On: The Sediments - far from nondescript ooze on
the bottom, the lake sediments tell a rich history of the
lake's development. We use a box core to collect large sediment
samples: one-half meter square and one meter deep. The box
core is then subsampled with plastic tubes. Clearly visible
in box cores are the red or gray glacio-lacustrine clays deposited
while the glaciers were receding 10,000 years ago. The advent
of European settlers is also frequently evident as a change
in sediment color and texture over the topmost 1-3 cm. Along
the Ashburton and Pukaskwa transects it is noteworthy how
little sediment has accumulated since the glaciers receded.
Course sediment textures also attest to turbulence in the
water that sweeps the fine particles to other resting sites.
A slow rate of food supply could well contribute to the small
size of the Diporeia populations along these transects. Return to Cruise