871 resultados para Accumulation rate, marine organic carbon


Relevância:

100.00% 100.00%

Publicador:

Relevância:

100.00% 100.00%

Publicador:

Resumo:

The Schwalbenberg II loess-paleosol sequence (LPS) denotes a key site for Marine Isotope Stage (MIS 3) in Western Europe owing to eight succeeding cambisols, which primarily constitute the Ahrgau Subformation. Therefore, this LPS qualifies as a test candidate for the potential of temporal high-resolution geochemical data obtained X-ray fluorescence (XRF) scanning of discrete samplesproviding a fast and non-destructive tool for determining the element composition. The geochemical data is first contextualized to existing proxy data such as magnetic susceptibility (MS) and organic carbon (Corg) and then aggregated to element log ratios characteristic for weathering intensity [LOG (Ca/Sr), LOG (Rb/Sr), LOG (Ba/Sr), LOG (Rb/K)] and dust provenance [LOG (Ti/Zr), LOG (Ti/Al), LOG (Si/Al)]. Generally, an interpretation of rock magnetic particles is challenged in western Europe, where not only magnetic enhancement but also depletion plays a role. Our data indicates leaching and top-soil erosion induced MS depletion at the Schwalbenberg II LPS. Besides weathering, LOG (Ca/Sr) is susceptible for secondary calcification. Thus, also LOG (Rb/Sr) and LOG (Ba/Sr) are shown to be influenced by calcification dynamics. Consequently, LOG (Rb/K) seems to be the most suitable weathering index identifying the Sinzig Soils S1 and S2 as the most pronounced paleosols for this site. Sinzig Soil S3 is enclosed by gelic gleysols and in contrast to S1 and S2 only initially weathered pointing to colder climate conditions. Also the Remagen Soils are characterized by subtle to moderate positive excursions in the weathering indices. Comparing the Schwalbenberg II LPS with the nearby Eifel Lake Sediment Archive (ELSA) and other more distant German, Austrian and Czech LPS while discussing time and climate as limiting factors for pedogenesis, we suggest that the lithologically determined paleosols are in-situ soil formations. The provenance indices document a Zr-enrichment at the transition from the Ahrgau to the Hesbaye Subformation. This is explained by a conceptual model incorporating multiple sediment recycling and sorting effects in eolian and fluvial domains.

Relevância:

100.00% 100.00%

Publicador:

Resumo:

Dissolved organic carbon (DOC) distribution and dynamics are investigated at the DYFAMED site (central Ligurian Sea, NW Mediterranean) in relation to hydrological and biological contexts, using a 4-year time-series dataset (1991-1994). The DYFAMED site is regarded as a one-dimensional station where simple hydrological mechanisms prevail and where the ecosystem is quite well understood. An average vertical profile of DOC concentration ([DOC]) indicates that maximal concentrations and variability are concentrated in the surface layers. For depths >800 m, the annual variations are on average similar to the analytical standard deviation (~2 µM). The "composite" [DOC] distribution (average distribution over a typical year, integrating about 40 monthly profiles) for surface waters (0-200 m) is closely related to hydrological and phytoplanktonic forcings. It exhibits summer DOC accumulation in surface waters, due to spring-summer stratification and successive phytoplanktonic events such as spring and summer blooms, and winter DOC removal to deeper waters, due to intense vertical mixing. The analysis of vertical [DOC] gradient at 100-m depth as a function of the integrated DOC content in the 0-100-m layer makes it possible to objectively distinguish three specific periods: the winter vertical mixing period, the period of stratification and spring phytoplankton bloom, and the period of stratification re-inforcement and summer-fall phytoplankton bloom. We recalculate the vertical DOC fluxes to deep waters using a larger original dataset, after the first direct calculation (Deep-Sea Res. 40 (10) (1993) 1963, 1972) that was reproduced for other oceanic areas. The seasonal variations of the "composite" [DOC] distribution in surface waters are significantly correlated to the apparent oxygen utilization distribution, but the biogeochemical significance of such a correlation is still under examination. The global significance of our local findings is presented and the role of the oceanic DOC in the global carbon cycle is emphasized, especially with respect to several current issues, such as the oceanic "missing sink" and the equivalence between new production and exported production.