Variation of Summer Oceanic <i>p</i>CO<sub>2</sub> and Carbon Sink in the Prydz Bay Using SOM Analysis Approach

Abstract. This study applies a neural network technique to produce maps of oceanic surface pCO2 in the Prydz Bay in the Southern Ocean on a 0.1 longitude × 0.1 latitude grid based on in-situ measurements during the 31th CHINARE cruise for February 2015. The study area was divided into three regions, Open-ocean region, Sea-ice region and Shelf region. The distribution of oceanic pCO2 was mainly affected by physical process in the Open-ocean region where mixing and upwelling became the main controls. While in the Sea-ice region, oceanic pCO2 changed sharply due to the strong change of seasonal ice. For the Shelf region, biological factor was the main control. The weekly oceanic pCO2 was estimated using a self-organizing map (SOM) by four proxy parameters (Sea Surface Temperature, Chlorophyll a concentration, Mixed Layer Depth, and Sea Surface Salinity) to resolve the nonlinear relationships under complicated biogeochemical conditions in Prydz Bay region. The reconstructed oceanic pCO2 coincides well with the in-situ investigated pCO2 from SOCAT, in the root-mean-square error of 22.14 μatm. Prydz Bay was mainly a strong CO2 sink in February 2015 with a monthly averaged uptake of 18.7 ± 4.93 TgC. The oceanic CO2 sink is pronounced in the Shelf region due to its lowest oceanic pCO2 with peak biological production. Strong potential anthropogenic CO2 uptake in the Shelf region will enhance the acidification in the deep water of Prydz Bay and affect the deep ocean acidification in the long run since it contributes to the formation of Antarctic bottom water.