Observation of Bottom­Trapped Topographic Rossby Waves on the Shelf Break of the Chukchi Sea

Abstract

This study investigates topographic Rossby waves (TRWs) with a period of approximately 35 h using a mooring observation at 194 m depth on the shelf break of the Chukchi Sea in the Arctic Ocean. We measured velocity, temperature, and salinity for about one year from August 2014 to August 2015. The observations reveal that the bottom-intensified up-slope current fluctuations were significantly coherent with near-bottom temperature fluctuations, with a phase lag of approximately 90°. Near the seafloor, the temperature increased with depth. Therefore, the temperature increases (decreases) with the up-slope (down-slope) currents. Theoretical estimates of the wavelength, angle of wavenumber vector, and bottom-trapping depth confirmed that the observed near 35-h TRWs are indeed plausible in the study area. Energetic TRWs were observed in September and October, during the sea-ice free season, whereas weak TRWs were observed in months with sea ice cover. The TRW events coincided with local wind-stress events, suggesting that the TRWs were triggered by atmospheric forcing. These findings imply that a longer ice-free season may allow for a more frequent occurrence of energetic TRWs, which may enhance the water exchange between the shallow continental shelf and the deep ocean.