Spatial and temporal variability of solar penetration depths in the Bay of Bengal and its impact on sea surface temperature (SST) during the summer monsoon

Giddings, Jack, Heywood, Karen J., Matthews, Adrian J., Joshi, Manoj M., Webber, Benjamin G. M., Sanchez-Franks, Alejandra, King, Brian A. and Vinayachandran, Puthenveettil N. (2021) Spatial and temporal variability of solar penetration depths in the Bay of Bengal and its impact on sea surface temperature (SST) during the summer monsoon. Ocean Science, 17 (4). pp. 871-890. ISSN 1812-0784

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Abstract

Chlorophyll has long been known to influence air-sea gas exchange and CO2 drawdown. But chlorophyll also influences regional climate through its effect on solar radiation absorption and thus sea surface temperature (SST). In the Bay of Bengal, the effect of chlorophyll on SST has been demonstrated to have a significant impact on the Indian summer (southwest) monsoon. However, little is known about the drivers and impacts of chlorophyll variability in the Bay of Bengal during the southwest monsoon. Here we use observations of downwelling irradiance measured by an ocean glider and three profiling floats to determine the spatial and temporal variability of solar absorption across the southern Bay of Bengal during the 2016 summer monsoon. A two-band exponential solar absorption scheme is fitted to vertical profiles of photosynthetically active radiation to determine the effective scale depth of blue light. Scale depths of blue light are found to vary from 12m during the highest (0.3-0.5mgm-3) mixed-layer chlorophyll concentrations to over 25m when the mixed-layer chlorophyll concentrations are below 0.1mgm-3. The Southwest Monsoon Current and coastal regions of the Bay of Bengal are observed to have higher mixed-layer chlorophyll concentrations and shallower solar penetration depths than other regions of the southern Bay of Bengal. Substantial sub-daily variability in solar radiation absorption is observed, which highlights the importance of near-surface ocean processes in modulating mixed-layer chlorophyll. Simulations using a one-dimensional K-profile parameterization ocean mixed-layer model with observed surface forcing from July 2016 show that a 0.3mgm-3 increase in chlorophyll concentration increases sea surface temperature by 0.35° C in 1 month, with SST differences growing rapidly during calm and sunny conditions. This has the potential to influence monsoon rainfall around the Bay of Bengal and its intraseasonal variability.

Item Type: Article
Additional Information: Data availability: The satellite chlorophyll a products were produced by the Ocean Colour project from the European Space Agency Ocean Colour–Climate Change Initiative (ESA OC-CCI; http://www.esa-oceancolour-cci.org, last access: 4 July 2018; https://doi.org/10.5285/9c334fbe6d424a708cf3c4cf0c6a53f5, Sathyendranath et al., 2018) version 3.1 and obtained from the CEDA archive. The absolute dynamic topography and geostrophic velocity products were produced by SSALTO/Duacs, distributed by AVISO (https://www.aviso.altimetry.fr, SSALTO/Duacs, 2018), and accessed using the Copernicus Marine Environment Monitoring Service (http://marine.copernicus.eu, Copernicus, 2018). The Argo profiling float datasets are freely available from the international Argo programme (https://argo.ucsd.edu/, http://argo.jcommops.org, last access: 30 October 2018; https://doi.org/10.17882/42182, Argo, 2018). The glider dataset is available from the British Oceanographic Data Centre (https://www.bodc.ac.uk/data/bodc_database/gliders/, BODC, 2019).
Uncontrolled Keywords: oceanography,palaeontology,sdg 13 - climate action ,/dk/atira/pure/subjectarea/asjc/1900/1910
Faculty \ School: Faculty of Science > School of Environmental Sciences
University of East Anglia > Faculty of Science > Research Centres > Tyndall Centre for Climate Change Research
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Depositing User: LivePure Connector
Date Deposited: 30 May 2021 00:01
Last Modified: 16 Oct 2021 00:50
URI: https://ueaeprints.uea.ac.uk/id/eprint/80176
DOI: 10.5194/os-17-871-2021

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