Monday, October 23, 2017

Coring the Past

posted by Caitlin McDonough MacKenzie

“I live in the present.  I only remember the past – and anticipate the future.”
 Thoreau in his Correspondence.  1848.

Last month I returned to my dissertation research site at Acadia National Park. But instead of hiking the ridge of Sargent Mountain to record this year’s flowering and leafing times, I plumbed the depths of Sargent Mountain Pond for evidence of past plant life that once fringed the granite kettle hole. I’ve traded historical ecology for paleoecology, and in my new postdoc position in Jacquelyn Gill’s BEAST (Biodiversity & Environments Across Space and Time) lab, I will focus on pollen grains trapped in ancient lake sediments.

Coring Sargent Mountain Pond: Caitlin pushes the corer into the lake sediment below the raft while Jacquelyn ties off the cable connected to the corer's piston.

I timed this fieldwork to coincide with a Sierra Club project: all week a group of Sierra Club members volunteered in Acadia. On Tuesday, they joined me and the BEAST lab as we hauled coring equipment — including giant inflatable pontoons and two 4x8’ plywood deck pieces — up to Sargent Mountain Pond. We carried in giant inflatable pontoons for a raft and two 4x8’ plywood decks: a major feat on a challenging trail. We hiked it all in, assembled the raft and inflated a kayak, and then launched our floating field site on to the pond. From our raft, we extracted cores of sediment from the deepest basin of the pond — over 11 feet deep — using a piston corer. The piston corer allows us to push deep into the lake bottom and pull up 1 m of sediment in each drive. Over the course of three days we cored nearly 9 meters of sediment. These cores represent a journey through over 4 meters of organic material under Sargent Mountain Pond, into the grey sands of a glacial landscape. We cored 4 meters deep twice: two overlapping records will give us a continuous chronicle of pollen through the last 15,000 years.
Caitlin celebrates with her first core!

We cored Sargent Mountain Pond because it sits just below treeline in Acadia and subalpine plant communities grow at its edge. As the Laurentide ice sheet retreated, Sargent Mountain Pond emerged as the “first pond in Maine”; the rest of its limnological siblings were under still ice. Previous coring research at Sargent Mountain Pond has confirmed this and sediments in the basin are over 16,000 years old.

The pollen trapped in the pond’s sediments will help us to answer questions about the history of the subalpine plant communities around Sargent Mountain Pond. How dynamic is treeline on Acadia’s granite ridges? Have Mount Desert Island’s subalpine communities persisted here since the last ice age? How have these species responded to past climatic changes?

It was lovely to be back in Acadia for fieldwork and I’m looking forward to splitting open our cores to study the long ecological history of this site.

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