Stable isotope record of benthic foraminifera and the planktic foraminifera Globigerinoides sacculifer from sediment core GIK13519-1, Sierra Leone Rise, eastern equatorial Atlantic

From a 10.7 m long gravity core from the Sierra Leone Rise (5°39.5' N, 19°51' W) a detailed oxygen and carbon isotope record of both planktonic and benthonic foraminifera species was obtained extending from the Recent to Jaramillo event. The analysis yielded six major results. 1. Benthos oxygen isotopes varied by 1.8-2.2 per mil from interglacial to glacial times and may indicate a synglacial cooling of North Atlantic Deep Water at 2800 m depth by 1-3°C. 2. Variable anomalies between the benthos and plankton d18O record indicate a cooling of sea-surface temperatures (SST) by up to 6 °C during some glacial stages. 3. Southerly trade winds and equatorial upwelling may excert the primary control off SST variations, in particular of extremee values of cold and warm stages and of the abrupt character of climate transitions and their leads and lags, and finally, of variable sedimentation rates. 4. The benthos d13C record correlates well with the flux and preservation of organic matter. 5. A new time scale, CARPOR, was established from the assumption that terrigenous sediment supply was ± constant bit CaCO3 varied considerably. When applied to the d18O record, three major and numerous short-term variations of sedimentation rates (0.8 to 4.0 cm/kyr) can be distinguished. 6. The climatic record was modified by bioturbation much more strongly during cold than during warm stages.

Stable oxygen and carbon isotope record of benthic foraminifera in Pliocene sediments of the Californian margin

New benthic foraminiferal stable isotopic records of northeast Pacific intermediate water (ODP Site 1014, 1177 m) and mid-depth water (ODP Site 1018, 2476 m) were compared to isotopic records of deep water in the tropical Pacific (ODP Site 849, 3851 m) for the reconstruction of vertical profiles of nutrient and physical properties from the Early Pliocene to the Early Pleistocene (approx. 5-1.4 Ma). Our data indicate that, for the entire interval, there was enhanced north Pacific intermediate water ventilation relative to today, and a similar to modern circulation pattern with northward flowing Pacific Bottom Water (PBW) beneath its southward flowing return flow. However, the core of maximally aged return flow resided as deep as ~2500 m (as compared to ~1500 m today), probably due to the strengthened intermediate water flow. Less apparent aging of deep water along its path before 2.7 Ma indicates that thermohaline overturning may have been more rapid in the warm period of the Early Pliocene. In addition, prior to 2.7 Ma, foraminiferal oxygen isotopic values at mid-depth sites are higher than at deep sites (a reversed vertical gradient relative to today) in both the Atlantic and Pacific Oceans. We suggest that NADW was warmer and more saline than today and that it influenced mid-depth waters throughout the Atlantic and Pacific Oceans. Enhanced Pliocene formation of warmer/saltier intermediate water in the north Pacific, and deep water in the north Atlantic, may have been a result of higher than modern high/mid-latitude sea surface temperatures, evaporation, and salinity.

Whole-rock oxygen and carbon isorope record across the Cretaceous/Tertiary boundary in ODP Hole 130-807C

Whole-rock d18O analyses of the Paleogene and Upper Cretaceous succession at Ocean Drilling Program Hole 807C suggest the presence of hiatuses between 876.95 and 894.47 mbsf and between 1138.82 and 1140.94 mbsf. The d13C data show a pronounced positive excursion between 1130 and 1180 mbsf that corresponds to the positive d13C values characteristic of the Paleocene. Despite the stratigraphic breaks in the section, the d18O data show a systematic increase between 1360 mbsf and the hiatus between 876.95 and 894.47 mbsf, which is consistent with previous suggestions of long-term climatic cooling through the Paleogene. The Cretaceous/Tertiary transition is apparently complete in this section and is of remarkable thickness. The expanded nature of this portion of the succession is probably the result of secondary depositional processes. High-resolution sampling across this boundary may reveal detailed structure of the d13C decline associated with the extinctions that mark the termination of the Cretaceous.

Stable carbon and oxygen isotope record of planktonic and benthic foraminifera at ODP Site 111-677 in the Panama Basin

Oxygen and carbon isotope ratio measurements are presented for Globigerinoides ruber and for benthic species (mainly Uvigerina spp.) in the Pleistocene and uppermost Pliocene section of ODP Hole 677A in the Panama Basin. This provides the best available continuous Pleistocene stable isotope records from any location, fully justifying the recoring of DSDP Site 504. Oxygen isotope stage 22 (age about 0.85 Ma) was of similar magnitude to the most extensive glacials of the Brunhes and constitutes a logical base for the middle Pleistocene. Oxygen isotope stages as defined by Ruddiman et al. (1986, doi:10.1016/0012-821X(86)90024-5) and by Raymo et al. (1989, doi:10.1029/PA004i004p00413) back to stage 104 are recognized. Although the internationally agreed base of the Quaternary at or near stage 62 (about 1.6 Ma) is not marked by a major isotopic event, it does approximate the base of a regime characterized by highly regular 41,000-yr climate cycles. The records at Site 677 are ideal for time-series analyses and will permit a new attempt to develop a chronology for the early Pleistocene based on tuning to the orbital frequencies. The carbon isotope records also appear to contain considerable variance at orbital frequencies throughout the sequence analyzed.

Osmium, and stable carbon and oxygen isotope record accross the PETM

In the latest Paleocene an abrupt shift to more negative d13C values has been documented at numerous marine and terrestrial sites (Bralower et al., 1997, doi:10.1130/0091-7613(1997)025<0963:HRROTL>2.3.CO;2; Cramer et al., 1999; Kaiho et al., 1996, doi:10.1029/96PA01021; Kennett and Stott, 1991, doi:10.1038/353225a0; Koch et al., 1992, doi:10.1038/358319a0; Stott et al., 1996; Thomas and Shackleton, 1996, doi:10.1144/GSL.SP.1996.101.01.20; Zachos et al., 1993). This carbon isotope event (CIE) is coincident with oxygen isotope data that indicate warming of surface waters at high latitudes of nearly 4°-6°C (Kennett and Stott, 1991, doi:10.1038/353225a0) and more moderate warming in the subtropics (Thomas et al., 1999, doi:10.1029/1999PA900031). Here we report 187Os/188Os isotope records from the North Atlantic and Indian Oceans which demonstrate a >10% increase in the 187Os/188Os ratio of seawater coincident with the late Paleocene CIE. This excursion to higher 187Os/188Os ratios is consistent with a global increase in weathering rates. The inference of increased chemical weathering during this interval of unusual warmth is significant because it provides empirical evidence supporting the operation of a feedback between chemical weathering rates and warm global climate, which acts to stabilize Earth's climate (Walker et al., 1981). Estimates of the duration of late Paleocene CIE (Bains et al., 1999, doi:10.1126/science.285.5428.724; Bralower et al., 1997, doi:10.1130/0091-7613(1997)025<0963:HRROTL>2.3.CO;2; Norris and Röhl, 1999, doi:10.1038/44545; Röhl et al., 2000, doi:10.1130/0091-7613(2000)28<927:NCFTLP>2.0.CO;2) in conjunction with the Os isotope data imply that intensified chemical weathering in response to warm, humid climates can occur on timescales of 104-105 years. This interpretation requires that the late Paleocene thermal maximum Os isotope excursion be produced mainly by increased Os flux to the ocean rather than a transient excursion to higher 187Os/188Os ratios in river runoff. Although we argue that the former is more likely than the latter, we cannot rule out significant changes in the 187Os/188Os ratio of rivers.

Composition of sediments, hydrothermal manifestations, interstitial waters, and aeolian material from the TAG Hydrothermal Field and Central Atlantic

The book is devoted to regularities of spatial distribution, mineralogy and geochemistry of hydrothermal and hydrothermal-sedimentary manifestations of the Mid-Atlantic Ridge rift zone.

Age determination and stable isotope record of ODP Hole 162-980B

The conversion of surface water to deep water in the North Atlantic results in the release of heat from the ocean to the atmosphere, which may have amplified millennial-scale climate variability during glacial times (Broecker et al., 1990, doi:10.1029/PA005i004p00469) and could even have contributed to the past 11,700 years of relatively mild climate (known as the Holocene epoch) (Bond et al., 2001, doi:10.1126/science.1065680; Alley et al., 1997, doi:10.1130/0091-7613(1997)025<0483:HCIAPW>2.3.CO;2; Keigwin and Boyle, 2000, doi:10.1073/pnas.97.4.1343). Here we investigate changes in the carbon-isotope composition of benthic foraminifera throughout the Holocene and find that deep-water production varied on a centennial-millennial timescale. These variations may be linked to surface and atmospheric events that hint at a contribution to climate change over this period.

Stable carbon and oxygen isotope record of Neogloboquadrina pachyderma and Cibicides lobatulus from the southwestern Greenland Sea

A core transect across the southwestern Greenland Sea reveals coeval events of extremely negative planktic and benthic delta13C excursions between 40 and 87 ka. The most pronounced event, event 1, began at peak Dansgaard-Oeschger stadial 22 (85 ka) with a duration of 18 k.y. During this episode, incursions of Atlantic Intermediate Water caused a bottom-water warming of up to 8 °C. The amplitude, timing, and geographic pattern of the delta13C events suggest that this bottom-water warming triggered clathrate instability along the East Greenland slope and a methane-induced depletion of delta13CDIC (DIC- dissolved inorganic carbon). Since delta13C event 1 matches a major peak in atmospheric CH4 concentration, this clathrate destabilization may have contributed to the rise in atmospheric CH4 and thus to climate warming over marine isotope stage 5.1.

Late Cretaceous-Early Neogene oxygen and carbon isotope record of the Indian Ocean

Stable isotopic data of calcareous nannofossil, monogeneric and monospecific planktic and benthic foraminifera from five Indian Ocean DSDP sites (212, 217, 220, 237, and 253), leads to the following paleoclimatic and paleoceanographic conclusions: - The latest Cretaceous oxygen isotopic record implies a cooling (3-4°C) during the Maastrichtian. At the Cretaceous/Tertiary boundary only a minor warming (about 2°C) has been recorded. The parallel delta13C decrease of more than 1? indicates a significant decrease in productivity. - During the latest Paleocene a positive delta13C excursion was detected in Sites 217 and 237. This transient enrichment in delta13C may be due to productivity changes on continents and/or a change in the storage rate of organic matter in marginal basins or shelf areas. - The most striking feature in the oxygen isotopic record is noted at the Early/Middle Eocene transition. The shift towards more positive values (which were probably enhanced to a certain extent by a preceding diagenetic alteration) delineates a dramatic climatic deterioration at high and mid latitudes during the earlier Tertiary. - Near the Eocene/Oligocene boundary a cooling is evident within the latest Eocene interval. During the earliest Oligocene time a hiatus at Sites 217 and 253 partially obscures the climatic record. - Several climatic fluctuations have been noted during the Oligocene: a cooling at the base of Zone NP 23, a warming at the top of Zone NP 23 through NP 24, and a cooling during Zone NP 25. - The Miocene oxygen isotopic record is dominated by changes in surface and bottom water environments during Zone NN5. The decreasing and then increasing delta18O values, together with the subsequent steepening of the vertical delta18O gradient, point towards major climatic instabilities. These events coincide with the Mid-Miocene build-up of Antarctic ice-sheets. During the latest Miocene to the earliest Pliocene the delta18O record of planktic foraminifera indicates a significant warming of the Indian Ocean at mid-latitudes. - The delta13C record during the Oligocene and Miocene reveals several cycles (delta13C enrichments: NP 24, NN2, NN5, NN9, and base NN 11) which are most likely related to changes in storage rates of organic matter and biological productivity due to climatic changes and transgression/regression cycles. In addition, changes in the circulation patterns may also have influenced the carbon isotopic record.

High resolution isotope and Mg/Ca record of sediment core GeoB12615-4

The importance of intermediate water masses in climate change and ocean circulation has been emphasized recently. In particular, Southern Ocean Intermediate Waters (SOIW), such as Antarctic Intermediate Water and Subantarctic Mode Water, are thought to have acted as active interhemispheric transmitter of climate anomalies. Here we reconstruct changes in SOIW signature and spatial and temporal evolution based on a 40 kyr time series of oxygen and carbon isotopes as well as planktic Mg/Ca based thermometry from Site GeoB12615-4 in the western Indian Ocean. Our data suggest that SOIW transmitted Antarctic temperature trends to the equatorial Indian Ocean via the "oceanic tunnel" mechanism. Moreover, our results reveal that deglacial SOIW carried a signature of aged Southern Ocean deep water. We find no evidence of increased formation of intermediate waters during the deglaciation.

Magnetobiostratigraphy and stable isotope record of Paleocene sediments from ODP Hole 122-761B in the subtropical Indian Ocean

Surface and deep water circulation patterns in the eastern Indian Ocean during the Paleocene Epoch are inferred based on an integrated magnetobiostratigraphic and stable isotope investigation of Ocean Drilling Program Hole 761B, drilled on the Wombat Plateau. A combination of magnetostratigraphy, biostratigraphy and isotope stratigraphy demonstrates that numerous deep sea sites that have been considered to show continuous, or nearly continuous sedimentation through the Paleocene are punctuated by a series of hiatuses, some of which exceeding a duration of 1 Myr. Therefore, our study is based on a detailed temporal interpretation of the stratigraphic successions we used for paleoceanographic reconstructions. We compare detailed planktonic and benthic foraminiferal carbon and oxygen isotope records from Hole 761B with several temporally correlative records published from different oceanic provinces in order to distinguish between local and global patterns within the eastern Indian Ocean. Although Site 761 was situated at low latitudes during the Paleocene, its surface waters were predominantly influenced by circulation originating from the Southern Ocean as indicated by inferred cool sea surface temperatures and reduced surface to deep water temperature gradients. We suggest that deep waters in the eastern Indian Ocean were not directly fed by the Southern or Tethys Oceans. Rather, the more negative delta13C composition of the bottom waters recorded by benthic foraminifera implies the presence and/or active contribution of aged deep waters from the Pacific during this time, at least prior to ~60.2 Ma and subsequent to ~59.0 Ma. The Indian continent, Ninetyeast Ridge, Kerguelen Plateau and Broken Ridge may have played a significant role as submarine barriers to deep water circulation during the Paleocene.

Inorganic geochemical record of ODP Holes 117-722B and 117-724C

High-resolution sampling from late Pleistocene (last 400 k.y.) sediments of Site 722 (upper 16 m) and Site 724 (upper 70 m), and subsequent inorganic geochemical analysis, has defined the history of productivity in the northwest Arabian Sea. Eolian dust input from the Arabian Peninsula and Somalia is characterized by the record of Ti/Al and Cr/Al. This dust record displays strong precessional periodicity (cycles at 25 k.y.) suggesting the Southwest Monsoon and associated winds play a key role in transporting terrigenous material from the land. High biological productivity results in the accumulation of biogenic CaCO3 and opal in the sediments, the latter having an unexpectedly minor contribution to the total mass flux. Due to dilution of the CaCO3 record by the terrigenous component, the record of biological productivity is best exemplified by Ba. Its record, together with that of other metals recording biological association and redox variability (Cu, Ni, Zn, V, U) clearly identifies the interglacial episodes as being more biologically productive. The striking agreement between Ba and the d18O record in planktonic foraminifers suggests that the supply of nutrients during these periods of high productivity is linked to ocean-wide changes in ocean fertility, and not just local upwelling conditions. High levels of phosphate accumulation in interglacial sediments is attributed to both diagenetic phosphorite formation and biogenic skeletal debris. This study provides a detailed record of productivity variation in the northwest Arabian Sea during the late Pleistocene.

Stable carbon and oxygen isotope record of planktonic foraminifera across the Paleocene-Eocene boundary

The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high d13C values in the late Paleocene to values that are 2 to 3 lower in the early Eocene. The shift is recorded in fossil carbonates from each ocean basin and represents a large change in the distribution of 12C between the ocean and other carbon reservoirs. Superimposed upon this long-term shift are several distinct carbon isotopic negative excursions that are also recorded globally. These carbon isotopic 'events' near the Paleocene-Eocene boundary provide strati-graphic information that can facilitate intersite correlations between marine and non-marine sequences. Here we present a detailed marine carbon isotopic stratigraphy across the Paleocene-Eocene boundary that is constrained by calcareous nannofossil and planktonic foraminifera bio-stratigraphy and magnetostratigraphy. We show that several distinct carbon isotopic changes are recorded in uppermost Paleocene and lowermost Eocene marine biogenic carbonate sediments. At least one of these isotopic changes in the ocean's carbon isotopic composition was transmitted to terrestrial carbon reservoirs, including plant biomass via atmospheric CO2. As a consequence of this exchange of 12C between the ocean and terrestrial carbon reservoirs, it is possible to use carbon isotope stratigraphy to correlate the uppermost Paleocene and lowermost Eocene non-fossiliferous terrestrial sediments of the Paris Basin with marine sequences.

Pliocene to Pleistocene calcium carbonate and organic carbon record of ODP Hole 117-722B

Site 722 provides high resolution records of percent CaCO3, magnetic susceptibility, d18O, organic carbon, and coarse fraction for the past 3.4 m.y. from the crest of the Owen Ridge, northwestern Arabian Sea. Within this time interval, most of the carbonate percent variations can be attributed to terrigenous dilution and do not reflect changes in the carbonate system. From the late Pliocene to Present, the average rate of calcium carbonate accumulation increases from 1 to 3 g/cm**2/k.y. and the average accumulation of organic carbon decreases from 75 to 30 mg/cm**2/k.y. The carbonate component is more dissolved in the older interval. The long-term variations in carbonate accumulation may reflect a greater input of organic matter in the late Pliocene, which decomposes to produce CO2 and dissolve carbonate. Magnetic susceptibility and % noncarbonate (100 - CaCO3%) reflect changes in the amount of the lithogenic component in the sediments. The period of variation of lithogenic material is the same period as the original forcing of the regional summer monsoon, however, the timing matches global aridity patterns and global ice volume (sea level) changes. This preliminary analysis suggests that the high frequency variation of lithogenic material persists for at least the last 3.4 m.y. Within the last million years, calcium carbonate accumulation has a large amplitude signal that covaries with major changes in ice volume. Both calcium carbonate and noncarbonate (mostly terrigenous) accumulation are greatest during glacial stages. Interglacial intervals are characterized by low mass accumulation rates, increased foraminifer fragmentation, and increased opal concentration. The accumulation of organic carbon matches the high frequency changes in sedimentation rates. We attribute this high correlation to enhanced preservation of organic carbon by increased sedimentation rate. Of the three major biological components studied, only opal exhibits the variations expected for a biological productivity system forced by monsoonal upwelling driven by changes in northern hemisphere summer radiation.