Archive for residence time

Do rivers supply nutrients to the open ocean?

Posted by mmaheigan 
· Wednesday, May 24th, 2017 

Rivers carry large amounts of nutrients (e.g., nitrogen and phosphorus) to the sea, but we do not know how much of that riverine nutrient supply escapes biological and chemical processing in shallow coastal waters to reach the open ocean. Most global ocean biogeochemical models, which are typically unable to resolve coastal processes, assume that either all or none of the riverine nutrients entering coastal waters actually contribute to open ocean processes.

While we know a good deal about the dynamics of individual rivers entering the coastal ocean, studies to date have been limited to a few major river systems, mainly in in developed countries. Globally, there are over 6,000 rivers entering the coastal ocean. In a recent study, Sharples et al (2017) devised a simple approach to obtain a global-scale estimate of riverine nutrient inputs based on the knowledge that low-salinity waters entering the coastal ocean tend to form buoyant plumes that turn under the influence of Earth’s daily rotation to flow along the coastline. Using published data on such flows and incorporating the effect of Earth’s rotation, they obtained estimates of typical cross-shore plume width and compared them to the local width of the continental shelf. This was used to calculate the residence time of riverine nutrients on the shelf, which is the key to estimating how much of a given nutrient is consumed in shelf waters vs. how much is exported to the open ocean.

Global distribution of the amount of riverine dissolved inorganic nitrogen that escapes the continental shelf to reach the open ocean.

The results indicate that, on a global scale, 75% (80%) of the nitrogen (phosphorus) supplied by rivers reaches the open ocean, whereas 25% (20%) of the nitrogen (phosphorus) is consumed on the shelf (e.g., fueling coastal productivity). Limited knowledge of nutrient cycling and consumption in shelf waters represents the primary source of uncertainty in this study. However, well-defined global patterns related to human land use (e.g., agricultural fertilizer use in developed nations) emerged from this analysis, underscoring the need to understand how land-use changes and other human activities will alter nutrient delivery to the coastal ocean in the future.

 

Authors:
Jonathan Sharples (School of Environmental Sciences, University of Liverpool, UK)
Jack Middelburg (Department of Earth Sciences, Utrecht University, Netherlands)
Katja Fennel (Department of Oceanography, Dalhousie University, Canada)
Tim Jickells (School of Environmental Sciences, University of East Anglia, UK)

Filter by Keyword

acidification air-sea interactions allometry AMOC Antarctica anthropogenic carbon aragonite saturation arctic argo Atlantic Atlantic modeling atmospheric CO2 atmospheric nitrogen deposition autonomous observing autonomous platforms BATS bcg-argo biogeochemical cycles biogeochemical models biological pump biological uptake bloom blue carbon bottom water calcification calcite carbon-climate feedback carbon cycle Caribbean CCS changing marine ecosystems changing ocean chemistry chlorophyll circulation climate change CO2 coastal and estuarine coastal carbon fluxes coastal ocean cobalt community composition conservation cooling effect copepod coral reefs deep convection deep ocean deep sea coral diatoms dimethylsulfide DOC domoic acid dust earth system models eddy Education Ekman transport emissions ENSO enzyme equatorial regions estuarine and coastal carbon fluxes estuary EXPORTS filter feeders filtration rates fish fisheries floats fluid dynamics fluorescence food webs forams geochemistry geoengineering GEOTRACES glaciers gliders global warming greenhouse gas Greenland Gulf of Maine Gulf of Mexico Gulf Stream gyre harmful algal bloom human impact hypoxia ice age ice cover iron iron fertilization isotopes katabatic winds kelvin waves kuroshio larvaceans lateral transport lidar ligands mangroves marine boundary layer marine snowfall marshes meltwater mesopelagic mesoscale metagenome metals methane microbes microlayer microorganisms microscale midwater mixed layer mixotrophy modeling mode water formation molecular diffusion NASA net community production new technology nitrogen nitrogen fixation nitrous oxide north atlantic north pacific nutricline nutrient budget nutrient cycling nutrient flux nutrient limitation nutrients ocean-atmosphere ocean carbon uptake and storage ocean color ocean observatories ODZ oligotrophic OMZ open ocean organic particles oxygen paleoceanography particle flux particulate organic carbon pCO2 PDO pH phosphorus photosynthesis physical processes physiology phytoplankton plankton polar regions pollutants primary productivity pteropods radioisotopes remineralization remote sensing residence time respiration rivers Rossby waves Ross Sea ROV salinity salt marsh satellite scale seagrass sea level rise seasonal patterns sediments sensors shelf system ship-based observations sinking particles SOCCOM southern ocean south pacific speciation species oscillations subduction submesoscale subpolar subtropical subtropical gyres subtropical mode water surface ocean teleconnections temperature thermohaline thorium time-series top predators trace elements trace metals trait-based transfer efficiency transient features trophic transfer tropical turbulence twilight zone upper ocean upper water column upwelling US CLIVAR velocity gradient ventilation vertical flux vertical migration vertical transport western boundary currents wetlands winter mixing zooplankton

Copyright © 2019 - OCB Project Office, Woods Hole Oceanographic Institution, 266 Woods Hole Rd, MS #25, Woods Hole, MA 02543 USA Phone: 508-289-2838  •  Fax: 508-457-2193  •  Email: ocb_news@us-ocb.org

link to nsflink to noaalink to WHOI

Funding for the Ocean Carbon & Biogeochemistry Project Office is provided by the National Science Foundation (NSF) and the National Aeronautics and Space Administration (NASA). The OCB Project Office is housed at the Woods Hole Oceanographic Institution.