Description: This theme brings together primarily technical briefs on the analysis of biogenic ca... more Description: This theme brings together primarily technical briefs on the analysis of biogenic calcium carbonate for paleoceanography and paleoclimatology. Papers address the technical problems associated with magnesium/calcium analysis of foraminifera for the estimation of oceanic temperature, its link to foraminiferal oxygen isotope measurements, and the measurement of Mg/Ca and other elemental ratios in foraminifera and other biogenic carbonates. The closing date of this theme is October 2004. A related theme ...
The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic fo... more The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic foraminifer species from Maud Rise, Weddell Sea (ODP Sites 689 and 690), the first such results from the Antarctic. The results provide information about large-scale changes in the evolution of temperatures, seasonally, and structure of the upper water column prior to the development of a significant Antarctic cryosphere. The early Paleocene was marked by cooler surface-water conditions compared to the Cretaceous and possibly a less well developed thermocline. The late Paleocene and early Eocene saw the expansion of the thermocline as Antarctic surface waters became warm-temperate to subtropical. The late Paleocene to early Eocene thermal maximum was punctuated by two brief excursions during which time the entire Antarctic water column warmed and the meridional temperature gradient was reduced. The first of these excursions occurred at the Paleocene/Eocene boundary, in association with a m...
The equator to high southern latitude sea surface and vertical temperature gradients are reconstr... more The equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals: late Paleocene, early Eocene, early middle Eocene, late Eocene, and early Oligocene. Paleotemperatures are calculated using standard oxygen isotope/temperature equations with adjustments to account for (1) variations in sea water delta18O related to changes in global ice volume over time and (2) latitudinal gradients in surface water delta18O. These reconstructions indicate that sea-surface temperatures (SST) of the Southern Oceans in the early Eocene were as high as 15°C, whereas temperatures during the late Paleocene and early middle Eocene reached maximum levels of 10°-12°C. By the late Eocene and early Oligocene high latitude SST had declined to 6 and 4°C, respectively. For most of the early Paleogene, low latitude sub-tropical temperatures remained constant and well within the range of Holocene temperatures (24°-25°C) but by the late Eocene and early Oligocene declined to values in the range of 18° to 22°C. The late Paleogene apparent decline in tropical temperatures, however, might be artificial because of dissolution of near-surface foraminifera tests which biased sediment assemblages toward deeper-dwelling foraminifera. Moreover, according to recent plate reconstructions, it appears that the majority of sites upon which the late Eocene and early Oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling. Global deepwater temperature on average paralleled southern ocean SST for most of the Paleogene. We speculate based on the overall timing and character of marine sea surface temperature variation during the Paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high-latitude warmth of the early Eocene.
ABSTRACT The thermocline of the Makassar Strait within the Indo-Pacific Warm Pool is strongly inf... more ABSTRACT The thermocline of the Makassar Strait within the Indo-Pacific Warm Pool is strongly influenced by the El Niño-Southern Oscillation (ENSO) and, to a lesser extent, by seasonal wind reversals associated with the monsoon cycle. The thermocline temperature and salinity changes associated with this variability are accompanied by changes in the production and flux of planktonic foraminifera, including the thermocline-dwelling Pulleniatina obliquiloculata. Here we evaluate how a change in the intra- or interannual production and flux of this species affects the distribution of delta18O values within a population of specimens sampled from a marine sediment core from the northern Makassar Strait (MD98-2177). The delta18O of 50-100 individual P. obliquiloculata was measured from the 20th century, the Little Ice Age and the Medieval Climate Anomaly sections of core MD98-2177. The distributions of delta18O values at each time horizon were compared to modeled monthly mean equilibrium delta18O values using temperature and salinity data for the period 1958-2000 from the Simple Ocean Data Assimilation (SODA) reanalysis. The delta18O values of foraminiferal calcite were calculated for the range of calcification depths that applies to P. obliquiloculata. The predicted monthly delta18O values were then weighted in relation to the hydrographic changes associated with the seasonal reversal of winds between the northwestern and southeastern monsoon and the interannual changes associated with a change in the monsoon strength and in association with ENSO. The weighting is based on observed flux changes as seen in a recent sediment trap study conducted south of Java. The calcification depths were assumed to remain constant over the seasonal to interannual timescale. The results suggest that although the intrannual and interannual variations in the flux of planktonic foraminifera associated with a change in monsoon strength do not affect the overall distribution of delta18O values within a population, the changes in flux that accompany strong El Niños do introduce a large bias in the weighted mean of the population. Consequently, this inter-annual variability in the production of foraminifera must be accounted for when using the delta18O of planktonic foraminifera to reconstruct hydrographic variability.
Benthic and planktonic 14C ages are presented for the last glacial termination from marine sedime... more 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 pul...
The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high d13C va... more 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 mar...
We present a reconstruction of El Niño Southern Oscillation (ENSO) variability for the last mille... more We present a reconstruction of El Niño Southern Oscillation (ENSO) variability for the last millennium using stable oxygen and carbon isotope data obtained by analyzing samples from a marine sediment core (core MD98-2177) collected in the Indonesian Seas, at the edge the western Pacific warm pool. At this location the delta18O of calcite produced by thermocline-dwelling planktonic foraminifers reflect the
Description: This theme brings together primarily technical briefs on the analysis of biogenic ca... more Description: This theme brings together primarily technical briefs on the analysis of biogenic calcium carbonate for paleoceanography and paleoclimatology. Papers address the technical problems associated with magnesium/calcium analysis of foraminifera for the estimation of oceanic temperature, its link to foraminiferal oxygen isotope measurements, and the measurement of Mg/Ca and other elemental ratios in foraminifera and other biogenic carbonates. The closing date of this theme is October 2004. A related theme ...
The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic fo... more The oxygen and carbon isotopic composition has been measured for numerous Paleogene planktonic foraminifer species from Maud Rise, Weddell Sea (ODP Sites 689 and 690), the first such results from the Antarctic. The results provide information about large-scale changes in the evolution of temperatures, seasonally, and structure of the upper water column prior to the development of a significant Antarctic cryosphere. The early Paleocene was marked by cooler surface-water conditions compared to the Cretaceous and possibly a less well developed thermocline. The late Paleocene and early Eocene saw the expansion of the thermocline as Antarctic surface waters became warm-temperate to subtropical. The late Paleocene to early Eocene thermal maximum was punctuated by two brief excursions during which time the entire Antarctic water column warmed and the meridional temperature gradient was reduced. The first of these excursions occurred at the Paleocene/Eocene boundary, in association with a m...
The equator to high southern latitude sea surface and vertical temperature gradients are reconstr... more The equator to high southern latitude sea surface and vertical temperature gradients are reconstructed from oxygen isotope values of planktonic and benthic foraminifers for the following five time intervals: late Paleocene, early Eocene, early middle Eocene, late Eocene, and early Oligocene. Paleotemperatures are calculated using standard oxygen isotope/temperature equations with adjustments to account for (1) variations in sea water delta18O related to changes in global ice volume over time and (2) latitudinal gradients in surface water delta18O. These reconstructions indicate that sea-surface temperatures (SST) of the Southern Oceans in the early Eocene were as high as 15°C, whereas temperatures during the late Paleocene and early middle Eocene reached maximum levels of 10°-12°C. By the late Eocene and early Oligocene high latitude SST had declined to 6 and 4°C, respectively. For most of the early Paleogene, low latitude sub-tropical temperatures remained constant and well within the range of Holocene temperatures (24°-25°C) but by the late Eocene and early Oligocene declined to values in the range of 18° to 22°C. The late Paleogene apparent decline in tropical temperatures, however, might be artificial because of dissolution of near-surface foraminifera tests which biased sediment assemblages toward deeper-dwelling foraminifera. Moreover, according to recent plate reconstructions, it appears that the majority of sites upon which the late Eocene and early Oligocene tropical temperatures were previously established were located either in or near regions likely to have been influenced by upwelling. Global deepwater temperature on average paralleled southern ocean SST for most of the Paleogene. We speculate based on the overall timing and character of marine sea surface temperature variation during the Paleogene that some combination of both higher levels of greenhouse gases and increased heat transport was responsible for the exceptional high-latitude warmth of the early Eocene.
ABSTRACT The thermocline of the Makassar Strait within the Indo-Pacific Warm Pool is strongly inf... more ABSTRACT The thermocline of the Makassar Strait within the Indo-Pacific Warm Pool is strongly influenced by the El Niño-Southern Oscillation (ENSO) and, to a lesser extent, by seasonal wind reversals associated with the monsoon cycle. The thermocline temperature and salinity changes associated with this variability are accompanied by changes in the production and flux of planktonic foraminifera, including the thermocline-dwelling Pulleniatina obliquiloculata. Here we evaluate how a change in the intra- or interannual production and flux of this species affects the distribution of delta18O values within a population of specimens sampled from a marine sediment core from the northern Makassar Strait (MD98-2177). The delta18O of 50-100 individual P. obliquiloculata was measured from the 20th century, the Little Ice Age and the Medieval Climate Anomaly sections of core MD98-2177. The distributions of delta18O values at each time horizon were compared to modeled monthly mean equilibrium delta18O values using temperature and salinity data for the period 1958-2000 from the Simple Ocean Data Assimilation (SODA) reanalysis. The delta18O values of foraminiferal calcite were calculated for the range of calcification depths that applies to P. obliquiloculata. The predicted monthly delta18O values were then weighted in relation to the hydrographic changes associated with the seasonal reversal of winds between the northwestern and southeastern monsoon and the interannual changes associated with a change in the monsoon strength and in association with ENSO. The weighting is based on observed flux changes as seen in a recent sediment trap study conducted south of Java. The calcification depths were assumed to remain constant over the seasonal to interannual timescale. The results suggest that although the intrannual and interannual variations in the flux of planktonic foraminifera associated with a change in monsoon strength do not affect the overall distribution of delta18O values within a population, the changes in flux that accompany strong El Niños do introduce a large bias in the weighted mean of the population. Consequently, this inter-annual variability in the production of foraminifera must be accounted for when using the delta18O of planktonic foraminifera to reconstruct hydrographic variability.
Benthic and planktonic 14C ages are presented for the last glacial termination from marine sedime... more 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 pul...
The early Cenozoic marine carbon isotopic record is marked by a long-term shift from high d13C va... more 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 mar...
We present a reconstruction of El Niño Southern Oscillation (ENSO) variability for the last mille... more We present a reconstruction of El Niño Southern Oscillation (ENSO) variability for the last millennium using stable oxygen and carbon isotope data obtained by analyzing samples from a marine sediment core (core MD98-2177) collected in the Indonesian Seas, at the edge the western Pacific warm pool. At this location the delta18O of calcite produced by thermocline-dwelling planktonic foraminifers reflect the
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