|Home away from home.|
Huge piles of rocks and dirt sit in front of Leverett Glacier as if a massive bulldozer had pushed them there and then left. In front of these piles, the landscape might as well be the Moon’s surface. No trees, grasses or even weeds take root here, and so there is nothing but mud, sand, rocks and ice. The only sign of life we saw was the occasional fox and geese tracks. As we hiked, we discovered several small ponds and a stream feeding back to the main river. There were also several springs of groundwater coming up through the rocks. One was obviously different. It was trickling out of the top of a 30-foot mound of ice and was blood red. To figure out what it was, we deployed our arsenal of water chemistry tools.
The first thing we checked was the electrical conductivity of the water. We do this to measure the amount of ions in the water. Ions are dissolved free elements or small combinations of elements floating freely through the water. Ions are either negatively or positively charged. For example, if you add table salt to a glass of water, you are adding sodium chloride salt (NaCl) that dissolves to Na+ and Cl-. Sodium has a +1 charge while chloride has a -1 charge and so no matter how much table salt you add to water, the total charge remains neutral but the conductivity of the water will increase. In fact, one of the most important laws of water chemistry is that all waters have an equal amount of negative and positive ions. Basically, our electrical conductivity meter measures the amount of salt dissolved in the water. For our purposes, a low conductivity measurement likely indicates recent snowmelt, whereas a high reading means the water is likely older and has traveled a long distance. Older water has spent more time weathering rocks and so contains more dissolved ions. We are most interested in water that has spent time under the glacier as it might tell us about the glacier itself. We assume that this "basal water" (water from the glacier's base) will have a significantly higher conductivity than recent snowmelt. The blood red ice spring had exceptionally high conductivity so we knew its water source was distant.
|Chemistry with a view.|
After taking a pH reading, we collected water to analyze back at our university labs. We fill multiple bottles of various sizes, each for a specific purpose. Some of these samples are filtered before they are collected while others are taken raw. How each bottle is filled is also important. For dissolved gas samples we fill and cap the bottle underwater to ensure there are no bubbles to lose gas through. In contrast, a head space is left at the top of each dissolved metal bottle as those bottles will be frozen and we don’t want them to burst. The things we can’t measure in the field include oxygen and deuterium isotopes, dissolved organic carbon, fatty lipids, anions, cations, metals, and alkalinity. Each of these parameters requires special equipment, trained technicians, and each analysis needs to be completed within a specified amount of time. The data will be used to build models, fuel interpretations, give talks, and publish papers.
At each site, I take as many notes as time allows. Each entry is dated and the time is recorded, and each stop is given a unique name (something like GRE-11-009). I also use a hand held global positioning unit (GPS) to record each location. In addition to recording all the parameters measured on site, I make sketches of the glacier and possible water flow paths. I also write down any interpretations made at each site. Phil Bennet, my master’s degree advisor would always tell me, “Interpret as you go!” and so I do. In the old days scientists would spend a great deal of time crafting their field notes, making detailed drawings and writing extensive interpretations. Today, I think some of this art is lost though most college level field courses grade heavily on a student’s field notes.
Finally, we take pictures of each field site and use notebooks, pencils and each other for scale. These pictures will wind up being projected on large screens at meetings when we present our findings and ideally, the pictures won’t show us with dumb looks on our faces.
|Red water. Why? Photo by Matt Charette|
Long ago, before Leverett Glacier existed, this area of Greenland was covered in trees and grasses. Then, over a long period of time, Leverett Glacier formed off of the Greenland Ice Sheet and bulldozed over all the vegetation covering it under layers and layers of ice. This ancient forest is still here except that now it is in the form of simple dissolved organic carbon. Today this carbon is food for an array of bacteria that have been slowly munching away on it ever since it was buried by the glacier. When these bugs eat carbon they need to dispose of the carbon’s electrons and so they give the electrons to oxygen. This is exactly what we do every time we take a breath. Under the glacier with no new source of oxygen, these oxygen-breathing bugs quickly used all the oxygen and died out. This made way for a new breed of bugs. These new bugs were breathing iron, pulling it out of the rocks to dispose of the electrons taken from carbon. When bacteria do this, the iron no longer wants to form minerals and becomes dissolved in the water. Today, the water flowing under Leverett Glacier is full of the used iron bugs have breathed, and when this iron reaches the surface at our blood red springs, it meets again with oxygen and forms a microcrystalline red mineral, rust, over everything the water touches. If there is one truth about life on Earth it is that if life can exist, it will. Even if it is under a glacier without any oxygen.
Jemma Wadham, the principle investigator of our team, is a professor of physical geography in the Bristol Glaciology Center at the University of Bristol, and Matt Charette, my advisor, is a scientist in the Department of Marine Chemistry and Geochemistry at the Woods Hole Oceanographic Institution.