In order to solve this question, the team took samples from the seabed, from the
boundary layer between the seabed and seawater, as well as from different water layers in the tropical oxygen
minimum zone during the Expedition M92 with the German research vessel METEOR in January 2013.
These include eastern
boundary current upwelling systems such as those off the U.S. west coast along coastal California, Oregon and Washington, deep - sea and subsurface oxygen
minimum zones, and coastal waters that are already experiencing excess nutrient levels (eutrophication) and low dissolved oxygen (hypoxia) due to human - driven nutrient pollution from land - based activities.