Quantitative Comparison of Algorithms for Estimating the Air-sea Exchange of Carbon Dioxide in Malacca Straits

A precise quantification of the sea surface partial pressure of carbon dioxide (pCO 2(water) ) at the water surface is required in order to define the role of the sea in air-sea exchange of CO 2 . Even though the pCO 2(water) can be measured directly, the semi-empirical model has seen numerous application in determining the pCO 2 (water) due to a time-and cost-efficient. This study aims to compare the pCO 2 and FCO 2 (Flux of CO 2 ) calculated using Zhai and Zhu algorithm with the underway datasets of pCO 2 obtained during the scientific cruise of CISKA-SPICE III in April 2013. The partial pressure of CO 2 (pCO 2 ) was measured using a high-accuracy electrochemical instrumentation underway HydroC/CO 2 FT (flow through) with an error ±1 μ atm. Furthermore, in order to calculate the pCO 2 and the FCO 2 employing widely used algorithms, some data were needed including wind speed, sea surface temperature and chlorophyll-a extracted from MODIS (Moderate Resolution Imaging Spectroradiometer). According to the results obtained, the difference between the pCO 2 and FCO 2 derived from those two algorithms are significant. The underway datasets of pCO 2 are ranging from 409.52-544.01 µatm. Meanwhile, the pCO 2 derived using the Zhai algorithm and Zhu algorithm are between 405.003–422.79 µatm and 398.94-752.06 µatm respectively. The FCO 2 are varied between 0.02–0.06 molC . m - 2 .day -1 (Zhai algorithm ), 0.02-0.57 molC . m - 2 .day -1  (Zhu algorithm ) dan 0.04-0.23 molC . m - 2 .day -1 (the underway datasets). A comparison of the two results reveals that pCO 2 derived using Zhai algorithm is closer with the underway datasets compared with the result of pCO 2 calculated using Zhu algorithm with the MRE (Mean Relative Estimation Error) as large as 19.4% and 39% respectively. Taken together, these results suggest that the Zhai algorithm is more appropriate to determine a lgorithms for e stimating the a ir-sea e xchange of carbon dioxide in the Malacca Straits. Keywords: carbon dioxide , Malacca Straits , pCO 2 , FCO 2 , Zhai and Zhu algorithm