(Table 1) Boron-isotope measurements of shallow-dwelling planktonic foraminifera of ODP Holes 144-817A, 144-872C and 143-865C

Knowledge of the evolution of atmospheric carbon dioxide concentrations throughout the Earth's history is important for a reconstruction of the links between climate and radiative forcing of the Earth's surface temperatures. Although atmospheric carbon dioxide concentrations in the early Cenozoic era (about 60 Myr ago) are widely believed to have been higher than at present, there is disagreement regarding the exact carbon dioxide levels, the timing of the decline and the mechanisms that are most important for the control of CO2 concentrations over geological timescales. Here we use the boron-isotope ratios of ancient planktonic foraminifer shells to estimate the pH of surface-layer sea water throughout the past 60 million years, which can be used to reconstruct atmospheric CO2 concentrations. We estimate CO2 concentrations of more than 2,000 p.p.m. for the late Palaeocene and earliest Eocene periods (from about 60 to 52 Myr ago), and find an erratic decline between 55 and 40 Myr ago that may have been caused by reduced CO2 outgassing from ocean ridges, volcanoes and metamorphic belts and increased carbon burial. Since the early Miocene (about 24 Myr ago), atmospheric CO2 concentrations appear to have remained below 500 p.p.m. and were more stable than before, although transient intervals of CO2 reduction may have occurred during periods of rapid cooling approximately 15 and 3 Myr ago.

Benthic and planktonic foraminifera of sediment core GIK17957-2

A detailed age model for core 17957-2 of the southern South China Sea was developed based on delta18O, coarse fraction, magnetostratigraphy, and biostratigraphy for the last 1500 kyr. The delta18O record has clear ~100-kyr cycles after the Mid-Pleistocene Revolution (MPR) at the entrance of marine isotopic stage (MIS) 22. Planktonic foraminifera responded to the MPR immediately, showing the increased sea surface temperature (SST) and dissolution after the MPR. Benthic foraminifera did not respond to it until the Brunhes/Matuyama boundary. Since the MPR, the depth of thermocline gradually became shallower until MISs 6-5. This major change within MISs 6-5 was also reflected in the decreased SSTs and increased productivity and Deep Water Mass. Thus two major Pleistocene paleoceanographic changes were found: One was around the MPR; the other occurred within MISs 6-5, which speculatively might be ascribed to the reorganization of surface and deep circulation, possibly induced by tectonic forces.

Cadmium/Calcium and stable isotope ratios of benthic foraminifera from the northeast Atlantic Ocean

The delta13C and Cd measurements from benthic foraminifera from Biogeochemical Ocean Flux Study (BOFS) northeast Atlantic Ocean sediment cores are presented. The delta13C values in glacial foraminifera are consistent with those from elsewhere in the North Atlantic Ocean. For intermediate water (1000 - 2000 m water depth), delta13C values were higher at the last glacial maximum than in present North Atlantic Deep Water (NADW), whereas for deep water (>2000 m) they were lower during the glacial maximum. The Cd concentrations of glacial northeast Atlantic intermediate water were lower than those of present NADW. However, deepwater Cd concentrations increased to values between NADW and present Pacific Deep Water (PDW). The delta13C and Cd data are consistent and show that the northeast Atlantic Ocean was strongly stratified with 13C enriched, low Cd intermediate water overlying 13C depleted, high Cd deep water. The glacial water column comprised two different water masses: deep water, similar in character to present Antarctic Bottom Water (AABW), and intermediate water, different in character from both AABW and NADW, and any present intermediate-depth North Atlantic water. The characteristics of glacial intermediate water were, however, similar to present near-surface waters in the North Atlantic, which suggests rapid ventilation of the glacial ocean to depths of up to 2000 m by cold, nutrient-depleted young surface waters.

Benthic foraminifera of cores from ODP Leg 117

The relative abundances of benthic foraminifers from the Oman margin have been analyzed from ODP Sites 725 and 726 near the upper boundary of the oxygen-minimum zone (OMZ) and 728 near the lower boundary. The relative abundance pattern of the benthic foraminiferal species in the two shallow sites show synchronous changes, which, together with variations in the faunal composition, may be attributed to changes in the location of the upper boundary of the OMZ during the last 7 million years. At the deeper site, the relative abundance pattern shows considerable variation in the faunal composition during the last 8 million years. The strong dominance of the shallow-water species Ammonia beccarii during the early Pliocene at Site 728 suggests a water depth less than 400 m during the early Pliocene and subsequent subsidence during the middle and late Pliocene to the present > 1400 m water depth.

Late Miocene-early Pliocene stable isotope record of benthic foraminifera from ODP Site 177-1088 in the sub-Antarctic South Atlantic

Benthic foraminiferal stable isotope records for the past 11 Myr from a recently drilled site in the sub-Antarctic South Atlantic (Site 1088, Ocean Drilling Program Leg 177, 41°S, 15°E, 2082 m water depth) provide, for the first time, a continuous long-term perspective on deep water distribution patterns and Southern Ocean climate change from the late Miocene through the early Pliocene. I have compiled published late Miocene through Pliocene stable isotope records to place the new South Atlantic record in a global framework. Carbon isotope gradients between the North Atlantic, South Atlantic, and Pacific indicate that a nutrient-depleted watermass, probably of North Atlantic origin, reached the sub-Antarctic South Atlantic after 6.6 Ma. By 6.0 Ma the relative proportion of the northern-provenance watermass was similar to today and by the early Pliocene it had increased to greater than the modern proportion suggesting that thermohaline overturn in the Atlantic was relatively strong prior to the early Pliocene interval of inferred climatic warmth. Site 1088 oxygen isotope values display a two-step increase between ~7.4 Ma and 6.9 Ma, a trend that parallels a published delta18O record of a site on the Atlantic coast of Morocco. This is perhaps best explained by a gradual cooling of watermasses that were sinking in the Southern Ocean. I speculate that relatively strong thermohaline overturn at rates comparable to the present day interglacial interval during the latest Miocene may have provided the initial conditions for early Pliocene climatic warmth. The impact of an emerging Central American Seaway on Atlantic-Pacific Ocean upper water exchange may have been felt in the North Atlantic beginning in the latest Miocene between 6.6 and 6.0 Ma, which would be ~1.5 Myr earlier than previously thought.

Planktonic foraminifera, nannofossils and stable isotope record across tghe Paleocene-Eocene thermal maximum of ODP Hole 113-690B

The carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the Paleocene-Eocene thermal maximum (PETM) (circa 55 Ma). The rapid release of large quantities of carbon into the ocean-atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion (CIE). The brevity (120-220 kyr) of the PETM reflects the rapid enhancement of negative feedback mechanisms within Earth's exogenic carbon cycle that served the dual function of buffering ocean pH and reducing atmospheric greenhouse gas levels. Detailed study of the PETM stratigraphy from Ocean Drilling Program Site 690 (Weddell Sea) reveals that the CIE recovery period, which postdates the CIE onset by ~80 kyr, is represented by an expanded (~2.5 m thick) interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate. Collectively, the micropaleontological and sedimentological changes preserved within the CIE recovery interval reflect a transient state when ocean-atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths. A prominent peak in the abundance of the clay mineral kaolinite is associated with the CIE recovery interval, indicating that continental weathering/runoff intensified at this time as well (Robert and Kennett, 1994). Such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering/runoff and carbonate precipitation helped sequester carbon during the PETM recovery period (e.g., Dickens et al., 1997, doi:10.1130/0091-7613(1997)025<0259:ABOGIT>2.3.CO;2 ; Zachos et al., 2005, doi:10.1126/science.1109004).

Quaternary oxygen isotope record of planktonic foraminifera from ODP Site 805 on the Ontong Java Plateau

The oxygen isotope records of G. sacculifer and Pulleniatina in the uppermost three cores at Ocean Drilling Program Hole 805C span the last 1.6 m.y., an estimate based on Fourier stratigraphy. The last 700,000 yr are dominated by both eccentricity and obliquity-related orbital fluctuations. The range of variation of delta18O values is about 1.5?, of which ca. 75% may be assigned to global ice-volume effect. The remainder of the range is shared by the effects of surface temperature variation, thermocline depth change (in the case of Pulleniatina, especially), and differential dissolution. Before 1 Ma, obliquity-related fluctuations dominate. The transition between obliquity- and eccentricity-dominated time occurs between ca. 1 and 0.7 Ma. It is marked by irregularities in phase relationships, the source of which is not clear. The age of the Brunhes/Matuyama boundary is determined as 794,000 yr by obliquity counting. However, an age of 830,000 yr also is compatible with the counts of both eccentricity and obliquity cycles. In the first case, Stage 19 (which contains the boundary) is coincident with the crest of the 19th obliquity cycle, setting the first crest downcore equal to zero, and counting backward (o19). In the second, Stage 19 coincides with o20. No evidence was found for fluctuations related to precession (23 and 19 k.y.) rising above the noise level, using plain Fourier expansion on the age model of the entire series. Detailed stratigraphic comparison with the Quaternary record of Hole 806B allows the recognition of major dissolution events (which increase the difference in delta18O values of G. sacculifer at the two sites). These occur at Stages 11-13, 16-17, and near 1.5 Ma (below o33).

Planktonic foraminifera of Oligocene sediments from DSDP Hole 77-538A in the Gulf of Mexico

A relatively extended Oligocene pelagic sequence with good to medium recovery, drilled during DSDP Leg 77 in the Gulf of Mexico, yielded rich and well diversified planktonic foraminiferal faunas. Planktonic foraminifera recorded in Hole 538A span the interval from Zone P19 through P22. Evolutionary lineages were observed among the globoquadrinids, the globigerinitids, and the "Globigerina" ciperoensis and Globigerinoides primordius groups. Quantitative analysis of planktonic foraminiferal assemblages shows that faunas fluctuate in abundance and species diversity throughout the sequence. A few of these fluctuations that could be related to selective dissolution are mainly confined to the early-mid Oligocene. A climatic curve was constructed using as warmer indicators, Turborotalia pseudoampliapertura, Globoquadrina tripartita, Dentoglobigerina globularis, Dentoglobigerina baroemoenensis,. "Globigerina" ciperoensis and Globigerinoides groups, and Cassigerinella chipolensis; and as coller indicators, Catapsydrax spp., Globorotaloides spp., Subbotina angiporoides group, Globigerina s. str., and the tenuitellides. Three major intervals are identifiable in the climatic curve: Interval 1 (lower) up to Zone P20 predominantly cooler: Interval 2 (intermediate) up to the upper part of Zone P21a with warm and cool fluctuations: and lnterval 3 (upper), warmer, with a large positive peak, due to abundant "G." angulisuturalis, at the beginning of Zone P21b with recooling midway in Zone P22. In Intervals 1 and 2 planktonic foraminiferal faunas are dominated by temperate forms. Interpretation of planktonic foraminiferal data suggests that cooler water conditions characterize the early-mid Oligocene: during the mid Oligocene (most of Zone P21a) water masses exhibit peculiar characteristics transitional to the warmer waters prevailing during the late Oligocene. Warmer conditions were not definitely settled in Zone P22, however, as indicated by the cooler episode following the warmest peak. These climatic trends are inconsistent with those inferred from oxygen isotopes except at small scale. In fact, oxygen isotope values for Oligocene Atlantic Ocean are too heavy (thus too cool) in comparison with the high abundance and diversity of warm taxa, expecially in Zone P22. When values are lighter (warmer), as in Zone P19 abundance and diversity of warm indices are too low. To explain such a cool isotope values in presence of highly diversified and abundant warm planktonic foraminifera, we suggest (1) that the oxygen isotope ratio used for estimating Oligocene paleotemperatures might be 1? heavier than Eocene values and further increased for the late Oligocene. This hypothesis implies the presence of a relatively extended ice cap in Antarctica in the early and mid Oligocene, and probably an increase in ice volume during the late Oligocenc: (2) heavier isotope values might be related to an increase in salinity, or (3) by a combination of both ice cap and increase in salinity.

Stable oxygen and carbon isotope ratios of Pliocene benthic foraminifera in the Atlantic Ocean

Large changes in benthic foraminiferal delta180 and delta13C occurred during the Pliocene (between 3.0 and 2.0 Ma) at Hole 665A. Oxygen isotopic compositions increased to maximum values at 2.4 Ma, correlating with an 18O enrichment observed at Hole 552A and other locations (Shackleton et al., 1984). As at Hole 606 (Keigwin, 1986), however, maximum delta180 values at 2.4 Ma were not as great as at Hole 552A, and enrichments in delta180 also occurred before 2.4 Ma. We believe that the section representing sediments from 2.5 to 2.7 or 2.8 Ma is missing at Hole 552A because of incomplete core recovery. Consequently, the older delta180 increases are not found at Hole 552A. Benthic foraminiferal delta13C values are much lower at Hole 665A than at Hole 552A, approaching the low values observed in the Pliocene Pacific Ocean. This geographic distribution of delta13C suggests that, like late Quaternary glaciations, the equatorial Atlantic Ocean was dominated during the Pliocene by deep water that originated in the Southern Ocean and had chemical characteristics very similar to the Pacific Ocean. Reduced O2 values were probably associated with low delta13C values and contributed to increased preservation of organic carbon during enriched 180 intervals of the Pliocene equatorial Atlantic.