocene; the Planulina wuellerstorfi Assemblage in the upper middle Miocene; the Globocassidulina spp. Assemblage in the upper Miocene; the Gavelinopsis lobatulus-Uvigerina proboscidea Assemblage in the Pliocene; and the Ehrenbergina spp. Assemblage in the Pleistocene. The major faunal changes are complex, but exist between the Lenticulina spp. Assemblage and the P. wuellerstorfi Assemblage at ~13.8 Ma, and between the Ehrenbergina spp. Assemblage and the G. lobatulus Assemblage at ~5 Ma. The development of the P. wuellerstorfi and Globocassidulina spp. Assemblages after 13.8 Ma is correlated with the decrease in temperature of the intermediate waters of the ocean, in turn related to Antarctic glacial expansion. The faunal changes at ~5 Ma are related to the development of low oxygen intermediate water, formed in the presence of a strong thermocline. At Site 756, six varimax assemblages are distributed as follows: the Cibicidoides cf. mundulus-Oridorsalis umbonatus Assemblage in the lower Oligocene; the Epistominella umbonifera-Cibicidoides mundulus Assemblage from the upper Oligocene to the lower Miocene; the Cibicidoides mundulus-Burseolinapacifica Assemblage from lower Miocene to the lower middle Miocene; the Globocassidulina spp. Assemblage from the upper lower Miocene to the Pliocene; the Uvigerina proboscidea Assemblage in the upper Miocene and the Pliocene; and the Globocassidulina sp. D Assemblage in the Pliocene. The main faunal change at this site is between the E. umbonifera Assemblage and the Globocassidulina spp. Assemblage, at ~17.1 Ma. The timing of this faunal change is coeval with faunal changes in the North Atlantic and the Pacific. The change is related to a change in bottom water characteristics caused by an increased influence of carbonate corrosive water from the Antarctic source region, and a change in surface productivity. A low oxygen event at Site 756, which started at about 7.3 Ma, occurred about 2.3 m.y. before that at Site 754. The different response to global paleoceanographic changes is not yet explained, but may be due to the difference of marine topography and the degree of upwelling

Planktic foraminiferal abundance and faunal-derived sea surface temperature of eastern equatorial Pacific ODP Site 202-1240

Glacial cooling (~1-5°C) in the eastern equatorial Pacific (EEP) cold tongue is often attributed to increased equatorial upwelling, stronger advection from the Peru-Chile Current (PCC), and to the more remote subpolar southeastern Pacific water mass. However, evidence is scarce for identifying unambiguously which process plays a more important role in driving the large glacial cooling in the EEP. To address this question, here we adopt a faunal calibration approach using planktic foraminifers with a new compilation of coretop data from the eastern Pacific, and present new downcore variation data of fauna assemblage and estimated sea surface temperatures (SSTs) for the past 160 ka (Marine Isotope Stage (MIS) 6) from ODP Site 1240 in the EEP. With significant improvement achieved by adding more coretop data from the eastern boundary current, our downcore calibration results indicate that most of the glacial cooling episodes over the past 160 ka in the EEP are attributable to increased influence from the subpolar water mass from high latitudes of the southern Pacific. By applying this new calibration of the fauna SST transfer function to a latitudinal transect of eastern Pacific (EP) cores, we find that the subpolar water mass has been a major dynamic contributor to EEP cold tongue cooling since MIS 6.

Planktonic foraminifera of sediment core MD01-2390

Sea-surface temperature (SST) estimates in the sediment core MD01-2390 based on planktonic foraminiferal species abundances using five different transfer function techniques suggest nearly unchanged or unusually higher temperatures in the tropical southern South China Sea (SCS) during the Last Glacial Maximum (LGM) relative to modern temperatures. These results are in contrast to substantial cooling of 2-5 °C inferred by geochemical (Uk'37, Mg/Ca ratios) and terrestrial proxies from the western tropical Pacific region. Using multivariate statistics we show that the glacial southern SCS harboured unique planktonic foraminiferal assemblages that have no modern analogs. Analyses of faunal variation through the core reveal that planktonic foraminiferal assemblages responded to temperature changes inferred from Mg/Ca data but that this signal is subdued by superimposed variations in the relative abundance of Pulleniatina obliquiloculata and Neogloboquadrina pachyderma (dextral). These species occur in glacial samples at proportions that are not observed in the calibration data set. The glacial high abundance of N. pachyderma (dextral) are interpreted to reflect a seasonal (winter) inflow of cold surface water from the northeast via the Bashi Strait due to the combined effects of an intensified winter monsoon, a southward shift of the polar front and the eastward migration of the Kuroshio Current. In contrast, processes controlling the high relative abundances of P. obliquiloculata during the LGM may be unique to the southern SCS. We propose a scenario involving a stronger (winter) mixing or enhanced upwelling due to an intensified winter monsoon that prevented shallow-dwelling, warm indicators to establish larger populations during the LGM. Our results indicate that a no-analog behaviour of planktonic foraminifera faunas is responsible for the warm glacial conditions in this part of the western Pacific warm pool as implied by foraminiferal transfer functions and that a more significant surface cooling in the region as implied by terrestrial and geochemical (Mg/Ca ratios; alkenone unsaturation index) marine proxies is a more likely scenario.