Variations in the summer oceanic pCO 2 and carbon sink in Prydz Bay using the self-organizing map analysis approach

Abstract

This study applies a neural network technique to produce maps of oceanic surface pCO 2 in Prydz Bay in the Southern Ocean on a weekly 0.1°longitude × 0.1°latitude grid based on in situ measurements obtained during the 31st CHINARE cruise from February to early March 2015. This study area was divided into three regions, namely, the open-ocean region, "sea-ice" region and "shelf" region. The distribution of oceanic pCO 2 was mainly affected by physical processes in the open-ocean region, where mixing and upwelling were the main controls. In the sea-ice region, oceanic pCO 2 changed sharply due to the strong change in seasonal ice. In the shelf region, biological factors were the main control. The weekly oceanic pCO 2 was estimated using a self-organizing map (SOM) with four proxy parameters (sea surface temperature, chlorophyll a concentration, mixed Layer Depth and sea surface salinity) to overcome the complex relationship between the biogeochemical and physical conditions in the Prydz Bay region. The reconstructed oceanic pCO 2 data coincide well with the in situ pCO 2 data from SOCAT, with a root mean square error of 22.14 μatm. Prydz Bay was mainly a strong CO 2 sink in February 2015, with a monthly averaged uptake of 23.57±6.36 TgC. The oceanic CO 2 sink is pronounced in the shelf region due to its low oceanic pCO 2 values and peak biological production.