Organic Carbon Origin, Benthic Faunal Consumption, and Burial in Sediments of Northern Atlantic and Arctic Fjords (60-81°N)

Fjords have been recently recognized as hot spots of organic carbon (C-org) sequestration in marine sediments. This study aims to identify regional and local drivers of variability of C-org burial in north Atlantic and Arctic fjords. We provide a comparative quantification of C-org, delta C-13, photosynthetic pigments content, benthic biomass, consumption, C-org accumulation, and burial rates in sediments in six fjords (60-81 degrees N). Higher sediment C-org content in southern Norway reflected longer phytoplankton growth season and higher productivity. Higher contributions of terrestrial C-org were noted in temperate/southern Norway (dense land vegetation and high precipitation) and Arctic/Svalbard (glacial erosion) than in subarctic/northern Norway locations. Benthic biomass and carbon consumption were best correlated to delta C-13 and photosynthetic pigments content indicating control by quality rather than quantity of available food. Benthic faunal consumption did not seem to affect the variability in C-org burial. Regional environmental factors (water temperature and latitude) combined with local factors (C-org, grain size, and pigment concentration) explained 94% of C-org burial variability. Based on the present study and literature data on C-org content, origin, and burial rates, the fjords were classified into four categories: temperate, subarctic, Arctic with glaciers, and Arctic without glaciers. The variability in marine productivity, terrestrial inflows, and carbon sequestration in fjords must be considered for global estimates of their role in blue carbon storage and for building scenarios of future changes in the course of climate warming.