Response of the Southern California current system to the mid‐latitude North Pacific coastal warming events of 1982–1983 and 1940–1941

The large-scale structure of the California Current during the 1982–1983 mid-latitude North Pacific coastal warming event showed several persistent (> 16 months), anomalous conditions: positive sea surface temperature anomalies (1–2.5oC), depression of the inshore thermocline by as much as 50 m greater than normal, anomalous high inshore steric heights (˜ 1.05 dyn. m) compared with normal values, anomalous high sea levels (˜ 25 cm), positive subsurface temperature anomalies (3–4oC), negative salinity anomalies (0.1-0.3%), positive dissolved oxygen anomalies (0.5-1.5 ml/1), and negative inshore nutrient anomalies. The magnitudes of the subsurface anomalies generally are much larger than those of the surface anomalies. The cross-shelf length scales of the subsurface anomalies vary between 300 and 500 km. During this same period, pronounced negative sea surface temperature anomalies (2–3oC) developed in the central mid-latitude North Pacific. The characteristic diagrams and sign reversals in the salinity, oxygen, and nutrient anomalies are consistent with enhanced onshore transport of Pacific subarctic water from the offshore California Current. The source of this water is primarily from the west-northwest. The subsurface anomalies were produced dynamically by a depression of the inshore thermocline, which, at least in part, resulted from convergence of mass at the coastal boundary. The surface anomalies, however, were produced by a combination of dynamical and local thermodynami-cal processes. Observed anomalous atmospheric forcing, as reflected in the 700 mb height anomaly and in negative upwelling indices, is consistent with enhanced onshore transport from offshore California Current. All the data support the conclusion that the expansion and intensification of the Aleutian Low and the decrease in strength of the North Pacific High produced an anomalous basin-wide atmospheric circulation that, coupled directly with the large-scale wind-driven oceanic circulation, produced a major component of the North Pacific coastal warming response observed during 1982–1983. Nearly identical mid-latitude atmospheric forcing and oceanic responses were observed during the 1940–1941 analog event. Anomalous phytoplankton and zooplankton distributions also were observed, and fish catch during this period decreased by about 40%, with nearshore pelagic species particularly affected. Not only was the abundance of single species affected, but also the community structure (i.e., rank order of abundance) was changed in response to the changing environmental conditions. The biological response appears to have been driven by the increased static stability, deeper thermocline, and reduced nutrient concentrations, which, in turn, resulted from the anomalous atmospheric circulation.

[1]  R. Lynn,et al.  The 1982-83 warm episode in the California Current , 1983 .

[2]  J. Namias,et al.  Sea Level at Southern California: A Decadal Fluctuation , 1972, Science.

[3]  J. Lumley,et al.  A First Course in Turbulence , 1972 .

[4]  Arnold W. Mantyla,et al.  The effect of the geostrophic flow upon coastal sea elevations in the northern North Pacific Ocean , 1976 .

[5]  James J. Simpson,et al.  The California Current system: The seasonal variability of its physical characteristics , 1987 .

[6]  P. Fiedler.  Satellite Observations of the 1982-1983 El Ni�o Along the U.S. Pacific Coast , 1984, Science.

[7]  J. S. Godfrey,et al.  The Large-Scale Environment of the Poleward-Flowing Leeuwin Current, Western Australia: Longshore Steric Height Gradients, Wind Stresses and Geostrophic Flow , 1985 .

[8]  A. F. Krueger.  The Climate of Autumn 1982—With a Discussion of the Major Tropical Pacific Anomaly , 1983 .

[9]  Barbara M. Hickey,et al.  The California current system—hypotheses and facts☆ , 1979 .

[10]  J. Bjerknes,et al.  A possible response of the atmospheric Hadley circulation to equatorial anomalies of ocean temperature , 1966 .

[11]  R. Haney,et al.  The relationship between wind and sea surface temperature anomalies in the mid‐latitude North Pacific Ocean , 1983 .

[12]  James J. Simpson,et al.  A simple model of the 1982‐83 Californian "El Nino" , 1984 .

[13]  Robert L. Smith,et al.  The signature of El Niño off Oregon, 1982–1983 , 1985 .

[14]  J. Simpson.  Processes Affecting Upper Ocean Chemical Structure in an Eastern Boundary Current , 1986 .

[15]  A. E. Gill.  Atmosphere-Ocean Dynamics , 1982 .

[16]  Roderick S. Quiroz,et al.  The Climate of the “El Niño” Winter of 1982–83—A Season of Extraordinary Climatic Anomalies , 1983 .

[17]  N. Christensen,et al.  A study of sub-inertial waves off the west coast of Mexico , 1983 .

[18]  W. Emery,et al.  Atmospheric forcing of interannual variability in the northeast Pacific Ocean: Connections with El Niño , 1985 .

[19]  L. Mysak,et al.  Atmospherically Forced Eddies in the Northeast Pacific , 1980 .

[20]  John M. Wallace,et al.  Planetary-Scale Atmospheric Phenomena Associated with the Southern Oscillation , 1981 .

[21]  James J. Simpson,et al.  El Nino‐induced onshore transport in the California Current during 1982‐1983 , 1984 .

[22]  J. Namias.  Some Statistical and Synoptic Characteristics Associated with El Niño , 1976 .

[23]  James J. Simpson,et al.  Large‐scale thermal anomalies in the California Current during the 1982‐1983 El Niño , 1983 .

[24]  S. Hicks,et al.  Sea level variations for the United States, 1855-1980 / Tides and Water Levels Branch ; Steacy D. Hicks, Henry A. Debaugh, Jr., Leonard E. Hickman, Jr , 1983 .

[25]  R. Weiss.  The solubility of nitrogen, oxygen and argon in water and seawater , 1970 .