The coastal ocean off Oregon, from 1961 to 2000: is there evidence of climate change or only of Los Ninos?

A zonal hydrographic section along 44.65 degreesN, from the coast of Oregon to 300 km offshore, was occupied regularly (at least seasonally) from 1961 to 1971 and then sporadically until recently. Regular monitoring of this section to 160 km offshore resumed in July 1997 as part of the GLOBEC Long Term Observational Program; the recent data provide observations in Oregon coastal waters of El Nino 1997-98 and La Nina conditions that followed. The complete seasonal data from the decade 1961-1971 provide a basis for comparison with the recent temperature and salinity sections, steric height profiles, geostrophic velocity, and water mass characteristics. These data, and sporadic observations in intervening years, allow us to compare conditions during several ENSO events with the recent event and to search for evidence of climate change. The PFEL Coastal Upwelling Index, sea level from the University of Hawaii Sea Level Center, the Multivariate ENSO Index (MEI), the Pacific Decadal Oscillation (PDO), and outflow from the Columbia River are used to distinguish local and remote causes of variability, in physical oceanographic conditions off Oregon. The sequence of El Nino/La Nina/El Nino in 1963-66, during a cool phase of PDO, provides a comparison to El Nino/La Nina of 1997-2000. El Nino in 1982-83 and 1997-98, during a warm phase of PDO, caused the largest oceanographic anomalies in the 40 years. The comparison indicates warming of the coastal ocean off Oregon and suggests a modulation of ENSO effects by PDO. Such modulation would mask evidence for secular climate change in our 40-year oceanographic data series. (C) 2001 Elsevier Science Ltd. All rights reserved.