Meltwater Seep Patches: The Results

During my field seasons, I blog about the field work we are conducting and the samples we collect. What do we do with all of the information we gather? When we finish measuring everything we want on the soil, we analyze the data, make graphs that show our results, and draw conclusions based on what we find. Here is an example:

A few seasons ago, you read about one of our field projects in which we were sampling meltwater seep patches. You can read about the field project from my blog post back in December of 2009. Seep patches appear as random wet spots in the soil. They're strange shapes and come in all sorts of sizes.

Here's a photo of me standing next to one of the larger seep patches.

The water making those wet patches is from ice. When snow, glaciers, or permafrost melt, that water percolates down through the soil. The water then moves through the bottom of the soil active layer with gravity. Because the air is so dry, the water can get drawn to the surface (when soil conditions are just right!) through capillary action. That's what makes a seep patch!

Recently, some summers have had major heat-waves, which causes extra melt and the appearance of more seep patches than usual. We wanted to know how those seep patches were changing the soil and the microscopic organisms living there. Obviously they're wetter, and that extra water can be very important for soil biology in a desert. But, what else gets put into the patches with that water? Nutrients can be dissolved in that water, which would also help fertilize soil biology. But, a lot of salts can also be dissolved in that water, which makes those seep patches not only wet, but also very salty. Salty environments can be harmful to soil biology.

To find out what conditions were like for soil biology inside the seep patches, we samples soil from inside seep patches to find out how much water, nutrients, and salts  were in the patches. That would tell us how good of a habitat they are for soil biology. We dug soil pits inside the seep patches to collect soil. We also dug soil pits outside the seep patches to see how inside compared to outside.

This is one of the seep patches we sampled. You can see little bags of soil at each soil pit we dug. After we took the soil samples, we filled the pits back in with the soil to minimize the damage we cause.

We sampled six seep patches that year. Here's a photo I took from a helicopter showing the area we sampled. Everywhere red number represents a seep patch that we sampled.

The inset at the bottom right shows our sampling method. The dark gray area represents a seep patch. At each of the six seep patches, we dug two bits at the Center of the seep patch (abbreviated Ca and Cb), two at the Edge of the seep patch (Ea and Eb), and two Outside the seep patch (Oa and Ob).

We took the soil from those pits back to the lab, and measured nutrient content and salt content. We learned that soil from inside the patch is a lot saltier than soil outside the patch.The graph below is made by an analysis called "principle components analysis" (abbreviated PCA). It's a bit difficult to explain, but in simple terms, it shows how each soil sample is related to the others in terms of salt content. Each symbol represents an individual soil sample. The soils from Center locations are circles. Soils from the Edge are squares, and soils from the Outside locations are diamonds. (Each sample is also labeled by the patch number and whether it was the "a" or "b", shown in the map above.) 

This is the graph made by an analysis called "Principle components analysis". It shows how each soil sample is related to the others in term of salt content

You can see in the graph that the Center and Edge samples cluster more towards the left side of the graph. There are also more arrows pointing towards the left side of the graph. Those arrows represent the salts that were measured in the soils. So, samples on the left side of the graph have higher amounts of those salts. The samples from Outside (the diamonds) cluster more towards the right, which means they're lower in those salts (because they're away from the arrows). The Outside samples also spread out a bit more. That means dry soils outside the seep patches are less salty, but pretty variable in salt content. Seep patches tend to make soils more similar to each other in that they are all very salty.

How does the soil biology respond to that saltier, wetter environment? What's more important for biology: getting the much-needed water or having to deal with the harmful salts? We took soil from the "Center" locations and the "Outside" locations and measured the amount of CO2 being respired. (Remember, respiration produces CO2, and we can measure respiration to tell us about how active the soil biology are.) We learned that not all patches are the same! Sometimes, there's more activity inside the seep patch, sometimes there's more activity outside the seep patch, and sometimes there's no difference!

This bar graph shows the amount of respiration (measured as "carbon mineralization") from inside and outside each of the six seep patches. Dark bars are the center of the patch, and the white bars are from outside the patch. The taller the bar, the more CO2 was respired from the soil, meaning the soil biology are more active.

We noticed that when the patch increased respiration (like Patch #1), the patch was much wetter but only somewhat saltier. That means the positive influence of water could overpower the negative influence of salts. When the patch decreased respiration (like Patch #2, 3, and 5), the patch was somewhat wetter but much saltier. That means the negative influence of salts can overpower the positive influence of water. So, the influence that seep patches have on soil biology depends on the relative size of the increase in water and the increase in salts.

Therefore, we are able to conclude that these meltwater seep patches aren't all the same. They will make the soils wetter and saltier at those spots, but they vary a bit in how much wetter or how much saltier the soil becomes. Since the relative increases in water and salt can cause the biology to respond in different ways, that means we can't predict how exactly a new seep patch will influence the soil biology. Future heat-waves and future climate warming will create more seep patches, which will create a lot of variability in the soil habitat and soil biological activity.

The citation for the paper publishing these results is: 
Ball, B. A. and R. A. Virginia. 2012. Meltwater seep patches increase heterogeneity of soil geochemistry and therefore habitat suitability. Geoderma 189-190:652-660.
You can also read more details about it in a poster presenting the results by clicking this link.

The OTHER Antarctic LTER

Much of my research in Antarctica has been through the National Science Foundation's Long-Term Ecological Research project (abbreviated LTER). I've worked in the dry valleys through the McMurdo LTER (abbreviated MCM). There is another Antarctic LTER that works on the other side of the continent: Palmer LTER (abbreviated PAL).

While our research in McMurdo is largely terrestrial (focusing on the land and planet Earth), Palmer LTER's research is mostly marine and oceanographic (focusing on the ocean). Want to learn more about what they do there? Here's a trailer for a documentary about some of the research happening at Palmer:
http://antarcticquest.rutgers.edu/

Research at WAIS Divide

Here are some great videos that explain some research being done in Antarctica at WAIS Divide, one of the remote field camps at the point where the West Antarctic Ice Sheet (WAIS) divides from the East Antarctic Ice Sheet.

Ancient Ice: Studying ice in Antarctica tells us about the planet's climate history. Understanding what our climate has done in the past will help us predict what will happen in the future. This video tells you how scientists study the Earth's climate history from the ice at WAIS Divide.





Life on the Ice: Learn about the experience lived by the scientists at WAIS Divide and the reason they're living on the edge to do this research.





Modeling Our Future Climate: What happens with all of that data they collect at WAIS Divide? It gets used in making climate models to predict our planet's future. This video tells you what happens to the ice cores once they get back to the scientists' labs in the U.S.

Back in New Zealand

I spent the past two days in McMurdo waiting to fly home. Luckily I didn't have to spend those days in Mactown alone! Brendan and Lily came back into Mactown, as well. Brendan was fixing his infrared camera. This camera is different from a regular camera because it takes pictures of heat, in the form of infrared energy. Surfaces that are warmer emit more infrared energy and show up white. Cooler areas emitting less infrared energy are dark. We took a picture of my face with the camera. You can see that my nose and cheeks are colder than the rest of my face. That makes sense, since I'm in Antarctica! 

Don't I look creepy in infrared?!

Brendan of course won't be using his infrared camera on faces. He will be using this on the the terrain in the dry valleys to help find water tracks. The infrared camera will show where the ground is warmer than the surrounding areas. That will help us visualize where there is likely to be liquid water in a water track without being able to see the water itself from the surface.

Then, today, I finally made it back to New Zealand! After being delayed by two days, we were finally able to take off. The runway that we normally use for the Airbus and C-17's has been closed until February, because it was melting. (A storm had blown a lot of black soil onto the runway, which caused it to melt faster in the unseasonably warm temperatures.) Instead, we had to fly in a different type of airplane that has skis: a LC-130. However, the skiway for these planes was not designed for planes so heavy as a LC-130 carrying passengers and enough fuel to get all the way to Christchurch. They're normally used for travel within the continent of Antarctica, not for going to New Zealand. So, we had to wait a few days while they did work on the runway to make it ready. They finally did it! Here's our group of passengers loading onto the plane. Most of us had been trying for several days to leave, so we were nervous the entire time that they would cancel us. Once we finally were in the air, everyone on the plane applauded! Now we're in New Zealand, but our journey has come to another halt. There are no seats available on the airline to get us home to the U.S.! So now we are once again sitting and waiting. At least we're one big step closer to home!

End of the season close-out

I'm back at McMurdo Station (which we refer to as being back in "Mactown"). I'm preparing myself to head back to the U.S. after a very short field season!

One thing I have to do is prepare all of my soil samples for transport back to Arizona State University. All of the samples that were scooped in the field were sent back to McMurdo Station where they were kept in a freezer. Yesterday, I carefully packaged all of those samples for shipment. They were double-bagged for extra protection and packaged into Thermosafe boxes. The Thermosafes are essentially big, sturdy cardboard boxes lined with styrofoam. Every sample I took is in the two boxes shown on the left. They're sitting in the -10 Celcius walk-in freezer in the lab, ready for their trip home! At temperatures that cold, we are able to prevent the soils from changing, so when I work with them from home, they will be as similar to field conditions as possible.

I've also packed up some of my sampling gear to be shipped home, as well. The samples and gear won't be flying home with me. They'll be taking the slow route on the vessel. At the end of every season, there are a few boats that come to McMurdo Station to deliver or carry away supplies. An ice breaker has to come in to clear a path through the ice. Then, the fuel tanker, research vessels full of marine scientists, and supply vessel can dock. The supply vessel brings down food and other supplies for the following year, and leaves with all of our samples and shipments. It will deliver the samples to Port Hueneme, California, which will take a while! I won't see my samples until March or April.

I was supposed to fly back to New Zealand today, but the ice runway is melting again! My flight today was canceled, but hopefully I'll be able to begin the journey home tomorrow. Wish me luck!

Other fancy equipment

Aside from our measurements and samples that we take in the field, we have a few other pieces of equipment we use in the field to learn about the water tracks.

Soil temperature is being measured continuously in the water tracks. Soil temperature, of course, influences the melting of the water that creates the water tracks. To measure soil temperature, sensors are buried in the soil. They are attached to a data logger above ground, which records the temperature on a regular basis all year. A solar panel provides enough power to keep it running most of the year. Each year, we have to stop by and download the data. Here is Joe downloading the data from one of those loggers and replacing it with a fresh logger.

We've also been mapping the topography of the water tracks. The shape of the land surface influences how the water flows, so it's important to record each bump and turn in the land. To map the topography, we use a process called LIDAR. There is a special laser that shoots out an infrared beam. That infrared beam bounces off the land surface back to the source, and the speed at which the beam is returned will be influenced by the shape of the land surface. (Just think: The beam hitting a hill will come back sooner than the beam hitting the land farther away below it.) This way you can create a model of the surface in a computer using millions and millions of data points! Using this modern technology, we can determine the shape of the surface down to the scale of centimeters, and we can see how water is flowing through the soil in Antarctica and providing nutrients to the delicate ecosystems that exist here.

One new piece of equipment that we're using this year is an induction sounder. It measures how salty the soil is as you walk along! It does this by using a metal coil (inside the orange thing Joe is carrying), which creates a magnetic field. (That's called "inducing" a magnetic field, which is why it's called an induction sounder.) That magnetic field shoots into the soil, which bounces back as an electric field. Saltier soil bounces the electric field back differently than less salty soil, which is why we're able to measure how salty the soil is as we walk. The reason for measuring soil salinity is because water tracks tend to be very salty. Even if we can't see the water track on the surface, we can find them based on how salty the soil is.


Today was my last official day of field work. Tomorrow, I head back to McMurdo Station to finish up my work, pack my gear, and get ready to head back to the U.S. A short, but productive, field season!