Currents and Upwelling Nutrients

A phytoplankton bloom off the coast of Vancouver Island seen from space. Phytoplankton are responsible for much of the oxygen in the Earth's atmosphere – half of the total amount produced by all plant life.

The changing climate produces more storms and stronger weather. Weather patterns have a strong relationship with ocean currents. Changes in ocean currents have an effect on the distribution of waters with certain temperatures and chemistry, which impacts where nutrients will well up from the depths.

Changes in these nutrient upwellings will change the distribution of species that depend on them, which in turn changes the distribution of other species, eventually affecting the entire ecosystem.

When storms occur, weather currents push air downwards toward the Earth in circular patterns. In a process called downwelling, storm winds hold the warm surface waters against the surface and sometimes push warm water down a few hundred meters. The flow of surface waters away from the center of the storm causes replacement by deep cold waters. Plumes of cold, nutrient rich waters rise to the surface in the process called upwelling.

According to Bill Crawford of Fisheries and Oceans Canada, the summer upwelling zone along the west coast is very productive. Both the direction and strength of the wind can affect that productivity. Usually by July there is a large North Pacific high (temperature and pressure pattern). As this high pressure expands there will be stronger winds from northwest along the B.C. coast (increasing in speed by about 5 percent). Winds from the north push surface waters offshore causing more upwelling nutrients.

What can we expect?

Based on IPCC models, winter changes on the B.C. coast can be expected to exceed natural variability by the 2050s.  The Aleutian low pressure pattern, indicating cold winters, will be moving north and should warm the Pacific northwest. We may see changes such as stronger westerly winds, ocean currents generally coming from the south, and warmer water in Queen Charlotte Strait.

B.C. may begin to see southward movement of cool water plumes down past the Scott Islands along the continental shelf break. The water in shallow areas cools quicker which should result in pressure build up in the north of Queen Charlotte Strait, causing outflow of water and eddy generation off of the south of Haida Gwaii. Summer eddies may also be produced off the south of Haida Gwaii due to freshwater input.

The changes in the sea due to climate impacts are tremendous and are taking place at a rapid rate. Knowing what changes will take place in ocean currents and nutrient distributions will help us to understand what will be happening with ecosystems and species distribution.