@article{KallmeyerGreweGlombitzaetal.2015,
  author    = {Kallmeyer, Jens and Grewe, Sina and Glombitza, Clemens and Kitte, J. Axel},
  title     = {Microbial abundance in lacustrine sediments: a case study from Lake Van, Turkey},
  series = {International journal of earth sciences},
  volume    = {104},
  journal   = {International journal of earth sciences},
  number    = {6},
  publisher = {Springer},
  address   = {New York},
  issn      = {1437-3254},
  doi       = {10.1007/s00531-015-1219-6},
  pages     = {1667 -- 1677},
  year      = {2015},
  abstract  = {The ICDP "PaleoVan" drilling campaign at Lake Van, Turkey, provided a long (> 100 m) record of lacustrine subsurface sedimentary microbial cell abundance. After the ICDP campaign at Potrok Aike, Argentina, this is only the second time deep lacustrine cell counts have been documented. Two sites were cored and revealed a strikingly similar cell distribution despite differences in organic matter content and microbial activity. Although shifted towards higher values, cell counts from Lake Potrok Aike, Argentina, reveal very similar distribution patterns with depth. The lacustrine cell count data are significantly different from published marine records; the most probable cause is differences in sedimentary organic matter composition with marine sediments containing a higher fraction of labile organic matter. Previous studies showed that microbial activity and abundance increase centimetres to metres around geologic interfaces. The finely laminated Lake Van sediment allowed studying this phenomenon on the microscale. We sampled at the scale of individual laminae, and in some depth intervals, we found large differences in microbial abundance between the different laminae. This small-scale heterogeneity is normally overlooked due to much larger sampling intervals that integrate over several centimetres. However, not all laminated intervals exhibit such large differences in microbial abundance, and some non-laminated horizons show large variability on the millimetre scale as well. The reasons for such contrasting observations remain elusive, but indicate that heterogeneity of microbial abundance in subsurface sediments has not been taken into account sufficiently. These findings have implications not just for microbiological studies but for geochemistry as well, as the large differences in microbial abundance clearly show that there are distinct microhabitats that deviate considerably from the surrounding layers.},
  language  = {en}
}
@article{CockellVoytekGronstaletal.2012,
  author    = {Cockell, Charles S. and Voytek, Mary A. and Gronstal, Aaron L. and Finster, Kai and Kirshtein, Julie D. and Howard, Kieren and Reitner, Joachim and Gohn, Gregory S. and Sanford, Ward E. and Horton, J. Wright and Kallmeyer, Jens and Kelly, Laura and Powars, David S.},
  title     = {Impact disruption and recovery of the deep subsurface biosphere},
  series = {Astrobiology},
  volume    = {12},
  journal   = {Astrobiology},
  number    = {3},
  publisher = {Liebert},
  address   = {New Rochelle},
  issn      = {1531-1074},
  doi       = {10.1089/ast.2011.0722},
  pages     = {231 -- 246},
  year      = {2012},
  abstract  = {Although a large fraction of the world's biomass resides in the subsurface, there has been no study of the effects of catastrophic disturbance on the deep biosphere and the rate of its subsequent recovery. We carried out an investigation of the microbiology of a 1.76 km drill core obtained from the similar to 35 million-year-old Chesapeake Bay impact structure, USA, with robust contamination control. Microbial enumerations displayed a logarithmic downward decline, but the different gradient, when compared to previously studied sites, and the scatter of the data are consistent with a rnicrobiota influenced by the geological disturbances caused by the impact. Microbial abundance is low in buried crater-fill, ocean-resurge, and avalanche deposits despite the presence of redox couples for growth. Coupled with the low hydraulic conductivity, the data suggest the microbial community has not yet recovered from the impact similar to 35 million years ago. Microbial enumerations, molecular analysis of microbial enrichment cultures, and geochemical analysis showed recolonization of a deep region of impact-fractured rock that was heated to above the upper temperature limit for life at the time of impact. These results show how, by fracturing subsurface rocks, impacts can extend the depth of the biosphere. This phenomenon would have provided deep refugia for life on the more heavily bombarded early Earth, and it shows that the deeply fractured regions of impact craters are promising targets to study the past and present habitability of Mars.},
  language  = {en}
}