Particulate organic matter dynamics and its isotopic signatures (δ13CPOC and δ15NPN) in relation to physical forcing in the central Arabian Sea during SW monsoon (2017–2018)

Silori, Saumya; Sharma, Deepak; Chowdhury, Mintu; Biswas, Haimanti; Cardinal, Damien; Mandeng-Yogo, M.

doi:10.1016/j.scitotenv.2021.147326

Cited by 7 publications

(5 citation statements)

References 73 publications

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“…It has been regarded that denitrification is dominant in the SOJ based on the box model using nutrient concentrations [Yanagi, 2002]: the denitrification rate in the SOJ is 15 mg N m -2 day -1 [Yanagi, 2002], which is the same level as the major oceans where the oxygen minimum zone is present, such as the Eastern Tropical North Pacific [Seitzinger et al, 2006]. The 15 N POM in this sea (class II:3.1 ± 1.2 ‰) was at the same level as the coastal area of the Kuroshio [Kodama et al, 2021] and open mid-latitude oceans [Horii et al, 2018;Mino et al, 2002], higher than that of nitrogen fixation-dominant water Horii et al, 2018;Kodama et al, 2021;Mino et al, 2020;, and much lower than that of denitrification waters [Matsubayashi et al, 2020;Shiozaki et al, 2014;Silori et al, 2021]. These results suggest that denitrification is not the primary process in the SOJ.…”

Section: Unique Nitrogen Dynamics In the Sojmentioning

confidence: 86%

Variations in the Ratio of Carbon and Nitrogen Stable Isotopes of Particulate Organic Matter in the Southern Sea of Japan

Kodama

Nishimoto

Nakamura

et al. 2022

Preprint

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Carbon and nitrogen dynamics in the Sea of Japan (SOJ) are rapidly changing. Here, we investigated the carbon and nitrogen isotope ratios of particulate organic matter (δ 13 C POM and δ 15 N POM , respectively) at a depth of [?] 100 m in the southern part of the SOJ from 2016 to 2021. Both δ 13 C POM and δ 15 N POM showed multimodal distributions and were divided into four classes (I-IV) using the Gaussian mixed model. Most of the samples were categorized into class II (n = 441), with the mean ± standard deviation (SD) of δ 13 C POM and δ 15 N POM being -23.7 ± 1.2 1.2 δ 15 N POM (-2.1 ± 0.8 class III by low δ 13 C POM (-27.1 ± 1.0 δ 13 C POM (-20.7 ± 0.8 34). Using the generalized linear model (GLM), temperature and chlorophyll-a concentration were found to positively impact δ 13 C POM in addition to sampling depth, latitude, salinity, and nitrate concentration, supporting the hypothesis that active photosynthesis and phytoplankton growth elevated δ 13 C POM . The mean δ 15 N POM value suggests that primary production mainly originates from nitrate in the SOJ. The δ 15 N POM variation, however, was explained by temperature and salinity but not by nitrate concentration in the GLM approach, which suggests that the Rayleigh distillation model was not observed in the SOJ. This suggests that primary production is supported by various nitrogenous sources from the Changjiang, Kuroshio, and atmospheric depositions in the SOJ.

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Section: Unique Nitrogen Dynamics In the Sojmentioning

confidence: 86%

Variations in the Ratio of Carbon and Nitrogen Stable Isotopes of Particulate Organic Matter in the Southern Sea of Japan

Kodama

Nishimoto

Nakamura

et al. 2022

Preprint

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“…The lateral advection of nitrate‐rich upwelled waters from the Omani Coast also supplements nutrients to the northern region of the central Arabian Sea (Kawamiya, 2001; Young & Kindle, 1994). Satellite‐derived SST profiles indicated the signatures of cooler surface waters advected from the Somali and Oman coasts to the central Arabian Sea were stronger in 2018 (AFJ and NFJ) than in 2017 (only up to AFJ) (Silori et al., 2021). The spatiotemporal difference in phytoplankton size class distribution was directly modulated by these factors and is discussed in the following sections.…”

Section: Discussionmentioning

confidence: 99%

“…Please note that ammonium was not analyzed due to some technical issues onboard. It should be noted that physicochemical parameters were published in our previous work (Chowdhury et al, 2021;Silori et al, 2021).…”

Section: Dissolved Inorganic Nutrient Analysesmentioning

confidence: 99%

“…This trend was consistent with earlier Joint Global Ocean Flux Study (JGOFS) reports. Interestingly, despite the decreasing contribution of microphytoplankton southward, particulate organic carbon (POC) contents were comparable (Silori et al., 2021) hinting at the possibility of the contribution of smaller phytoplankton to the POC pool. Nevertheless, using microscopy (Utermöhl, 1958) estimating the contributions of smaller size classes (nano and pico) to phytoplankton biomass remained inconclusive and needs specialized methods like marker pigment‐based analysis (Wright & Jeffrey, 2006) or flow cytometry.…”

Section: Introductionmentioning

confidence: 99%

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Spatiotemporal Variability in Phytoplankton Size Class Modulated by Summer Monsoon Wind Forcing in the Central Arabian Sea

Chowdhury,

Biswas,

Silori

et al. 2023

JGR Oceans

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The Arabian Sea is an area of intense ocean‐atmospheric coupling that impacts its physicochemical, and biological processes. During the summer monsoon (June‐September), in the central Arabian Sea, a low‐level atmospheric jet blows parallel to the Arabian Peninsula causing open ocean upwelling in the north and downwelling in the south of the jet axis. High wind speeds are witnessed in the jet axis which advect nutrients from the Somali coast. Consequently, hydrography and physicochemical parameters show high spatial variability. In this dynamic region, phytoplankton size class distribution, directly controlled by nutrient supply, can be modulated by monsoon wind variability via upwelling, advection, and entrainment, however, has not been investigated recently. We studied phytoplankton size class related to atmospheric forcing, hydrography, and nutrient stoichiometry in August 2017 and 2018 along 64°E (11°N–21°N). Chemical taxonomy‐based analysis (CHEMTAX and manual) revealed that in the north, upwelling‐driven nutrient enrichment supported microphytoplankton, mostly diatoms contributing ∼50% to phytoplankton biomass. A stronger upwelling due to higher wind forcing in 2018 compared to 2017 resulted in an enhanced nutrient supply as well as an increased contribution of diatoms. Prymnesiophytic nanophytoplankton distribution was linked to mixed layer depths with insignificant spatial variability (20%–30%). Conversely, in the nutrient‐poor southern region, zeaxanthin and DV‐Chla containing picocyanobacteria and prochlorophytes contributed >50% to the total phytoplankton biomass and were associated with high temperatures. Likely, increasing warming and related changes in monsoon intensity might directly influence phytoplankton size classes impacting trophic transfer and carbon cycling.

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“…values of particulate organic matter ( 15 NPOM,Silori et al 2021) revealed that nutrient enrichment mostly takes place via advection from the upwelling system as well as entrainment close to the axis (16-18° N). Earlier studies also noticed the presence of slightly low saline waters in this region probably due to advection from the western Arabian Sea (PrasannaKumar et al, 2000).…”

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confidence: 99%

Comment on egusphere-2024-845

Schmidt

2024

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Particulate organic matter dynamics and its isotopic signatures (δ13CPOC and δ15NPN) in relation to physical forcing in the central Arabian Sea during SW monsoon (2017–2018)

Cited by 7 publications

References 73 publications

Variations in the Ratio of Carbon and Nitrogen Stable Isotopes of Particulate Organic Matter in the Southern Sea of Japan

Variations in the Ratio of Carbon and Nitrogen Stable Isotopes of Particulate Organic Matter in the Southern Sea of Japan

Spatiotemporal Variability in Phytoplankton Size Class Modulated by Summer Monsoon Wind Forcing in the Central Arabian Sea

Comment on egusphere-2024-845

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