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Implications of eddy cancellation for nutrient distribution within subtropical gyres

Citation

Doddridge, EW and Marshall, DP, Implications of eddy cancellation for nutrient distribution within subtropical gyres, Journal of Geophysical Research: Oceans, 123, (9) pp. 6720-6735. ISSN 2169-9275 (2018) [Refereed Article]


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DOI: doi:10.1029/2018JC013842

Abstract

The role of mesoscale eddies within the nutrient budget of subtropical gyres remains poorly understood and poorly constrained. We explore a new mechanism by which mesoscale eddies may contribute to these nutrient budgets, namely eddy cancellation. Eddy cancellation describes the rectified effect of mesoscale eddies acting to oppose the Eulerian-mean Ekman pumping. We present an idealized axisymmetric two-layer model of a nutrient in a wind-driven gyre and explore the sensitivity of this model to variations in its parameter values. We find that the residual Ekman pumping velocity has a substantial impact on nutrient concentration, as does mode water thickness. These results suggest the response to both residual Ekman pumping and mode water thickness is nonmonotonic: for small values of these parameters the nutrient concentration decreases as the parameter increases. However, beyond a critical value, further increases in Ekman pumping or mode water thickness increase nutrient concentration throughout our highly idealized model. A thin mode water layer promotes vertical diffusion of nutrients from the abyss, while a thicker mode water layer increases productivity by reducing the parametrized particulate flux through the thermocline. The impact of mode water thickness is modulated by the residual Ekman pumping velocity: strong Ekman pumping suppresses the influence of mode water thickness on nutrient concentrations. We use satellite and in situ measurements to assess the influence of mode water thickness on primary productivity and find a statistically significant relationship; thicker mode water correlates with higher productivity. This result is consistent with a small residual Ekman pumping velocity.

Item Details

Item Type:Refereed Article
Keywords:mesoscale eddy, nutrient supply, subtropical gyre
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Physical oceanography
Objective Division:Environmental Management
Objective Group:Marine systems and management
Objective Field:Oceanic processes (excl. in the Antarctic and Southern Ocean)
UTAS Author:Doddridge, EW (Dr Edward Doddridge)
ID Code:150149
Year Published:2018
Web of Science® Times Cited:7
Deposited By:Oceans and Cryosphere
Deposited On:2022-05-30
Last Modified:2022-06-01
Downloads:0

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