Organic carbon burial and sediment accumulation in the fjords of South Georgia, sub-Antarctic

Abstract

Fjords are among the most efficient marine environments for trapping sediments and organic carbon (OC). They represent an important part of the global carbon cycle. Yet, quantitative data on OC burial rates are scarce in the Southern Hemisphere. Here, we present 210Pb-derived sediment accumulation rates (SAR), OC burial rates, and sediment properties from 10 sediment cores collected in the fjords of South Georgia, the largest sub-Antarctic island: Antarctic Bay, Fortuna Bay, Stromness Bay, and Cumberland Bay. SARs range from 2.1 ± 0.4 to 14.9 ± 2.8 mm/yr, total organic carbon (TOC) from 0.28% to 2.1%, and modern OC burial rates from 17.4 ± 1.2 to 64.6 ± 12.1 gOC/m2/yr, placing them towards the upper range of values reported globally. High rates reflect large sediment supply from steep, glacierised catchments, intense precipitation, and relatively high primary productivity. A strong relationship between SAR and OC burial rate indicates sediment delivery as the primary control, with the highest modern OC burial rate at a glacier-proximal site combining the highest SAR and lowest TOC. Tidewater glacier-fed fjords show higher SAR and OC burial rates than river-dominated systems. However, the maximum recorded burial rate (95.9 ± 8.3 gOC/m2/yr) occurred in King Edward Cove during the early 20th century, driven by the whaling industry, while the modern value (55.5 ± 4.8) is about half. These results suggest that OC burial in tidewater glacier-dominated fjords may increase in the short term under warming due to enhanced meltwater discharge, but decline in the longer term as retreat transforms fjords into river-dominated systems.