Biogeochemical cycling of permeable sediments in a shelf sea environment: Celtic Sea, a seasonal study.

Sarah Reynolds1, Jessica Katharina Klar2, Vassilis A Kitidis3, Lesley Chapman-Greig1, Anouska Panton1, Charlie Thompson4, Peter John Statham5 and Gary R Fones6, (1)University of Portsmouth, School of Earth & Environmental Sciences, Portsmouth, United Kingdom, (2)Univesity of Southampton, School of Ocean and Earth Science, Southampton, United Kingdom, (3)Plymouth Marine Laboratory, Plymouth, United Kingdom, (4)University of Southampton, Southampton, United Kingdom, (5)University of Southampton, Southampton, SO14, United Kingdom, (6)University of Portsmouth, School of the Environment, Geography and Geosciences, Portsmouth, United Kingdom
Abstract:
Shelf seas are globally important in contributing to the biogeochemical cycling of carbon and nutrients. Much of the benthic environment found in shelf seas comprise of relic permeable sands whereby advective pore-water flow processes govern the biogeochemical cycling within these sediments. To further elucidate our understanding of the biogeochemistry of these systems, flow-through reactors were employed during a field campaign as part of the UK led Shelf Sea Biogeochemistry Programme. Three cruises took place in the southern Celtic Sea in 2015 and were timed to sample pre-bloom, post-bloom and late summer conditions. Preliminary data show marked differences with the pre-bloom and late summer flow-through incubations when compared with the post-bloom. Pre-bloom and late summer oxygen consumption rates ranged between 0.18 mmol O2 m-3 d-1 and 0.15 mmol O2 m-3 d-1 respectively. However, post-bloom oxygen consumption rates were almost double at 0.29 mmol O2 m-3 d-1. Differences were also observed in the amount of iron (II) being released with no marked releases from the pre-bloom and late summer but with significant contributions of up to 140 nM during the post-bloom incubation. These initial findings demonstrate the seasonal variability and extent of the biogeochemical cycling of benthic permeable sediments. Additional measurements of inorganic nutrients, dissolved organic carbon and denitrification rates will contribute further to our understanding of sandy sediments in a shelf sea environment and their capacity to act as a carbon and nutrient source or sink.