Global variability of high-nutrient low-chlorophyll regions using neural networks and wavelet coherence analysis
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Published:2023-07-06
Issue:4
Volume:19
Page:973-990
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ISSN:1812-0792
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Container-title:Ocean Science
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language:en
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Short-container-title:Ocean Sci.
Author:
Basterretxea Gotzon, Font-Muñoz Joan S.ORCID, Hernández-Carrasco IsmaelORCID, Sañudo-Wilhelmy Sergio A.
Abstract
Abstract. We examine 20 years of monthly global ocean color data and
modeling outputs of nutrients using self-organizing map (SOM) analysis to
identify characteristic spatial and temporal patterns of high-nutrient low-chlorophyll (HNLC) regions and their association with different climate
modes. The global nitrate-to-chlorophyll ratio threshold of
NO3 : Chl > 17 (mmol NO3 mg Chl−1) is estimated to be a good indicator
of the distribution limit of this unproductive biome that, on average,
covers 92 × 106 km2 (∼ 25 % of the ocean). The
trends in satellite-derived surface chlorophyll (0.6 ± 0.4 % yr−1 to 2 ± 0.4 % yr−1) suggest that HNLC regions in polar and subpolar areas
have experienced an increase in phytoplankton biomass over the last decades,
but much of this variation, particularly in the Southern Ocean, is produced
by a climate-driven transition in 2009–2010. Indeed, since 2010, the extent
of the HNLC zones has decreased at the poles (up to 8 %) and slightly
increased at the Equator (< 0.5 %). Our study finds that
chlorophyll variations in HNLC regions respond to major climate variability
signals such as the El Niño–Southern Oscillation (ENSO) and Meridional
Overturning Circulation (MOC) at both short (2–4 years) and long (decadal)
timescales. These results suggest global coupling in the functioning of
distant biogeochemical regions.
Funder
Ministerio de Ciencia e Innovación Govern de les Illes Balears Universitat de les Illes Balears
Publisher
Copernicus GmbH
Subject
Cell Biology,Developmental Biology,Embryology,Anatomy
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