Changing Sea Ice Conditions and Arctic Marine Ecosystems -- The shrinking area of Arctic sea ice in summer is one of the most often cited examples of anthropogenic climate change. The areal extent of sea ice at the time of the September minimum has declined by about 1% per year since satellite observations began 35 years ago. Sea ice is very different from lake ice. A brine is created as ice crystallizes, a portion of which remains in channels within the ice and provides habitat for microscopic plankton. These organisms include photosynthetic algae and microscopic animals that feed on the algae, and they then become food for shrimp and fish under and at the edges of the ice. This production is the base of the food web that supports marine mammals and birds that flourish in the Arctic during spring and summer. Climate models project that, with additional warming from greenhouse gases, summer sea ice could vanish in the Arctic my mid-century, with profound implications for many iconic species. Jim McCarthy is Professor of Biological Oceanography at Harvard University. Free and open to the public.