Fig. 1: Observational site.
a Location of the Tsugaru Strait. b, c Mean surface velocities and relative vorticity (2014–2021) for December and January–June (b) and July–November (c), respectively, derived from OSCAR surface velocities. d Monthly (2014–2021 average) time series of relative vorticity (normalized to an inertial frequency of 41°N) derived from OSCAR surface velocities in the regions indicated by the yellow rectangles in (b) and (c). The black line and shaded range represent the bootstrap mean and 95% confidence interval, respectively. e Distribution of the pixelwise arithmetic mean surface chlorophyll-a data for August and September from 2014 to 2022, divided by the root of its pixelwise temporal variance relative to the arithmetic mean, defined as an index of Ichl:\({I}_{{chl}}(x,y)={\left\langle {chl}\left(x,y\right)\right\rangle }_{t}/{\left[(\frac{1}{n-1})\sum {\{{chl}(x,y)-{\left\langle {chl}(x,y)\right\rangle }_{t}\}}^{2}\right]}^{1/2}\), where x, y, and n denote longitude, latitude, and the number of data at each pixel, respectively, and t denotes time. The vectors in (e) represent the mean current velocities for August and September from 2014 to 2021, sourced from OSCAR. The magenta points and squares represent stations where the turbulence measurements were deployed and where a carousel water sampler was used, respectively (26th August 2021; Supplementary Table 1). The grey contours denote bathymetry. The black rectangle denotes the area of estimated water column-integrated primary production (40.75°N–41.75°N, 141.75°E–142.75°E; refer to the main text for its estimation details). The onshore circular symbols and labels denote the stations utilized for estimating sunshine duration (refer to Methods for details; Supplementary Table 2). The upward triangles indicate the location of the antenna of the high-frequency radar system. f, The frequency distribution of chlorophyll-a for August and September from 2014 to 2022 is shown in the light green rectangle in (e). Source data are provided as a Source Data file.
