Quantifying mesoscale-driven nitrate supply: a case study

Pidcock, Rosalind E.M.; Martin, Adrian P. ORCID: https://orcid.org/0000-0002-1202-8612; Painter, Stuart C.; Allen, John T.; Srokosz, Meric A. ORCID: https://orcid.org/0000-0002-7347-7411; Forryan, Alex; Stinchcombe, Mark; Smeed, David A. ORCID: https://orcid.org/0000-0003-1740-1778. 2016 Quantifying mesoscale-driven nitrate supply: a case study. Global Biogeochemical Cycles, 30 (8). 1206-1223. https://doi.org/10.1002/2016GB005383

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Text © Publisher 2016 This is the peer reviewed version of the following article: Pidcock, Rosalind E.M., Martin, Adrian P., Painter, Stuart C., Allen, John T., Srokosz, Meric A., Forryan, Alex, Stinchcombe, Mark and Smeed, David A. (2016) Quantifying mesoscale-driven nitrate supply: a case study. Global Biogeochemical Cycles, which has been published in final form at doi:10.1002/2016GB005383. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving. gbc20442.pdf - Accepted Version Restricted to NORA staff only Download (3MB)

Abstract/Summary

The supply of nitrate to surface waters plays a crucial role in maintaining marine life. Physical processes at the mesoscale (~10-100?km) and smaller have been advocated to provide a major fraction of the global supply. Whilst observational studies have focussed on well-defined features, such as isolated eddies, the vertical circulation and nutrient supply in a typical 100-200?km square of ocean will involve a turbulent spectrum of interacting, evolving and decaying features. A crucial step in closing the ocean nitrogen budget is to be able to rank the importance of mesoscale fluxes against other sources of nitrate for surface waters for a representative area of open ocean. While this has been done using models, the vital observational equivalent is still lacking. To illustrate the difficulties that prevent us from putting a global estimate on the significance of the mesoscale observationally, we use data from a cruise in the Iceland Basin where vertical velocity and nitrate observations were made simultaneously at the same high spatial resolution. Local mesoscale nitrate flux is found to be an order of magnitude greater than that due to small-scale vertical mixing and exceeds coincident nitrate uptake rates and estimates of nitrate supply due to winter convection. However, a non-zero net vertical velocity for the region introduces a significant bias in regional estimates of the mesoscale vertical nitrate transport. The need for synopticity means that a more accurate estimate can not be simply found by using a larger survey area. It is argued that time-series, rather than spatial surveys, may be the best means to quantify the contribution of mesoscale processes to the nitrate budget of the surface ocean.

Item Type:	Publication - Article
Digital Object Identifier (DOI):	https://doi.org/10.1002/2016GB005383
ISSN:	08866236
Additional Keywords:	mesoscale; nitrate; North Atlantic; dipole; eddy; primary production
Date made live:	09 Aug 2016 10:49 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/514208

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