The 2013-2015 marine heatwave, known as The North Pacific Blob, was the most significant marine heatwave on record. Now, data collected with the help of elephant seals is giving scientists a deeper understanding of the event.
Much of the information from The Blob event was collected from relatively small, shallow areas. However, elephant seals allowed for a more thorough investigation.
“Female elephant seals go out into the open ocean where a ship might go through and collect data only once in awhile, whereas we have elephant seals out there collecting data all over the place,” explained first author Rachel Holser. “It’s unusual to have this kind of data at the resolution we have in both time and space, and at depths below several hundred meters.”
Researchers have been collecting data from elephant seal migrations in the North Pacific Ocean for decades. They use advanced sensors to collect depth, temperature, and salinity data.
“The elephant seals collect data in different locations than existing oceanographic platforms,” said study senior author Christopher Edwards, a professor of ocean sciences at UC Santa Cruz. “This is an underutilized dataset that can inform us about important oceanographic processes, as well as helping biologists understand the ecology of northern elephant seals.”
The sensors revealed that The Blob created abnormally warm temperatures as far as 1,000 meters (3,280 feet) beneath the surface. The temperatures didn’t return to normal until 2017, two years after the incident occurred. Experts are still unsure precisely what caused the subsurface temperature to rise dramatically.
“Those temperature anomalies are so deep it’s unlikely it would be due to mixing from the surface,” Edwards said. “One reasonable mechanism is that the unusually warm waters were transported northward from further south. What we don’t know yet is whether that northward transport is directly or indirectly related to the surface warming. Changes at the surface could have altered deeper currents transiently to draw southern waters to the north.”
Sub-surface warming has enormous impacts on ocean ecology and human economics. The authors hope the information in this study will help us better protect the oceans and prepare for the future.
“The more information we can collect, the better off we’ll be in terms of understanding what’s happening and facing the challenges. This study shows the value of collaborating with elephant seals to collect oceanographic data that is complementary to other methods,” said Holser.
The study is published in the Journal of Geophysical Research: Oceans.