Importance of salt fingering for new nitrogen supply in the oligotrophic ocean.
Authors
Fernández-Castro, B. (Bieito); Mouriño-Carballido, B. (Beatriz); Marañón, E.; Chouciño, P.; Gago, J. (Jesús); Ramírez-Cárdenas, T. (Teodoro); Vidal, M.; Bode, A. (Antonio); Blasco, D.; Royer, S.-J.; Estrada, M.; Simó, R.Date
2015-09-09Type
articleKeywords
salinitynutrients
nitrogen
diazotrophy
Trichodesmium
ocean
global
turbulence
Abstract
The input of new nitrogen into the euphotic zone constrains the export of organic carbon to
the deep ocean and thereby the biologically mediated long-term CO2 exchange between
the ocean and atmosphere. In low-latitude open-ocean regions, turbulence-driven nitrate
diffusion from the ocean’s interior and biological fixation of atmospheric N2 are the main
sources of new nitrogen for phytoplankton productivity. With measurements across the
tropical and subtropical Atlantic, Pacific and Indian oceans, we show that nitrate diffusion
(171±190 mmolm 2 d 1) dominates over N2 fixation (9.0±9.4 mmolm 2 d 1) at the time
of sampling. Nitrate diffusion mediated by salt fingers is responsible for ca. 20% of the new
nitrogen supply in several provinces of the Atlantic and Indian Oceans. Our results indicate
that salt finger diffusion should be considered in present and future ocean nitrogen budgets,
as it could supply globally 0.23–1.00 TmolNyr 1 to the euphotic zone.
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