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Seasonal and spatial variations in spice generation in the South Indian Ocean salinity maxima

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Abstract

Spiciness anomalies generated in the salinity maxima region are important for several atmospheric and oceanic factors as they move along the geostrophic pathways towards the equator and resurface. Subduction and injection mechanisms are responsible for the spiciness generation in the South Indian Ocean (SIO) salinity maxima region. Using ECCO data from 1992 to 2017, here we study monthly variations of spiciness associated with both of these mechanisms in the SIO salinity maxima region. Using a Lagrangian approach, we estimated the monthly evolution of the subduction rate. A maximum subduction rate of 35–38 m/mon occurs during September and consequently decreases towards the end of the year. The effective subduction rate in the salinity maxima region shows the dominance of temporal induction (mixed layer tendency) term, with a sharp gradient in total subduction rate along the 30∘S associated with large mixed layer depth variation. Further, a high Turner angle (> 66∘) to the south of 30∘S confirms the generation of spiciness by injection mechanism. We found that the decrease in mixed layer salt (MLS) coincides with the increase in salinity below the mixed layer. To explore the significance of MLS changes in spiciness generation, we further addressed the monthly evolution of spiciness through MLS budget. Our results suggest that the entrainment and meridional advection terms are key to monthly variations in MLS changes and thus the spiciness.

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Data Availability

The datasets generated and/or analysed in the current study are available from the corresponding author on reasonable request. The following dataset are used for the analysis: ECCOv4 dataset is downloaded from http://apdrc.soest.hawaii.edu/las/v6/dataset?catitem=4941). ARGO data sourced from (http://apdrc.soest.hawaii.edu/las/v6/dataset?catitem=9). Atmospheric fluxes are downloaded through the Copernicus Climate Change Service (C3S) climate Data store (https://cds.climate.copernicus.eu/cdsapp#!dataset/reanalysis-era5-single-levels-monthly-means.

Code Availability

The subduction rate calculation by using lagrangian approach is performed using Ocean parcels (https://github.com/OceanParcels/parcels). Codes for the mixed layer budget calculation can be available from corresponding author.

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Acknowledgements

This work has been carried out at India Institute of Technology Kharagpur, India. Authors would like to thank Institute for providing all needed support to carry out this research. We would like to thank the anonymous reviewers for their comments and suggestions which helped to improve the manuscript significantly. Madhu Kaundal thanks Ministry of Human Resource Development, Government of India for the research fellowship. All the analysis and plotting is done in python using packages numpy, xarray, and matplotlib.

Funding

DS was funded by the Ministry of Education Academic Research Fund MOE2019-T3-1-004, the National Research Foundation Singapore, and the Singapore Ministry of Education, under the Research Centres of Excellence initiative. This work comprises Earth Observatory of Singapore contribution no. 434. MKD was funded by the climate change project of Department of Science and Technology, Govt. of India.

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Authors and Affiliations

  1. Centre for Oceans, Rivers, Atmosphere and Land Sciences, Indian Institute of Technology Kharagpur, Kharagpur, India

    Madhu Kaundal & Mihir Kumar Dash

  2. Department of Aerospace Engineering, Indian Institute of Technology Madras, Chennai, India

    Nadimpalli Jithendra Raju

  3. Earth Observatory of Singapore, Nanyang Technological University, Singapore, Singapore

    Dhrubajyoti Samanta

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  1. Madhu Kaundal
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  2. Nadimpalli Jithendra Raju
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  3. Dhrubajyoti Samanta
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  4. Mihir Kumar Dash
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Correspondence to Mihir Kumar Dash.

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Kaundal, M., Raju, N.J., Samanta, D. et al. Seasonal and spatial variations in spice generation in the South Indian Ocean salinity maxima. Ocean Dynamics 72, 313–323 (2022). https://doi.org/10.1007/s10236-022-01502-2

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