Towards a global understanding of the role of urea in the ocean nitrogen cycle

Peter L Croot, iCRAG (Irish Centre for Research in Applied Geosciences), Earth and Ocean Sciences, School of Natural Sciences and Ryan Institute, University of Galway, Galway, Ireland, Alina Wieczorek, National University of Ireland Galway, Earth and Ocean Sciences, School of Natural Sciences and Ryan Institute, Glaway, Ireland and Maija Iris Heller, Pontificia Universidad Católica de Valparaíso Chile, Escuela de Ciencias del Mar, Valparaiso, Chile
Urea CO(NH2)2 is produced through the metabolism of nitrogen containing compounds by organisms, it can also be used as a nitrogen source by bacteria and phytoplankton. In the open ocean urea is, along with ammonia, thought to be an important part of the recycling of nutrients through the microbial loop. In the coastal ocean, inputs of urea from the land are increasing due to atmospheric deposition and riverine input via animal waste and the use of urea-based fertilizers. Urea forms part of the Dissolved Organic Nitrogen (DON) pool in the ocean, though due to analytical constraints, currently there is a lack of data specifically for urea in all global oceans despite its importance in Nitrogen biogeochemistry. Renewed interest in urea has been driven recently by new advances in omics and techniques to measure urea concentrations and uptake. Over the last few years we have begun to make regular shipboard measurements for urea to examine the distribution of this nitrogen species over a wide range of biogeochemical environments. Our work forms part of a related study into Ni biogeochemistry as Ni is the metal co-factor in the urease enzyme that converts urea into CO2 and NH3.

This presentation will focus on providing insights on urea cycling via new data on the distribution of urea collected recently in and across global oceanic basins (i) The South Pacific Gyre (Sonne expedition SO245, Antofagasta, Chile to Wellington, New Zealand Dec 2015 – Jan 2016), (ii) Indian Ocean (GO-SHIP I08, Japanese GO-SHIP expedition onboard the RV Mirai MR19-04, Nov 2019 – Feb 2020) and (iii) North East Atlantic Shelf region (WESPAS, Celtic Explorer 2017 - 2019).