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Nutrient-Rich Subarctic Water Invades California Current
Reference
Freeland, H.J., Gatien, G., Huyer, A. and Smith, R.L. 2003. Cold halocline in the northern California Current: An invasion of subarctic water. Geophysical Research Letters 30: 10.1029/2002GL016663

What was done
The authors analyzed water temperature and salinity measurements that were made at a number of depths over a period of several years along two lines emanating from central Oregon and Vancouver Island westward into the Pacific Ocean.

What was learned
Subsurface waters in an approximate 100-meter-thick layer located between 30 and 150 meters depth off central Oregon were, in the words of the authors, "unexpectedly cool in July 2002." Specifically, mid-depth temperatures over the outer continental shelf and upper slope were more than 0.5C colder than the historical summer average calculated by Smith et al. (2001) for the period 1961-2000, which the authors say "might be cooler than a longer-term mean because the 1961-71 decade coincided with a cool phase of the Pacific Decadal Oscillation (Mantua et al., 1997)." At the most offshore station, in fact, the authors report "the upper halocline is >1C colder than normal and about 0.5C colder than any prior observation [our italics]." In addition to being substantially cooler, the anomalous water was also considerably fresher; and the combined effects of these two phenomena made the water less spicy, as the authors describe it, so much so, in fact, that they refer to the intensity of the "spiciness anomaly" as "remarkable."

Along the line that runs from the mouth of Juan de Fuca Strait to Station Papa at 50N, 145W in the Gulf of Alaska -- which was sampled regularly between 1959 and 1981, but irregularly thereafter -- similar low spiciness was observed, and the authors say there is little doubt it is the same feature as that detected off the coast of central Oregon. In this case, they report that "conditions in June 2002 [were] well outside the bounds of all previous experience [our italics]," and that "in summer 2001 the spiciness of this layer was already at the lower bound of previous experience."

What it means
The authors say their data imply that "the waters off Vancouver Island and Oregon in July 2002 were displaced about 500 km south of their normal summer position." Is this observation an indication the Pacific Ocean is beginning to experience a shift from what Chavez et al. (2003) call a "warm, sardine regime" to a "cool, anchovy regime"? It is tempting to suggest that it is. However, Freeland et al. caution against jumping to such a conclusion too quickly, saying there are no obvious signals of such a regime shift in several standard climate indices and that without evidence of a large-scale climate perturbation, the spiciness anomaly may simply be, well, anomalous. Hence, although the pattern of Pacific Ocean regime shifts documented by Chavez et al. suggests that a change from warmer to cooler conditions is imminent, there is not yet sufficient climatic evidence to claim that it is indeed in process of occurring.

On the other hand, in reference to the 1976-77 regime shift in the Pacific, Chavez et al. note that "it took well over a decade to determine that a regime shift had occurred in the mid-1970s" and, hence, that "a regime or climate shift may even be best determined by monitoring marine organisms rather than climate," as suggested by Hare and Mantua (2000). Enlarging on this concept, they cite several recent studies that appear to provide such evidence, including "a dramatic increase in ocean chlorophyll off California," which would appear to be a logical response to what the authors of the article we are reviewing describe as "an invasion of nutrient-rich Subarctic waters."

Other pertinent evidence cited by Chavez et al. includes "dramatic increases in baitfish (including northern anchovy) and salmon abundance off Oregon and Washington," as well as "increases in zooplankton abundance and changes in community structure from California to Oregon and British Columbia, with dramatic increases in northern or cooler species [our italics]."

Clearly, something dramatic is in the works; and it could well be a return to cooler conditions in the Pacific. Biological and climatic studies over the next few years should enlighten us considerably on this point, as well as what such a regime shift would portend for the global warming debate.

References
Chavez, F.P., Ryan, J., Lluch-Cota, S.E. and Niquen C., M. 2003. From anchovies to sardines and back: multidecadal change in the Pacific Ocean. Science 299: 217-221.

Hare, S.R. and Mantua, N.J. 2000. Empirical evidence for North Pacific regime shifts in 1977 and 1989. Progress in Oceanography 47: 103-145.

Mantua, N.J., Hare, S.R., Zhang, Y., Wallace, J.M. and Francis, R.C. 1997. A Pacific interdecadal climate oscillation with impacts on salmon production. Bulletin of the American Meteorological Society 78: 1069-1079.

Smith, R.L., Huyer, A. and Fleischbein, J. 2001. The coastal ocean off Oregon from 1961 to 2000: Is there evidence of climate change or only of Los Nios? Progress in Oceanography 49: 63-93.


Reviewed 5 March 2003