FY 1989

Linkage of ocean and fjord dynamics at decadal period

Ebbesmeyer, C.C., C.A. Coomes, G.A. Cannon, and D.E. Bretschneider

In Aspects of Climate Variability in the Pacific and the Western Americas, D.J. Peterson (ed.), Geophys. Monogr. 55, American Geophysical Union, Wash., D.C., 399–417 (1989)

At decadal period (10­20 years), dynamic linkage was evident between atmospheric low pressure systems over the North Pacific Ocean and circulation in a Pacific Northwest fjord (Puget Sound). As the Aleutian low pressure center shifts, storms arriving from the North Pacific Ocean deposit varying amounts of precipitation in the mountains draining into the estuarine system; in turn, the fluctuating addition of fresh water changes the density distribution near the fjord basin entrance sill, thereby constraining the fjord's vertical velocity structure.

The linkage was examined using time series of 21 environmental parameters which covaried between the 2 regimes associated with cycling of the Aleutian Low between its eastern and westernmost winter positions. Observations from 1899 to 1987 suggest that, in the 20th century, approximately 5 cycles may have occurred between these regimes. Covariation in all but one of the time series (Puget Sound's main basin salinity) occurred because of the high degree of correlation between parameters and the strong decadal cycles compared with long-term averages, interannual variability, and seasonal cycles. Basin salinity was relatively steady due to opposing influences of oceanic source water salinity and the addition of fresh water in each regime. However, the decadal signal for the other parameters characterizing Puget Sound water are apparently amplified twofold compared with that of the atmosphere over the North Pacific Ocean.

"As to Holmes, I observed that he sat frequently for half an hour on end, with knitted brows and an abstracted air, but he swept the matter away with a wave of his hand when I mentioned it. "Data! data! data!" he cried impatiently. "I can't make bricks without clay."

A. Conan Doyle
The Adventure of the Copper Beeches