What Proportion of the North Pacific Current finds its way into the Gulf of Alaska?

1. What Proportion of the North Pacific Current finds its wayinto the Gulf of Alaska? Howard Freeland Dept. of Fisheries and Oceans Institute of Ocean Sciences N. Saanich, BC, Canada FreelandHj@pac.dfo-mpo.gc.ca

2. The standard picture of the circulation of the N.E. Pacific

3. A very short history of the problem This was first investigated by Doe in 1955, who concluded that the latitude of the bifurcation was very different in 1951 compared with 1950. Wickett examined the issue in 1966, believed that variations were occurring but couldn’t monitor them. He did believe that such variations could have biological effects. Chelton and Davis (1982) looked at sea levels along the Pacific coast of N. America and found that the dominant mode of variability was a negative correlation between flows in the Alaska Gyre and California Current. Hare et al (1991) reported “inverse production regimes” and suggested that the sort of mechanism reported by Chelton and Davis could be a powerful means of relating the oceanographic changes to biological systems. Bograd and Lynn (2003) suggested that there was a southward shift of the N. Pacific bifurcation during 2002. This period was certainly associated with profound changes in the N.E. Pacific ecosystems. All evidence to date is indirect and this seems to be a problem peculiarly well suited to direct investigation using the Argo array.

4. The circulation of the N. E. Pacific Using the methods described in Freeland and Cummins, Argo: a new tool for environmental assessment and monitoring of the world’s oceans. Progress in Oceanog. 64(1), 31-44, 2005. • Compute dynamic height relative to 1000 dbars at every float location. • Compute and subtract mean dynamic height and compute variance. • Project these onto 20 EOFs of the stream function field derived from a quasi-geostrophic model of the N.E. Pacific and compute weights. • Sum mean and the weighted EOFs. • Typically this accounts of 87-93% of the total variance.

5. A few specimen maps. We see clear evidence of variability, but no annual cycle.

6. A few specimen maps. We see clear evidence of variability, but no annual cycle.

7. Does the latitude of the N. Pacific Current change?

9. Current strengths (Delta-dynamic height) are also variable. DNPC f = DGAk/ DNPC DGAk DCCurr

10. Principal Component Analysis on the time series of DNPC, DGAk and DCCurr On average: 61% of NPC water flows into the Gulf of Alaska 39% of NPC water flows into the California Current system Variability: EOF #1 – 70.4% of variance associated with vector (.688, .473, .551) EOF #2 – 29.6% of variance associated with vector (.021, -.771, .636) GAk NPC CCurr GAk NPC CCurr

11. Is there a biological response? CPR Sections courtesy of Sonia Batten, SAHFOS

12. Conclusions • On average 60% of the water arriving off N. America in the North Pacific Current ultimately heads northwards. • Variability is dominated by the “breathing mode” - i.e. if more water arrives in the N. Pacific Current it empties into both northbound and southbound branches. • This is not in agreement with the analysis of the problem by Chelton and Davis (1980). • There is good evidence that variations in the position of the bifurcation produce a strong biological response.