In June and July of 2006, we flew to an unnamed lake on the Culrose Island of the Prince William Sound.  The bedrock surrounding the lake is granitic; as such, muscovite is abundant in the lake’s sediment.  Because of this distinguishing characteristic, we named the lake, Mica lake. 

Mica lake is an hydrologically open lake (has an outflow). The water in the epilimnion, therefore, probably has a short residence time when the lake is ice-free.  Using an In Situ TROLL water monitoring device, we observed the thermocline at ~13 m.  The water layer below the thermocline is referred to as the hypolimnion and, during the summer, does not mix with the epilimnion.  Planktonic diatoms form in the epilimnion while benthic diatoms form in the hypolimnion.  I am most interested in the planktonic diatoms because, during formation, their oxygen-isotope composition is representative of conditions at the lake surface (e.g. climatic and watershed conditions).

The landscape surrounding the lake is heavily vegetated; hemlock is abundant as well as low shrubs.  A short residence time and the abundant vegetation in the lake’s watershed are ideal conditions that we hoped to find while selecting lakes.  The short residence time insures that the surface water will largely be seasonal and the abundant vegetation will provide nutrients for diatoms. 

We took 3 long sediment cores up to 3.1 m long and collected a suite of modern water samples (e.g. precip, snowpack, inflow, and outflow).  Core MC-2 has the longest record and is the focus of this study (see core lithology figure). Diatoms will be isolated from the long core sediment for oxygen-isotope analysis of the late-Holocene and the water samples will be used to better understand the relationship between climate and the oxygen-isotope composition of the surrounding watershed.

Mass spectrometers cannot differentiated between oxygen derived from diatoms from other lake sediment. Therefore, diatoms must be isolated from othe lake sediment before analysis. A multiple stage "clean-up" protocal was used for this purpose as illustrated in the figure below.