Biogeochemical budgets in the eastern boundary current system of the North Atlantic: Evidence of net heterotrophy and nitrogen fixation
Thermohaline and chemical data from three WOCE (World Ocean Circulation Experiment) cruises conducted in 1997 and 1998 define the MedBox region, bounded by the Strait of Gibraltar, 24uN, 41uN, and 22uW. The carbon budget indicates that the MedBox is a heterotrophic region, where carbon is mineralize...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.577.8294 http://www.aslo.org/lo/toc/vol_52/issue_4/1328.pdf |
| Summary: | Thermohaline and chemical data from three WOCE (World Ocean Circulation Experiment) cruises conducted in 1997 and 1998 define the MedBox region, bounded by the Strait of Gibraltar, 24uN, 41uN, and 22uW. The carbon budget indicates that the MedBox is a heterotrophic region, where carbon is mineralized at a net rate of 17 6 11 g C m22 yr21, supported by the input of allochthonous organic matter, mainly in the dissolved form, from the adjacent ocean. Dissolved organic carbon accounts for 90 % of the organic carbon demand. In vitro measurements to estimate the net community production of the study area differ largely from our geochemical budget estimation, likely reflecting different spatial and temporal scales and/or terms or processes not taken into account by both methods. The nitrogen budget of the MedBox pointed to a significant atmospheric input via N2 fixation (3.4 6 3.1 g N m22 yr21). The metabolic state of the ocean is defined as the balance between in situ gross primary production (GPP) and total respiration (R); a system is autotrophic if it produces more organic matter than it consumes and heterotrophic if organic matter consumption exceeds in situ production. Assessing whether the ocean, from the local to the global scale, is heterotrophic or autotrophic still remains a burning issue. Contrasting conclusions are achieved depending on the approach used: (1) regional budgets of nutrient salts (e.g., Álvarez et al. 2002) or organic matter (e.g., Hansell et al. 2004a) versus (2) extrapolation of in vitro net community production (NCP) estimates relying on empir-ical relationships between GPP (Williams 1998) or net primary production (del Giorgio et al. 1997) and total (Duarte and Agustı ́ 1998; Williams 1998) or bacterial (del |
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