Potential mechanisms responsible for spatial variability in intensity and thickness of oxygen minimum zone in the Bay of Bengal

Date 2021-05-26
Temporal extent 2013-01 -2020-06
Author(s) Udaya Bhaskar Tvs1, Sarma Vvss2, Pavan Kumar J1
Affiliation(s) 1 : Indian National Centre for Ocean Information Services, Pragathi Nagar, Hyderabad
2 : CSIR-National Institute of Oceanography, Regional Centre, 176 Lawsons Bay Colony, Visakhapatnam
3 : Indian National Centre for Ocean Information Services, Pragathi Nagar, Hyderabad
DOI 10.17882/80792
Publisher SEANOE
Keyword(s) oxygen minimum zone, BioGeoChemical-Argo floats, Bay of Bengal
Abstract

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 boundary of the OMZ varied from 60 to 200 m and 100 to 800 m respectively with the thickness of 80 to 650m in the BoB. Relatively thicker OMZ is noticed in the northern than southern BoB associated with stratification. The salinity difference between surface and 100 m is higher in the northeastern (NE; >2.5) followed by northwestern (NW; 1.8-2.5) and lower in the southern BoB (0.6 - 1.2) indicating weaker stratification in the latter region associated with weaker OMZ. The oxygen concentrations in the OMZ in the NW was low (<1.5 mM) than NE BoB (2.5 mM) 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 towards offshore from shelf indicating organic matter from the shelf sediments may be supporting bacterial carbon demand in the OMZ. The particle back-scatter signal peaked in the OMZ region with 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 control the intensity of the OMZ in the BoB, as anticyclonic eddies ventilate oxygen, therefore weakens OMZ, whereas cyclonic eddies intensify OMZ through increase in primary production and upwelling of oxygen-poor waters. Therefore, this study suggests that spatial variations in intensity of OMZ in the BoB is governed by stratification, primary production, sinking carbon fluxes and organic matter decomposition within the OMZ and modification of oxygen concentration in the OMZ by eddies.

Licence CC-BY
Acknowledgments This study was supported through the project “Influence of anticyclonic eddies on oxygen minimum zone and carbon sequestration in the Bay of Bengal”, as a part of OMASCOT program. All BGC-Argo data are available at ftp://ftp.ifremer.fr/ifremer/argo/dac/. These data were collected and made freely available by the International Argo Program and the national programs that contribute to it. (https://argo.ucsd.edu, https://www.ocean-ops.org). The Argo Program is part of the Global Ocean Observing System. The authors wish to thank the Argo Data Management team (ADMT) and the BGC-Argo Data Management team (BGC ADMT). Authors declare no conflict of interest.
Sensor metadata

The float sensors were the Aanderra Optode 4330 measuring dissolved oxygen, ECO Triplet (Three Channel Sensor; WET Labs, Inc., USA) measuring the chlorophyll-a fluorescence and the scattering of light at 700 nm and an angle of 124°)

Data
File Size Format Processing Access
Float 2902086 2 MB NC, NetCDF Quality controlled data Open access
Float 2902087 3 MB NC, NetCDF Quality controlled data Open access
Float 2902113 290 KB NC, NetCDF Quality controlled data Open access
Float 2902114 3 MB NC, NetCDF Quality controlled data Open access
Float 2902156 2 MB NC, NetCDF Quality controlled data Open access
Float 2902158 2 MB NC, NetCDF Quality controlled data Open access
Float 2902160 2 MB NC, NetCDF Quality controlled data Open access
Float 2902161 2 MB NC, NetCDF Quality controlled data Open access
Float 2902179 1 MB NC, NetCDF Quality controlled data Open access
Float 2902189 5 MB NC, NetCDF Quality controlled data Open access
Float 2902193 5 MB NC, NetCDF Quality controlled data Open access
Float 2902195 5 MB NC, NetCDF Quality controlled data Open access
Float 2902196 5 MB NC, NetCDF Quality controlled data Open access
Float 2902216 1 MB NC, NetCDF Quality controlled data Open access
Float 2902217 817 KB NC, NetCDF Quality controlled data Open access
Float 2902238 7 MB NC, NetCDF Quality controlled data Open access
Float 2902239 7 MB NC, NetCDF Quality controlled data Open access
Float 2902243 6 MB NC, NetCDF Quality controlled data Open access
Float 2902244 7 MB NC, NetCDF Quality controlled data Open access
Float 2902245 7 MB NC, NetCDF Quality controlled data Open access
Float 2902294 2 MB NC, NetCDF Quality controlled data Open access
Top of the page

How to cite 

Udaya Bhaskar Tvs, Sarma Vvss, Pavan Kumar J (2021). Potential mechanisms responsible for spatial variability in intensity and thickness of oxygen minimum zone in the Bay of Bengal. SEANOE. https://doi.org/10.17882/80792