When I met Woods Hole Oceanographic Institution coastal hydrologist Julia Guimond and post-doc Elisa Boles in a Chatham salt marsh in late April, not everything was going according to plan.
"The winter’s really brutal on all of our sensors. It’s just like, they’re not meant for sub-zero conditions," Guimond said as a loud "beep" indicated a system coming to life. "It’s connecting! We have data!"
They were at Cockle Cove to retrieve data from sensors along the marsh channel.
"We're downloading data that's been out here for almost a year now to see what's happening in the marsh in terms of the water flow, the soil temperatures, the chemistry," Guimond explained.
Their work is part of a three-year National Science Foundation project to learn more about how salt marshes function in the winter.
"The idea is that a lot of what we know about marshes comes from the summer when people want to do field work when it's warmer, when there's a lot more green vegetation," she said. "And that leaves these winter periods pretty understudied, comparatively."
This is one of four salt marsh sites in the study; the other three are in Maine. Each site contains monitoring wells, surface water loggers and creek instrumentation to help answer a number of questions that Guimond outlined:
"Do the marshes freeze? How cold do they get? How deep do they freeze? How does that change how water moves through the system? How does that change the chemistry? With this sort of overarching goal of understanding how it impacts how much carbon is being exported to the coastal ocean."
Post-doc Elisa Boles has been analyzing the data from all four sites for the past year, in search of answers. She’s anxious to see how this past harsh winter on the Cape factors in.
"I'm really excited to see the data from this site," Boles said. "Being the southernmost site, it's in some ways less extreme than the ones further north, but we saw, I mean, a big nor'easter event this winter, and just being out here earlier this year, a lot of freezing – this whole creek was frozen over for quite a good amount of time."
Ask any high school earth science student, and chances are they can tell you all about the carbon cycle. Oceans and forests are carbon sinks. They absorb more carbon than they release into the atmosphere. Carbon sources – from people and animals breathing and dying, to volcanoes and burning fossil fuels – introduce carbon into the atmosphere in the form of carbon dioxide.
But scientists like Guimond and Boles are still working out some of the finer details.
"So these marsh systems are what we call blue carbon habitats," said Guimond. "So they store more carbon than they emit to the atmosphere. But within that knowledge, there's not a great understanding of what happens to the carbon in the winter."
Guimond said studying how marshes function in the winter will help scientists understand their overall potential for carbon sequestration.
"Part of what we're doing is collecting a bunch of data in the winter to understand sort of the movement of carbon during this period that hasn't been thought about and then incorporating that into carbon budgets," she said.
Guimond said, as water at and below the surface flows through the marsh, it interacts with living and dead plant matter and mineral deposits on its way to the ocean.
"And that water is very carbon rich," Guimond said. "Once it hits the tidal channel it can go out to the coastal ocean which is thought to be another sort of carbon sink in this cycle."
But, she says, they’re still working out the details.
"And so that is the area that there's a lot of uncertainty," she said. "You can imagine, you know, trying to track water that you can't see and then monitoring the discharge and then estimating what's going out to the ocean."
Guimond and Boles are collaborating with scientists at Old Dominion University and the United States Geological Survey Woods Hole Center to help unlock this particular carbon cycle mystery.
