Premium
Decline and Bidecadal Oscillations of Dissolved Oxygen in the Oyashio Region and Their Propagation to the Western North Pacific
Author(s) -
Sasano Daisuke,
Takatani Yusuke,
Kosugi Naohiro,
Nakano Toshiya,
Midorikawa Takashi,
Ishii Masao
Publication year - 2018
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/2017gb005876
Subject(s) - isopycnal , subarctic climate , oceanography , mixed layer , latitude , oxygen , climatology , hydrography , atmospheric sciences , environmental science , geology , chemistry , geodesy , organic chemistry
During the period 1954–2014, concentrations of dissolved oxygen (O 2 ) in the Oyashio region of the western subarctic North Pacific has been oscillating over bidecadal timescales and significantly decreasing over the isopycnal layer spanning σ θ = 26.6–27.5 kg/m 3 . The cycles of oscillation (16.4–19.6 years) are almost consistent and synchronized within 1 year over this density layer and are probably controlled by the nodal tidal cycle of 18.6 years and/or atmospheric forcing. The mean rate of the long‐term decrease is the highest (−0.70 ± 0.06 μmol · kg −1 · year −1 ) in the temperature minimum layer. The O 2 decline there is predominantly attributed to a reduction of ventilation in winter due to warming and freshening. On the other hand, the O 2 decline in deeper layers down to the oxygen minimum layer is attributable to a reduction in ventilation in the Sea of Okhotsk associated with a reduction in sea ice formation and propagation of its impact through diapycnal mixing adjacent to the Bussol' Strait. These trends of bidecadal oscillations and decline of O 2 were also found in the downstream to the east in the 165°E section at latitudes 30°N–42.5°N on σ θ = 26.8 kg/m 3 and with attenuated amplitudes at latitudes of 40°N–45°N in the oxygen minimum layer on σ θ = 27.4 kg/m 3 . These results indicate that the signal of secular declines of O 2 , together with bidecadal oscillations, is being propagated broadly from the Oyashio source region into the interior of the Pacific Ocean.