Big Round Lake (BRD) is a proglacial lake located on northeastern Baffin Island, Arctic Canada. This 36-meter-deep lake is fed by glacial meltwater from an inflow channel to the east and drains from an outflow channel to the west. Cores of the upper 20-40 cm of lake sediment were taken along a transect from the inflow to the deep basin in the center of the lake. BRD is, in general, a round lake with a diameter of about 1400 meters. Cores were taken at about 415 m (25 m depth), 685 m (33 m depth), and 920 m (36 m depth) from the inflow.

BRD contains annually laminated sediments (varves) in its deepest basin, which have been analyzed in order to relate varve thickness to past climate change (see Thomas and Briner, this volume). Often, one core is taken from a site for paleoclimate research as a representative of sedimentation within an entire lake. Here, three cores taken along the transect have been compared to one another to test this approach. Magnetic susceptibility, organic matter content (loss-on-ignition), and plutonium data were used to compare the cores. Known dates in the plutonium record are 1952 (start of nuclear testing) and 1963 (peak of nuclear testing). These dates have been used as time markers for determining age versus depth in individual cores and to correlate between cores. The depth to these time markers is higher near the inflow and lower away from the inflow, revealing that the sedimentation rate decreases along the transect, away from the inflow. Wiggle-matching the magnetic susceptibility and organic matter content of the cores independently confirms the plutonium chronology.

Although all of the cores have laminations, of the three cores studied along this transect, the core taken in the deepest part of the basin is the only one that contains varves (see Ridgeway et al., this volume). This suggests that the deepest part of a lake basin is the ideal place to collect sediments for varve studies. Figure 1 shows a thin section of the core taken at 685m from the inflow stream, in which the plutonium dates have been marked. There are not enough laminations between the two established points in the core to account for the time difference between the markers, if they are varves. Underwater currents and gravity flows could be eroding the laminations when sediment is being deposited in the lake. Evidence of scouring is present in the thin sections of the two cores proximal to the inflow.

The practice of analyzing one core as a general representative of an entire lake basin is common, however this research shows that it is necessary to core the deepest part of the basin for varve studies. Finally, multiple cores taken from one lake allow for a more detailed view of lake sedimentation.