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Nitrous oxide and methane in the Atlantic Ocean between 50˚N and 52˚S: latitudinal distribution and sea-to-air flux

Lookup NU author(s): Grant Forster, Professor Robert Upstill-GoddardORCiD, Dr Guenther Uher

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Abstract

We discuss nitrous oxide (N₂O) and methane (CH₄) distributions in 49 vertical profiles covering the upper 300 m of the water column along two 13,500 km transects between 50°N and 52°S during the Atlantic Meridional Transect (AMT) programme (AMT cruises 12 and 13). Vertical N₂O profiles were amenable to analysis on the basis of common features coincident with Longhurst provinces. In contrast, CH₄ showed no such pattern. The most striking feature of the latitudinal depth distributions was a well-defined “plume” of exceptionally high N₂O concentrations coincident with very low levels of CH₄, located between 23.5°N and 23.5°S; this feature reflects the upwelling of deep waters containing N₂O derived from nitrification, as identified by an analysis of N₂O, apparent oxygen utilization (AOU) and NO₃⁻, and presumably depleted in CH₄ by bacterial oxidation. Sea-to-air emissions fluxes for a region equivalent to 42% of the Atlantic Ocean surface area were in the range 0.40–0.68 Tg N₂O yr⁻¹ and 0.81–1.43 Tg CH₄ yr⁻¹. Based on contemporary estimates of the global ocean source strengths of atmospheric N₂O and CH₄, the Atlantic Ocean could account for 6–15% and 4–13%, respectively, of these source totals. Given that the Atlantic Ocean accounts for around 20% of the global ocean surface, on unit area basis it appears that the Atlantic may be a slightly weaker source of atmospheric N₂O than other ocean regions but it could make a somewhat larger contribution to marine-derived atmospheric CH₄ than previously thought.

Publication metadata

Author(s): Forster GL, Upstill-Goddard RC, Gist N, Robinson R, Uher G, Woodward EMS

Publication type: Article

Publication status: Published

Journal: Deep Sea Research II: Topical Studies in Oceanography

Year: 2009

Volume: 56

Issue: 15

Pages: 964-976

ISSN (print): 0967-0645

Publisher: Pergamon

URL: http://dx.doi.org/10.1016/j.dsr2.2008.12.002

DOI: 10.1016/j.dsr2.2008.12.002

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