Contribution of Carbon Fixation Toward Carbon Sink in the Ocean Twilight Zone

Saxena, Himanshu; Sahoo, Deepika; Nazirahmed, Sipai; Kumar, Deepak; Khan, Mohammad Atif; Sharma, Niharika; Kumar, Sanjeev; Singh, Arvind

doi:10.1029/2022gl099044

Cited by 8 publications

(6 citation statements)

References 60 publications

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“…Dark carbon fixation rates in the Yangtze Estuary and its adjacent coastal waters were comparable to those reported in the Columbia River's Estuary (0.9–1.4 μmol C L −1 day −1 ; Bräuer et al, 2013) and a tropical estuarine system (0.4–1.3 μmol C L −1 day −1 ; Signori et al, 2017), but significantly higher than those detected in seawaters such as the North Atlantic (3.0 × 10 −5 –1.0 × 10 −2 μmol C L −1 day −1 ; Pachiadaki et al, 2017) and the Arabian Sea (5.0 × 10 −4 –1.2 × 10 −2 μmol C L −1 day −1 ; Saxena et al, 2022). Compared with freshwater ecosystems, DCF rates measured in the Yangtze estuarine and coastal waters were significantly higher than those reported in deep groundwater of Sweden (3.9 × 10 −3 –1.9 × 10 −2 μmol C L −1 day −1 ; Overholt et al, 2022) and in the Maggiore Lake (1.3 × 10 −2 –2.1 × 10 −2 μmol C L −1 day −1 ; Callieri et al, 2014).…”

Section: Discussionmentioning

confidence: 93%

“…The importance of DCF in the biogeochemical cycle of carbon has been confirmed in estuarine and coastal ecosystems (Signori et al, 2017). However, the potential response of Saxena et al, 2022). Compared with freshwater ecosystems, DCF rates measured in the Yangtze estuarine and coastal waters were significantly higher than those reported in deep groundwater of Sweden (3.9 × 10 −3 -1.9 × 10 −2 μmol C L −1 day −1 ; Overholt et al, 2022) and in the Maggiore Lake (1.3 × 10 −2 -2.1 × 10 −2 μmol C L −1 day −1 ; Callieri et al, 2014).…”

Section: Dcf Capacity Under Different Warming Scenariosmentioning

confidence: 99%

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Potential response of dark carbon fixation to global warming in estuarine and coastal waters

Zheng

Hou

et al. 2023

Global Change Biology

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Dark carbon fixation (DCF), through which chemoautotrophs convert inorganic carbon to organic carbon, is recognized as a vital process of global carbon biogeochemical cycle. However, little is known about the response of DCF processes in estuarine and coastal waters to global warming. Using radiocarbon labelling method, the effects of temperature on the activity of chemoautotrophs were investigated in benthic water of the Yangtze estuarine and coastal areas. A dome-shaped thermal response pattern was observed for DCF rates (i.e., reduced rates at lower or higher temperatures), with the optimum temperature (T opt ) varying from about 21.9 to 32.0°C. Offshore sites showed lower T opt values and were more vulnerable to global warming compared with nearshore sites. Based on temperature seasonality of the study area, it was estimated that warming would accelerate DCF rate in winter and spring but inhibit DCF activity in summer and fall. However, at an annual scale, warming showed an overall promoting effect on DCF rates. Metagenomic analysis revealed that the dominant chemoautotrophic carbon fixation pathways in the nearshore area were Calvin-Benson-Bassham (CBB) cycle, while the offshore sites were co-dominated by CBB and 3-hydroxypr opionate/4-hydroxybutyrate cycles, which may explain the differential temperature response of DCF along the estuarine and coastal gradients. Our findings highlight the importance of incorporating DCF thermal response into biogeochemical models to accurately estimate the carbon sink potential of estuarine and coastal ecosystems in the context of global warming.

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Section: Discussionmentioning

confidence: 93%

Section: Dcf Capacity Under Different Warming Scenariosmentioning

confidence: 99%

Potential response of dark carbon fixation to global warming in estuarine and coastal waters

Zheng

Hou

et al. 2023

Global Change Biology

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“…Trichodesmium is a buoyant and a high‐light‐adapted cyanobacterium which fixes N 2 concurrently with photosynthesis in the daylight (Finzi‐Hart et al., 2009; Gardner et al., 2023; Held et al., 2022). Notably, we found an order of magnitude higher euphotic zone NFR at the surface of SK1 than that at the rest of the stations (Figure 1b), which coincides with the highest contribution of N 2 fixation to primary production (11%) at the surface of station SK1, whereas it was <6% (average = 1%, n = 24) at the other depths and stations (the contribution was calculated after converting euphotic zone NFR to equivalent primary production based on the molar C:N ratio of natural particulate organic matter and then calculating the percentage of equivalent primary production with respect to the observed primary production from the same expedition, Saxena et al., 2022). Our observation of high NFRs near the coast supports previous arrays of evidences that ocean margins contribute a larger amount of new N (>100 μmol N m −2 d −1 ) (Selden et al., 2019 and references therein).…”

Section: Discussionmentioning

confidence: 99%

Winter Convective Mixing Mediating Coupling of N‐Gain and ‐Loss in the Arabian Sea

Saxena,

Sahoo,

Nazirahmed

et al. 2024

JGR Oceans

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Marine dinitrogen (N2) fixation fuels primary production and thereby influences the Earth's climate. Yet, its geographical distribution and controlling environmental parameters remain debatable. We measured N2 fixation rates from the two spatially and physicochemically contrasting regions of the Arabian Sea during the winter monsoon: (a) the colder and nutrient‐rich waters in the northern region owing to winter convection and (b) the warmer and nutrient‐poor waters in the southern region unaffected by winter convection. We found higher N2 fixation rates at the surface of northern region due to convective mixing driven supply of phosphate (intuitively iron also) from the underlying suboxic waters. N2 fixation was favored by high nutrient concentrations in the euphotic waters, whereas remained unaffected by nutrient availability in the aphotic waters. We conclude that diazotrophs dwelling in the euphotic zone chose phosphate over fixed nitrogen‐poor waters. However, we found that among oligotrophic waters, anticyclonic eddy extremes the barrier of fixed nitrogen supply, and thereby, elevates N2 fixation. While the Arabian Sea loses about 20%–40% of the global ocean fixed nitrogen, we estimate that N2 fixation in the Arabian Sea offsets only up to 42% of its fixed nitrogen‐loss by denitrification, but this offset could be higher if diazotrophic activity is further examined up to the deeper depths of the Arabian Sea.

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“…Dried PM filters were fumigated with HCl for 24 h to remove inorganic carbon. For PBC analysis, the CTO-375 method was employed [24,28]. Briefly, the fumigated filters were subjected to thermal oxidation at 375 °C for 24 h in active airflow to remove the organic C fraction.…”

Section: Laboratory Analysismentioning

confidence: 99%

“…Research on PBC in freshwater systems is limited across the globe (figure 1(a)) and a few available studies are largely focused on the dissolved black carbon (DBC) fraction [10,21]. With more studies exploring the degradation of BC in the environment [22][23][24], it becomes imperative to understand the cycling of BC in riverine systems, which act as active conduits along the land-ocean continuum. Bowring et al [25] highlighted the challenges of constraining the impact of fire derived carbon offsets on the terrestrial C balance due to lack of understanding of the mineralisation of BC in aquatic systems.…”

Section: Introductionmentioning

confidence: 99%

Demystifying the particulate black carbon conundrum in aquatic systems

Sarkar,

Rathi,

Khan

et al. 2024

Environ. Res. Commun.

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Particulate black carbon (PBC) constitutes a notable fraction of riverine particulate carbon (C), and is considered to be a potent sink of C due to its refractory nature in the environment. However, its potential to regulate global climate has been challenged with recent arguments of transformation of BC in the environment. In this study, we explore the transport and transformation of PBC along the continuum of six river basins in western India. Using the CTO-375 method and measuring the concentration and stable isotopic composition of the soot fraction of the BC spectrum, we examined the reasons for its variation in the river continuum. Our investigation suggested that changes in concentration and isotopic composition were due to allochthonous inputs and degradation, implying that BC may not be as recalcitrant as previously thought. We also estimated riverine export fluxes of PBC to the Arabian Sea, which was a minor fraction of the current global flux estimates.

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Contribution of Carbon Fixation Toward Carbon Sink in the Ocean Twilight Zone

Cited by 8 publications

References 60 publications

Potential response of dark carbon fixation to global warming in estuarine and coastal waters

Potential response of dark carbon fixation to global warming in estuarine and coastal waters

Winter Convective Mixing Mediating Coupling of N‐Gain and ‐Loss in the Arabian Sea

Demystifying the particulate black carbon conundrum in aquatic systems

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