Interannual Bottom-Intensified Current Thickening Observed on the Continental Slope Off the Southeastern Coast of Hokkaido, Japan

Abstract

By rotary empirical orthogonal function and coastal-trapped wave mode analyses, we analyzed current velocity data, collected from 2001 to 2016. The data were obtained by an acoustic Doppler current profiler, deployed upward at a location of 41°39.909′ N, 144°20.695′ E, on a 2630-m deep continental slope seabed off the southeastern coast of Hokkaido, Japan. The results indicate that the current intensifies toward the bottom and is directed nearly toward the shore, reaching an average speed of ~2.5 cm s−1 just above the bottom. The thickness of the along-slope northward component of the bottom-intensified current varied within the range of 50–350 m. We found that the current thickness change was caused by oceanic barotropic disturbances, produced by the intensification of the Aleutian Low, largely related to the El Niño–Southern Oscillation and modified through the excitation of bottom-trapped modes of coastal-trapped waves. This finding improves the prediction accuracy of the the bottom-intensified current change, being beneficial for suspended sediment studies, construction and maintenance of marine structures, planning of deep drilling, and so on.

Analysis of and Reduction in Noise in Current Measurement of XCP under the Laboratory Condition

“…The expendable current profiler (XCP) is a disposable marine environmental measurement profiler that can quickly obtain sea current profile information. Because of its low cost, convenient operation, and real-time measurement, it is widely used in marine surveys and marine dynamic environment research [1][2][3]. As seawater moves massively in the geomagnetic field, it generates induced electric potential and induces currents by cutting the magnetic lines of force of the geomagnetic field.…”

Editorial Summary: Boundary Layer Processes in Geophysical/Environmental Flows

“…Nagano et al [31] advance the understand of the ocean bottom boundary layer through observations performed around Japan under a unique cooperative project among oceanographers and seismologists, which has unveiled the ocean variabilities near the bottom [32][33][34][35][36]. In this Special Issue, a bottom-intensified current was found on the continental slope off the southeast coast of Hokkaido, Japan.…”