Stable carbon and oxygen isotope record of Cretaceous planktonic foraminifera from DSDP (Table 1)

The Cretaceous Heterohelix moremani (Cushman) was the only biserial planktonic foraminiferal species from its first appearance in the late Albian up to the Cenomanian/Turonian boundary. Within that time, it increased gradually in abundance relative to other planktonic foraminifera in five Circum-North Atlantic sections. It is generally rare in upper Albian sediments, common in most of the Cenomanian and very abundant in sediments representing the latest Cenomanian Oceanic Anoxic Event. Short-term variations on the overall abundance trend correlate with positive excursions in the bulk carbonate delta13C record. Maximum rain rates of H. moremani during OAE2 show that this species was an opportunist that did well in extreme conditions, but its overall distribution indicates that it is not necessarily a marker for very high palaeoproductivity environments. Stable oxygen and carbon isotope measurements on foraminiferal species indicate that H. moremani was a surface water dweller at least in part of its geographic range, but incorporated 13C out of equilibrium with ambient seawater. It is depleted in delta13C relative to other planktonic foraminifera, which is attributed to vital effects related to its opportunistic character.

Oxygen isotope values from biogenic apatie (conodont elements and fish teeth) from the Lower Triassic Mianwali Formation (Salt Range, Pakistan)

Recovery from the end-Permian mass extinction is frequently described as delayed, with complex ecological communities typically not found in the fossil record until the Middle Triassic epoch. However, the taxonomic diversity of a number of marine groups, ranging from ammonoids to benthic foraminifera, peaked rapidly in the Early Triassic. These variations in biodiversity occur amidst pronounced excursions in the carbon isotope record, which are compatible with episodes of massive CO2 outgassing from the Siberian Large Igneous Province. Here we present a high-resolution Early Triassic temperature record based on the oxygen isotope composition of pristine apatite from fossil conodonts. Our reconstruction shows that the beginning of the Smithian substage of the Early Triassic was marked by a cooler climate, followed by an interval of warmth lasting until the Spathian substage boundary. Cooler conditions resumed in the Spathian. We find the greatest increases in taxonomic diversity during the cooler phases of the early Smithian and early Spathian. In contrast, a period of extreme warmth in the middle and late Smithian was associated with floral ecological change and high faunal taxonomic turnover in the ocean. We suggest that climate upheaval and carbon-cycle perturbations due to volcanic outgassing were important drivers of Early Triassic biotic recovery.

A high-resolution record of the atmospheric CO2 concentration from 60-20 kyr BP from the Taylor Dome ice core, Antarctica

A high-resolution record of the atmospheric CO2 concentration from 60 to 20 thousand years before present (kyr BP) based on measurements on the ice core of Taylor Dome, Antarctica is presented. This record shows four distinct peaks of 20 parts per million by volume (ppmv) on a millennial time scale. Good correlation of the CO2 record with temperature reconstructions based on stable isotope measurements on the Vostok ice core (Antarctica) is found.

Stable isotope record of Cretaceous samples of DSDP Hole 71-511

Oxygen isotope data for upper Turonian planktonic foraminifera at Deep Sea Drilling Project Site 511 (Falkland Plateau, 60°S paleolatitude) exhibit an ~2 per mil excursion to values as low as -4.66 per mil (Vienna Peedee belemnite standard; PDB) coincident with the warmest tropical temperature estimates yet obtained for the open ocean. The lowest planktonic foraminifer d18O values suggest that the upper ocean was as warm as 30-32°C. This is an extraordinary temperature for 60°S latitude but is consistent with temperatures estimated from apparently coeval mollusc d18O from nearby James Ross Island (65°S paleolatitude). Glassy textural preservation, a well-defined depth distribution in Site 511 planktonics, low sediment burial temperature (~32°C), and lack of evidence of highly depleted pore waters argue against diagenesis (even solid state diffusion) as the cause of the very depleted planktonic values. The lack of change in benthic foraminifer d18O suggests brackish water capping as the mechanism for the low planktonic d18O values. However, mixing ratio calculations show that the amount of freshwater required to produce a 2 per mil shift in ambient water would drive a 7 psu decrease in salinity. The abundance and diversity of planktonic foraminifera and nannofossils, high planktonic:benthic ratios, and the appearance of keeled foraminifera argue against lower-than-normal marine salinities. Isotope calculations and climate models indicate that we cannot call upon more depleted freshwater d18O to explain this record. Without more late Turonian data, especially from outside the South Atlantic basin, we can currently only speculate on possible causes of this paradoxical record from the core of the Cretaceous greenhouse.

40-year long monthly-resolved Sr/Ca record from 2.35 ka Bonaire coral, sample BON-6-A

We present a 40-year long monthly resolved Sr/Ca record from a fossil Diploria strigosa coral from Bonaire (Southern Caribbean Sea) dated with U/Th at 2.35 ka before present (BP). Secondary modifiers of this sea surface temperature (SST) proxy in annually-banded corals such as diagenetic alteration of the skeleton and skeletal growth-rate are investigated. Extensive diagenetic investigations reveal that this fossil coral skeleton is pristine which is further supported by clear annual cycles in the coral Sr/Ca record. No significant correlation between annual growth rate and Sr/Ca is observed, suggesting that the Sr/Ca record is not affected by coral growth. Therefore, we conclude that the observed interannual Sr/Ca variability was influenced by ambient SST variability. Spectral analysis of the annual mean Sr/Ca record reveals a dominant frequency centred at 6-7 years that is not associated with changes of the annual growth rate. The first monthly resolved coral Sr/Ca record from the Southern Caribbean Sea for preindustrial time suggests that fossil corals from Bonaire are suitable tools for reconstructing past SST variability. Coastal deposits on Bonaire provide abundant fossil D. strigosa colonies of Holocene age that can be accurately dated and used to reconstruct climate variability. Comparisons of long monthly resolved Sr/Ca records from multiple fossil corals will provide a mean to estimate seasonality and interannual to interdecadal SST variability of the Southern Caribbean Sea during the Holocene.

Stable carbon and oxygen isotope record of diagenetic carbonates from the New Jersey shelf

Carbon cycling is an important but poorly understood process on passive continental margins. In this study, we use the ionic and stable isotopic composition of interstitial waters and the petrology, mineralogy, and stable isotopic composition of authigenic carbonates collected from Ocean Drilling Program (ODP) Leg 174A (Sites 1071 and 1072) to constrain the origin of the carbonates and the evolution of methane on the outer New Jersey shelf. The pore fluids of the New Jersey continental shelf are characterized by (1) a fresh-brackish water plume, and (2) organic matter degradation reactions, which proceed through sulfate reduction. However, only minor methanogenesis occurs. The oxygen isotopic composition of the pore fluids supports a meteoric origin of the low salinity fluids. Authigenic carbonates are found in nodules, thin (~1-cm) layers, and carbonate cemented pavements. Siderite is the most common authigenic carbonate, followed by dolomite and calcite. The oxygen isotopic composition of the authigenic carbonates, i.e. 1.3-6.5 per mil PeeDee Belemnite (PDB), indicates an origin in marine pore fluids. The carbon isotopic composition of dolomite cements range from -16.4 to -8.8 per mil PDB, consistent with formation within the zone of sulfate reduction. Siderite d13C values show a greater range (-17.67-16.4 per mil), but are largely positive (mean=2.8 per mil) and are interpreted to have formed throughout the zone of methanogenesis. In contrast, calcite d13C values are highly negative (as low as -41.7 per mil)and must have formed from waters with a large component of dissolved inorganic carbon derived from methane oxidation. Pore water data show that despite complete sulfate reduction, methanogenesis appears not to be an important process presently occurring in the upper 400 m of the outer New Jersey shelf. In contrast, the carbon isotopic composition of the siderites and calcites document an active methanogenic zone during their formation. The methane may have been either oxidized or vented from shelf sediments, perhaps during sea-level fluctuations. If this unaccounted and variable methane flux is an areally important process during Neogene sea-level fluctuations, then it likely plays an important role in long-term carbon cycling on passive continental margins

Cenozoic oxygen isotopic values for benthic foraminifera from DSDP and ODP low and high latitude marine sediment cores

The climate during the Cenozoic era changed in several steps from ice-free poles and warm conditions to ice-covered poles and cold conditions. Since the 1950s, a body of information on ice volume and temperature changes has been built up predominantly on the basis of measurements of the oxygen isotopic composition of shells of benthic foraminifera collected from marine sediment cores. The statistical methodology of time series analysis has also evolved, allowing more information to be extracted from these records. Here we provide a comprehensive view of Cenozoic climate evolution by means of a coherent and systematic application of time series analytical tools to each record from a compilation spanning the interval from 4 to 61 Myr ago. We quantitatively describe several prominent features of the oxygen isotope record, taking into account the various sources of uncertainty (including measurement, proxy noise, and dating errors). The estimated transition times and amplitudes allow us to assess causal climatological-tectonic influences on the following known features of the Cenozoic oxygen isotopic record: Paleocene-Eocene Thermal Maximum, Eocene-Oligocene Transition, Oligocene-Miocene Boundary, and the Middle Miocene Climate Optimum. We further describe and causally interpret the following features: Paleocene-Eocene warming trend, the two-step, long-term Eocene cooling, and the changes within the most recent interval (Miocene-Pliocene). We review the scope and methods of constructing Cenozoic stacks of benthic oxygen isotope records and present two new latitudinal stacks, which capture besides global ice volume also bottom water temperatures at low (less than 30°) and high latitudes. This review concludes with an identification of future directions for data collection, statistical method development, and climate modeling.

Stable isotope record of benthic foraminifera from DSDP Site 68-502

Benthic foraminiferal delta13C data from site 502 in the Caribbean Sea (sill depth ?1800 m) indicate that throughout the past 2.6 m.y., glacial delta13C values in the middepth Atlantic were higher during glaciations than interglaciations. This is interpreted as indicating a greater proportion of Upper North Atlantic Deep Water (UNADW) relative to southern source waters during glaciations. The contribution of UNADW during interglaciations to the middepth Atlantic remained approximately constant, and the contribution during glaciations may have been as much as 10 % higher in the late Pleistocene than in the late Pliocene. This small increase is in striking contrast to the much larger decrease in glacial Lower North Atlantic Deep Water (LNADW) contribution relative to southern sources, from about 80% to about 20%, that occurred over the past 2.6 m.y. Glacial intensification over the past 2.6 m.y. was probably coupled with a decrease in northward heat transport by the upper limb of the North Atlantic circulation cell, as was previously suggested on the basis of a LNADW record alone. Late Pleistocene (1 Ma-present) delta13C values in the Caribbean Sea were approximately 0.2? higher than they were from 2.6 to 2.0 Ma. The delta13C rise is not due to an increase in the mean ocean delta13C value, nor can it be entirely attributed to an increase in the proportion of high-delta13C source waters. An increase in the delta13C value of the surface source waters must have contributed to the delta13C rise.

Stable isotope record of Cibicidoides spp. from Late Miocene sediments of the Southern Ocean

Deepwater circulation plays an important role in climate modulation through its redistribution of heat and salt and its control of atmospheric CO2. Oppo and Fairbanks (1987, doi:10.1016/0012-821X(87)90183-X) showed that the Southern Ocean is an excellent monitor of deepwater circulation changes for two reasons: (1) the Southern Ocean is a mixing reservoir for incoming North Atlantic Deep Water and recirculated water from the Pacific and Indian oceans; and (2) the nutrient/delta13C tracers of deepwater are not significantly changed by surficial processes within the Southern Ocean. We can extend these principles to the late Miocene because tectonic changes in the Oligocene and early and middle Miocene developed near-modern basinal configurations. However, on these time scales, changes in the oceanic carbon reservoir and mean ocean nutrient levels also affect the delta13C differences between ocean basins. From 9.8 to 9.3 Ma, Southern Ocean delta13C values oscillated between high North Atlantic values and low Pacific values. The Southern Ocean recorded delta13C values similar to Pacific values from 9.2 to 8.9 Ma, reflecting a low contribution of Northern Component Water (NCW). The delta13C differences between the NCW and Pacific Outflow Water (POW) end-members were low from 8.9 to 8.0 Ma, making it difficult to discern circulation patterns. NCW production may have completely shutdown at 8.6 Ma, allowing Southern Component Water (SCW) to fill the North Atlantic and causing the delta13C values in the North Atlantic, Pacific, and Southern oceans to converge. Deepwater delta13C patterns resembling the modern distributions evolved by 7.0 Ma: delta13C values were near 1.0 per mil in the North Atlantic; 0.0 per mil in the Pacific; and 0.5 per mil in the Southern Ocean. Development of near-modern delta13C distributions by 7.0 Ma resulted not only from an increase in NCW flux but also from an increase in deepwater nutrient levels. Both of these processes increased the delta13C difference between the North Atlantic and Pacific oceans. Deepwater circulation patterns similar to today's operated as early as 9.8 Ma, but were masked by the lower nutrient/delta13C differences. During the late Miocene, 'interglacial' intervals prevailed during intervals of NCW production, while 'glacial' intervals occurred during low NCW production.

Isotopic and micropaleontological record of sediments of the Baffin Bay

The oxygen and carbon isotopic compositions of the planktonic foraminifer, Neogloboquadrina pachyderma (sinistral), were determined at 20-cm intervals through the 'composite' top ~ 22 m of sediments at ODP Site 645 (Holes 645B, 645C, 645F, and 645G) and at 10-cm intervals through a 9-m piston core (85-027-016) collected during the Hudson site survey. Quantitative analyses of palynomorphs, notably dinocysts, and of planktonic foraminifers were performed. Organic and nitrogen contents and isotopic composition of nitrogen and carbon in organic matter also were determined. These data provide a high-resolution record of changes that occurred in surface-water masses during the last glacial cycle in Baffin Bay. The basin experienced low planktonic productivity during most of the late Pleistocene, either from dilution in surface water by meltwater discharges from the surrounding ice-sheet or from the presence of a relatively dense sea-ice cover. Peaks of meltwater discharge are indicated by d18O values as low as about 1.5 per mil, correlative d13C- d18O shifts, low concentration of planktonic foraminifers, high concentrations of glacially reworked pre-Quaternary palynomorphs, and low-salinity dinocyst assemblages. As a whole, d18O values ranging between 4.5 and 2.5 per mil allow the establishment of an 18O stratigraphy spanning isotopic stages 5 to 1. Because of the poor core recovery, the general paucity of microflora and microfauna, and the possible occurrence of slumping or debris flow at Site 645, further interpretation remains problematic.