High-resolution sedimentological and paleontological record of ODP Site 167-1019

Holocene and latest Pleistocene oceanographic conditions and the coastal climate of northern California have varied greatly, based upon high-resolution studies (ca. every 100 years) of diatoms, alkenones, pollen, CaCO3%, and total organic carbon at Ocean Drilling Program (ODP) Site 1019 (41.682°N, 124.930°W, 980 m water depth). Marine climate proxies (alkenone sea surface temperatures [SSTs] and CaCO3%) behaved remarkably like the Greenland Ice Sheet Project (GISP)-2 oxygen isotope record during the Bølling-Allerod, Younger Dryas (YD), and early part of the Holocene. During the YD, alkenone SSTs decreased by >3°C below mean Bølling-Allerod and Holocene SSTs. The early Holocene (ca. 11.6 to 8.2 ka) was a time of generally warm conditions and moderate CaCO3 content (generally >4%). The middle part of the Holocene (ca. 8.2 to 3.2 ka) was marked by alkenone SSTs that were consistently 1-2°C cooler than either the earlier or later parts of the Holocene, by greatly reduced numbers of the gyre-diatom Pseudoeunotia doliolus (<10%), and by a permanent drop in CaCO3% to <3%. Starting at ca. 5.2 ka, coastal redwood and alder began a steady rise, arguing for increasing effective moisture and the development of the north coast temperate rain forest. At ca. 3.2 ka, a permanent ca. 1°C increase in alkenone SST and a threefold increase in P. doliolus signaled a warming of fall and winter SSTs. Intensified (higher amplitude and more frequent) cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature (enhanced El Niño-Southern Oscillation [ENSO] cycles) have characterized the Site 1019 record since about 3.5 ka.

Pleistocene sedimentation in the Benguela Current, southeastern Atlantic

We infer variations in paleoproductivity and eolian input at ODP Site 1082 in the Walvis Basin from stable oxygen isotope compositions of the planktonic foraminifera Globorotalia inflata, total organic carbon mass accumulation rates (TOC MAR), and X-ray fluorescence analyses of Fe content. The most pronounced paleoclimatic changes correspond to the time at about 0.9 Ma, when glacial conditions in the northern hemisphere (NH) led to the onset of pronounced 100-kyr glacial-interglacial cycles. We used Fe intensity as a proxy for eolian terrigenous input, and TOC MAR as a paleoproductivity indicator. Paleoproductivity and eolian input show generally higher-amplitude variations of glacial-interglacial cyclicity from 1.5 to 0.58 Ma, indicating pronounced variations in upwellingfavorable winds in this area. At 0.58 Ma, paleoproductivity and eolian input shifted abruptly to lower-amplitude variations with a periodicity of 100 kyr while delta18O values show a trend toward more negative isotope values for the past 0.65 Myr. Especially during glacial periods, oxygen isotope values indicate increasingly warmer sea-surface temperatures toward the end of the Pleistocene. To evaluate the relative influences of NH glaciation and southern hemisphere (SH) insolation as potential forcing mechanisms for variations of eolian input and productivity in the northern Benguela system, we filtered our proxy records at orbital frequencies. The filtered records of Fe intensity and TOC MAR indicate a strong influence of the 100-kyr and 41-kyr frequency bands, supporting our assumption that strong ice buildup in the NH is the dominant trigger for climate changes on the continent and probably in trade-wind intensity. SH insolation and low-latitude precession-related insolation changes were important for paleoproductivity variations in the northern Benguela system, modifying the nutrient supply by southern ocean intermediate waters and the zonal direction of upwelling-inducing trades by the African monsoon system, respectively.

Siliceous components of Pliocene-Holocene sediments of the South Atlantic

The Pliocene-Holocene sediments recovered on ODP Leg 114 from Holes 699A, 701C, and 704B are the subject of a detailed investigation to interpret changes in the Oceanographic environment of the South Atlantic in the vicinity of the Polar Front Zone (PFZ). The cores sample sediments at shallow (Hole 704B, 2532 m), intermediate (Hole 699A, 3716 m), and basinal (Hole 701C, 4647 m) depths. Sites 699 and 704 come under the influence of the Antarctic Circumpolar Current (ACC) and Circumpolar Deep Water. It is possible that the upper reaches of Antarctic Bottom Water (AABW) may also affect Hole 699A. Site 701 is influenced by AABW. Closely spaced samples were analyzed for grain-size distribution, sand fraction components, biosiliceous microfossils, organic carbon, and water content. PFZ migrations are traced using changes in bulk sedimentaccumulation rates and the abundance of the diatoms Actiniscus ssp. and Genus et species indet. 1 Fenner (1991), as well as changes in sediment grain size and composition. Diatomaceous sediments of Gilbert age in Hole 699A indicate that the PFZ was positioned over this site, but during the Gauss it migrated north, bringing in less productive Antarctic Surface Water. All cores document a very gradual southerly movement of the PFZ throughout the Matuyama (with some sharp fluctuations of the northen PFZ border over Site 704 between 1.45 and 1.83 m.y.). This regressive shift culminated in the late Matuyama. The latest Matuyama to earliest Brunhes record in Hole 699A has been removed by a hiatus lasting from 1.0 to 0.6 m.y., which was probably caused by intensification of the deep-reaching ACC. The corresponding interval in Hole 704B, the shallowest core, contains evidence of winnowing. Sharp fluctuations of large amplitude and high frequency in the lithology of the sediments from Hole 704B in the eastern South Atlantic, starting at about 0.75 m.y. and characterizing the whole Brunhes Epoch, record the rapid movement of the northern border of the PFZ over the site. These reflect strong glacial/interglacial alternations in climate. To a lesser extent, lithologic fluctuations in Hole 701C reflect the same phenomenon, whereas in Hole 699A the lithology does not vary as dramatically.

Biogenic sedimentation of DSDP Site 85-574

The equatorial Pacific is an important part of the global carbon cycle and has been affected by climate change through the Cenozoic (65 Ma to present). We present a Miocene (12-24 Ma) biogenic sediment record from Deep Sea Drilling Project (DSDP) Site 574 and show that a CaCO3 minimum at 17 Ma was caused by elevated CaCO3 dissolution. When Pacific Plate motion carried Site 574 under the equator at about 16.2 Ma, there is a minor increase in biogenic deposition associated with passing under the equatorial upwelling zone. The burial rates of the primary productivity proxies biogenic silica (bio-SiO2) and biogenic barium (bio-Ba) increase, but biogenic CaCO3 decreases. The carbonate minimum is at ~17 Ma coincident with the beginning of the Miocene climate optimum; the transient lasts from 18 to 15 Ma. Bio-SiO2 and bio-Ba are positively correlated and increase as the equator was approached. Corg is poorly preserved, and is strongly affected by changing carbonate burial. Terrestrial 232Th deposition, a proxy for aeolian dust, increases only after the Site 574 equator crossing. Since surface production of bio-SiO2, bio-Ba, and CaCO3 correlate in the modern equatorial Pacific, the decreased CaCO3 burial rate during the Site 574 equator crossing is driven by elevated CaCO3 dissolution, representing elevated ocean carbon storage and elevated atmospheric CO2. The length of the 17 Ma CaCO3 dissolution transient requires interaction with a 'slow' part of the carbon cycle, perhaps elevated mantle degassing associated with the early stages of Columbia River Basalt emplacement.

Lipid biomarkers in urface sediments of the Southeast Atlantic

Surface sediments from the eastern South Atlantic were investigated for their lipid biomarker contents and bulk organic geochemical characteristics to identify sources, transport pathways and preservation processes of organic components. The sediments cover a wide range of depositional settings with large differences in mass accumulation rates. The highest marine organic carbon (OC) contributions are detected along the coast, especially underlying the Benguela upwelling system. Terrigenous OC contributions are highest in the Congo deep-sea fan. Lipid biomarker fluxes are significantly correlated to the extent of oxygen exposure in the sediment. Normalization to total organic carbon (TOC) contents enabled the characterization of regional lipid biomarker production and transport mechanisms. Principal component analyses revealed five distinct groups of characteristic molecular and bulk organic geochemical parameters. Combined with information on lipid sources, the main controlling mechanisms of the spatial lipid distributions in the surface sediments are defined, indicating marine productivity related to river-induced mixing and oceanic upwelling, wind-driven deep upwelling, river-supply of terrigenous organic material, shallow coastal upwelling and eolian supply of plant-waxes.

Supplementary material: XRF core scanning data, CaCO3 values, foraminiferal carbon and oxygen isotope data, Mg/Ca data, clay mineralogy and helium isotope results

The Paleocene-Eocene Thermal Maximum (PETM; ~56 Ma) is associated with abrupt climate change, carbon cycle perturbation, ocean acidification, as well as biogeographic shifts in marine and terrestrial biota that were largely reversed as the climatic transient waned. We report a clear exception to the behavior of the PETM as a reversing climatic transient in the eastern North Atlantic (Deep-Sea Drilling Project Site 401, Bay of Biscay) where the PETM initiates a greatly prolonged environmental change compared to other places on Earth where records exist. The observed environmental perturbation extended well past the d13C recovery phase and up to 650 kyr after the PETM onset according to our extraterrestrial 3He-based age-model. We observe a strong decoupling of planktic foraminiferal d18O and Mg/Ca values during the PETM d13C recovery phase, which in combination with results from helium isotopes and clay mineralogy, suggests that the PETM triggered a hydrologic change in western Europe that increased freshwater flux and the delivery of weathering products to the eastern North Atlantic. This state change persisted long after the carbon-cycle perturbation had stopped. We hypothesize that either long-lived continental drainage patterns were altered by enhanced hydrological cycling induced by the PETM, or alternatively that the climate system in the hinterland area of Site 401 was forced into a new climate state that was not easily reversed in the aftermath of the PETM.

Magnetic susceptibility of deep-sea cores from the Scotia Sea

We studied two deep-sea cores from the Scotia Sea to reconstruct past atmospheric circulation in the southern hemisphere and to resolve a long-standing debate on the interpretation of magnetic susceptibility (MS) records in Southern Ocean (SO) sediment. High-sedimentation sites MD07-3134 (0.2 - 1.2 m/kyr) and MD07-3133 (0.3 - 2 m/kyr) cover the last 92.5 kyr and 36 kyr, respectively. Both exhibit a one-to-one coupling of the MS and Ca2+ signal to the non-sea salt (nss) Ca2+ signal of the EDML ice core, clearly identifying atmospheric circulation as means of distribution. Comparison of additional proxies also excludes major influence by volcanic sources, sea-ice, icebergs, or oceanic current transport. The close resemblance of the dust proxies over the last glacial cycle, in turn, allows for the establishment of an age model of unprecedented resolution and precision for SO deep-sea sediment because atmospheric transport involves no major leads or lags. This is of particular importance because MS is routinely measured on deep-sea cores in the SO but the sediments usually lack biogenic carbonate and therefore had only limited stratigraphic control so far. Southern South America (SSA) is the likely source of eolian material because Site MD07-3133, located closer to the continent, has slightly higher MS values than Site MD07-3134, and also the MS record of Patagonian Site SALSA shows comparable variability. Patagonia was the dust source for both the Scotia Sea and East Antarctica. Dust fluxes were several times higher during glacial times, when atmospheric circulation was either stronger or shifted in latitude, sea level was lowered, shelf surfaces were exposed, and environmental conditions in SSA were dominated by glaciers and extended outwash plains. Hence, MS records of SO deep-sea sediment are reliable tracers of atmospheric circulation, allowing for chronologically-constrained reconstructions of the circum Antarctic paleoclimate history.

Organic sedimentation of ODP Sites 124-767 and 124-768

This study relates the organic sedimentation characteristics to the lithostratigraphic successionsthat were observed at Site 767 (Celebes Sea) and Site 768 (Sulu Sea) during ODP Leg 124. It is based on the total organic carbon content (TOC) of the sediments, on the petrographictype and maturity of the organic matter, and on the TOC accumulation rates calculated for the lithostratigraphic units. In the Celebes and Sulu Seas sediments, the organic matter is mainly of terrestrial origin with the highest concentrations and TOC accumulation rates occurring in the middle Miocene turbiditic sequences that correspond to a major compressive event between the Philippine Mobile Belt and the Palawan, Cagayan, and Sulu Ridges. Petrographic analysis of the Eocene and lower Miocene organic matter in the Celebes Sea shows that it consists only of highly degraded terrestrial particles. This observation and the very low TOC accumulation rates indicate poor conditions for organic carbon preservation during this open-ocean phase of the Celebes Basin formation. The organic matter, either of marine or terrestrial origin, is much better preserved in the younger sediments, suggesting physico-chemical changes in the depositional environment. Because of the dilution phenomena by turbidites, it is difficult to observe the progressive improvement of the organic matter preservation throughout the turbiditic series. The same change in preservation is broadly observed in the Sulu Sea from the early Miocene (rapid opening phase of the basin with massive pyroclastic deposits) to the present.

Concentration of the rare-earth elements in metalliferous sediments from DSDP Leg 92 holes

DSDP Leg 92 drilled at four sites along an east-west transect at 19°S on the western flank of the East Pacific Rise (EPR), in an area where sediments are essentially a mixture of hydrothermal and biogenic components, with only a minimal contribution of clastic material. Rare-earth element (REE) data on the metalliferous (non-carbonate) fraction of samples ranging in age from ~2 to ~27 Ma indicate the existence of two distinct groups of patterns corresponding to two broad age groups, one <=8 Ma, the other >=10 Ma. Within each group, REE patterns have characteristics which are near-uniform, despite large variations in total REE abundances. Sediments of the younger group are enriched in light REE (LREE) relative to deep bottom waters influenced by the hydrothermal plume extending west from the EPR at 19°S. Sediments of the older groups show further relative LREE enrichment and/or heavy REE (HREE) depletion. Surficial sediments deposited beneath the lysocline have high Sum REE concentrations resulting from slow accumulation rates, and patterns resembling older sediments due to early diagenetic effects. A correlation between the mass accumulation rates (MAR) of Sum REE and Fe + Mn suggests that ferromanganese particulate matter supplied by the hydrothermal plume scavenges REE; during this process the LREE are preferentially removed from plume seawater. The MAR of Fe + Mn shows a general decrease with age above basement, whereas Sum REE concentrations in the metalliferous component increase with age above basement. This supports the Ruhlin and Owen model wherein limited scavenging of REE, due to rapid burial of sediment near the palaeo-axis, leads to low concentrations (but high MAR-values) for the REE. Following deposition and burial of the hydrothermal component, further relative flattening of the REE pattern takes place, probably the result of diagenetic reactions over several million years. Phase partitioning data indicate that the proportion of REE residing in more poorly crystalline phases tends to increase with age (from ~45% to 90% of Sum REE). This suggests that as initial ferromanganese precipitates undergo diagenetic recrystallization, REE are transferred to the poorly crystalline phases, and/or are scavenged from pore waters by these phases. Because of the various modifications to REE patterns apparently produced both in the water column and post-depositional settings, the REE patterns of metalliferous sediments will not reflect fine-scale REE variations in associated oceanic water masses.

Late Miocene to Pleistocene paleoceanographic records from the Feni and Gardar Drifts: Pliocene reduction in abyssal flow

Magnetic fabric analyses from two North Atlantic drift deposits provide proxies for determining relative variations in the strength of abyssal flow over the last 10 my. The data show a cessation of current-controlled sedimentation at the shallower Feni Drift (2417 m) at the time of onset of Northern Hemisphere glaciation (2.6 Ma). Drift formation ended nearly 2 my earlier (4.2 Ma) at the deeper Gardar Drift (3220 m), implying stepwise reduction in deep-water flow. Relatively light delta18O values at the deeper Gardar Drift indicate a warmer, thus also more salty, water mass site prior to 6 Ma. We interpret this as representing Mediterranean Sea water, which flowed north at depths greater than that of the Feni Drift Site. The supply of Mediterranean Water to the North Atlantic was shut off as the Gibraltar Straits closed, causing the Messinian salinity crisis, and never returned to that position in the water column after the Mediterranean opened again.

Stable isotope and geochemical record of ODP Hole 124-769A

Deep marine late Pleistocene sediments from Ocean Drilling Program Sulu Sea Site 769 contain a high-resolution record of paleoceanographic change in this strongly monsoonal climatic setting in the tropical western Pacific. Detailed time series of planktonic foraminifer (G.ruber; white variety) d18O, d13C, and bulk CaCO3 mass accumulation rate (MAR) were generated, spanning the last 750 k.y. Sedimentation rates in this portion of the record average 8.5 cm/k.y., and vary from 4 to 16 cm/k.y. Cross spectral analysis of the d18O and d13C time-series demonstrate that each contains increased variance at the primary orbital periodicities. The d18O record shows strong variability in the precessional-band and closely correlates with the SPECMAP d18O record and other high-resolution records. The dominance of a 23-k.y cycle in the d18O record agrees with other studies of the monsoon system in the Indian Ocean that have documented the importance of precessional insolation as a monsoon-forcing mechanism. In addition, d13C is strongly coherent, with d18O at a period of 41 k.y (obliquity), suggesting a connection between surface water CO2 chemistry in the Sulu Sea and high- latitude climatic change. The d18O and d13C time-series both contain increased spectral variance at a period of 30 k.y. Although the source of 30-k.y. variability is unknown, other studies have documented late Pleistocene Pacific Oceanographic variability with a period of 30 k.y. Major- and trace-metal analyses were performed on a second, less-detailed sample series to independently assess paleoproductivity changes and bottom-water conditions through time. Glacial periods are generally times of increased calcium carbonate and copper accumulation. The positive association between these independent indicators of paleoproductivity suggests an increase in productivity in the basin during most glacial episodes. Changing bottom-water redox conditions were also assessed using the geochemical data. Low concentrations of molybdenum throughout the record demonstrate that bottom waters at this site were never anoxic during the last 750 k.y. The bioturbated character of the sediments agrees with this interpretation.

Eolian deposition on the Ontong Java Plateau

The record of eolian deposition on the Ontong Java Plateau (OJP) since the Oligocene (approximately 33 Ma) has been investigated using dust grain size, dust flux, and dust mineralogy, with the goal of interpreting the paleoclimatology and paleometeorology of the western equatorial Pacific. Studies of modern dust dispersal in the Pacific have indicated that the equatorial regions receive contributions from both the Northern Hemisphere westerly winds and the equatorial easterlies; limited meteorological data suggest that low-altitude westerlies could also transport dust to OJP from proximal sources in the western Pacific. Previous studies have established the characteristics of the grain-size, flux, and mineralogy records of dust deposited in the North Pacific by the mid-latitude westerlies and in the eastern equatorial Pacific by the low-latitude easterlies since the Oligocene. By comparing the OJP records with the well-defined records of the mid-latitude westerlies and the low-latitude easterlies, the importance of multiple sources of dust to OJP can be recognized. OJP dust is composed of quartz, illite, kaolinite/chlorite, plagioclase feldspar, smectite, and heulandite. Mineral abundance profiles and principal components analysis (PCA) of the mineral abundance data have been used to identify assemblages of minerals that covary through all or part of the OJP record. Abundances of quartz, illite, and kaolinite/chlorite covary throughout the interval studied, defining a mineralogical assemblage supplied from Asia. Some plagioclase and smectite were also supplied as part of this assemblage during the late Miocene and Pliocene/Pleistocene, but other source areas have supplied significant amounts of plagioclase, smectite, and heulandite to OJP since the Oligocene. OJP dust is generally coarser than dust deposited by the Northern Hemisphere westerlies or the equatorial easterlies, and it accumulates more rapidly by 1-2 orders of magnitude. These relationships indicate the importance of the local sources on dust deposition at OJP. The grain-size and flux records of OJP dust do not exhibit most of the events observed in the corresponding records of the Northern Hemisphere westerlies or the equatorial easterlies, because these features are masked by the mixing of dust from several sources at OJP. The abundance record of the Asian dust assemblage at OJP, however, does contain most of the features characteristic of dust flux by means of the Northern Hemisphere westerlies, indicating that the paleoclimatic and paleometeorologic signal of a particular source area and wind system can be preserved in areas well beyond the region dominated by that source and those winds. Identifying such a signal requires "unmixing" the various dust assemblages, which can be accomplished by combining grain-size, flux, and mineralogic data.