UNDER-ICE OBSERVATIONS OF WATER COLUMN TEMPERATURE, SALINITY AND SPRING PHYTOPLANKTON DYNAMICS - EASTERN BERING SEA SHELF

The inundation of two moored platforms by sea ice in late winter and e arly spring of 1995 provided unique time series of water column temper ature, salinity, estimated chlorophyll-a, and phytoplankton fluorescen ce under advancing and retreating sea ice. One platform was located at 72 m in the weakly advective middle shelf regime. Here, chlorophyll-a concentrations began increasing shortly after the arrival of the ice (March) during the period of weak stratification and continued to incr ease while wind actively mixed the water column to greater-than-60 m. Changes in water column structure and properties resulted from an even t of strong advection rather than vertical fluxes. During winter, such advective events can replenish the nutrients required to support the rich blooms that occur over the middle shelf during spring. The advanc ing ice was associated with the coldest waters and a deep (greater-tha n-50 m) mixed layer. The ice melt enhanced the two-layer system previo usly established by advection. A second mooring was located at the 120 m isobath on the more advective outer shelf. The ice reached this sit e on April 6, and chlorophyll-a concentrations increased as the sea ic e melted. At the third mooring, located on the shelf farther south bey ond the range of ice, the spring bloom began on similar to May 9.