The accumulation of wind blown (eolian) dust in deep-sea sediments reflects the aridity/humidity ... more The accumulation of wind blown (eolian) dust in deep-sea sediments reflects the aridity/humidity conditions of the continental region supplying the dust, as well as the "gustiness" of the climate system. Detailed studies of Pleistocene glacial-interglacial dust fluxes suggest changes in accumulation rates corresponding to orbital variations in solar insolation (Milankovitch cycles). While the orbital cycles found in sedimentary archives of the Pleistocene are intricately related to glacial growth and decay, similar global orbital signals recognized in deep-sea sediments of early Paleogene age, the last major greenhouse interval ∼65-45 million years ago, could not have been linked to the waxing and waning of large ice sheets. Thus orbital signals recorded in early Paleogene sediments must reflect some other climate response to changes in solar insolation. To explore the potential connection between orbital forcing and the climate processes that control dust accumulation, we generated a high-resolution dust record for ∼58 Myr old sediments from Shatsky Rise (ODP Site 1209, paleolatitude ∼15°N-20°N). The dust accumulation data provide the first evidence of a correlation between dust flux to the deep sea and orbital cyclicity during the early Paleogene, indicating dust supply responded to insolation forcing during the last major interval of greenhouse climate. Furthermore, the relative amplitude of the dust flux response during the early Paleogene greenhouse was comparable to that during icehouse climates. Thus, subtle variations in solar insolation driven by changes in Earth's orbit about the Sun may have had a similar impact on climate during intervals of overall warmth as they did during glacial-interglacial states.
Proceedings of the Ocean Drilling Program, 199 Initial Reports, 2002
Ocean Drilling Program (ODP) Leg 199, "The Paleogene Equatorial Transect" (Sites 1215-1222), was ... more Ocean Drilling Program (ODP) Leg 199, "The Paleogene Equatorial Transect" (Sites 1215-1222), was designed to study the evolution of the equatorial Pacific current and wind system as Earth went from maximum Cenozoic warmth to initial Antarctic glaciations. The drilling program was primarily devoted to a transect along the 56-to 57-Ma crust, old enough to capture the Paleocene/Eocene boundary in the basal, more carbonate-rich sediments. The Leg 199 transect extends from a paleolatitude of ~4°N-~4°S to encompass a relatively thick lower Eocene sediment section perhaps 8° north of the paleoequator. One site (1218) was also drilled on ~40-Ma crust to collect a near-equatorial sediment sequence from the middle Eocene to the Oligocene in order to investigate the transition in global climate from the Eocene "greenhouse" to Oligocene "icehouse." The Pacific plate has drifted northward through Cenozoic time transporting biogenic sediments deposited under the high-productivity equatorial belt into a zone of extremely slow sediment (red clay) accumulation. Thus, the central tropical North Pacific Ocean is an ideal region in which to sample shallowly buried Paleogene sequences of equatorially deposited biogenic sediments. The thin Neogene cover of red clay in the area means that the entire Paleogene sediment section is potentially drillable by ODP advanced piston coring and extended core barrel methods. 1 Examples of how to reference the whole or part of this volume. 2 Shipboard Scientific Party addresses.
Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropica... more Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific). LYNCH-STIEGLITZ ET AL.
Grain size analyses of the mineral component of abyssal Pacific surface sediments show two distin... more Grain size analyses of the mineral component of abyssal Pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic, respectively. In the range of 1 to 30 Ima, eolian grains show a distinct size mode at about 2 gm (9•) and little material coatset than about 16 gm (6•). Hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 gm (9•) and important amounts of material coatset than 16 gm (6•). This ability to distinguish between hemipelagic and eolian grains will obviate some longstanding concerns in the interpretation of deep-sea sediments. Examples of the utility of this technique are given for the North Pacific and South Atlantic. the southwest Atlantic shows distinctly the influence of abyssal flow on those sediments. Johnson et al. [1988] were able to characterize the strength of the Western Boundary Undercurrent during the past 90 kyr based on size analysis of the detrital silts. Dowling and McCave [1993] were able to define the late glacial and post glacial history of bottom flow along the Fermi Drift based upon the varying importance of size modes in the silt range.
Atmospheric CO 2 concentrations and climate are regulated on geological time scales by the balanc... more Atmospheric CO 2 concentrations and climate are regulated on geological time scales by the balance between carbon input and its removal by weathering feedbacks involving the erosion of silicate and organic carbon bearing rocks, which also controls the depth in the oceans at which carbonate is dissolved. Here
Deep Sea Drilling Project (DSDP) Site 215 provides an expanded section across the Paleocene/Eocen... more Deep Sea Drilling Project (DSDP) Site 215 provides an expanded section across the Paleocene/Eocene boundary, the most complete mid-latitude sequence from a Southern Hemisphere location in the Indo-Pacific area. The events of this transition occurred during a span of about 1.2 m.y. Oxygen isotope values derived from benthic foraminiferal calcite decrease by about 1.0°/oo, a decrease most likely related to warming of deep ocean waters. Turnovers of benthic foraminifera accompany <5 ls O changes and culminate in the predominant extinction event at the end of the Paleocene Epoch. Carbon isotope ratios also shift dramatically toward lighter values near the end of the Paleocene, beginning about 0.45 m.y. after oxygen isotope values start to change. The intensity of Southern Hemisphere atmospheric circulation as recorded by grain sizes of eolian particles shows a large and rapid reduction beginning another 0.45 m.y. later. A significant reduction of zonal wind strength at the Paleocene/Eocene boundary, until now observed only at Northern Hemisphere locations, appears to have been a global phenomenon related to decreased latitudinal thermal gradients occasioned by more effective poleward heat transport via the deep ocean.
• An eastern equatorial Pacific stable oxygen isotope depth profile shows a weak and deep thermoc... more • An eastern equatorial Pacific stable oxygen isotope depth profile shows a weak and deep thermocline during the Last Glacial Maximum • Regional compilation of surface to subsurface dwelling foraminifera shows the thermocline was deep throughout the Eastern Equatorial Pacific
The South Pacific is relatively unexplored and is almost devoid of digitally-acquired seismic ref... more The South Pacific is relatively unexplored and is almost devoid of digitally-acquired seismic reflection data. While surveying for an IODP cruise on R/V Melville in February-March 2005, we identified a region of zero sediment accumulation nearly two million square kilometers in area in the Southwest Pacific Basin. This South Pacific Bare Zone is bounded approximately between the Menard Fracture Zone
Core V21-146 provides a continuous record of northwest Pacific pelagic sedimentation spanning the... more Core V21-146 provides a continuous record of northwest Pacific pelagic sedimentation spanning the past 530,000 years. Downcore variations of •5•80 from benthic foraminiferal calcite were correlated to the SPECMAP record to provide an age model for late Pleistocene paleoclimatic and paleoceanographic variation. Fluxes of CaCO3 and eolian material have been determined by combining information about linear sedimentation rates, bulk densities and component percentages. The mass accumulation rate (MAR) of CaCO3 varies from 58 to 1435 mg(cm2kyr)-• and exhibits the Pacific Ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record. However, the pattern of CaCO3accumulation appears to shift during the mid-Brunhes so that prior to 350,000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods. The flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loesssoil stratigraphy in China. Dust fluxes range from 43 to 718 mg(cm2kyr)-1 and are greater by a factor of about 4 during glacial times. Cross-spectral analysis of the eolian flux and oxygen isotope records shows an inphase and Copyright 1991 by the American Geophysical Union. Paper number 91PA00559. 0883-8305/91/91PA-00559 $10.00 coherent relationship at each of the major orbital periodicities of 100, 41, and 19 kyr. Eolian grain sizes, generally used as a proxy record of wind intensity, range from 8.4• (2.9 !.tm) to 6.2• (13.6 gm). A change in grain size variability occurs near about 300 ka such that the older portion is characterized by lowerfrequency and higher-amplitude fluctuations than the younger portion. Power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25-35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities. The phase relationship for eccentricity between the eolian grain size and •5180 records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions. Hovan et al.: Northwest Pacific Sediment Record link the marine and continental records directly thereby enabling more complete global understanding of climatic variability. To do this, we have determined •80, CaCO3, eolian flux, and eolian grain size variations in V21-146, recovered from a site in the North Pacific downwind from China (Figure 1) and used the eolian flux information to tie the China loess sequence to the marine record. The initial results of this effort have been presented by Hovan et al. [1989]; here we examine the spectral characteristics of the eolian flux and grain size records as well as the record of CaCO3 accumulation in the northwestern Pacific. PROXY INDICATORS Marine Sediments Oxygen isotopic variations in calcite from benthic foraminifera tests reflect variations in continental ice volumes during the Pleistocene [Shackleton and Opdyke, 1973]. Since the oceans mix within approximately 1000-2000 years, the variations in the isotopic composition of the oceans are essentially synchronous and can be correlated globally in oceanic sediments. The SPECMAP project has defined the timing of the relative enrichments and depletions of isotopic ratios of oxygen in the oceans for the past 800,000 years, providing the basic chronostratigraphy for paleoclimatic investigations of the late Pleistocene [Imbrie et al., 1984]. The accumulation of calcium carbonate on the seafloor is controlled by two main factors, the rate of biological production near the ocean surface and the rate of dissolution in the water column and on the seafloor. in the equatorial Pacific during the late Pleistocene [Farrell and Prell, 1989]. Productivity plays a lesser, though identifiable, role [Adelsek and Anderson,
Oxygen and carbon isotopic records have been developed for the Cenozoic carbonate oozes of Sites ... more 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.
The late Cenozoic history of eolian sedimentation in the eastern Indian Ocean was developed from ... more The late Cenozoic history of eolian sedimentation in the eastern Indian Ocean was developed from samples recovered during drilling of Sites 752, 754, and 756. Temporal changes in the mass accumulation rate of eolian material reflect major climatic shifts in the southern African source region. A significant drop in dust mass flux values occurs near the end of the lower Oligocene. Younger sediments are characterized by a gradual reduction in dust accumulation rates until the middle Miocene after which values remain consistently low throughout the late Cenozoic, although a slight increase in eolian accumulation rate occurs near 2.5 Ma. This pattern of dust mass flux appears related to the supply of dust-sized particles in the source region and represents a shift in the climatic regime of southern Africa to increasingly more arid conditions throughout the late Cenozoic.
The composition and character of terrigenous sediments can be used to trace eolian and marine tra... more The composition and character of terrigenous sediments can be used to trace eolian and marine transportation processes such as winds, surface currents and deep currents. We analyzed more than 80 surface sediment samples from the pelagic realm of the Atlantic Ocean for variations in terrigenous grain size and major element geochemistry. A subset of these were also analyzed for radiogenic Nd and Sr isotopic ratios. These radioisotopic data were key in recognizing samples with distinctly different source regions and when viewed in conjunction with grain size and elemental data, broadly define several different regional transport modes. Terrigenous sediment transported to the tropical and subtropical Atlantic in deeper regions away from the continental margin is composed of a mixture of eolian and hemipelagic sediment supplied from the Sahar-Sahel regions of northern Africa. At sites closer to the continental margin a similar provenance is found but turbidites and hemipelagic processes ...
Sea surface temperature (SST) reconstructions from the Western and Eastern Equatorial Pacific (WE... more Sea surface temperature (SST) reconstructions from the Western and Eastern Equatorial Pacific (WEP and EEP) indicate the Equatorial Pacific was in a permanent El Niño-like state during the early Pliocene. Specifically, SST in the WEP was nearly the same as today, while SST in the EEP cold tongue region was 2-3 °C warmer than today. Climatic transitions recorded in the EEP are of particular interest due to the region’s sensitivity to changes in upwelling and thermocline depth, and due to its role in the global ocean heat balance. However, not much is known about the evolution of the EEP cold tongue. This study aims to reconstruct the east-west and north-south gradients within the EEP using new SST and sub-surface temperature records from ODP Sites 848, 849, and 853 and published paleoceanographic records from the EEP to examine the temporal and spatial evolution of the EEP cold tongue from the Pliocene to Recent. Mg/Ca analyses on Globigerinoides sacculifer and Globorotalia tumida an...
Studying the terrigenous component of marine sediment gathered during ODP Leg 199 (Paleogene Equa... more Studying the terrigenous component of marine sediment gathered during ODP Leg 199 (Paleogene Equatorial Transect) will help unravel the paleoceanographic evolution of the central equatorial Pacific Ocean. For example, grain size and mineralogic data from the operationally defined eolian dust (ODED) component of marine sediment in the Pacific have commonly been used to assess changes in wind intensity and continental aridity. Assuming this eolian component is representing the weathering products of the upper continental crust, geochemical studies of Th, Sc, and REE distributions (e.g., Olivarez et al., 1991; Weber et al. 1996) have suggested the presence of two endmember components in ODED: the upper continental crust itself (the eolian-transported weathering products) as well as ocean crust (primarily volcanogenic material). Expanding upon these studies, we are examining the complete geochemical composition (major, trace, and REE concentrations) of the extracted eolian component as ...
Today in the Eastern Equatorial Pacific, a shallow thermocline and rigorous wind-driven upwelling... more Today in the Eastern Equatorial Pacific, a shallow thermocline and rigorous wind-driven upwelling brings cool, nutrient-rich water to the surface. In contrast, during the warm Pliocene (~3-5 Ma), sea surface temperatures in the Eastern Equatorial Pacific were much warmer than modern. Warm sea surface temperatures in upwelling regions, which have global effects on atmospheric circulation and the heat budget, could be caused by changes in wind-driven upwelling and/or changes in thermocline depth. As changes in wind-driven upwelling cannot entirely explain warm sea surface temperatures in upwelling regions, we investigate changes in subsurface temperature to monitor thermocline depth. We measured subsurface temperature records from Eastern Equatorial Pacific ODP transect Sites 848, 849, and 853 using Mg/Ca records from Globorotalia tumida, which has a depth habitat of ~100 m. Prior to closure of the Isthmus of Panama (5.2-4.8 Ma), subsurface temperatures were ~6-8°C warmer than modern,...
The accumulation of wind blown (eolian) dust in deep-sea sediments reflects the aridity/humidity ... more The accumulation of wind blown (eolian) dust in deep-sea sediments reflects the aridity/humidity conditions of the continental region supplying the dust, as well as the "gustiness" of the climate system. Detailed studies of Pleistocene glacial-interglacial dust fluxes suggest changes in accumulation rates corresponding to orbital variations in solar insolation (Milankovitch cycles). While the orbital cycles found in sedimentary archives of the Pleistocene are intricately related to glacial growth and decay, similar global orbital signals recognized in deep-sea sediments of early Paleogene age, the last major greenhouse interval ∼65-45 million years ago, could not have been linked to the waxing and waning of large ice sheets. Thus orbital signals recorded in early Paleogene sediments must reflect some other climate response to changes in solar insolation. To explore the potential connection between orbital forcing and the climate processes that control dust accumulation, we generated a high-resolution dust record for ∼58 Myr old sediments from Shatsky Rise (ODP Site 1209, paleolatitude ∼15°N-20°N). The dust accumulation data provide the first evidence of a correlation between dust flux to the deep sea and orbital cyclicity during the early Paleogene, indicating dust supply responded to insolation forcing during the last major interval of greenhouse climate. Furthermore, the relative amplitude of the dust flux response during the early Paleogene greenhouse was comparable to that during icehouse climates. Thus, subtle variations in solar insolation driven by changes in Earth's orbit about the Sun may have had a similar impact on climate during intervals of overall warmth as they did during glacial-interglacial states.
Proceedings of the Ocean Drilling Program, 199 Initial Reports, 2002
Ocean Drilling Program (ODP) Leg 199, "The Paleogene Equatorial Transect" (Sites 1215-1222), was ... more Ocean Drilling Program (ODP) Leg 199, "The Paleogene Equatorial Transect" (Sites 1215-1222), was designed to study the evolution of the equatorial Pacific current and wind system as Earth went from maximum Cenozoic warmth to initial Antarctic glaciations. The drilling program was primarily devoted to a transect along the 56-to 57-Ma crust, old enough to capture the Paleocene/Eocene boundary in the basal, more carbonate-rich sediments. The Leg 199 transect extends from a paleolatitude of ~4°N-~4°S to encompass a relatively thick lower Eocene sediment section perhaps 8° north of the paleoequator. One site (1218) was also drilled on ~40-Ma crust to collect a near-equatorial sediment sequence from the middle Eocene to the Oligocene in order to investigate the transition in global climate from the Eocene "greenhouse" to Oligocene "icehouse." The Pacific plate has drifted northward through Cenozoic time transporting biogenic sediments deposited under the high-productivity equatorial belt into a zone of extremely slow sediment (red clay) accumulation. Thus, the central tropical North Pacific Ocean is an ideal region in which to sample shallowly buried Paleogene sequences of equatorially deposited biogenic sediments. The thin Neogene cover of red clay in the area means that the entire Paleogene sediment section is potentially drillable by ODP advanced piston coring and extended core barrel methods. 1 Examples of how to reference the whole or part of this volume. 2 Shipboard Scientific Party addresses.
Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropica... more Much uncertainty exists about the state of the oceanic and atmospheric circulation in the tropical Pacific over the last glacial cycle. Studies have been hampered by the fact that sediment cores suitable for study were concentrated in the western and eastern parts of the tropical Pacific, with little information from the central tropical Pacific. Here we present information from a suite of sediment cores collected from the Line Islands Ridge in the central tropical Pacific, which show sedimentation rates and stratigraphies suitable for paleoceanographic investigations. Based on the radiocarbon and oxygen isotope measurements on the planktonic foraminifera Globigerinoides ruber, we construct preliminary age models for selected cores and show that the gradient in the oxygen isotope ratio of G. ruber between the equator and 8°N is enhanced during glacial stages relative to interglacial stages. This stronger gradient could reflect enhanced equatorial cooling (perhaps reflecting a stronger Walker circulation) or an enhanced salinity gradient (perhaps reflecting increased rainfall in the central tropical Pacific). LYNCH-STIEGLITZ ET AL.
Grain size analyses of the mineral component of abyssal Pacific surface sediments show two distin... more Grain size analyses of the mineral component of abyssal Pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic, respectively. In the range of 1 to 30 Ima, eolian grains show a distinct size mode at about 2 gm (9•) and little material coatset than about 16 gm (6•). Hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 gm (9•) and important amounts of material coatset than 16 gm (6•). This ability to distinguish between hemipelagic and eolian grains will obviate some longstanding concerns in the interpretation of deep-sea sediments. Examples of the utility of this technique are given for the North Pacific and South Atlantic. the southwest Atlantic shows distinctly the influence of abyssal flow on those sediments. Johnson et al. [1988] were able to characterize the strength of the Western Boundary Undercurrent during the past 90 kyr based on size analysis of the detrital silts. Dowling and McCave [1993] were able to define the late glacial and post glacial history of bottom flow along the Fermi Drift based upon the varying importance of size modes in the silt range.
Atmospheric CO 2 concentrations and climate are regulated on geological time scales by the balanc... more Atmospheric CO 2 concentrations and climate are regulated on geological time scales by the balance between carbon input and its removal by weathering feedbacks involving the erosion of silicate and organic carbon bearing rocks, which also controls the depth in the oceans at which carbonate is dissolved. Here
Deep Sea Drilling Project (DSDP) Site 215 provides an expanded section across the Paleocene/Eocen... more Deep Sea Drilling Project (DSDP) Site 215 provides an expanded section across the Paleocene/Eocene boundary, the most complete mid-latitude sequence from a Southern Hemisphere location in the Indo-Pacific area. The events of this transition occurred during a span of about 1.2 m.y. Oxygen isotope values derived from benthic foraminiferal calcite decrease by about 1.0°/oo, a decrease most likely related to warming of deep ocean waters. Turnovers of benthic foraminifera accompany <5 ls O changes and culminate in the predominant extinction event at the end of the Paleocene Epoch. Carbon isotope ratios also shift dramatically toward lighter values near the end of the Paleocene, beginning about 0.45 m.y. after oxygen isotope values start to change. The intensity of Southern Hemisphere atmospheric circulation as recorded by grain sizes of eolian particles shows a large and rapid reduction beginning another 0.45 m.y. later. A significant reduction of zonal wind strength at the Paleocene/Eocene boundary, until now observed only at Northern Hemisphere locations, appears to have been a global phenomenon related to decreased latitudinal thermal gradients occasioned by more effective poleward heat transport via the deep ocean.
• An eastern equatorial Pacific stable oxygen isotope depth profile shows a weak and deep thermoc... more • An eastern equatorial Pacific stable oxygen isotope depth profile shows a weak and deep thermocline during the Last Glacial Maximum • Regional compilation of surface to subsurface dwelling foraminifera shows the thermocline was deep throughout the Eastern Equatorial Pacific
The South Pacific is relatively unexplored and is almost devoid of digitally-acquired seismic ref... more The South Pacific is relatively unexplored and is almost devoid of digitally-acquired seismic reflection data. While surveying for an IODP cruise on R/V Melville in February-March 2005, we identified a region of zero sediment accumulation nearly two million square kilometers in area in the Southwest Pacific Basin. This South Pacific Bare Zone is bounded approximately between the Menard Fracture Zone
Core V21-146 provides a continuous record of northwest Pacific pelagic sedimentation spanning the... more Core V21-146 provides a continuous record of northwest Pacific pelagic sedimentation spanning the past 530,000 years. Downcore variations of •5•80 from benthic foraminiferal calcite were correlated to the SPECMAP record to provide an age model for late Pleistocene paleoclimatic and paleoceanographic variation. Fluxes of CaCO3 and eolian material have been determined by combining information about linear sedimentation rates, bulk densities and component percentages. The mass accumulation rate (MAR) of CaCO3 varies from 58 to 1435 mg(cm2kyr)-• and exhibits the Pacific Ocean pattern of higher accumulation associated with glacial periods for the younger portion of the record. However, the pattern of CaCO3accumulation appears to shift during the mid-Brunhes so that prior to 350,000 years ago it exhibits an opposite pattern of greater accumulation during interglacial periods. The flux of eolian dust is a proxy measure of the source area aridity and correlates well to the loesssoil stratigraphy in China. Dust fluxes range from 43 to 718 mg(cm2kyr)-1 and are greater by a factor of about 4 during glacial times. Cross-spectral analysis of the eolian flux and oxygen isotope records shows an inphase and Copyright 1991 by the American Geophysical Union. Paper number 91PA00559. 0883-8305/91/91PA-00559 $10.00 coherent relationship at each of the major orbital periodicities of 100, 41, and 19 kyr. Eolian grain sizes, generally used as a proxy record of wind intensity, range from 8.4• (2.9 !.tm) to 6.2• (13.6 gm). A change in grain size variability occurs near about 300 ka such that the older portion is characterized by lowerfrequency and higher-amplitude fluctuations than the younger portion. Power spectra for the eolian grain size record show dominant peaks at 100 and 50 kyr and a broad 25-35 kyr peak but coherency to the oxygen isotope curve at only the 100 and 33 kyr periodicities. The phase relationship for eccentricity between the eolian grain size and •5180 records suggests that at the 100 kyr frequency the smallest grain sizes are associated with glacial conditions. Hovan et al.: Northwest Pacific Sediment Record link the marine and continental records directly thereby enabling more complete global understanding of climatic variability. To do this, we have determined •80, CaCO3, eolian flux, and eolian grain size variations in V21-146, recovered from a site in the North Pacific downwind from China (Figure 1) and used the eolian flux information to tie the China loess sequence to the marine record. The initial results of this effort have been presented by Hovan et al. [1989]; here we examine the spectral characteristics of the eolian flux and grain size records as well as the record of CaCO3 accumulation in the northwestern Pacific. PROXY INDICATORS Marine Sediments Oxygen isotopic variations in calcite from benthic foraminifera tests reflect variations in continental ice volumes during the Pleistocene [Shackleton and Opdyke, 1973]. Since the oceans mix within approximately 1000-2000 years, the variations in the isotopic composition of the oceans are essentially synchronous and can be correlated globally in oceanic sediments. The SPECMAP project has defined the timing of the relative enrichments and depletions of isotopic ratios of oxygen in the oceans for the past 800,000 years, providing the basic chronostratigraphy for paleoclimatic investigations of the late Pleistocene [Imbrie et al., 1984]. The accumulation of calcium carbonate on the seafloor is controlled by two main factors, the rate of biological production near the ocean surface and the rate of dissolution in the water column and on the seafloor. in the equatorial Pacific during the late Pleistocene [Farrell and Prell, 1989]. Productivity plays a lesser, though identifiable, role [Adelsek and Anderson,
Oxygen and carbon isotopic records have been developed for the Cenozoic carbonate oozes of Sites ... more 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.
The late Cenozoic history of eolian sedimentation in the eastern Indian Ocean was developed from ... more The late Cenozoic history of eolian sedimentation in the eastern Indian Ocean was developed from samples recovered during drilling of Sites 752, 754, and 756. Temporal changes in the mass accumulation rate of eolian material reflect major climatic shifts in the southern African source region. A significant drop in dust mass flux values occurs near the end of the lower Oligocene. Younger sediments are characterized by a gradual reduction in dust accumulation rates until the middle Miocene after which values remain consistently low throughout the late Cenozoic, although a slight increase in eolian accumulation rate occurs near 2.5 Ma. This pattern of dust mass flux appears related to the supply of dust-sized particles in the source region and represents a shift in the climatic regime of southern Africa to increasingly more arid conditions throughout the late Cenozoic.
The composition and character of terrigenous sediments can be used to trace eolian and marine tra... more The composition and character of terrigenous sediments can be used to trace eolian and marine transportation processes such as winds, surface currents and deep currents. We analyzed more than 80 surface sediment samples from the pelagic realm of the Atlantic Ocean for variations in terrigenous grain size and major element geochemistry. A subset of these were also analyzed for radiogenic Nd and Sr isotopic ratios. These radioisotopic data were key in recognizing samples with distinctly different source regions and when viewed in conjunction with grain size and elemental data, broadly define several different regional transport modes. Terrigenous sediment transported to the tropical and subtropical Atlantic in deeper regions away from the continental margin is composed of a mixture of eolian and hemipelagic sediment supplied from the Sahar-Sahel regions of northern Africa. At sites closer to the continental margin a similar provenance is found but turbidites and hemipelagic processes ...
Sea surface temperature (SST) reconstructions from the Western and Eastern Equatorial Pacific (WE... more Sea surface temperature (SST) reconstructions from the Western and Eastern Equatorial Pacific (WEP and EEP) indicate the Equatorial Pacific was in a permanent El Niño-like state during the early Pliocene. Specifically, SST in the WEP was nearly the same as today, while SST in the EEP cold tongue region was 2-3 °C warmer than today. Climatic transitions recorded in the EEP are of particular interest due to the region’s sensitivity to changes in upwelling and thermocline depth, and due to its role in the global ocean heat balance. However, not much is known about the evolution of the EEP cold tongue. This study aims to reconstruct the east-west and north-south gradients within the EEP using new SST and sub-surface temperature records from ODP Sites 848, 849, and 853 and published paleoceanographic records from the EEP to examine the temporal and spatial evolution of the EEP cold tongue from the Pliocene to Recent. Mg/Ca analyses on Globigerinoides sacculifer and Globorotalia tumida an...
Studying the terrigenous component of marine sediment gathered during ODP Leg 199 (Paleogene Equa... more Studying the terrigenous component of marine sediment gathered during ODP Leg 199 (Paleogene Equatorial Transect) will help unravel the paleoceanographic evolution of the central equatorial Pacific Ocean. For example, grain size and mineralogic data from the operationally defined eolian dust (ODED) component of marine sediment in the Pacific have commonly been used to assess changes in wind intensity and continental aridity. Assuming this eolian component is representing the weathering products of the upper continental crust, geochemical studies of Th, Sc, and REE distributions (e.g., Olivarez et al., 1991; Weber et al. 1996) have suggested the presence of two endmember components in ODED: the upper continental crust itself (the eolian-transported weathering products) as well as ocean crust (primarily volcanogenic material). Expanding upon these studies, we are examining the complete geochemical composition (major, trace, and REE concentrations) of the extracted eolian component as ...
Today in the Eastern Equatorial Pacific, a shallow thermocline and rigorous wind-driven upwelling... more Today in the Eastern Equatorial Pacific, a shallow thermocline and rigorous wind-driven upwelling brings cool, nutrient-rich water to the surface. In contrast, during the warm Pliocene (~3-5 Ma), sea surface temperatures in the Eastern Equatorial Pacific were much warmer than modern. Warm sea surface temperatures in upwelling regions, which have global effects on atmospheric circulation and the heat budget, could be caused by changes in wind-driven upwelling and/or changes in thermocline depth. As changes in wind-driven upwelling cannot entirely explain warm sea surface temperatures in upwelling regions, we investigate changes in subsurface temperature to monitor thermocline depth. We measured subsurface temperature records from Eastern Equatorial Pacific ODP transect Sites 848, 849, and 853 using Mg/Ca records from Globorotalia tumida, which has a depth habitat of ~100 m. Prior to closure of the Isthmus of Panama (5.2-4.8 Ma), subsurface temperatures were ~6-8°C warmer than modern,...
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