Monster Seminar JAM - What are the past, present and future dynamics of hypoxia on the Oregon Shelf?
Dr. Francis Chan, Oregon State University
In recent years, the Oregon coast has been impacted by the
repeated summertime occurrence of hypoxic or low oxygen zones. Because mass die-off of marine life can occur as a result of low oxygen conditions, such areas are also commonly referred to as "dead zones." Although the low oxygen zone has varied in intensity from year to year, 2006 saw an unexpected expansion and degradation in oxygen conditions. At least 3,000 square kilometers of the continental shelf along the Oregon coast were affected. Analyses of historical records indicate that oxygen levels declined to levels unprecedented in five decades of oceanographic observations on the Oregon shelf. The immediate affects of this severe low oxygen event have been dramatic. Remotely operated submersible surveys revealed the loss of benthic fish from nearshore underwater reefs that are normally home to diverse communities of rockfish species. Acute oxygen deficits also resulted in extensive mass die-off of marine life such as seastars, crabs, marine worms and anemones that make up the food web of the seafloor. Along the world's major eastern boundary current systems, coastal upwelling often injects nutrient-rich but oxygen poor on to continental
shelves thus subjecting productive large marine ecosystems to risk of low oxygen events. Ecosystem sensitivity to extreme oxygen deficits nevertheless varies greatly across upwelling shelves. For example, anoxia occurs some but not all portions of the Humboldt and Namibian Current Systems and has been traditionally absent from the shallow shelves of the California Current System (CCS). The conditions that regulate spatial patterns in hypoxia/anoxia risks and the potential for climate modification of those risks are poorly resolved. These uncertainties pose important challenges for understanding and predicting the future dynamics of coupled climate-ecosystem processes in the Pacific Northwest. Off the Oregon coast, the appearance of shelf hypoxia has coincided with a number of remarkably strong yet divergent episodes of climate anomalies along the California
Current System (CCS). I will present finding from a multi-year observational program along the Oregon shelf to examine the factors that regulate ecosystem sensitivity to hypoxia and the possible linkages between climate forcing and the onset and severity of hypoxia.
University of Washington
The Old Fisheries Center Auditorium (rm 201)
Date and Time:
March 8, 2007,
11:00 am - 12:30 pm