From vast swirling flowers to tiny populations, photosynthetic phytoplankton that drift near the surface of the ocean are often captured in snapshots of satellites that detect chlorophyll. However, phytoplankton at greater depths escapes detection, so researchers must rely on other methods to study them.
Now Cornec et al. present the first worldwide direct detection analysis of a key oceanic signature of underground phytoplankton populations: the deepest chlorophyll maximum, which is the subterranean layer with the highest chlorophyll concentration. A deep deep chlorophyll may represent a corresponding maximum concentration of phytoplankton biomass (maximum deep biomass) or an increase in the amount of chlorophyll found in each phytoplankton cell (maximum deep photoacclimatization).
Previous research on maximum deep chlorophyll has focused on different ocean stations and regions, with different studies applying different methodologies. Therefore, much remains to be learned about the general processes that make up maximum deep chlorophyll, as well as its role on a global scale in the carbon cycle.
The new study is based on data from a global network of more than 500 biogeochemical floats – Argo to analyze the locations, types and engines of the deepest deep chlorophylls around the world. Free-floating floats contain a wide variety of sensors, including chlorophyll sensors, and return data from different ocean depths around the world.
Analysis of the float data reveals that the dynamics of deep deep chlorophylls depend on location and station. For example, deep deep chlorophyll is seen permanently or frequently in tropical and subtropical regions. Meanwhile, at high latitudes, they are less frequent and occur mainly in summer in the form of deep maximum biomass.
In low-nutrient (oligotrophic) oceanic regions, the analysis detected deep photoaclimation maxima that are permanent features, but are sometimes replaced by deep biomass maxima in summer. Waters in the north or south of the equatorial regions appear to house permanent peaks of deep biomass, thanks to light and abundant nutrients.
The analysis also suggests that the availability of light in the upper layer of the ocean is the main factor driving the development and depth of deep deep chlorophylls around the world.
This study establishes a new basis for a better understanding of the deep phytoplankton of the deep oceans and their role in the global carbon cycle.
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M. Cornec et al. Deep chlorophyll maximum in the global ocean: occurrences, engines and characteristics, Global biogeochemical cycles (2021). DOI: 10.1029 / 2020GB006759
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Citation: First world view of a key phytoplankton proxy (2021, May 12) retrieved May 12, 2021 at https://phys.org/news/2021-05-worldwide-view-key-phytoplankton-proxy. html
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