Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 15, issue 7
Biogeosciences, 15, 1895-1918, 2018
https://doi.org/10.5194/bg-15-1895-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 15, 1895-1918, 2018
https://doi.org/10.5194/bg-15-1895-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 03 Apr 2018

Research article | 03 Apr 2018

Biological production in the Indian Ocean upwelling zones – Part 1: refined estimation via the use of a variable compensation depth in ocean carbon models

Mohanan Geethalekshmi Sreeush1,2, Vinu Valsala1, Sreenivas Pentakota1, Koneru Venkata Siva Rama Prasad2, and Raghu Murtugudde3 Mohanan Geethalekshmi Sreeush et al.
  • 1Indian Institute of Tropical Meteorology, Pune, India
  • 2Department of Meteorology and Oceanography, Andhra University, Visakhapatnam, India
  • 3ESSIC, University of Maryland, College Park, MD, USA

Abstract. Biological modelling approach adopted by the Ocean Carbon-Cycle Model Intercomparison Project (OCMIP-II) provided amazingly simple but surprisingly accurate rendition of the annual mean carbon cycle for the global ocean. Nonetheless, OCMIP models are known to have seasonal biases which are typically attributed to their bulk parameterisation of compensation depth. Utilising the criteria of surface Chl a-based attenuation of solar radiation and the minimum solar radiation required for production, we have proposed a new parameterisation for a spatially and temporally varying compensation depth which captures the seasonality in the production zone reasonably well. This new parameterisation is shown to improve the seasonality of CO2 fluxes, surface ocean pCO2, biological export and new production in the major upwelling zones of the Indian Ocean. The seasonally varying compensation depth enriches the nutrient concentration in the upper ocean yielding more faithful biological exports which in turn leads to accurate seasonality in the carbon cycle. The export production strengthens by  ∼ 70% over the western Arabian Sea during the monsoon period and achieves a good balance between export and new production in the model. This underscores the importance of having a seasonal balance in the model export and new productions for a better representation of the seasonality of the carbon cycle over upwelling regions. The study also implies that both the biological and solubility pumps play an important role in the Indian Ocean upwelling zones.

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A simple modification to the existing methodology for calculating biological production in global ocean model is proposed here. A space- and time-varying production depth is found in the upper few metres of the ocean based on sunlight and nutrient availability. This new method is tested for Indian Ocean biological production zones. With this new method the carbon cycling in the surface of the Indian Ocean is simulated better in the model. A reason for the improvement is detailed in the paper.
A simple modification to the existing methodology for calculating biological production in...
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