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Supplementary data to: Characterizing regional oceanography and bottom environmental conditions at two contrasting sponge grounds on the northern Labrador Shelf.

<p>Supplementary data to the article:&nbsp;</p> <p><strong>Characterizing regional oceanography and bottom environmental conditions at two contrasting sponge grounds on the northern Labrador Shelf.</strong></p> <p>&nbsp;</p> <p>&nbsp;</p> <p>Published in Biogeosciences in 2024: https://bg.copernicus.org/articles/21/5407/2024/</p> <p><a href="https://bg.copernicus.org/articles/21/5407/2024/">BG - Characterizing regional oceanography and bottom environmental conditions at two contrasting sponge grounds on the northern Labrador Shelf</a></p> <p>DOI : https://doi.org/10.5194/bg-21-5407-2024</p> <p>Abstract:&nbsp;</p> <p>Deep-sea sponge grounds are distributed globally and are considered hotspots of biological diversity and biogeochemical cycling. To date, little is known about the environmental conditions that allow high sponge biomass to develop in the deep sea. Here, we characterize oceanographic conditions at two contrasting sites off the northern Labrador Shelf with high- and low-sponge-biomass. Data were collected by year-long benthic lander deployments equipped with current meters, a turbidity and chlorophyll-<em>a</em> measuring device, and a sediment trap. Additionally, regional oceanography was described by analyzing vertical conductivity-temperature-depth (CTD) casts, Argo float profiles, and surface buoy drifter data for the northern Labrador Shelf from 2005 to 2022. Stable isotopic composition of benthic fauna was determined to investigate food web structure at the sponge grounds. Our results revealed strong (0.26 &plusmn; 0.14 m s^-1; mean &plusmn; SD) semidiurnal tidal currents at the high-sponge-biomass site, but twofold weaker currents (0.14 &plusmn; 0.08 m s^-1; mean &plusmn; SD) at the low-sponge-biomass site. Tidal analysis suggests that, at the high-sponge-biomass site, kinetic energy is dissipated from barotropic tide to baroclinic tide/turbulence, which could enhance food availability for benthic organisms. Bottom nutrient concentrations were elevated at the high-sponge-biomass site which would benefits growth in deep-sea sponges. Organic matter flux to the seafloor was increased at the high-sponge-biomass site and consisted of fresher material. Finally, both sponge grounds demonstrated tight benthic-pelagic coupling prior to the onset of stratification. Stable isotope signatures indicated that soft corals (<em>Primnoa resedaeformis</em>) fed on suspended particulate organic matter, while massive sponges (<em>Geodia</em> spp.) likely utilized additional food sources. Our results imply that benthic fauna at the high-sponge-biomass site benefit from strong tidal currents, which increases food supply, and favourable regional ocean currents that increase nutrient concentration in bottom waters.</p>