Areas of the ocean in and around ice shelves in Antarctica are inaccessible to scientists looking to gather data about changes in currents, salinity, and temperature. Researchers have found a unique way to enhance remotely sensed and field-collected data about ocean conditions in these areas by equipping seals with sensors.
There are various species of seals that hunt for food in the Southern Ocean and Arctic Ocean. These seals will dive to great depths underneath the frozen sea ice and ice shelves.
Weddell seal foraging behavior
Weddell seals, for example, are known to dive to depths of up to 600 meters (approximately 2,000 feet) in search of food from the ocean floor. This includes prawns, crustaceans, fish, octopus, and squid.
Weddell seals take advantage of fast ice, which is ice attached to the shoreline, by creating breathing holes. These holes in the sea ice allow the seals to dive deep beneath the ice to hunt for food. This ice also provides a stable platform for resting and shelter from predators.
By attaching animal sensors to the heads of seals, scientists can collect ocean current as well as chlorophyll fluorometers. Chlorophyll fluorometers measure the amount of phytoplankton in the ocean waters.
Seals are tagged during the mating season as they are more accessible when they come ashore. The tags are attached with glue and remain on the seal until the molting season as the shedding of fur dislodges the tag.
Tracking seal behavior in the oceans sub-mesoscale fronts
The data collected during the one-year period offers researchers insights into not only ocean conditions but also how those conditions are affecting seal behavior. Some seals, like elephant seals, hunt in ocean areas known as sub-mesoscale fronts. These fronts are where vertical movement of ocean water stirs up nutrients and becomes a feeding ground for these seals.
For over twenty years, scientists have been tagging seals on the Kerguelen Islands in the Antarctic to study their behavior as part of a French program known as SO-MEMO (Observing System – Mammals as Samplers of the Ocean Environment). In 2014, they started using a new sensor that records every dive, resulting in a highly detailed oceanographic data set.
Case study: understanding the Antarctic Circumpolar Current
In one study, Jet Propulsion Laboratory scientist, Lia Siegelman, and her team of researchers tagged a female southern elephant seal to better understand how the ocean transports heat between its upper and lower layers. The data is being used to augment our understanding of the Antarctic Circumpolar Current, a major ocean current that connects the Atlantic, Pacific, and Indian Oceans. This current plays a significant role in heat exchange among these oceans. However, its turbulent nature and the formation of eddies (vortices of water) make it difficult to study.
A tagged elephant seal equipped with a specialized sensor collected data over a three-month, 3,520 miles (5,665 kilometers) through the waters of the Antarctic Circumpolar Current. The seal’s dives, a total of 6,942, reached depths of 550 to 1,090 yards daily, provided continuous data on vertical heat movement within the ocean.
Researchers were able to glean more accurate information about the movement of heat within this current. Contrary to previous models suggesting heat moves from the surface to the ocean interior, the data collected from this elephant seal indicated that these fronts carry heat from the interior back to the surface.
Ocean insights from seal tagging research
The insights gained from seal-tagging studies not only improve researcher’s knowledge of marine ecosystems but also refine climate models by revealing the complexities of heat transport within ocean currents. Tagging seals has allowed for the collection of detailed data on currents, salinity, temperature, and phytoplankton levels as these marine mammals dive far below the surface of the Antarctic oceans.
References
Dove, L. (2024, July 25). Tagging seals with sensors helps scientists track ocean currents and a changing climate. The Conversation.
Siegelman, L., O’toole, M., Flexas, M., Rivière, P., & Klein, P. (2019). Submesoscale ocean fronts act as biological hotspot for southern elephant seal. Scientific reports, 9(1), 5588. DOI: 10.1038/s41598-019-42117-w
Siegelman, L., Klein, P., Rivière, P., Thompson, A. F., Torres, H. S., Flexas, M., & Menemenlis, D. (2020). Enhanced upward heat transport at deep submesoscale ocean fronts. Nature Geoscience, 13(1), 50-55.
Smith, E. (2019, May 2). Data with flippers? Studying the ocean from a seal’s point of view. NASA Science.
