Substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump

Dall’Olmo, Giorgio; Dingle, James; Polimene, Luca; Brewin, Robert J. W.; Claustre, Hervé

doi:10.1038/ngeo2818

Cited by 124 publications

(172 citation statements)

References 36 publications

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“…Amongst these, 40 profiles were associated with subduction events. Seventy five percent of the events occurred in late spring and summer (supporting information Figure S2a) when subducted water is more likely to remain isolated from the surface during weeks or months without being re‐entrained into the mixed layer (Dall'Olmo et al, ). Episodic subduction occurs throughout the year but the anomalies are easily eroded under strong winter mixing.…”

Section: Resultsmentioning

confidence: 99%

Evaluating Southern Ocean Carbon Eddy‐Pump From Biogeochemical‐Argo Floats

et al. 2018

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The vertical transport of surface water and carbon into ocean's interior, known as subduction, is one of the main mechanisms through which the ocean influences Earth's climate. New instrumental approaches have shown the occurrence of localized and intermittent subduction episodes associated with small‐scale ocean circulation features. These studies also revealed the importance of such events for the export of organic matter, the so‐called eddy‐pump. However, the transient and localized nature of episodic subduction hindered its large‐scale evaluation to date. In this work, we present an approach to detect subduction events at the scale of the Southern Ocean using measurements collected by biogeochemical autonomous floats (BGCArgo). We show how subduction events can be automatically identified as anomalies of spiciness and Apparent Oxygen Utilization (AOU) below the mixed layer. Using this methodology over more than 4,000 profiles, we detected 40 subduction events unevenly distributed across the Sothern Ocean. Events were more likely found in hot spots of eddy kinetic energy (EKE), downstream major bathymetric features. Moreover, the bio‐optical measurements provided by BGCArgo allowed measuring the amount of Particulate Organic Carbon (POC) being subducted and assessing the contribution of these events to the total downward carbon flux at 100 m (EP100). We estimated that the eddy‐pump represents less than 19% to the EP100 in the Southern Ocean, although we observed particularly strong events able to locally duplicate the EP100. This approach provides a novel perspective on where episodic subduction occurs that will be naturally improved as BGCArgo observations continue to increase.

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Section: Resultsmentioning

confidence: 99%

Evaluating Southern Ocean Carbon Eddy‐Pump From Biogeochemical‐Argo Floats

et al. 2018

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“…This mechanism assumes that the abundance of zooplankton is correlated with grazing pressure on phytoplankton, the rate of fecal pellet production and the contribution of fecal pellets to export flux, as demonstrated experimentally (e.g., Cavan et al, 2015;Ebersbach & Trull, 2008;Landry, 1995). LP-HE regimes may also be associated with transient, nonbiological processes which may contribute to high export efficiency, for example, the mixed layer pump (Dall'Olmo et al, 2016;Giering et al, 2016), in which variability in the mixed layer depth results in detrainment of particles. Unfortunately, there are insufficient temporally resolved observations in our data set to examine this potential seasonality.…”

Section: Discussionmentioning

confidence: 99%

“…Additionally, our meta-analysis approach cannot account for all the complexities of the processes thought to influence export flux, such as the interplay between gravitational settling and particle type or size (McDonnell & Buesseler, 2010), details of the community structure (e.g., type of zooplankton, characteristics of different diatom species, and TEP producers; De La Rocha & Passow, 2007;Turner, 2015), transport of organic carbon via the diel vertical migration of zooplankton (Steinberg et al, 2000), export of dissolved organic carbon (Roshan & DeVries, 2017), or the nonbiological transport of particles below the mixed layer by detrainment or subduction (Dall'Olmo et al, 2016;Omand et al, 2015). Additionally, our meta-analysis approach cannot account for all the complexities of the processes thought to influence export flux, such as the interplay between gravitational settling and particle type or size (McDonnell & Buesseler, 2010), details of the community structure (e.g., type of zooplankton, characteristics of different diatom species, and TEP producers; De La Rocha & Passow, 2007;Turner, 2015), transport of organic carbon via the diel vertical migration of zooplankton (Steinberg et al, 2000), export of dissolved organic carbon (Roshan & DeVries, 2017), or the nonbiological transport of particles below the mixed layer by detrainment or subduction (Dall'Olmo et al, 2016;Omand et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

Drivers of Carbon Export Efficiency in the Global Ocean

Henson

Moigne

Giering

2019

Global Biogeochemical Cycles

110

114

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The export of organic carbon from the surface ocean forms the basis of the biological carbon pump, an important planetary carbon flux. Typically, only a small fraction of primary productivity (PP) is exported (quantified as the export efficiency: export/PP). Here we assemble a global data synthesis to reveal that very high export efficiency occasionally occurs. These events drive an apparent inverse relationship between PP and export efficiency, which is opposite to that typically used in empirical or mechanistic models. At the global scale, we find that low PP, high export efficiency regimes tend to occur when macrozooplankton and bacterial abundance are low. This implies that a decoupling between PP and upper ocean remineralization processes can result in a large fraction of PP being exported, likely as intact cells or phytoplankton‐based aggregates. As the proportion of PP being exported declines, macrozooplankton and bacterial abundances rise. High export efficiency, high PP regimes also occur infrequently, possibly associated with nonbiologically mediated export of particles. A similar analysis at a biome scale reveals that the factors affecting export efficiency may be different at regional and global scales. Our results imply that the whole ecosystem structure, rather than just the phytoplankton community, is important in setting export efficiency. Further, the existence of low PP, high export efficiency regimes imply that biogeochemical models that parameterize export efficiency as increasing with PP may underestimate export flux during decoupled periods, such as at the start of the spring bloom.

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“…Consistent with the study of Giering et al () and Dall'Olmo et al (), our results suggest that regions characterized by a clear deepening of the mixed layer may be characterized by a high export of organic carbon toward deep waters. The supply of organic carbon under the photic zone could constitute an important food source for organisms that inhabit the mesopelagic zone.…”

Section: Discussionmentioning

confidence: 99%

Vertical Mixing Effects on Phytoplankton Dynamics and Organic Carbon Export in the Western Mediterranean Sea

et al. 2018

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A 3‐D high‐resolution coupled hydrodynamic‐biogeochemical model of the western Mediterranean was used to study phytoplankton dynamics and organic carbon export in three regions with contrasting vertical regimes, ranging from deep convection to a shallow mixed layer. One month after the initial increase in surface chlorophyll (caused by the erosion of the deep chlorophyll maximum), the autumnal bloom was triggered in all three regions by the upward flux of nutrients resulting from mixed layer deepening. In contrast, at the end of winter, the end of turbulent mixing favored the onset of the spring bloom in the deep convection region. Low grazing pressure allowed rapid phytoplankton growth during the bloom. Primary production in the shallow mixed layer region, the Algerian subbasin, was characterized by a long period (4 months) of sustained phytoplankton development, unlike the deep convection region where primary production was inhibited during 2 months in winter. Despite seasonal variations, annual primary production in all three regions is similar. In the deep convection region, total organic carbon export below the photic layer (150 m) and transfer to deep waters (800 m) was 5 and 8 times, respectively, higher than in the Algerian subbasin. Although some of the exported material will be injected back into the surface layer during the next convection event, lateral transport, and strong interannual variability of MLD in this region suggest that a significant amount of exported material is effectively sequestrated.

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Substantial energy input to the mesopelagic ecosystem from the seasonal mixed-layer pump

Cited by 124 publications

References 36 publications

Evaluating Southern Ocean Carbon Eddy‐Pump From Biogeochemical‐Argo Floats

Evaluating Southern Ocean Carbon Eddy‐Pump From Biogeochemical‐Argo Floats

Drivers of Carbon Export Efficiency in the Global Ocean

Vertical Mixing Effects on Phytoplankton Dynamics and Organic Carbon Export in the Western Mediterranean Sea

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