Role of eddies on controlling total and size-fractionated primary production in the Bay of Bengal

Sarma, V. V. S. S.; Chopra, Manish; Rao, D.N.; Priya, M.; Rajula, G.R.; Lakshmi, D.S.R.; Rao, V.D.

doi:10.1016/j.csr.2020.104186

Cited by 38 publications

(15 citation statements)

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“…1 The role of the Bay of Bengal in primary production in the global ocean -a historical perspective Marine primary producers contribute around 50 % to global net primary production (Behrenfeld et al, 2001), leading to a carbon flux from the atmosphere into the ocean of 45-50 Pg C and up to 90 Pg C yr −1 (Longhurst et al, 1995;Sabine et al, 2004;Sarmiento and Gruber, 2002). Changes in ocean primary production exert an important control on atmospheric carbon dioxide (CO 2 ) concentrations, and thus on global climate (Falkowski et al, 1998).…”

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confidence: 99%

Reviews and syntheses: Trends in primary production in the Bay of Bengal – is it at a tipping point?

Löscher

2021

Biogeosciences

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Abstract. Ocean primary production is the basis of the marine food web, sustaining life in the ocean via photosynthesis, and removing carbon dioxide from the atmosphere. Recently, a small but significant decrease in global marine primary production has been reported based on ocean color data, which was mostly ascribed to decreases in primary production in the northern Indian Ocean, particularly in the Bay of Bengal. Available reports on primary production from the Bay of Bengal (BoB) are limited, and due to their spatial and temporal variability difficult to interpret. Primary production in the BoB has historically been described to be driven by diatom and chlorophyte clades, while only more recent datasets also show an abundance of smaller cyanobacterial primary producers visually difficult to detect. The different character of the available datasets, i.e., direct counts, metagenomic and biogeochemical data, and satellite-based ocean color observations, make it difficult to derive a consistent pattern. However, making use of the most highly resolved dataset based on satellite imaging, a shift in community composition of primary producers is visible in the BoB over the last 2 decades. This shift is driven by a decrease in chlorophyte abundance and a coinciding increase in cyanobacterial abundance, despite stable concentrations of total chlorophyll. A similar but somewhat weaker trend is visible in the Arabian Sea, where satellite imaging points towards decreasing abundances of chlorophytes in the north and increasing abundances of cyanobacteria in the eastern parts. Statistical analysis indicated a correlation of this community change in the BoB to decreasing nitrate concentrations, which may provide an explanation for both the decrease in eukaryotic nitrate-dependent primary producers and the increase in small unicellular cyanobacteria related to Prochlorococcus, which have a comparably higher affinity to nitrate. Changes in community composition of primary producers and an overall decrease in system productivity would strongly impact oxygen concentrations of the BoB's low-oxygen intermediate waters. Assuming decreasing nitrate concentrations and concurrent decreasing biomass production, export, and respiration, oxygen concentrations within the oxygen minimum zone would not be expected to further decrease. This effect could be enhanced by stronger stratification as a result of future warming and thus possibly counteract oxygen decrease as a direct effect of stratification. Therefore, given a decrease in primary production, the BoB may not be at a tipping point for becoming anoxic, unless external nutrient inputs increase.

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confidence: 99%

Reviews and syntheses: Trends in primary production in the Bay of Bengal – is it at a tipping point?

Löscher

2021

Biogeosciences

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“…This feature suggests that other factors may have contributed to the intensive θ ′ in these regions. An alternative scenario may be that, in these mesotrophic‐eutrophic regions, upwelling in CEs uplifted nutrient‐rich subsurface waters to the near‐surface and promoted the growth of phytoplankton (McGillicuddy et al., 1998; Sarma et al., 2020) (vice versa for AEs, giving rise to the negative C Phyto ′ and Chl′ in Figure 2). This increase in nutrient supply also facilitated the synthesis of intracellular Chl (Arteaga et al., 2016; Halsey & Jones, 2015), thus resulting in positive θ ′.…”

Section: Resultsmentioning

confidence: 99%

“…For example, an increase in nutrient supply may not only promote the division rate of phytoplankton cells but also facilitates the synthesis of intracellular Chl (Arteaga et al., 2016; Halsey & Jones, 2015), resulting in an increase in both phytoplankton biomass and intracellular pigmentation. This paradigm may possibly be responsible for the simultaneous negative C Phyto ′ and positive θ ′ in the midlatitude oceans and boundary current systems, where eddy dynamics were suggested able to apparently alter the vertical supply of nutrients (Huang & Xu, 2018; McGillicuddy et al., 1998; Sarma et al., 2020). In addition, laboratory experiments showed considerable difference in θ for cells grown at 10 and 18 °C across a wide range of irradiances (Thompson, 1999).…”

Section: Discussion and Summarymentioning

confidence: 99%

Eddy‐Induced Near‐Surface Chlorophyll Anomalies in the Subtropical Gyres: Biomass or Physiology?

Zhan

Cai

et al. 2021

Geophysical Research Letters

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Satellite observations show higher near‐surface phytoplankton chlorophyll (Chl) in anticyclonic eddies (AEs) than in cyclonic eddies (CEs) in the subtropical gyres, which is opposite to the prevailing features in midlatitude oceans. Recent studies have attributed this anomalous effect solely to changes in phytoplankton biomass, therefore reached a conclusion that AEs are more productive than CEs, contrary to the conventional eddy pumping paradigm. Here, we show that the Chl variations are due mainly to physiological adjustments instead. The high Chl in AEs is mostly explained by photoacclimation to low‐light environment caused by deepened mixing and more rapid light attenuation, and vice versa for CEs. Such a scenario indicates that phytoplankton are likely more cellular pigmented, rather than more abundant, in the AEs than in the CEs. These findings invite us to rethink the effects of eddies on oceanic productivity and carbon cycling in the subtropical gyres.

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“…The salinity of BoB is obtained from spatial-gridded Argo data in the sea close to the coast (APDRC 2020). The mean concentration of inorganic nutrients, DIN and DIP of the coastal BoB for the period 2018-2019 was collected based on Sarma et al (2020).…”

Section: Study Area Sampling and Analysismentioning

confidence: 99%

Nutrient dynamics and budgeting in a semi-enclosed coastal hypersaline lagoon

Vijay

Kumaraswami

Reghu

et al. 2021

Environ Sci Pollut Res

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Biogeochemical and ecological responses to limited external nutrient loading are poorly understood in tropical semi-enclosed coastal lagoons which are highly influenced by hydrological and salinity regimes. With objectives towards ecosystem sustainability via better management of the nutrient inputs, investigations were carried out to estimate the water, salt, and nutrient budget of "Pulicat" hypersaline coastal lagoon for the year 2018-2019. The budget revealed that the annual rate of precipitation and evaporation are the major driving factors regulating the annual residual flow in the lagoon. Limited exchange of water and material had resulted in a hypersaline condition with high spatial and temporal variation in salinity ranging from 20 to 103. In the absence of external loading, nutrient enrichment by internal compensation had resulted in DIN enrichment. DIN constituents are mainly contributed by ammonia, indicative of remineralisation through benthic regeneration. The extended water residence time and enhanced primary production has converted the inner lagoon into a limited phosphate system. The TRIX index also indicates a decline in the trophic status transforming the lagoon from a mesotrophic to a eutrophic system.

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Role of eddies on controlling total and size-fractionated primary production in the Bay of Bengal

Cited by 38 publications

References 50 publications

Reviews and syntheses: Trends in primary production in the Bay of Bengal – is it at a tipping point?

Reviews and syntheses: Trends in primary production in the Bay of Bengal – is it at a tipping point?

Eddy‐Induced Near‐Surface Chlorophyll Anomalies in the Subtropical Gyres: Biomass or Physiology?

Nutrient dynamics and budgeting in a semi-enclosed coastal hypersaline lagoon

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