Puget Sound freshens up with a little help from winter snowpack

In the latest “Eyes Over Puget Sound” report, one little note caught my attention: “Puget Sound is fresher than it’s ever been the past 17 years.”

Jellyfish are largely missing this fall from Puget Sound. Some patches of red-brown algae, such as this one in Sinclair Inlet, have been observed.
Photo: Washington Department of Ecology

At least temporarily, something has changed in the waters of Puget Sound over the past few months. It may not last, but it appears to be a good thing.

The monthly EOPS report, compiled by a team of state environmental experts, lays out recent water-quality data for the Department of Ecology. The report also includes personal observations, aerial photographs and scientific interpretations that keep readers abreast of recent conditions while putting things in historical context.

The “fresh” conditions called out in the report refers to the salinity of Puget Sound, which is driven largely by the freshwater streams flowing into the waterway. The reference to 17 years is a recognition that the overall salinity hasn’t been this low since the current program started 17 years ago.

Dissolved oxygen, essential to animals throughout the food web, was higher this fall than we’ve seen in some time. Hood Canal, which I’ve watched closely for years, didn’t come close to the conditions that have led to massive fish kills in the past. The only problem areas for low oxygen were in South Puget Sound.

Water temperatures in the Sound, which had been warmer than normal through 2015 and 2016, returned to more average conditions in 2017. Those temperatures were related, in part, to the warm ocean conditions off the coast, often referred to as “the blob.” In South Puget Sound, waters remained warm into October.

Why is the water fresher this fall than it has been in a long time? The reason can be attributed to the massive snowpack accumulated last winter, according to oceanographer Christopher Krembs, who leads the EOPS analysis. That snowpack provided freshwater this past spring, although rivers slowed significantly during the dry summer and continued into September.

“We had a really good snowpack with much more freshwater flowing in,” Christopher told me, adding that the Fraser River in southern British Columbia was well above average in July before the flows dropped off rapidly. The Fraser River feeds a lot of freshwater into northern Puget Sound.

Freshwater, which is less dense than seawater, creates a surface layer as it comes into Puget Sound and floats on top of the older, saltier water. The freshwater input fuels the circulation by generally pushing out toward the ocean, while the heavier saltwater generally moves farther into Puget Sound.

“The big gorilla is the upwelling system,” Christopher noted, referring to the rate at which deep, nutrient-rich and low-oxygen waters are churned up along the coast and distributed into the Puget Sound via the Strait of Juan de Fuca. Lately, that system has been turned down to low as a result of larger forces in the ocean.

In an advisory issued today (PDF 803 kb), NOAA’s Climate Prediction Center says a weak La Niña is likely to continue through the winter. For the northern states across the country, that usually means below-average temperatures and above-average precipitation. (It’s just the opposite for the southern states.)

With a favorable snowpack already accumulating in the mountains, experts can’t help but wonder if we might repeat this year’s conditions in Puget Sound over the next year.

Christopher told me that during aerial flights this fall, he has observed fewer jellyfish and blooms of Noctiluca (a plankton known to turn the waters orange) than during the past two years. Most people think this is a good thing, since these organisms prevail in poor conditions. Such species also have a reputation as a “dead end” in the food web, since they are eaten by very few animals.

Christopher said he noticed a lot of “bait balls,” which are large schools of small fish that can feed salmon, birds and a variety of creatures. “I assume most of them are anchovies,” he said of the schooling fish.

I would trade a jellyfish to get an anchovy on any day of the year.

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