25th International Meeting on Organic Geochemistry IMOG 2011

P-170
Microbial activity and abundance in sediments Lake Van
(Turkey), first results from ICDP Project PALEOVAN
Clemens Glombitza, Jens Kallmeyer
University of Potsdam, Potsdam, Germany (corresponding author:clemens.glombitza@geo.uni-potsdam.de)
Studies during the past two decades have
demonstrated the importance of microbial life in the
deep subsurface. So far, most studies focused on life
in the subseafloor, only few dealt with terrestrial
environments. With the exception of some very few
and solitary projects, lacustrine sediments received
almost no attention.
In summer 2010 the ICDP drilling operation at Lake
Van (Eastern Anatolia, Turkey) recovered long
sediment cores at two sites (Northern Basin and Ahlat
Ridge). At both sites, sample material was obtained
from undisturbed core catchers and selected whole
round cores, ranging in depth from the sediment
surface down to 140 mblf (meters below lake floor).
Coring was mainly carried out by hydraulic piston
coring, providing largely uncontaminated samples, as
seen by the porewater composition in the sample.
However, certain intervals with thick layers of volcanic
ash required extended core barrel and rotary coring,
the obtained cores were at least partially infiltrated by
drilling fluid. Additionally, short gravity cores of 75 cm
length were retrieved at both sites, providing the
undisturbed sediment-water interface, which is too
liquid to be recovered by hydraulic coring.
Radiotracer experiments for the quantification of
sulfate reduction, anerobic oxidation of methane and
methanogenesis were initiated on site, using the
mobile Geomicrobiology Laboratory BugLab, owned
by GFZ Potsdam. Porewater was squeezed and split
between the different working groups. Samples for
cell enumeration and anion porewater analysis were
preserved for analysis at the University of Potsdam.
Although the distance between the two sites is only
approx. 7 km, they exhibit significant differences,
both in porewater geochemistry and in microbial
abundance and activity.
The results of the cell enumeration are strikingly
different to marine sediments. Whether these trends
are the result of sedimentological changes or lateral
fluid flow remains unclear at the moment, as a full
sedimentological description of the cores is still
lacking. Cell abundance appears to be slightly higher
at the Northern Basin site, at which sulfate reduction
rates measured by radiotracer are also generally
higher than at Ahlat Ridge. Despite the higher sulfate
reduction rates at the Norther Basin site, sulfate
penetrates down to 40 mblf, about twice as deep than
at Ahlat Ridge. This is most probably caused by the
lateral influx of a saline brine between 20 and 40 mblf.
The significant biogeochemical differences between
both sites indicate that lacustrine sediments are very
sensitive to changes in sedimentary and organic
matter input. Studies of the deep subsurface of lake
sediments are still in their infancy but due to strong
biogeographical gradients they may offer a unique
chance to study the effects of even small geological
changes on deep subsurface life.
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