Short-term variability of the density stratification at the continental slope of Peter the Great Bay, the Sea of Japan

Abstract

Using CTD casts from the autonomous moored Aqualog profiler installed at the continental slope within the Primorye Current zone eastward of Peter the Great Bay (the Sea of Japan) from April 18 through October 15, 2015, fluctuations in density field below seasonal pycnocline were determined. Using the Hilbert–Huang transform, the typical periods of vertical waves whose amplitudes greatly differed during observations were determined. Such periods were estimated as 2–3.5 and 8–13 days which can be linked to travel times, above the mooring of submesoscale and mesoscale dynamic structures, respectively. A more regular signal with the approximate period of 18–20 days was also detected, probably related to the passage of coastal waves above the installation site. Extremely strong irregular low-frequency fluctuations lasting 2 weeks each were detected from mid April through late May, with pycnocline deepening, then shallowing, and then deepening again and each phase lasting about two weeks. The pycnocline shallowing from late May through mid August and deepening afterwards was also detected. No linkages with local wind stress curl were found, implying a non-local origin of the detected fluctuations which probably propagate from the upstream Primorye Current zone.