Surface Sediment Accumulation and Fluxes of Diatom Species, Biogenic Opal and Particulate Organic Carbon in the Gulf of Maine

The productive Gulf of Maine shelf system is generally divided into eastern and western regions based on hydrography. The eastern gulf exhibits weaker stratification, stronger tidal flows, periodic upwelling, and higher nutrient levels than the more stratified western gulf. We hypothesize that diatom fluxes and accumulation will be distinctly different between the east and west, reflecting the variable water column characteristics. While it has been shown that inter- and intra-annual variations exist between western and eastern gulf regions in terms of the mass flux of organic carbon and biogenic opal, the seasonal flux and deep-water delivery of diatoms has not been examined. In the present study, time-series sediment traps were deployed in Wilkinson and Jordan Basins (western and eastern gulf, respectively) to quantify the inter-annual variation of total and individual diatom species fluxes, as well as simultaneous particulate organic carbon (POC) and opal exports. Surface sediments at both locations were also collected and analyzed for diatom accumulation. Distinct inter-basinal differences were observed in which the mean, daily subsurface diatom (valve) flux measured in Jordan Basin was 4-fold greater than that for Wilkinson Basin. In both regions, Thalassionema nitzschioides was found to be a common species in all trap-collected samples, though the seasonal abundance levels of the species varied substantially between regions. Comparison of the species' abundance in upper-water column traps to near-bottom traps revealed a strong depth-related decrease of T. nitzschioides in the eastern versus the western gulf. This finding may partially explain the similar percentage of T. nitzschioides in the surface sediments of both regions (~8.4% of total planktonic diatom valves) despite the greater upper water column fluxes in the east. We discuss implications of these data relative to the use of T. nitzschioides as a recent paleo-proxy of primary production in the gulf.