Two years of rainwater samples collected at the Tudor Hill Marine Atmospheric Observatory enabled a team of researchers from BIOS, Brown University and Princeton University to track sources of nitrogen to the open ocean. They came to the surprising discovery that the ammonium in rainwater came from natural marine sources rather than from human activities in the United States.  Ammonium is a form of nitrogen and a common culprit in nutrient pollution due to agricultural practices.  Their results are in contrast to the way other human-produced pollutants disperse from the continents to the ocean, and challenges assumptions about the marine nitrogen cycle.  The results are presented in a new study co-authored by Dr. Andrew Peters and published in the journal Global Biogeochemical Cycles.