Geographical inhomogeneity and temporal variability of mixing property and driving mechanism in the Arctic Ocean

Upper ocean mixing plays a key role in the atmosphere-ocean heat transfer and sea ice extent and thickness via modulating the upper ocean temperatures in the Arctic Ocean.Observations of diffusivities in the Arctic that directly indicate the ocean mixing properties are sparse.Therefore,the spatiotemporal pattern and magnitude of diapycnal diffusivities and kinetic energy dissipation rates in the upper Arctic Ocean are important for atmosphere-ocean heat transfers and sea ice changes.These were first estimated from the Ice-Tethered Profilers dataset(2005–2019)using a strain-based fine-scale parameterization.The resultant mixing properties showed signifi cant geographical inhomogeneity and temporal variability.Diapycnal diff usivities and dissipation rates in the Atlantic sector of the Arctic Ocean were stronger than those on the Pacific side.Mixing in the Atlantic sector increased significantly during the observation period;whereas in the Pacific sector,it weakened before 2011 and then strengthened.Potential impact factors include wind,sea ice,near inertial waves,and stratifi cation,while their relative contributions vary between the two sectors of the Arctic Ocean.In the Atlantic sector,turbulent mixing dominated,while in the Pacific sector,turbulent mixing was inhibited by strong stratification prior to 2011,and is able to overcome the stratifi cation gradually after 2014.The vertical turbulent heat fl ux constantly increased in the Atlantic sector year by year,while it decreased in the Pacific sector post 2010.The estimated heat flux variability induced by enhanced turbulent mixing is expected to continue to diminish sea ice in the near future.

Outflow from under the Pine Island Bay Ice Shelf: finescale structure and its temporal variability

The water column structure of the ice shelf cavity outflow from under Pine Island Glacier and its temporal variability were investigated using a hourly time series of yo-yo CTD and LADCP data collected over -24 h at the southern end of the ice shelf front. The primary water types present over the continental shelf off Pine Island Bay were Circumpolar Deep Water （CDW）, modified Circumpolar Deep Water （mCDW）, Shelf Water （SW）, and Ice Shelf Water （ISW）. As CDW transited the shelf, it transitioned into cooler, mCDW. In the upper 200 m, ISW dominated within 100 km of the ice shelf and SW further offshore. Within Pine Island Bay, the water column was partitioned into two primary layers based on their behavior： an upper outflowing layer from 100 m to 450 m composed of ISW with a significant meltwater component, 1%-2%, over an inflowing layer from -550 m to the sea bed composed of mCDW. Due to the small cavity extent, the outflowing water was warmer than the seawater freezing point. The upper ISW layer was further split into upper ISW layer #1 （100-300 m） and upper ISW layer #2 （320450 m） with the transition coinciding with the ice shelf draft. Small step-like features with heights from 1-50 m existed within both the ISW layers and were more prominent in upper ISW layer #1. A baroclinic signal at the semidiurnal frequency existed within both primary layers with the strongest signal, - 10 cm·s^-1, propagating vertically in the upper ISW layer.