Arctic Great Rivers Observatory. This research examines how climate induced changes in the Arctic impact not only the quantity of OM exported but also the composition of OM, and thus the important role that it plays in downstream geochemistry. Ongoing work in tropical ecosystems, particularly in the Congo Basin has also focused on riverine carbon transport, geochemistry, release of greenhouse gases to the atmosphere, and addressing the fate of terrestrial OM in coastal waters. This research has shown the role of photochemical degradation processes in removing terrestrially derived DOM and shifts in the molecular signature of the DOM toward that of marine DOM, thus considerably complicating the task of tracking it in the coastal ocean. Additionally this work has linked hydrologic and land cover properties to carbon cycling across a range of sites throughout the Congo Basin. Ultimately through the results from these projects we aim to provide the critical geochemical observations to understand how climate change in the Arctic and human impacts such as land-use change in the tropics will impact the OM exported from these systems and how its processing and fate are changing with ramifications for the global carbon cycle.