Ocean Carbon & Biogeochemistry
Studying marine ecosystems and biogeochemical cycles in the face of environmental change
  • Home
  • About OCB
    • About Us
    • Project Office
    • Scientific Steering Committee
    • OCB Subcommittees
      • Ocean Time-series Committee
      • US Biogeochemical-Argo Subcommittee
      • Ocean-Atmosphere Interaction Committee
    • Scientific Breadth
      • Biological Pump
      • Changing Marine Ecosystems
      • Changing Ocean Chemistry
      • Estuarine and Coastal Carbon Fluxes
      • Ocean Carbon Uptake and Storage
      • Ocean Observatories
    • Get Involved
  • Activities
    • Summer Workshops
    • Scoping Workshops
    • Other Workshops
    • Science Planning
      • Coastal CARbon Synthesis (CCARS)
      • North Atlantic-Arctic
    • Small Group Activities
      • Aquatic Continuum OCB-NACP Focus Group
      • CMIP6 Working Group
      • Fish Carbon Working Group
      • Lateral Carbon Flux in Tidal Wetlands
      • Metaproteomic Intercomparison
      • N-Fixation Working Group
      • Ocean Carbon Uptake Working Groups
      • Phytoplankton Taxonomy Working Group
    • Ocean Acidification PI Meetings
    • Training Activities
  • Science Support
    • Data management and archival
    • Early Career
    • Funding Sources
    • Jobs and Postdocs
    • Meeting Calendar
    • Meeting List
    • Outreach & Education
    • Promoting your science
    • Student Opportunities
    • OCB Activity Proposal Solicitations
    • Travel Support
  • Publications
    • Ocean Carbon Exchange
    • Newsletter Archive
    • Science Planning and Policy
    • OCB Workshop Reports
  • OCB Science Highlights
  • News

Primary productivity à la mode

Posted by mmaheigan 
· Wednesday, October 10th, 2018 

The presence of large-scale Ekman downwelling is the textbook explanation for low nutrient concentrations, and hence low productivity, in subtropical gyres. However, recent research has suggested that mesoscale eddies oppose and substantially reduce this downwelling, a process known as eddy cancellation (Doddridge et al, 2016). Eddy cancellation represents a substantial alteration to the widely accepted notion of large-scale Ekman downwelling in subtropical gyres, and motivates our study of the processes that determine nutrient concentration within subtropical gyres.

Figure 1: Sensitivity experiments for mode water thickness (hmode) with two values of residual Ekman pumping. a) With no residual Ekman pumping, phosphate concentration responds strongly to mode water thickness. b) When Ekman pumping is strong, phosphate concentration does not depend on mode water thickness. The dashed lines represent transects of climatological phosphate concentration in the euphotic zone of the North Atlantic subtropical gyre (Garcia et al., 2013).

A recent paper published in the Journal of Geophysical Research: Oceans and featured in an MIT News article describes an idealized model for nutrient concentration in subtropical gyres that can account for this reduction in Ekman pumping. The model predicts that surface productivity is sensitive to the thickness of the underlying subtropical mode water layer, provided that the residual Ekman pumping is small (Figure 1). Comparison of this prediction with observations from the Bermuda Atlantic Time series Study (BATS) shows that surface productivity increases as the thickness of the underlying mode water increases (Figure 2), as predicted by the idealized model in the absence of substantial Ekman pumping.

Figure 2: Annually averaged primary productivity and mode water thickness from the BATS dataset. The linear fit between mode water thickness and primary productivity is statistically significant (p ≈ 0.027) and explains 19.5% of the variance in primary productivity.

The observed relationship between productivity and mode water thickness at BATS is consistent with a small residual Ekman pumping, indicating highly effective eddy cancellation in the subtropical North Atlantic. Previous research (Palter et al., 2005) has suggested that as the subtropical mode water layer thickens, it blocks nutrient entrainment from below, resulting in lower productivity in the euphotic zone. However, this study suggests that a thicker subtropical mode water layer actually increases the surface nutrient concentrations by promoting more effective recycling of nutrients within the gyre. With a thicker mode water layer, more of the nutrients in the particulate flux are remineralized before they pass through the thermocline and become isolated from the surface ocean. This means that a thicker mode water layer leads to higher nutrient concentrations and supports primary productivity in subtropical gyres. This represents a fundamental change in our understanding of how nutrients are supplied to the surface waters of subtropical gyres.

Authors:
Edward Doddridge (Department of Earth, Atmospheric and Planetary Sciences, MIT)
David Marshall (Atmospheric, Oceanic & Planetary Physics, University of Oxford)

See the Eos spotlight on this research

Filter by Keyword

acidification air-sea interactions AMOC anthropogenic carbon aragonite saturation state arctic argo Atlantic atmospheric CO2 autonomous observing autonomous platforms bcg-argo Bermuda Atlantic Time-series Study (BATS) biogeochemical cycles biogeochemical models biological pump biological uptake bloom blue carbon bottom water calcification California Current System carbon-climate feedback carbon cycle carbon dioxide Caribbean CCS changing marine ecosystems changing ocean chemistry circulation climate change Coastal ocean cobalt community composition conservation cooling effect coral reefs deep convection deep ocean deep waters diatoms dimethylsulfide DOC domoic acid dust earth system models eddy Education Ekman pumping Ekman transport emissions ENSO enzyme equatorial regions estuarine and coastal carbon fluxes estuary EXPORTS filter feeders filtration rates fisheries floats fluid dynamics fluorescence food webs forams geoengineering GEOTRACES glaciers gliders global warming greenhouse gas Greenland Gulf of Maine Gulf of Mexico Gulf Stream gyre harmful algal bloom hotspots human impact ice age ice cover iron iron fertilization isotopes katabatic winds Kelvin waves kuroshio larvaceans lateral carbon flux lateral transport lidar ligands mangroves marine boundary layer marine snowfall marshes meltwater mesopelagic mesoscale mesoscale processes metagenome metals methane microbes microlayer Microorganisms microscale midwater mixed layer mixotrophy modeling models 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 limitation nutrients ocean-atmosphere ocean carbon uptake and storage ocean color ocean observatories ocean observing ODZ oligotrophic OMZ open ocean organic particles oxygen paleoceanography particle flux pCO2 PDO pH phosphorus photosynthesis physical processes physiology phytoplankton plankton polar regions pollutants primary production primary productivity pteropods remineralization remote sensing residence time respiration rivers Rossby waves Ross Sea ROV salinity satellite scale seagrass seasonality seasonal patterns sediments sensors shelf system ship-based observations sinking particles SOCCOM southern ocean South Pacific speciation submesoscale subpolar subtropical subtropical gyres subtropical mode water surface ocean teleconnections temperature thermohaline time-series top predators trace elements transfer efficiency transient features trophic transfer tropical turbulence upper ocean upper water column upwelling US CLIVAR velocity gradient ventilation vertical flux vertical migration vertical transport western boundary currents wetlands winter mixing working group 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.