Biogeochemical consequences of a changing Arctic shelf seafloor ecosystem

Abstract

Unprecedented and dramatic transformations are occurring in the Arctic in response to climate change, but academic, public, and political discourse has disproportionately focussed on the most visible and direct aspects of change, including sea ice melt, permafrost thaw, the fate of charismatic megafauna, and the expansion of fisheries. Such narratives disregard the importance of less visible and indirect processes and, in particular, miss the substantive contribution of the shelf seafloor in regulating nutrients and sequestering carbon. Here, we summarise the biogeochemical functioning of the Arctic shelf seafloor before considering how climate change and regional adjustments to human activities may alter its biogeochemical and ecological dynamics, including ecosystem function, carbon burial, or nutrient recycling. We highlight the importance of the Arctic benthic system in mitigating climatic and anthropogenic change and, with a focus on the Barents Sea, offer some observations and our perspectives on future management and policy.

Benthic Organic Matter Transformation Drives pH and Carbonate Chemistry in Arctic Marine Sediments

“…Benthic OM degradation is donor controlled (Burdige, 2006) and rates of OM degradation in the Barents Sea scale with OM input at the SWI (März et al., 2022). Our results show that changes in OM input exert an important influence on carbonate precipitation, and to a lesser extent on dissolution rates (Figure 8).…”

“…Calcite dissolution rates slightly increase with lower OM deposition at the northern sites due to a shift in metabolic pathways. An OM content that is half of baseline conditions increases the relative contribution of aerobic OM degradation from 52% to 74% (Freitas et al., 2020) to 68%–88% (März et al., 2022). Under such conditions, there is deepening of the oxic layer into the sediments, which generally results in sustained low pH values (Forja et al., 2004; Jourabchi et al., 2005; Mucci et al., 2000; Soetaert et al., 2007).…”

“…Mechanistically understanding how these processes will critically tip the delicate balance of pH and carbonate dynamics in Arctic Ocean sediments is crucial. The Arctic Ocean is rapidly changing and will continue to do so (Huntington et al., 2022; Khosravi et al., 2022; März et al., 2022; Thomas et al., 2022; Tuerena et al., 2022). Here, we offer some systematic insights that can help in building a comprehensive picture for the entire Barents Sea shelf and foster further investigations to interrogate other biogeochemical drivers.…”

“…Further, using a similar approach employed in our previous work (März et al., 2022), we explore how the effect of changes in OM deposition fluxes at the SWI may impact carbonate dynamics at the seafloor. We emphasize that our sensitivity tests are limited to just a few factors because the model has already been carefully calibrated and validated for the present‐day dynamics on the basis of a comprehensive porewater and sediment data set (Freitas et al., 2020) and it is beyond our scope to explore the response of benthic fluxes to the full range of projected environmental change.…”

“…Here, we select sedimentation rates, OM, metal oxide, and calcite to offer a first‐order estimate of how the benthic carbonate system may respond to changes in these input fluxes. More specifically, from our baseline conditions (this work; Freitas et al., 2020; März et al., 2022), we test the following cases at each site: 2x sedimentation rates; 0.5x and 2x OM; 0.5x and 2x calcite; 0.5x and 2x metal oxides. We use these outputs to assess the impact on rates of dissolution and precipitation, as well as benthic fluxes of DIC and TA.…”