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

Abstract

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 CO 2 fluxes, surface ocean pCO 2 , 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.

The exploitation of marine resources at Saruq al‐Hadid: Insights into the movement of people and resources in Bronze and Iron Age south‐eastern Arabia

“…Their focus on the marine resource reflected the abundance of fish in coastal waters due to seasonal upwelling (e.g. Disspain et al, : 429; Standen et al, : 163), a mechanism that also causes an abundance of fish stocks off the coast of Oman (Cleuziou & Tosi, : 14; Sreeush et al, ). Similarly, Aboriginal groups in the western desert of Australia are known to utilise different environmental zones in the landscape, including river fish and wild game, on a seasonal basis (Cane, ).…”

High resolution <sup>14</sup>C bomb-peak dating and climate response analyses of subseasonal stable isotope signals in wood of the African baobab – A case study from Oman

“…However, they were found notably lower than NH3 and even SH3, around the bomb peak period (1964( -1967. A potential influencing factor to be addressed might be the close proximity to the coast of the Arabian Sea, where upwelling of nutrient and carbon rich waters causes an outgassing of 'older' CO2 into the atmosphere (Takahashi et al, 2009;Sreeush et al, 2018) that dilutes the bomb peak signal. But this dilution effect should also be seen in pre-bomb peak F 14 C data.…”

Biophysical Control on Variability in Phytoplankton Production and Composition in the South-Western Tropical Indian Ocean During Monsoon 2014

“…Fluctuations in the vertical mixing process also influences the overall time span of light experienced by the phytoplankton (McCreary et al, 1996) in the water column. Moreover, the variability in bio-physical processes in SWTIO region are mostly controlled by the strength and duration of the monsoon winds and associated nutrient dynamics, and the downward trend in biological production, if any, in these upwelling systems has immense ramification on the marine foodweb and economic status of the fishing community of this region (Roxy et al, 2016;Sreeush et al, 2018).…”

“…Resplandy et al (2009) have shown that interannual variability of the thermocline and its role modulating the response to Madden-Julian Oscillation (MJO) controls the chlorophyll-a and export flux of carbon. Further, recent study has shown that Ocean Carbon-Cycle Model Intercomparison Project (OCMIP-II)based estimated CO 2 flux and pCO 2 underestimated the SCTR variability portraying it as a CO 2 sink region (Sreeush et al, 2018). Studies carried out in the SCTR region either describe the role of physical forcings in modulating the phytoplankton biomass (chlorophyll-a) concentrations (George et al, 2013;Roxy et al, 2016;Dilmahamod et al, 2016) and/or satellite or model-based PP (Resplandy et al, 2009;Sreeush et al, 2018); however, none of the studies have reported any in situ measured phytoplankton C-uptake rates (PP), phytoplankton size class/community, and phytoplankton physiological perspective vis-à-vis the physical forcings prevailing in this oligotrophic region.…”