Temporal variability of winter mixed layer in the mid-to high-latitude North Pacific |
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| Authors: | Eitarou Oka Lynne D Talley Toshio Suga |
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| Institution: | (1) Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Kanagawa 237-0061, Japan;(2) Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, 92093-0230, U.S.A.;(3) Department of Geophysics, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan;(4) Present address: Ocean Research Institute, The University of Tokyo, Nakano-ku, Tokyo 164-8639, Japan |
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| Abstract: | Temperature and salinity data from 2001 through 2005 from Argo profiling floats have been analyzed to examine the time evolution
of the mixed layer depth (MLD) and density in the late fall to early spring in mid to high latitudes of the North Pacific.
To examine MLD variations on various time scales from several days to seasonal, relatively small criteria (0.03 kg m−3 in density and 0.2°C in temperature) are used to determine MLD. Our analysis emphasizes that maximum MLD in some regions
occurs much earlier than expected. We also observe systematic differences in timing between maximum mixed layer depth and
density. Specifically, in the formation regions of the Subtropical and Central Mode Waters and in the Bering Sea, where the
winter mixed layer is deep, MLD reaches its maximum in late winter (February and March), as expected. In the eastern subarctic
North Pacific, however, the shallow, strong, permanent halocline prevents the mixed layer from deepening after early January,
resulting in a range of timings of maximum MLD between January and April. In the southern subtropics from 20° to 30°N, where
the winter mixed layer is relatively shallow, MLD reaches a maximum even earlier in December–January. In each region, MLD
fluctuates on short time scales as it increases from late fall through early winter. Corresponding to this short-term variation,
maximum MLD almost always occurs 0 to 100 days earlier than maximum mixed layer density in all regions. |
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| Keywords: | Winter mixed layer North Pacific temporal variability Argo |
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