Geochemistry and sedimentation rates of ODP Leg 199 sites and of surface sediments in the eastern Pacific ocean

We present the first high-resolution organic carbon mass accumulation rate (MAR) data set for the Eocene equatorial Pacific upwelling region, from Sites 1218 and 1219 of the Ocean Drilling Program. A maximum Corg MAR anomaly appears at 41 Ma and corresponds to a high carbonate accumulation event (CAE). Independent evidence suggests that this event (CAE-3) was a time of rapid cooling. Throughout the Eocene, organic carbon burial fluxes were an order of magnitude lower than fluxes recorded for the Holocene. In contrast, the expected organic carbon flux, calculated from the biogenic barium concentrations for these sites, is roughly equal to modern. A sedimentation anomaly appears at 41 Ma, when both the measured and the expected organic carbon MAR increases by a factor of two-three relative to the background Eocene fluxes. The rain of estimated Corg and barium from the euphotic zone to the sediments increased by factors of three and six, respectively. We suggest that the discrepancy between the expected and measured Corg in the sediments is a direct consequence of the increased metabolic rates of all organisms throughout the Eocene oceans and sediments. This hypothesis is supported by recent work in ecology and biochemical kinetics that recognizes the fundamental basis of ecology as following from the laws of thermodynamics. This dependence is now elucidated as the Universal Temperature Dependence (UTD) "law" of metabolism and can be applied to all organisms over their biologically relevant temperature range. The general pattern of organic carbon and barium deposition throughout the Eocene is consistent with the UTD theory. In particular, the anomaly at 41 Ma (CAE-3) is associated with rapid cooling, an event that triggered slower metabolic rates for all organisms, slower recycling of organic carbon in the water and sediment column, and, consequently, higher deposition of organic carbon in the sediments. This "metabolism-based" scenario is consistent with the sedimentation patterns we observe for both Sites 1218 and 1219.

Sea surface productivity and temperature detected by coccolith accumulation rates from the southeastern Pacific off Chile

Recent coccoliths from 74 surface sediment samples recovered from the southeastern Pacific off Chile were examined quantitatively to investigate modern regional gradients of sea surface productivity and temperature. All findings are based on coccolith accumulation rates. Therefore an approach was designed to estimate recent sedimentation rates based on 210Pb and bulk chemistry analyses of the same set of surface samples. Highest total coccolith accumulation rates were found off north-central Chile, where seasonal upwelling takes place. Based on amultiple linear regression between calculated coccolith accumulation rates andWorld Ocean Atlas derived sea surface temperatures, a calibrationmodel to reconstruct annual average temperatures of the uppermost 75 mof thewater column is provided. Themodelwas cross-validated and the SST estimateswere compared with SST observed and SST estimates based on diatoms and planktonic foraminifera, showing a good correlation.

Physical and chemical properties, 14C ages and palynology of sediment cores from the Western Baltic Sea

Sea level related radiocarbon, palynological and stratigraphical data from sediment cores in the Western Baltic have been tested against the existing sea level curves for the region. The relative sea level rise curves for the beginning of the Holocene show no significant deviations between the Kiel, Mecklenburg und Lübeck Bays and hence do not support the previously reported differences in the averaged regional subsidence rates for this time interval. Local subsidence and upheaval due to salt tectonics probably played a greater role than previously suspected in the region. The sea level possibly stagnated around -28 m during the early Holocene before rising very rapidly to -14 m. The submarine terraces at -30 m and perhaps also at -27 m were formed during the lacustrine phase of the Western Baltic when the water levels were controlled by the main thresholds in the Great Belt.

Extraterrestrial 3He estimation across the Paleocene-Eocene thermal maximum at ODP Site 208-1266

In the deep-sea, the Paleocene-Eocene Thermal Maximum (PETM) is often marked by clay-rich condensed intervals caused by dissolution of carbonate sediments, capped by a carbonate-rich interval. Constraining the duration of both the dissolution and subsequent cap-carbonate intervals is essential to computing marine carbon fluxes and thus testing hypotheses for the origin of this event. To this end, we provide new high-resolution helium isotope records spanning the Paleocene-Eocene boundary at ODP Site 1266 in the South Atlantic. The extraterrestrial 3He, 3HeET, concentrations replicate trends observed at ODP Site 690 by Farley and Eltgroth (2003, doi:10.1016/S0012-821X(03)00017-7). By assuming a constant flux of 3HeET we constrain relative changes in accumulation rates of sediment across the PETM and construct a new age model for the event. In this new chronology the zero carbonate layer represents 35 kyr, some of which reflects clay produced by dissolution of Paleocene (pre-PETM) sediments. Above this layer, carbonate concentrations increase for ~165 kyr and remain higher than in the latest Paleocene until 234 +48/-34 kyr above the base of the clay. The new chronology indicates that minimum d13C values persisted for a maximum of 134 +27/-19 kyr and the inflection point previously chosen to designate the end of the CIE recovery occurs at 217 +44/-31 kyr. This allocation of time differs from that of the cycle-based age model of Röhl et al. (2007, doi:10.1029/2007GC001784) in that it assigns more time to the clay layer followed by a more gradual recovery of carbonate-rich sedimentation. The new model also suggests a longer sustained d13C excursion followed by a more rapid recovery to pre-PETM d13C values. These differences have important implications for constraining the source(s) of carbon and mechanisms for its subsequent sequestration, favoring models that include a sustained release

Age models, iron intensity, magnetic susceptibility records and dry bulk density of sediment cores from around the Canary Islands

A set of 43 sediment cores from around the Canary Islands is used to characterise this region, which intersects meridional climatic regimes and zonal productivity gradients in a high spatial resolution. Using rapid and nondestructive core logging techniques we carried out Fe intensity and magnetic susceptibility (MS) measurements and created a stack on the basis of five stratigraphic reference cores, for which a stratigraphic age model was available from d18O and 14C analyses on planktonic foraminifera. By correlation of the stack with the Fe and MS records of the other cores, we were able to develop age depth models at all investigated sites of the region. We present the bulk sediment accumulation rates (AR) of the Canary Islands region as an indicator of shifts in the upwelling-influenced areas for the Holocene (0-12 ky), the deglaciation (12-18 ky) and the last glacial (18-40 ky). General observations are an enhanced productivity during glacial times with highest values during the deglaciation. The main differences between the analysed time intervals we interpret as result of the sea-level effects, changes in the extent of high productivity areas, and current intensity.

Calcium carbonate in sediments at DSDP Leg 92

The carbonate contents of sediments recovered at Leg 92 Sites 597, 598, and 601 were determined at 5-cm intervals. The long-term record of carbonate variation at Sites 597 and 598 shows the effect of decreasing dilution by hydrothermal phases as the sites moved away from the ridge crest at which they formed. Superimposed on this trend are high-amplitude variations in carbonate content. In the lower portions of Sites 597 and 598 the high-amplitude variations have a duration of a few hundred thousand years. The upper portion of the sediment column at both sites was deposited below the lysocline, and high-amplitude variations in this interval represent 1 to 2 m.y. The data suggest that only very intense carbonate dissolution events can be identified reliably at sites with low accumulation rates. At sites like Site 598, where the sedimentation rate is higher, the details of carbonate variation can be correlated with the carbonate lithostratigraphies developed for sites in the equatorial and North Pacific oceans.

Benthic oxygen isotope and dust flux record from ODP Site 108-659 in the North Atlantic

High-resolution benthic oxygen isotope and dust flux records from Ocean Drilling Program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the Atlantic from 2.85 Ma back to 5 Ma. Spectral analysis of the delta18O record indicates that the 41-kyr period of Earth's orbital obliquity dominates the Pliocene record. This is shown to be true regardless of fundamental changes in the Earth's climate during the Pliocene. However, the cycles of Sahelian aridity fluctuations indicate a shift in spectral character near 3 Ma. From the early Pliocene to 3 Ma, the periodicities were dominantly precessional (19 and 23 kyr) and remained strong until 1.5 Ma. Subsequent to 3 Ma, the variance at the obliquity period (41 kyr) increased. The timescale tuned to precession suggests that the Pliocene was longer than previously estimated by more than 0.5 m.y. The tuned ages for the magnetic boundaries Gauss/Gilbert and Top Cochiti are about 6-8% older than the ages of the conventional timescale. A major phase of Pliocene northern hemisphere ice growth occurred between 3.15 Ma and 2.5 Ma. This was marked by a gradual increase in glacial Atlantic delta18O values of 1per mil and an increase in amplitude variations by up to 1.5 per mil, much larger than in the Pacific deepwater record (site 846). The first maxima occured in cold stages G6-96 between 2.7 Ma and 2.45 Ma. Prior to 3 Ma, the isotope record is characterized by predominantly low amplitude fluctuations (< 0.7 per mil). When obliquity forcing was at its minimum between 4.15 and 3.6 Ma and during the Kaena interval, delta18O amplitude fluctuations were minimal. From 4.9 to 4.3 Ma, the delta18O values decreased by about 0.5 per mil, reaching a long-term minimum at 4.15 Ma, suggesting higher deepwater temperatures or a deglaciation. Deepwater cooling and/or an increase in ice volume is indicated by a series of short-term delta18O fluctuations between 3.8 and 3.6 Ma.

Geochemistry of sediment core PS2456-4

Sediment core PS2458 from the Laptev Sea continental margin (983-m water depth) stems from a position close to the paleoriver mouth of Lena and Yana rivers. It was dated by AMS-14C and analyzed in high resolution for oxygen isotopes of planktic foraminifers. Except the uppermost 100 cm and possibly the lowermost meter of the 8-m-long core, the sediments were deposited during the last deglaciation (14.5-8.0 cal-ka). According to 210Pb data, the uppermost 100 cm represents only the last 200 years. Planktic foraminifers are present throughout the dated deglacial interval, with the exception of a short time after ca. 13 cal-ka. Taking into account the global "ice volume effect" on the oxygen isotopic composition of the foraminifers, the isotopic record is considered to reflect salinity changes which were influenced by variable freshwater runoff and a growing marine influence during the postglacial transgression of the Laptev Sea shelf. The most conspicuous feature in the isotopic record is an outstanding peak dated to ca. 13 cal-ka. It is proposed that it represents a rapid outburst of large amounts of freshwater, possibly from an ice-dammed lake in the hinterland. Possible correlations to the onset of the cool Younger Dryas event in the northern hemisphere are discussed.

Geochemistry of Neogene sediments of ODP Hole 115-711A

Pelagic sedimentation in the northwest Indian Ocean has been studied using sediments from Hole 711A (the section from 0 to 70.5 mbsf, 0-22 Ma), a deep site (4428 m) drilled during Ocean Drilling Program Leg 115. The clay fraction of the sediments represents poorly developed pelagic deposits with considerably lower contents of Mn, Ba, Cu, Ni, Cr, and Zn than is typical for well-oxidized pelagic sediments formed far from the continents (e.g., in the central Indian or Pacific oceans). Geochemical provenance models, representing conservative mixing models with terrigenous, exhalative-volcanic, and biogenous matter as the only inputs, explain most of the compositional variations in the sediments. The models show that terrigenous matter accounts for about 96%-100% of all SiO2, Al2O3, TiO2, and Zr; about 73%-85% of all Fe2O3, V, and Ni; and about 40%-60% of the Cu and Zn abundances. Exhalative-volcanic matter delivers a large fra tion of Mn (78%-85%), some Fe (15%-219/o), and possibly some Cu (38%-51%). Biogenous deposition is generally of restricted significance; at most 6%-35% of all Cu and Zn may derive from biogenic matter. The exhalative-volcanic matter is slightly more abundant in the oldest deposits, reflecting a plate tectonic drift away from the volcanic Carlsberg Ridge. The Al/Ti ratio reveals that silicic crustal matter plays a somewhat larger role in the upper and lower part of the section studied, whereas the basaltic input is slightly higher in the intermediate levels (age 5-15 m.y.). The sediment abundances of Ba generally exceed those predicted by the models, an anomalous behavior also observed in equatorial Pacific sediments. This is possibly caused by poor knowledge of the input components. Several changes in accumulation rates seem to correlate with climatic changes (onset of monsoon-driven upwellings and sea-level regressions of about 50-100 m at 10, 15-16, and 20-21 Ma). A number of constituents show higher accumulation rates at or shortly after these regressions, suggesting an accelerated removal of fines from shallow oceanic areas. Furthermore, the SiO2/Al2O3 ratio shows a small increase in sediments younger than 10 Ma, implying an increase in biological productivity, particularly after the onset of monsoon-driven upwelling in the northwest Indian Ocean. This trend is paralleled by a general increase in the accumulation rates of Ba and CaCO3. However, these accumulation rates are generally significantly lower than under the biological high-productivity zone in the equatorial Pacific. The onset of these upwelling systems about 10 Ma is probably related to the closing of the gap between India and the main Asiatic continent, preventing free circulation around the Indian subcontinent.

Organic carbon and biomarker record from the Laptev Sea continental margin

In order to understand the processes controlling organic carbon deposition (i.e., primary productivity vs. terrigenous supply) and their paleoceanographic significance, three sediment cores (PS2471, PS2474. and PS2476) from the Laptev Sea continental margin were investigated for their content and composition of organic carbon. The characterization of organic matter indudes the determination of buk parameters (hydrogen index values and C/N ratios) and the analysis of specific biomarkers (n-alaknes, fatty acids, alkenones, and pigments). Total organic carbon (TOC) values vary between 0.3 and 2%. In general, the organic matter from the Laptev Sea continental margin is dominated by terrigenous matter throughout. However. significant amounts of marine organic carbon occur. The turbidites, according to a still preliminary stratigraphy probably deposited during glacial Oxygen Isotope Stages 2 and 4, are characterized by maximum amounts of organic carbon of terrigenous origin. Marine organic carbon appears to show enhanced relative abundances in the Termination I (?) and early Holocene time intervals, as indicated by maximum amounts of short chain n-alkanes, short-chain fatty acids, and alkenones. The increased amounts of faity acids, however, may also have a freshwater origin due to increased river discharge at that time. The occurrence of alkenones is suggested to indicate an intensification of Atlantic water inflow along the Eurasian continental margin starting at that time. Oxygen Isotope Stage l accumutation rates of total organic carhon are 0.3, 0.17, and 0.02 C/cm**2/ky in cores PS2476, PS2474, and PS2471, respectively.

Sedimentology, geochemistry and paleomagnetic of ODP Hole 151-913B

The Eocene and Oligocene epochs (55 to 23 million years ago) comprise a critical phase in Earth history. An array of geological records (Zachos et al., 2001, doi:10.1126/science.1059412; Lear et al., 2000, doi:10.1126/science.287.5451.269; Coxall et al., 2005, doi:10.1038/nature03135; Pekar et al., 2005; doi:10.1130/B25486.1; Strand et al., 2003, doi:10.1016/S0031-0182(03)00396-1) supported by climate modelling (DeConto and Pollard, 2003, doi:10.1038/nature01290) indicates a profound shift in global climate during this interval, from a state that was largely free of polar ice caps to one in which ice sheets on Antarctica approached their modern size. However, the early glaciation history of the Northern Hemisphere is a subject of controversy (Coxall et al., 2005, doi:10.1038/nature03135; Tripati et al., 2005, doi:10.1038/nature03874; Wolf-Welling et al., 1996, doi:10.2973/odp.proc.sr.151.139.1996; Moran et al., 2006, doi:10.1038/nature04800). Here we report stratigraphically extensive ice-rafted debris, including macroscopic dropstones, in late Eocene to early Oligocene sediments from the Norwegian-Greenland Sea that were deposited between about 38 and 30 million years ago. Our data indicate sediment rafting by glacial ice, rather than sea ice, and point to East Greenland as the likely source. Records of this type from one site alone cannot be used to determine the extent of ice involved. However, our data suggest the existence of (at least) isolated glaciers on Greenland about 20 million years earlier than previously documented (Winkler et al., 2002, doi:10.1007/s005310100199), at a time when temperatures and atmospheric carbon dioxide concentrations were substantially higher.

Geochemistry of sediments from the upwelling off Morocco

The high-productive upwelling area off Morocco is part of one of the four major trade-wind driven continental margin upwelling zones in the world oceans. While coastal upwelling occurs mostly on the shelf, biogenic particles derived from upwelling are deposited mostly at the upper continental slope. Nutrient-rich coastal water is transported within the Cape Ghir filament region at 30°N up to several hundreds of kilometers offshore. Both upwelling intensity and filament activity are dependent on the strength of the summer Trades. This study is aimed to reconstruct changes in trade wind intensity over the last 250,000 years by the analysis of the productivity signal contained in the sedimentary biogenic particles of the continental slope and beneath the Cape Ghir filament. Detailed geochemical and geophysical analyses (TOC, carbonate, C/N, delta13Corg, delta15N, delta13C of benthic foraminifera, delta18O of benthic and planktic foraminifera, magnetic susceptibility) have been carried out at two sites on the upper continental slope and one site located further offshore influenced by the Cape Ghir filament. A second offshore site south of the filament was analyzed (TOC, magnetic susceptibility) to distinguish the productivity signal related to the filament signal from the general offshore variability. Higher productivity during glacial times was observed at all four sites. However, the variability of productivity during glacial times was remarkably different at the filament-influenced site compared to the upwelling-influenced continental slope sites. In addition to climate-related changes in upwelling intensity, zonal shifts of the upwelling area due to sea-level changes have impacted the sedimentary productivity record, especially at the continental slope sites. By comparison with other proxies related to the strength and direction of the prevailing winds (Si/Al ratio as grain-size indicator, pollen) the productivity record at the filament-influenced site reflects mainly changes in trade-wind intensity. Our reconstruction reveals that especially during glacial times trade-wind intensity was increased and showed a strong variability with frequencies related to precession.

Palynology of ODP Leg 127 sites

This initial survey of pollen from 192 samples from Hole 794A, supplemented by 189 samples from Hole 795 and 797B, suggests that marine pollen assemblages from the southwestern Sea of Japan provide a consistent Neogene pollen stratigraphy and a solid basis for regional paleoenvironmental reconstructions. Late Miocene vegetation inferred from these pollen data, a mix of conifer and broad-leaf elements with now-extinct Tertiary types well represented, appears similar to Aniai-type floras of Japan. During the late Miocene through early Pliocene, as Tertiary types declined, conifers (including the Sequoia/Cryptomeria group) became more prominent than broad-leaf elements, and herbs played an increasing role in the vegetation. Middle Pliocene pollen assemblages imply significant changes in forest composition. In a 500,000-yr interval centered at ~4 m.y., Tertiary and warm-temperate deciduous types re-expanded and were comparable to or greater than middle-late Miocene levels. Temperate and cold-temperate conifers {Picea, Abies, Tsuga) were minimal. Subsequently, Tertiary and deciduous forest components (including Quercus) decreased, Picea, Tsuga, and Abies were again prominent, and herbs formed an increasingly larger part of the vegetation. Between ~3 m.y. and -2.5 m.y., conifers, except for Cryptomeria types, were prominent, Quercus continued to decline, and other broad-leaf trees were minor. Over the last 2 Ma, the very large and frequent changes in forest composition inferred from pollen in the Sea of Japan correspond to forest dynamics inferred from changes in pollen and floral assemblages throughout Japan. Given present vegetation/climate relationships, broad trends in Neogene climate inferred from these preliminary pollen data include decreasing temperatures, increasing seasonality in temperatures and precipitation, and increasing amplitude and frequency of climatic change. Two significant events, centered at ~9 m.y. and ~4 m.y., punctuate the gradual deterioration of the equable warm, humid subtropical/warm temperate late Miocene and early Pliocene climates. The first indication of cold-temperate conditions comparable to those of Pleistocene glacial intervals occurs ~3 m.y. Subsequently, regional climates oscillated rapidly between temperate and cold-temperate regimes that supported conifer and mixed broad-leaf forests; however, climatic extremes were apparently never great enough to displace warm-temperate and temperate forests from Honshu nor to produce arctic climates on the west coast of Japan.

CaCO3 deposits in the eastern tropical Pacific

We constructed biogenic mass accumulation rate (MAR) time series for eastern Pacific core transects across the equator at ~105° and ~85°W and along the equator from 80° to 140°W. We used empirical orthogonal function (EOF) analysis to extract spatially coherent patterns of CaCO3 deposition for the last 150 kyr. EOF mode 1 (51% variance) is a CaCO3 MAR spike centered in marine oxygen isotope stage 2 (MIS 2) found under the South Equatorial Current. EOF mode 2 (19% of variance) is high north of the equator. EOF mode 3 (9% of variance) is an east-west mode centered along the North Equatorial Counter Current. The MIS 2 CaCO3 spike is the largest event in the eastern Pacific for the last 150 kyr: CaCO3 MARs are 2-3 times higher at 18 ka than elsewhere in the record, including MIS 6. It is caused by high CaCO3 production rather than minimal dissolution. EOF 2, while it resembles deep water flow patterns, nevertheless, shows coherence to Corg deposition and is probably also driven by CaCO3 production.