Archive for nutrient limitation

Can phytoplankton help us determine ocean iron bioavailability?

Posted by mmaheigan 
· Wednesday, March 11th, 2020 

Iron (Fe) is a key element to sustaining life, but it is present at extremely low concentrations in seawater. This scarcity limits phytoplankton growth in large swaths of the global ocean, with implications for marine food webs and carbon cycling. The acquisition of Fe by phytoplankton is an important process that mediates the movement of carbon to the deep ocean and across trophic levels. It is a challenge to evaluate the ability of marine phytoplankton to obtain Fe from seawater since it is bound by a variety of poorly defined organic complexes.

Figure 1: Schematic representation of the reactions governing dissolved Fe (dFe) bioavailability to phytoplankton (a) Bioavailability of dFe in seawater collected from various basins and depth and probed with different iron-limited phytoplankton species under dim laboratory light and sunlight (b) (See paper for further details on samples and species)

A recent study in The ISME Journal proposes a new approach for evaluating seawater dissolved Fe (dFe) bioavailability based on its uptake rate constant by Fe-limited cultured phytoplankton. The authors collected samples from distinct regions across the global ocean, measured the properties of organic complexation, loaded these complexes with a radioactive Fe isotope, and then tracked the internalization rates from these forms to a diverse set of Fe-limited phytoplankton species. Regardless of origin, all of the phytoplankton acquired natural organic complexes at similar rates (accounting for cell surface area). This confirms that multiple Fe-limited phytoplankton species can be used to probe dFe bioavailability in seawater. Among water types, dFe bioavailability varied by ~4-fold and did not clearly correlate with Fe concentrations or any of the measured Fe speciation parameters. This new approach provides a novel way to determine Fe bioavailability in samples from across the oceans and enables modeling of in situ Fe uptake rates by phytoplankton based simply on measured Fe concentrations.

 

Authors:
Yeala Shaked (Hebrew University of Jerusalem)
Kristen N. Buck (University of South Florida)
Travis Mellett (University of South Florida)
Maria. T. Maldonado (University of British Columbia)

 

Nutrient and carbon limitation drive broad-scale patterns of mixotrophy in the ocean

Posted by mmaheigan 
· Tuesday, May 14th, 2019 

In the ocean, unicellular eukaryotes are often mixotrophic, which means they photosynthesize and also consume prey. In recent decades, it has become clear that mixotrophs are ubiquitous in sunlit ocean habitats. Additionally, models predict that mixotrophs have important impacts on productivity, nutrient cycling, carbon export, and food web structure. However, there is little understanding of the environmental conditions that select for a mixotrophic lifestyle, and it is unclear how mixotrophs succeed in competition with autotrophic and heterotrophic specialists. A recent study in PNAS that synthesized measurements of mixotrophic nanoflagellates showed that mixotrophs are more abundant in stratified, well-lit, low latitude environments (Figure 1A). They are also more abundant, relative to pure heterotrophs, in productive coastal environments (Figure 1B). A trait-based model analysis revealed that the success of mixotrophs depends on the fact that they are less nutrient-limited than autotrophs (due to prey-derived nutrients) and less carbon-limited than heterotrophs (due to photosynthesis). This synergy requires sufficient light, leading to success in low latitude environments. Similarly, a greater supply of dissolved nutrients relative to prey, as commonly observed in coastal environments, favors mixotrophs relative to heterotrophs. One implication of these results is that carbon fixation at lower latitudes may be enhanced by mixotrophy, while limiting nutrients may be more efficiently transferred to higher trophic levels.

Figure 1. Estimated abundance of autotrophic, mixotrophic, and heterotrophic nanoflagellates across environmental gradients in the ocean.

 

Author:
Kyle Edwards (Univ. Hawaii at Manoa)

Widespread nutrient co-limitation discovered in the South Atlantic

Posted by mmaheigan 
· Thursday, March 15th, 2018 

Unicellular photosynthetic microbes—phytoplankton—are responsible for virtually all oceanic primary production, which fuels marine food webs and plays a fundamental role in the global carbon cycle. Experiments to date have suggested that the growth of phytoplankton across much of the ocean is limited by either nitrogen or iron. But simultaneously low concentrations of these and other nutrients have been measured over large areas of the open ocean, raising the question: Are phytoplankton communities only limited by a single nutrient?

Authors of a study recently published in Nature tested this by conducting nutrient addition experiments on a GEOTRACES cruise in the nutrient-deficient South Atlantic gyre. Seawater samples were amended with nitrogen, iron, and cobalt both individually and in various combinations. Concurrent nitrogen and iron addition stimulated increased phytoplankton growth, yielding a ~40-fold increase in chlorophyll a. Supplementary addition of cobalt or cobalt-containing vitamin B12 further enhanced phytoplankton growth in several experiments.

Experiments conducted throughout the southeast Atlantic GEOTRACES GA08 cruise transect (left panel) demonstrated that nitrogen and iron had to be added to significantly stimulate phytoplankton growth (right panel). Supplementary addition of cobalt (or cobalt-containing vitamin B12) stimulated significant additional growth.

In addition to co-limited sites, the study identified ‘singly’ and ‘serially’ limited sites. These limitation regimes could be predicted by the measured ambient seawater nutrient concentrations, demonstrating the potential for using nutrient datasets to make confident predictions about limitation at larger spatial scales, an approach that is being more widely used in programmes like GEOTRACES,.

Finally, a complex, state-of-the-art biogeochemical ocean model suggested a much smaller extent of nutrient co-limitation than the experiments indicated. Authors attributed this to relatively restricted microbial and nutrient diversity in the model. These findings have implications for how such models are constructed if they are to represent nutrient co-limitation in the ocean and accurately project changes in ocean productivity in the future.

 

Authors:
Thomas J. Browning (GEOMAR)
Eric P. Achterberg (GEOMAR)
Insa Rapp (GEOMAR)
Anja Engel (GEOMAR)
Erin M. Bertrand (Dalhousie University)
Alessandro Tagliabue (University of Liverpool)
Mark Moore (University of Southampton)

Filter by Keyword

abundance acidification africa air-sea interactions alkalinity allometry ammonium AMOC anoxia anoxic Antarctic anthropogenic carbon aragonite saturation arctic arsenic Atlantic Atlantic modeling atmospheric CO2 atmospheric nitrogen deposition authigenic carbonates autonomous platforms bacteria BATS benthic bgc argo bioavailability biogeochemical cycles biogeochemical models biogeochemistry biological pump biological uptake biophysics bloom blooms blue carbon bottom water boundary layer buffer capacity CaCO3 calcification calcite carbon-climate feedback carbon-sulfur coupling carbon cycle carbon dioxide carbon sequestration Caribbean CCA CCS changing marine ecosystems changing ocean chemistry chemoautotroph chl a chlorophyll circulation climate change CO2 coastal ocean cobalt Coccolithophores community composition conservation cooling effect copepod coral reefs currents cyclone DCM decomposers decomposition deep convection deep ocean deep sea coral deoxygenation depth diagenesis diatoms DIC diel migration dimethylsulfide dissolved inorganic carbon dissolved organic carbon DOC DOM domoic acid dust DVM earth system models eddy Education Ekman transport emissions ENSO enzyme equatorial regions error ESM estuarine and coastal carbon fluxes estuary euphotic zone eutrophication evolution export EXPORTS extreme weather events faecal pellets filter feeders filtration rates fish Fish carbon fisheries floats fluid dynamics fluorescence food webs forams freshening freshwater frontal zone future oceans geochemistry geoengineering GEOTRACES glaciers gliders global carbon budget global warming go-ship grazing greenhouse gas Greenland groundwater Gulf of Maine Gulf of Mexico Gulf Stream gyre harmful algal bloom high latitude human food human impact hydrothermal hypoxia ice age ice cores ice cover industrial onset inverse circulation iron iron fertilization isotopes jellies katabatic winds kelvin waves krill kuroshio land-ocean continuum larvaceans lateral transport lidar ligands light light attenuation mangroves marine heatwave marine snowfall marshes Mediterranean meltwater mesopelagic mesoscale metagenome metals methane microbes microlayer microorganisms microscale microzooplankton midwater mixed layer mixed layers mixotrophy modeling mode water molecular diffusion MPT multi-decade NASA NCP net community production new technology nitrate nitrogen nitrogen fixation nitrous oxide north atlantic north pacific nutricline nutrient budget nutrient cycling nutrient limitation nutrients OA ocean-atmosphere ocean acidification ocean carbon uptake and storage ocean color ocean observatories ODZ oligotrophic omics OMZ open ocean optics organic particles overturning circulation oxygen pacific paleoceanography particle flux pCO2 PDO peat pelagic pH phenology phosphorus photosynthesis physical processes physiology phytoplankton plankton POC polar regions pollutants prediction primary productivity Prochlorococcus proteins pteropods pycnocline radioisotopes remineralization remote sensing residence time resource management respiration resuspension rivers rocky shore Rossby waves Ross Sea ROV salinity salt marsh satell satellite scale seafloor seagrass sea ice sea level rise seasonal patterns seaweed sediments sensors shelf system shells ship-based observations silicate sinking particles size SOCCOM soil carbon southern ocean south pacific spatial covariations speciation SST subduction submesoscale subpolar subtropical surface surface ocean Synechococcus teleconnections temperate temperature temporal covariations thermocline thermohaline thorium tidal time-series time of emergence top predators total alkalinity trace elements trace metals trait-based transfer efficiency transient features trophic transfer tropical turbulence twilight zone upper ocean upper water column upwelling US CLIVAR validation velocity gradient ventilation vertical flux vertical migration vertical transport volcano water quality western boundary currents wetlands winter mixing zooplankton

Copyright © 2021 - 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.