Marine barite in sediments of DSDP Site 54-424

The distribution of barite in sediments from D.S.D.P. sites 424 and 424A at the Galapagos hydrothermal mounds field is determined and the process of its formation is deduced. Barite in these deposits is associated with calcareous sediments and is completely absent from the hydrothermal material (manganese crusts and nontronite). Its concentrations tend to increase in the deeper sediments. Since manganese crusts contain significant amounts of Ba, a lack of barite in them is probably due to low concentrations of [SO4]2 in the sediment-seawater interface where they form. The formation of barite occurs within buried sediments, the interstitial waters of which are saturated with [SO4]2. The most probable source of [SO4]2- is the oxidation of H2S which is released from the hydrothermal fluids percolating upwards through the sediments. Although nontronite is formed within buried sediments the environmental conditions occurring during its formation (reducing) prevent barite formation. The association of barite with calcareous sediments is due to the release of Ba by calcareous microorganisms and/or to high concentrations of Ca in the pore waters which maintain a high pH and hence [SO4]2- is stable.

Geochemistry of sediments cores in the Mediterranean Sea

We investigated five time-equivalent core sections (180-110 kyr BP) from the Balearic Sea (Menorca Rise), the easternmost Levantine Basin and southwest, south, and southeast of Crete to reconstruct spatial patterns of productivity during deposition of sapropels S5 and S6 in the Mediterranean Sea. Our indicators are Ba, total organic carbon and carbonate contents. We found no indications of Ba remobilization within the investigated core intervals, and used the accumulation rate of biogenic Ba to compute paleoproductivity. Maximum surface water productivity (up to 350 g C/m2/yr) was found during deposition of S5 (isotope stage 5e) but pronounced spatial variability is evident. Coeval sediment intervals in the Balearic Sea show very little productivity change, suggesting that chemical and biological environments in the eastern and western Mediterranean basins were decoupled in this interval. We interpret the spatial variability as the result of two different modes of nutrient delivery to the photic zone: riverderived nutrient input and shoaling of the pycnocline/nutricline to the photic zone. The productivity increase during the formation of S6 was moderate compared to S5 and had a less marked spatial variability within the study area of the eastern Mediterranean Sea. Given that S6 formed during a glacial interval, glacial boundary conditions such as high wind stress and/or cooler surface water temperatures apparently favored lateral and vertical mixing and prevented the development of the spatial gradients within the Eastern Mediterranean Sea (EMS) observed for S5. A non-sapropel sediment interval with elevated Ba content and depleted 18O/16O ratios in planktonic foraminifer calcite was detected between S6 and S5 that corresponds to the weak northern hemisphere insolation maximum at 150 kyr. At this time, productivity apparently increased up to five times over surrounding intervals, but abundant benthic fauna show that the deep water remained oxic. Following our interpretation, the interval denotes a failed sapropel, when a weaker monsoon did not force the EMS into permanent stratification. The comparison of interglacial and glacial sapropels illustrates the relevance of climatic boundary conditions in the northern catchment in determining the facies and spatial variability of sapropels within the EMS.

Carbonate and terrigenous content and chemical composition of sediments in the Central Equatorial Pacific

This study addresses changes in the absolute magnitude and spatial geometry of particle flux and export production in a meridional transect across the central equatorial Pacific Ocean's upwelling system during oxygen isotope Stage 11 and Stage 12 and compares these time periods to the current Holocene interglacial system. Temporal and spatial variability in several chemical proxies of export production, and in particular the distributions of Ba, scavenged Al, and P, are studied in a suite of sediment cores gathered along a cross-equator transect at 5°S, 2°S, 0°, 2°N, and 4°N. Because this latitudinal range preserves strong gradients in biogenic particle flux in the modern equatorial Pacific Ocean, we are able to assess variations in the relative magnitude of export production as well as the meridional width of the equatorial system through the late Quaternary glacial/interglacial cycles. During interglacial oxygen isotope Stage 11 the chemical proxies each indicate lower particle flux and export production than during Stage 12. These records are consistent throughout the transect during this time period, but geographic narrowing (during the interglacial) and widening (during the glacial) of the meridional gradient also occurs. Although carbonate concentration varies dramatically through glacial/interglacial cycles at all latitudes studied, the productivity proxies record only minimal glacial/interglacial change at 5°S and 4°N, indicating that the carbonate minima at these latitudes is controlled dominantly by dissolution rather than production. The chemical data indicate that although the spatial geometry of the system during Stages 11 and 12 indicates maximum productivity at the equator during both glacial and interglacial conditions, the absolute magnitude of export production integrated from 5°S to 4°N during Stage 11 was 25-50% less than during Stage 12, and also was 25-50% less than it is now.

Geochemistry, lithology, and bulk density of Cricket Flat paleosol samples

The high-resolution marine isotope climate record indicates pronounced global cooling during the Langhian (16-13.8 Ma), beginning with the warm middle Miocene climatic optimum and ending with significant Antarctic ice sheet expansion and the transition to "icehouse" conditions. Terrestrial paleoclimate data from this interval is sparse and sometimes conflicting. In particular, there are gaps in the terrestrial record in the Pacific Northwest during the late Langhian and early Serravallian between about 14.5 and 12.5 Ma. New terrestrial paleoclimate data from this time and region could reconcile these conflicting records. Paleosols are particularly useful for reconstructing paleoenvironment because the rate and style of pedogenesis is primarily a function of surface environmental conditions; however, complete and well-preserved paleosols are uncommon. Most soils form in erosive environments that are not preserved, or in environments such as floodplains that accumulate in small increments; the resulting cumulic soils are usually thin, weakly developed, and subject to diagenetic overprinting from subsequent soils. The paleosol at Cricket Flat in northeastern Oregon is an unusually complete and well-preserved paleosol from a middle Miocene volcanic sequence in the Powder River Volcanic Field. An olivine basalt flow buried the paleosol at approximately 13.8 ± 0.6 Ma, based on three 40Ar/39Ar dates on the basalt. We described the Cricket Flat paleosol and used its physical and chemical profile and micromorphology to assess pedogenesis. The Cricket Flat paleosol is an Ultisol-like paleosol, chemically consistent with a high degree of weathering. Temperature and rainfall proxies suggest that Cricket Flat received 1120 ± 180 mm precipitation y-1 and experienced a mean annual temperature of 14.5 ± 2.1 °C during the formation of the paleosol, significantly warmer and wetter than today. This suggests slower cooling after the middle Miocene climatic optimum than is seen in the existing paleosol record.

Grain size and diatom valves in sediment cores KS82-30 and KS82-31

Diatoms were studied quantitatively in six latest Quaternary (~70 kyr B.P. to Recent) piston cores from the westernmost Mediterranean, the Alboran Basin, and the Atlantic region immediately to the west of the Straits of Gibraltar. The Atlantic cores completely lack diatoms. In the Alboran Basin, diatoms are common from late Stage 3 (~27.5 kyr B.P.) to Termination lb (9 kyr B.P.) and in Recent core tops, but are absent in the other latest Quaternary intervals. Maximum accumulation of diatoms and highest abundance of species normally in sediments associated with increased productivity occurred during the latest Quaternary deglaciation, in the first phase of Termination I (~14.8 kyr B.P.). In the modern Alboran Basin, a region of high biological productivity occurs immediately east of the Gibraltar Straits. This high productivity results from upwelling associated with the interaction between the Atlantic inflow and the bottom topography near the Spanish coast. The upwelled nutrient-rich waters are then advected to the east and southeast by the surficial anticyclonic gyral circulation. Late Quaternary variations in diatom abundance are considered to reflect changes in this upwelling intensity with highest diatom abundances inferred to result from increased upwelling associated with an intensification of the anticyclonic gyral circulation. Highest inferred upwelling rates occurred during the first phase of latest Quaternary deglaciation. It is possible that an intensification of circulation within the Mediterranean Basin as a whole occurred from late Stage 3 to mid Termination I because widespread hiatus formation has been reported at this time in the Straits of Sicily due to an increase in the formation of intermediate waters. Diatoms were not preserved in other latest Quaternary intervals due to insufficient productivity to counterbalance their dissolution.

Hydroclimate records and radiocarbon dating of sediment cores SO189/2 _39KL, SO189/2 _119KL, and SO189/2 _144KL from the eastern tropical Indian Ocean

The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells1, 2, 3, 4, 5, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.

Properties, sedimentation and accumulation rates, and chemical composition of bottom sediments from the Deryugin Basin, Sea of Okhotsk

Results of a study of contents and accumulation rates of Fe, Mn, and some trace elements in Upper Quaternary sediments of the Deryugin Basin are presented. Maps of average contents and accumulation rates of excessive Fe, Mn, Zn, Ba, Ni, Pb, Cu, and Mo in sediments of the first oxygen isotope stage (OIS) have been plotted. Anomalous contents and accumulation rates are confined to peripheral zones of the Deryugin sedimentary basin and large fracture zones. Different mechanisms of influence of fluid-dynamic processes on rate of hydrogenic and biogenic accumulation of ore elements are assumed.

A Late Pleistocene sea level stack

Late Pleistocene sea level has been reconstructed from ocean sediment core data using a wide variety of proxies and models. However, the accuracy of individual reconstructions is limited by measurement error, local variations in salinity and temperature, and assumptions particular to each technique. Here we present a sea level stack (average) which increases the signal-to-noise ratio of individual reconstructions. Specifically, we perform principal component analysis (PCA) on seven records from 0-430 ka and five records from 0-798 ka. The first principal component, which we use as the stack, describes ~80 % of the variance in the data and is similar using either five or seven records. After scaling the stack based on Holocene and Last Glacial Maximum (LGM) sea level estimates, the stack agrees to within 5 m with isostatically adjusted coral sea level estimates for Marine Isotope Stages 5e and 11 (125 and 400 ka, respectively). When we compare the sea level stack with the d18O of benthic foraminifera, we find that sea level change accounts for about ~40 % of the total orbital-band variance in benthic d18O, compared to a 65 % contribution during the LGM-to-Holocene transition. Additionally, the second and third principal components of our analyses reflect differences between proxy records associated with spatial variations in the d18O of seawater.

Sea urchin response to rising pCO2 shows ocean acidification may fundamentally alter the chemistry of marine skeletons

Ocean acidification caused by an increase in pCO2 is expected to drastically affect marine ecosystem composition, yet there is much uncertainty about the mechanisms through which ecosystems may be affected. Here we studied sea urchins that are common and important grazers in the Mediterranean (Paracentrotus lividus and Arbacia lixula). Our study included a natural CO2 seep plus reference sites in the Aegean Sea off Greece. The distribution of A. lixula was unaffected by the low pH environment, whereas densities of P. lividus were much reduced. There was skeletal degradation in both species living in acidified waters compared to reference sites and remarkable increases in skeletal manganese levels (P. lividus had a 541% increase, A. lixula a 243% increase), presumably due to changes in mineral crystalline structure. Levels of strontium and zinc were also altered. It is not yet known whether such dramatic changes in skeletal chemistry will affect coastal systems but our study reveals a mechanism that may alter inter-species interactions.