[M-IS19] Integrated Analysis of Geoscience Observations from the Floor to Surface of the Ocean

[MIS19-P01] Bottom-intensified current observed by a bottom-mounted ADCP off the southeastern coast of Hokkaido, Japan

*Akira Nagano¹, Takuya Hasegawa^2,3, Keisuke Ariyoshi¹, Hiroyuki Matsumoto¹ (1.JAMSTEC Japan Agency for Marine-Earth Science and Technology, 2.Hokkaido University, 3.Tohoku University)

Keywords:Deep Sea Floor Observatory Off Kushiro-Tokachi, ADCP, Deep current

For physical oceanographers and seismologists, hydrostatic pressure on the seafloor is an important parameter because it variation is related to geostrophic current variation and crustal deformation, respectively. Thus, together with seismometer, ocean bottom pressure gauges and pressure gauges installed to submarine cable communication systems such as DONET and S-net have been deployed on the continental slopes around Japan. Seafloor pressure change is mostly consistent with changes in sea surface height (SSH) and subsurface water density. However, full-depth conductivity-temperature-depth (CTD) observations are sometimes impracticable because of limited ship time, measurable maximum pressure of instruments, and so on. The water density changes below the maximum depths of CTD observations may produce substantial discrepancies between measured seafloor pressure and estimated pressure estimated from the SSH and CTD data. Analyses of other kinds of parameters such as current velocity are useful to clarify processes which possibly cause the discrepancies. An acoustic Doppler current profiler (ADCP) was deployed on the seabed at PG1 (41.7040N, 144.4375E) in the region off the southeastern coast of Hokkaido, Japan. We obtained current velocity data up to 380 m from near the seabed (i.e., from 2150 to 2530 m depths) on the shoreside slope and examined the characteristics of the deep current velocity variation observed by the ADCP from 2000 to 2016. In addition to current velocity fluctuations on timescales of months, the near-bottom current in a layer deeper than 2450 m is stronger than the overlying current. The bottom-intensified current is thicker than the bottom Ekman layer and its variation probably affects the seafloor pressure variation.