Haida Eddies

Rivers flowing off the North American continent supply the continental shelf in the Hecate Strait with warmer, fresher, and nutrient-enriched water.

This forms a series of plumes which can merge into large eddies that are shed into the northeast Pacific Ocean by late winter, and may persist for up to two years.

Due to their large size, it was not until the satellite era that scientists were able to observe the full scale and life cycles of Haida eddies.

The primary focus was to study fronts, eddies, winds, waves, and tides; each of these processes produce a change in sea surface height of several meters.

[6] Also in 1987, researchers Richard Thomson, Paul LeBlond, and William Emery observed that ocean drifters deployed in the Gulf of Alaska at 100–120 meters below the surface had stopped their eastward motion and actually began to move westward counter to the predominant current.

In 1992, Haida eddies were observed by researchers Meyers and Basu as positive sea surface height anomalies using TOPEX-POSEIDON, an altimetry-based satellite platform (like GEOSAT).

Haida eddies have been documented to form predominantly in the winter[6] when bifurcation is south, and favorable atmospheric conditions are met to intensify the subpolar gyre.

With these conditions, Haida eddy formation has also been documented to occur from baroclinic instabilities from alongshore wind reversals,[10] equatorial Kelvin waves,[11] and bottom topography.

[6] Stratification increases between these warmer, less-saline vortices and the surrounding waters by effectively depressing background lines of constant temperature (isotherms) and salinity (isohalines) (shown in figure).

As Haida eddies break away from the coast into the subpolar gyre, they transport water properties such as temperature, salinity and kinetic energy.

[14] Upon eddy formation in winter, surface water concentrations are high in nutrients including nitrate, carbon, iron, and others that are important for biological production.

However, they are quickly consumed by phytoplankton through spring and summer, until fall when the now reduced nutrient concentrations can be slowly replenished by mixing with the sub-surface core waters.

The southeast and central Gulf of Alaska tends to be iron-limited, and Haida eddies deliver large quantities of iron-rich coastal waters into these regions.

[17] This iron flux into the photic zone (where light is abundant to support growth), is associated with an increase in spring and summer primary production, and drawdown of macronutrients as they are consumed by phytoplankton.

[18] Total dissolved iron concentrations in Haida eddies are approximately 28 times higher than open ocean waters of the Alaska gyre.

This resulted in the highest chlorophyll concentrations measured within an eddy, and the most intense phytoplankton bloom in the last ten years in the northeast Pacific.

[20] Concentrations of dissolved inorganic carbon (DIC) and nitrate (NO3−), which are important macronutrients for photosynthesis, are quickly depleted in Haida eddy surface waters through most of their first year due to uptake by biological primary production.

This process also leads to a summertime reduction in total alkalinity, which is a measure of the capacity of seawater to neutralize acids, and is largely determined by bicarbonate and carbonate ion concentrations.

[14] Net atmospheric CO2 removal by Haida eddies is estimated to be 0.8-1.2 x 106 tons per year,[17] underscoring the important role they play in the Gulf of Alaska.

[22] Large quantities of dissolved aluminum and manganese ions are also supplied to the Gulf of Alaska via eddy transport of coastal waters enriched from riverine inputs.

[21] The core of the eddy contains warm, fresh, nutrient-rich waters formed in winter, and with the addition of sunlight, produces strong spring blooms of primary productivity offshore.

This process has an effect hundreds of kilometers offshore, and facilitates the exchange of nutrients between shelf to deep ocean from late winter to the following autumn.

[2] Nutrients trapped and transported by Haida eddies support more biological growth compared to surrounding, low-nutrient ocean water.

Spring blooms are caused by sufficient light reaching the warm, nutrient-rich water contained in the middle of the eddy, due to anticyclonic rotation.

A late summer bloom can occur if storms produce vertical convection of the mixed layer, causing it to deepen and trap nutrients from below into the region of primary production.

They are thought to influence winter feeding habits of northern fur seals by providing food at a low energy expense.

Northwest coast of British Columbia, and southeast Alaska.
NASA Visible Earth image; ocean color from the SeaWIFS satellite, showing an anticyclonic Haida eddy in the Alaskan Current, southwest of Haida Gwaii.
North Pacific Current splitting into southward California Current and northward Alaska Current (bifurcation in image occurring around 45°N). Haida eddies occur within the subpolar Alaska Gyre to the north of the Pacific Current. Arrows indicate the direction of the current.
An idealized eddy in the Gulf of Alaska. "Isotherms" are lines connecting points of equal temperature. Warm, nutrient-rich coastal water spirals clockwise, forming the core of the eddy. Phytoplankton are concentrated in the edges of the eddy near the ocean surface, nourished by the nutrient-rich eddy water.