Time dependent bio-optical and temperature measurements beneath Arctic pack ice

Abstract:

As part of the Arctic Observing Network, a new ice-tethered buoy has been developed for monitoring under-ice light and temperature fields. A 20 to 50 m string supports sensors both within and below the ice for the collection of hourly estimates of vertically resolved downwelling irradiance (412, 443, 555 nm and PAR), temperature, chlorophyll a (Chl a) backscatter, and colored dissolved organic material (CDOM) fluorescence. Two buoys are currently operating. Buoy 1 was deployed in the Beaufort Sea in March 2014 and buoy 2 was deployed at the Barneo ice camp in collaboration with the North Pole Environmental observatory in April 2014.

At both locations, attenuation of light in the uppermost 20 – 50 m of the water column was dominated by CDOM in the early spring. Buoy 1 drifted into the Chukchi Sea in June and experienced a switch from CDOM to phytoplankton dominated absorption. Buoy 2 has continued to drift south, but remains in the central basin. It has moved into water with reduced light attenuation properties, indicating low CDOM and low Chl a concentrations. Both buoys have observed water column temperature increases without associated increases in absorbed energy, indicating proximal open water. These buoys offer a unique opportunity to observe the seasonal evolution of the light field and associated warming of the upper water column in ice-covered seas.