The Mystery of the Pacific Northwest (Archive)
Originally posted February 7, 2018.
Hally Stone is a physical oceanographer who studies coastal upwelling dynamics in the Pacific Northwest coastal ocean. In particular, she looks at the relationship between primary productivity and wind patterns, and how this relationship changes, both in space and on seasonal to interannual timescales.
There’s a mystery in the Pacific Northwest. Okay, there’s another mystery. This mystery, which might seem mundane, is actually quite crucial to the economic and cultural identity to the region. And that mystery is:
Why are the phytoplankton here so productive?
Fisheries, like the salmon and oyster fisheries, are really important in the PNW. For example, in 2015 in WA and OR combined, the commercial and recreational fisheries generated $3.9 billion in revenue. However, these fish don’t swim into the region, waiting to be caught – they grow up here. And while they’re growing, they’re eating lots of tiny animals, which, in turn, eat lots of phytoplankton.
What are phytoplankton? Phytoplankton are tiny plants that live in the surface ocean. Like plants that live on land, they use energy from the sun to grow, so they’re usually found near the sunlit ocean’s surface. In addition to sunlight, plants on land and in the ocean need nutrients to grow, which they get from their environment. Unlike in your garden, where the plants get their nutrients from the soil, in the ocean these nutrients tend to fall down in the water to depths without any light. The continual struggle in the ocean is to bring these nutrients back up into the light so that phytoplankton can use them.
How are these sinking nutrients brought to the surface? On the West Coast, we experience “coastal upwelling”, which is a mechanism through which deep, nutrient-rich water is brought up to the surface by wind. Specifically, when wind blows over the ocean’s surface, it pushes the surface water away from the coast and deeper water is then pulled up the surface to replace it. This deep water carries those sinking nutrients and thus provides nutrients to the phytoplankton at the ocean’s surface. With coastal upwelling, stronger winds bring more nutrient-rich water up to the surface than do weaker winds. On the West Coast, the strongest winds are generally off of CA; however, the most productive region in terms of phytoplankton growth is the PNW. Herein lies our mystery!
Source: NOAA National Ocean Service
Why are the phytoplankton here so productive? Some recent studies suggest a few reasons. First, the PNW has submarine canyons that enhance this upwelling, allowing for deeper, more nutrient-rich water to upwell to the surface, even with our weaker local winds. Second, outflow through the Strait of Juan de Fuca, carrying water from the Salish Sea (including Puget Sound), is full of nutrients. In fact, nutrients from this outflow account for nearly half of phytoplankton growth off of Vancouver Island, a third of growth off of WA, and a fifth of growth off of OR. Third, river input, particularly from the Columbia River, delivers land-derived nutrients to the ocean’s surface and facilitates mixing of deeper, nutrient-rich ocean water to the surface. Additionally, the straight coastlines and wide continental shelf of the PNW allow phytoplankton more time to grow in the surface waters, and the remote influence of strong winds off of CA helps enhance the effects of local upwelling winds in this region. Combined with the geography and the remote wind influence, the local inputs of additional nutrients fuel the high phytoplankton productivity of the PNW.
Perhaps this mystery isn’t actually that exciting at face value. However, understanding why our region’s fisheries (and phytoplankton) are so productive can help us prepare for future changes. While the geography may not change very much, wind patterns and outflow from both rivers and the Strait of Juan de Fuca may change in the future as the climate changes. If we can understand how these changes will affect our phytoplankton’s productivity, we can predict how the productivity of our fisheries may change both seasonally and from year to year, and thus be better prepared for the future.
Davis, K. A, Banas, N. S., Giddings, S. N., Siedlecki, S. A, Maccready, P., Lessard, E. J., Kudela, R. M., and Hickey, B. M. (2014). Estuary-enhanced upwelling of marine nutrients fuels coastal productivity in the U.S. Pacific Northwest. Journal of Geophysical Research: Oceans RESEARCH, 8778–8799. http://doi.org/10.1002/2014JC010248
Hickey, B. M., & Banas, N. S. (2008). Why is the Northern End of the California Current System So Productive ? Oceanography, 21(4), 90–107.
National Marine Fisheries Service. 2017. Fisheries Economics of the United States, 2015. U.S. Dept. of Commerce, NOAA Tech. Memo. NMFS-F/SPO-170, 247p