Sep 252020

Carcasses of 6,540 common murres washed onto this beach near Whittier, Alaska, on January 1 and January 2, 2016. Researchers blame a marine heat wave that diminished the murres’ key food supply.David B. Irons

The Blob, that large mass of warm water off the coast of North America, was a massive marine heat wave that wreaked havoc on marine life for three years not long ago. A new study published on September 25, 2020, shows that in the past 40 years, marine heatwaves have become considerably longer and more pronounced in all of the world’s oceans. “The recent heatwaves have had a serious impact on marine ecosystems, which need a long time to recover afterwards—if they ever fully recover,” said Charlotte Laufkötter, a marine scientist at the University of Bern in Switzerland and the lead author of the study. “Some of these couldn’t even have occurred without climate change.”

Using statistical analyses and climate simulations, her team found that major marine heatwaves have become more than 20 times more frequent due to human influence. While they only occurred every hundred or thousand years in the pre-industrial age, they are projected to become the norm. If we are able to limit global warming to 1.5 degrees, marine heatwaves will occur once every decade or century. If temperatures rise by 3 degrees, however, the Blob will visit the world’s oceans every decade or even every year.

In their analysis of sea surface temperature between 1981 and 2017, they noted that in the first decade of that period, 27 major heatwaves occurred which lasted 32 days on average, reaching maximum temperatures of 4.8 degrees Celsius above the long-term average temperature. But from 2007 to 2018, 172 major events occurred, lasting an average of 48 days and reaching peaks of 5.5 degrees above the long-term average temperature. Sea temperatures usually fluctuate only slightly. Week-long deviations of 5.5 degrees over an area of 1.5 million square kilometers—an area 35 times the size of Switzerland—present an extraordinary challenge to marine organisms.

History of the Blob

The Blob was first detected in late 2013, continued spreading throughout 2014 and 2015, and then resurfaced again in September 2016. It got its name in June 2014 when it reached a size of 1,000 miles (1,600 km) long, 1,000 miles (1,600 km) wide, and 300 feet (91 m) deep. By the time it was done, it had been the longest marine heat wave (MHW) on record, and had expanded to more than one million square miles in area, covering waters from Alaska down to Mexico.

This marine heat wave was compounded by a lower than usual water circulation resulting in a static upper layer of nutrient-poor sea water. From 2015-2016, the Blog was responsible for the deaths of about 1 million seabirds; specifically the common murres (Uria aalge), according to a study published on January 15, 2020.

It was also responsible for the unusual mortality event (UME) involving California sea lions which occurred from January 1, 2013 to September 30, 2016 along the California coast, mostly along Central and Southern California. Total strandings included 8,122 juvenile California sea lions documented, with 93% stranding alive (n=7,587, of which 3,418 were released after rehabilitation) and 7% (n=531) stranded dead.

Number of juvenile sea lions that stranded by year. The horizontal line is the mean number of Sea lions stranding from 2006-2012 (pre-UME) and the dotted lines are plus/minus one standard deviation. The years in which the UME occurred are in color.


To see past blog posts about California sea lions during this time period, see The Plight of the California Sea Lion and The Plight of the California Sea Lion, Part 2.

Kelp Forests

The Blob also adversely affected the temperate kelp forests, which are among the most productive and species-rich marine ecosystems in the world. A study published on September 9, 2020 found that from 2014-16, kelps declined in abundance from Baja, Mexico to Alaska, mostly in the southern and northern California ecoregions.

Data from 469 sites from Alaska, to Baja California were analyzed, including 373 species (assigned to 18 functional groups). For this ambitious endeavor, a team of scientists and countless volunteers from 14 different organizations documented the northward migration of kelp forests due to warming waters. Each region had a different type of volunteer divers collecting the information—from undergraduate students and tourist divers in California to women from fishing communities at Isla Natividad in Mexico, known as “Las Sirenas del Mar,” who were trained as divers and have been active participants in the underwater community-based monitoring program.

By analyzing the data from each separate group and area as a whole, the researchers found that edges of the distribution are more sensitive and kelp is migrating northward. But the researchers also noticed that as the kelp migrates, only the species that eat it directly appear to migrate with it. This leaves a broken food web behind.

Across the entire region, declines in phytoplankton and zooplankton abundance corresponded with the anomalously warm water temperatures and reduced nutrient availability (i.e., nitrate concentrations) in the photic zone.

The results suggest that coastal communities that are dependent on kelp forests will be more impacted in the southern portion of the California Current region, highlighting the urgency of implementing adaptive strategies to sustain livelihoods and ensure food security.



University of Bern, Marine heatwaves are human-made

Laufkötter C, Zscheischler J, Frölicher TL, High-impact marine heatwaves attributable to human-induced global warming, Science : 1621-1625

Wikipedia, The Blog (Pacific Ocean)

Eric Wagner, ‘The blob’ revisited: Marine heat waves and the Salish Sea

Piatt JF, Parrish JK, Renner HM, Schoen SK, Jones TT, Arimitsu ML, et al. (2020) Extreme mortality and reproductive failure of common murres resulting from the northeast Pacific marine heatwave of 2014-2016. PLoS ONE 15(1): e0226087.

NOAA Fisheries, Office of Protected Resources, 2013-2016 California Sea Lion Unusual Mortality Event in California

Tim Stephens, Sarah Buckleitner, Cooperative research effort documents northward migration of kelp forests

Beas‐Luna, R, Micheli, F, Woodson, CB, et al. Geographic variation in responses of kelp forest communities of the California Current to recent climatic changes. Glob Change Biol. 2020; 00: 117.


Carcasses of 6,540 common murres, David B. Irons, The ‘Blob,’ a massive marine heat wave, led to an unprecedented seabird die-off

Figure 1, Number of juvenile sea lions stranded by year, NOAA Fisheries, California Sea Lion Data