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Oxygen and nutrient fluxes from a Cold-Water Coral reef at Rockall Bank, NE Atlantic

de Froe, Evert; Maier, Sandra; Mienis, Furu; Duineveld, Gerard; Lavaleye, Marc; van Oevelen, Dick

ATLAS work package 2 presentation at ATLAS 3rd General Assembly

Cold-water coral reefs are biodiversity hotspots and play an important role in organic matter processing and the carbon cycle. These reefs are globally distributed across the deep-sea floor, mostly on the edges of continental margins. In recent years, researchers have become increasingly interested in the biogeochemistry of cold-water coral reefs as a tool to understand and quantify organic matter dynamics and food-utilization on these reefs. Previous work on the biogeochemistry of cold-water coral reefs has reported either on in-situ oxygen dynamics or oxygen and nutrient dynamics of individual components of a cold-water coral reef (e.g., coral fragments, sponges). In this research, we aimed to fill-in this knowledge gap by measuring oxygen and nutrient fluxes of a cold-water coral reef and a nearby soft-sediment station. We will present the first results of on-board box core incubations performed at Rockall Bank. During a research cruise to the Rockall bank in May 2017, six large box cores (50 cm diameter) were taken from two coral reef seamounts and subsequently incubated for ±24h for oxygen consumption and nutrient release. After the incubation, coral framework, sediment characteristics samples and, pigment samples were taken. Initial results show that the sediment underneath the coral reef has more fine material and higher organic carbon content. Oxygen consumption of the coral mound box cores was, with 16.2 ± 11.3 mmol O2 m-2 d-1 (mean ± SD) against 2.12 ± 1.42 mmol O2 m-2 d-1 for the sediment cores, significantly higher on the coral mound (p<0.05). For nutrient fluxes, the ammonium (NH4+) flux was significantly higher in the coral mound box cores than in the sediment cores. Other nutrient fluxes, such as phosphate (PO4), Nitrite (NO2), Nitrate (NO3) and, Silicate (SiO2) showed a similar pattern of a higher flux at the coral mounds although the difference was not statistically significant. These results provide further evidence of the increased metabolic activity of a cold-water coral reef compared to its surrounding sediment and highlight the importance of these reefs in marine biogeochemical cycling.

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