(Table T1) Ice rafted debris characteristics of ODP Site 177-1092

We have carried out a multiphase analysis of samples from ODP Site 177-1092, Meteor Rise, subantarctic South Atlantic. Samples were analyzed for ice-rafted debris (IRD [see Table T1]) and stable isotopes from benthic foraminifera [see Murphy et al., 2002, doi:10.1016/S0031-0182(01)00495-3]. Both analyses were performed on the same samples. Additional work was performed to identify the paleomagnetic stratigraphy. The analyzed samples range in age from about 2.6(?) Ma to 4.6 Ma, a time span that saw considerable global warmth, but witnessed overall global refrigeration and the transition to truly bipolar glaciations. IRD arrived frequently during the Early and early Late Pliocene, but only as 'background rafting' (occasional grains per sample). The first identifiable IRD above background rafting is associated with marine isotope stage (MIS) KM4 (~3.18 Ma). Successive IRD peaks become larger, the same pattern as noted at nearby Site 114-704. A very large peak near the top of the record, approximately 2.8 Ma, is considered to represent a hiatus. Peaks below 51.3 meters composite depth (mcd) coincide with positive excursions of the oxygen isotopic record, and with negative excursions of the carbon isotopic curve, a pattern also noted at Site 114-704. However, the reasonably large IRD peak at 51 mcd (tentatively identified with MIS G11) coincides with a positive excursion on the carbon isotopic curve and negative excursion on the oxygen isotopic curve. This relationship suggests a northern hemisphere interglacial, rising sea level, destabilization of the Antarctic margin, and delivery of Antarctic icebergs to the Southern Ocean. Such a mechanism has recently been suggested by Kanfoush et al. (2000, doi:10.1126/science.288.5472.1815) for latest Pleistocene stadial/interstadial oscillations. Here we suggest that such a mechanism may have been in place on glacial/interglacial time scales as early as the Late Pliocene.

Geochemistry of Eocene/Oligocene sediments of ODP Hole 154-925A

Paleoproductivity, nutrient burial, and carbon cycling were investigated across the Eocene/Oligocene (E/O) boundary (begin to end; 36.9-32.7 Ma at ~40 kyr resolution, timescale of Shackleton et al. (1999, doi:10.1098/rsta.1999.0407) at Ocean Drilling Program Site 925 on the Ceara Rise in the western equatorial Atlantic (3040 m present water depth; 748.26-850.70 mbsf). Downcore bulk sediment records of biogenic barium, total reactive phosphorus, biogenic silica, and calcium carbonate are interpreted to represent export production, net nutrient burial, biogenic opal production, and inorganic carbon burial, respectively. The global positive excursion in d13C subsequent to the E/O boundary is recorded at Site 925. Export production appears to have been externally forced by orbital parameters at eccentricity frequencies during the study interval, based on spectral analysis of the biogenic barium and reactive phosphorus records. Biogenic silica production or preservation increased after the Eocene/Oligocene boundary to a higher baseline, although overall productivity and nutrient burial did not increase, based on barium and reactive phosphorus records. Thus, although absolute production did not increase at this site, a shift in relative abundance of siliceous versus carbonate productivity may have resulted in a change in relative organic carbon burial. This may have contributed to the positive excursion in global oceanic d13C subsequent to the Eocene/Oligocene boundary, although the silica maximum persists after the carbon isotope excursion ends.

(Table 1) Stable carbon isotope record and calculated recycled DIC for sediment core ANDRA_HTM102

The prominent negative stable carbon isotope excursion in both carbonate and organic carbon recorded in organic-rich sediments deposited during the Toarcian oceanic anoxic event (OAE) has commonly been explained by recycling of 13C-depleted CO2 (the so-called Küspert model). More recently, the massive release of 13C-depleted methane or other forms of 13C-depleted carbon was also proposed to account for the observed negative d13C excursions in organic carbon of terrigenous as well as of marine origin. The occurrence of diagenetic products of the carotenoid isorenieratene (isorenieratane and other aryl isoprenoids) in Toarcian black shales has been regarded as supporting evidence for the Küspert hypothesis as they point to strong stratification of the epicontinental seas. A section of a drill core straddling the Toarcian of the Paris Basin (Cirfontaine-en-Ornois) contained intact isorenieratane, providing evidence that photosynthetic green sulphur bacteria were present at the time of deposition, even prior to the OAE. However, the isorenieratane abundances are very low in the section where the negative d13C excursion in organic carbon and phytane, a chemical fossil derived from chlorophyll, occurs. The abundance of the isorenieratene derivatives increases, once the d13C records have shifted to more positive values. The d13C of isorenieratane (generally circa -13.1 ± 0.5 per mil) indicates that the respired CO2 contribution at the chemocline was low and is thus not likely to be the main cause of the prominent up to 7per mil negative d13C shift recorded in Toarcian organic carbon records.

Planktonic foraminiferal assemblages of the Paleocene-Eocene Thermal Maximum of ODP Hole 113-690B

High-resolution study of Antarctic planktonic foraminiferal assemblages (Ocean Drilling Program Site 690, Weddell Sea) shows that these microplankton underwent a stepwise series of changes during the Paleocene-Eocene thermal maximum (PETM). Initiation of this response coincides with the onset of the carbon isotope excursion (CIE) but precedes the benthic foraminiferal mass extinction. The "top-to-bottom" succession in the biotic response indicates that the surface ocean/atmosphere was affected before the deep sea. The earliest stage of the faunal response entailed a conspicuous turnover within the shallow-dwelling genus Acarinina and a succession of stratigraphic first appearances. The genus Morozovella, large (>180 µm) biserial planktonics, and A. wilcoxensis are all restricted to the lower CIE within this PETM section. Acarininid populations crashed as the ocean/climate system ameliorated during the CIE recovery, reflecting atypical surface water conditions. This transient decline in acarininids is paralleled by a marked increase in carbonate content of sediments. It is postulated that this interval of carbonate enrichment, and its unusual microfauna, reflects enhanced carbon storage within reservoirs of the global carbon cycle other than the marine carbonate system (sensu Broecker et al., 1993, doi:10.1029/93PA00423; Ravizza et al., 2001, doi:10.1029/2000PA000541).

Age determination of Pacific Ocean sediments

Benthic and planktonic 14C ages are presented for the last glacial termination from marine sediment core VM21-30 from 617 m in the eastern equatorial Pacific. The benthic-planktonic 14C age differences in the core increased to more than 6000 years between Heinrich 1 time and the end of the Younger Dryas period. Several replicated 14C ages on different benthic and planktonic species from the same samples within the deglacial section of the core indicate a minimal amount of bioturbation. Scanning electron microscopy reveals no evidence of calcite alteration or contamination. The oxygen isotope stratigraphy of planktonic and benthic foraminifera does not indicate anomalously old (glacial age) values, and there is no evidence of a large negative stable carbon isotope excursion in benthic foraminifera that would indicate input of old carbon from dissociated methane. It appears, therefore, that the benthic 14C excursion in this core is not an artifact of diagenesis, bioturbation, or a pulse of methane. A benthic D14C stratigraphy reconstructed from the 14C ages from the deglacial section of VM21-30 appears to match that of Baja margin core MV99-MC19/GC31/PC08 (705 m), but the magnitude of the low-14C excursion is much larger in the VM21-30 record. This would seem to imply that the VM21-30 core was closer to the source of 14C-depleted waters during the deglaciation, but the source of this CO2 remains elusive.

Stable isotope record, carbonate and organic carbon content of the Miocene section of IODP Site 321-U1337

The Miocene Climatic Optimum (~17-14.7 Ma) represents one of several major interruptions in the long-term cooling trend of the past 50 million years. To date, the processes driving high-amplitude climate variability and sustaining global warmth during this remarkable interval remain highly enigmatic. We present high-resolution benthic foraminiferal and bulk carbonate stable isotope records in an exceptional, continuous, carbonate-rich sedimentary archive (Integrated Ocean Drilling Program Site U1337, eastern equatorial Pacific Ocean), which offer a new view of climate evolution over the onset of the Climatic Optimum. A sharp decline in d18O and d13C at ~16.9 Ma, contemporaneous with a massive increase in carbonate dissolution, demonstrates that abrupt warming was coupled to an intense perturbation of the carbon cycle. The rapid recovery in d13C at ~16.7 Ma, ~200 k.y. after the beginning of the MCO, marks the onset of the first carbon isotope maximum within the long-lasting "Monterey Excursion". These results lend support to the notion that atmospheric pCO2 variations drove profound changes in the global carbon reservoir through the Climatic Optimum, implying a delicate balance between changing CO2 fluxes, rates of silicate weathering and global carbon sequestration. Comparison with a high-resolution d13C record spanning the onset of the Cretaceous Oceanic Anoxic Event 1a (~120 Ma ago) reveals common forcing factors and climatic responses, providing a long-term perspective to understand climate-carbon cycle feedbacks during warmer periods of Earth's climate with markedly different atmospheric CO2 concentrations.

Stable carbon isotope ratios of alkane of IODP Hole 302-M0004A

The Palaeocene/Eocene thermal maximum represents a period of rapid, extreme global warming approx ~55 million years ago, superimposed on an already warm world (Zachos et al., 2003, doi:10.1126/science.1090110; Bowen et al., 2004, doi:10.1038/nature03115; Thomas et al., 2002, doi:10.1130/0091-7613(2002)030<1067:WTFFTF>2.0.CO;2). This warming is associated with a severe shoaling of the ocean calcite compensation depth **4 and a >2.5 per mil negative carbon isotope excursion in marine and soil carbonates (Zachos et al., 2003, doi:10.1126/science.1090110; Bowen et al., 2004, doi:10.1038/nature03115; Thomas et al., 2002, doi:10.1130/0091-7613(2002)030<1067:WTFFTF>2.0.CO;2; Zachos et al., doi:10.1126/science.1109004). Together these observations indicate a massive release of 13C-depleted carbon (Zachos et al., doi:10.1126/science.1109004) and greenhouse-gas-induced warming. Recently, sediments were recovered from the central Arctic Ocean (Backman et al., 2006, doi:10.2204/iodp.proc.302.2006), providing the first opportunity to evaluate the environmental response at the North Pole at this time. Here we present stable hydrogen and carbon isotope measurements of terrestrial-plant- and aquatic-derived n-alkanes that record changes in hydrology, including surface water salinity and precipitation, and the global carbon cycle. Hydrogen isotope records are interpreted as documenting decreased rainout during moisture transport from lower latitudes and increased moisture delivery to the Arctic at the onset of the Palaeocene/Eocene thermal maximum, consistent with predictions of poleward storm track migrations during global warming (Backman et al., 2006, doi:10.2204/iodp.proc.302.2006). The terrestrial-plant carbon isotope excursion (about ~4.5 to ~6 per mil) is substantially larger than those of marine carbonates. Previously, this offset was explained by the physiological response of plants to increases in surface humidity (Bowen et al., 2004, doi:10.1038/nature03115). But this mechanism is not an effective explanation in this wet Arctic setting, leading us to hypothesize that the true magnitude of the excursion - and associated carbon input - was greater than originally surmised. Greater carbon release and strong hydrological cycle feedbacks may help explain the maintenance of this unprecedented warmth.of this unprecedented warmth.

Late Paleocene to Eocene stable isotope record od ODP Site 143-865

An expanded and largely complete upper Paleocene to upper Eocene section was recovered from the pelagic cap overlying Allison Guyot, Mid-Pacific Mountains at Ocean Drilling Program (ODP) Site 865 (18°26'N, 179°33'W; paleodepth 1300-1500 m). Reconstructions show that the site was within a few degrees of the equator during the Paleogene. Because no other Paleogene sections have been recovered in the Pacific Ocean at such a low latitude, Site 865 provides a unique record of equatorial Pacific paleoceanography. Detailed stable isotopic investigations were conducted on three planktonic foraminiferal taxa (species of Acarinina, Morozovella, and Subbotina). We studied benthic foraminiferal isotopes at much lower resolution on species of Cibicidoides and Lenticulina, Nuttallides truempyi and Gavelinella beccariiformis, because of their exceptional rarity. The d18O and d13C stratigraphies from Site 865 are generally similar to those derived from other Paleocene and Eocene sections. The planktonic foraminiferal records at Site 865, however, include significantly less short-term, single-sample variability than those from higher-latitude sites, indicating that this tropical, oligotrophic location had a comparatively stable water column structure with a deep mixed layer and less seasonal variability. Low-amplitude (0.1-0.8 per mil) oscillations on timescales of 250,000 to 300,000 years correlate between the d13C records of all planktonic taxa and may represent fluctuations in the mixing intensity of surface waters. Peak sea surface temperatures of 24°-25°C occurred in the earliest Eocene, followed by a rapid cooling of 3-6°C in the late early Eocene. Temperatures remained cool and stable through the middle Eocene. In the late Eocene, surface water temperatures decreased further. Vertical temperature gradients decreased dramatically in the late Paleocene and were relatively constant through much of the Eocene but increased markedly in the late Eocene. Intermediate waters warmed through the late Paleocene, reaching a maximum temperature of 10°C in the early Eocene. Cooling in the middle and late Eocene paralleled that of surface waters, with latest Eocene temperatures below 5°C. Extinction patterns of benthic foraminifera in the latest Paleocene were similar to those observed at other Pacific sites and were coeval with a short-term, very rapid negative excursion in d13C values in planktonic and benthic taxa as at other sites. During this excursion, benthic foraminiferal d18O values decreased markedly, indicating warming of 4 to 6°C for tropical intermediate waters, while planktonic taxa show slight warming (1°C) followed by 2°C of cooling. Convergence of d18O values of planktonic and benthic foraminifera suggests that thermal gradients in the water column in this tropical location collapsed during the excursion. These data are consistent with the hypothesis that equatorial Pacific surface waters were a potential source of warm, higher salinity waters which filled portions of the deep ocean in the latest Paleocene. Oxygen isotopic data indicate that equator to high southern latitude sea surface thermal gradients decreased to as little as 4°C at the peak of the excursion, suggesting some fundamental change in global heat transport.

Middle Miocene isotope stratigraphy and paleoceanographic evolution of the northwest and southwest Australian margins (Wombat Plateau and Great Australian Bight)

The benthic stable isotope record from ODP Site 761 (Wombat Plateau, NW Australia, 2179.3 m water depth) documents complete recovery of the middle Miocene delta13C excursion corresponding to the climatic optimum and subsequent expansion of the East Antarctic Ice Sheet. The six main delta13C maxima of the "Monterey Excursion" between 16.4 and 13.6 Ma and the characteristic stepped increase in delta18O between 14.5 and 13.9 Ma are clearly identified. The sedimentary record of the shallower ODP Sites 1126 and 1134 [Great Australian Bight (GAB), SWAustralia, 783.8 and 701 m water depth, respectively] is truncated by several unconformities. However, a composite benthic stable isotope curve for these sites provides a first middle Miocene bathyal record for southwest Australia. The delta18O and delta13C curves for Sites 1126 and 1134 indicate a cooler, better-ventilated water mass at ~700 m water depth in the Great Australian Bight since approximately 16 Ma. This cooler and younger water mass probably originated from a close southern source. Cooling of the bottom water at ~16 Ma started much earlier than at other sites of equivalent paleodepths in the central and western parts of the Indian Ocean. At Site 761, the delta18O curve shows an excellent match with the global sea level curve between ~11.5 and 15.1 Ma, and thus closely reflects changes in global ice volume. Prior to 15.1 Ma, the mismatch between the delta18O curve and the sea level curve indicates that delta18O fluctuations are mainly due to changes in bottom water temperature.

Mineral and foraminifer composition of sediments across the Paleocene/Eocene Thermal Maximum from ODP Leg 198 sites

The Paleocene/Eocene Thermal Maximum (PETM) was a transient interval of global warming ~55 m.y. ago associated with transformation of ecosystems and changes in carbon cycling. The event was caused by the input of massive amounts of CO2 or CH4 to the ocean-atmosphere system. Rapid shoaling of the lysocline and calcite compensation depth (CCD) is a predicted response of CO2 or CH4 input; however, the extent of this shoaling is poorly constrained. Investigation of Ocean Drilling Program (ODP) Sites 1209-1212 at Shatsky Rise, which lies along a depth transect, suggests a minimum lysocline shoaling of ~500 m in the tropical Pacific Ocean during the PETM. The sites also show evidence of CaCO3 dissolution within the sediment column, carbonate "burn-down" below the level of the carbon isotope excursion, and a predicted response to a rapid change in deepwater carbonate saturation. Close examination of several foraminiferal preservation proxies (i.e., fragmentation, benthic/planktonic foraminiferal ratios, coarse fraction, and CaCO3 content) and observations of foraminifers reveal that increased fragmentation levels most reliably predict intervals with visually impoverished foraminiferal preservation as a result of dissolution. Low CaCO3 content and high benthic/planktonic ratios also mirror intervals of poorest preservation.

Age determination of three sediment cores

A total of five sediment cores from three sites, the Arctic Ocean, the Fram Strait and the Greenland Sea, yielded evidence for geomagnetic reversal excursions and associated strong lows in relative palaeointensity during oxygen isotope stages 2 and 3. A general similarity of the obtained relative palaeointensity curves to reference data can be observed. However, in the very detail, results from this high-resolution study differ from published records in a way that the prominent Laschamp excursion is clearly characterized by a significant field recovery when reaching the steepest negative inclinations, whereas only the N-R and R-N transitions are associated with the lowest values. Two subsequent excursions also reach nearly reversed inclinations but without any field recovery at that state. A total of 41 accelerator mass spectrometry (AMS) 14C ages appeared to allow a better age determination of these three directional excursions and related relative palaeointensity variations. However, although the three sites yielded more or less consistent chronological as well as palaeomagnetic results a comparison to another site, PS2644 in the Iceland Sea, revealed significant divergences in the ages of the geomagnetic field excursions of up to 4 ka even on basis of uncalibrated AMS 14C ages. This shift to older 14C ages cannot be explained by a time-transgressive character of the excursions, because the distance between the sites is small when compared with the size of and the distance to the geodynamo in the Earth's outer core. The most likely explanation is a difference of reservoir ages and/or mixing with old 14C-depleted CO2 from glacier ice expelled from Greenland at site PS2644.