Reconstructing Past Arctic Climates

What did Greenland's climate look like hundreds, or thousands, of years ago? And how has it changed over time? These are becoming increasingly important questions as we face a warming climate, which threatens to melt the Greenland ice sheet. The ice sheet is the Northern hemisphere's largest mass of ice, and melting would lead to changes in sea level and oceanic circulation. To understand how Greenland will respond to rising temperatures, reconstructing past change in the region is invaluable. Although humans climate records do not extend thousands of years into the past, Greenland's past climates are archived via chemical clues in lacustrine sediments--lake mud. My name is Hannah Dion-Kirschner, and I study Environmental Science (as well as music performance) here at NU. This summer I will be working to improve the way we interpret these chemical keys to the past. My hope is that, by clarifying what the chemistry can and can't tell us about climate, I'll help contribute to the picture researchers are working to paint of how the Arctic responds to changing climate. My research is advised by the Osburn and Axford labs and is generously supported by Northwestern's undergraduate research grant program.

When plans change

One lesson in research: you can never expect things to go according to plan.

 

 

 

 

 

 

 

Although last week was in many ways really exciting for me and my lab group, and involved lots of new instruments and new opportunities, we also hit a number of road bumps. The freeze dryer, an essential step in preparing sediment samples for extraction, spent three days forgetting how to vacuum down, and a number of sample vials were broken in the process. The gas chromatograph, the workhorse of lipid analysis, ran a leak overnight and needed two days’ worth of troubleshooting. An unexpected power fail in the building luckily didn’t damage our most important instruments, which have backup power, but it interrupted overnight tests and fried a computer. Every road bump cost me the ability to continue with my primary work that day.

The photos that I posted from this week capture the excitement of scientific research, of using new tools and finding surprises and making progress. It’s easiest to gloss over the tough parts, the times when you do the same thing over and over with no success or spend precious hours babysitting a broken machine. For one thing, this stuff is not nearly as fun to talk about. But road bumps and long days are the reality of research in most settings: there will be progress and excitement, but they’ll always be accompanied by troubleshooting or frustration or mind-numbing lab methods.

It can be hard to keep perspective in the moment, but I do try to remind myself to take the bad with the good. Was this week difficult? Yes, but given the circumstances, I was lucky to make as much progress as I did. Did things go according to plan? No, but I am lucky to have two wonderful, bright, inspiring advisors and a number of fantastic coworkers who are here to help. Broken vials are all part of the process.

Core sampling week, in pictures

As compared to usual, lots happened this week! Here’s a summary of what’s been happening, told in pictures.

 

Testing out our brand-new core splitter on an empty core tube.

 

My very own freshly split core!

 

The new core scanner took super-high-definition photos of my core so that changes in color and texture were easier to see.

 

Our first chance to test out the new core sampling tools we made out of sheet metal.

 

Making my way down the core! The larger sample vials will be used for lipid extractions (my main project, and what I talk about all the time), and the smaller tubes will be used to take carbon to nitrogen ratios (which can help us understand whether more terrestrial or more aquatic plants are represented).

 

This section has shells!!

 

Shell fragments held up on a spatula.

 

These samples are ready to freeze dry!

Commence Phase Two

Tomorrow is the big day…the day we’ve all been waiting for…the day we split the sediment core!

If you’ve read your way through my blog, you’ll know that right now, the core looks like this:


The core was sampled from the bottom of Little Sugarloaf Lake in the summer of 2015, and ever since it was shipped from Greenland to the Axford lab on campus, it’s lived in its coring tube in a huge walk-in freezer. Looking through the plastic, there’s very little we can learn about the core. Basically, we know that the dark brown color indicates a lot of organic material, and that’s about it.

But tomorrow, we’ll split the cylindrical core in half (to give us two half-moon shaped slices of sediment), allowing us to see what’s inside and look at it in two ways. First, we’ll give it a good old-fashioned visual inspection. Are there any places where the color changes? What about the texture? Are the changes stark, or gradual? We’ll also look to find anything we could send out for radiocarbon dating (especially animals’ shells) to get some boundaries on the age of the core.

The more exciting way of looking at the core will be to use the Axford lab’s brand new very shiny Geotek core scanner (installed in the lab today!!). It looks a lot like this…

…and, for scale, I don’t think it would fit in my bedroom! This magnificent metal giant can do just about any analysis anyone would think about doing on an intact core. It takes incredible high definition photos, converts colors to numerical data to more precisely identify color changes, scans for the abundances of numerous elements, and tests for magnetism, among multiple other functions. Gathering all this information will only take a couple hours at most, and it’ll help me get a fuller picture of what the core contains. I’ll be keeping in mind what I learn when I start to explore the biomarkers that are preserved in the sediment, and try to interpret what they mean.

Splitting and scanning the core will start the ramp up top what I’m calling Phase Two (does that give it a top-secret very-important-science vibe?). Phase One, which is starting to wrap up, was the process of extracting, chemically separating, and analyzing the plant samples. I’m very close to having a complete set of data about the plants’ lipid chain lengths and their isotope ratios, so in not too long I’ll be able to analyze and interpret these data, looking for how different groups of plants may have different chemical signatures. But Phase Two is where I’ll get the opportunity to look into the past, traveling back in time as I extract sediment from deeper and deeper in the core (i.e., deeper and deeper layers of mud from the bottom of Little Sugarloaf Lake). Stay tuned for when the time travel begins!

A little rest for the wicked

 

I’m spending this week out in Washington state, taking a break from the lab to visit my dad and his family over the 4th. It’s always rejuvenating to get out and breathe some fresh air—I spend so much time thinking about the environment and earth processes, but I too rarely make the time to put on some sturdy shoes and interact with the outdoors face-to-face.

For most of my life I’ve loved spending time outside, walking along Lake Michigan or learning the bird calls in my neighborhood. But having a new perspective from earth and environmental science has, if anything, increased my wonder for the world around me. Staying on Puget Sound, I can hunt for sea stars in the tide pools and wonder which of their neighbors compete with them for dinner.

For me, one of the greatest rewards of studying earth science has been how it’s enriched my life even outside of the lab. What I’ve learned has given me the chance to take in a scene of natural beauty and realize that the picture is so much more than what I can see in a human moment. It took billions of years of astronomical, geological, chemical, and evolutionary changes to form a shoreline where I’ll spend an afternoon. It’s hard to even wrap my mind around!

This week I plan to soak up as much of the outdoors as I can, and then it’s back to the lab. But the week is allowing me to reconnect with one of the fundamental reasons I love the work I do—all the time I am thinking and learning about the processes that make up our beautiful miraculously habitable planet.

Ready for analysis!

Last Monday I began the journey to analyze my plant samples on the IRMS (isotope ratio mass spectrometer). This beast of a machine is really a scientific marvel: using what is essentially a fancy lightbulb filament and a giant magnet, it sort out the lighter isotopes from the heavier ones and counts the relative abundances of each.

The information you can get from IRMS analysis is invaluable, but the price to pay is time—with appropriate quality control, the IRMS lab manager and I can only run about eight samples a day. I have 48 samples to run now, and later this summer, I’ll have another 70 or so. So, for the last week I’ve been in and out of the IRMS lab, which is just down the hall from the research lab where I usually spend my day. Aside from troubleshooting, once the lab manager sets up the instrument it pretty much runs itself, but it takes a watchful eye to make sure all is going well. The rest of the work involved is mostly data management (excel spreadsheet stuff).

The exciting part will be the process of sorting out the isotopic differences from plant to plant and looking for patterns. Is there a specific plant species or family that tends to be isotopically heavier or isotopically lighter? Is there a noticeable difference between plants that grew further from the lake compared to plants that grew on the shoreline? Are the patterns similar to or different from other findings from the region? Answering these questions will help me interpret what my sediment core tells about past climate.

I can’t quite answer these types of questions yet—the data fresh off the IRMS still has to be processed mathematically before I can draw any conclusions. But I’m excited to be one step closer!

From the field to the vial

The project that I’m doing this summer is actually a continuation of work I’ve done since last September, and it builds off of fieldwork that a Ph.D. student in my lab completed in the summers of 2015 and 2016. Here’s the rundown of everything that’s happened so far:

A sediment core, a bit over half a meter long, was taken from the bottom of Little Sugarloaf Lake in southwest Greenland.

 

 

 

 

 

Many plant samples were collected from offshore, alongside a handful of aquatic plants and plankton growing in the lake.

 

 

 

 

 

 

 

 

 

The plants and sediment core were shipped from Greenland to our lab on the Evanston campus, frozen, and stored.

 

 

 

 

 

 

 

 

 

Since September, I’ve freeze-dried and solvent-extracted the plants, developed a method for filtering and chemically separating the extracted compounds, and prepared the extracts for analysis. 

 

 

 

 

 

 

 

 

Step by step, I’ve been working to prepare the samples for analysis (via gas chromatography/mass spectrometryGC-MSand isotope ratio mass spectrometryIRMS). Only after those measurements are complete will I be able to reach any conclusions about Little Sugarloaf Lake’s paleoenvironment.

How do you measure past climates, anyway?

It can be tricky to grasp the mechanics of paleoclimate research. In part, that’s because it usually involves taking something we can measure, and using it as a proxy for something we can’t. For example, maybe we’d like to know what temperatures were typical in the Midwest a million years ago, or how the Greenland Ice Sheet has changed in the last ten thousand years. We don’t have direct records of temperature, humidity, or other climate parameters that go back past human observations, so we use leftover clues to piece together a picture.

For example, in my research I am taking samples from a sediment core and measuring two parameters: the chain lengths, and the carbon and hydrogen isotope ratios, of the leaf wax biomarkers preserved in the sediment. But the reason I’m making these measurements is to use them as a proxy for the things we actually want to know.

The chain lengths of the leaf waxes—AKA the number of carbon atoms in a row—vary based on the type of plant they came from. So, by knowing what chain lengths are preserved in a sediment core, I can picture what plants were growing around the lake when the sediment was deposited.

 

The isotope ratios—AKA the ratio of 13C to 12C and of 3H to 2H—vary based on a number of factors. Isotope ratios of leaf waxes are affected by the type of plant that made the waxes, where that plant got its water, the temperature while the plant was growing, and a few other factors. So, by measuring the isotope ratios of the leaf waxes preserved in the core, I can understand patterns of temperature and precipitation from when the plants grew.

That’s the general idea of my project: I’m analyzing what is there (the leaf waxes that have been preserved) to get the information that isn’t.

 

First start!

This summer I will be living in Evanston, spending my days in Dr. Maggie Osburn’s isotope geobiology lab and Dr. Yarrow Axford’s paleolimnology lab. What motivates me to spend eight-hour days in a room with minimal windows (apart from grant funding…)? I am looking to answer questions about how Greenland’s climate has changed over the past several thousand years—questions that are increasingly relevant as we see rapid melting of the Greenland Ice Sheet, the largest ice mass in the Northern hemisphere. In the process of seeking understanding of Greenland’s paleoclimate (its climate in the past), my day-to-day work will be, mostly, banal. However, I’m excited to gradually assemble a better picture of past climate parameters (it’s hard to know yet, but I might be able to learn about how things like temperature, humidity, or the source of precipitation have shifted for Greenland over thousands of years), and maybe even share with a reader or two.