Where is the Carbon? Spatially Mapping Organic Carbon on the Seafloor in the Eastern Shore Islands, Nova Scotia, Canada

Abstract

Coastal sediments contain some of the largest stocks of organic carbon on earth and play a vital role in influencing the carbon cycle. Protecting organic carbon hotspots is essential to mitigating climate change since coastal development and bottom trawling can disturb the seafloor, driving the remineralization of organic carbon into carbon dioxide. Terrestrial carbon stocks are well studied and mapped, but our knowledge of standing stocks of marine sedimentary carbon and the role that it can play in minimizing the effects of climate change are poorly understood. One of the challenges in mapping the seafloor environment is the issue of characterizing spatial heterogeneity of different substrata, which is critical in estimating organic carbon standing stocks in the marine environment. In this study, we use high-resolution multibeam echosounder (MBES) data from the Eastern Shore Islands off Nova Scotia to predict the distribution of percent organic carbon in surface sediments. We applied benthic habitat mapping approaches, utilizing high-resolution continuous coverage environmental variables (bathymetry, backscatter, ruggedness, and slope) combined with subsea video and sediment grab sample ground truthing to generate thematic maps of sediment types for the area. We then compared that to organic carbon measurements from the sediment samples to estimate organic carbon standing stocks by substrate type. The sediment map had a 60 % mean of the squared prediction error, yet the substrate pattern was like previous substrate maps that were done in the Eastern Shore Islands. We also found that the standing stock of carbon range was 613,536 to 10,915,548 kg/km2. Our findings demonstrated that high-resolution sediment classification maps are necessary to improve our understanding of spatial patterns of OC. They can also help identify carbon hotspots, which are essential for seabed management and climate mitigation strategies. Key words: Organic Carbon, Ocean Sediment, Seafloor Mapping, Marine Carbon Stocks, Seabed Acoustics