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Quantifying mesoscale-driven nitrate supply: a case study

Quantifying mesoscale-driven nitrate supply: a case study
Quantifying mesoscale-driven nitrate supply: a case study
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.
mesoscale, nitrate, North Atlantic, dipole, eddy, primary production
0886-6236
1206-1223
Pidcock, Rosalind E.M.
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Martin, Adrian P.
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Painter, Stuart C.
29e32f35-4ee8-4654-b305-4dbe5a312295
Allen, John T.
17bc259e-c288-4d19-b23b-35bb3926e679
Srokosz, Meric A.
f1701d3e-01b3-43d0-8993-9fd523032a79
Forryan, Alex
4e753ae9-7f12-495f-933a-2c5a1f554a0e
Stinchcombe, Mark
433dd398-15f7-4730-9f1e-992d65bec70b
Smeed, David A.
79eece5a-c870-47f9-bba0-0a4ef0369490
Pidcock, Rosalind E.M.
2cd7ddf8-b9cc-48e6-bdf0-607561cb731b
Martin, Adrian P.
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Painter, Stuart C.
29e32f35-4ee8-4654-b305-4dbe5a312295
Allen, John T.
17bc259e-c288-4d19-b23b-35bb3926e679
Srokosz, Meric A.
f1701d3e-01b3-43d0-8993-9fd523032a79
Forryan, Alex
4e753ae9-7f12-495f-933a-2c5a1f554a0e
Stinchcombe, Mark
433dd398-15f7-4730-9f1e-992d65bec70b
Smeed, David A.
79eece5a-c870-47f9-bba0-0a4ef0369490

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, 30 (8), 1206-1223. (doi:10.1002/2016GB005383).

Record type: Article

Abstract

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.

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Accepted/In Press date: 7 July 2016
e-pub ahead of print date: 29 August 2016
Published date: 29 August 2016
Keywords: mesoscale, nitrate, North Atlantic, dipole, eddy, primary production
Organisations: Ocean and Earth Science, Marine Biogeochemistry, Physical Oceanography, Marine Physics and Ocean Climate

Identifiers

Local EPrints ID: 399238
URI: http://eprints.soton.ac.uk/id/eprint/399238
ISSN: 0886-6236
PURE UUID: fb5e38e5-d626-471a-9776-bbcb5ebc8c8a

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Date deposited: 09 Aug 2016 10:51
Last modified: 09 Jan 2022 05:25

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Contributors

Author: Rosalind E.M. Pidcock
Author: Adrian P. Martin
Author: Stuart C. Painter
Author: John T. Allen
Author: Meric A. Srokosz
Author: Alex Forryan
Author: Mark Stinchcombe
Author: David A. Smeed

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