Archive for south pacific

Dust-borne iron in the Southern Ocean was more bioavailable during glacial periods

Posted by mmaheigan 
· Wednesday, January 23rd, 2019 

The Southern Ocean is iron (Fe)-limited, and increased fluxes of dust-borne Fe to the Southern Ocean during the Last Glacial Maximum (LGM) have been associated with phytoplankton growth and CO2 drawdown. Dust contains different mixes of Fe-bearing minerals, depending on the source region. Fe(II) silicate minerals from physical weathering are more bioavailable than Fe(III) oxyhydroxide minerals from chemical weathering. The Fe(II) silicates are dominant in dust sources that have been weathered from bedrock by glaciers in Patagonia, but the impact of glacial activity on dust-borne Fe speciation (Fe oxidation state and mineral composition) and bioavailability over the last glacial cycle has not previously been quantified.

Figure 1. The fraction of Fe(II) in dust (Fe(II)/Fetotal, dominated by Fe(II) silicates, shown as blue dots connected with dotted lines on blue axes) in marine sediment cores from (A) the South Atlantic and (B) the South Pacific plotted with the total dust flux (grey lines on grey axes).

A recent study in PNAS reconstructs the speciation of dust-borne Fe over the last glacial cycle in South Atlantic and South Pacific marine sediment cores using Fe K-edge X-ray absorption spectroscopy. The authors observed that the highly bioavailable Fe(II) silicate content of dust-borne Fe is higher in both regions during cold glacial periods, suggesting that a given flux of Fe is more bioavailable in glacial versus interglacial periods (Figure 1). Therefore, all Fe cannot be considered equal in biogeochemical models working on glacial-interglacial timescales. The bioavailability of a given flux of Fe at the LGM was likely a dominant driver of phytoplankton growth, with more bioavailable Fe driving increased phytoplankton activity and associated atmospheric CO2 drawdown and subsequent cooling. The observed association between glacial periods and increased Fe bioavailability in the Southern Ocean may indicate an important positive feedback mechanism between glacial activity and cold glacial temperatures through Fe speciation and the efficiency of the biological pump.

Paper link: https://doi.org/10.1073/pnas.1809755115

Authors:
Elizabeth M. Shoenfelt (Lamont-Doherty Earth Observatory, Columbia University)
Gisela Winckler (Lamont-Doherty Earth Observatory, Columbia University)
Frank Lamy (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research)
Robert F. Anderson (Lamont-Doherty Earth Observatory, Columbia University)
Benjamin C. Bostick (Lamont-Doherty Earth Observatory, Columbia University)

 

Filter by Keyword

acidification air-sea interactions AMOC anthropogenic carbon aragonite saturation state arctic argo Atlantic atmospheric CO2 autonomous observing autonomous platforms BATS bcg-argo 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 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 fish 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 human impact 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 limitation nutrients ocean-atmosphere ocean acidification ocean carbon uptake and storage ocean color ocean observatories 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 productivity pteropods radioisotopes remineralization remote sensing residence time respiration rivers Rossby waves Ross Sea ROV salinity salt marsh satellite scale seagrass 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 trace metals 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 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.