Lithium sources in pore fluids of Peru slope

High Li concentrations, up to a maximum of 1155 µM are observed in the pore fluids of the Peru convergent margin slope sediments. At Ocean Drilling Program Sites 683 and 685 (ca. 9°S), the Li concentration depth gradients are twice as steep as at Site 682 and 688 (ca. 11°S). Within the sediments, the most important Li sources are from aluminosilicate minerals. Biogenic opal-A contains little Li and thus dilutes the Li concentration of the bulk sediments. The sediment compositions and the thermal regimes are similar at 9° and 11°S, suggesting there is an additional, non-sedimentary source for the observed high Li concentrations in the northern pore fluids. At 9°S, the 87Sr/86Sr ratios reach a maximum value of 0.709958. The observed radiogenic 87Sr/86Sr values in the pore fluids support the suggestion that the additional Li may derive from exchange reactions with underlying continental crust. The high concentrations of Li at 11°S may derive from basalt alteration at moderate to high temperatures, as suggested by the non-radiogenic 87Sr/86Sr ratios in these pore fluids, which reach a minimum value of 0.707218. Based on (1) Li concentrations in the pore fluids in slope sediments from Peru and several other margins, and (2) an approximate estimate of fluid flux from continental margins into the ocean, continental margins provide an estimated 1 to 3 * 10**10 moles Li/yr to the ocean. This source of oceanic Li, which has not been considered previously, is of the same order of magnitude as some estimates of hydrothermal and river Li fluxes and may have important consequences for the oceanic Li isotope budget. The sink is unknown for this newly discovered and possibly large Li source, but it may be more pervasive low-temperature alteration of oceanic basement than previously estimated, or burial of mineral phases, such as authigenic clay minerals, or metal oxyhydroxides which may be Li-rich.

Geochemistry of ODP Leg 125 peridotites

Ocean Drilling Program Leg 125 recovered serpentined harzburgites and dunites from a total of jive sites on the crests and flanks of two serpen finite seamounts, Conical Seamount in the Mariana forearc and Torishima Forearc Seamount in the Izu-Bonin forearc. These are some of the first extant forearc peridotites reported in the literature and they provide a window into oceanic, supra-subduction zone (SSZ) mantle processes. Harzbutrgites from both seamounts are very refractory with low modal clinopyroxene (<4%), chrome-rich spinels (cx-number = 0.40-0.80), very low incompatible element contents, and (with the exception of amphibole-bearing samples) U-shaped rare earth element (REE) profiles with positive Eu anomalies. Both sets of peridotites have olivine-spinel equilibration temperatures that are low compared with abyssal peridotites, possibly because of water-assisted diffusional equilibration in the SSZ environment However, other features indicate that the harzburgites from the two seamounts have very different origins. Harzburgites from Conical Seamount are characterized by calculated oxygen fugacities between FMQ (fayalite- magnetite- quartz) - 1.1 (log units) and FMQ + 0.4 which overlap those of mid-ocean ridge basalt (MORB) peridotites. Dunites from Conical Seamotmt contain small amounts of clinopyroxene, orthopyroxene and amphibole and are light REE (LREE) enriched. Moreover; they are considerably more oxidized than the harzburgites to which they are spatially related, with calculated oxygen fugacities of FMQ -0.2 toFMQ + 1.2. Using textural and geochemical evidence, we interpret these harzburgites as residual MORB mantle (from 15 to 20 % fractional melting) which has subsequently been modified by interaction with boninitic melt ivithin the mantle wedge, and these dunites as zones of focusing of this melt in which pyroxene has preferentially been dissolved from the harzbutgite protolith. In contrast, harzburgites from Torishima Forearc Seamount give calculated oxygen fugacities between FMQ + 0.8 and FMQ + l.6, similar to those calculated for other subduction-zone related peridotites and similar to those calculated for the dunites (FMQ + 1.2 to FMQ + 1.8) from the same seamount. In this case, we interpret both the harzburgites and dunites as linked to mantle melting (20-25 % fractional melting) in a supra-subduction zone environment The results thus indicate that the forearc is underlain by at least two types of mantle lithosphere, one being trapped or accreted oceanic lithosphere, the other being lithosphere formed by subduction-related melting. They also demonstrate that both types of mantle lithosphere may have undergone extensive interaction with subduction-derived magmas.

Radiocarbon age and sedimentation rates of bottom sediments in the Obskaya Gube (Ob River estuary

Complex geological-geochemical studies of water column and bottom sediments were carried out during Cruise 49 of R/V "Dmitry Mendeleev" in the Kara Sea shelf zone along the Obskaya Guba (Ob River estuary) from the Pur River and Taz River mouths to 76°N. Carbon-14 concentrations in organic matter from bottom sediments were determined at 5 stations. Constant initial 14C concentration model was used to determine sedimentation rates that were taken as a basis for calculating ages of sediment cores and their separate parts and for inferring location of a depocenter, i.e. a region of maximal discharge of fine-dispersed fraction of suspended matter of river run-off. Sedimentation rate in the depocenter is 170 cm/ka. Southward moves of the depocenter were recorded for periods of sea-level rises 2 and 5 thousand years ago. Bottom sediments in the depocenter contain 45% of organic matter primary produced in the Obskaya Guba. This organic matter is an energetic basis for bottom fauna life. About 55% of organic matter comes with river run-off.

Chemical and mineral compositions of basalts and volcanic glasses from DSDP Sites 65-483 and 65-485

Major and rare earth element (REE) data for basalts from Holes 483, 483B, and 485A of DSDP Leg 65, East Pacific Rise, mouth of the Gulf of California, support a simple fractional crystallization model for the genesis of rocks from this suite. The petrography and mineral chemistry (presented in detail elsewhere) provide no evidence for magma mixing, but rather a simple multistage cooling process. Based on its lowest TiO2 content (0.88%), FeO*/MgO ratio (0.95 with total Fe as FeO), and Mg# (100 Mg/Mg + Fe" = 70), sample 483-17-2-(78-83) has been selected as the most primitive primary magma of the samples analyzed. This is supported by the REE data which show this sample has the lowest total REE content, a La/Sm_cn (chondrite-normalized) = 0.36, and Eu/Sm_cn = 1.05. Because other samples analyzed have higher SiO2, lower Mg#, and a negative Eu anomaly (Eu/Sm_cn as low as 0.89), they are most likely derivative magmas. Wright-Doherty and trace element modelling support fractional crystallization of 14.1% plagioclase (An88), 6.7% olivine (Fo86), and 4.7% clinopyroxene (Wo41En49Fs10) from 483-17-2-(78-83) to form the least differentiated sample with Mg# = 63. The La/Sm_cn of this derivative magma is almost identical to the parent magma (0.35 to 0.36), but the other samples have higher La/Sm_cn (0.45 to 0.51), more total REE, and lower Mg# (60 to 56). Both Wright-Doherty and trace element modelling indicate that the primary magma chosen cannot produce these more evolved samples. For the major elements, the TiO2 and P2O5 are too low in the calculated versus the observed (1.38 to 1.90; 0.11 to 0.17, respectively, for example). Rayleigh fractionation calculates a lower La/Sm_cn and requires about 60% crystal removal versus 40% for the Wright-Doherty. These more evolved samples must be derived from a parent magma different from the one selected here and, unfortunately, not sampled in this study. A magma formed by a smaller degree of partial melting with slightly more residual clinopyroxene left in the mantle than for sample 483-17-2-(78-83) is required.

Photosynthetically active radiation and microalgae and protist occurrence at ice stations of POLARSTERN cruise ARK-XIX/1

Pack ice around Svalbard was sampled during the expedition ARK XIX/1 of RV "Polarstern" (March-April 2003) in order to determine environmental conditions, species composition and abundances of sea-ice algae and heterotrophic protists during late winter. As compared to other seasons, species diversity of algae (total 40 taxa) was not low, but abundances (5,000-448,000 cells/l) were lower by one to two orders of magnitude. Layers of high algal abundances were observed both at the bottom and in the ice interior. Inorganic nutrient concentrations (NO2, NO3, PO4, Si(OH)4) within the ice were mostly higher than during other seasons, and enriched compared to seawater by enrichment indices of 1.6-24.6 (corrected for losses through the desalination process). Thus, the survival of algae in Arctic pack ice was not limited by nutrients at the beginning of the productive season. Based on less-detailed physical data, light was considered as the most probable factor controlling the onset of the spring ice-algal bloom in the lower part of the ice, while low temperatures and salinities inhibit algal growth in the upper part of the ice at the end of the winter. Incorporation of ice algae probably took place during the entire freezing period. Possible overwintering strategies during the dark period, such as facultative heterotrophy, energy reserves, and resting spores are discussed.

Radiocarbon ages of bottom sediments and sedimentation rates in depressions of the Red Sea rift zone

Sedimentation rates (SR) for metalliferous and ore sediments containing ore material in 15 depressions of the Red Sea rift zone are discussed. SR for normal sediments was ca. 3.2 cm/ka in the second half of Holocene, 14.3 cm/ka yrs in the first half of Holocene, and 21.3 cm/ka in Late Würmian. Accumulation of metalliferous and ore sediments requires considerable accumulation of hydrothermal matter. Ore sediments have been found primarily in the Atlantis II and Chain Deeps; average sedimentation rate in these depressions is 90.0 cm/ka. In other depressions geothermal activity during considered time intervals was lower, and ore material occurs as admixture or in layers.

High-resolution isotope stratigraphy of ODP Site 184-1144

Narrow-spaced oxygen and carbon stable isotope records of the planktonic foraminifer Globigerinoides ruber (white) were obtained at Ocean Drilling Program Leg 184 Site 1144 to establish a first record of high-resolution Pleistocene monsoon variability on orbital to centennial timescales in the northern South China Sea. The new records extend from the Holocene back to marine isotope Stage (MIS) 34 (1.1 Ma). Sedimentation rates average 0.56 m/k.y. for the upper Matuyama and Brunhes Chrons and increase to 1.8 m/k.y. over the last 100 k.y. Stable isotope records thus reach an average time resolution of 270-500 yr for the last 375 k.y. and 570 yr further back to 700 ka. On the other hand, major stratigraphic gaps were identified for peak warm Stages 5.5, 7.5 (down to 8.4), 11.3, and 15.5. These gaps probably resulted from short-lasting events of contour current erosion induced by short-term enhanced incursions of Upper Pacific Deep Water near the end of glacial terminations. A further major hiatus extends from MIS 34 to MIS 73(?). The long-term variations in monsoon climate were largely dominated by the 100-k.y. eccentricity cycle. Planktonic delta13C values culminated near 30, 480, and 1035 ka and reflect an overlying 450-k.y. eccentricity cycle of minimum nutrient concentrations in the surface ocean. Superimposed on the orbital variations, millennial-scale cycles were prominent throughout the last 700 k.y., mainly controlled by short-term changes in monsoon-driven precipitation and freshwater input from mainland China. During the last 110 k.y. these short-lasting oscillations closely match the record of 1500-yr Dansgaard-Oeschger climate cycles in the Greenland ice core record.

Mercury content and isotopic composition of teeth, and sex and age of skulls of polar bears collected in Svalbard

We examined the use of mercury (Hg) and nitrogen and carbon stable isotopes in teeth of polar bear (Ursus maritimus) from Svalbard as biotracers of temporal changes in Hg pollution exposure between 1964 and 2003. Teeth were regarded as a good matrix of the Hg exposure, and in total 87 teeth of polar bears were analysed. Dental Hg levels ranged from 0.6 to 72.3 ng/g dry weight and increased with age during the first 10 years of life. A decreasing time trend in Hg concentrations was observed over the recent four decades while no temporal changes were found in the stable isotope ratios of nitrogen (d15N) and carbon (d13C). This suggests that the decrease of Hg concentrations over time was more likely due to a lower environmental Hg exposure in this region rather than a shift in the feeding habits of Svalbard polar bears.

Stable isotope composition of early Danian sediments from the Atlantic Ocean

A long-standing question in Paleogene climate concerns the frequency and mechanism of transient greenhouse gas-driven climate shifts (hyperthermals). The discovery of the greenhouse gas-driven Paleocene-Eocene Thermal Maximum (PETM; ~55 Ma) has spawned a search for analogous events in other parts of the Paleogene record. On the basis of high-resolution bulk sediment and foraminiferal stable isotope analyses performed on three lower Danian sections of the Atlantic Ocean, we report the discovery of a possible greenhouse gas-driven climatic event in the earliest Paleogene. This event - that we term the Dan-C2 event - is characterized by a conspicuous double negative excursion in delta13C and delta18O, associated with a double spike in increased clay content and decreased carbonate content. This suggests a double period of transient greenhouse gas-driven warming and dissolution of carbonates on the seafloor analogous to the PETMin the early Paleocene at ~65.2 Ma. However, the shape of the two negative carbon isotope excursions that make up the Dan-C2 event is different from the PETM carbon isotope profile. In the Dan-C2 event, these excursions are fairly symmetrical and each persisted for about ~40 ky and are separated by a short plateau that brings the combined duration to ~100 ky, suggesting a possible orbital control on the event. Because of the absence of a long recovery phase, we interpret the Dan-C2 event to have been associated with a redistribution of carbon that was already in the biosphere. The Dan-C2 event and other early Paleogene hyperthermals such as the short-lived early Eocene ELMO eventmay reflect amplification of a regular cycle in the size and productivity of the marine biosphere and the balance between burial of organic and carbonate carbon.

Geochemistry of altered phases, basalts and sediments of ODP Site 136-843

40Ar-39Ar incremental heating experiments on a relatively unaltered basalt from Site 843 yield a crystallization age of 110 ± 2 Ma for the central Pacific Ocean igneous basement near Hawaii. Previous estimates of the age of the basement inferred by indirect methods and from radiometric dates of the South Hawaiian Seamounts are too young by 20-30 m.y. Phyllosilicate alteration minerals from veins in the Site 843 basalts define a Rb/Sr isochron with an age of 94.5 ± 0.5 Ma. The isochron records the last equilibration of the phyllosilicate minerals with a hydrothermal fluid at about 16 m.y. after the formation of the igneous basement. The last event recorded by calcite veins is the sealing of the crust by a sufficient thickness of sediment to impede the free circulation of seawater into the crust. The chemistry of the alteration minerals indicates the rare earth elements in the hydrothermal solutions were derived from alteration of the basalts and, furthermore, were transported in solution as metal species and carbonate complexes. Calcite with approximately seawater 87Sr/86Sr, but Sr contents too low to precipitate directly from seawater, is suggested to have formed at a late stage in the alteration history of the crust by the reaction of seawater with calcite precipitated earlier from basalt-dominated hydrothermal fluids.

Pb isotope and geochemical record of Arctic sediments

Elemental and Pb isotope measurements were performed on leachates and residues from surface sediments and two <50 cm cores (MC04 and MC16) collected along a NE-SW transect through Fram Strait. Geochemical and isotopic properties of residues from surface sediments define three distinct spatial domains within the Strait: 1) the easternmost edge of the Strait; 2) the eastern part of the Strait off the Svalbard margins; and 3) the western part of the Strait, influenced by supplies from Svalbard, the Nordic seas with possible contributions from northwestern Siberian margins, and sea ice and water outflow from the Arctic, respectively. Core MC16, in the third domain beneath the outflowing Arctic waters, spans the Last Glacial Maximum present interval. Sediments from this core were leached to obtain detrital (residues) and exchangeable (leachates) fractions. Detrital supplies to core MC16 are believed to originate mainly from melting of the overlying sea ice and thus can be used to document changes in Arctic sedimentary sources. Detrital 206Pb/204Pb and 208Pb/206Pb ratios illustrate two mixing trends, Trends A and B, corresponding to the pre- and post-Younger Dryas (YD) intervals, respectively. These trends represent binary mixtures with a common end-member (Canadian margins) and either a Siberian (Trend A) or Greenland (Trend B) margin end-member. The YD is marked by an isotopic excursion toward the Canadian end-member, suggesting a very active Beaufort Gyre possibly triggered by massive drainage of the Laurentide ice sheet. Pb isotope compositions of leachates, thought to represent the signature of the overlying water masses, define a unique linear trend coincident with Trend A. This suggests that water masses acquired their signature through exchange with particulate fluxes along the Canadian and Siberian continental margins.

Foraminiferal trace element ratios from South Atlantic sediments

The rate of uranium accumulation in oceanic sediments from seawater is controlled by bottom water oxygen concentrations and organic carbon fluxes-two parameters that are linked to deep ocean storage of CO2. To investigate glacial-interglacial changes in what is known as authigenic U, we have developed a rapid method for its determination as a simple addition to a procedure for foraminiferal trace element analysis. Foraminiferal calcite acts as a low U substrate (U/Ca < 15 nmol/mol) upon which authigenic U accumulates in reducing sediments. We measured a downcore record of foraminiferal U/Ca from ODP Site 1090 in the South Atlantic and found that U/Ca ratios increase by 70-320 nmol/mol during glacial intervals. There is a significant correlation between U/Ca records of benthic and planktonic foraminiferal species and between U/Ca and bulk sediment authigenic U. These results indicate that elevated U/Ca ratios are attributable to the accumulation of authigenic U coatings in sediments. Foraminiferal Mn/Ca ratios were lower during the glacial intervals, suggesting that the observed U accumulation on the shells is not directly linked to U incorporation into secondary manganese phases. Thus, foraminiferal U/Ca ratios may provide useful information on past changes in sediment redox conditions.

Ion concentrations and extracelluar pH of Calanus glacialis in Billefjorden, Svalbard

Arctic shelf zooplankton communities are dominated by the copepod Calanus glacialis. This species feeds in surface waters during spring and summer and accumulates large amounts of lipids. Autumn and winter are spent in dormancy in deeper waters. Lipids are believed to play a major role in regulating buoyancy, however, they cannot explain fine-tuning of the depth distribution. To investigate whether ion exchange processes and acid-base regulation support ontogenetic migration as suggested for Antarctic copepods, we sampled C. glacialis in monthly intervals for 1 yr in a high-Arctic fjord and determined cation concentrations and the extracellular pH (pHe) in its hemolymph. During the winter/spring transition, prior to the upward migration of the copepods, Li+ ions were exchanged with cations (Na+, Mg2+, and Ca2+) leading to Li+ concentrations of 197 mmol/L. This likely decreased the density and promoted upward migration in C. glacialis. Our data thus suggest that Li+ has a biological function in this species. Ion and pHe regulation in the hemolymph were not directly correlated, but the pHe revealed a seasonal pattern and was low (5.5) in winter and high (7.9) in summer. Low pHe during overwintering might be related to metabolic depression and thus, support diapause.

Geochemistry of Mid-Atlantic Ridge sediments

Geochemical compositions and Sr and Nd isotopes were measured in two cores collected ~2 and 5 km from the Rainbow hydrothermal vent site on the Mid-Atlantic Ridge. Overall, the cores record enrichments in Fe and other metals from hydrothermal fallout, but sequential dissolution of the sediments allows discrimination between a leach phase (easily leachable) and a residue phase (refractory). The oxy-anion and transition metal distribution combined with rare earth element (REE) patterns suggest that (1) the leach fraction is a mixture of biogenic carbonate and hydrothermal Fe-Mn oxy-hydroxide with no significant contribution from detrital material and (2) >99.5% of the REE content of the leach fraction is of seawater origin. In addition, the leach fraction has an average 87Sr/86Sr ratio indistinguishable from modern seawater at 0.70916. Although we lack the epsilon-Nd value of present-day deep water at the Rainbow vent site, we believe that the REE budget of the leach fraction is predominantly of seawater origin. We suggest therefore that the leach fraction provides a record of local seawater epsilon-Nd values. Nd isotope data from these cores span the period of 4-14 ka (14C ages) and yield epsilon-Nd values for North East Atlantic Deep Water (NEADW) that are higher (-9.3 to -11.1) than those observed in the nearby Madeira Abyssal Plain from the same depth (-12.4 ± 0.9). This observation suggests that either the Iceland-Scotland Overflow Water (ISOW) and Lower Deep Water contributions to the formation of NEADW are higher along the Mid-Atlantic Ridge than in the surrounding basins or that the relative proportion of ISOW was higher during this period than is observed today. This study indicates that hydrothermal sediments have the potential to provide a higher-resolution record of deep water epsilon-Nd values, and hence deepwater circulation patterns in the oceans, than is possible from other types of sediments.

Sedimentology and Th, Pa, U, and N isotopic composition of core MD84-527

High-resolution records of opal, carbonate, and terrigenous fluxes have been obtained from a high-sedimentation rate core (MD84-527: 43°50'S; 51°19'E; 3269 m) by normalization to 230Th. This method estimates paleofluxes to the seafloor on a point-by-point basis and distinguishes changes in sediment accumulation due to variations in vertical rain rates from those due to changes in syndepositional sediment redistribution by bottom currents. We also measured sediment delta15N to evaluate the changes in nitrate utilization in the overlying surface waters associated with paleoflux variations. Our results show that opal accumulation rates on the seafloor during the Holocene and stage 3, based on 14C dating, were respectively tenfold and fivefold higher than the vertical rain rates, At this particular location, changes in opal accumulation on the seafloor appear to be mainly controlled by sediment redistribution by bottom currents rather than variations in opal fluxes from the overlying water column. Correction for syndepositional sediment redistribution and the improved time resolution that can be achieved by normalization to 230Th disclose important variations in opal rain rates. We found relatively high but variable opal paleoflux during stage 3, with two maxima centered at 36 and 30 kyr B.P., low opal paleoflux during stage 2 and deglaciation and a pronounced maximum during the early Holocene, We interpret this record as reflecting variations in opal production rates associated with climate-induced latitudinal migration of the southern ocean frontal system. Sediments deposited during periods of high opal paleoflux also have high authigenic U concentrations, suggesting more reducing conditions in the sediment, and high Pa-231/Th-230 ratios, suggesting increased scavenging from the water column. Sediment delta15N is circa 1.5 per mil higher during isotopic stage 2 and deglaciation. The low opal rain rates recorded during that period appear to have been associated with increased nitrate depletion. This suggests that opal paleofluxes do not simply reflect latitudinal migration of the frontal system but also changes in the structure of the upper water column. Increased stratification during isotopic stage 2 and deglaciation could have been produced by a meltwater lid, leading to lower nitrate supply rates to surface waters.