Online

Belrose, Ashliegh Theresa

Geology

2015

MS

Sediment accumulated on a lakebed archives information about past climate and changes in the regional environment. Previous studies (Burgess, 2007; Koff, 2011; Palmer, 2012) in the Northeast Arm of Lake Champlain, specifically Missisquoi Bay and Saint Albans Bay, showed a period (~9,400 - 8,600 yBP) of elevated organic matter deposition in both bays, indicating a productive event that pre-dated any possible anthropogenic influence. However, the record was abruptly cut off and any documentation representing the span of time leading up to this event was not found. The elevated organic matter levels were explained as being the result of a warm, dry environment that reduced lake level and promoted productivity within the bay. A new goal was formulated to lengthen the Holocene record for Missisquoi Bay (MSB) and Saint Albans Bay (SAB) in order to compare paleorecords and capture the span of time leading up to this highly productive event, possibly related to the Champlain Sea/Lake Champlain Transition (~10,000 yBP). One sediment core was taken from each bay as close to the original coordinates as the sediment cores obtained in previous studies (Koff, 2011; Palmer, 2012). The sediment cores were processed in the lab and sediment samples were tested for water content (WC), %C, %N, C:N, and diatom content. Each bay's sediment record consisted of a distinct marker representing lowest water level, separating a Champlain Sea unit at the bottom and an overlying Lake Champlain unit. A warming climate coupled with low lake level during this time may be the cause of the increase of productivity (%C) associated with the markers in both bays. Between ~8,600 - 9,400 yBP, a distinct marker represented evidence of a wetland in Saint Albans Bay before the onset of Lake Champlain. Diatom content in the wetland sediments indicated a generally shallow oligotrophic and alkaline body of water that shifted back and forth from brackish to freshwater. The record shows the wetland was eventually drowned as water level continued to rise, slowly transitioning into the Lake Champlain unit. Proxy results showed that internal processes within the lake continued to change in response to climatic and environmental drivers until present day conditions were reached. At ~9,400 yBP in Missisquoi Bay, there is an erosional unconformity between the Champlain Sea and Lake Champlain units, which corresponds to the low water levels also inferred from the SAB record during that time. After this unconformity, %C results show production within MSB fluctuated, similar to SAB, in response to changing climate and water levels until the present-day conditions of Lake Champlain were established. In sum, MSB and SAB each contain evidence of an ancient shoreline marker in different forms. Both markers indicate that lowest water levels occurred ~9,400 yBP and that lake level has risen ~7 - 8.5 meters since that time. The rise in lake level is associated with the transition into Lake Champlain. This Champlain Sea/Lake Champlain Transition lasted from ~9,400 yBP until ~8,600 yBP. Therefore, the oldest Lake sediment in the Northeast Arm of Lake Champlain is only 8,600 yBP.