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

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.

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.

Disciplines

Chemical oceanography

Keywords

oxygen minimum zone, BioGeoChemical-Argo floats, Bay of Bengal

Location

25N, 0S, 80E, 100W

Devices

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

FileSizeFormatProcessingAccess
Float 2902086
2 MoNetCDFQuality controlled data
Float 2902087
3 MoNetCDFQuality controlled data
Float 2902113
290 KoNetCDFQuality controlled data
Float 2902114
3 MoNetCDFQuality controlled data
Float 2902156
2 MoNetCDFQuality controlled data
Float 2902158
2 MoNetCDFQuality controlled data
Float 2902160
2 MoNetCDFQuality controlled data
Float 2902161
2 MoNetCDFQuality controlled data
Float 2902179
1 MoNetCDFQuality controlled data
Float 2902189
5 MoNetCDFQuality controlled data
Float 2902193
5 MoNetCDFQuality controlled data
Float 2902195
5 MoNetCDFQuality controlled data
Float 2902196
5 MoNetCDFQuality controlled data
Float 2902216
1 MoNetCDFQuality controlled data
Float 2902217
817 KoNetCDFQuality controlled data
Float 2902238
7 MoNetCDFQuality controlled data
Float 2902239
7 MoNetCDFQuality controlled data
Float 2902243
6 MoNetCDFQuality controlled data
Float 2902244
7 MoNetCDFQuality controlled data
Float 2902245
7 MoNetCDFQuality controlled data
Float 2902294
2 MoNetCDFQuality controlled data
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
In addition to properly cite this dataset, it would be appreciated that the following work(s) be cited too, when using this dataset in a publication :
Udaya Bhaskar T. V. S., Sarma V. V. S. S., Pavan Kumar J. (2021). Potential Mechanisms Responsible for Spatial Variability in Intensity and Thickness of Oxygen Minimum Zone in the Bay of Bengal. Journal of Geophysical Research: Biogeosciences, 126 (6), -. https://doi.org/10.1029/2021JG006341

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