Geochemistry, chlorin concentrations and diatom abundance in sediments of lake Rotsee, Switzerland

The effects of eutrophication on short term changes in the microbial community were investigated using high resolution lipid biomarker and trace metal data for sediments from the eutrophic Lake Rotsee (Switzerland). The lake has been strongly influenced by sewage input since the 1850s and is an ideal site for studying an anthropogenically altered ecosystem. Historical remediation measures have had direct implications for productivity and microbial biota, leading to community composition changes and abundance shifts. The higher sewage and nutrient input resulted in a productivity increase, which led predominantly to a radiation in diatoms, primary producers and methanogens between about 1918 and 1921, but also affected all microorganism groups and macrophytes between about 1958 and 1972. Bacterial biomass increased in 1933, which may have been related to the construction of a mechanical sewage treatment plant. Biomarkers also allowed tracing of fossil organic matter/biodegraded oil contamination in the lake. Stephanodiscus parvus, Cyclotella radiosa and Asterionella formosa were the dominant sources of specific diatom biomarkers. Since the 1850s, the cell density of methanogenic Archaea (Methanosaeta spp.) ranged within ca. 0.5-1.8 x 10**9 cells/g dry sediment and the average lipid content of Rotsee Archaea was ca. 2.2 fg iGDGTs/cell. An altered BIT index (BITCH), indicating changes in terrestrial organic matter supply to the lake, is proposed.

Stable oxygen isotope composition of planktonic foraminifera in the Canary Islands region

Seasonal depth stratified plankton tows, sediment traps and core tops taken from the same stations along a transect at 29°N off NW Africa are used to describe the seasonal succession, the depth habitats and the oxygen isotope ratios (delta18O(shell)) of five planktic foraminiferal species. Both the delta18O(shell) and shell concentration profiles show variations in seasonal depth habitats of individual species. None of the species maintain a specific habitat depth exclusively within the surface mixed layer (SML), within the thermocline, or beneath the thermocline. Globigerinoides ruber (white) and (pink) occur with moderate abundance throughout the year along the transect, with highest abundances in the winter and summer/fall season, respectively. The average delta18O(shell) of G. ruber (w) from surface sediments is similar to the delta18O(shell) values measured from the sediment-trap samples during winter. However, the delta18O(shell) of G. ruber (w) underestimates sea surface temperature (SST) by 2 °C in winter and by 4 °C during summer/fall indicating an extension of the calcification/depth habitat into colder thermocline waters. Globigerinoides ruber (p) continues to calcify below the SML as well, particularly in summer/fall when the chlorophyll maximum is found within the thermocline. Its vertical distribution results in delta18O(shell) values that underestimate SST by 2 °C. Shell fluxes of Globigerina bulloides are highest in summer/fall, where it lives and calcifies in association with the deep chlorophyll maximum found within the thermocline. Pulleniatina obliquiloculata and Globorotalia truncatulinoides, dwelling and calcifying a part of their lives in the winter SML, record winter thermocline (~180 m) and deep surface water (~350 m) temperatures, respectively. Our observations define the seasonal and vertical distribution of multiple species of foraminifera and the acquisition of their delta18O(shell).

Nd isotopes an geochemistry of bulk deep sea sediments of the Atlantic Ocean

Nd isotopes preserved in fossil fish teeth and ferromanganese crusts have become a common tool for tracking variations in water mass composition and circulation through time. Studies of Nd isotopes extracted from Pleistocene to Holocene bulk sediments using hydroxylamine hydrochloride (HH) solution yield high resolution records of Nd isotopes that can be interpreted in terms of deep water circulation, but concerns about diagenesis and potential contamination of the seawater signal limit application of this technique to geologically young samples. In this study we demonstrate that Nd extracted from the > 63 µm, decarbonated fraction of older Ocean Drilling Program (ODP) sediments using a 0.02 M HH solution produces Nd isotopic ratios that are within error of values from cleaned fossil fish teeth collected from the same samples, indicating that the HH-extractions are robust recorders of deep sea Nd isotopes. This excellent correlation was achieved for 94 paired fish teeth and HH-extraction samples ranging in age from the Miocene to Cretaceous, distributed throughout the north, tropical and south Atlantic, and composed of a range of lithologies including carbonate-rich oozes/chalks and black shales. The strong Nd signal recovered from Cretaceous anoxic black shale sequences is unlikely to be associated with ferromanganese oxide coatings, but may be derived from abundant phosphatic fish teeth and debris or organic matter in these samples. In contrast to the deep water Nd isotopic signal, Sr isotopes from HH-extractions are often offset from seawater values, suggesting that evaluation of Sr isotopes is a conservative test for the integrity of Nd isotopes in the HH fraction. However, rare earth elements (REE) from the HH-extractions and fish teeth produce distinctive middle REE bulge patterns that may prove useful for evaluating whether the Nd isotopic signal represents uncontaminated seawater. Alternatively, a few paired HH-extraction and cleaned fish teeth samples from each site of interest can be used to verify the seawater composition of the HH-extractions. The similarity between isotopic values for the HH-extraction and fish teeth illustrates that the extensive cleaning protocol applied to fish teeth samples is not necessary in typical, carbonate-rich, deep sea sediments.

Radium 228 and Radium 226 in surface water of the Kara Sea and Laptev Sea

The surface water in the Transpolar Drift in the Arctic Ocean has a strong signature of 228Ra. In an earlier study of 228Ra in the open Arctic we showed that the major 228Ra source had to be in the Siberian shelf seas, but only a single shelf station was published so far. Here we investigate the sources of this signal on the Siberian shelves by measurements of 228Ra and 226Ra in surface waters of the Kara and Laptev Sea, including the Ob, Yenisey and Lena estuaries. In the Ob and Lena rivers we found an indication for a very strong and unexpected removal of both isotopes in the early stage of estuarine mixing, presumably related to flocculation of organic-rich material. Whereas 226Ra behaves conservatively on the shelf, the distribution of 228Ra is governed by large inputs on the shelves, although sources are highly variable. In the Kara Sea the maximum activity was found in the Baydaratskaya Bay, where tidal resonance and low freshwater supply favour 228Ra accumulation. The Laptev Sea is a stronger source for 228Ra than the Kara Sea. Since a large part of Kara Sea water flows through the Laptev Sea, the 228Ra signal in the Transpolar Drift can be described as originating on the Laptev shelf. The combined freshwater inputs from the Eurasian shelves thus produce a common radium signature with a 228Ra/226Ra activity ratio of 4.0 at 20% river water. The radium signals of the individual Siberian rivers and shelves cannot be separated, but their signal is significantly different from the signal produced on the Canadian shelf (Smith et al., in press). In this respect, the radium tracers add to the information given by Barium. Moreover, with the 5.8 year half-life of 228Ra, they have the potential to serve as a tracer for the age of a water mass since its contact with the shelves.

(Table 1) Gas molecules, isotopic composition and delta Deuterium in DSDP Holes 95-603D and 95-613

Methane is the major hydrocarbon gas measured in Vacutainer samples from Holes 603D and 613 ( C1/sumCn > 0.999). In Hole 613 the concentration of this dry hydrocarbon gas is highest (7.4 x 10 **5 ppm max.) in the upper 60 to 120 m, then decreases erratically to low trace levels by 261 m sub-bottom (lower Pliocene). No gas accumulations were observed in older sediments. Methane from both holes is strongly depleted in both 13C (d13C, - 75 to -85 per mil) and deuterium (D/H, - 175 to -262 per mil), indicating the biogenic origin of the methane. The C and H isotopic compositions support methanogenesis via the CO2-reduction pathway; this is also corroborated by the dissolved-sulfate and alkalinity minima at these depths. The relationship between D/H of the methane and coexisting interstitial water from Site 613 further show the methanogenesis to be primarily by CO2 reduction.

Paleotemperatures, stable isotopes and alkenones of samples from the South Atlantic

Carbon dioxide is one of the most important greenhouse gases which are increasing in atmospheric concentration due to human activities. For using natural CO2 dynamics as a key to understanding the climatic consequences of anthropogenic pCO2 rise, the ocean plays an important role due to its much larger carbon pool compared to the atmosphere. By studying the ratio of stable carbon isotopes in organic matter from marine sediments, it is possible to estimate the partial pressure of CO2 in surface waters during ancient times. The organic compound C37:2 alkenone, whose sole origin is from autotrophic marine algae, was chosen for d13C analysis and its isotopic composition used to reconstruct past PCO2 levels in the surface layer of the eastern Angola Basin for the last 200,000 years. In addition to the variation of ancient concentrations of dissolved CO2 ([CO2(aq)] = ce), the effect of carbon demand which depends on algal growth rate was considered. Here to, carbon isotopic fractionation of C37:2 alkenones (ep) in core-top sediments from the equatorial and the South Atlantic was calibrated against pre-industrial [CO2(aq)] and phosphate concentrations in surface waters. From these data, a variable b = (25 per mil - ep) * ce which reflects intracellular carbon demand was calculated. This variable b correlates with the ambient concentration of seawater phosphate and depends on growth rates. The bulk sediment d15N was used as a proxy parameter for calculating ancient b-values, taking into account that d15N in core-top sediments is correlated to phosphate concentration in modern surface waters. On this basis, the alkenone d13C record of GeoB1016-3 documents a permanent oceanic source for atmospheric carbon dioxide during the last 200,000 years. As a consequence of using d15N derived b-values instead of b = constant, the Angola Basin appears to have been an even stronger CO2 source during glacial periods than at present. Qualitatively similar results were reported by Jasper et al. (1994) for the central Equatorial Pacific. These observations suggest that enhanced productivity of low-latitude upwelling areas during glacial periods is not responsible for the lower CO2 content of the glacial atmosphere.

Natural high pCO2 increases autotrophy in Anemonia viridis (Anthozoa) as revealed from stable isotope (C, N) analysis

Contemporary cnidarian-algae symbioses are challenged by increasing CO2 concentrations (ocean warming and acidification) affecting organisms' biological performance. We examined the natural variability of carbon and nitrogen isotopes in the symbiotic sea anemone Anemonia viridis to investigate dietary shifts (autotrophy/heterotrophy) along a natural pCO2 gradient at the island of Vulcano, Italy. delta 13C values for both algal symbionts (Symbiodinium) and host tissue of A. viridis became significantly lighter with increasing seawater pCO2. Together with a decrease in the difference between delta 13C values of both fractions at the higher pCO2 sites, these results indicate there is a greater net autotrophic input to the A. viridis carbon budget under high pCO2 conditions. delta 15N values and C/N ratios did not change in Symbiodinium and host tissue along the pCO2 gradient. Additional physiological parameters revealed anemone protein and Symbiodinium chlorophyll a remained unaltered among sites. Symbiodinium density was similar among sites yet their mitotic index increased in anemones under elevated pCO2. Overall, our findings show that A. viridis is characterized by a higher autotrophic/heterotrophic ratio as pCO2 increases. The unique trophic flexibility of this species may give it a competitive advantage and enable its potential acclimation and ecological success in the future under increased ocean acidification.

Trace elements in benthic foraminifera of sediment core V30-49

Eastern tropical Atlantic benthic foraminiferal Ba/Ca and Cd/Ca data from core V30-949 (3093 m) reveal large inferred changes in nutrient concentrations of deep Atlantic waters during the last 250 kyr. Relative changes in North Atlantic Deep Water contribution to this site are estimated by scaling the V30-49 Cd/Ca record to values of modern end-member water masses; these estimates agree well with the relative structure and timing of circulation changes in the eastern tropical Atlantic reconstructed from a d13C record-based mixing model (Raymo et al., 1997, doi:10.1029/97PA01019). Temporal differences between V30-49 Cd/Ca and Ba/Ca records suggest that the Ba/Ca record reflects changes in circulation with an additional increase in the Ba composition of deep Atlantic water masses during glacial episodes, possibly resulting from increased productivity. Similarity between the d13C and Ba/Ca records suggests that carbon isotopes in the deep glacial Atlantic also reflect productivity increases.

(Table 1) Chemical and isotopic composition of pore fluids in cores TGC-1 and TGC-6

The role of sediment diagenesis in the marine cycles of Li and B is poorly understood. Because Li and B are easily mobilized during burial and are consumed in authigenic clay mineral formation, their abundance in marine pore waters varies considerably. Exchange with the overlying ocean through diffusive fluxes should thus be common. Nevertheless, only a minor Li sink associated with the low-temperature alteration of volcanic ash has been observed. We describe a low-temperature diagenetic environment in the Black Sea dominated by the alteration of detrital plagioclase feldspars. Fluids expelled from the Odessa mud volcano in the Sorokin Trough originate from shallow (~100-400 m deep) sediments which are poor in volcanic materials but rich in anorthite. These fluids are depleted in Na+, K+, Li+, B, and 18O and enriched in Ca2+ and Sr2+, indicating that anorthite is dissolving and authigenic clays are forming. Using a simple chemical model, we calculate the pH and the partial pressure of CO2 (PCO2) in fluids associated with this alteration process. Our results show that the pH of these fluids is up to 1.5 pH units lower than in most deep marine sediments and that PCO2 levels are up to several hundred times higher than in the atmosphere. These conditions are similar to those which favor the weathering of silicate minerals in subaerial soil environments. We propose that in Black Sea sediments enhanced organic matter preservation favors CO2 production through methanogenesis and results in a low pore water pH, compared to most deep sea sediments. As a result, silicate mineral weathering, which is a sluggish process in most marine diagenetic environments, proceeds rapidly in Black Sea sediments. There is a potential for organic matter-rich continental shelf environments to host this type of diagenesis. Should such environments be widespread, this new Li and B sink could help balance the marine Li and Li isotope budgets but would imply an apparent imbalance in the B cycle.

Results of the coupled atmosphere-land surface model ECHAM5-JSBACH in NetCDF format

In this study we present first results of a new model development, ECHAM5-JSBACH-wiso, where we have incorporated the stable water isotopes H218O and HDO as tracers in the hydrological cycle of the coupled atmosphere-land surface model ECHAM5-JSBACH. The ECHAM5-JSBACH-wiso model was run under present-day climate conditions at two different resolutions (T31L19, T63L31). A comparison between ECHAM5-JSBACH-wiso and ECHAM5-wiso shows that the coupling has a strong impact on the simulated temperature and soil wetness. Caused by these changes of temperature and the hydrological cycle, the d18O in precipitation also shows variations from -4 permil up to 4 permil. One of the strongest anomalies is shown over northeast Asia where, due to an increase of temperature, the d18O in precipitation increases as well. In order to analyze the sensitivity of the fractionation processes over land, we compare a set of simulations with various implementations of these processes over the land surface. The simulations allow us to distinguish between no fractionation, fractionation included in the evaporation flux (from bare soil) and also fractionation included in both evaporation and transpiration (from water transport through plants) fluxes. While the isotopic composition of the soil water may change for d18O by up to +8 permil:, the simulated d18O in precipitation shows only slight differences on the order of ±1 permil. The simulated isotopic composition of precipitation fits well with the available observations from the GNIP (Global Network of Isotopes in Precipitation) database.