Dissolved methane distribution in the South Pacific and the Southern Ocean in austral summer

• Main Authors: Yoshida Osamu, Inoue Hisayuki Y., Watanabe Shuichi, Suzuki Koji, Noriki Shinichiro
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2011
• Subjects: methane; Pacific; Southern Ocean; Antarctic; Austral; Antarc*; Antarctic Krill
• Online Access: https://rakuno.repo.nii.ac.jp/?action=repository_uri&item_id=1628; http://hdl.handle.net/10659/2966; https://rakuno.repo.nii.ac.jp/?action=repository_action_common_download&item_id=1628&item_no=1&attribute_id=21&file_no=1

[1] Oceanic methane (CH_4) was examined in the South Pacific and the Southern Ocean from December 2001 to February 2002. From the oligotrophic South Pacific (10°S) to the Subtropical Front (STF), we observed the maximum concentrations of CH_4 in the subsurface layer which ranged from 2.7 to 3.9 nmol kg^<−1>. South of the STF, higher levels of CH_4 were often detected in both the surface and the subsurface layers. Elevated surface CH_4 concentrations (3.4-6.1 nmol kg^<−1>) south of the STF tended to be higher than those north of the STF. Higher CH_4 were often concomitant with an increase in chlorophyll a levels in the Seasonal Ice Zone (SIZ). Considering that phytoplankton does not generate methane directly, the high CH_4 production probably resulted from the grazing processes of Antarctic krill and/or zooplankton fed on phytoplankton and the subsequent microbial methanogenesis in addition to the aerobic CH_4 production in the water column. Present results showed a good relation between surface CH_4 data (<50 m) and σ_θ between 10°S and the Polar Front (PF), which allow us to provide interpolation/extrapolation schemes for CH_4 concentration and sea-air CH_4 flux in the wide area ([CH_4] = 0.15 σ_θ − 0.98 (RMS = 0.21 nmol kg^<−1>, r = 0.68, n = 49, p < 0.001). The sea-air fluxes estimated during our survey were from 2.4 to 4.9 mol CH_4 km^<−2> d^<−1> between 10°S and the PF (54°S), and from 0.8 to 2.3 mol CH_4 km^<−2> d^<−1> south of the PF, where the sea-air CH_4 flux was largely affected by the wind speed.