Aquatic siliceous microbiota team excelling with summer research at The College of Wooster

I am honored to be working with a great research team this summer in Scovel Hall at The College of Wooster. Our topic has been the analysis of the siliceous sponges and diatoms in a sediment core from Brown’s Lake near Shreve, Wayne County, Ohio. Above are Minnie Pozefsky on the left and Garrett Robertson on the right conferring on Garrett’s magnificent chalkboard notes. (Yes, there are more sliding boards filled with text behind these.) Minnie, soon to be an entering student at Williams College, is our diatom expert; Garrett is a rising senior at Wooster and our sponge person. This work is part of Garrett’s Senior Independent study project.

Brown’s Lake is well known to Wooster Earth Scientists and readers of this blog. Dr. Greg Wiles started a series of projects in this lake and bog system many years ago, and hundreds of Wooster students have visited it on class field trips and for research at many levels. This is a kettle lake formed at the end of the last Ice Age when a huge block of ice (“dead ice”) was left at the margin of the retreating continental glacier. That melting ice block was surrounded by glacial sediments and eventually became a lake. This means the sediment in the lake goes back at least 11,000 years to the retreat of the last glaciers in this part of the world.

We have access to a beautiful core taken from the center of the lake by our colleagues at the University of Cincinnati. (We share an NSF grant with them for this work.) This core is 1.5 m long and extends from the very recent at the top to probably the 16th century at the bottom. (We are awaiting radiometric dates for a better age estimate.) The core is laminated, meaning the sediment accumulated in undisturbed layers, year after year. This is critical for our analysis of each layer because their relative ages are retained. The core is mostly peat in the bottom 75 cm or so, and then a silty layer begins to appear above. This represents the anthropological effect of European-American settlement of the area in the early 19th century. Our research objective is to describe the paleoenvironments recorded sequentially through this core using the skeletons of diatoms and sponges entombed in the sediment. We already see the dramatic effects of clearing and farming the land. We hope to go back further to see if we can detect climate changes prior to European settlement.

Minnie is spending a lot of time at this photomicroscope identifying, counting, and recording diatoms in smear slides made every 5 cm from the core sediment.

This is a typical microscope view for Minnie this summer. The fish-like form and two circles above the scale bar are diatom frustules (the name for their skeletons). Diatoms are single-celled algae with siliceous skeletons. They are incredibly diverse in most aquatic systems. They are photosynthetic and may produce up to a third of atmospheric oxygen. Most important for us, their frustules are easily preserved, and their taxonomy and abundance can be used as proxies for changing environmental conditions.

Our diatom pioneering forebear Justine Paul Berina (’22) made this beautiful image of the diatom Pinnularia during his Independent Study project. He and Richard Torres (’23) developed many of the lab techniques we’re using this summer.

Garrett Robertson (’24) is here in one of our Scovel labs preparing slides of sponge spicules and diatoms by essentially removing most of the organic materials from the core sediments. It involves hot hydrogen peroxide and centrifuges.

The spiky object at the top of this image is a sponge spicule (with a diatom beneath it). The sponge spicules we have are, like the diatoms, made of resistant silica. In life they formed the internal skeletons of sponges. Like our own bones, a single sponge has many different sizes and shapes of spicules.

This is another sponge spicule, an image taken two years ago by Justine Paul Berina.

The 2023 aquatic siliceous microbiota team! We occasionally get chances to leave the lab. Here we are in the woods near Brown’s Lake and Brown’s Lake Bog. (Picture taken by my brother Wynn Wilson.) Minnie and Garrett were assisting this year’s AMRE Team as they extracted cores from trees.

So far we have found very interesting patterns in the distribution of sponge spicules and diatoms in the Brown’s Lake core. The ecological collapse associated with forest clearing and drainage from new farms is obvious. We think that we also have a record of a possible cooling event in the 17th century, but we have much more work to nail that hypothesis down.

This has been great fun. As always, I have learned much from our work.

About Mark Wilson

Mark Wilson is a Professor of Geology at The College of Wooster. He specializes in invertebrate paleontology, carbonate sedimentology, and stratigraphy. He also is an expert on pseudoscience, especially creationism.
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