ALBERT

Beschreibung: The methane concentration in the atmosphere andsurface water was surveyed along 58° N acrossthe North Sea. In addition, the vertical methanedistribution in the water column was determined at sixstations along the transect. The methane contents ofthe surface water as well as in the water column wereextremely inhomogeneous. Input by freshwater fromriver discharge and injection of methane from thesediment were both observed. The survey continued fromthe western side of the North Sea to the Elbe Riverestuary. The Elbe River appears to have low methaneconcentrations compared to other European rivers, itsaverage input into the North Sea is estimated to be70 nmol s-1 of methane. Near 58° N,1°40' E, an abandoned drill site releases about 25 % ofthe North Sea's emission of methane to the atmosphere.The advective methane transport induced by watercirculation was assessed for May 16, 1994, using a 3-DNorth Sea circulation model. For the period of thissurvey, the North Sea's source strength foratmospheric methane is estimated using in situwind velocities. In comparison to the advectivetransport by the water circulation, the gas flux tothe atmosphere appears to be the dominant sink ofNorth Sea methane. This flux is estimated to bebetween 1500 · 106 mol a-1 and 3100 ·106mol a-1, depending on the relationbetween wind speed and gas transfer velocity

Beschreibung: Progress in modeling the oceanic circulation has been achieved in the last few years by increasing the speed of computers and by refining modeling techniques. The dynamics of major current systems such as the Gulfstream-North Atlantic Current and their corresponding eddy variability is reasonably well understood [58, 32]. Climate models predict global warming as a result of increasing CO2 in the atmosphere and forecast El Nino events in the equatorial Pacific [50]. Freshwater imbalances in the deep convection regions of the polar and subpolar regions of the North Atlantic result in alternating multiple equilibrium states of the global thermohaline vertical circulation - the ”conveyor belt” [53]. On the other hand, large scale modeling relies heavily on the parametrization of ”subgrid” processes. This is especially true for the oceanic boundary layer. Here the modeling suffers from inappropriate information on the fluxes at the air-sea interface. Most coupled models with simplified fluxes do not represent the surface temperature well enough and water mass characteristics drift away from the initial state. Restoring conditions at the sea surface are needed to force the model back to the observations. The fluxes analyzed from runs with restoring conditions show substantial errors. It is evident that progress in the reliability of long-term predictions of climate variations can only be made with a better representation of mixed layer dynamics.

Beschreibung: In steady state, the export of photosynthetically fixed organic matter to the deep ocean has to be balanced by an upward flux of nutrients into the euphotic zone1. Indirect geochemical estimates2 of the nutrient supply to surface waters have been substantially higher than direct biological and physical measurements3, particularly in subtropical regions. A possible explanation for the apparent discrepancy is that the sampling strategy of the direct measurements has under-represented episodic nutrient injections forced by mesoscale eddy dynamics, whereas geochemical tracer budgets integrate fluxes over longer time and space scales. Here we investigate the eddy-induced nutrient supply by combining two methods potentially capable of delivering synoptic descriptions of the ocean's state on a basin scale. Remotely sensed sea-surface height data from the simultaneous TOPEX/Poseidon and ERS-1 satellite missions are assimilated into a numerical eddy-resolving coupled ecosystem–circulation model of the North Atlantic Ocean. Our results indicate that mesoscale eddy activity accounts for about one-third of the total flux of nitrate into the euphotic zone (taken to represent new production) in the subtropics and at mid-latitudes. This contribution is not sufficient to maintain the observed primary production in parts of the subtropical gyre, where alternative routes of nitrogen supply will have to be considered.

Beschreibung: Eukaryotic algae are a diverse group of organisms. Their lipid compositions have been less studied than those of higher plants but, nevertheless, we now have sufficient data to be able to make some broad generalizations. Algae contain many of the major lipids of plants, such as the glycosylglycerides and the usual phosphoglycerides. In addition, more unusual compounds such as the betaine lipids, chlorosulfolipids or various other sulfolipids may be major components of some species or orders. Where information is available specifically about chloroplast membranes, it seems that the three glycosylglycerides, monogalactosyldiacylglycerol, digalactosyldiacylglycerol and sulfoquinovosyldiacylglycerol, and phosphatidylglycerol are the main acyl lipids, as in plants. These four lipids have characteristic fatty acid compositions and are often highly enriched in polyunsaturated fatty acids which may contain as many as six double bonds. The positional distribution of fatty acids on the thylakoid lipids of Chlamydomonas indicates that the former are made exclusively within the chloroplast.

Beschreibung: Ikaite is a rare form of carbonate – calciumcarbonate hexahydrate (CaCO3·6H2O) and isthe precursor to thinolites. Metastable 'ikaite'crystals, discovered in unconsolidated marinesediments in the King George Basin in the BransfieldStrait, Antarctica, are related to diageneticremineralization reactions of organic matter. StableC, O, and H-isotopes track the response of ikaitecrystals, during growth, to changing interstitialfluid conditions as a result of bacterial sulphatereduction and methanogenesis. Ikaites form inpreference over calcite or aragonite at the prevailingsurface sediment conditions of -1.6 °C and 200bar in the King George Basin. The calcareous tufa towers of the terrestrial,hypersaline Mono Lake of northern California areCaCO3-precipitates formed by the influx ofsubmerged springs of calcium-rich freshwaters enteringthe alkaline lake (ΣCO2 = 0.5 m, pH =9.8). Under current climatic conditions the mineralcalcite precipitates, but during the colder Tiogaglacial period of Late Wisconsian age (12,000 to 9,000years BP), and possibly present day during the winterseason, the monoclinic calcium carbonate hexahydrate(ikaite) was the dominant phase formed. Thesepaleo-ikaites have since recrystallized to form thecalcitic pseudomorph 'thinolites'. They are foundelsewhere in recent and ancient sediments of polarregions, e.g., as 'glendonites'. The environmentaloccurrence of ikaites and their pseudomorphs deem themas potential paleoclimatic indicators of coldenvironments. The larger crystals are typicallyrestricted to colder, deeper organic-rich sediments orin moderately evaporitic basins. In these cases, theikaite formation and decomposition may be influencedby additives such as phosphate or amino acids.