Differentiation of charcoal, soot and diagenetic black carbon in soil: method comparison and perspectives
P.J. Roth, E. Lehndorff, S. Brodowski, L. Bornemann, L. Sánchez-García, Ö. Gustafsson, W. Amelung. Differentiation of charcoal, soot and diagenetic black carbon in soil: method comparison and perspectives. Organic Geochemistry. 2012, Vol. 46, p. 66-2012.
The cycling of carbon on the Arctic shelves, including outgassing of CO2 to the atmosphere, is not clearly understood.
Degradation of terrestrial organic carbon (OCter) has recently been shown to be pronounced over the East Siberian Arctic
Shelf (ESAS), i.e. the Laptev and East Siberian Seas, producing dissolved inorganic carbon (DIC). To further explore the
processes affecting DIC, an extensive suite of shelf water samples were collected during the summer of 2008, and assessed
for the stable carbon isotopic composition of DIC (d13CDIC). The d13CDIC values varied between 7.2& to +1.6& and
strongly deviated from the compositions expected from only mixing between river water and seawater. Model calculations
suggest that the major processes causing these deviations from conservative mixing were addition of (DIC) by degradation
of OCter, removal of DIC during primary production, and outgassing of CO2. All waters below the halocline in the ESAS
had d13CDIC values that appear to reflect mixing of river water and seawater combined with additions of on average
70 ± 20 lM of DIC, originating from degradation of OCter in the coastal water column. This is of the same magnitude as
the recently reported deficits of DOCter and POCter for the same waters. The surface waters in the East Siberian Sea had higher
d13CDIC values and lower DIC concentrations than expected from conservative mixing, consistent with additions of DIC
from degradation of OCter and outgassing of CO2. The outgassing of CO2 was equal to loss of 123 ± 50 lM DIC. Depleted
d13CPOC values of 29& to 32& in the mid to outer shelf regions are consistent with POC from phytoplankton production.
The low d13CPOC values are likely due to low d13CDIC of precursor DIC, which is due to degradation of OCter, rather than
reflecting terrestrial input compositions. Overall, the d13CDIC values confirm recent suggestions of substantial degradation of
OCter over the ESAS, and further show that a large part of the CO2 produced from degradation has been outgassed to the
atmosphere.
The cycling of carbon on the Arctic shelves, including outgassing of CO2 to the atmosphere, is not clearly understood.
Degradation of terrestrial organic carbon (OCter) has recently been shown to be pronounced over the East Siberian Arctic
Shelf (ESAS), i.e. the Laptev and East Siberian Seas, producing dissolved inorganic carbon (DIC). To further explore the
processes affecting DIC, an extensive suite of shelf water samples were collected during the summer of 2008, and assessed
for the stable carbon isotopic composition of DIC (d13CDIC). The d13CDIC values varied between 7.2& to +1.6& and
strongly deviated from the compositions expected from only mixing between river water and seawater. Model calculations
suggest that the major processes causing these deviations from conservative mixing were addition of (DIC) by degradation
of OCter, removal of DIC during primary production, and outgassing of CO2. All waters below the halocline in the ESAS
had d13CDIC values that appear to reflect mixing of river water and seawater combined with additions of on average
70 ± 20 lM of DIC, originating from degradation of OCter in the coastal water column. This is of the same magnitude as
the recently reported deficits of DOCter and POCter for the same waters. The surface waters in the East Siberian Sea had higher
d13CDIC values and lower DIC concentrations than expected from conservative mixing, consistent with additions of DIC
from degradation of OCter and outgassing of CO2. The outgassing of CO2 was equal to loss of 123 ± 50 lM DIC. Depleted
d13CPOC values of 29& to 32& in the mid to outer shelf regions are consistent with POC from phytoplankton production.
The low d13CPOC values are likely due to low d13CDIC of precursor DIC, which is due to degradation of OCter, rather than
reflecting terrestrial input compositions. Overall, the d13CDIC values confirm recent suggestions of substantial degradation of
OCter over the ESAS, and further show that a large part of the CO2 produced from degradation has been outgassed to the
atmosphere.