April 17, 2015
Of sardines, sea lions, and “the blob” in the Pacific
If you’ve been following the news about the Pacific Ocean, there’s a lot going on these days. First, there have been the heartbreaking deaths of thousands of starving sea lion pups along the California coast. Then, this week, the Federal Fisheries Council voted to call off both the spring and summer sardine fishing seasons in response to a precipitous decline in the population of these small but critical forage fish.
Also this week, there have been countless headlines about a mysterious blob of warm water that’s hunkered down in the Pacific, which scientists have linked to everything from the California drought to the cold weather that has hammered eastern US. And, of course, there’s the question of climate change and whether it’s to blame.
If you’re confused, that’s perfectly understandable. Here’s how everything fits together.
The sea lion deaths seem to have resulted primarily from the sardine fishery’s calamitous collapse, although the blob may have played a supporting role by suppressing the upwelling of cool, nutrient-rich waters from below. Sardines form a staple of the sea lion diet — without them, mothers have to swim farther and dive deeper for other food sources like squid and anchovies, whose numbers have moved north to escape the blob. This year, sea lion colonies simply couldn’t support the all the new pups (their population has actually been growing for the last few decades).
So, what caused the sardine collapse? Was it the blob? Probably not, experts say, since sardines thrive in warmer waters. Instead, it’s likely that a number of other forces have conspired to reduce the sardine population, including the natural boom-and-bust cycle inherent to forage fish like sardines, the lingering effects of cold surface waters in previous years, and overfishing. Even as the council closed the fishery this week, managers and conservationists continued to debate the relative importance of these factors.
In contrast, the recent mass die-off of seabirds called Cassin’s auklets does appear to be directly related to the blob. The auklets’ primary food sources — tiny krill and copepods — don’t fare well in warm temperatures and last fall, up to 100,000 young birds washed up along the west coast. Although it’s too early to tell, Pacific salmon could feel the effects too, since they depend on the same species. (Warm-tolerant fish, on the other hand, are using the blob to explore new territory; fishermen have spotted skipjack tuna and sunfish off the coast of Alaska.)
Alright, then, what about this blob? Well, first of all, it’s actually made up of a few sub-blobs that together span a distance of about a thousand miles and penetrate a few hundred feet deep. Up and down the west coast, it has brought temperatures that vary from 2 to 7 degrees Fahrenheit warmer than normal. But even though the total heat content of the ocean continues to rise thanks to global warming, it doesn’t seem like climate change is the culprit here. Instead, scientists say it’s an example of natural variability within the climate system, which may give a preview of what climate change will bring.
A recent study found that the blob formed as the result of a particular atmospheric circulation pattern that persisted over the eastern Pacific for the last several years. It was marked by a high pressure “ridge” that deflected storms and calmed the winds that would usually suck heat from the ocean’s surface, allowing the blob to grow. This pattern of atmospheric circulation (not the blob itself) also seems to have contributed to some of the wacky weather that the US has seen in the last few years, like the continuing California drought and the frigid winters that have gripped the Northeastern US.
(It’s worth mentioning that even though climate change probably didn’t produce the blob, it may have influenced US weather in other ways. For instance, global warming may have contributed to the drought by increasing temperatures across California and changing how much precipitation falls as rain instead of snow. In addition, some scientists think the loss of Arctic sea ice may be influencing the jet stream, allowing polar air to dip down into the eastern US.)
One puzzling aspect of the blob is that it doesn’t really fit neatly into any of the well-known temperature patterns that regularly occur in the Pacific, like El Niño or La Niña. Nate Mantua of NOAA told the Washington Post that the blob could be an exaggerated form of the Pacific Decadal Oscillation, a natural variation which flips modes every few decades, as the name suggests. Others, like Dennis Hartmann from the University of Washington, say it’s something distinct, known as the North Pacific Mode.
Perhaps most importantly, though, scientists say that if the appearance of the blob marks a shift in the state of the Pacific, it could herald an era of rapidly warming global temperatures. Many scientists think the Pacific Ocean has been storing much of the heat that has built up on the planet over the last decade or so, causing the apparent slowdown in surface warming (the commonly used term “hiatus” is misleading, since temperatures have continued to rise, albeit more gradually). If the ocean has changed modes, studies show it may now begin to release that heat, ushering in a period of accelerated warming.
In the coming years, scientists will continue to study the blob and it’s impacts. Without a doubt, the story of the Pacific is far from over.
Learn more about changing ocean ecosystems in our module on researcher Kevin Arrigo and his work in the Arctic.
Find out why the blob may bring an end to more than a decade of slow global warming in this story from Nautilus.
Written by Julia Rosen
Julia Rosen is a freelance science writer and PhD student at Oregon State University. She received a Bachelors degree in Geological and Environmental Sciences from Stanford University before beginning her doctoral research on polar ice cores and climate change. In between, she did her Master's in backpacking around the world and skiing. Julia is a periodic contributor to Oregon States research magazine, Terra, and helps write blog content and develop learning modules for Visionlearning.