Matthew James Mason

Despite increasing recognition of the importance of polar fjords as an emerging carbon sink, relatively few estimates of organic carbon stocks, deposition and accumulation potential exist for the West Antarctic Peninsula (WAP). We assessed the long-term accumulation of organic carbon in three deglaciating Antarctic fjords by combining total organic carbon (TOC) and 210Pb measurements. These data enabled calculations of carbon flux and sequestration (carbon remaining after 100 years), while the susceptibility of the carbon pool to further degradation was assessed by thermogravimetric analysis (TGA). Organic carbon surface deposition rates were highly variable (11.99 ± 8.27 g C m-2 yr-1), while organic carbon burial rates were more consistent (3.55 ± 1.75 g C m-2 yr-1). Burial efficiencies ranged from 30.59% to 54.44% (mean 39.84%). These results are comparable with previous predictions of carbon sequestration in WAP fjords, highlighting the role of fjords as global hotspots of long-term accumulation, and support the hypothesis that deglaciating polar fjords act as a significant negative (mitigating) feedback on global climate change.

Our understanding of the marine system is limited by the brevity of instrumental time series relative to the timescales of potential natural climatic and ecological variability. Sclerochronology, the study of the variability in annual growth increments in marine and aquatic organisms, has increasingly been used to reconstruct pre-instrumental marine variability. However, these sclerochronological records remain relatively sparse and drivers of growth are not fully understood. The English Channel hosts one of the longest-running marine climatological and ecological monitoring stations in the world - the Western Channel Observatory's E1 mooring station - as well as regular routes for the Continuous Plankton Recorder (CPR) survey. It also contains an abundant population of Glycymeris glycymeris, a key species in sclerochronological research. Here, we present the first centennial length sclerochronology for the English Channel, covering CE 1884-2012. The G. glycymeris chronology demonstrates statistically significant positive correlations (p < 0.05) with both sea surface temperature (SST) (r = 0.58) and bottom water temperature (r = 0.53) at the sampling site. Split-calibration verification statistics confirm that the chronology contains significant skill at reconstructing local SST. Notably, the chronology exhibits a significant negative correlation (p < 0.05) with phytoplankton abundance as captured by the CPR, though shows no significant relationship with the Phytoplankton Colour Index, a proxy for primary productivity. These results suggest that G. glycymeris may feed on a mixed food-source of small phytoplankton and non-planktonic organic matter, with implications for benthic-pelagic coupling. Overall, our results show that G. glycymeris growth-increment chronologies can serve as reliable proxies for past SSTs, though further research is necessary to clarify how these relationships are mediated by pelagic ecosystems.