Oceanic nitrogen cycling and N2O flux perturbations in the Anthropocene. Issue 8 (13th August 2017)

• Record Type: Journal Article
• Authors: Landolfi, A.; Somes, C. J.; Koeve, W.; Zamora, L. M.; Oschlies, A.
• Is Part Of: Global biogeochemical cycles. Volume 31:Issue 8(2017:Aug.)
• Page Start: 1236
• Page End: 1255
• Publication Date: 2017-08-13
• Subjects: marine N cycle -- marine biogeochemical modeling -- climate change -- atmospheric N deposition -- marine export production -- oceanic N2O cycle; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1002/2017GB005633
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: There is currently no consensus on how humans are affecting the marine nitrogen (N) cycle, which limits marine biological production and CO2 uptake. Anthropogenic changes in ocean warming, deoxygenation, and atmospheric N deposition can all individually affect the marine N cycle and the oceanic production of the greenhouse gas nitrous oxide (N2 O). However, the combined effect of these perturbations on marine N cycling, ocean productivity, and marine N2 O production is poorly understood. Here we use an Earth system model of intermediate complexity to investigate the combined effects of estimated 21st century CO2 atmospheric forcing and atmospheric N deposition. Our simulations suggest that anthropogenic perturbations cause only a small imbalance to the N cycle relative to preindustrial conditions (∼+5 Tg N y −1 in 2100). More N loss from water column denitrification in expanded oxygen minimum zones (OMZs) is counteracted by less benthic denitrification, due to the stratification‐induced reduction in organic matter export. The larger atmospheric N load is offset by reduced N inputs by marine N2 fixation. Our model predicts a decline in oceanic N2 O emissions by 2100. This is induced by the decrease in organic matter export and associated N2 O production and by the anthropogenically driven changes in ocean circulation and atmospheric N2 O concentrations. After comprehensively accounting for a series of complex physical‐biogeochemical interactions, this study suggests that N flux imbalances are limited by biogeochemical feedbacks that help stabilize the marine N inventory against anthropogenic changes. These findings support the hypothesis that strong negative feedbacks regulate the marine N inventory on centennial time scales. Key Points: Negative nitrogen cycle feedbacks reduce anthropogenic perturbations Oceanic N2 O emissions are predicted to decline by 2100 Anthropogenically driven changes in ocean circulation and atmospheric N deposition combine to intensify OMZs