Aspects of the Surface Circulation of the Chukchi Sea: A Lagrangian Perspective

Six clusters of CODE-type (1-m drogue) satellite-tracked drifters were deployed at both nearshore (< 20 km from the coast) and offshore (> 100 km seaward from the coast) locations in the northeastern Chukchi Sea in August and September of 2013 and 2014. Each cluster contained 12 – 26 drifters. Northeasterly (coastal-upwelling favorable) winds prevailed at the time of each deployment. The results indicate the potential for very large westward displacements of near surface waters, including the transport of warm, fresh Alaskan Coastal Water (ACW) westward from Pt. Hope across Hope Sea Valley into Herald Valley and Long Strait. Similarly ACW was transported westward from the Alaskan coast near Pt. Lay into the Central Channel. Farther north, cold, dilute meltwaters from around Hanna Shoal were drifted westward across the Chukchi Sea shelf, entering, and then transiting Herald Valley from the north to the south. These observations suggest a multiplicity of lateral mixing processes that might substantially alter the water mass properties of the shelf. Concurrent hydrographic data and the clustered nature of the deployments allow exploring the circulation dynamics for some of the clusters. The Hanna Shoal drifter trajectories, occurring where the shelf contains a strong and shallow pycnocline, appear to be governed principally by the Stokes’ drift and Ekman dynamics. In contrast, drifter trajectories deployed far to the south of Hanna Shoal and adjacent to the Alaskan coast, where the stratification is weaker, appear to be largely controlled by geostrophic and Ekman dynamics.