#11 - Salmon Valley

Salmon Valley: Hangin' out in the Royal Society Range, Seals and stuff!

Near the end of our seal sampling journey we made trips to the Royal Society valleys nearby and a trip to Marble/Gneiss point along the coast. All the seals sampled in my video included in the last email were from Salmon Valley. Since there isn't a whole lot to talk about about Salmon Valley (other than that we found no salmon,) I'll talk about the seal carcass weathering process and how we think it relates to age and environment. 

 

Left - A view of the ridge separating Garwood and Salmon Valleys from the air. The Ross Ice Sheet, Brown Peninsula, Black Island and White Island lie in the background.  Right - Salmon Valley Glacier

 

Left - Looking at the light snow left behind from a localized snow storm. Snow dropped in regional storms sublimates (instead of snow melting and then evaporating, ice goes straight from a solid phase to gas) and creates smaller localized storms inside individual valleys, often making weather very different between valleys that are even right next to each other. 

 

Left - Close to Salmon Glacier. The older, more experienced folk (Brenda and Paul) decided to skirt the edge of the glacier looking for seals, nobly putting themselves in dangers way instead of us kids. According to US Antarctic Program official Risk Assessment guidelines, this was rather risky. Many seals were found in the ice just beneath the glacier. Note how ice had recently broken off the face to the left of Paul and Brenda.  

Seal Carcass Weathering: How old are these things, anyway?

We developed the carcass weathering scale adapted from a paper that touches on the subject (Barwick & Balham 1967), and compiled by Laura Niven and I in the lab after some thought that this system could give us a good way of measuring seals in the field. Since we don't have the budget to measure the age of every sample we collected, we will be trying to use this weathering system to figure out a general age of the animals. After we fix radiocarbon ages to the mummies, we'll be able to extrapolate general ages to the state of the carcasses. Something to note is that this scale really only applies to mummies on the surface, buried mummies will undergo a different weathering process that is controlled by chemical microbial destruction, rather than the sun and wind, or mechanical action from glaciers grinding mummies. 

A - Complete. Fresh. Undamaged from wind erosion, no dessication. We didn't find really any seals that fit this definition; however, in Taylor Valley an unfortunate Leopard wandered in and died in December. While we couldn't and didn't want to sample such a fresh seal (we do not have a permit to collect anything that died after 1972 due to the Marine Mammal Protection Act), That seal would fall under that category.

B - Complete. Slightly weathered. Partial erosion of hair on exposed surfaces, cracks in skin exposing deeper tissues or bones in the flippers or cranium. We did find many seals in this condition. The seal below, for example, was found with most of its fur intact, however the wind was beginning to have an effect on the carcass. This seal was also close enough to the coast to have its eyes scavenged by Skuas. 

C-  Incomplete. Extensive erosion and exposure of bones of upward part of body (skull, ribs, limbs). Skeleton undamaged but soft tissues eroding between bony elements. The majority of seal mummies we found happened to be C or D. At this point mummies are often heavily wind abraded on one side with skin and fur preserved on the other as the exposed part breaks down more readily in the sun and wind.

D- Incomplete. Extensive erosion with regional destruction of bone and tissues. Vertebral column completely exposed and 40-50% tissue is destroyed. As you can see in the mummy below, the head is missing. This is a common occurrence in the world of vertebrate paleontology as heads are attached by relatively weak neck vertebrae and break off as soon as the soft tissue around it decays. 

E-  Very incomplete. > 50% of carcass is eroded. Vertebral column and cranium incomplete; limbs and rib cage becoming remnants. Difficult or impossible to identify species, sex, size. In the specimen below, you can see that the seal is a unrecognizable mess of tissue and bone. The best we can hope for is that an identifiable bone is present so we can try to figure out what species it is. While it might seem that a sample from a nearly destroyed carcass is useless, we can still use bone and tissue samples for DNA, radiocarbon, and stable isotope data, which will tell us the species, age, and diet of the animal. 

F- Fragments or isolated bones. We found many isolated bones, many of which are potentially very old and will be useful for identifying the long term population dynamics of different seal species over the past several thousand years. 

We have a similar system for measuring bone weathering, since isolated bones will also go through a similar weathering process where certain parts of bones will break apart faster than others. And that wraps it up for this email, thanks for reading!