Characterization of bathymetric constraints on deep ocean circulation in the Kauai Deep region around Station ALOHA

Episodic overflows of cold abyssal water from a deep basin (Maui Deep) into another (Kauai Deep) through a dividing sill have been observed at Station ALOHA (22.75° N, 158° W), 100 km north of Oahu, Hawaii. New high-resolution (0.0005°) bathymetry dataset and a new sill-finding algorithm based on Otto and Thurnherr (2007) were used to develop a detailed characterization of the sill region separating the two deep basins. The controlling sill that is expected to hydraulically regulate these abyssal overflows is found to be located at 22.4855° N, 156.9420° W, at a depth of 4644 m. This is deeper and further south than reported by previous studies that used lower-resolution bathymetry. The sill region has very complex bathymetry and an overflowing water mass is expected to pass through multiple channels along the boundary between basins to achieve the volume flux estimates from past studies. For these transports, the bulk of overflowing water from the Maui Deep would pass through the broad, shallower channel to the north of the controlling sill. The specifics of the sill on the northwest side of the Kauai Deep could not be determined due to low data quality in that region; however, that sill appears to be deeper than the eastern sill. Targeted observations in the region are needed to further the characterization of the dynamics of cold events and to better understand the influences of bottom topography on abyssal circulation and water mass properties at Station ALOHA.