Impact of increased temperature and altered POC composition on soft-sediment ecosystems

The Atlantic Ocean as a whole is already experiencing significant abiotic changes and will continue to experience global climate change effects in the coming decades, which are expected to be more severe in some areas and more rapid in the deeper ocean layers, with decreased particulate organic carbon (POC) flux along with warmer temperatures. Since deep-sea ecosystems strongly depend on surface primary production and POC export flux to the seafloor, models predict that ocean warming and decline in POC quality will affect the deep benthic biomass in different ways, depending on regional productivity. In this sense, deepening knowledge of biodiversity and ecological processes in Atlantic deep benthic ecosystems can also help to predict their resilience in the face of future climate change projections.

Therefore, in this deliverable we developed an experimental approach with bottom sediments and their benthic communities sampled on the Cabo Verde Basin (CVB), Equatorial Atlantic during the iAtlantic iMirabilis2 expedition in August 2021. In order to characterize the benthic community, determine trophic webs, and assess and quantify the effects of climate change stressors on these benthic assemblages, we conducted an incubation enrichment experiment with 13C and 15N labelled diatoms Phaeodactylum tricornutum as organic matter and four different treatments aligned with climate projections (temperature and POC quality) for the next century.

We present preliminary results on the characterization of the macrofauna community from CVB, together with measurements of bacterial biomass, and the response of benthic organisms (Sediment Community Oxygen Consumption (SCOC) and Dissolved Inorganic Carbon (DIC) rates) to climate change stressors. We also compare these results with other studies in the Atlantic. These experimental approaches will be crucial in developing strategies for sustainable use of marine resources, living and non-living, in addition to advising the decision-making process for deep-sea habitat protection in areas of territorial economic exclusivity (EEZ’s).