Carbon and oxygen stable isotope composition of bulk sediment and abundance of Braarudospahaera in ODP Site 122-762 (Table 1)

Nannofossil assemblages enriched in Braarudosphaera occur in lower Oligocene to lower Miocene sediments at Ocean Drilling Program Sites 762 and 763 on the central Exmouth Plateau. Braarudosphaerids appear here rather abruptly in the lower Oligocene (in Zone NP21). They reach their greatest numbers in the lower Oligocene (in Zones NP22 and NP23), where they comprise up to 10% of some samples. Braarudosphaera bigelowii is the overwhelmingly dominant species, occurring together with rare specimens of B. discula and Micrantholithus pinguis. The holococcoliths Peritrachelina joidesa and Lantemithus minutus are also associated with the Braarudosphaera enrichment. There are two populations of B. bigelowii: one of normal size (10-14 µm) and one of large specimens (20-22 µm). The larger braarudosphaerids are more common than the smaller forms. Braarudosphaera-rich sediments are absent at Wombat Plateau sites during the same time interval. We attribute this to latitudinal control, because the Wombat sites are about 4° north of the central Exmouth Plateau sites. We believe that the occurrence of braarudosphaerids is related to an Oligocene to early Miocene oceanographic event on the Exmouth Plateau. We suspect that mid-ocean up welling of cool, low-salinity, nutrient-rich water along a divergent zone created the Braarudosphaera-nch sediments in the South Atlantic and Indian oceans.

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.

Stable carbon and oxygen isotope composition of Late Cretaceous benthic foraminifera from the southern South Atlantic

The stable carbon and oxygen isotope composition of different benthic foraminiferal species of the latest Campanian and earliest Maastrichtian from Ocean Drilling Project Hole 690C (Weddell Sea, southern South Atlantic, ~1800 m paleowater depth) have been investigated. The total range of measured isotope values of all samples exceeds ~4 per mil for delta 13C and 1.1 per mil for delta 18O. Carbon isotope values of proposed deep infaunal species are generally similar or only slightly lower when compared to proposed epifaunal to shallow infaunal species. Interspecific differences vary between samples probably reflecting temporal changes in organic carbon fluxes to the sea floor. Constantly lower delta 13C values for Pullenia marssoni and Pullenia reussi suggest the deepest habitat for these species. The strong depletion of delta 13C values by up to 3 per mil within lenticulinids may be attributed to a deep infaunal microhabitat, strong vital effects, or different feeding strategy when compared to other species or modern lenticulinids. The mean delta 18O values reveal a strong separation of epifaunal to shallow infaunal and deep infaunal species. Epifaunal to shallow infaunal species are characterized by low delta 18O values, deep infaunal species by higher values. This result possibly reflects lower metabolic rates and longer life cycles of deep infaunal species or the operating of a pore water [CO3]2- effect on the benthic foraminiferal stable isotopes. Pyramidina szajnochae shows an enrichment of oxygen isotopes with test size comprising a total of 0.6 per mil between 250 and 1250 µm shell size. Although delta 13C lacks a corresponding trend these data likely represent the presence of changes in metabolic rates during ontogenesis. These results demonstrate the general applicability of multi-species stable isotope measurements of pristine Cretaceous benthic foraminifera to reconstruct past microhabitats and to evaluate biological and environmental effects on the stable isotope composition.

Pliocene-Pleistocene oxygen isotope record DSDP Site 586, Ontong Java Plateau, Pacific Ocean i

Oceanographic changes in the western equatorial Pacific during the past 6 Ma are inferred from oxygen isotopic analyses of planktic and benthic foraminifera from Ontong Java Plateau (DSDP Site 586). The taxa are Globigerinoides sacculifer, Pulleniatina, Cibicidoides wuellerstorfi, and Oridorsalis umbonatus. Cooling and ice buildup are indicated by an 18O enrichment of 0.3 per mil in the planktic species near 3.4 Ma. This shift apparently is compensated in the benthic data by a warming of the deep waters by between 1° and 2° C. We suggest that the dominant source of upper deep water supply to the Pacific changed from Antarctic to North Atlantic at that time, the North Atlantic-derived water being warmer. Near 2.8 Ma (approximately) the planktic foraminifera again record an enrichment in 18O (Delta delta18O=0.25 per mil). We suggest ice buildup in the northern hemisphere as the cause, because of subsequent sharp increase in fluctuations of the delta18O signal, that is, instability. The enrichment is magnified in the benthic foraminifera (Delta delta18O = 0.5 per mil) by a cooling of the deep water by 1.5° at the time, presumably signalling a glacial-type reduction of North Atlantic Deep Water (NADW) production. Episodic divergence between the signals of G. sacculifer and Pulleniatina in the Pleistocene apparently reflects periods of increased upwelling in the western equatorial Pacific. The amplitude of ice volume fluctuations cannot be reconstructed from delta18O data alone, unless there are constraints on temperature variations. The increase in amplitude of fluctuation of the benthic and planktic signals during the Pleistocene may be attributed either to an increase in maximum ice volume, or to an increase in the fractionation of continental ice, or a combination of both causes.

Mineral and oxygen isotopic compositions in a profile through the altered lower oceanic crust, ODP Hole 176-735B

ODP Hole 735B located on the Southwest Indian Ridge at 57°E is an in situ sampled long, continuous section of lower oceanic crust. Oxygen isotope compositions of constituent minerals of Leg 176 gabbros have been measured by UV-laser oxygen isotope microprobe. Together with existing data from Leg 118, a complete oxygen isotope profile through the lower oceanic crust has been obtained. Most clinopyroxenes and olivines have normal mantle values of ~5.5 per mil and ~5.2 per mil, respectively, while plagioclases show slight d18O enrichment relative to its mantle value of 6.1per mil. Down-hole variations of Hole 735B gabbro indicate a downward decreasing d18O profile, with a kink at a depth of about 800 m below sea floor. Above this depth, gabbros are depleted in 18O relative to unaltered basalts, while below ~800 m they show nearly unmodified d18O values. Abundant seawater penetration appears to be limited to the upper part of the lower crust at ODP site 735 (~800 m into the gabbroic layer and ~2-2.5 km into the oceanic crust from the top of pillow basalts). Mass balance calculations show that the lower crust formed under this ultra-slow-spreading ridge has an average d18O value of 5.5 per mil. The whole crust at Site 735 has an overall 18O enrichment with d18O values of 6.0 per mil to 7.8 per mil, depending on the possible variation of the d18O values of the upper pillow basalts and sheeted dykes. The apparent difference in oxygen isotope compositions of ocean crusts formed with different spreading rates has important implications on the buffering of ocean water over geological time, as well as on the oxygen recycling between crust and mantle through subduction. The difference of seawater penetration between fast- and slow-spreading ridges could be related to their particular magmatic-tectonic history during the formation and aging of the crust. However, more analyses on continuous sections through oceanic and ophiolitic crust in different tectonic settings are required to derive any predictive models.

Oxygen contents, sulfate concentrations, and changes of IPLs under different storage conditions of samples from ODP Leg 204 and IODP Expedition 311

We have studied the effects of slow infiltration of oxygen on microbial communities in refrigerated legacy samples from ocean drilling expeditions. Storage was in heat-sealed, laminated foil bags with a N2 headspace for geomicrobiological studies. Analysis of microbial lipids suggests that Bacteria were barely detectable in situ but increased remarkably during storage. Detailed molecular examination of a methane-rich sediment horizon showed that refrigeration triggered selective growth of ANME-2 archaea and a drastic change in the bacterial community. Subsequent enrichment targeting methanogens yielded exclusively methylotrophs, which were probably selected for by high sulfate levels caused by oxidation of reduced sulfur species. We provide recommendations for sample storage in future ocean drilling expeditions.

Oxygen and carbon isotope composition of Globoquadrina venezuelana and Oridorsalis umbonatus at DSDP Leg 85 Holes

Oxygen and carbon isotope stratigraphies are given for the planktonic foraminifer Globoquadrina venezuelana (a deep-dwelling species) at three DSDP sites located along a north-south transect at approximately 133°W across the Pacific equatorial high-productivity zone. The records obtained at Sites 573 and 574 encompass the lower Miocene. At Site 575 the record includes the middle Miocene and extends into the lowermost lower Miocene. The time resolution of the planktonic foraminifer isotope record varies from 50,000 to 500,000 yr. The benthic foraminifer Oridorsalis umbonatus was analyzed for isotope composition at a few levels of Site 575. Isotope stratigraphies for all three sites are compared with carbonate, foraminifer preservation, and grain size records. We identified a number of chemostratigraphic signals that appear to be synchronous with previously recognized signals in the western equatorial Pacific and the tropical Indian Ocean, and thus provide useful tools for chronostratigraphic correlations. The sedimentary sequence at Site 573 is incomplete and condensed, whereas the sequences from Sites 574 and 575 together provide a complete lower Miocene record. The expanded nature of this record, which was recovered with minimum disturbance and provides excellent calcareous and siliceous biostratigraphic control, offers a unique opportunity to determine the precise timing of early Miocene events. Paleomagnetic data from the hydraulic piston cores at Site 575 for the first time allow late early Miocene paleoceanographic events to be tied directly to the paleomagnetic time scale. The multiple-signal stratigraphies provide clues for paleoceanographic reconstruction during the period of preconditioning before the major middle Miocene cooling. In the lowermost lower Miocene there is a pronounced shift toward greater d13C values (by -1%) within magnetic Chron 16 (between approximately 17.5 and 16.5 Ma). The "Chron 16 Carbon Shift" coincides with the cessation of an early Miocene warming trend visible in the d18O signals. Values of d13C remain high until approximately 15 Ma, then decrease toward initial (early Miocene) values near 13.5 Ma. The broad lower to middle Miocene d13C maximum appears to correlate with the deposition of organic-carbon-rich sediments around the margin of the northern Pacific in the Monterey Formation of California and its lateral equivalents. The sediments rimming the Pacific were probably deposited under coastal upwelling conditions that may have resulted from the development of a strong permanent thermocline. Deposition in the upwelling areas occurred partly under anaerobic conditions, which led to the excess extraction of organic carbon from the ocean. The timing of the middle Miocene cooling, which began after the Chron 16 Carbon Shift, suggests that the extraction of organic carbon preconditioned the ocean-atmosphere system for subsequent cooling. A major carbonate dissolution event in the late early Miocene, starting at approximately 18.7 Ma, is associated with the enrichment in 13C. The maximum dissolution is coeval with the Chron 16 Carbon Shift. It corresponds to a prominent acoustic horizon that can be traced throughout the equatorial Pacific.

Oxygen and carbon isotope stratigraphy of ODP Holes 107-653A and 107-654A

Stable isotope analysis of two species (or groups of species) of planktonic foraminifers: Globigerinoides ruber (or G. obliquus and G. obliquus extremus) and Globigerina bulloides (or G. falconensis and G. obesa) from ODP Hole 653A and Site 654 in the Tyrrhenian basin, records the Pliocene-Pleistocene glacial history of the Northern Hemisphere. The overall increase in mean d18O values through the interval 4.6-0.08 Ma is 1.7 per mil for G. bulloides and 1.5 per mil for G. ruber. The time interval 3.1-2.5 Ma corresponds to an important phase of 18O enrichment for planktonic foraminifers. In this interval, glacial d18O values of both species G. bulloides and G. ruber increase by about l per mil, this increase being more progressive for G. ruber than for G. bulloides. The increase of interglacial d18O values is higher for G. bulloides (1.5 per mil) than for the Gruber group (1 per mil). These data suggest a more pronounced seasonal stratification of the water masses during interglacial phases. Large positive d18O fluctuations of increasing magnitude are also recorded at 2.25 and 2.15 Ma by G bulloides and appear to be diachronous with those of Site 606 in the Atlantic Ocean. Other events of increasing d18O values are recorded between 1.55 and 1.3 Ma, at 0.9 Ma, 0.8 Ma, and near 0.34 Ma. In the early Pliocene the d18O variability recorded by the planktonic species G. bulloides was higher in the Mediterranean than in the Atlantic at the same latitude. This suggests that important cyclic variations in the water budget of the Mediterranean occurred since that time. Step increases in the d18O variability are synchronous with those of the open ocean at 0.9 and 0.34 Ma. The higher variability as well as the higher amplitude of the peaks of 18O enrichment may be partly accounted for by increase of dryness over the Mediterranean area. In particular the high amplitude d18O fluctuations recorded between 3.1 and 2.1 Ma are correlated with the onset of a marked seasonal contrast and a summer dryness, revealed by pollen analyses. Strong fluctuations towards d13C values higher than modern ones are recorded by the G. ruber group species before 1.7 Ma and suggest a high production of phytoplankton. When such episodes of high primary production are correlated with episodes of decreasing 13C content of G. bulloides, they are interpreted as the consequence of a higher stratification of the upper water masses resulting itself from a marked seasonality. Such episodes occur between 4.6 and 4.05 Ma, 3.9 and 3.6 Ma, and 3.25 and 2.66 Ma. The interval 2.66-1.65 Ma corresponds to a weakening of the stratification of the upper water layers. This may be related to episodes of cooling and increasing dryness induced by the Northern Hemisphere Glaciations. The Pleistocene may have been a less productive period. The transition from highly productive to less productive surface waters also coincides with a new step increase in dryness and cooling, between 1.5 and 1.3 Ma. The comparison of the 13C records of G ruber and G. bulloides in fact suggests that a high vertical convection became a dominant feature after 2.6 Ma. Increases in the nutrient input and the stratification of the upper water masses may be suspected, however, during short episodes near 0.86 Ma (isotopic stage 25), 0.57-0.59 Ma (isotopic stage 16), 0.49 Ma (isotopic stage 13), 0.4-0.43 Ma (isotopic stage 11), and 0.22 and 0.26 Ma (part of isotopic stage 7 and transition 7/8). In fact, changes in the C02 balance within the different water masses of the Tyrrhenian basin as well as in the local primary production did not follow the general patterns of the open ocean.

Oxygen, hydrogen, and carbon isotopic compositions in deep sea cherts, porcellanites, and coexisting carbonates from DSDP Legs 2, 3, 6, 7, 11, 14, 16, 17, and 20

Seventy four samples of DSDP recovered cherts of Jurassic to Miocene age from varying locations, and 27 samples of on-land exposed cherts were analyzed for the isotopic composition of their oxygen and hydrogen. These studies were accompanied by mineralogical analyses and some isotopic analyses of the coexisting carbonates. d18O of chert ranges between 27 and 39%. relative to SMOW, d18O of porcellanite - between 30 and 42%. The consistent enrichment of opal-CT in porcellanites in 18O with respect to coexisting microcrystalline quartz in chert is probably a reflection of a different temperature (depth) of diagenesis of the two phases. d18O of deep sea cherts generally decrease with increasing age, indicating an overall cpoling of the ocean bottom during the last 150 m.y. A comparison of this trend with that recorded by benthonic foraminifera (Douglas and Savin, 1975; http://www.deepseadrilling.org/32/volume/dsdp32_15.pdf) indicates the possibility of d18O in deep sea cherts not being frozen in until several tens of millions of years after deposition. Cherts of any Age show a spread of d18O values, increasing diagenesis being reflected in a lowering of d18O. Drusy quartz has the lowest d18O values. On-land exposed cherts are consistently depleted in 18O in comparison to their deep sea time equivalent cherts. Water extracted from deep sea cherts ranges between 0.5 and 1.4 wt %. dD of this water ranges between -78 and -95%. and is not a function of d18O of the cherts (or the temperature of their formation).

Stable Oxygen and carbon isotope record of benthic foraminifera of ODP Leg 121 holes

Oxygen and carbon isotopic records have been developed for the Cenozoic carbonate oozes of Sites 752, 754, 756, and 757 based on the analysis of monospecific benthic foraminifers. The intent of this report is to provide a basic isotopic stratigraphy for use in other paleoceanographic studies. The oxygen isotope record displays the enrichments associated with cooling or ice volume buildup at the Eocene/Oligocene boundary, in the middle Miocene, and in the upper Pliocene. The carbon isotopic record contains the Chron 16 enrichment in the lower Miocene and the Chron 6 depletion in the uppermost Miocene.

Oxygen and carbon isotopic composition in Eocene and Oligocene planktonic and benthic foraminifera from DSDP sediments

Oxygen and carbon isotope ratios in Eocene and Oligocene planktonic and benthic foraminifera have been investigated from Atlantic, Indian, and Pacific Ocean locations. The major changes in Eocene-Oligocene benthic foraminiferal oxygen isotopes were enrichment of up to 1 per mil in 18O associated with the middle/late Eocene boundary and the Eocene/Oligocene boundary at locations which range from 1- to 4-km paleodepth. Although the synchronous Eocene-Oligocene 18O enrichment began in the latest Eocene, most of the change occurred in the earliest Oligocene. The earliest Oligocene enrichment in 18O is always larger in benthic foraminifera than in surface-dwelling planktonic foraminifera, a condition that indicates a combination of deep-water cooling and increased ice volume. Planktonic foraminiferal d18O does not increase across the middle/late Eocene boundary at our one site with the most complete record (Deep Sea Drilling Project Site 363, Walvis Ridge). This pattern suggests that benthic foraminiferal d18O increased 40 m.y. ago because of increased density of deep waters, probably as a result of cooling, although glaciation cannot be ruled out without more data. Stable isotope data are averaged for late Eocene and earliest Oligocene time intervals to evaluate paleoceanographic change. Average d18O of benthic foraminifera increased by 0.64 per mil from the late Eocene to the early Oligocene d18O maximum, whereas the average increase for planktonic foraminifera was 0.52 per mil. This similarity suggests that the Eocene/Oligocene boundary d18O increase was caused primarily by increased continental glaciation, coupled with deep sea cooling by as much as 2°C at some sites. Average d18O of surface-dwelling planktonic foraminifera from 14 upper Eocene and 17 lower Oligocene locations, when plotted versus paleo-latitude, reveals no change in the latitudinal d18O gradient. The Oligocene data are offset by ~0.45 per mil, also believed to reflect increased continental glaciation. At present, there are too few deep sea sequences from high latitude locations to resolve an increase in the oceanic temperature gradient from Eocene to Oligocene time using oxygen isotopes.

Late Pliocene stable oxygen isotope record of the Mediterranean Sea

Detailed pollen analyses and oxygen isotope records of three foraminiferal species, Globigerina bulloides, Uvigerina peregrina and Cibicides pachyderma, from the Semaforo and Vrica composite sections (Crotone, southern Italy) have been compared to the global climatic changes depicted by late Pliocene-early Pleistocene foraminiferal d18O records of Site 607 in the North Atlantic, and Hole 653A in the Tyrrhenian basin, West Mediterranean. Major overturns in the mid-altitude vegetation are shown near isotopic stages 82, 60, 58 and 50, at about 2.03 Ma, 1.6 Ma and 1.37 Ma according to the Raymo et al. (1989, doi:10.1029/PA004i004p00413) and Ruddiman et al. (1989, doi:10.1029/PA004i004p00353) timescales. At the same dates, glacial 18O maxima either became higher or display step increases in the western Mediterranean or in the open ocean as well. This suggests that size increases of Northern Hemisphere ice sheets were the driving factor for regional or local marine and continental environmental changes within the Mediterranean basin. Near isotopic stages 62-60, close to the conventional Plio-Pleistocene boundary, the climatic conditions severed enough within the Mediterranean basin to modify the continental environment, as depicted by a sudden increase of Artemisia percentages, while the first significant southward migration of the North Polar Front may have been recorded by an influx of left coiling Neogloboquadrina pachyderma in the central Mediterranean. It also appears that 'Boreal Guests' entered the Mediterranean during phases of 18O enrichment of foraminiferal calcite. There does not seem to be any discrepancy between the climatic concept of the Pliocene-Pleistocene boundary and its chronostratigraphic definition.

Stable oxygen and carbon isotope composition of benthic foraminifera from the western Mediterranean Sea

The influence of microhabitat, organic matter flux, and metabolism on the stable oxygen and carbon isotope composition of live (Rose Bengal stained) and dead (empty tests) deep-sea benthic foraminifera from the Gulf of Lions (western Mediterranean Sea) have been studied. The total range of observed foraminiferal isotope values exceeds 1.0 per mil for d18O and 2.2 per mil for d13C demonstrating a wide range of coexisting disequilibria relative to d18O of equilibrium calcite (d18OEQ) and d13C of bottom water dissolved inorganic carbon (d13CDIC). The mean d18O values reveal strongest disequilibria for the studied epifaunal to shallow infaunal species (Cibicidoides pachydermus, Uvigerina mediterranea, Uvigerina peregrina) while values approach equilibrium in deep infaunal species (Globobulimina affinis, Globobulimina pseudospinescens). The mean d13C values decrease with increasing average living depths of the different species, thus reflecting a dominant microhabitat (pore water) signal. At the axis of the Lacaze-Duthier Canyon a minimum d13CDIC pore water gradient of approximately -2.1 per mil is assessed for the upper 6 cm of the surface sediment. Although live individuals of U. mediterranea were found in different depth intervals their mean d13C values are consistent with calcification at an average living depth around 1 cm. The deep infaunal occurrence of U. mediterranea specimens suggests association with macrofaunal burrows creating a microenvironment with geochemical characteristics similar to the topmost centimeter. This also explains the excellent agreement between stable isotope signals of live and dead individuals. The ontogenetic enrichment in both d18O and d13C values of U. mediterranea suggests a slow-down of metabolic rates during test growth similar to that previously observed in planktic foraminifera. Enhanced organic carbon fluxes and higher proportion of resuspended terrestrial organic material at the canyon axis are reflected by d13C values of U. mediterranea on average 0.58 per mil lower than those from the open slope. These results demonstrate the general applicability of the d13C signal of this species for the reconstruction of past organic matter fluxes in the Mediterranean Sea. Further studies on live specimens are needed for a more quantitative paleoceanographic approach.

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.