Secular trends and seasonal variations of partial pressure of carbon dioxide in the surface sea water in the Australian secutor of the Southern Ocean

• Main Authors: Gen Hashida, Shin-ichiro Nakaoka, Hisashi Ono, Takakiyo Nakazawa, Hisayuki Yoshikawa, Shuji Aoki, Shinji Morimoto, Takashi Yamanouchi, Tsuneo Odate, Mitsuo Fukuchi
• Format: Article in Journal/Newspaper
• Language: English; Japanese
• Published: National Institute of Polar Research 2010
• Subjects: Geography (General); G1-922; Antarctic; Indian; Southern Ocean; The Antarctic; Antarc*; Icebreaker
• Online Access: https://doi.org/10.15094/00009566; https://doaj.org/article/579c3e5e33ba4949883bceefb2672fc5

In order to elucidate the secular trends of oceanic CO_2 uptake in the Indian sector of the Southern Ocean, pCO_2, the partial pressure of CO_2 in the ocean surface layer, has been measured since 1987 on board the icebreaker Shirase. Meridional distributions of pCO_2 along 110゜E in early December clearly show steep changes at such fronts as the subtropical front, subantarctic front, and polar front. Although pCO_2 of each zone shows interannual variation, secular trend is detectable. For example, the estimated rate of increase of pCO_2 in the permanent open ocean zone between the polar front (around 53゜S) and the northern edge of winter ice cover (63゜S) is about 1.3 μatm y, which is slightly lower than the rate of increase of the atmospheric CO_2 concentration. From the results obtained by multi-ship observations with 4 research vessels in the Southern Ocean in summer, we found that the values of pCO_2 off the coast of the Antarctic Continent (66゜S) varied temporally by 100 μatm for 5 months. We also found that nDIC decreased with time from December 2001 to March 2002 in the upper layer from 100 to 200 m due to biological activity during summer.