Variations in the summer oceanic &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and carbon sink in Prydz Bay using the self-organizing map analysis approach

Keyhong Park,Suqing Xu,Di Qi,Yanmin Wang,Bingrui Li,Liqi Chen

doi:10.5194/bg-16-797-2019

Abstract

Abstract. This study applies a neural network technique to produce maps of oceanic surface pCO2 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 pCO2 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 pCO2 changed sharply due to the strong change in seasonal ice. In the shelf region, biological factors were the main control. The weekly oceanic pCO2 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 pCO2 data coincide well with the in situ pCO2 data from SOCAT, with a 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 23.57±6.36 TgC. The oceanic CO2 sink is pronounced in the shelf region due to its low oceanic pCO2 values and peak biological production.

Highlights

The amount of carbon uptake occurring in the ocean south of 60◦ S is still uncertain despite its importance in regulating atmospheric carbon and the fact that the region as a net sink for anthropogenic carbon (Sweeney et al, 2000; Sweeney, 2002; Morrison et al, 2001; Sabine et al, 2004; Metzl et al, 2006; Takahashi et al, 2012)
The Antarctic Divergence Zone was characterized by high nutrient concentrations and low chlorophyll concentrations, with high pCO2 attributed to the upwelling of deep waters, suggesting the importance of physical processes in this area (Burkill et al, 1995; Edwards et al, 2004)
In the western part of this region, the oceanic pCO2 decreased slightly due to the mixture of low pCO2 from higher latitudes brought by the large gyre

Summary

Introduction

The amount of carbon uptake occurring in the ocean south of 60◦ S is still uncertain despite its importance in regulating atmospheric carbon and the fact that the region as a net sink for anthropogenic carbon (Sweeney et al, 2000; Sweeney, 2002; Morrison et al, 2001; Sabine et al, 2004; Metzl et al, 2006; Takahashi et al, 2012). Situated in the Indian Ocean, Prydz Bay is located close to the Amery Ice Shelf to the southwest and the West Ice Shelf to the northeast, with Cape Darnley to the west and the Zhongshan and Davis stations to the east (Fig. 1). In this region, the water depth increases sharply northward from 200 to 3000 m. When the CoC reaches the shallow Fram Bank, it turns north and partly flows westward, while some of it turns eastward, back to the inner shelf, resulting in the clockwiserotating Prydz Bay gyre (see Fig. 1). The circulation to the north of the bay is characterized by a large cyclonic gyre, ex-

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Results

Conclusion