(Table 1) Lipid biomarkers in surface sediments from the Gulf of Genoa

A series of molecular organic markers were determined in surface sediments from the Gulf of Genoa (Ligurian Sea) in order to evaluate their potential for palaeo-environmental reconstructions. Allochthonous input can be characterized by the distributions of n-C29 and n-C31 alkanes, n-C26 and n-C28 alkanols and branched glycerol dialkyl glycerol tetraethers (GDGTs), whose concentrations are generally highest near the river mouths. In the open basin however, terrestrial n-alkanes and n-alkanols may have an additional, aeolian source. Autochthonous input is represented by crenarchaeol and isoprenoid GDGTs. Their concentrations are highest in the open basin showing the preference of Thaumarchaeota for oligotrophic waters. Indications of a significant degradation of sterols and C37 alkenones exclude these lipids as reliable productivity proxies. Using terrestrial and aquatic lipids as end-members allows estimating the percentage of terrestrial organic matter between 20% and 58% in the coastal area decreasing to 1 to 30% in the deep basin. The spatial distribution of sea surface temperature (SST) estimates using the alkenone-based UK'37 index is very similar to the autumnal (November) mean satellite-based SST distribution. Conversely, TEXH86-derived SST estimates are close to winter SSTs in the coastal area and summer SSTs in the open basin. This pattern reflects presumably a shift in the main production of Thaumarchaeota from the coastal area in winter to the open basin in summer. This study represents a major prerequisite for the future application of lipid biomarkers on sediment cores from the Gulf of Genoa.

Marine and terrigenous lipids in ODP Leg 175 holes

Lipid compositions of sediments recovered during Ocean Drilling Program Leg 175 in the eastern South Atlantic reflect a variety of oceanographic and climatological environments. Most of the identified lipids can be ascribed to marine sources, notably haptophytes, eustigmatophytes, dinoflagellates, archaea, and diatoms. Elevated concentrations of cholesterol suggest zooplankton herbivory, characteristic for sites influenced by upwelling. At these sites, sulfurized highly branched isoprenoids from diatoms are also present in high amounts. Sterols, sterol ethers, hopanoids, and midchain hydroxy fatty acids could also be detected. Terrigenous lipids are n-alkanes, fatty acids, n-alcohols, and triterpenoid compounds like taraxerol and -amyrine. n-Alkanes, fatty acids, and n-alcohols are derived from leaf waxes of higher land plants and transported to the sea by airborne dust or fresh water. Triterpenoid compounds are most probably derived from mangroves and transported solely by rivers. Lipid compositions below the Congo low-salinity plume are strongly influenced by terrigenous material from the Congo River. Elevated organic carbon contents and predominantly marine lipid distributions at the Angola margin may indicate a highly productive plankton population, probably sustained by the Angola Dome. Sedimentary lipids in the Walvis Basin contain an upwelling signal, likely transported by the Benguela Current. Sedimentary lipids off Lüderitz Bay and in the southern Cape Basin are dominated by plankton lipids in high to intermediate amounts, reflecting persistent and seasonal upwelling, respectively.

Plant-wax, alkenone and major element analyses of ODP Site 659 for the Last Glacial cycle and associated coretop data

We present a hydrologic reconstruction of the Sahara-Sahel transition, covering the complete last glacial cycle (130 ka), based on a combination of plant-wax-specific hydrogen (dD) and carbon isotopes (d13C). The dD and d13C signatures of long-chain n-alkanes from ODP Site 659 off NW Africa reveal a significant anti-correlation. Complementary to published pollen data, we infer that this plant-wax signal reflects sensitive responses of the vegetation cover to precipitation changes in the Sahel region, as well as varying contributions from biomes north of the Sahara (C3 domain) by North-East Trade Winds (NETW). During arid phases, especially the northern parts of the Sahel likely experienced crucial water stress, which resulted in a pronounced contraction of the vegetation cover, thus reducing the amount of C4 plant waxes from the region. The increase in NETW strength during dry periods further promoted a more pronounced C3-plant-wax signal derived from the North African C3 plant domain. During humid periods, the C4-dominated Sahelian environments spread northward into the Saharan realm, in association with lower NETW inputs of C3 plant waxes. Arid-humid cycles deduced from plant-wax dD are in accordance with concomitant changes in weathering intensity reflected in varying major element distributions. Environmental shifts are generally linked to periods with large fluctuations in Northern Hemisphere summer insolation. During Marine Isotope Stages 2 and 3, when insolation variability was low, coupling of the hydrologic regime to alkenone-based estimates of NE Atlantic sea-surface temperatures becomes apparent.

Isotopic signatures and mercury content of arctic char and their prey, and water chemistry of 18 arctic Canadian lakes

Concentrations of mercury (Hg) have increased slowly in landlocked Arctic char over a 10- to 15-year period in the Arctic. Fluxes of Hg to sediments also show increases in most Arctic lakes. Correlation of Hg with trophic level (TL) was used to investigate and compare biomagnification of Hg in food webs from lakes in the Canadian Arctic sampled from 2002 to 2007. Concentrations of Hg (total Hg and methylmercury [MeHg]) in food webs were compared across longitudinal and latitudinal gradients in relation to d13C and d15N in periphyton, zooplankton, benthic invertebrates, and Arctic char of varying size-classes. Trophic magnification factors (TMFs) were calculated for the food web in each lake and related to available physical and chemical characteristics of the lakes. The relative content of MeHg increased with trophic level from 4.3 to 12.2% in periphyton, 41 to 79% in zooplankton, 59 to 72% in insects, and 74 to 100% in juvenile and adult char. The d13C signatures of adult char indicated coupling with benthic invertebrates. Cannibalism among char lengthened the food chain. Biomagnification was confirmed in all 18 lakes, with TMFs ranging from 3.5 ± 1.1 to 64.3 ± 0.8. Results indicate that TMFs and food chain length (FCL) are key factors in explaining interlake variability in biomagnification of [Hg] among different lakes.

Biomarker records of DSDP Hole 24-231 and terrestrial sediments

ntegrated terrestrial and marine records of northeast African vegetation are needed to provide long high resolution records of environmental variability with established links to specific terrestrial environments. In this study, we compare records of terrestrial vegetation preserved in marine sediments in the Gulf of Aden [Deep Sea Drilling Project (DSDP) Site 231] and an outcrop of lacustrine sediments in the Turkana Basin, Kenya, part of the East African Rift System. We analyzed higher plant biomarkers in sediments from both deposits of known equivalent age, corresponding to a ca. 50-100 ka humid interval prior to the b-Tulu Bor eruption ca. 3.40 Ma, when the Lokochot Lake occupied part of the Turkana Basin. Molecular abundance distributions indicate that long chain n-alkanoic acids in marine sediments are the most reliable proxy for terrestrial vegetation (Carbon Preference Index, CPI = 4.5), with more cautious interpretation needed for n-alkanes and lacustrine archives. Marine sediments record carbon isotopic variability in terrestrial biomarkers of 2-3 per mil, roughly equivalent to 20% variability in the C3/C4 vegetation contribution. The proportion of C4 vegetation apparently increased at times of low terrigenous dust input. Terrestrial sediments reveal much larger (2-10 per mil) shifts in n-alkanoic acid delta13C values. However, molecular abundance and isotopic composition suggest that microbial sources may also contribute fatty acids, contaminating the lacustrine sedimentary record of terrestrial vegetation.

Radiocarbon ages and major n-alkane homologues of peat cores LVPS4 and LVPS5B, Russian Arctic

Coupled analyses of n-alkane biomarkers and plant macrofossils from a peat plateau deposit in the northeast European Russian Arctic were carried out to assess the effects of past hydrology on the molecular contributions of plants to the peat. The n-alkane biomarkers accumulated over 9.6 kyr of local paleohydrological changes in this complex peat profile in which a succession of vegetation changes occurred during a transition from a wet fen to a relatively dry peat plateau bog. This study shows that the contribution of the n-C31 alkane from rootlets to peat layers rich in fine and dark roots is important. The results further indicate that the n-alkane Paq and n-C23/n-C29 biomarker proxies that have been useful to reconstruct past water table levels in many peat deposits can be misleading when the contributions of Betula and Sphagnum fuscum to the peat are large. Under these conditions, the C23/(C27 + C31) n-alkane ratio seems to correct for the presence of Betula and S. fuscum and provides a better description for the relative amounts of moisture. The average chain length (ACL) n-alkane proxy also appears to be a good paleohydrology proxy in having larger values during dry and cold conditions in this Arctic bog setting.

General descriptions, organic contents and ratios of geolipid components at DSDP Leg 74 Holes

Two samples of Miocene sediments from Site 525 and four samples of sediments ranging in age from Pleistocene to Miocene from Site 528 have been analyzed for concentrations of organic and carbonate carbon, carbon/nitrogen ratios of organic matter, and extractable hydrocarbons and fatty acids. Organic carbon concentrations average 0.32% and show a diagenetic decrease with greater sediment age. Distributions of n-alkanes and n-alkanoic acids give evidence of considerable microbial reworking and of eolian contributions of terrigenous components. Organic contents of these sediments reflect a history of low marine productivity and poor preservation of organic matter in the eastern South Atlantic since middle Miocene times.