The Blob

The waters of the northeast Pacific have been warmer than normal since the fall of 2013. The reasons why are still being investigated by many, but the scale and intensity of this phenomenon make it unlike anything observed before. Scientists currently believe that the cause of the warm ocean waters is that they simply didn’t cool off like they were supposed to in the fall and winter of 2013-2014.

During that time of year, the main mechanism for cooling this region of the ocean is a reasonably stable atmospheric low pressure system south of the Aleutian Islands. The Aleutian Low, as this system is called, was much weaker than normal, due to unknown causes. The higher atmospheric pressures resulted in slower than normal winds at the ocean surface. Winds blowing over the ocean mix and cool the surface layer of the ocean just like blowing on the surface of hot coffee stirs and cools the coffee. Without these typical winter winds the ocean remained warm throughout 2014 (see the panels below). This temperature difference is most striking when comparing October 2013 and January 2014, where, in just 3 months, the sea surface went from slightly cooler than normal to nearly 4 degrees C warmer than normal (shown in the panel of sea surface temperature anomalies below).

Over the spring and summer of 2014, The Blob shifted towards the coast where these warm waters increased stratification and inhibited mixing. This stratification reduced the amount of nutrients that could be brought from the deep ocean to the surface through the process of upwelling. The coastal environment depends regular nutrient delivery for its incredible biological productivity and without the nutrient supply, some species may struggle.

Monthly averaged sea surface temperatures anomaly, or difference from the long-term average for that month, beginning in January 2013 through July 2015. Note: Grey patches in the ocean are indicative of persistant cloud cover making satellite measurement impossible. Source: NOAA CoastWatch

It remains unclear if The Blob is a temporary condition or is a feature that will persist for years, or possibly decades, to come. Based on the conditions in the fall, winter, and spring of 2015, there is some thought that these warm coastal waters are indicative of a shift to a warm phase of the Pacific Decadal Oscillation, or PDO. The PDO is one of two known North Pacific cousins of El Nino (the other being the North Pacific Gyre Oscillation). Like El Nino, with PDO there is a fluctuation between warmer and colder waters. However, with PDO the location of this oscillation is primarily in the midlatitudes between 25-55 degrees N and the oscillations between warm and cool take approximately 20-30 years. This timeframe is much longer than El Nino’s roughly 2 year cycle and the location more directly affects BC coastal waters. During the warm phase of the PDO (below left) the coastal waters are warmer than normal leading to enhanced biological productivity in Alaska and decreased productivity in southern BC and northwest US states. The opposite conditions are true for the cool phase (below right).

Diagrams of Pacific Decadal Oscillation (PDO) warm (left) and cool (right) phases. Color is indicative of the magnitude of the temperature anomaly. Arrow size and length is indicative of wind strength and direction anomaly. Source: N.J. Mantua 2000

So what does this warm coastal water mean?

While research is ongoing, scientific hypotheses link The Blob to:

Fisherman have been reporting catching yellowfin tuna, a species normally found much farther south, off the coast of Vancouver Island, and fisheries managers are struggling to set appropriate catch quotas for 2016 and beyond in light of these dramatic changes. The effects of these temperatures are being felt throughout the entire marine ecosystem, and the atmosphere-ocean connection has also likely had many effects on regional weather systems.

Chlorophyll concentrations, a proxy for phytoplankton biomass, in July 2015 off the west coast of North America showing the extent of the record setting algae bloom. Source: NOAA

This phenomenon is still very much an area of active research and scientists came together in May 2015 for the first of two multi-day workshops dedicated to the discussion of small-, and large-, scale observations of this anomaly. The second workshop is slated for this coming fall or winter in Seattle.

If you would like to keep up to date on the status of The Blob, there’s now a dedicated Blob blog from the Alaska Ocean Observing System.

Source materials for this article came from the 2014-2015 Pacific Anomalies Science and Techonology Workshop unless otherwise stated.


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