Satellite-tagged Seals And Underwater Robots Uncover Ocean Secrets
Although outer space is often considered “the final frontier”, there is still so much of our oceans we have not been able to explore and study. Understanding ocean currents is one of these unexplored areas, due to the depth and seasonality of these currents. Determining how ocean currents are changing in response to an increasingly warming climate is a key question for climate scientists. New methods are being adopted to determine exactly how ocean currents are being affected by climate change.
More Than Just Some Blubber
Elephant seals (genus Mirounga) are often perceived as large, lazy mounds of blubber, lounging on beaches and starting the occasional loud argument with their neighbors. However, these seals have become invaluable data capturers in the Southern Ocean. These seals have joined an ever-increasing population of tagged marine creatures to assist scientists to gather data on our oceans. Elephant seals spend 9 to 10 months of the year at sea, and more than 90 percent of that time is spent underwater, allowing them plenty of time to collect data over a large area. They average 80 dives a day, staying underwater for up to two hours at a time. They also dive down to more than 1 mile underwater, making them the deepest divers of all seals.
Tags are glued to the seals’ heads in accordance with established ethical standards when they come onshore to breed or molt. The tags are removed again after the seal spends a period of time at sea. Tags also drop off when the seals return to land to molt and shed their dead skin.
Elephant seals are being tagged by devices designed by the Sea Mammal Research Unit at the University of St. Andrews in Scotland. These tags are able to collect information on ocean conductivity, temperature, and depth, known as CTD Profiles. When the tagged seals break the surface of the water, the collected data is related to a global satellite system known as Argos, which is then decoded by computers and analyzed by biologists, oceanographers and meteorologists.
The tagging of the seals on the Edwards Islands forms part of the iSTAR project, a multidisciplinary project that aims to understand ice loss in West Antarctica – particularly at Pine Island Glacier, which flows into the Amundsen Sea. The iSTAR project used to be limited to collecting data only during the summer months, as harsh winter conditions posed a threat to the technology used by the research team. The elephant seals are however able to go where research instruments cannot, allowing for year-round data collection. Other tagging programs include the French research program known as Observing System – Mammals as Samplers of Ocean Environment (SO-MEMO), where seals from the Kerguelen Islands are tagged.
In total, the seals collected more than 12 000 CTD profiles, and revealed a path towards the Pine Island ice shelf where warmer water current flows, which speeds up glacial melting.
Swarming Robots And Ocean Currents
Researchers at the Scripps Institution of Oceanography have developed a novel way to study currents, which does not require the use of seals. Autonomous miniature robots have been designed that can work together as a swarm and explore our oceans in a new way.
The Mini-Autonomous Underwater Explorers (M-AUEs) have been able to record the 3D movements of the ocean currents and internal waves – slow moving waves within the ocean that form between water layers of differing density – a feat traditionally used instruments cannot achieve. Each M-AUE is a robot about the size and weight of a grapefruit, and has an antenna on one end and measurement instrumentation on the other. They are equipped with temperature and other sensors to measure the surrounding ocean conditions, and they are able to “swim” up and down to maintain a constant depth by adjusting their buoyancy.
These robots were deployed to test a theory – aspects of plankton’s ecology and their ability to form large patches of plankton are due to ocean currents pushing and pulling plankton together and apart. This theory was based on ocean physics, water density and internal wave dynamics (waves under the surface of the ocean). Sixteen of the robots were deployed and programmed to stay 10 meters deep in the ocean off the coast of Torrey Pines, California. The results of the study were nearly identical to the original plankton theory – the M-AUE formed a tightly packed patch in the warm waters of internal wave troughs, but dispersed over the internal wave crests. This helped researchers confirm that free-floating plankton can use ocean dynamics – such as internal waves – to congregate into swarms to fulfill their fundamental life needs.
What Is The Data Used For?
National weather services are able to use data collected by tagged elephant seals to enhance their ocean condition forecasts, which informs navies, air forces, shipping companies as well as offshore oil and gas companies.
Global warming is changing important ocean currents, which in turn affect Antarctic melt rates, therefore data collected from these remote polar seas is valuable. The Southern Ocean is among the most important areas when it comes to influencing the global circulation of ocean waters. Changes in global ocean currents could have significant effects on the global climate, as a large portion of the sun’s heat is stored in the ocean.
The collected data also assists scientists to learn more about the structure of the Southern Ocean, and will improve their predictions for how ocean circulations and sea ice conditions in the Southern Hemisphere may change.
The use of the swarm of robots goes beyond understanding ocean currents, and there is hope that with slightly different instrumentation, the robots can be used when an oil spill occurs to help track the harmful toxins. If deployed with microphones the swarm can also listen to whales and dolphins to further research in bio-acoustics. The robots might also in the future be able to study the movement of larvae between marine protected areas, as well as monitor harmful red tide blooms. Understanding how currents and internal waves affect plankton transport has many other implications, including for commercial fisheries of lobsters, oysters and crabs.