Recent distribution and accumulation of organic carbon on the continental margin west off Spitsbergen

Abstract

[1] The study compiles the controlling factors for organic matter sedimentation patterns from a suite of organogeochemical parameters in surface sediments off Spitsbergen and direct seabed observations using a Remotely Operated Vehicle (ROV). In addition we assess its storage rates as well as the potential of carbon sinks on the northwestern margin of the Barents Sea with short sediment cores from a selected fjord environment (Storfjord). While sedimentation in the fjords is mainly controlled by river/meltwater discharge and coastal erosion by sea ice/glaciers resulting in high supply of terrigenous organic matter, Atlantic water inflow, and thus enhanced marine organic matter supply, characterizes the environment on the outer shelf and slope. Local deviations from this pattern, particularly on the shelf, are due to erosion and out washing of fine-grained material by bottom currents. Spots dominated by marine productivity close to the island have been found at the outer Isfjord and west off Prins Karls Forland as well as off the Kongsfjord/Krossfjord area and probably reflect local upwelling of nutrient-rich Atlantic water-derived water masses. Accumulation rates of marine organic carbon as well as reconstructed primary productivities decreased since the middle of the last century. Negative correlation of the Isfjord temperature record with reconstructed productivities in the Storfjord could be explained by a reduced annual duration of the marginal ice zone in the area due to global warming. Extremely high accumulation rates of marine organic carbon between 5.4 and 17.2 g m À2 yr À1 mark the Storfjord area, and probably high-latitude fjord environments in general, as a sink for carbon dioxide.

Middle to late Holocene paleoproductivity reconstructions for the western Barents Sea: a model-data comparison

“…Paleoproductivity (PP) reconstruction for the last 100 years from organic carbon burial in Storfjorden, southern Spitsbergen, shows a negative correlation to shrinking sea ice and increasing air temperatures [76]. This suggests that less sea ice in the Barents Sea may not cause an increase in marine productivity contrary to what is suggested by Ellingsen et al [11].…”

“…The prominent decline in production rates in our northernmost location (St1245) has previously been explained by a reduced annual duration of the MIZ in the area due to global warming [76]. Interestingly, a parallel site (JM10) shows a similar pattern with a gradual PP decline towards the present day.…”

“…The cores were sub-sectioned and samples were frozen at -20°C until freeze-drying prior to analyses. The current investigations are supplemented by published results from Winkelmann and Knies [76] (multicore St1245) and Risebrobakken et al [48] (gravity core PSh-5159N). Core JM10-10GC is referred to as JM10 in text and figures and core R87MC006 as R87.…”

“…The episodic melting/freezing of sea ice in the polynya seems to allow for constant high production rates (Fig. 7) and high organic carbon burial [76] with seemingly little influence of cold/ warm spells during the last 1000 years. In contrast, the drop at MIZ location St20 around 500 years BP may be the result of the climate deterioration during the Medieval Climate Anomaly (MCA)/Little Ice Age (LIA) transition.…”

“…Marine organic carbon (MOC) and terrestrial organic matter (TOM) were distinguished in Barents Sea sediments using a mixing model based on total organic carbon (TOC), nitrogen content, and stable isotopes of organic matter (d 13 C org ) [29,40,76] to define the endmembers of the mixing model. For the purposes of this paper, the set of Barents Sea surface samples of Knies and Martinez [29] is used as the calibration data set and the endmembers determined therein are used here.…”