The Partial Pressure of CO2 and Fluxes of CO2 in Semarang Bay, Indonesia

Abstract

The CO₂ characteristics of the Semarang Bay system on the Northern coast of Java were investigated to understand the roles in carbon dioxide flux. The flux of carbon dioxide at the sea surface between seawater and atmosphere is essential for mitigating atmospheric CO₂.  The aims of this study were to assess the variation of CO₂ partial pressure seawater (pCO_2sea) and CO₂ flux and to analyse the water quality variable which has the larger influence on CO₂ flux in the waters of Semarang Bay. The variables in this study were temperature, pH, salinity, and DO. Different methods were adopted in the analysis of water samples: spectrophotometric to measure chlorophyll-a and phosphate and titration method to measure Total Alkalinity (TA) and Dissolved Inorganic Carbon (DIC). A CO₂ meter was used to measure the CO_2atm. The lowest CO₂ flux value was (1.86 mmol CO₂ m^-2 day^-1) during the morning period while the pCO_2sea reached 461.04 μatm and CO₂ flux 83.79 mmol CO₂ m^-2 day^-1 at night. At noon time, with increased temperature, pCO_2sea was 461.04 μatm, and CO₂ flux was 83.79 mmol CO₂ m^-2 day^-1. The high concentration of chlorophyll-a ranged between 3.55–4.11 mg.L^-1.  This chlorophyll-a concentration has a negative correlation with CO₂ flux, and it was found that TA and DIC concentrations have no relationship with CO₂ flux. Based on PCA analysis, it was found that the variability of CO₂ flux in Semarang Bay is influenced by the variability of pCO_2sea, sea surface temperature and k_wa (affected by wind speed).