Hypoxia

In the summer of 2002, oxygen levels in the water near the Oregon coast plunged so low that fishes, crabs, and other marine organisms had to flee or die in the suffocating waters. These low oxygen conditions, commonly called hypoxia, had never been seen in Oregon prior to 2002, but have recurred every summer since. PISCO scientists are working to understand how upwelling, a normal event that brings rich, life-giving water to the Oregon coast, can turn deadly, causing one of the largest known hypoxic dead zones in the world (how do Dead Zones form?). PISCO scientists are also looking closely at how Oregon’s marine life is responding to the dead zone.

Hypoxic Event Video

Since 2002, hypoxia has occurred every summer, although the size, duration, and severity of the dead zone varies from year to year. The map below shows the known extent of hypoxia in 2006 and 2007. The most severe event occurred in the summer of 2006 when oxygen levels dropped to historic lows and hypoxic water could be found in large areas along the Washington and Oregon coasts. Detailed information about hypoxia is available on our Frequently Asked Questions page.

Read more about hypoxic conditions prior to 2002.

Browse photos  of research during hypoxic events off the Oregon Coast.

Screen capture from ROV-based video transect surveys of nearshore (50-55m depth) rocky reef habitats at 44.25ºN illustrating a) pre-anoxia rockfish (Sebastes spp.) and b) macroscopic benthic invertebrate communities in 2000 and 2001, respectively, c, d) widespread mortality of macro-invertebrates during the 2006 anoxia event, e) formation of putative sulphide-oxidizing bacterial mats in 2006, and f) close-up of bacterial mats. Reference laser points are spaced at 10cm apart.

Dead Zone Observations

Observations from a remotely operated vehicle (ROV) by PISCO and ODFW researchers have revealed the immediate loss of many species of bottom dwelling marine organisms when oxygen declines to hypoxic and anoxic levels. Marine animals are either suffocated by the lack of oxygen or are forced to move close to the surface or very close to shore to find higher oxygen environments. When dead zones are short-lived or moderate in severity, the risk of marine life mortality events has been low. In 2006, the dead zone lasted 4 months and large areas of the coastal ocean were affected by oxygen levels that dropped as low as zero. ROV surveys revealed mass die-offs of many marine invertebrates that inhabit near-shore reefs in the core anoxia region. Because dead zones are a new disturbance, the long term consequences are difficult to predict, but recurrent hypoxia could cause wide-spread changes to the marine ecosystem.  How do scientists study hypoxia?

Monitoring and Research

The repeated hypoxic events of recent years suggest a fundamental shift in ocean conditions off the Pacific Northwest coast. These changes are complex and may include either oceanic or atmospheric changes or both. New results from other researchers show a slight, decrease in ocean oxygen levels world-wide, likely due to climate change. This small decrease in overall oxygen levels has probably primed the pump for hypoxia in the Pacific Northwest. The other major factors contributing to Pacific Northwest hypoxia are changes in winds and ocean circulation. We have evidence for both. These changes underscore the need for long-term scientific monitoring and research in coastal and open waters. These observations can enable scientists to better forecast where and when future low oxygen zones are likely to occur.