Data from elephant seals reveal new features of marine heatwave ‘The Blob’

Newswise – The North Pacific Blob, an ocean heatwave that began in late 2013 and lasted through 2015, was the largest and longest-lasting ocean heatwave on record. A new study using data collected from elephant seals shows that in addition to the well-documented surface warming, deeper warm water anomalies associated with the blob were much more extensive than previously reported.

The new findings were reported by a team of biologists and marine scientists at UC Santa Cruz in a Article published July 4 in Journal of Geophysical Research: Oceans.

“The elephant seals collect data in different locations than existing oceanographic platforms,” ​​explained lead author Christopher Edwards, professor of marine sciences at UC Santa Cruz. “This is an underutilized dataset that can inform us about important oceanographic processes and help biologists understand the ecology of northern elephant seals.”

For decades, UCSC elephant seal researchers, led by co-author Daniel Costa, professor of ecology and evolutionary biology and director of UCSC’s Institute for Marine Sciences (IMS), have used advanced tagging technology to track the month-long migrations of elephant seals in the North Pacific.

“While seals have been used to study the physical oceanography of polar regions for some time, this is one of the first studies to use data collected from seals to answer physical oceanographic questions in temperate regions like the North Pacific,” Costa said.

The sensors worn by animals record depth, temperature and salinity as the animals repeatedly dive to great depths during their migrations of about 6,000 miles across the North Pacific.

“Female elephant seals go out to the open ocean where a ship might collect data every now and then, while we have elephant seals out there collecting data everywhere,” said first author and IMS research biologist Rachel Holser. “It is unusual to have this type of data in the temporal and spatial resolution and at depths below several hundred meters.”

Elephant seal data collected during the blob showed unusually warm temperatures extending 1,000 meters (3,280 feet) below the surface. Subsurface warming continued into 2017, long after surface temperatures had returned to normal.

The blob has been well studied in terms of surface heating driven by atmospheric conditions, which subsided in late 2015. The widespread warming of the subsurface raises questions about the mechanisms behind it, Edwards said.

“These temperature anomalies are so deep that they are unlikely to be due to mixing from the surface,” he said. “A reasonable mechanism is that the unusually warm water was transported from further south to the north. What we don’t yet know is whether this northward transport is directly or indirectly related to surface warming. Changes on the surface may have temporarily altered deeper currents to pull southern waters north.”

Marine heat waves are expected to increase in frequency, magnitude and duration as global temperatures continue to rise. These events can have significant impacts on marine life as well as economic consequences for local communities that rely on marine fisheries and ecosystems. Understanding the physical processes involved in marine heatwaves will help scientists predict their onset and evolution, and allow people to anticipate and address the environmental and economic consequences.

“Just like with terrestrial heatwaves, we’ve seen a dramatic increase in the frequency and strength of marine heatwaves over the past decade,” Holser said. “The more information we can gather, the better we can understand what is happening and face the challenges. This study demonstrates the value of working with elephant seals to collect oceanographic data that complement other methods.”

In addition to Holser, Edwards, and Costa, marine science PhD student Theresa Keates also contributed to the study and is a co-author of the paper. This work was supported by the US Office of Naval Research and the Central & Northern California Ocean Observing System (CeNCOOS). With the continued support of CeNCOOS, the Costa Laboratory, in collaboration with Edwards and Professor Raphael Kudela of Ocean Science, continues to collect oceanographic data using elephant seals.