Deep sea floor observations of typhoon driven enhanced ocean turbulence
During June 2017 and April 2018, an array of 100-Hz sampling-rate geophysical broadband Ocean Bottom Seismometers (OBSs) and an oceanographic 0.5-Hz sampling-rate vertical temperature sensor string covering the water phase between 7 and 207 m above the seafloor were deploy at about 3000 m depth east of Lanyu Island, Taiwan. The unprecedented physical and geophysical ocean data set reveal the impact of a Category 4 cyclone Typhoon Talim on the near bottom deep ocean. The typhoon induced inertial temperature oscillations at 3000 m seafloor was recorded by the instruments one day before the arrival of Talim. For 10 days, a group of near-inertial motions were observed most clearly in temperature. It contained the largest inertial amplitudes in the ten month time series, which correspond to turbulence kinetic energy dissipation rates O(10−7 m2 s−3). The observation reflects the importance of barotropic response to a cyclone and the propagation of inertio-gravity waves in weak density stratification. In addition to internal tides, these waves drove turbulent overturns larger than 200 m that were concurrently recorded by OBSs. The turbulent signals were neither due to seismic activity nor to ocean-surface wave action. Typhoons can generate not only microseisms and earth hums but also turbulence in the water column, producing additional ground motions. Quantified turbulence processes may help constrain models on sediment resuspension and its influence on deep-sea benthic life.
Haren, H. v., W.-C. Chi, C.-F. Yang, Y. J. Yang, and S. Jan (2020). Deep sea floor observations of typhoon driven enhanced ocean turbulence. Progress in Oceanography. 184, https://doi.org/10.1016/j.pocean.2020.102315