Date of Award
Bachelor of Science
The magnetic properties of Pea Porridge Pond, NH were analyzed in an attempt to reconstruct Holocene climate change. Magnetic measurements include magnetic susceptibility (χ), anhysteretic remanent magnetization (ARM), isothermal remanent magnetization (IRM), saturation isothermal remanent magnetization (SIRM), coercivity distributions of IRM, and hysteresis loops. ARM/IRM and S-ratios were calculated, and a Day (Day et al., 1977) plot was created using data from the hysteresis loops. The sediment magnetic record is divided into six zones. High concentration-dependent parameters in Zone 1 (prior to 14 ka) suggest an initial unstable landscape in which erosion contributed to the input of magnetic minerals. Zone 1 is dominated by clastic, sedimentary input and detrital magnetic minerals are coarse-grained. The overall sediment magnetic properties are dominated by low-coercivity minerals. Zone 2 (14.0-13.6 ka) is characterized by an increase in organic matter and a decrease in the concentration of magnetic minerals. A warmer climate stimulates lake productivity and causes anoxic conditions in the sediment, resulting in decreasing concentration-dependent parameters. The minerals are still coarse-grained and of low-coercivity. Sediments deposited during Zone 3 (13.6 -10.0 ka) are likely affected by the processes of dilution and dissolution and show a dramatic decrease in concentrationdependent parameters (χ, ARM, IRM). The spruce maximum (~11.0 ka) occurs during this zone and may lead to the acidification of soil and the dissolution of Fe-minerals. Narrow coercivity distributions from this zone indicate the production of biogenic magnetite likely stimulated from the addition of dissolved Fe. Zone 4 (10.5-8.5 ka) shows a transition from paramagnetic clays to diamagnetic, organic matter. Zone 5 (8.5-3.0 ka) shows little change in sedimentary input but magnetic properties indicate a high-coercivity component and samples are almost entirely diamagnetic. Zone 6 (<3.0 ka) indicates an increase in detrital sedimentary input, likely occurring because of erosion due to anthropogenic activities. A decreasing sediment accumulation rate from Zone 1 until Zone 5 indicates a dry climate, and increasing sediment accumulation throughout Zones 5 and 6 suggest a moister climate.
Payton, Brittney M., "Sediment Magnetic Proxies Reflect Post-Glacial Climate Change for East-Central New Hampshire". Senior Theses, Trinity College, Hartford, CT 2012.
Trinity College Digital Repository, http://digitalrepository.trincoll.edu/theses/255