Release of significant fraction of primary production as dissolved organic carbon in the Bay of Bengal

Rao, D.N.; Chopra, Manish; Rajula, G.R.; Durgadevi, D.S.L.; Sarma, V. V. S. S.

doi:10.1016/j.dsr.2020.103445

Cited by 14 publications

(7 citation statements)

References 52 publications

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“…Patchiness of phytoplankton primary productivity and nutrient availability within eddies may thus lead to spatial heterogeneity of extracellular release rates (e.g. Lasternas et al, 2013;Rao et al, 2021) and DOM quality (e.g. Wear et al, 2020).…”

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confidence: 99%

Eddy-enhanced primary production sustains heterotrophic microbial activities in the Eastern Tropical North Atlantic

et al. 2022

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Abstract. Mesoscale eddies modulate the ocean's physical, chemical, and biological properties. In cyclonic eddies (CEs), nutrient upwelling can stimulate primary production by phytoplankton. Yet, how this locally enhanced autotrophic production affects heterotrophy and consequently the metabolic balance between the synthesis and the consumption of dissolved organic matter (DOM) remains largely unknown. To fill this gap, we investigated the horizontal and vertical variability in auto- and heterotrophic microbial activity (biomass production and respiration) within a CE that formed off Mauritania and along the ∼ 900 km zonal corridor between Mauritania and the Cape Verde islands in the Eastern Tropical North Atlantic (ETNA). Our results show how the physical disturbances caused by the CE affected the biomass distribution of phyto- and bacterioplankton and their metabolic activities. The injection of nutrients into the sunlit surface resulted in enhanced autotrophic pico- and nanoplankton abundance and generally increased autotrophic activity as indicated by chlorophyll a (Chl a) concentration, primary production (PP), and extracellular release rates. However, the detailed eddy survey also revealed an uneven distribution of these variables with, for example, the highest Chl a concentrations and PP rates occurring near and just beyond the CE's periphery. The heterotrophic bacterial activity was similarly variable. Optode-based community respiration (CR), bacterial respiration (BR) estimates, and bacterial biomass production (BP) largely followed the trends of PP and Chl a. Thus, a submesoscale spatial mosaic of heterotrophic bacterial abundance and activities occurred within the CE that was closely related to variability in autotrophic production. Consistent with this, we found a significant positive correlation between concentrations of semi-labile dissolved organic carbon (SL-DOC; here the sum of dissolved hydrolysable amino acids and dissolved combined carbohydrates) and BR estimates. Extracellular release of carbon as indicated by primary production of dissolved organic carbon (PPDOC) was variable with depth and laterally and not always sufficient to compensate the bacterial carbon demand (BCD: BR + BP), with PPDOC accounting for between 28 % and 110 % of the BCD. Bacterial growth efficiency (BGE: BP / BCD) ranged between 1.7 % and 18.2 %. We estimated the metabolic state to establish whether the CE was a source or a sink of organic carbon. We showed that the CE carried a strong autotrophic signal in the core (PP / CR > 1). Our results suggest that submesoscale (0–10 km) processes lead to highly variable metabolic activities in both photoautotrophic and heterotrophic microorganisms. Overall, we revealed that the CEs not only trap and transport coastal nutrients and organic carbon to the open ocean but also stimulate phytoplankton growth, generating freshly produced organic matter during westward propagation. This drives heterotrophic processes and may contribute to the previously observed net heterotrophy in open Atlantic surface waters.

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confidence: 99%

Eddy-enhanced primary production sustains heterotrophic microbial activities in the Eastern Tropical North Atlantic

et al. 2022

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“…However higher concentrations of organic nutrients (both nitrogen and phosphorus) were reported recently and also its role on primary production has been established (Rao et al, 2021;Sarma et al, 2019). Nevertheless, it may not increase the export production as picophytoplankton are dominant (up to 75% of total phytoplankton biomass) in the BoB (Sarma et al, 2016(Sarma et al, , 2019 and about 50% of primary production is exudated as dissolved organic matter (Rao et al, 2021). Despite such conducive conditions, primary production is low in the NE BoB due to presence of high suspended matter as evidenced from the higher particle back-scatter signals in the surface (Figure not shown) and also 300 m (Figure 4a).…”

Section: Ne Bay Of Bengal (Ne Bob)mentioning

confidence: 99%

“…Several recent investigations suggested that low saline waters in the upper 25 m of water column are devoid of inorganic nutrients to support primary production (Sarma et al, 2016(Sarma et al, , 2019. However higher concentrations of organic nutrients (both nitrogen and phosphorus) were reported recently and also its role on primary production has been established (Rao et al, 2021;Sarma et al, 2019). Nevertheless, it may not increase the export production as picophytoplankton are dominant (up to 75% of total phytoplankton biomass) in the BoB (Sarma et al, 2016(Sarma et al, , 2019 and about 50% of primary production is exudated as dissolved organic matter (Rao et al, 2021).…”

Section: Ne Bay Of Bengal (Ne Bob)mentioning

confidence: 99%

“…Recently Rao et al. (2021) estimated that about 50% of the primary production exudates as dissolved organic carbon in the BoB and it may be recycled within the upper ocean rather than exported resulting in low sinking carbon fluxes. The role of stratification on intensity of OMZ is reported, both in the coastal and offshore regions (Sarma et al., 2013, 2016), due to limitation of vertical oxygen transport to the OMZ, which is identified to be a major source of oxygen to the OMZ (Sarma, 2002).…”

Section: Introductionmentioning

confidence: 99%

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Potential Mechanisms Responsible for Spatial Variability in Intensity and Thickness of Oxygen Minimum Zone in the Bay of Bengal

2021

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Spatial variability in boundaries and thickness of oxygen minimum zone (OMZ) is derived based on measured dissolved oxygen data obtained from sensors on board biogeochemical (BGC) Argo floats between 2013 and 2019 in the Bay of Bengal (BoB). Upper and lower boundaries of the OMZ varied from 60 to 200 m and 100 to 800 m respectively with the thickness of 80–650 m in the BoB. Relatively thicker OMZ is noticed in the northern than southern BoB associated with stratification. The oxygen concentrations in the OMZ in the NW was low (<1.5 μM) than NE BoB (2.5 μM) indicating that thick and intense OMZ occurs in the NW region associating with stratification and high primary production. Significant decrease in particle‐back‐scatter signal was observed toward offshore from shelf indicating organic matter from the shelf sediments may be supporting bacterial carbon demand in the OMZ. The particle backscatter signal peaked in the OMZ region with a higher signal in the north than southern BoB and it is consistent with the low oxygen concentration in the former indicating that organic matter from shelf sediments may be supporting carbon needs in the OMZ. In addition to this, the occurrence of eddies significantly controls the intensity of the OMZ in the BoB through mixing at the upper boundary of OMZ. Therefore, this study suggests that spatial variations in intensity of OMZ in the BoB are governed by stratification, primary and export productions, organic matter decomposition, and eddy‐driven mixing.

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“…Patchiness of phytoplankton primary productivity and nutrient limitation within eddies may thus lead to spatial heterogeneity of extracellular release rates (e.g. Lasternas et al, 2013, Rao et al, 2021 with distinct quality (e.g. Wear et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

Eddy enhanced primary production accelerates bacterial growth in the Eastern Tropical North Atlantic

Devresse

Becker

Bendinger

et al. 2022

Preprint

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Abstract. Mesoscale eddies play essential roles in modulating the ocean's physical, chemical, and biological properties. In cyclonic eddies (CE) nutrient upwelling can stimulate primary production by phytoplankton. Yet, how this locally enhanced autotrophic production affects heterotrophic bacterial activities (biomass production and respiration) and consequently the metabolic balance between the synthesis and the consumption of dissolved organic matter (DOM) remains largely unknown. To address this gap, we investigated the horizontal and vertical variability of phytoplankton and heterotrophic bacterial activity along ~900 km zonal corridor between the coast of Mauretania and the Cape Verde Islands in the eastern tropical North Atlantic (ETNA). We additionally collected samples from a CE along this transect at high spatial resolution. Our results show cascading effects of physical disturbances induced by a CE on phyto- and bacterioplankton biomass and metabolic activities. Specifically, the injection of nutrients into the sunlit surface resulted in enhanced autotrophic plankton abundance and activity as indicated by Chlorophyll a (Chl-a) concentration, DOM exudation, and primary productivity (PP). However, the detailed eddy survey revealed an uneven distribution of these parameters with, for example, the highest Chl-a concentrations and PP rates near and just beyond the CE’s periphery. The heterotrophic bacterial activity was similarly variable. Optode-based bacterial respiration (BR) and biomass production (BP) largely followed the trends of PP and Chl-a. Thus, a submesoscale spatial mosaic of heterotrophic bacterial abundance and activities occurred within the CE studied here that was closely related to variability in autotrophic production. This was supported by a significant positive correlation between concentrations of semi-labile organic carbon (SL-DOC; the sum of dissolved hydrolyzable amino acids and combined carbohydrates) and BR measurements. Bacterial growth efficiency (BP/(BR+BP)) was variable (1.4–10.5 %) within the CE and carbon exudation was not always sufficient to compensate the bacterial carbon demand (BR+BP; 28.3–114.5 %). We have additionally estimated the metabolic state in our samples, which showed that the CE carried a strong autotrophic signal (PP/(BR+BP) > 1). Overall, our results show that submesoscale (0–10 km) processes lead to highly variable metabolic activities of both phototrophic and heterotrophic microbes, which has implications for biogeochemical models estimating oceanic carbon fluxes. Additionally, we revealed that the CE not only traps and transports coastal nutrients and carbon to the open ocean but also stimulates phytoplankton growth generating freshly produced organic matter during westward propagation. This organic matter may fuel heterotrophic processes in the open ocean and may help to explain the often-observed net heterotrophic metabolic state of these environments.

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Release of significant fraction of primary production as dissolved organic carbon in the Bay of Bengal

Cited by 14 publications

References 52 publications

Eddy-enhanced primary production sustains heterotrophic microbial activities in the Eastern Tropical North Atlantic

Eddy-enhanced primary production sustains heterotrophic microbial activities in the Eastern Tropical North Atlantic

Potential Mechanisms Responsible for Spatial Variability in Intensity and Thickness of Oxygen Minimum Zone in the Bay of Bengal

Eddy enhanced primary production accelerates bacterial growth in the Eastern Tropical North Atlantic

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