Observing and Understanding the Impacts of a Thinning and Retreating Sea Ice Cover on Light Propagation, Primary Productivity, and Biogeochemistry in the Pacific Arctic Region

The Arctic sea ice cover is undergoing tremendous change. There has been a pronounced decrease in the summer sea ice extent (Comiso et al., 2008; Serreze et al., 2007; Stroeve et al., 2007), an overall thinning of the ice, a lengthening of the summer melt season (Markus et al., 2009) and a fundamental shift to a primarily seasonal sea ice cover (Rigor and Wallace, 2004; Nghiem, et al. 2007, 2007; Maslanik et al., 2007, 2011). Some of the greatest changes have been observed in the Chukchi and Beaufort Seas, where there has been a substantial loss of summer ice.

These changes in the physical system are affecting the biological and biogeochemical systems. Results from the NASA sponsored ICESCAPE program are demonstrating how these physical changes affect primary productivity. A massive phytoplankton bloom was unexpectedly found under the melting sea ice cover (Arrigo et al., 2012). There were ample nutrients available in the upper water column and there was sufficient sunlight transmitted to the upper ocean to fuel this large bloom. Thinner ice contributed to increased light transmittance, but the major factor was the shift from multiyear to seasonal ice. Seasonal ice is more heavily ponded than multiyear ice (Perovich and Polashenski, 2012), and ponds have substantially lower albedo and higher transmittance than bare ice. Changes in the small-scale physics of light transmission through the ice resulted in a large-scale biological response.

This project will address the impacts of physical changes in the sea ice cover on biology and biogeochemistry through an interdisciplinary effort that synthesizes a large range of data types, including: satellite and aircraft remote sensing data, in situ observations from ICESCAPE, ICEBRIDGE, Distributed Biological Observatories, and the Arctic Observing Network. The effort will also entrain process models of ice melt, radiative transfer, and primary productivity, along with regional and large scale sea ice models. We will develop methods to meet the major challenge that an underice bloom poses for remote sensing detection. Areas of open water within the ice cover and the widespread ponding on seasonal ice afford possibilities to detect chorophyll signatures using high resolution visible imagery.

The overarching goal of this work is to determine the impact of physical changes in the sea ice cover of the Chukchi and Beaufort Sea on the biogeochemistry, with a particular emphasis on underice phytoplankton blooms.