TY - JOUR
T1 - Subsurface water masses in the Central North Pacific transition region
T2 - The repeat section along the 180° meridian
AU - Suga, Toshio
AU - Motoki, Kazunori
AU - Hanawa, Kimio
N1 - Funding Information:
We are grateful to the crew of T/V Oshoro Maru and the scientists at Graduate School of Fisheries, Hokkaido University for their efforts to maintain the repeat section for a long time. We thank members of the Physical Oceanography Group, Tohoku University for helpful comments and useful discussion. Dr. M. J. McPhaden kindly provided the CTD data collected by NOAA/PMEL. Many useful comments from F. M. Bingham and an anonymous reviewer are greatly appreciated. This study was made as part of Subarctic Gyre Experiment (SAGE), which was financially supported by the former Science and Technology Agency and the present Ministry of Education, Culture, Sports, Science and Technology. The authors (TS and KH) were also supported by the Japan Society for Promotion of Science (Grant-in-Aid for Scientific Research (B), No. 13440138).
PY - 2003/8
Y1 - 2003/8
N2 - A repeat hydrographic section has been maintained over two decades along the 180° meridian across the subarctic-subtropical transition region. The section is naturally divided into at least three distinct zones. In the Subarctic Zone north of 46°N, the permanent halocline dominates the density stratification, supporting a subsurface temperature minimum (STM). The Subarctic Frontal Zone (SFZ) between 42°-46°N is the region where the subarctic halocline outcrops. To the south is the Subtropical Zone, where the permanent thermocline dominates the density stratification, containing a pycnostad of North Pacific Central Mode Water (CMW). The STM water colder than 4°C in the Subarctic Zone is originated in the winter mixed layer of the Bering Sea. The temporal variation of its core temperature lags 12-16 months behind the variations of both the winter sea surface temperature (SST) and the summer STM temperature in the Bering Sea, suggesting that the thermal anomalies imposed on the STM water by wintertime air-sea interaction in the Bering Sea spread over the western subarctic gyre, reaching the 180° meridian within a year or so. The CMW in this section originates in the winter mixed layer near the northern edge of the Subtropical Zone between 160°E and 180°. The CMW properties changed abruptly from 1988 to 1989; its temperature and salinity increased and its potential density decreased. It is argued that these changes were caused by the climate regime shift in 1988/1989 characterized by weakening of the Aleutian Low and the westerlies and increase in the SST in the subarctic-subtropical transition region.
AB - A repeat hydrographic section has been maintained over two decades along the 180° meridian across the subarctic-subtropical transition region. The section is naturally divided into at least three distinct zones. In the Subarctic Zone north of 46°N, the permanent halocline dominates the density stratification, supporting a subsurface temperature minimum (STM). The Subarctic Frontal Zone (SFZ) between 42°-46°N is the region where the subarctic halocline outcrops. To the south is the Subtropical Zone, where the permanent thermocline dominates the density stratification, containing a pycnostad of North Pacific Central Mode Water (CMW). The STM water colder than 4°C in the Subarctic Zone is originated in the winter mixed layer of the Bering Sea. The temporal variation of its core temperature lags 12-16 months behind the variations of both the winter sea surface temperature (SST) and the summer STM temperature in the Bering Sea, suggesting that the thermal anomalies imposed on the STM water by wintertime air-sea interaction in the Bering Sea spread over the western subarctic gyre, reaching the 180° meridian within a year or so. The CMW in this section originates in the winter mixed layer near the northern edge of the Subtropical Zone between 160°E and 180°. The CMW properties changed abruptly from 1988 to 1989; its temperature and salinity increased and its potential density decreased. It is argued that these changes were caused by the climate regime shift in 1988/1989 characterized by weakening of the Aleutian Low and the westerlies and increase in the SST in the subarctic-subtropical transition region.
KW - Climate regime shift
KW - Dichothermal water
KW - North Pacific Central Mode Water
KW - Subsurface temperature minimum
KW - Western subarctic gyre
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U2 - 10.1023/A:1025536531583
DO - 10.1023/A:1025536531583
M3 - Article
AN - SCOPUS:0142218463
VL - 59
SP - 435
EP - 444
JO - Journal of Oceanography
JF - Journal of Oceanography
SN - 0916-8370
IS - 4
ER -