The slideshow above shows image from the 2004 Russian-American Long-Term Census of the Arctic (RUSALCA) mission. During the 2009 RUSALCA expedition, scientists will again visit the Bering Strait and northwards to the Pacific side of the Arctic Ocean, as they did in 2004. The area is thought to be particularly sensitive to global climate change because steep temperature, salinity and nutrient gradients in the ocean meet equally steep temperature gradients in the atmosphere. On the first leg of the mission, scientists will replace eight mooring buoys across the Bering Strait. Sensors on the buoys have already revealed that water pouring into the Arctic from the Pacific is warming and freshening, and likely contributing to sea ice retreat. On the second leg, scientists will track multiple environmental parameters, including seafloor flux of methane from thawing sub-sea permafrost, ocean currents, nutrient pathways, and changes in the benthic (bottom) and water-column ecosystems.