The North Pacific Blob, a marine heat wave that began in late 2013 and continued through 2015, was the largest and longest marine heat wave on record. A new study using data collected by elephant seals finds that in addition to the well-documented surface warming, the 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 ocean scientists from UC Santa Cruz in a article published on July 4 in the Journal of Geophysical Research: Oceans.
“Elephant seals collect data in places different from existing oceanographic platforms,” explained lead author Christopher Edwards, professor of ocean science at UC Santa Cruz. “This is an underutilized dataset that can tell us about important oceanographic processes and help biologists understand the ecology of northern elephant seals.”
For decades, elephant seal researchers at UCSC, led by co-author Daniel Costa, professor of ecology and evolutionary biology and director of UCSC’s Institute of Marine Science (IMS), used advanced tagging technology to track months-long migrations of elephant seals in the North Pacific Ocean.
“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 by seals to answer physical oceanographic questions in polar regions. temperate, such as the North Pacific Ocean,” Costa said. .
Sensors worn by the animals record depth, temperature and salinity as the animals repeatedly dive to great depths during migrations of around 6,000 miles across the North Pacific.
“Female elephant seals go out on the high seas where a ship may pass and only collect data once in a while, whereas we have elephant seals that collect data everywhere,” said Rachel Holser, first author and IMS research biologist. “It’s unusual to have this kind of data at the resolution we have in time and space, and at depths less than several hundred meters.”
Elephant seal data collected during the Blob revealed abnormally warm temperatures extending 1,000 meters (3,280 feet) below the surface. Subsurface warming persisted in 2017, well after surface temperatures returned to normal.
The Blob has been well-studied with respect to surface warming, which was atmospherically driven and waning by the end of 2015. The significant subsurface warming raises questions about the mechanisms underlying 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 exceptionally warm waters were transported northward from further south. What we don’t yet know is whether this northward transport is directly or indirectly related to surface warming. Changes at the surface may have transiently altered deeper currents to pull southerly waters northward.”
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 depend on fisheries and marine ecosystems. Understanding the physical processes involved in marine heatwaves will help scientists predict their onset and development and enable people to anticipate and cope with ecological and economic consequences.
“Like terrestrial heat waves, we have seen a dramatic increase in the frequency and magnitude of marine heat waves over the past decade,” Holser said. “The more information we can collect, the better off we will be in terms of understanding what is happening and dealing with the challenges. This study shows the value of collaborating with elephant seals to collect oceanographic data that complements other methods.”
In addition to Holser, Edwards and Costa, graduate ocean science 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 Aystem (CeNCOOS). With continued support from CeNCOOS, the Costa lab, in collaboration with Edwards and ocean science professor Raphael Kudela, continues to collect oceanographic data using elephant seals.