Enhanced Turbulent Diapycnal Mixing in the Northern Sargasso Sea Inferred From a Finescale Parameterization
Zhuoran Li, Zhao Jing, Lixin Wu, Rodney J. Johnson, Zhibin Yang, Zhuo Song, Zhaohui Chen, Bolan Gan, Xiaohui Ma
Published in Journal of Geophysical Research, December 2023
The Sargasso Sea, accommodating marine species and mode water, is highly productive relative to other oligotrophic subtropical regions with intense air-sea carbon and heat exchanges. Turbulent diapycnal mixing regulates these processes and is generally thought to be weakened in a more stratified ocean under anthropogenic forcing. However, by applying a finescale parameterization to long-term hydrographic profiles collected during the Bermuda Atlantic Time-Series Study (BATS), we show that its intensity has become stronger from 1994 to 2019 in the permanent thermocline. The enhanced turbulent diapycnal mixing is mainly attributed to the increase of wind power on internal waves along the Gulf Stream extension. Numerical simulations suggest that stronger internal waves excited along the Gulf Stream extension radiate downward and equatorward, causing enhanced turbulent diapycnal mixing in the northern Sargasso Sea including the BATS station. The findings have important implications for understanding responses of mode water and ecosystem in the Sargasso Sea to anthropogenic forcing.
Fig. Bathymetrical and hydrographic features of the BATS station. (a) Bathymetry and geographic distribution of the profiles. Yellow points denote the locations of the hydrographic profiles collected from 1994 to 2019. The black dashed line encompasses the region within which the profiles are used in this study. (b) Climatological mean (1994–2018) wind power on near-inertial internal waves WI in the Northwest Atlantic. (c) and (d) Vertical profiles of climatological mean squared buoyancy frequency N2 and turbulent kinetic energy dissipation rate ε at the BATS station. The light shading in (d) is 95% confidence interval of the climatological mean εestimated from a bootstrap method. The green triangle denotes the location of the BATS station.
Li, Z., Jing, Z., Wu, L., Johnson, R. J., Yang, Z., Song, Z., et al. (2023). Enhanced turbulent diapycnal mixing in the northern Sargasso Sea inferred from a finescale parameterization. Journal of Geophysical Research: Oceans, 128, e2023JC020220. https://doi.org/10.1029/2023JC020220