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  • Nature Research  (2)
  • ELSEVIER SCIENCE BV  (1)
  • 1
    Publication Date: 2021-02-08
    Description: The Kryos Basin is a deep-sea hypersaline anoxic basin (DHAB) located in the Eastern Mediterranean Sea (34.98°N 22.04°E). It is filled with brine of re-dissolved Messinian evaporites and is nearly saturated with MgCl2-equivalents, which makes this habitat extremely challenging for life. The strong density difference between the anoxic brine and the overlying oxic Mediterranean seawater impedes mixing, giving rise to a narrow chemocline. Here, we investigate the microbial community structure and activities across the seawater–brine interface using a combined biogeochemical, next-generation sequencing, and lipid biomarker approach. Within the interface, we detected fatty acids that were distinctly 13C-enriched when compared to other fatty acids. These likely originated from sulfide-oxidizing bacteria that fix carbon via the reverse tricarboxylic acid cycle. In the lower part of the interface, we also measured elevated rates of methane oxidation, probably mediated by aerobic methanotrophs under micro-oxic conditions. Sulfate reduction rates increased across the interface and were highest within the brine, providing first evidence that sulfate reducers (likely Desulfovermiculus and Desulfobacula) thrive in the Kryos Basin at a water activity of only ~0.4 Aw. Our results demonstrate that a highly specialized microbial community in the Kryos Basin has adapted to the poly-extreme conditions of a DHAB with nearly saturated MgCl2 brine, extending the known environmental range where microbial life can persist.
    Type: Article , PeerReviewed
    Format: text
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  • 2
    Publication Date: 2020-06-18
    Description: Investigating past interglacial climates not only help to understand how the climate system operates in general, it also forms a vital basis for climate predictions. We reconstructed vertical stratification changes in temperature and salinity in the North Atlantic for a period some 400 ka ago (MIS11), an interglacial time analogue of a future climate. As inferred from a unique set of biogeochemical, geochemical, and faunal data, the internal upper ocean stratification across MIS 11 shows distinct depth-dependent dynamical changes related to vertical as well as lateral shifts in the upper Atlantic meridional circulation system. Importantly, transient cold events are recognized near the end of the long phase of postglacial warming at surface, subsurface, mid, and deeper water layers. These data demonstrate that MIS 11 coolings over the North Atlantic were initially triggered by freshwater input at the surface and expansion of cold polar waters into the Subpolar Gyre. The cooling signal was then transmitted downwards into mid-water depths. Since the cold events occurred after the main deglacial phase we suggest that their cause might be related to continuous melting of the Greenland ice sheet, a mechanism that might also be relevant for the present and upcoming climate.
    Type: Article , PeerReviewed
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  • 3
    Publication Date: 2019-07-17
    Description: Although commonly reported in marine and freshwater environments, little is known about the biological sources of long chain alkyl 1,13- and 1,15-diols, and factors controlling their distributions. Here we analyzed the occurrence and distribution of these lipids in a comprehensive set of marine surface sediments and compare their distributions with environmental conditions like sea surface temperature (SST), salinity and nutrient concentrations. Fractional abundances of the C28 1,13-, C30 1,13- and C30 1,15-diols show a strong correlation with SST and based on these results, we propose the Long chain Diol Index (LDI), which expresses the C30 1,15-diol abundance relative to those of C28 1,13-, C30 1,13- and C30 1,15-diols. The LDI shows a strong linear correlation with SST (LDI = 0.033 � SST + 0.095; R2 = 0.969, n = 162) over a temperature range of �3 to 27 �C. Long chain diol distributions in sediments from the South Atlantic close to the Congo River outflow (West Africa) provided a 43 kyr LDI SST record. This record reflects several known climatic events and shows similarities with an alkenone- derived SST record obtained using the same suite of sediments, both in trend and in terms of absolute SST. This confirms the potential of the LDI as a proxy for palaeo-SST reconstruction.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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