Distribution and sea-to-air fluxes of nitrous oxide and methane from a seasonally hypoxic coastal zone in the southeastern Arabian Sea.

Autor: Arya KS; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India; Cochin University of Science and Technology, Kerala, India., Gireeshkumar TR; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India. Electronic address: gkumar@nio.org., Vignesh ER; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India; Cochin University of Science and Technology, Kerala, India., Muraleedharan KR; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India., D'cunha MS; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India., Emil John CR; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India., Snigtha; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India., Cyriac M; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India., Ravikumar Nair C; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India., Praveena S; CSIR - National Institute of Oceanography, Regional Centre, Kochi 682 018, India.
Jazyk: angličtina
Zdroj: Marine pollution bulletin [Mar Pollut Bull] 2024 Aug; Vol. 205, pp. 116614. Date of Electronic Publication: 2024 Jun 25.
DOI: 10.1016/j.marpolbul.2024.116614
Abstrakt: The seasonal variability, pathways, and sea-to-air fluxes of nitrous oxide (N 2 O) and methane (CH 4 ) in the coastal environment, where coastal upwelling and mudbanks co-exist are presented based on the monthly time-series measurements from November 2021 to December 2022. Upwelling-driven hypoxic water's shoreward propagation and persistence were the major factors controlling the N 2 O concentrations, while the freshwater influx and sedimentary fluxes modulate CH 4 concentrations. The N 2 O concentrations were high during the southwest monsoon (up to 35 nM; 19 ± 8 nM)), followed by spring inter-monsoon (up to 19 nM; 10 ± 5 nM), and lowest during the northeast monsoon (up to 13 nM; 8 ± 2 nM), whereas the CH 4 levels were high during the spring inter-monsoon (8.4 to 65 nM), followed by southwest monsoon (6.8 to 53.1 nM) and relatively lower concentrations during the northeast monsoon (3.3 to 32.6 nM). The positive correlations of excess N 2 O with Apparent Oxygen Utilisation (AOU) and the sum of nitrate and nitrite (NO x ) indicate that nitrification is the primary source of N 2 O in the mudbank regime. The negative correlation of CH 4 concentrations with salinity indicates considerable input of CH 4 through freshwater influx. CH 4 exhibited a highly significant positive correlation with Chlorophyll-a throughout the study period. Furthermore, it displayed a statistically significant positive correlation with phosphate (PO 4 3- ) during the northeast monsoon while a strong negative correlation with PO 4 3- during the spring inter-monsoon, pointing towards the role of aerobic CH 4 production pathways in the mudbank regime. N 2 O and CH 4 exhibited a contrasting seasonal pattern of sea-to-air fluxes, characterised by the highest N 2 O fluxes during the southwest monsoon (hypoxia) (13 ± 10 μM m -2 d -1 ), followed by spring inter-monsoon (12 ± 16 μM m -2 d -1 ), and the lowest during the northeast monsoon (0.6 ± 3 μM m -2 d -1 ). Conversely, the highest sea-to-air fluxes of CH 4 were noticed during the spring inter-monsoon (74 ± 56 μM m -2 d -1 ), followed by the southwest monsoon (45 ± 35 μM m -2 d -1 ), and the lowest values during the northeast monsoon (19 ± 16 μM m -2 d -1 ). Long-term time-series measurements will be invaluable in understanding the longer-term impacts of climate-driven variability on marine biogeochemical cycles in dynamic nearshore systems.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
(Copyright © 2024 Elsevier Ltd. All rights reserved.)
Databáze: MEDLINE
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