Observations and derived nutrient/turbulence variables from the 2025 cruise in the western North Pacific

This dataset contains observations and derived quantities from the R/V TAN KAH KEE cruise conducted in the western North Pacific between 20 May and 2 July 2025. The survey spanned a west–east transect at ~20°N within the North Pacific Subtropical Gyre (NPSG) and a south–north transect along ~165°E from 20.8°N to 50.8°N, crossing the NPSG, the transition zone, and the Western Subarctic Gyre (WSG). At 15 stations, turbulence microstructure was profiled using a free-fall MSS90L (Sea & Stream Ocean Technology). Nutrient samples were analyzed onboard by continuous-flow autoanalysis (micromolar) and liquid-waveguide/flow-injection systems (nanomolar). The data are provided in a single Microsoft Excel file (.xlsx) with individual sheets for each parameter. All parameters are given at a 1 m vertical resolution (interpolated where necessary) and are accompanied by depth and station identifier. The sheets include: Nutrient concentrations (µmol L−1): NOx− (NO3− + NO2−), NO2−, NH₄⁺, DIP, Si(OH)4. Turbulence properties: turbulent kinetic energy dissipation rate ε (W kg−1), squared buoyancy frequency N² (s−2), diapycnal diffusivity Kv (m2 s−1). Diapycnal fluxes (µmol m⁻² d⁻¹): diffusive flux (Fdiff) and effective flux (Fe) for NOx−, DIP, and Si(OH)4. Definitions and methods: N² (s−2): the square of the buoyancy frequency, computed from the vertical potential density gradient; a measure of stratification intensity. Kv (m2 s⁻¹): diapycnal diffusivity, estimated from ε and N² using the Osborn (1980) model with a mixing efficiency Γ = 0.2. Fdiff (µmolm−2 d−1): the diapycnal diffusive nutrient flux, calculated as –Kv × (∂C/∂z). Fe (µmolm−2 d−1): the effective diapycnal nutrient flux (Fdiff + diapycnal advective flux – along-isopycnal divergence) representing the net nutrient supply to the upper water column. Detailed descriptions of the cruise, data and flux calculations can be found in the associated manuscript (Du et al., submitted to JGR-Oceans) and in Du et al. (2017, 2025). References Du, C., Liu, Z., Kao, S. J., & Dai, M. (2017). Diapycnal fluxes of nutrients in an oligotrophic oceanic regime: The South China Sea. Geophysical Research Letters, 44(22), 11,510-511,518. https://doi.org/10.1002/2017GL074921. Du, C., Dai, M., Liu, Z., Hu, Z., Yang, J.-Y. T., Zhou, K., et al. (2025). Diapycnal fluxes of nutrients in the North Pacific Subtropical Gyre. Global and Planetary Change, 253, 104973. https://doi.org/10.1016/j.gloplacha.2025.104973.