Characterization of sorbed volatile hydrocarbons from the Peru margin

Bacterial and thermogenic hydrocarbons are present in the sorbed-gas fraction of Peru margin sediments. At Ocean Drilling Program (ODP) Sites 681, 682, 684, and 686, bacterial gases are restricted to the early diagenetic zones, where dissolved sulfate has been exhausted and methanogenesis occurs. Methane migrating into the sulfate zone at Sites 681, 684, 686, and possibly 682, has been consumed anaerobically by methanotrophs, maintaining the low concentrations and causing an isotope shift in d13C(CH4) to more positive values. Significant amounts of C2+ hydrocarbons occur at the shelf Sites 680/681, 684, and 686/687, where these hydrocarbons may be associated with hypersaline fluids. There is evidence at Site 679 that sorbed C2+ hydrocarbons may also have been transported by hypersaline fluids. This characteristic C2+ hydrocarbon signature in the sorbed-gas fractions of sediments at Site 679 is not reflected in data obtained using the conventional "free-," "canned-," or "headspace-gas" procedures. The molecular and isotope compositions of the sorbed-gas fraction indicate that this gas may have a thermogenic source and may have spilled over with the hypersaline fluids from the Salaverry Basin into the Lima Basin. These traces of thermogenic hydrocarbon gases are over-mature (about 1.5% Ro) and are discordant with the less-mature sediments in which they are found. This observation supports the migration of these hydrocarbons, possibly from continental sources. Sorbed-gas analyses may provide important geochemical information, in addition to that of the free-gases. Sorbed-gases are less sensitive to activities in the interstitial fluids, such as methanogenesis and methanotrophy, and may faithfully record the migration of hydrocarbons associated with hypersaline fluids.

Coccolithophore size, abundance and calcification across Drake Passage (Southern Ocean), 2009

This data was collected during a cruise across Drake Passage in the Southern Ocean in February 2009. This data consists of coccolithophore abundance, calcification and primary production rates, carbonate chemistry parameters and ancillary data of macronutrients, chlorophyll-a, average mixed layer irradiance, daily irradiance above the sea surface, euphotic and mixed layer depth, temperature and salinity.

Environmental observations from Station Ssagastyr during the first International Polar Year 1882/83 (digitized tables)

Vorliegender Band enthält die für alle internationalen Polarstationen obligatorischen meteorologischen Beobachtungen der russischen Polarstation an der Lenamündung für den Zeitraum vom 1. September 1882 bis 31. August 1883 und vom 1. September 1883 bis zum 6. Juli 1884.

Revised composite depth scale, Fe content and orbital tuning of Middle Eocene Climate Optimum samples from ODP Site 207-1260

A high-resolution stratigraphy is essential toward deciphering climate variability in detail and understanding causality arguments of events in earth history. Because the highly dynamic middle to late Eocene provides a suitable testing ground for carbon cycle models for a waning warm world, an accurate time scale is needed to decode climate-driving mechanisms. Here we present new results from ODP Site 1260 (Leg 207) which covers a unique expanded middle Eocene section (magnetochrons C18r to C20r, late Lutetian to early Bartonian) of the tropical western Atlantic including the chron C19r transient hyperthermal event and the Middle Eocene Climate Optimum (MECO). To establish a detailed cyclostratigraphy we acquired a distinctive iron intensity records by XRF scanning Site 1260 cores. We revise the shipboard composite section, establish a cyclostratigraphy and use the exceptional eccentricity modulated precession cycles for orbital tuning. The new astrochronology revises the age of magnetic polarity chrons C19n to C20n, validates the position of very long eccentricity minima at 40.2 and 43.0 Ma in the orbital solutions, and extends the Astronomically Tuned Geological Time Scale back to 44 Ma. For the first time the new data provide clear evidence for an orbital pacing of the chron C19r event and a likely involvement of the very long eccentricity cycle contributing to the evolution of the MECO.

Biological, physical and chemical characteristics of water and sediment samples from the Volga River delta, northern Caspian

Based on the data of synchronous observations of hydrophysical and biogeochemical parameters in the near-mouth and shallow-water areas of the northern Caspian in 2000-2001, the scale of spatiotemporal variability in the following characteristics of the water-bottom system was estimated (1) flow velocity and direction within vortex structures formed by the combined effect of wind, discharge current, and the presence of higher aquatic plants; (2) dependence of the spatial distribution of the content and composition of suspended particulate matter on the hydrodynamic regime of waters and development of phytoplankton; (3) variations in the grain-size, petrographic, mineralogical, and chemical compositions of the upper layer of bottom sediments at several sites in the northern Caspian related to the particular local combination of dominant natural processes; and (4) limits of variability in the group composition of humus compounds in bottom sediments. The acquired data are helpful in estimating the geochemical consequences of a sea level rise and during the planning of preventive environmental protection measures in view of future oil and gas recovery in this region.

Petrologic data from Site U1308 over the last three glaciations

A composite North Atlantic record from DSDP Site 609 and IODP Site U1308 spans the past 300,000 years and shows that variability within the penultimate glaciation differed substantially from that of the surrounding two glaciations. Hematite stained grains exhibit similar repetitive down-core variations within the Marine Isotope Stage (MIS) 8 and 4-2 intervals, but little cyclic variability within the MIS 6 section. There is also no petrologic evidence, in terms of detrital carbonate-rich (Heinrich) layers, for surging of the Laurentide Ice Sheet through the Hudson Strait during MIS 6. Rather, very high background concentration of ice-rafted debris (IRD) indicates near continuous glacial meltwater input that likely increased thermohaline disruption sensitivity to relatively weak forcing events, such as expanded sea ice over deepwater formation sites. Altered (sub)tropical precipitation patterns and Antarctic warming during high orbital precession and low 65° N summer insolation appears related to high abundance of Icelandic glass shards and southward sea ice expansion. Differing European and North American ice sheet configurations, perhaps aided by larger variations in eccentricity leading to cooler summers, may have contributed to the relative stability of the Laurentide Ice Sheet in the Hudson Strait region during MIS 6.

Results of n-alkane biomarker analyses and paleoclimate reconstruction

The current study presents quantitative reconstructions of tree cover, annual precipitation and mean July temperature derived from the pollen record from Lake Billyakh (65°17'N, 126°47'E, 340 m above sea level) spanning the last ca. 50 kyr. The reconstruction of tree cover suggests presence of woody plants through the entire analyzed time interval, although trees played only a minor role in the vegetation around Lake Billyakh prior to 14 kyr BP (<5%). This result corroborates low percentages of tree pollen and low scores of the cold deciduous forest biome in the PG1755 record from Lake Billyakh. The reconstructed values of the mean temperature of the warmest month ~8-10 °C do not support larch forest or woodland around Lake Billyakh during the coldest phase of the last glacial between ~32 and ~15 kyr BP. However, modern cases from northern Siberia, ca. 750 km north of Lake Billyakh, demonstrate that individual larch plants can grow within shrub and grass tundra landscape in very low mean July temperatures of about 8 °C. This makes plausible our hypothesis that the western and southern foreland of the Verkhoyansk Mountains could provide enough moist and warm microhabitats and allow individual larch specimens to survive climatic extremes of the last glacial. Reconstructed mean values of precipitation are about 270 mm/yr during the last glacial interval. This value is almost 100 mm higher than modern averages reported for the extreme-continental north-eastern Siberia east of Lake Billyakh, where larch-dominated cold deciduous forest grows at present. This suggests that last glacial environments around Lake Billyakh were never too dry for larch to grow and that the summer warmth was the main factor, which limited tree growth during the last glacial interval. The n-alkane analysis of the Siberian plants presented in this study demonstrates rather complex alkane distribution patterns, which challenge the interpretation of the fossil records. In particular, extremely low n-alkane concentrations in the leaves of local coniferous trees and shrubs suggest that their contribution to the litter and therefore to the fossil lake sediments might be not high enough for tracing the Quaternary history of the needleleaved taxa using the n-alkane biomarker method.

Brown trout thermal niche and climate change: expected changes in the distribution of cold-water fish in central Spain

This paper addresses the determination of the realized thermal niche and the effects of climate change on the range distribution of two brown trout populations inhabiting two streams in the Duero River basin (Iberian Peninsula) at the edge of the natural distribution area of this species. For reaching these goals, new methodological developments were applied to improve reliability of forecasts. Water temperature data were collected using 11 thermographs located along the altitudinal gradient, and they were used to model the relationship between stream temperature and air temperature along the river continuum. Trout abundance was studied using electrofishing at 37 sites to determine the current distribution. The RCP4.5 and RCP8.5 change scenarios adopted by the International Panel of Climate Change for its Fifth Assessment Report were used for simulations and local downscaling in this study. We found more reliable results using the daily mean stream temperature than maximum daily temperature and their respective seven days moving-average to determine the distribution thresholds. Thereby, the observed limits of the summer distribution of brown trout were linked to thresholds between 18.1ºC and 18.7ºC. These temperatures characterise a realised thermal niche narrower than the physiological thermal range. In the most unfavourable climate change scenario, the thermal habitat loss of brown trout increased to 38% (Cega stream) and 11% (Pirón stream) in the upstream direction at the end of the century; however, at the Cega stream, the range reduction could reach 56% due to the effect of a ?warm-window? opening in the piedmont reach.

Geochemistry of organic carbon at DSDP Sites 75-530 and 75-532

CHN analyses of sediments and rocks sampled during DSDP Leg 75 in the South Atlantic have provided concentrations of organic carbon and atomic C/N ratios of organic matter from two sites. High values of organic carbon were measured in sediments deposited during Neogene and Cretaceous times at Site 530 in the Angola Basin; sediments deposited at other times contain less than 0.5% organic carbon. Development of the Benguela Current and associated upwelling-supported biological productivity is recorded in late Miocene to Holocene sediments which contain 1 to 7% organic carbon. These sediments include debris flows and turbidites composed of predominantly biogenic materials originally deposited on the Walvis Ridge and on the African continental margin. Organic-carbon-rich black shales containing up to 17% organic carbon occur in late Albian to Coniacian turbidite sequences. These Cretaceous black shale layers are commonly several centimeters thick and are separated by bioturbated fine-grained organic-carbon-poor turbidites which are usually much thicker. At Site 532 on the Walvis Ridge, biogenic sediments deposited between late Miocene and Holocene times contain 1 to 9% organic carbon. Fluctuations in the intensity of high biological productivity associated with the Benguela Current are preserved in alternating light and dark layers of sediments. C/N ratios of organic matter in sediments from both sites are typical of marine sources

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