Variability in Water-Column Respiration and Its Dependence on Organic Carbon Sources in the Canary Current Upwelling Region

Arı́stegui, Javier; Montero, María F.; Hernández‐Hernández, Nauzet; Alonso-González, Iván J.; Baltar, Federico; Calleja, María Ll.; Duarte, Carlos M.

doi:10.3389/feart.2020.00349

Cited by 12 publications

(10 citation statements)

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“…Initial concentrations of DOC were similar to those typically found in surface waters of the Canary Islands oceanic region (Arístegui et al, 2003, 2004, 2020; Burgoa et al, 2020) and other locations in the North Atlantic subtropical gyre (Goldberg et al, 2010; Lomas et al, 2013). Concentrations quickly increased following nutrient depletion and the collapse of the diatom-dominated phytoplankton bloom (Ortiz et al, 2022).…”

Section: Discussionsupporting

confidence: 77%

Artificial upwelling leads to a large increase in surface dissolved organic matter concentrations

Gómez‐Letona

Sebastián

Baños

et al. 2022

Preprint

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In the face of climate change there is a need to reduce atmospheric CO2 concentrations. Artificial upwelling of nutrient-rich deep waters has been proposed as a method to enhance the biological carbon pump in oligotrophic oceanic regions in order to increase carbon sequestration. However, the fate of the newly produced organic matter, and specifically of its resulting dissolved fraction, is not clearly understood. Here we examine the effect of different upwelling intensities and modes (single pulse versus recurring pulses) on the dissolved organic matter pool (DOM). We introduced nutrient-rich deep water to large scale mesocosms (∼44 m3) in the oligotrophic subtropical North Atlantic and found that artificial upwelling strongly increased DOM concentrations and changed its characteristics. The magnitude of the observed changes was related to the upwelling intensity: more intense treatments led to higher accumulation of dissolved organic carbon (>70 μM of excess DOC over ambient waters for the most intense) and to comparatively stronger changes in DOM characteristics (increased proportions of chromophoric DOM (CDOM) and humic-like fluorescent DOM), suggesting a transformation of the DOM pool at the molecular level. Moreover, the single upwelling pulse resulted in higher CDOM quantities with higher molecular weight than the recurring upwelling mode. Together, our results indicate that under artificial upwelling, large DOM pools may accumulate in the surface ocean without being remineralised in the short-term. Possible reasons for this persistence could be a combination of the molecular diversification of DOM due to microbial reworking, nutrient limitation and reduced metabolic capabilities of the prokaryotic communities inside the mesocosms. Our study demonstrates the importance of the DOC pool when assessing the carbon sequestration potential of artificial upwelling.

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Section: Discussionsupporting

confidence: 77%

Artificial upwelling leads to a large increase in surface dissolved organic matter concentrations

Gómez‐Letona

Sebastián

Baños

et al. 2022

Preprint

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“…Initial concentrations of DOC similar to those typically found in surface waters of the Canary Islands oceanic region (Arı ́stegui et al, 2003;Arı ́stegui et al, 2004;Arı ́stegui et al, 2020;Burgoa et al, 2020) and other locations in the North Atlantic subtropical gyre (Goldberg et al, 2010;Lomas et al, 2013). Concentrations quickly increased following nutrient depletion and the collapse of the diatom-dominated phytoplankton bloom (Ortiz et al, 2022b).…”

Section: Doc Accumulation In the Water Columnsupporting

confidence: 65%

The importance of the dissolved organic matter pool for the carbon sequestration potential of artificial upwelling

Gómez‐Letona

Sebastián²,

Baños³

et al. 2022

Front. Mar. Sci.

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In the face of climate change there is a need to reduce atmospheric CO2 concentrations. Artificial upwelling of nutrient-rich deep waters has been proposed as a method to enhance the biological carbon pump in oligotrophic oceanic regions in order to increase carbon sequestration. Here we examine the effect of different artificial upwelling intensities and modes (single pulse versus recurring pulses) on the dynamics of the dissolved organic matter pool (DOM). We introduced nutrient-rich deep water to large scale mesocosms (~44 m3) in the oligotrophic subtropical North Atlantic and found that artificial upwelling strongly increased DOM concentrations and changed its characteristics. The magnitude of the observed changes was related to the upwelling intensity: more intense treatments led to higher accumulation of dissolved organic carbon (>70 μM of excess DOC over ambient waters for the most intense) and to comparatively stronger changes in DOM characteristics (increased proportions of chromophoric DOM (CDOM) and humic-like fluorescent DOM), suggesting a transformation of the DOM pool at the molecular level. Moreover, the single upwelling pulse resulted in higher CDOM quantities with higher molecular weight than the recurring upwelling mode. Together, our results indicate that under artificial upwelling, large DOM pools may accumulate in the surface ocean without being remineralized in the short-term. Possible reasons for this persistence could be a combination of the molecular diversification of DOM due to microbial reworking, nutrient limitation and reduced metabolic capabilities of the prokaryotic communities within the mesocosms. Our study demonstrates the importance of the DOC pool when assessing the carbon sequestration potential of artificial upwelling.

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“…The distribution of DOC, POC and PON in mesopelagic waters showed the expected decrease with depth due to production in the surface layer and subsequent mineralization at depth. POC concentration was very low compared to other studies in the Canary Current System (Alonso-Gonzaĺez et al, 2009;Arıśtegui et al, 2020). As shown in Valiente et al (2022), these differences could be due to the influence of the giant filament of Cape Blanc, which exports the suspended POC fraction further offshore whereas the sinking POC fraction is mineralized in the epipelagic and upper mesopelagic waters.…”

Section: Local Mineralization In the Water Masses Of The Mesopelagic ...mentioning

confidence: 55%

“…The low contribution of DOC and POC to local mineralization also suggests sinking POC should be the primary support for the local oxygen demand. Nevertheless, other works further north in the Canary Current system (Arıśtegui et al, 2003;Arıśtegui et al, 2020), where the concentration of suspended POC is much higher, found that this fraction was the main support for mesopelagic respiration there. These authors argued that advection of this suspended particulate material from the adjacent coastal productive waters is the reason behind this behavior.…”

Section: Local Mineralization In the Water Masses Of The Mesopelagic ...mentioning

confidence: 86%

High-resolution variability of dissolved and suspended organic matter in the Cape Verde Frontal Zone

et al. 2022

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Distributions of dissolved (DOM) and suspended (POM) organic matter, and their chromophoric (CDOM) and fluorescent (FDOM) fractions, are investigated at high resolution (< 10 km) in the Cape Verde Frontal Zone (CVFZ) during fall 2017. In the epipelagic layer (< 200 m), meso- and submesoscale structures (meanders, eddies) captured by the high resolution sampling dictate the tight coupling between physical and biogeochemical parameters at the front. Remarkably, fluorescent humic-like substances show relatively high fluorescence intensities between 50 and 150 m, apparently not related to local mineralization processes. We hypothesize that it is due to the input of Sahara dust, which transports highly re-worked DOM with distinctive optical properties. In the mesopelagic layer (200-1500 m), our results suggest that DOM and POM mineralization occurs mainly during the transit of the water masses from the formation sites to the CVFZ. Therefore, most of the local mineralization seems to be due to fast-sinking POM produced in situ or imported from the Mauritanian upwelling. These local mineralization processes lead to the production of refractory CDOM, an empirical evidence of the microbial carbon pump mechanism. DOM released from these fast-sinking POM is the likely reason behind the observed columns of relatively high DOC surrounded by areas of lower concentration. DOM and POM dynamics in the CVFZ has turned out to be very complex, in parallel to the complexity of meso- and submesoscale structures present in the area. On top of this high resolution variability, the input of Sahara dust or the release of DOM from sinking particles have been hypothesized to explain the observed distributions.

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Variability in Water-Column Respiration and Its Dependence on Organic Carbon Sources in the Canary Current Upwelling Region

Cited by 12 publications

References 50 publications

Artificial upwelling leads to a large increase in surface dissolved organic matter concentrations

Artificial upwelling leads to a large increase in surface dissolved organic matter concentrations

The importance of the dissolved organic matter pool for the carbon sequestration potential of artificial upwelling

High-resolution variability of dissolved and suspended organic matter in the Cape Verde Frontal Zone

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