Methane concentration and porewater acetate of sediment cores from the IODP Expedition 301 Site U1301

In deep subsurface sediments of the Juan de Fuca Ridge Flank, porewater acetate that is depleted in 13C relative to sedimentary organic matter indicates an acetogenic component to total acetate production. Thermodynamic calculations indicate common fermentation products or lignin monomers as potential substrates for acetogenesis. The classic autotrophic reaction may contribute as well, provided that dihydrogen (H2) concentrations are not drawn down to the thermodynamic thresholds of the energetically more favorable processes of sulfate reduction and methanogenesis. A high diversity of novel formyl tetrahydrofolate synthetase (fhs) genes throughout the upper half of the sediment column indicates the genetic potential for acetogenesis. Our results suggest that a substantial fraction of the acetate produced in marine sediment porewaters may derive from acetogenesis, in addition to the conventionally invoked sources fermentation and sulfate reduction.

Stable carbon and oxygen isotope record of foraminifera of IODP Site 303-1307

A major tipping point of Earth's history occurred during the mid-Pliocene: the onset of major Northern-Hemisphere Glaciation (NHG) and of pronounced, Quaternary-style cycles of glacial-to-interglacial climates, that contrast with more uniform climates over most of the preceding Cenozoic and continue until today (Zachos et al., 2001, doi:10.1126/science.1059412). The severe deterioration of climate occurred in three steps between 3.2 Ma (warm MIS K3) and 2.7 Ma (glacial MIS G6/4) (Lisiecki and Raymo, 2005, doi:10.1029/2004PA001071). Various models (sensu Driscoll and Haug, 1998, doi:10.1126/science.282.5388.436) and paleoceanographic records (intercalibrated using orbital age control) suggest clear linkages between the onset of NHG and the three steps in the final closure of the Central American Seaways (CAS), deduced from rising salinity differences between Caribbean and the East Pacific. Each closing event led to an enhanced North Atlantic meridional overturning circulation and this strengthened the poleward transport of salt and heat (warmings of +2-3°C) (Bartoli et al., 2005, doi:10.1016/j.epsl.2005.06.020). Also, the closing resulted in a slight rise in the poleward atmospheric moisture transport to northwestern Eurasia (Lunt et al., 2007, doi:10.1007/s00382-007-0265-6), which probably led to an enhanced precipitation and fluvial run-off, lower sea surface salinity (SSS), and an increased sea-ice cover in the Arctic Ocean, hence promoting albedo and the build-up of continental ice sheets. Most important, new evidence shows that the closing of the CAS led to greater steric height of the North Pacific and thus doubled the low-saline Arctic Throughflow from the Bering Strait to the East Greenland Current (EGC). Accordingly, Labrador Sea IODP Site 1307 displays an abrupt but irreversible EGC cooling of 6°C and freshening by ~2 psu from 3.25/3.16-3.00 Ma, right after the first but still reversible attempt of closing the CAS.

Quantitative coccolithophore analyses in sediment core MD01-2446

Quantitative coccolithophore analyses were performed in core MD01-2446, located in the mid-latitude North Atlantic, to reconstruct climatically induced sea-surface water conditions throughout Marine Isotope Stages (MIS) 14-9. The data are compared to new and available paleoenvironmental proxies from the same site as well as other nearby North Atlantic records that support the coccolithophore signature at glacial-interglacial to millennial climate scale. Total coccolithophore absolute abundance increases during interglacials but abruptly drops during the colder glacial phases and deglaciations. Coccolithophore warm-water taxa (wwt) indicate that MIS11c and MIS9e experienced warmer and more stable conditions throughout the whole photic zone compared to MIS13. MIS11 was a long-lasting warmer and stable interglacial characterized by a climate optimum during MIS11c when a more prominent influence of the subtropical front at the site is inferred. The wwt pattern also suggests distinct interstadial and stadial events lasting about 4-10 kyr. The glacial increases of Gephyrocapsa margereli-G. muellerae 3-4 µm along with higher values of Corg, additionally supported by the total alkenone abundance at Site U1313, indicate more productive surface waters, likely reflecting the migration of the polar front into the mid-latitude North Atlantic. Distinctive peaks of G. margereli-muellerae (> 4 µm), C. pelagicus pelagicus, Neogloboquadrina pachyderma left coiling, and reworked nannofossils, combined with minima in total nannofossil accumulation rate, are tracers of Heinrich-type events during MIS12 and MIS10. Additional Heinrich-type events are suggested during MIS12 and MIS14 based on biotic proxies, and we discuss possible iceberg sources at these times. Our results improve the understanding of mid-Brunhes paleoclimate and the impact on phytoplankton diversity in the mid-latitude North Atlantic region.

Stable isotope record of benthic and planktonic foraminifera in sediment cores of ODP Leg 177, Southern Ocean

While onboard ship during Leg 177, we used variations in sediment physical properties (mainly percent color reflectance) in conjunction with biomagnetostratigraphy to correlate among sites and predict the position of marine isotope stages (MISs) (e.g., see fig. F11 in Shipboard Scientific Party, 1999, p. 45). Our working assumption was that physical properties of Leg 177 sediments are controlled mainly by variations in carbonate content. Previous studies of Southern Ocean sediment cores have shown that carbonate concentrations are relatively high during interglacial stages and low during glacial stages at sites located within the Polar Frontal Zone (PFZ). Today, the PFZ marks a lithologic boundary in underlying sediment separating calcareous oozes to the north and silica-rich facies to the south (Hays et al., 1976). Although there is debate whether the position of the "physical" PFZ actually moved during glacial-interglacial cycles (Charles and Fairbanks, 1990; Matsumoto et al., 2001), the "biochemical" PFZ, as expressed by the CaCO3/opal boundary in sediments, certainly migrated north during glacials and south during interglacials. This gave rise to lithologic variations that are useful for stratigraphic correlation. At Leg 177 sites located north of the PFZ and at sublysoclinal depths, we expected the same pattern of carbonate variation because cores in the Atlantic basin are marked by increased carbonate dissolution during glacial periods and increased preservation during interglacials (Crowley, 1985).

Age models and stabile isotope ratios from SO35 cores

Stable isotope measurements on the planktonic foraminifer Globigerinoides ruber (white) have been carried out on a number of selected deep-seas sediment cores from the South Lau and Norlh Fiji Basins. The d18O-curves show good correlation with the inter-ocean oraphic correlation composite d18O-record of the standard reference section (Prell et al. 1986), which, in combination with the chronostratigraphic classifications of Herterich & Sarnthein (1984, modified) and Imbrie et al. 1984), allows a detailed dating of the sedimentary sequences. The deepest layers in core no. 119 (southern Lau Basin) could be assigned to Isotope Stage 24. Measurements made on bulk carbonate in two cores show a much higher glacial-interglacial amplitude, allowing the general identification of the conventional oxygen isotope stages. The d13C-values of the benthic foraminifer Cibicidoides wuellerstorfi show progressively lighter values northwards reflecting an increasing contribution of the isotopically lighter CO2 from the remineralisation of organic matter during the general northward movement of the deep water masses. Cyclicities in the sedimentation rates were observed in core nos. 117 and 119 (both southern Lau Basin) where the interglacials exhibit higher levels than the glacials. Calculated new or export paleoproductivity show that the glacials had higher productivity in the euphotic zone. From the oxygen isotope stratigraphy, the five ash layers in core nos. 117 and 119 could be dated as about 530 ka B.P. in Stage 14, 695 ka B.P. in Stage 18, 775 ka B.P. in Stage 21, 790 ka B.P. and 825 ka B.P. in Stage 22. Carbonate dissolution occurred during stages 5, 8 and 10 to 12.