text and images by Linda Welzenbach
Science advances in many ways, with enhancements in methods and instruments that improve the quality of the data we collect and enable the exploration of new frontiers. Yet despite all we know about our ocean, it arguably remains one of Earth’s greatest remaining frontiers. Add in icebergs, sea ice, and bad weather, gathering information from this frontier around Antarctica can be a real challenge! Yet many of the fundamental science requirements of THOR and the other teams that comprise the International Thwaites Glacier Collaboration depend on the collection of a wide range of data from the ocean that surrounds and interacts with the ice shelves around Antarctica. It turns out one of science’s most effective partners in this effort to collect data comes from some of the “locals”: the seals of the Antarctic oceans.
Beyond the obvious complications of dodging icebergs and plowing through sea ice, the ocean itself is incredibly complex; it is not just a body of bitterly cold, incredibly beautiful, deep blue water. The ocean is actually layered like a cake, where each water layer from top to bottom can have its own biota (from microscopic plants to megafauna such as whales), temperature, salinity, and currents (e.g. pathways) around the continent. Pathways are probably some of the most difficult types of information to track, and trying to understand how the water moves around the ice shelves is critical to understanding what is causing thinning of the ice shelf at Thwaites Glacier. That’s where the seals offer their help as rather unique partners in science.
Why seals? Because they can go places we can’t. They are amazing divers that also travel amazing distances. Since 2014, 14 Antarctic seal partners with their unique science payloads have logged more than 6,700 water temperature and salinity profiles within the Amundsen sea. This information tells us about the layer of water that causes melting and thinning of the ice shelf in front of Thwaites (and Pine Island Glacier) called circumpolar deep water.
Circumpolar deep water, or CDW, is derived from a mixture of all the world’s oceans. It originates from the outer ring of water known as Antarctic Circumpolar Current (ACC). The CDW moves from the deeper ACC up onto the shallower continental shelf (but still at depths of more than 300 meters!) carrying saltier water with a temperature of 1-2o C (which is above freezing and therefore melts ice). The CDW is several degrees warmer than the overlying colder surface water because that layer is supplied with fresh water from melting ice. We know this because scientists use devices to measure a temperature and salinity profile from the ocean surface to depths of thousands of meters. This device has the rather unglamorous name CTD, which stands for Conductivity (salinity) and Temperature with Depth.
Joee Patterson (see The J Team) led me into the warm and humid Baltic room, a large space with a noisy heater fan and floors damp from residual sea water. Next to the big black and yellow checkered door which opens directly to the ocean, the six-foot-tall CTD sits tethered to a strong steel cable that will not only carry this nearly 1,000-pound instrument 3,350 meters into the Amundsen Sea, but includes an information umbilical cord that receives data and allows scientists to also send commands. The MT’s are in charge of its setup, modification, and deployment. That day, the CTD had some interesting modifications – passengers, if you will – attached to the bottom ring of the frame. These were micro CTD’s, future riders on our seal science partners. They would be activated to gather the same data as their larger cousin and use the better resolved data set of the host CTD to standardize the temperature, pressure, and salinity data that the micro-versions gathered.
These portable dataloggers, or ‘tags’, were devised and constructed by Dr. Lars Boehme; he is a physical oceanographer at the University of St. Andrews, and works within the Sea Mammals Research Unit, Marine Alliance for Science and Technology Scotland, Scottish Oceans Institute. Over the last decade, he has tagged over 150 seals, to include nearly all the species from around the world. The programming in each tag can be modified to gather a variety of data types, from studies in seal behavior to information about their ocean environments by location. Lars’ knowledge and admiration of seals and their abilities is obvious in the reverence and enthusiasm he conveys when he describes their role in his oceanographic research and exploration.
As for his partners in Antarctica, he has been permitted to tag as many as 16 individuals from among the population of Elephant and Weddell seals who live near the Amundsen sea. The seals that are selected meet a very important qualification: they must have already shed their previous year’s fur. That ensures that the tag Lars and his team glue to the seal’s head is secure. After a year, the seal will molt again, shedding both the previous year’s fur and the tag. Using these partners has also led him to study their biology and ecology. The tag apparently has no impact on their behavior or normal seal activities. And it’s those activities that are critical to providing data about the water in places where humans cannot go.
Elephant seals are the champions of diving, logging marathon dives of up to 1,500 meters (5,000 feet) for up to two hours, although they typically dive 300-600 meters (up to 2,000 feet) for 20 minutes at a time, with 2-3 minute rests between each dive. Weddell seals tend to be shallower divers, only going to 600 meters for up to an hour. The water depths in the Amundsen sea near Thwaites Glacier range from less than 300 meters at the continent to 1,600 meters in the deepest glacial melt water channels, which scientists suspect may funnel CDW right to the base of the ice shelf. This makes the seals perfect natural explorers of the Antarctic shelf.
The day we visited an island among Schaefer group, Lars and his team were just finishing tagging a Weddell seal. After checking over the male Elephant seal, they determined that the big male was still molting and moved on to the other Weddell. After pulling on her fur, Lars deemed her a good candidate.
Seals are large and potentially dangerous animals, so they need to be sedated. This is where Lars’ skill and experience are important for the safety of the humans and the seals. From there, tagging is pretty straightforward. Using epoxy, they put a small amount on the bottom of the tag to make a sticky template on the seal’s head. More is applied to the template and then smoothed around like cake icing. The tag is held in place until the epoxy is set. The final step is to apply a bead around the edges, much like we do when we put caulk around our bath tubs. This keeps water from getting under the tag when they dive, which would lift it off the seal’s head.
At the end, Lars sits with the seal, putting himself between it and the water to ensure that the seal recovers fully before allowing her to return to the sea. Suddenly, as we are watching Lars quietly and reverently watch over his sleepy charge, the first seal swims by. Lars then says excitedly “Quick! Take pictures of the seal in the water!” In all his years of work, he has always focused on the animals and had apparently not taken any pictures of a tagged seal swimming.
The second Weddell seal was the fourth seal tagged since the start of the cruise. To date, the four seals have made 1,537 dives and collected 105 CDT profiles. Each time a seal surfaces, the data that they have acquired is transmitted via satellite to Lars and his team. They can even get a rough approximation of the location of the seal if more than one satellite picks up the signal. This is already more than we have collected from the ship, and the seals’ measurements are likely to far outnumber any additional ship-based measurements we can achieve by the end of the cruise.
The hope is that these partners for science, who live in the Amundsen Sea, will dive around and below the sea ice at Thwaites where we can’t go, bearing witness over the next year to the temperature and salinity of the CDW, reporting the data they collect to help us determine the path and extent of this warm water below the glacier.