Ed. note: Over the past few years we’ve been following the adventures of oceanographer and mathematician, David Holland (New York University), and his wife Denise, logistical right-hand and project documentarian during their Greenlandic adventures. We caught up with them via email during their recent transit between Abu Dhabi, where they’ve spearheaded NYU’s Center for Global Sea Level Change, and Ilulissat, where they’re headed for their latest fieldwork tagging ringed seals with oceanographic instruments.
Polar Field Services (PFS): What are you doing in the United Arab Emirates? You're a long ways away from any glaciers!
Denise Holland: For the past three years we've been running the Center for Global Sea Level Change (CSLC) at New York University's Abu Dhabi campus in the United Arab Emirates (UAE). It may not appear obvious, but when it comes to sea-level change, cities such as Abu Dhabi and New York are extremely vulnerable. We've been putting together a team of scientists who are looking at some of the issues that can cause sea level to change. We also hold yearly workshops gathering top experts in specific areas that need to be studied if we are to better understand all the components involved in changes to sea level.
PFS: Describe your current study that involves seal populations. Which species do you focus on and why? How will you use the data?
DH: We tag mostly ringed seals. They stay close to the coast and they swim and dive inside fjords, such as the Ilulissat Ice Fjord in West Greenland and the Sermilik Fjord in East Greenland, exactly places where we want data. You can read more about our tagging efforts here.
The Arctic Observing Network (AON) of the National Science Foundation has funded us for five years to carry out this project, and in August 2014 we will tag six more seals. It’s turning out to be a fabulous data set that the seals are acquiring. Once collected, we make it available to the science community over the web.
PFS: What are the seals doing?
Holland: Ringed seals help Holland create a more robust model of ocean circulation and fjord conditions throughout the year.
PFS: Why are seals best for this job?
DH: The seals are a natural choice for those areas that we the scientists cannot easily get to due to harsh and dangerous conditions such as heavy sea ice, or large icebergs. Particularly valuable in their data-gathering skills, the seals provide year-round data, giving us insight into the conditions in the fjords during the long polar night. The seals are also able to penetrate much further into the fjord than we can and they send us many more data points in space and time as they dive and surface than we could dream to collect ourselves. We receive data on our rooftop receiving station at NYU for almost a year from any given seal, and then the seal will molt and the tag drops off.
PFS: What's the methodology for tagging a seal? Where do the tags go? How many do you plan to tag? When is the optimal time for tagging seals? How do you choose THE seal? Have you named them?
DH: The method is straightforward and exerts the least amount of stress on the animal as possible. We have gone through extensive approval procedures through the NYU animal welfare committee (UAWC) to ensure our procedures are fully in line with the proper treatment of these marine mammals. The seal is placed in a sort of 'hammock', and then the sensor is glued to its back with a small amount of epoxy glue. It takes about 15 minutes for the glue to set, and then the seal is released. The sensor stays in place for just about a year, and when the seal molts, the device falls off.
We aim to tag 6 seals per year if we are lucky and it is done usually in late summer. We don't get to choose which seal we tag, but I do name them all. Dr. Asvid-Rosing sends us photos and so far we've had Binky, Earl and Flo that I can recall.
PFS: Please elaborate on the sensors - what do they measure, how big are they, how are they affixed to the tag?
DH: The sensor is very small - it fits in the palm of your hand and has a small ARGOS antenna attached to it. They are attached to the back neck of the seal with a small amount of epoxy glue. When the seal dives, the sensor records temperature, salinity and depth. When it surfaces, the sensor contacts a satellite relaying that data which is then sent to a rooftop receiving station on the top of an NYU building. The sensors have batteries that last a year and are lost when the animal molts. You can see a picture of it here.
PFS: What have you learned about seals that surprised you?
DH: How deep they dive! Normally we see the seals diving to about a depth of 200 meters. But we've seen a couple recently that go as deep as 600 meters. It's great for us because it makes our data set even more varied!
PFS: What have you learned about fjord circulation? What else do you hope to learn over the next few years?
DH: We've learned from expendable current probes that there is actually a jet or current of water at the very bottom of the fjord that rushes inwards towards the calving front. This is interesting because waters at the surface can be seen visually to flow outwards, and now we know what the deep waters are doing. The next few years will hopefully be fruitful because all our instruments (sea floor moorings, CTD casts from boat, seal-tag CTD data, and expendable probe drops) are coming together to produce a really interesting data set that will give us a gauge of what the ocean waters around the fjord are doing. In turn this will help us to make better computer simulations modeling global sea-level change.
PFS: Why is studying fjord circulation so important?
DH: Two reasons really. The glacier is retreating more and more each year and ultimately this is going to impact global sea rise. We need to know what is going on with the warm and cold waters circulating inside the fjord, we need to gather that data so that we can make our computer models better at projecting what might happen should more glacial ice fall into the ocean.
Second, the Ilulissat fjord is an excellent place to try to understand fjord circulation and if we can nail that, we can make steps forward in projecting the glaciers of Antarctica which is where the biggest impact on global sea level rise will likely be felt, should that ice go into the ocean.
PFS: Do you and David have some animal-handling background we should know given about? How does an ocean scientist get to tag seals? Are you bringing on board others who possess these skills?
DH: David and I leave the work of the actual tagging to Dr. Aqqalu Asvid-Rosing, our colleague in Nuuk who is the biologist and seal-handling expert at the Greenland Department of Natural Resources. Next year we will accompany him to a camp to document this work and hopefully take some students with us so that they can understand and experience what it's like to gather data in the field.
PFS: Subsistence hunting still plays a big role in people's lives in western Greenland - do you worry about your seals being hunted? Have you learned anything from the local human population about changing habits of seals possibly related to climate change?
DH: We try not to worry about losing a seal to the hunt, but of course that can happen. We always hope that if a seal is taken, that the hunter would return our tag to us and we would be able to refurbish it and use it on another seal, so the data set can continue.
PFS: Will these data be integrated into existing models or visualization packages?
DH: Yes most definitely. We are working on that as we speak! You can see the pathways the seals take on this website. —Marcy Davis