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Pervasive iron limitation at subsurface chlorophyll maxima of the California Current
- Source :
- Proceedings of the National Academy of Sciences of the United States of America, Proceedings of the National Academy of Sciences of the United States of America, vol 115, iss 52, 13300-13305
- Publication Year :
- 2018
- Publisher :
- National Academy of Sciences, 2018.
-
Abstract
- Significance The vertical distribution of phytoplankton cells and chlorophyll concentrations throughout the sunlit water column is rarely uniform. In many ocean regions, chlorophyll concentrations peak in distinct and persistent layers deep below the surface called subsurface chlorophyll maximum layers (SCMLs). SCML formation is hypothesized to reflect the consequences of phytoplankton light/macronutrient colimitation, behavior, and/or photoacclimation. We discovered unexpectedly persistent and widespread phytoplankton iron limitation and iron/light colimitation in SCMLs of the California Current and at the edge of the North Pacific Subtropical Gyre using shipboard incubations, metatranscriptomics, and biogeochemical proxies. These results suggest that interactions and feedbacks between iron and light availability play an important and previously unrecognized role in controlling the productivity and biogeochemical dynamics of SCMLs.<br />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.
- Subjects :
- 0301 basic medicine
Biogeochemical cycle
010504 meteorology & atmospheric sciences
01 natural sciences
03 medical and health sciences
Water column
Earth, Atmospheric, and Planetary Sciences
iron
Phytoplankton
Ecosystem
14. Life underwater
Life Below Water
0105 earth and related environmental sciences
Deep chlorophyll maximum
nutrient limitation
Multidisciplinary
Picoeukaryote
biology
fungi
Biological Sciences
deep chlorophyll maximum
biology.organism_classification
California Current
030104 developmental biology
Oceanography
Diatom
13. Climate action
Physical Sciences
Environmental science
Upwelling
light
Environmental Sciences
Subjects
Details
- Language :
- English
- ISSN :
- 10916490 and 00278424
- Volume :
- 115
- Issue :
- 52
- Database :
- OpenAIRE
- Journal :
- Proceedings of the National Academy of Sciences of the United States of America
- Accession number :
- edsair.doi.dedup.....f4b351ff4e865e9dec075d14bb2b62a4