Hypoxic Areas Off the Oregon Coast
Researchers Find Widespread Regions of Low Oxygen in the Northwest
Studies of the California Current have recorded an increase in the occurrence of dead zones, free of oxygen off the coasts of Washington and Oregon.
Scientists studying the California Current are recording an increasing number of instances were dead zones, areas of water that are hypoxic or lacking oxygen are occurring off the coast of Oregon and Washington. In a paper titled Emergence of Anoxia in the California Current Large Marine Ecosystem, published in the peer-reviewed journal Science, researchers could find little evidence of this problem occurring prior to the year 2000.
In announcing the paper, NOAA oceanographer William Peterson says, “We’re now seeing low oxygen levels that are much more widespread and far more intense than what has been recorded in the past. The fish have simply moved out of these areas and are probably doing fine elsewhere, but animals that can’t move to better waters like Dungeness crabs, sea urchins and starfish will perish."
Undersea Carnage - The California Current is a slow moving stream of cold water that travels along the west coast from Mexico to British Columbia. In studying the current off the coast of Oregon with a submersible craft in 2006, researchers found many areas devoid of fish that previously held healthy populations between 2000 and 2004. Shallow areas seemed particularly hard hit, they few bottom dwelling creatures and increased levels of anaerobic bacteria. Some regions were literally graveyards for thousands of crabs littered with the bodies of many other animals like echinoderms and sea worms.
Formation of Dead Zone or Anoxic Areas - Oxygen free areas are linked to the process of coastal upwelling that transports nutrient rich cold water to the surface. Oxygen levels below 1.4 milliliters per liter are considered hypoxic for marine animals. There were many areas off the Oregon coast that fell below this basic threshold and some became anoxic or lacked any free oxygen. There is a sequence of events that cause a dead zone:
- Cold nutrient rich water flows up from the depths to shallower waters
- During the summer these nutrients spark a bloom of plankton growth
- Plankton not consumed by larger creature dies and sinks to the ocean floor
- Decomposing plankton increases biological oxygen demand and use up all free oxygen
A Connection to Global Warming? - Scientists think the increase in hypoxic areas is linked to climate change. Surface winds cause ocean currents to flow up from deep. Recent climate change has seen an increase in wind speed and duration that has prolonged the period of time that the upwelling occurs. Increasing this time period creates a greater surplus of unutilized biomass available for decomposition over a larger area of ocean floor.
There haven't been any effects to hypoxic areas observed with passing El Nino or La Nina events. Since this low oxygen phenomenon has occurred each year since 2002, researchers are starting to think that the occurrence of off shore dead zones in Oregon may be the new normal. Benthic or bottom dwelling creatures that cannot quickly adapt to changing conditions are at greatest risk.
