Scientists Warn About Dead Zones Off Oregon and Washington Coasts
Large expanses of oxygen-depleted waters pose serious threat to marine life.
NOAA recently confirmed that a large area of oxygen-depleted water is growing off Pacific Northwest shores. Data from local moorings, measurements collected by fishermen using dissolved-oxygen sensors provided by NOAA, and oceanic measurements collected during a NOAA scientific cruise corroborate the presence of hypoxic (oxygen-depleted) waters off the Washington and Oregon coasts.
“Low dissolved oxygen levels have become the norm in the Pacific Northwest, but this event started much earlier than we’ve seen in our records,” says Oregon State University professor Francis Chan, director of NOAA cooperative institute CIMERS.
Oxygen-depleted bottom waters occur seasonally along Washington and Oregon’s continental shelf when strong winds in spring and summer trigger upwellings that bring deep, cold, nutrient-rich water to the surface. These waters fuel plankton blooms, and when the blooms die off, they sink to the bottom, where their decomposition consumes oxygen.
Concerns first arose in March, when a NOAA wind-measurement station observed an early shift in winds that initiate upwellings. Winds strengthened in April, when the first measurements of hypoxic conditions were recorded. In late May, a NOAA Fisheries survey off Washington and Oregon found large phytoplankton blooms and hypoxic conditions on the continental shelf in the area of Grays Harbor, Washington, at about the same time beachgoers reported great numbers of dead crabs washing ashore in Ocean Shores. In June and July, samples along the Newport
Line, a long-term monitoring transect off Newport, Oregon, also showed hypoxic waters.
Meanwhile, commercial fishermen were reporting strange occurrences nearby. They were pulling up pot after pot of dead crabs, and an octopus climbed up some ropes to escape something they couldn’t see. It wasn’t until Chan dropped underwater sensors in the area that he realized what was wrong: Oxygen levels had plummeted so low that sea creatures started to flee any way they could. Those that couldn’t died, leaving a mass graveyard along the ocean floor.
NOAA ship Ronald H. Brown left port June 13 on a 45-day mission to survey ocean conditions to better understand the factors that influence ocean acidification and hypoxia, which are related.
During the research cruise, there was one discovery that had scientists anxious to get back into the laboratory. A net retrieved vertically from depths of 100 meters surfaced with a large amount of a greenish-black substance. “It was phytoplankton, the kind responsible for creating hypoxic conditions as it sinks into the deeper water and decays,” said Richard Feely, an oceanographer with NOAA’S Pacific Marine Environmental Laboratory, who also found that dissolved oxygen and ocean acidity measurements were consistent with an event with the potential to create dead zones that could spell disaster for bottomfish, crabs and other marine life.
Chan describes the root causes of hypoxic zones as two levers. One is dictated by basic chemistry, the other has to do with currents and wind patterns, which have been altered by a changing global environment.
Feely believes the hypoxic layer likely covers the continental shelf region from the Olympic Peninsula in Washington to Heceta Bank on the central Oregon coast. The Washington Post recently reported that the deadly waters now stretch across 7,700 square miles. And indications are that the hypoxic waters will persist, perhaps intensify, and remain through fall.