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Fall 2005




Extended Family

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Raising His Game

Never Mind the Weather?

If You Can Make it There

Peg Riley Wants a New Drug

A Capitol Guy

What They've Learned


Mysteries in the Muck
Probing Lower Mystic Lake in Medford for clues to climates past

LOWER MYSTIC LAKE, WHICH STRADDLES Medford and Arlington, is fed by the Aberjona River from the north and is connected to the Atlantic Ocean by the Mystic River to the south. During a drought in the mid-1960s, noxious gases started bubbling up from the bottom, causing paint to peel on the surrounding houses. Not good for homeowners or, for that matter, anyone who breathes oxygen. The Metropolitan District Commission promptly built the Amelia Earhart Dam downstream to prevent such a thing from happening again.

The special characteristics of Lower Mystic Lake that make it a challenge for municipal planners also make it an ideal place to go looking for clues about climate events in the distant past. And that’s what graduate student Mark Besonen has been doing for about 10 years.
Lower Mystic Lake is what is known as a meromictic lake. This means that the lower portion never circulates, creating a dead zone, devoid of life and at the same time trapping gases and allowing the sediment to build up in annual layers without being disturbed. Another characteristic of this body of water is that it is near enough to the Atlantic Ocean that tidal waters sometimes flow into it, but far enough that this only happens when the surf is especially high, such as during hurricanes.

Ah ha, say people like Besonen when they hear of such lakes. By examining the sedimentary layers, they can determine with a high degree of accuracy when hurricanes occurred in the days before written history. In fact, core samples that Besonen is basing his doctoral thesis on are yielding a record going back 1,000 years. The fact that there are written records documenting storm surges for the last 400 or so of those years means he can look at the part of the record that corresponds to known events, thereby extracting rich meaning from the earlier portions.

But there is one hitch. The meromictic characteristics of the lake, while making the formation of sedimentary layers possible, also means that when you probe the bottom, theretofore-undisturbed gases start to churn, disrupting the upper layers. And without the upper layers, it is hard to establish a starting point from which to count backward.

Besonen has found a solution. Instead of sending down a conventional coring device, he has lowered a hollow wedge into the soft muck at the bottom of the lake. The wedge contained crushed dry ice and ethanol, which caused a crust of super frozen sediment to form on the outside of the wedge at a temperature of minus 80 degrees Celsius. Using this technique, he has been able to get a sample with a 2002 baseline. Amazingly, there are only two and a half yards between the upper layers of the present day and those from a millennium ago.

It has taken a lot of work over the course of a decade for Besonen to gain this vantage point on the paleoclimate. But the investment of time and energy doesn’t bother him. “Science is like a huge puzzle with 500,000 pieces or an infinite number,” he says. “Everyone in their lifetime tries to link a couple up, and that leads to a bigger picture.”

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Mysteries in the Muck

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