A1 Refereed original research article in a scientific journal
Pervasive iron limitation at subsurface chlorophyll maxima of the California Current
Authors: Hogle SL, Dupont CL, Hopkinson BM, King AL, Buck KN, Roe KL, Stuart RK, Allen AE, Mann EL, Johnson ZI, Barbeau KA
Publisher: NATL ACAD SCIENCES
Publication year: 2018
Journal: Proceedings of the National Academy of Sciences of the United States of America
Journal name in source: PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Journal acronym: P NATL ACAD SCI USA
Volume: 115
Issue: 52
First page : 13300
Last page: 13305
Number of pages: 6
ISSN: 0027-8424
DOI: https://doi.org/10.1073/pnas.1813192115
Self-archived copy’s web address: https://research.utu.fi/converis/portal/Publication/44318834
Subsurface chlorophyll maximum layers (SCMLs) are nearly ubiquitous in stratified water columns and exist at horizontal scales ranging from the submesoscale to the extent of oligotrophic gyres. These layers of heightened chlorophyll and/or phytoplankton concentrations are generally thought to be a consequence of a balance between light energy from above and a limiting nutrient flux from below, typically nitrate (NO3). Here we present multiple lines of evidence demonstrating that iron (Fe) limits or with light colimits phytoplankton communities in SCMLs along a primary productivity gradient from coastal to oligotrophic offshore waters in the southern California Current ecosystem. SCML phytoplankton responded markedly to added Fe or Fe/light in experimental incubations and transcripts of diatom and picoeukaryote Fe stress genes were strikingly abundant in SCML metatranscriptomes. Using a biogeochemical proxy with data from a 40-y time series, we find that diatoms growing in California Current SCMLs are persistently Fe deficient during the spring and summer growing season. We also find that the spatial extent of Fe deficiency within California Current SCMLs has significantly increased over the last 25 y in line with a regional climate index. Finally, we show that diatom Fe deficiency may be common in the subsurface of major upwelling zones worldwide. Our results have important implications for our understanding of the biogeochemical consequences of marine SCML formation and maintenance.
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