THE INFLUENCE OF NON-REDFIELD DISSOLVED ORGANIC MATTER CYCLING ON THE GLOBAL OCEANIC FIXED NITROGEN BUDGET
Dissolved organic matter (DOM) plays a crucial role in surface nutrient cycling that does not behave in a Redfield manner. The current state of DOM in global biogeochemical models is either to neglect DOM cycling altogether or include a simple DOM scheme with Redfield cycling. Here we use the UVic-Kiel climate model to investigate the importance of non-Redfield DOM cycling on the global fixed nitrogen budget. We conduct experiments with no dissolved organic matter, Redfield DOM cycling, preferential recycling of DOP versus DON, and DOP uptake by phytoplankton including N-fixers. Our experiments show including DOM in the model reduced nutrient trapping in the tropics that resulted in less primary production, a smaller volume of suboxic water, and water column denitrification rates that decreased by 18%. Allowing phytoplankton including N-fixers to consume DOP after phosphate is depleted resulted in 12% more N fixation globally, most notably in the tropical/subtropical North Atlantic. Including these non-Redfield DOM cycling effects resulted in a balanced fixed nitrogen inventory, whereas in our experiment without DOM, it was underestimated by 10%. We show that these non-Redfield experiments also produced patterns of DON and DOP that are more consistent with available datasets. This study highlights the importance of non-Redfield DOM cycling and the need for a global climatological database to further constrain and quantify their influence on ocean biogeochemistry.
Somes, C. J., GEOMAR, Germany, email@example.com
Oschlies, A., GEOMAR, Germany, firstname.lastname@example.org
Location: 319 AB
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