“Why do you think a scientist would rather take a sediment core from the bottom of Lake Itasca in winter than in summer?”
I regularly ask students, staff, and faculty this question during my introduction talks in the Biome Center. People sometimes catch on to the answer if they like ice fishing, but usually, I hear silence. Then, I give them a hint by telling them that during “hard water” season at Itasca, air temps can drop below -40 degrees Fahrenheit and ice thickness can exceed 24 inches. It feels weird to walk on the top of the lake, particularly when it groans and heaves, but ice that thick can support a fully-loaded trailer truck (40 tons).
My “hard water” hint usually causes movement in the crowd — stirring, giggling, gasping — but some eyes will light up. The answer to the sediment core question is that it is easier to control a sediment coring device when you are standing on ice instead of bobbing around in a boat. It allows retrieval of a vertical, small-diameter cylinder of sedimentary material that has its layers of history stacked up neatly, without disruption. This is what Dr. Betsy Swanner would call precision coring. The sediment inside the metal-shafted corer should look like a stack of dimes instead of a pile of coins, each dime representing a period of history.
Dr. Swanner has been coming annually from Iowa State University to Itasca in the dead of winter, with a team of scientists funded by a National Science Foundation CAREER grant. Precision coring is similar to archaeologists who use stratigraphy to date a dinosaur bone if they know in which layer of sediment it was embedded. If you can date the sediments, you can date the age of embedded things. This also works for pollen — this is how we know specifically when Itasca’s vegetation changed in the past 10,000 years. It also works for smaller things, even molecules. Researchers, like Dr. Swanner, and a University of Minnesota Duluth-based effort (collaborative with the U.S. Geological Survey) called the Midwest Varves Project, use sophisticated coring tools in winter to lock everything in place. They retrieve cores that look like the perfect stack of dimes. We can learn a lot about our future by understanding (and overlaying) the sequence of biogeochemical and ecological events in our past.
Is winter “hard water” science work easy? No. It presents obvious risks and requires planning. But Itasca has the know-how and gear (pulk sleds, quilted “clam” tents, a side-by-side vehicle with tank treads, augers, etc.) to make this happen, and sediments are not the only reason people sample Itasca’s lakes during this season. In addition to Swanner’s group, other researchers find their way north to follow the biological action under the ice. Some aquatic organisms are just as active in winter as they are in summer, and with a “lid” on top of a mostly-liquid lake system, researchers are finding that these understudied dynamics need research attention. Dr. Jim Cotner visits from Saint Paul to sample Lake Itasca, Elk Lake, and others as part of a Legislative Citizen Commission on Minnesota Resources-funded project focused on the role of microbes emitting carbon dioxide and methane in lakes. The Minnesota Department of Natural Resources also visits for water quality monitoring and coring, as well as sampling algae, and our own Victoria Simons and Associate Director Emily Schilling track water quality and macroinvertebrates during winter, respectively.
“Hard water” science is cool (literally). If you think of Itasca as having a summer high season, remember that for some, the best time to head north is when it is the quietest. –Jonathan Schilling