Sediment accumulation rates and carbon burial in West Antarctic Peninsula fjords

Abstract

Fjords act as palaeoenvironmental archives, recording past glacial histories in remarkably thick sediment accumulations. Furthermore, high primary productivity combined with rapid burial make fjords important organic carbon sinks. Reconstructing recent rates of sediment accumulation provides context for assessing past and future changes, and, in combination with measurements of carbon content, can inform on carbon sequestration potential. Recent research has indicated that fjords may represent areas of high carbon burial. However, these estimates are based on surface sediment carbon stocks combined with global averages of carbon preservation, without consideration of regional variability in burial efficiencies.

Here, seven sediment cores from three fjords on the Antarctic Peninsula are analysed. 210Pb, a radio-isotope with a half-life of 22 years, is used to construct age-depth models and estimate rates of sediment mass accumulation. These data are then combined with measurements of core carbon content to estimate rates of modern carbon deposition and long-term carbon burial.

Core-averaged sediment mass accumulation rates ranged from 0.08 to 0.42 g cm-2 yr-1. No long-term trends in accumulation rates were observed at any of the sites over the past century, though in Börgen Bay synchronous peaks in sedimentation rates were observed at similar ages across different sediment cores. At Marian Cove, South Shetland Islands, the typical proximal-distal gradient in accumulation rates was absent, suggesting a diverse source of sediments, most notably the input from pro-glacial meltwater streams from land-terminating ice.

Surface deposition rates of organic carbon ranged from 3 to 26 g C m-2 yr-1. However, whilst surface sediment organic carbon flux was high, burial efficiencies were found to be significantly lower than those previously reported for other sites on the continental shelf, resulting in similar rates of long-term storage. This has important implications for our understanding of the carbon sequestration potential of high-latitude fjords.