First direct measurements of luxury iron uptake in natural phytoplankton communities: surprising results!

Joint Science Highlight with the US Ocean Carbon & Biogeochemistry Programme (OCB).

The uptake of iron by phytoplankton is a key part of the marine iron cycle, but we still have a rudimentary understanding of the controls on this process. It is generally assumed that dissolved iron availability controls phytoplankton iron. Combining data from the GP16 GEOTRACES section and three other GEOTRACES-compliant cruises in the eastern Pacific, Twining et al. (2020, see reference below) show that phytoplankton iron contents (aka, quotas) vary 40-fold across environmental gradients. Further, taxa prone to nitrogen limitation such as diatoms accumulate iron more than expected, even under extremely low iron conditions. Modeling indicates that this is a widespread occurrence in the low-Fe oligotrophic Pacific. This study provides the first direct measurements of luxury iron uptake in natural communities and shows how it can vary between diatom taxa, with Pseudo-nitzschia able to accumulate luxury iron even in the low-Fe sub-Arctic North Pacific. These findings demonstrate the importance of biology and ecology to understanding iron biogeochemistry.

Figure. Response of iron quotas to nutrient gradients in the South Pacific Ocean. a) location of stations on GP16 cruise, plotted over bathymetry. b) phytoplankton abundance (total Chl a), nitrate, dFe, and relative diatom abundance (% fucoxanthin, a pigment proxy for diatoms) across the onshore-offshore gradient. Data are means of upper 50m at each station. Dashed blue lines delineate putative coastal, HNLC, and oligotrophic regions (Boiteau et al. 2016). c) Taxon-specific Fe quotas (geometric means +/- SE) as a function of location. Dashed red line indicates the optimal Fe/C estimated for open-ocean phytoplankton under low dFe. Symbol colors are as indicated in panel d legend: red – autotrophic flagellates (aflag), green – centric diatoms (centric), blue – pennate diatoms (pennate). d) Taxon-specific Fe quotas as a function of dFe. Also plotted is predicted FeCopt. e) Response of taxon-specific Fe quotas to gradients in ambient nitrate and dFe. Symbol color indicates Fe/C (mol/umol). Arrows indicate direction of cruise track, moving from shelf westward into the gyre.

Reference:

Twining, B. S., O. Antipova, P. D. Chappell, N. R. Cohen, J. Jacquot, E. L. Mann, A. Marchetti, D. C. Ohnemus, S. Rauschenberg, and A. Tagliabue. 2020. Taxonomic and nutrient controls on phytoplankton iron quotas in the ocean. Limnology & Oceanography Letters. Access the paper: https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lol2.10179

Latest highlights

Science Highlights

High resolution of dissolved and particulate barium distributions in the Atlantic and Pacific Ocean reveal the importance of the margin sources on the oceanic Ba budget

Rahman and co-workers performed intensive samplings and analyses of barium along the GEOTRACES GA03 and GP16 transects.

06.07.2022

Science Highlights

The most important thorium-234 disequilibrium compilation you ever saw

Elena Ceballos-Romero and her colleagues propose a comprehensive global oceanic compilation of Thorium-234 measurements.

23.06.2022

Science Highlights

Machine learning approach led to the first iron climatology

Huang and co-workers propose the first data-driven surface-to-seafloor dissolved iron climatology.

21.06.2022

Science Highlights

Insight on the aluminium cycling during the inter-monsoon period in the Arabian Sea and Equatorial Indian Ocean

Full vertical water column profiles were established by Singh and Singh along the GI05 transect in the Indian Ocean during the fall inter-monsoon period in 2015.

Rechercher