FORAMINIFERAL CONTRIBUTION TO SEDIMENTARY CARBON POOL IN HIGH-LATITUDE FJORDS

Benthic foraminifera are amongst the most abundant calcifying organisms in modern oceans, but their role in carbon burial processes remains understudied and thus unknown. As the increase of CO₂ is one of the main drivers behind modern global warming, it is important to assess the pathways of carbon burial. Our study is the first to quantify the contribution of foraminiferal carbon to the sedimentary carbon pool of Norwegian fjords. In our study we 1) calculated the amount of foraminifera-derived organic and inorganic carbon in sediments of selected fjords and 2) defined the factors that potentially impacted the amount of foraminiferal carbon. Our study was conducted in four high-latitude fjords, one located in Svalbard, one located in northern Norway and two located in southern Norway. The study sites were chosen because 1) high-latitude fjords are important carbon sinks due to their high sedimentation rates and high supply of terrestrial organic matter 2) the high-latitude location of fjords makes them more susceptible to the modern climate as the Arctic warms up faster than the rest of the world. We found that foraminifera can make up to 39% of the inorganic carbon pool in the sediments studied fjords. In the southern Norwegian fjords, the contribution of foraminiferal carbon to the inorganic carbon pool was lower but still reached over 15%. However, the contribution of foraminifera to the organic carbon pool was low and did not exceed 5% in all study stations. We also found that foraminifera abundance was not the only factor dictating the amount of foraminifera-derived carbon. The species composition was also important, as large foraminifera with thick tests (i. e. Nonionellina labradorica) contributed to the sedimentary carbon pool most significantly. Species associated with low-oxygen conditions (i. e. Bolivina skagerrakensis and Stainforthia fusiformis) were found to have a low carbon content in their tests, most probably due to their thin tests being an adaptation to dysoxic conditions. Our results imply that benthic foraminifera could play an important role in inorganic carbon burial in the sediments, and the increasing ocean deoxygenation could potentially lead to a decrease of foraminiferal inorganic carbon in the sediments of high-latitude fjords.