1272 / 2024-09-20 21:41:30

Understanding spatial differences in particulate organic carbon in Kongsfjorden sediments by fractionating particle size and density

arctic,sediment,Isotope,svalbard,fractionation

Rapid changes in Arctic climate, such as warming and desalination of the Arctic Ocean, are increasing the amount of organic carbon entering the ocean. Fjords are areas with high organic carbon burial rates per unit area, up to 100 times the global average. It is estimated that 55–62% of this organic carbon is of terrestrial origin, making it a large source of organic carbon from terrestrial sources. Physical properties such as particle size and density are important in the transport and deposition of organic matter in suspended solids. In this study, we separated sediments of Kongsfjorden by particle size and density to determine the composition, transport mechanisms, and origin of organic carbon based on their physical properties. Samples were collected from surface sediments at seven stations in the inner fjord, approximately 4km from Kronebreen, from the inner fjord outward to the outer fjord. The surface sediments were separated into three ranges based on grain size and density, and the separated Kongsfjorden sediments were analyzed for carbon and nitrogen concentrations, stable isotopes. As for grain size, the proportion of grains smaller than 20μm was highest at all stations except for St.5, located at the mouth of the Bayelva River, the largest river in Kongsfjorden. St.5 had the highest proportion of particles larger than 63μm, which is thought to be due to the deposition of larger particles from the river. OC and TN increased in value towards the outer fjord, which is thought to be due to higher turbidity in the inner fjord and higher primary production in the outer fjord. The C/N molar ratio showed a decreasing trend in sediments smaller than 20μm towards the outer fjord, which is interpreted to mean that sediments smaller than 20μm are more influenced by marine organic matter towards the outer fjord. δ¹³C showed a decreasing trend towards the outer fjord in all samples except for sediments larger than 63μm, which is thought to be due to the lower δ¹³C values of phytoplankton in the lower temperature region, with decreasing values towards the outer fjord where biomass is higher. In addition, the C/N molar ratio and δ¹³C values in sediments larger than 63μm suggest that the sediments larger than 63 are strongly influenced by glaciers at sites 1 and 2, rivers at sites 3, 4, 5, and 6, and primary production at sites 6 and 7, with similar ranges of values at each station.