Estimating summer sea surface pCO2 on a river-dominated continental shelf using a satellite-based semi-mechanistic model

Abstract A satellite-based semi-mechanistic model was developed to estimate the sea surface partial pressure of CO 2 ( p CO 2 ) on the river-dominated Louisiana Continental Shelf (LCS) in summer months using satellite-derived products including chlorophyll-a concentration (Chl-a _sat ), sea surface salinity (SSS _sat ), and sea surface temperature (SST _sat ). The model analytically expresses p CO 2 as the sum of physical ( p CO 2,mix ) and biological (Δ p CO 2,bio ) contributions which are the primary controlling factors associated with the p CO 2 variability on the LCS. The SSS _sat , derived from a locally calibrated retrieval algorithm, was used in a two-end member river-ocean mixing model to estimate the concentrations of dissolved inorganic carbon (DIC) and total alkalinity (TA) resulting from physical mixing. The mixing-induced DIC and TA were used together with SST _sat to calculate the p CO 2,mix resulting from the mixing processes at the in situ temperature. The biological uptake of p CO 2 through net community production (Δ p CO 2,bio ) was derived from a previously validated local Chl-a _sat product along with the difference between the p CO 2,mix and the extensive in situ underway p CO 2 data. The satellite-derived p CO 2 agreed with in situ measurements with a median absolute difference of 37 μatm, mean difference of −5 μatm, and a root mean square difference of 58 μatm for five summer cruises spanning 2006–2009. The semi-mechanistic remote sensing model differentiates physical and biological influences on the p CO 2 variability, which will help to better investigate the variability and the underlying controlling mechanisms of p CO 2 and CO 2 flux on the LCS. This study demonstrates that the use of locally calibrated satellite products (Chl-a _sat , SSS _sat ) should be promoted to improve the satellite estimation of p CO 2 in coastal waters. This method can potentially be applied in other river-dominated continental shelves with local tuning.