PACLIM25 class Spring 2025.
These 6 meters of mud record the transitions from the end of the last ice age (~15,000 years) through ~4,2000 years. Description of the core is the first step.
Paleoclimate 2025 (PACLIM25) is a class in the Department of Earth Sciences at The College of Wooster. A goal of the course is to learn about past climates, their relevance to future climates, and to have the class contribute to the study of past climates. One of the key sites of environmental change in North America is the sediment record from the past 15,000 years at Browns Lake Bog, Wayne Count, Ohio. This long-studied site (Lutz et al., 2007; Glover et al, 2011) has revealed the presence of abrupt climate changes (ACCs) including the Younger Dryas and the 8.2 ka event.
The core worked on this semester was taken in 2021 through collaboration of Wooster and the University of Cincinnati (UC).
The successful coring of these records is largely the result of the experience and skill of Dr. T.V. Lowell (UC) who has developed, built and perfected techniques and equipment to recover lake record around the globe. Dr. Lowell met with the class this semester to field questions about our findings giving us insights based on decades of his work on ACCs in the Northern and Southern Hemispheres.
The magnetics team measured the susceptibility of the core, which is a measure of grain size and magnetic minerals (results below).
Magnetic susceptibility – the high values in the 600-800 cm range is the transition from the Ice Age. The spike at 400 cm is consistent with the 8.2 ka event, but also occurs at a break in the core.
We will start at the base of the section – from previous cores and Wooster student theses, we know this is about 15,000 year old when the ice left this part of Ohio at the end of the Ice Age. You can see pebbles and blebs of coarse sands as the world warmed. This deep sediment is largely devoid of organics.
One of the data sources is smear slides examined under the microscope.
Examining diatoms, sponge spicules along with insect parts and mineral matter.
Dating is everything and here the group is sampling organic disseminated in the mud for C-14 dating.
A C-14 age (see below) places this “bright” layer – likely loess in time. This layer and the dating so far defines, in part, the Younger Dryas at Browns Lake.
Calibrated C-14 age obtained in 2021 – other ages are now submitted and results are pending to better define the timing of deposition of this layer.
Photographing the core is crucial as the colors of the core change as it dries. Thanks to the Wooster Chemistry Department, we are able to store the core in their walk in cooler “keeping it fresh”.
The group argues about the timing of the events – this is the Bolling-Allerod group.
Above the Younger Dryas is the relatively well documented 8.2 ka event (Lutz et al., 2007). The dating in this core is shown below. Note the A and B layers are bright and are, like the YD interpreted as loess in the core. The reason the 8.2 ka event is a double layer is unknown.
Dating of this section of the core yielded the calibrated date above consistent with the 8.2 ka event documented in our previous studies.
More photography and discussion of the sediments and their origin.
The next transition of note is the “Strange transition” layer dated to about 6,000 year ago (see below). This is the time when the Laurentide Icesheet is largely gone from North America and today’s (late Holocene) climate sets in. In this meter of sediment the group found a pebble and sand layers suggesting flooding into the lake basin consistent with this warm, wet and stormy interval.
Calibrated C-14 age at the “Strange Transition”.
Crucial to any successful lake core study is a positive attitude.
References (Wooster students, staff and faculty in bold):
Glover, K.C., Lowell, T.V., Wiles, G.C., Pair, D., Applegate, P., and Hajdas, I., 2011, Deglaciation, basin formation and post-glacial climate change from a regional network of sediment core sites in Ohio and eastern Indiana: Quaternary Research, v. 76, p. 401–410, doi:10.1016/j.yqres.2011.06.004.
Lutz, B., Wiles, G., Lowell, T., and Michaels, J., 2007, The 8.2-ka abrupt climate change event in Brown’s Lake, northeast Ohio: Quaternary Research, v. 67, p. 292–296, doi:10.1016/j.yqres.2006.08.007.