Deep Chlorophyll Maxima in the Global Ocean: Occurrences, Drivers and Characteristics

Cornec, M.; Claustre, Hervé; Mignot, Alexandre; Guidi, Lionel; Lacour, Léo; Poteau, Antoine; D’Ortenzio, Fabrizio; Gentili, Bernard; Schmechtig, Catherine

doi:10.1029/2020gb006759

Cited by 84 publications

(124 citation statements)

References 141 publications

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“…DCM profiles were then further segregated into photoacclimation (DAM) or biomass maxima (DBM) following Cornec et al. ( 2021 ). The characterization of DCM profiles was assessed through the depth of the DCM (Z DCM ) as well as (Chl a ) and b bp at the DCM depth ([Chl a ] DCM and b bpDCM , proxies of DCM intensity; Hopkinson & Barbeau, 2008 ).…”

Section: Methodsmentioning

confidence: 99%

“…Nitrate concentration at each depth was retrieved from the dissolved oxygen profiles through the neural network‐based method CANYON‐B (Bittig et al., 2018 ; Sauzède et al., 2017 , see SI: Text S2 ). Surface values of Photosynthetically Available Radiation (PAR) were computed with a clear‐sky model (Gregg & Carder, 1990 ), then propagated to depth using a regional attenuation coefficient based on empirical bio‐optical relations with (Chl a ) (Cornec et al, 2021 , adapted from Morel et al., 2007 ). Cloud‐cover coefficients were applied per month and per 10°‐latitude band on the PAR profiles (Cornec et al., 2021 ; Lacour et al., 2017 ).…”

Section: Methodsmentioning

confidence: 99%

“…Surface values of Photosynthetically Available Radiation (PAR) were computed with a clear‐sky model (Gregg & Carder, 1990 ), then propagated to depth using a regional attenuation coefficient based on empirical bio‐optical relations with (Chl a ) (Cornec et al, 2021 , adapted from Morel et al., 2007 ). Cloud‐cover coefficients were applied per month and per 10°‐latitude band on the PAR profiles (Cornec et al., 2021 ; Lacour et al., 2017 ). The iPAR was then derived at each profile depth by integrating the PAR profiles over the day‐length (Lacour et al., 2017 ).…”

Section: Methodsmentioning

confidence: 99%

“…Deep Chlorophyll Maxima (DCM) are ubiquitous phytoplanktonic features observed in the global ocean (Baldry et al., 2020 ; Cornec et al., 2021 ; Cullen, 2015 ; Mignot et al., 2014 ; Silsbe & Malkin, 2016 ), and more specifically in stratified systems (Cullen, 2015 ; Estrada et al., 1993 ). These active phytoplankton layers at depth are often indiscernible via satellite observation (Joint & Groom, 2000 ; Platt et al., 1988 ).…”

Section: Introductionmentioning

confidence: 99%

“…Our analysis of DCMs relies on BGC‐Argo's global data set of vertical measurements of fluorescence of Chl a (Fchl a ) and optical backscattering of particles ( b bp ) in addition to hydrological parameters and up to four additional core BGC parameters (Chai et al., 2020 ; Claustre et al., 2020 ; Roemmich et al., 2019 ). Fchl a and b bp are respectively proxies of the concentrations of (Chl a ) (Roesler et al., 2017 ) and particulate organic carbon (POC) (Cetinić et al., 2012 ; Loisel & Morel, 1998 ; Stramski et al., 1999 ), whose combined analysis allows identification of DCMs and discrimination between DAMs and DBMs (Cornec et al., 2021 ). Meanwhile, to probe into eddies, we co‐located the global data set of BGC‐Argo profiles with the TOEddies database (Laxenaire et al., 2018 ) providing a global atlas of mesoscale eddies automatically detected from Absolute Dynamical Topography (ADT) obtained via multi‐satellite altimetry.…”

Section: Introductionmentioning

confidence: 99%

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Impact of Mesoscale Eddies on Deep Chlorophyll Maxima

Cornec

Laxenaire

Claustre

et al. 2021

Geophysical Research Letters

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To better understand their dynamics, it is necessary to assess the drivers affecting their environmental properties, in particular, those affecting light and nutrient availability at depth. Small-scale ocean dynamics, such as internal waves or mesoscale eddies, may act as altering factors synced with phytoplankton responses, as they can induce vertical perturbations of the water column (McGillicuddy et al., 1998;Uz et al., 2001). Mesoscale eddies are ubiquitous structures in the global ocean (Chaigneau Abstract Deep Chlorophyll Maxima (DCM) are ubiquitous features in stratified oceanic systems.Their establishment and maintenance result from hydrographical stability favoring specific environmental conditions with respect to light and nutrient availability required for phytoplankton growth. This stability can potentially be challenged by mesoscale eddies impacting the water column's vertical structure and thus the environmental parameters that condition the subsistence of DCMs. Here, data from the global BGC-Argo float network are collocated with mesoscale eddies to explore their impact on DCMs. We show that cyclonic eddies, by providing optimal light and nutrient conditions, increase the occurrence of DCMs characterized by Deep Biomass Maxima for phytoplankton. In contrast, DCMs in anticyclonic eddies seem to be driven by photoacclimation as they coincide with Deep Acclimation Maxima without biomass accumulation. These findings suggest that the two types of eddies potentially have different impacts on the role of DCMs in global primary production. Plain Language SummaryIn the global ocean, phytoplankton can be found at depths where their growth is limited by their access to light from the surface and nutrient supply from below. Depending on the combination of environmental conditions, phytoplankton at depth can either accumulate in densely populated layers or deploy adaptive survival strategies such as multiplying their internal light sensors. Given their dependence on environmental variations, phytoplankton can be affected by physical disturbances that alter the vertical structure of the water column's properties. Among these are mesoscale eddies, large water structures dominated by rotation on the horizontal plane which also induce vertical physical movements. In this study, we associate data from autonomous robots that drift with ocean currents and sample physical and biological properties down to a depth of 2,000 meters, with mesoscale eddies detected by satellite. We show that on a global scale, cold mesoscale eddies promote the growth of phytoplankton at depth.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Impact of Mesoscale Eddies on Deep Chlorophyll Maxima

Cornec

Laxenaire

Claustre

et al. 2021

Geophysical Research Letters

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Relative depths of the subsurface peaks of phytoplankton abundance conserved over ocean provinces

Sato

Shiozaki

Hashihama

et al. 2022

Limnology & Oceanography

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Flow cytometric data collected from more than 250 stations in the Pacific and Indian Oceans were analyzed to determine the factors affecting the depth and magnitude of the subsurface abundance maximum of Synechococcus, Prochlorococcus, and small eukaryotes (< 6 μm). The peak depth of each phytoplankton population estimated by curve fitting was strongly correlated with the depth of the subsurface chlorophyll maximum (SCM). The slope of the regression line demonstrated that the peak depths of Synechococcus, Prochlorococcus, and small eukaryotes were 74% AE 1%, 88% AE 1%, and 104% AE 1% of the SCM depth (with confidence interval of 95%), respectively. This trend was largely conserved across the different ocean provinces of the Pacific and Indian Oceans. The peaks of Synechococcus frequently appeared in the nitrate-depleted layer of subtropical waters, suggesting their high affinity for regenerated and/or organic nutrients. The estimated daily irradiance received at the peak depths of Synechococcus and Prochlorococcus did not show a distinct latitudinal trend and fluctuated among neighboring stations, whereas that of small eukaryotes slightly increased toward the subarctic region. The present results show that the peak depths of Synechococcus, Prochlorococcus, and small eukaryotes relative to SCM were globally conserved on average, which is largely in line with the difference in their ability to acquire light and nutrients. However, the absolute light level and nutrient concentrations at the peak depths varied dramatically among neighboring stations, likely affected by physical movements.

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Physiological mortality of planktonic ciliates: Estimates, causes, and consequences

Weisse

2024

Limnology & Oceanography

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Contrasting physiological mortality with predator‐induced mortality is of tremendous importance for the population dynamics of many organisms but is difficult to assess. This is especially true for tiny organisms, such as most protists, which do not leave any carcasses behind. I performed a meta‐analysis using planktonic ciliates as model organisms to estimate the maximum physiological mortality rates (δmax) across pelagic ecosystems in relation to environmental and biotic factors. The median δmax of planktonic ciliates was 0.62 d−1 and did not differ between marine and freshwater species. Maximum ciliate mortality rates were species‐specific and affected by their specific growth rates (rmax), cell volume, and ability to encyst. Cyst‐forming species had, on average, higher δmax than species unable to encyst. Maximum mortality rates were positively related to rmax, but, in contrast to the latter, δmax appeared unaffected by temperature. I conclude that (1) in the ocean, physiological mortality is more critical for controlling ciliate population size than ciliate losses imposed by microcrustacean predation, but (2) in many lakes, the opposite holds; (3) cyst formation is an effective ciliate trait to cope with the high mortality of motile cells upon starvation. The lack of a temperature effect on δmax deserves further study; if correct, planktonic ciliates may take advantage of rising ocean and lake temperatures, with important implications for the pelagic food web.

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Deep Chlorophyll Maxima in the Global Ocean: Occurrences, Drivers and Characteristics

Cited by 84 publications

References 141 publications

Impact of Mesoscale Eddies on Deep Chlorophyll Maxima

Impact of Mesoscale Eddies on Deep Chlorophyll Maxima

Relative depths of the subsurface peaks of phytoplankton abundance conserved over ocean provinces

Physiological mortality of planktonic ciliates: Estimates, causes, and consequences

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