Taphonomy and organic matter in bone

The bone bed found on a beach at Bahia Thetis

All that history in my last post leads to the reason for this travel in the first place: the collection of historic samples. Up until this current trip, I've looked at samples of fur seals and sea lions form archaeological sites. The majority of these are from the earliest known site with animal remains, Tunel, named after the Estancia Tunel not far from Ushuaia. I also have some samples that were collected in other sites along the Beagle Channel, Peninsula Mitre, and Isla de los Estados that extend my data set both geographically and temporally to the end of the marine hunting and gathering lifestyle employed by the indigenous people of Tierra del Fuego. With this new collection, I'll be able to see if the massive changes that happened culturally with the arrival of industrial marine exploitation also had an impact ecologically. Significant changes have been observed in ecosystems around the world, including in California with the near elimination of sea otters. The extent of ecological impacts of industrial exploitation in comparison to subsistence exploitation of marine animals in Tierra del Fuego remains a mystery...until I run these samples in a few weeks!

Sea lion and whale bone in an archaeological site

But the understanding of the process of what happens to a body after death (the field of taphonomy) is a pretty important for interpreting stable isotopic results from my bone samples. Much of this field was pioneered by Behrensmeyer in multidecadal studies in Kenya with observations of the breakdown of bodies, separation into different parts, and ultimately into individual bones that break apart themselves. There are many different things that influence this process, including biological: scavengers, which can rip apart the body, limbs and chew on bones; microbes, which can feast on soft tissues, fat and oils of the body and the bones, and produce byproducts such as acids that chew away at bone mineral. Physical processes can include transport, for example, a bone traveling down a stream, bumping and grinding against rocks; damage from sunlight, which bleaches the surface and wears down the mineral, leading to cracking and flaking in the bone surface; and chemical weathering, the dissolution of bone mineral from acids.

One of the reasons I've been able to analyze samples from here is because the climate and conditions here in Tierra del Fuego generally buffer or slow down these taphonomic processes. Bones from the even the earliest sites have nearly the amount of organic matter in them that you would find in modern samples. This is because they've been buried almost immediately after being processed by humans. As a sub-antarctic climate, its generally very cold here, like throwing your steak into a refrigerator, it'll last longer than sitting out in the open on the Kenyan savannah, In addition, they've been buried in piles of shells. These shells are largely calcium carbonate, which counteracts acids that could be introduced by rain, trees, and soil bacteria.

Bones from partially articulated sea lions 

In contrast, some of the bones I have were buried in sand, allowing more of these chemical processes to reduce the organic matter in my bones, noticeably reducing the amount of organic matter. The samples we recovered from the seal greasery at Bahia Thetis are in an even worse state. After the carcasses were thrown into the bay, biological agents surely ate away at the soft tissue, leaving behind bones. Tidal action moved the bones/carcasses along the floor of the bay, before they were washed up onto the beaches during extreme storm events. Despite these destructive forces, a large number of identifiable bones can be found up on the beaches. However, bones on the surface tend not to last very long at all, and almost all the bones we found were in an advanced state of deterioration despite being only 70 years old. It may end up being difficult to extract the organic matter from these, but we have a large volume to extract from, so even if a small fraction is there, we'll get it.

We did find a fully articulated skeleton buried in the beach, with just a piece of its skull sticking out on the surface. The buried bones were in a much better state that the buried elements. I imagine this carcass was buried before it could be disarticulated by external forces. It stands to reason that there are probably many more articulated skeletons and bones either buried in the beaches or still in the bay where they were originally deposited. Likewise, there are surely many seals and sea lions buried in shell middens which have yet to be excavated, of which there are thousands known in Tierra del Fuego.

Return from Bahia Thetis

Anchor from a shipwreck in Peninsula Mitre

After twelve days and much work, I've had a few days to rest and reflect on our mission to collect and sample sea lion, fur seals, kelp, water, birds, fish and shellfish from Bahia Thetis, one of the most remote parts of the island of Tierra del Fuego. And it was a absolute success: In total, we collected 101 left sea lion and fur seal jaws (the majority being adult female sea lions), around ~50 femurs, and 10 skin and fur samples from the 1940s factory site. In addition, we made three 50x50cm excavations of shell middens, containing numerous more bones, stone and glass artifacts and tools including the first harpoon point ever found in the peninsula.

I learned a lot about this part of the world, and Peninsula Mitre in particular, which I think is important for understanding the context of the work I'm doing here. Peninsula Mitre is different in a number of ways from the land surrounding the Beagle Channel. The Beagle Channel is characterized by steep mountains and sharp glacial features, drumlins, canyons and overall rocky with forest. The peninsula, and much of the Atlantic coast of Tierra del Fuego, has softer rolling hills, less forest, dominated by peat bogs, and shallow coastline with  a slowly descending continental slope that extends for hundreds of kilometers. This shallow coastline proved treacherous for navigating, resulting in many shipwrecks, many of which were scavenged to build ranch buildings.

A more recent shipwreck from the 1980s

Geographic differences also played out ethnographically between indigenous groups. The Yamana occupied the Beagle Channel and southern archipelago, the Selk'nam in the interior and northern parts of Tierra del Fuego, the Alakuf on the western archipelago in Chile and the Haush in Peninsula Mitre. It is important to note that boundaries were not absolute for these groups, language and culture mixed and created gradients. The Haush and Selk'nam commonly incorporated more terrestrial animals into their diets, especially Guanaco, but they also hunted sea lions and seals like the more marine oriented Yamana.

Bahia Policarpo, site of the Policarpo family sheep ranching operation

When European settlers arrived, such as the Anglican missionary Thomas Bridges, they first set up in the Beagle Channel. However, it didn't take long for others to settle in other parts of Tierra del Fuego. Estancia Policarpo was established in the late 1800s by a Chilean family southeastern Atlantic coast of Tierra del Fuego, extending from the easternmost part of the Island at Cabo San Diego to its northern border with Estancia Maria Luisa some 50 km away. Like the ranch at Harberton, Estancia Policarpo exploited sheep for their wool. Estancia Policarpo operated until the mid 20th century, succumbing to falling wool prices from technological innovations in synthetic fabrics and wool that was cheaper to produce elsewhere. A caretaker maintained the what was left of the ranch until the 1980s, but most of the ranch buildings fell into disrepair throughout the late 20th century. Today the estancia is operated as a cattle ranch.

Blubber boiling vats

One way to subsidize the cost of the operation of the failing ranch was the exploitation of pinnipeds. In the 1940s, over one hundred Chileans, experienced in seal in sea lion hunting more common on the western coast of South America, set up a seal oil production facility in Bahia Thetis. The company would raid the multiple sea lion colonies that existed along the shores of Estancia Policarpo, killing over 30,000 seals and sea lions over a decade. The pinnipeds would be killed at the site of their colonies, loaded onto boats and taken to Bahia Thetis, were they were skinned, stripped of blubber and thrown into the bay. The blubber was then boiled in large vats, producing oil, much in the same way as whale blubber. In 1952, sealing was banned and the operation abandoned, leaving behind ruins of both the seal greasery and the ranch.

Bahia Thetis, site of the 1940s seal greasery facilities

That's I've got for today, stay tuned for more!

Estancia Harberton

Estancia Harberton, home of missionary Thomas Bridges and family in 1886. Imported brick by brick from England to Tierra del Fuego. Located east of Ushuaia by 50 km or so.

Yesterday I joined the archaeologist crew to collect some of my own samples and help carry bags of rocks. They were very heavy and my arms are quite tired still. But it was quite a productive day trip! We managed to carry 145 rocks over several kilometers, which will eventually help my fellow graduate student Carmen determine the source of lithic tools that were used by the Yamana. For my own sampling, I took some samples of kelp and some water samples, one of each from a bay exposed to a river mouth and one from the bay facing the Estancia Harberton (pictured above) which does not have a direct freshwater input. I doubt there will be significant differences between the two areas but good to measure extra just in case. The waters of the Beagle Channel are known to be exceptionally fresh compared to ocean waters from other parts of the world, due to the high amount of precipitation and freshwater inputs (from snowmelt and glaciers), but I will find this out and verify this claim personally!

Loading a large bag of rocks to be carried back to the truck.

The purpose of sampling water here is two fold. First I'm interested in differences in the waters of the Beagle Channel and the southern Atlantic/Argentine Sea, specifically to see what differences in water chemistry there might be, especially when it comes to nutrients and trace elements. Different nutrient loads can have an impact on the productivity of food webs, which would in turn have effects on species high in the food chain, like top predators such as fur seals, sea lions, and cetaceans (whales and dolphins). Trace elemental analysis can help me not only differentiate bodies of water, but serve as an independent method that would potentially verify where my fur seals and sea lions spend their time. Trace elements are incorporated into your tissues just like stable isotopes are and can (hopefully) be used a tracer.

A figure showing the interaction of different bodies of water in South America (from  Acha, E. M., et al. Marine fronts at the continental shelves of austral South America: Physical and ecological processes. J. Mar. Syst. 44, 83–105 (2004).) 

The measurement of kelp will serve a similar purpose. Giant kelp, Macrocystis pyrifera, grows around the world, from the coasts of Alaska, New Zealand, Japan, all the way down to Tierra del Fuego, It's a very successful species, one of the fasting growing on the planet (a meter a day in the right conditions) and forms the basis of many highly productive food webs around the world. Constraining the variation between southern Atlantic kelp and Beagle Channel kelp will give me an understanding of what to expect when I compare the stable isotopic values between giant kelp, kelp based fish and ultimately fur seals and sea lions. Fur seals and sea lions might be moving back and forth from open ocean to kelp ecosystems or changing their degree of residency in kelp ecosystems over time so it's important to understand what the kelp ecosystem looks like versus the open ocean.

Soon I leave for the Atlantic Coast, Peninsula Mitre and Bahia Thetis, site of the abandoned sealing operation that ran from 1946 to 1952. Bahia Thetis was formerly known as the Bay of Good Success, I hope it lives up to its name!

Wild horses seen while sampling near Estancia Harberton

Ushuaia 2017

The recreational airport club overlooking Ushuaia Bay and downtown Ushuaia

 After a bit of a hiatus I return to describe what may be my last trip to Tierra del Fuego. Since I've last updated this blog, quite a bit has happened:

• I've measured more samples (including fish!)
• I've passed my qualifying exam (hooray!)
• I've moved universities from Environmental Systems at UC Merced to Earth Sciences at UC Riverside (possibly invalidating my qualifying exam)
• and, finally, I've returned to Ushuaia for (maybe) the last time

But what opportunity awaits while I'm here! I've got some big plans. Next week I'll be traveling to Harberton Ranch to collect water and kelp samples, which eventually should help me do some forensics on where my fur seals, sea lions, fish and other members of the marine food web spent their time (open ocean or kelp forest? Beagle Channel, Atlantic, or Southern Ocean?) At the same time I'll be helping a fellow grad student who has been collecting rocks in a radial fashion around an archaeological site to identify their availability for making tools. 

In about a week and a half, I'll be leaving for Peninsula Mitre, the easternmost point of the Island of Tierra del Fuego. There are no roads to this place, and my colleagues normally reach this place by helicopter. However, we'll be taking the scenic route by horse which will take 3-4 days each way. Very few scientists use horses in their fieldwork these days, so it'll be harkening back to the days of old adventuring. Some French tourists may be accompanying us for the ride, so it'll surely be an interesting experience. I'll be journaling the experience and sharing with you all when I return!

The primary objective of traveling to this place is to collect fur seal and sea lion remains from industrial seal hunting that occurred during the 20th century. So far I've previously looked at fur seal and sea lion remains produced at indigenous archaeological sites, dating from roughly 6000 years ago to the 1700s. I expect to see significant changes in the diets of these animals as human influences changed from subsistence hunting to wholesale slaughter, but I'll find out when we return with the samples to the lab. I'll also be collecting more water and kelp samples, while my archaeologist colleagues will be digging some test pits to compare cultural differences between ancient sites on the peninsula versus sites to the west in the Beagle Channel. 

An inset historic map from James Cook's expedition, one of the first European explorers to document the area. Note that north is pointing to the right on this map and, that the Beagle Channel has not yet been identified. We'll be riding to the far western edge to the Strait of Marie (Detroit de le Maire). I've analyzed some samples from the area labeled "Baye de Valentin" and "Terre des Etats" already (Valentine's Bay, or Bahia Valentin and Staaten Island, or Isla de los Estados today).

Finally, I've spent a bit of time thinking about my PhD journey over the past several weeks and thought I'd share a bit about the process. I came in starting this degree with an idea for my PhD thesis fairly well formed within the first few months of starting at Merced. Those original ideas have shifted as logistics and preliminary data came into view. The questions I originally set out to ask changed and become more focused since the broader questions turned out to be more difficult to answer than expected. This realization required me to think about different types of methods to be used, the learning of new tools to help answer those questions and the number, and all the while scale and scope of the project increased. But it's this process that I think is probably the core of what a PhD is about: to come up with good questions and find a way to answer them, given limited time and resources. Of course, this sort of thing takes some planning so I made a timeline to illustrate it. Just in case you might considering a PhD, maybe you will find this helpful!

La Campaña: En la Casa

A late afternoon view toward the Southwest from Moat Bay. Isla Picton with Isla Navarino in the background, the opening of the Beagle Channel to the Pacific in the west (right).

Buenas tardes folks,

Now that its been a few weeks and I've settled back into the routine here in Ushuaia, it seems like a good idea to describe in some detail what life was like, what I learned and how I'm moving forward as a result of this fieldwork.

You should know by now I'm interested in studying food webs and ecology using remains of hunted fur seals and sea lions from archaeological sites. While it's possible I could've just gone and asked my colleagues to just send bones to me in the US, that would've been no fun and I'd be missing out on understand how and why these bones showed up in the first place, both in the context of the culture of the peoples who hunted them and in the natural climate and taphonomic processes. Over the month I was in the field, being outside everyday, I not only learned what it was like to live as an Argentine in Tierra del Fuego, but also what weather the Yamana may faced (which was not very much like California).

Rain over the Beagle Channel, looking Southwest. Moat Bay extends to the left, while our ranch and nearby lake are on the right. The dirt highway, Ruta J, continues for about 20km to the east before ending.

From Ushuaia, which is near the middle of the Beagle Channel, we packed up some trucks with nine people and our gear for the month; three professors, three graduate students (including me), two undergraduates working on their senior theses, and a lab assistant. After we piled in we drove 3-4 hours east of Ushuaia, past Estancia Harberton, to Moat Bay. Moat bay is located at opening of the Beagle Channel to the Atlantic Ocean, which provides a stunning view of Islands to the south in Chilean territory; Isla Nuevo, Lennox, Picton, and Navarino.

A rainbow over our ranch house, during our daily afternoon water refill routine.

We arrived at a remote ranch, and luckily for us we had a guest house to stay in. Despite having a kitchen, bathroom with a flushing toilet, and generator for power, there was no running water as the pump had broke. As a result, we carried buckets of water from the nearby lake and drank water from the rain that collected in a barrel off the roof. The lake water had a bit of an algal taste, and was preferred by some of our members to the rain barrel water, which had a distinct "wooden barrel aged" taste, even though the barrel was plastic.

Our fully stocked kitchen at the beginning of the campaign.

Generally, we'd wake up around 8 most mornings, after tough days or celebrations we might sleep until 9. We'd have a light breakfast of coffee and tea, bread and jam or butter, or if lucky facturas (basically donuts) that were brought by visitors or our members who had left and come back. When we ran out of bread, it was a sad day since we were left with crackers and maybe some cookies. But usually that was a short lived experience because someone would show up at the ranch with a fresh resupply of bread and pastries, and maybe even wine or beer!

Lunches were also fairly light, we'd generally eat a mix of bread, cheese, crackers, and dried sausage or salami; some fruits and vegetables, like salad, carrots and apples, followed by cookies and chocolate. Later on we needed to use our leftover pasta, so we'd cook some at our field sites. We generally also snacked on crackers and cookies while working, but careful not to drop any food in the field pits. Lunch is a later than what I'm used to, usually around 1, but sometimes later. We'd spend about an hour on break. And, of course, we wouldn't have survived without Mate, the shared Argentinian tea-like beverage which helps keep you working. We generally drank mate continuously throughout the mornings and afternoons. 

When we returned back to the ranch house and were exhausted, we would go get more water from the lake, maybe take a bath or at least wash our hands and face, and make some more coffee and mate. On more difficult days we'd have fernet and coke, the favorite drink of Cordoba (a province in Argentina) and the Porteños (the residents of Buenos Aires) from which almost everyone in our group shares culturally. 

A fine chicken dish in a big wok!

Dinner in Argentina is late. You might start cooking at 9, and start eating at 10 or later. We'd break open boxes of cheap wine (easier to transport in the field, and easily disposable containers) and have different kinds of meals. Sometimes it was a meat or fish stew (giso), sometimes pasta (with ñoquies, a potato derived noodle), pizza or the famous Asado (steak BBQ). In any case, dinner was always much appreciated and we ate well. Afterward, if we had enough energy, we'd sit to play a game of cards or dice, usually jodete or generala. After that we'd be truly exhausted and hit the sack, meaning a pile of sleeping bags laid out on the floor of the living room in front of the warm pot bellied stove.

Until next time, here's some highlights from the house area:

Starting up the truck in the morning...easier said than done

And starting up the generator in the evening

Practicing the recorder, taking a walk during some downtime while the weather was good. You can see the ranch house in the background. 

Sorting out a knot problem on the living room floor

The hummocky road leading to the beach, facing south from the house.

Another view of that (double) rainbow to the east, showing the length of Moat Bay

Vuelva a Ushuaia

Ushuaia Bay upon landing

Hello once again!

I figure it's a good time to start writing again since it's been several months since I last updated the blog. Quite a bit has happened in the intervening months. I've ran the South American fur seal samples I collected and they've provided some puzzling results. I measured the carbon and nitrogen stable isotope from the bits of processed seal bits (collagen if you recall from my previous posts). Stable isotopic values of various elements will show you varying characteristics of the world based on how they cycle through biogeochemical systems (and an animal's biochemistry). Carbon and nitrogen are particularly useful for measuring ecological characteristics, like finding out one's trophic level (if you are a vegan, vegetarian, or a meat eater.)

When interpreting the results of these isotopic values, there isn't much of a basis for comparison if you have nothing to compare against. In classical studies, you need to know what the values are at the base of the food chain as well as potential dietary components of your study animal. Even without this info, there are some inferences we can make. There are some noticeable differences between male and female fur seals from 6400 BP, but age did not seem to have a large effect. Most of the fur seals seem to cluster together toward a lighter carbon isotopic ratio.

Pulled from the latest version of my proposal

Based on literature values of fur seal dietary components from modern collections, I can see if diet corrected values of my ancient seals fall within expected dietary boundaries of modern fur seals. Essentially, you connect the dots of the most extreme dietary values, creating a diet polygon, and should see your animal's diet corrected values fall within the polygon. From there you can create an isotopic mixing model to see which dietary components contribute the most to the animals diet. For example, I should be able to see if the seals are eating mostly squid or mostly fish.

Alas, this is not what happened when I compared modern diet to ancient animal. There has clearly been some kind of shift over time as none of my seals fell within the diet polygon. Modern dietary components are much lighter in carbon than the more recent seals. Something has changed in the carbon. One might argue "Hey wait a sec, what about the Suess effect?"

The Suess effect is a change in the ratio of the atmospheric concentrations of heavy isotopes of carbon (¹³C and ¹⁴C) by the admixture of large amounts of fossil-fuel derived CO₂, which is depleted in ¹³CO₂ and contains no ¹⁴CO₂.

However, I had already applied a Suess affect correction based on literature values, and not including this correction would have actually made some of the individuals fall within the diet polygon. In any case, I have more work to do grappling with this issue and doing some ANOVAs.

Analysis of variance (ANOVA) is a collection of statistical models used to analyze the differences among group means and their associated procedures (such as "variation" among and between groups), developed by statistician and evolutionary biologist Ronald Fisher.

Ok enough Wikipedia citations. My guess at the moment is that there's been a shift in the base of the food web over the years and seals are probably eating roughly the same things that were 6400 years ago. I won't be able to find out whether that's true or not until I find some way to measure the base of the food web, either by looking directly at animals near the base of the food web (preserved in the archaeological record) or by looking doing compound specific amino acid stable isotope analysis of seals over time. The idea is that certain amino acids do not change in as they move up the food web as they undergo minimal chemical reactions (aka source amino acids). I just got to try out this technique before leaving Merced, and while it's certainly time intensive I plan to do a lot more of it when I return.

Also I will be leaving for fieldwork (ie. doing Indiana Jones style excavation of sites) in two days at a place called Moat Bay for almost a month. I'll be taking lots of pictures, but I won't be able to post them until I return. Expect some lots of photos in the future!

On a boat

I've fallen behind on my posting since a lot has happened in the last week! I left Ushuaia this morning and am now vacationing in Buenos Aires, so I can relax and reflect a bit. Last week I was lucky enough to go on a boat trip to see some of my fur seal and sea lion friends in live form, which was certainly different from seeing them from the perspective of half destroyed skulls. The sea lions down south were similar in many ways to the ones you find on coastal California, but one thing that was different and immediately obvious is that they appear shorter and fatter. They vocalized quite a bit, just like the sea lions to the north, but the way they vocalized was completely different. They sounded mostly like old men yelling, unlike the barking kind of noises you hear to the north.

The Blue Eyed cormorant with many Sea lions (Otaria flavescens). 

Sea lions in the Beagle Channel. The large sea lion in the foreground is an alpha male, guarding his harem

Selfie shot

We traveled a bit further up the channel, circling a mostly abandoned lighthouse except for a few stray cormorants. This was the spot most popular with the tourists, everyone had to get their selfie with the lighthouse (including me). Something that struck me as unique was how calm and tranquil the waters were in the Beagle Channel, surely nice for both the explorers who used the channel to avoid the rough seas of the Southern Ocean and easy fishing and sealing for the Yamana in their little canoes. Even so there are a large number of recorded shipwrecks around this area. As I learned in one of the museums, insurance fraud led to the demise of many of these.

We circled around and stopped by another island on the way back to Ushuaia harbor. This one was much quieter than the one with the sea lions, but had a number of relatively quiet Fur seals on it (Arcophoca australis). There were also a good number rafting in the water, holding there fins up out of the water. This is a common behavior in Otariids, a thermoregulatory technique (something humans are having trouble with) that allow them to either cool down or absorb heat, depending on the conditions.

Rafters on the right!

This concludes my posting for tonight I think, I'll continue typing some business later!