JpGU-AGU Joint Meeting 2017

Presentation information

[JJ] Poster

A (Atmospheric and Hydrospheric Sciences) » A-CG Complex & General

[A-CG52] [JJ] Biogeochemical linkages between the ocean and the atmosphere during phytoplankton blooms

Thu. May 25, 2017 3:30 PM - 4:45 PM Poster Hall (International Exhibition Hall HALL7)

[ACG52-P02] Fine- and micro-scale observations in the Oyashio in winter

*Takahiro Tanaka1, Ichiro Yasuda1, Yasutaka Goto1, Jun Nishioka2 (1.Atmosphere and Ocean Research Institute University of Tokyo, 2.Institute of Low Temperature Science, Hokkaido University)

Keywords:turbulent mixing, Oyashio

During the R/V Hakuho-maru cruise in Mar. 2015, fine- and microstructure measurements in the Oyashio water were conducted using a CTD/LADCP and vertical microstructure profiler in order to know the spatial variability of wintertime turbulence field, which has not been reported so far at this area. At a station off the shelf break, whose bottom depth is about 530 m, one-day repeated observations were also conducted to know the temporal variability of turbulence intensity.
The energy dissipation rate, ε, was patchily elevated to O(10-8) [W/kg] and was typically O(10-10 - 10-9) [W/kg] in the upper 400 m depth (less dense than 27.0 σθ) across the Oyashio. Off the shelf break, where the one-day observation was conducted, strong turbulence with ε = O(10-7) [W/kg] and = O(10-3 - 10-2) [m2/s] was observed at around 60 - 70 m depth (26.4 σθ), and ε = O(10-8) [W/kg] and = O(10-3) [m2/s] at around 350 m depth (26.7 σθ) corresponding to the period of isopycnal heaving of about 50m. This strong mixing around 26.4 σθ (26.7 σθ) was enhanced when the along-isobath (down-sill) flow and its associated shear was strengthened. Harmonic analysis shows that the diurnal tidal flow was large in the upper 50 m, while the mean and semi-diurnal flow were also important at around 26.7 σθ suggesting that the tidal flow may impact on the turbulence field at this place.