What proportion of riverine nutrients reaches the open ocean?

Sharples, Jonathan, Middelburg, Jack J., Fennel, Katja and Jickells, Timothy D. (2017) What proportion of riverine nutrients reaches the open ocean? Global Biogeochemical Cycles, 31 (1). 39–58. ISSN 0886-6236

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Globally, rivers deliver significant quantities of nitrogen (N) and phosphorus (P) to the coastal ocean each year. Currently, there are no viable estimates of how much of this N and P escapes biogeochemical processing on the shelf to be exported to the open ocean; most models of N and P cycling assume that either all or none of the riverine nutrients reach the open ocean. We address this problem by using a simple mechanistic model of how a low-salinity plume behaves outside an estuary mouth. The model results in a global map of riverine water residence times on the shelf, typically a few weeks at low latitudes and up to a year at higher latitudes, which agrees well with observations. We combine the map of plume residence times on the shelf with empirical relationships that link residence time to the proportions of dissolved inorganic N (DIN) and P (DIP) exported and use a database of riverine nutrient loads to estimate the global distribution of riverine DIN and DIP supplied to the open ocean. We estimate that 75% of DIN and 80% of DIP reaches the open ocean. Ignoring processing within estuaries yields annual totals of 17 Tg DIN and 1.2 Tg DIP reaching the open ocean. For DIN this supply is about 50% of that supplied via atmospheric deposition, with significant east-west contrasts across the main ocean basins. The main sources of uncertainty are exchange rates across the shelf break and the empirical relationships between nutrient processing and plume residence time.

Item Type: Article
Uncontrolled Keywords: rivers,ocean,nutrients,nitrogen,phosphorus
Faculty \ School: Faculty of Science > School of Environmental Sciences
University of East Anglia Research Groups/Centres > Theme - ClimateUEA
UEA Research Groups: Faculty of Science > Research Groups > Marine and Atmospheric Sciences (former - to 2017)
Faculty of Science > Research Groups > Climate, Ocean and Atmospheric Sciences (former - to 2017)
Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
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Depositing User: Pure Connector
Date Deposited: 26 Jan 2017 02:39
Last Modified: 20 Mar 2023 12:38
URI: https://ueaeprints.uea.ac.uk/id/eprint/62173
DOI: 10.1002/2016GB005483


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