Research papersHydrographic variability over the northeastern Chukchi Sea shelf in summer-fall 2008-2010

- We examined seasonal (summer-fall) variations in Chukchi shelf water properties.
- These are due to air-sea heat exchange and ocean advection of heat and salt.
- Warm, moderately salty Bering waters replace cool, dilute meltwater and cold, salty winter water.
- Differential advection causes large gradients over small (~50-100 km) length scales.
- Interannual variability due to regional winds and transports through Bering Strait.

We used shipboard CTD, mooring, meteorological, glider, and high-frequency radar data to examine spatial and temporal (seasonal and interannual) variations in the circulation and water properties over the central portion of the northeastern Chukchi Sea shelf from August-October of 2008, 2009, and 2010. Seasonally, warm and moderately saline Bering Sea Water (BSW) replaces cool, dilute surface meltwaters and cold, saline, sub-surface, winter-formed waters. BSW advection thus affects shelf stratification and the heat budget with oceanic heat flux convergence supplanting solar heating as the dominant shelf heat source by September. BSW spreads eastward from the Chukchi's Central Channel, so that water property and stratification transitions proceed from west to east across the study region. Models predict a mean clockwise flow around Hanna Shoal (which lies to the north of the study area) suggesting winter-formed waters from northeast of the Shoal are advected southwestward into a portion of the study area. The observations, though limited, support this notion. We hypothesize that the convergence of BSW from the west and winter waters from the northeast leads, in some years, to large horizontal variations in water properties, stratification, and ocean heat flux convergence over spatial scales of ~50-100 km.Interannual variations in summer/fall shelf water properties appear linked to processes occurring in the Bering and/or southern Chukchi Sea, and the regional winds (which affect the local circulation). Although there were large interannual differences in shelf-wide ice retreat patterns from May-July, these differences were not reflected in late summer water properties.