The Arctic atmosphere has been warming 3-4 times faster than the rest of the planet and receives large amounts of river freshwater from the watersheds surrounding the Arctic Ocean. This study is mapping the distribution of freshwater and its organic matter content in the Arctic Ocean with unprecedented spatial detail. In addition, the new data set is being compared to historical data collected by the researchers in 2005 and 2015 to create a 20-year perspective for these observations. Combining the information on organic matter composition and distribution with other parameters like salinity, temperature, and the isotopic composition of water molecules is allowing the investigators to identify sources and distribution of freshwater in the Arctic Ocean and advance understanding of freshwater sources (rivers, ice melt, precipitation) and their variability. The organic matter entering the Arctic from surrounding continents can be used as a tracer for the formation of the halocline, a water layer in the Arctic Ocean that isolates the sea ice on the surface from the much warmer subsurface Atlantic layer. Understanding the stability of the Arctic halocline is essential to predict future changes to sea ice cover and regional climate in the Arctic. This project is training undergraduate and graduate students and exposing them to international and multidisciplinary research through participation in expeditions and data workshops with collaborators. Undergraduate students are writing ne