Abstract
Recently, the discovery of active microbial life in deep-sea sediments has triggered a rapid development of the field known as the “deep biosphere.” Geomicrobiological investigations in lacustrine basins have also shown a substantial microbial impact on lake sediments similar to that described for the marine record. Although only 30 % of the lake sites drilled by the International Continental Drilling Program (ICDP) have included microbial investigations, these lakes cover a relatively wide range of salinities (from 0.15 to 33.8 %), pH (from 6.0 to 9.8) and environmental conditions (from very arid to humid subtropical conditions). Here, we analyze results of very recent ICDP lake sites including subsurface biosphere research from southern Patagonia (Laguna Potrok Aike) to the Levantine area (Dead Sea) as well as the East Anatolian high plateau (Lake Van) and Macedonia (Lake Ohrid). These various settings allow the examination of the impact of contrasting environments on microbial activity and their subsequent role during early diagenesis. Furthermore, they permit the identification of biosignatures of former microbial activity recorded in the sediments as well as investigating the impact of microbes in biogeochemical cycles. One of the general outcomes of these preliminary investigations is data to support the hypothesis that microbes react to climatically driven environmental changes that have a direct impact on their subsurface distribution and diversity. This is clear at conspicuous levels associated with well-known climatic periods such as the Medieval Climatic Anomaly or the Little Ice Age. Although more research is needed, this relationship between prevailing microbial assemblages and different climatic settings appears to dominate the lacustrine sites studied until to date.
Highlights
In the past few years, geomicrobiological investigations in the lacustrine subsurface have shown that microbial metabolism, as in their marine counterparts, can have a substantial impact on lake sediments
While ocean drilling programs (ODP and IODP) pioneered the study of the “deep biosphere” (e.g., D’Hondt et al 2002, 2004; Hinrichs and Inagaki 2012; Horsfield et al 2006; Inagaki 2010; Lever et al 2013; Lomstein et al 2012; Røy et al 2012), lake sediments provide a range of characteristics worth investigating
The lake has been the target of multidisciplinary investigations through continental drilling
Summary
In the past few years, geomicrobiological investigations in the lacustrine subsurface have shown that microbial metabolism, as in their marine counterparts, can have a substantial impact on lake sediments. We present an overview of the scientific results already available from these sites (Fig. 3, large gray dots) to provide plausible answers to some fundamental standing questions in the field of geomicrobiology They include (1) the impact of environmental change on the subsurface biosphere; (2) its influence on paleoenvironmental and paleoclimatical proxies, minerals and hydrocarbon reservoirs; (3) the source, composition and significance of subsurface communities; and (4) the limits of life in the subsurface of lakes under contrasting physicochemical conditions. We propose a close collaboration with the marine research community to draw upon the much wider experience in sampling and sampling handling already gained during a large number of IODP drilling operations This subsaline maar lake is located in a volcanic field in the southernmost tip of Patagonia, east of the Andes cordillera at 51°58′S and 70°22′W (Fig. 3). The lake has been the target of multidisciplinary investigations through continental drilling
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