Carbon isotopes and lipid biomarker investigation of sources, transport and degradation of 1 terrestrial organic matter in the Buor-Khaya Bay, SE Laptev Sea
E.S. Karlsson, A. Charkin, O. Dudarev, I. Semiletov, J.E.Vonk, L. Sánchez-García, A. Andersson and Ö. Gustafsson. Carbon isotopes and lipid biomarker investigation of sources, transport and degradation of 1 terrestrial organic matter in the Buor-Khaya Bay, SE Laptev Sea. Biogeosciences. 2011, Vol. 8, p. 1865-2011.
The world’s largest continental shelf, the East
Siberian Shelf Sea, receives substantial input of terrestrial
organic carbon (terr-OC) from both large rivers and erosion
of its coastline. Degradation of organic matter from thawing
permafrost in the Arctic is likely to increase, potentially
creating a positive feedback mechanism to climate warming.
This study focuses on the Buor-Khaya Bay (SE Laptev Sea),
an area with strong terr-OC input from both coastal erosion
and the Lena river. To better understand the fate of this terr-
OC, molecular (acyl lipid biomarkers) and isotopic tools (stable
carbon and radiocarbon isotopes) have been applied to
both particulate organic carbon (POC) in surface water and
sedimentary organic carbon (SOC) collected from the underlying
surface sediments.
Clear gradients in both extent of degradation and differences
in source contributions were observed both between
surface water POC and surface sediment SOC as well as over
the 100 s km investigation scale (about 20 stations). Depleted
13C-OC and high HMW/LMW n-alkane ratios signaled that
terr-OC was dominating over marine/planktonic sources.
Despite a shallow water column (10–40 m), the isotopic
shift between SOC and POC varied systematically from +2
to +5 per mil for 13C and from +300 to +450 for 114C from
the Lena prodelta to the Buor-Khaya Cape. At the same time, the ratio of HMW n-alkanoic acids to HMW n-alkanes as
well as HMW n-alkane CPI, both indicative of degradation,
were 5–6 times greater in SOC than in POC. This suggests
that terr-OC was substantially older yet less degraded in the
surface sediment than in the surface waters. This unusual
vertical degradation trend was only recently found also for
the central East Siberian Sea.
Numerical modeling (Monte Carlo simulations) with 13C
and 114C in both POC and SOC was applied to deduce the
relative contribution of – plankton OC, surface soil layer
OC and yedoma/mineral soil OC. This three end-member
dual-carbon-isotopic mixing model suggests quite different
scenarios for the POC vs SOC. Surface soil is dominating
(63±10 %) the suspended organic matter in the surface water
of SE Laptev Sea. In contrast, the yedoma/mineral soil
OC is accounting for 60±9% of the SOC. We hypothesize
that yedoma-OC, associated with mineral-rich matter from
coastal erosion is ballasted and thus quickly settles to the
bottom. The mineral association may also explain the greater
resistance to degradation of this terr-OC component. In contrast,
more amorphous humic-like and low-density terr-OC
from surface soil and recent vegetation represents a younger
but more bioavailable and thus degraded terr-OC component
held buoyant in surface water. Hence, these two terr-
OC components may represent different propensities to contribute
to a positive feedback to climate warming by converting
OC from coastal and inland permafrost into CO2.
The world’s largest continental shelf, the East
Siberian Shelf Sea, receives substantial input of terrestrial
organic carbon (terr-OC) from both large rivers and erosion
of its coastline. Degradation of organic matter from thawing
permafrost in the Arctic is likely to increase, potentially
creating a positive feedback mechanism to climate warming.
This study focuses on the Buor-Khaya Bay (SE Laptev Sea),
an area with strong terr-OC input from both coastal erosion
and the Lena river. To better understand the fate of this terr-
OC, molecular (acyl lipid biomarkers) and isotopic tools (stable
carbon and radiocarbon isotopes) have been applied to
both particulate organic carbon (POC) in surface water and
sedimentary organic carbon (SOC) collected from the underlying
surface sediments.
Clear gradients in both extent of degradation and differences
in source contributions were observed both between
surface water POC and surface sediment SOC as well as over
the 100 s km investigation scale (about 20 stations). Depleted
13C-OC and high HMW/LMW n-alkane ratios signaled that
terr-OC was dominating over marine/planktonic sources.
Despite a shallow water column (10–40 m), the isotopic
shift between SOC and POC varied systematically from +2
to +5 per mil for 13C and from +300 to +450 for 114C from
the Lena prodelta to the Buor-Khaya Cape. At the same time, the ratio of HMW n-alkanoic acids to HMW n-alkanes as
well as HMW n-alkane CPI, both indicative of degradation,
were 5–6 times greater in SOC than in POC. This suggests
that terr-OC was substantially older yet less degraded in the
surface sediment than in the surface waters. This unusual
vertical degradation trend was only recently found also for
the central East Siberian Sea.
Numerical modeling (Monte Carlo simulations) with 13C
and 114C in both POC and SOC was applied to deduce the
relative contribution of – plankton OC, surface soil layer
OC and yedoma/mineral soil OC. This three end-member
dual-carbon-isotopic mixing model suggests quite different
scenarios for the POC vs SOC. Surface soil is dominating
(63±10 %) the suspended organic matter in the surface water
of SE Laptev Sea. In contrast, the yedoma/mineral soil
OC is accounting for 60±9% of the SOC. We hypothesize
that yedoma-OC, associated with mineral-rich matter from
coastal erosion is ballasted and thus quickly settles to the
bottom. The mineral association may also explain the greater
resistance to degradation of this terr-OC component. In contrast,
more amorphous humic-like and low-density terr-OC
from surface soil and recent vegetation represents a younger
but more bioavailable and thus degraded terr-OC component
held buoyant in surface water. Hence, these two terr-
OC components may represent different propensities to contribute
to a positive feedback to climate warming by converting
OC from coastal and inland permafrost into CO2.