Organic nutrients and excess nitrogen in the North Atlantic subtropical gyre
Abstract. To enable an accurate estimate of total excess ni-trogen (N) in the North Atlantic, a new tracer TNxs is de-fined, which includes the contribution of organic nutrients to the assessment of N:P stoichiometric anomalies. We mea-sured the spatial distribution of TNxs within the subtropical No...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.654.8823 http://www.biogeosciences.net/5/1199/2008/bg-5-1199-2008.pdf |
| Summary: | Abstract. To enable an accurate estimate of total excess ni-trogen (N) in the North Atlantic, a new tracer TNxs is de-fined, which includes the contribution of organic nutrients to the assessment of N:P stoichiometric anomalies. We mea-sured the spatial distribution of TNxs within the subtropical North Atlantic using data from a trans-Atlantic section across 24.5 ◦ N occupied in 2004. We then employ three different approaches to infer rates of total excess nitrogen accumula-tion using pCFC-12 derived ventilation ages (a TNxs verti-cal integration, a one end-member and a two-end member mixing model). Despite some variability among the differ-ent methods the dissolved organic nutrient fraction always contributes to about half of the TNxs accumulation, which is in the order of 9.38±4.18×1011 mol N y−1. We suggest that neglecting organic nutrients in stoichiometric balances of the marine N and P inventories can lead to systematic er-rors when estimating deviations of nitrogen excess or deficit relative to the Redfield ratio in the oceans. For the North Atlantic the inclusion of the organic fraction to the excess ni-trogen pool leads to an upward revision of the N supply by N2 fixation to 10.2±6.9×1011 mol N y−1. 1 |
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