Geologic Boundaries: Identifying the Transition to the Anthropocene in Lake Wononscopomuc, CT

What: The main scientific goal of the project is to identify a candidate for the Holocene-Anthropocene boundary in the unlithified sediments of Lake Wononscopomuc in northwestern Connecticut. The secondary scientific goal is to correlate the sedimentary record at Lake Wononscopomuc with other candidates for the Holocene-Anthropocene boundary.

When: June 15-July 18, 2025

Where: Amherst College, Amherst, MA and the AGU Annual Meeting in New Orleans, LA (December, 2025)

Who: Nine students, a peer mentor, and project directors Dr. David Jones (Amherst College), Dr. Anna Martini (Amherst College), Dr. Tim Ku (Wesleyan University).

Prerequisites:  Because this experience is a Gateway Project for rising sophomores, there are no specific coursework prerequisites.

Expectations and Obligations:
1. Participation in all project-related work during the summer (5 weeks)
2. Submission of an abstract (individual or in groups) and presentation of a paper (poster or talk) at the American Geophysical Union Meeting in New Orleans, LA in December, 2025 (all expenses covered).

PROJECT DESCRIPTION

Project Goals: The main scientific goal of the project is to identify a candidate for the Holocene-Anthropocene boundary in the unlithified sediments of Lake Wononscopomuc in northwestern Connecticut. The secondary scientific goal is to correlate the sedimentary record at Lake Wononscopomuc with other candidates for the Holocene-Anthropocene boundary. The main educational goal of the project is for students to collaborate on a field and laboratory project that has direct bearing on a contemporary geological debate with wide-ranging implications for society beyond the geosciences. Secondary goals include developing skills in reading scientific literature and project planning/management, making stratigraphic correlations, learning field and lab techniques, and understanding the short-term carbon cycle through geochemical and modeling tools. 

Significance: Even before Darwin, geologic boundaries held profound intellectual significance, whether used more prosaically as in John Smith’s famous map, or as evidence of God’s hand upon creation. While we often focus on the divides that create momentous changes in the history of life, such as the mass extinction marking the Permian-Triassic boundary, or the Cretaceous-Paleogene event which changed forever the paths of mammalian development, stratigraphic boundaries are a fundamental way to interpret the sedimentary record. The youngest recognized boundary represents the climatic change from the Ice Age, or Pleistocene, to the relatively stable climate in which human civilization has flourished, the Holocene.

However, in the past few decades there has been a growing sense that another boundary is upon us, one created by humans. The term “Anthropocene” was coined, or at least popularized, in 2000, marking the beginnings of a serious discussion in the geologic community of whether we had entered a new geologic interval. While still under considerable debate, the Anthropocene Working Group (AWG) this past summer chose Crawford Lake in Ontario, Canada as representing the Global Boundary Stratotype Section and Point (GSSP) for this new epoch (or series). The lake’s deep sediments contain multiple proxies of 20th century industrialization and plutonium spikes left behind through atmospheric testing of nuclear weapons. If ratified by the wider geoscience community, it will officially be declared in August 2024, and its first “age”, following convention, could be the “Crawfordian” (Witze 2023; McCarthy et al. 2023).

In this Gateway Project, we will advance another candidate into contention for the honor of defining the base of the Anthropocene – the sediments of Lake Wononscopomuc, CT. Students will enter the scientific conversation surrounding the Anthropocene boundary, employing a wide range of proxies. Alongside this great debate, they will learn field and laboratory skills that will be applicable to diverse future projects. Crawford Lake has many advantages for the GSSP, including its small size, well-laminated sediments and low development along the lakeshore. However, we expect that Lake Wononscopomuc will compare favorably on many measures, and using this proposition will help focus innovative debate among project participants while constructing a scientifically sound argument. We expect this approach to be a creative way to stimulate critical thinking amongst our Gateway students.

Figure 1. Lake Wononscopomuc, in NW CT, with 1o ft contours and blue and red symbols indicating the location of preliminary data at the site.

Preliminary Data

The thermocline begins ~10 m depth where lake temperatures fall from approximately 20°C at the surface in summer to ~ 5°C at depth (Figure 2). This thermocline also divides the shallow waters, which are supersaturated with respect to calcite, from deeper waters which are undersaturated in the water column. This change in the saturation state is due in part to temperature effects on the K_cal (calcite dissolves more readily in colder water) and the lowering of pH in conjunction with the respiration of organic matter in the water column. This respiration also shows up clearly in the lowering of dissolved oxygen (DO) in the water column.

CH₂O + O₂ → CO₂ + H₂O                                          respiration

CO₂ + H₂O + CaCO₃ ←→ Ca²⁺ + 2HCO ^–     calcite dissolution

Preliminary gravity cores taken at shallow (~7.5 m) and deep (~30 m) sites show highly variable concentrations of organic carbon (OC) and CaCO₃ relative to the depth of the water column (Figure 3). For the deeper core, CaCO₃ remains below 10 wt. %, whereas in shallower waters carbonate can reach ~80 wt%. The overall shifts in organic carbon (OC) are similar between the sites, with higher relative concentrations at depth (<40 cm for shallow site and ~70 cm for the deep one), a middle zone with lower OC (light blue), and a slow rise in the most recent sediments (green zone). This rise in the youngest sediments is likely due in part to nutrients (from fertilizer/sewage) entering the lake (Canavan and Siver, 1995).

Figure 2: Depth profiles through the water column at the deepest site (blue circle in Fig. 1) showing the thermocline and changes in pH and dissolved oxygen.

Figure 4. For the deep gravity core, mercury concentrations normalized to the total amount of organic carbon in the core provide a useful proxy for age constraints.

One aim of our study will be to explore the control that primary productivity (PP) has on the inorganic and organic carbon concentrations, as well as the sedimentation rates, amongst cores from different water depths. In a system where PP dominates, it is expected that OC and CaCO₃ concentrations will exhibit positive correlations (Teranes and Bernasconi, 2005). However, inverse relationships occur with high (>10%) organic carbon concentrations due to higher additions of CO₂ via respiration and subsequent lowering of pH leading to CaCO₃ dissolution (Dean, 1999). In Lake Wononscopomuc the depth in the water column clearly influences the “resiliency” of carbonate materials. However, another influence may be the in situ production of CaCO₃ by aquatic charophytes growing in the photic zone (Pelechaty et al., 2013).

The mercury profile (Figure 4) further suggests a period of early industrialization around the lake (perhaps corresponding to the initial rise in Hg at ~ 70 cm), to the “peak” Hg in the 50’s-60’s, and finally to the EPA clean air act in the 1970’s where Hg atmospheric concentrations began to drop (top ~30 cm in the core). The early rise of Hg may be linked to certain developments around the lake such as the operation of an iron forge built in 1748 along the lakeshore (Rome, 1977). While it was located at the outlet of the lake (for hydraulic power), its effects in terms of rapid population growth and thus land development, should be observable in the sediments within the lake. The forge finally shut down in 1847, and the area turned back to mainly an agricultural and dairy economy (Rand, 1968).

One of our key goals for the study is to further constrain the ages within each sediment core to determine arrival times of various proxies. In addition, it would be expected that sedimentation rates in the lake have changed as the activities within the watershed have shifted over time (Field et al., 1996). Using Hg only, and the correlation in the region with peak Hg occurring around 1960, a qualitative sedimentation rate of 0.5 cm/yr can be calculated. We will use radiometric dating techniques (²¹⁰Pb, ¹³⁷Cs, ¹⁴C) to quantify these rates at various depths in the cores.

Taken together, these records from less than a meter of core contain multiple proxies of the transition from the Holocene to the Anthropocene. Our goal will be to interrogate these proxies with high resolution geochemistry. We will correlate across a minimum of 3 core sites representing a transect from the deepest basin of the lake to the edges, allowing us to observe changes from photic to profundal zone, from anoxic to oxic, and from higher energy zones to low. Our Gateway students will assign a “marker bed” for the transition, and provide the scientific rationale for their choice. Coring equipment we have inhouse (Uwitec Gravity corer and freeze corer) will allow us to sample the relevant intervals for the Anthropocene transition.

Potential Student Projects

Students on this project will be introduced to the scientific conversation growing around the proposed new geologic epic, the Anthropocene. While not yet formally adopted, it has been a focal point for engaged conversation since first introduced in 2000. Currently, there is no agreement to the marker bed that would separate it from the Holocene. During the Gateway project we will debate the proxies and measure many of the leading candidates under consideration.

Students will explore using multiple tools a potential “geologic boundary” differentiating the Holocene epoch from a new age, the Anthropocene using multiple cores they have collected from Lake Wononscopomuc. Depending on the proxy you choose, the Holocene/Anthropocene boundary should be well represented in these lake deposits. Working in teams of two or three within the larger Gateway project group, students will investigate a variety of proxies chosen from among the following:

Project 1: Radionuclides. We will send sediment samples out for dating using lead-210 and to pinpoint the cesium-137 spike that serves as a marker for atmospheric nuclear testing. The ¹³⁷Cs fallout is first widely measured in sediments beginning in 1954 with a peak corresponding to 1963, at the height of atmospheric nuclear testing (Drexler, Fuller, and Archfield 2018).

Project 2: Metal accumulation. Atmospheric deposition of metals such as mercury and lead also help constrain the age of the sediments and serve as a meaningful marker for the rise of industrialization (Woodruff et al. 2013; Varekamp, Pasternack, and Rowe 2000). The presence of an active iron smelter on the Lakeshore from mid-1700’s to the mid-1800’s may make this signal more “localized” than at other sites (Rome, 1977). However, it may lead to a more precise stratigraphy within the lake sediments, especially from one core to another as pollution entering the lake would carry across.

Project 3: Sedimentation rate. Human activity, from early farming and forest clearing to later urbanization, all have the potential of increasing the sediment-loading to the lake (Wilkinson and McElroy 2007). Accurate measurements of various dating proxies along with careful interpretation of changing concentrations of calcite, organic carbon (OC) as well as siliciclastic sediments should help us constrain this potential signal.

Project 4: Carbon cycle. The carbon cycle has been obviously disturbed by our use of fossil fuels. This disturbance is strongly apparent in the isotopic carbon record found in lake deposits. For carbonate-rich lakes, such as Lake Wononscopomuc, the signal of fossil fuel use, a depletion in the amount of ¹³C in carbon dioxide, is apparent and can be corrected for using the “Seuss” equation (Olsen and Ninnemann 2010). The carbon cycle for both organic and inorganic components is also greatly affected by changes in the lake’s productivity, again induced by anthropogenic forcings.

Project 5: Nutrient-cycle. Changes in productivity in the lake, while recorded by the carbon isotopic signatures of dissolved inorganic carbon (DIC), organic carbon (OC) and calcium carbonate (CaCO₃), are often linked to changes in total nutrient load to lakes. In most temperate lakes, human sewage, fertilizer use and other land disturbances have led to “eutrophication” of many While Lake Wononscopomuc is still categorized as “mesotrophic”, local groups have been working to try to restore its health. We will be able to look at C/N ratios as well as δ¹⁵N in OC and will examine the phosphorus content in the carbonate materials precipitated using selective leaching along with ICP-OES techniques (Ruban et al., 1999).

Project 6: Plastics. Finally, we will search for plastic debris that is caught up in the lake sediments as a final marker for the Anthropocene (Bhateria and Jain 2016; Li, Liu, and Paul Chen 2018; Coppock et al. 2017).

Project Logistics

Travel, Room, and Board

This nine-student Gateway Project will run in Summer 2025 from June 15^th to July 18^th, and will be based out of Amherst College in Amherst, MA. Students will fly to nearby Bradley International Airport (BDL) in CT on the 15^th and depart on July 18^th. They will be housed in Amherst College dorms and will eat meals in the Amherst College Dining Hall, which provides options for most if not all dietary restrictions.

Lab Work at Amherst College and Field Work at Lake Wononscopomuc

The first week will be on-campus at Amherst College with instruction in the scientific background and context, research project discussions, training in laboratory techniques and safety, and preparing for the field work. The second week will be spent on Lake Wononscopomuc, about a two hour drive from Amherst. There we will spend three to four days sampling the lake water and sediment (water column measurements, shorter gravity cores and longer Livingston-type cores). The boats will be provided by Wesleyan University. During the field work, students and faculty will stay at lodging close to the lake.

References

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Bhateria, Rachna, and Disha Jain. 2016. “Water Quality Assessment of Lake Water: A Review.” Sustainable Water Resources Management 2 (2): 161–73.

Canavan, R.W. and Siver, P.A. (1995) Connecticut lakes : a study of the chemical and physical properties of fifty-six Connecticut lakes. Published by the Connecticut College Arboretum, New London, CT.

Coppock, Rachel L., Matthew Cole, Penelope K. Lindeque, Ana M. Queirós, and Tamara S. Galloway. 2017. “A Small-Scale, Portable Method for Extracting Microplastics from Marine Sediments.” Environmental Pollution 230 (November): 829–37.

Dean, W.E. (1999) The carbon cycle and biogeochemical dynamics in lake sediments. Journal of Paleolimnology 21, 375-393.

Drexler, Judith Z., Christopher C. Fuller, and Stacey Archfield. 2018. “The Approaching Obsolescence of 137Cs Dating of Wetland Soils in North America.” Quaternary Science Reviews 199 (November): 83–96. 

Field, C.K., Siver, P.A. and Lott, A.-M. (1996) Estimating the Effects of Changing Land Use Patterns on Connecticut Lakes. Journal of Environmental Quality 25, 325-333.

Li, Jingyi, Huihui Liu, and J. Paul Chen. 2018. “Microplastics in Freshwater Systems: A Review on Occurrence, Environmental Effects, and Methods for Microplastics Detection.” Water Research 137 (June): 362–74.

McCarthy, Francine Mg, R. Timothy Patterson, Martin J. Head, Nicholas L. Riddick, Brian F. Cumming, Paul B. Hamilton, Michael Fj Pisaric, et al. 2023. “The Varved Succession of Crawford Lake, Milton, Ontario, Canada as a Candidate Global Boundary Stratotype Section and Point for the Anthropocene Series.” The Anthropocene Review 10 (1): 146–76.

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Rand, C. (1968) The changing landscape; Salisbury, Connecticut. New York, Oxford University Press, New York.

Rodgers, J. (1985) Bedrock Geological Map of Connecticut. Connecticut Department of Environmental Protection (DEEP).

Rome, A.W. (1977) Connecticut’s Cannon: The Salisbury Furnace in the American Revolution. The American Revolution Bicentennial Commission of Connecticut, Hartford, Connecticut.

Ruban, V., López-Sánchez, J., Pardo, P., Rauret, G., Muntau, H., & Quevauviller, P. (1999). Selection and evaluation of sequential extraction procedures for the determination of phosphorus forms in lake sediment. Journal of Environmental Monitoring, 1(1), 51-56.

Teranes, J.L. and Bernasconi, S.M. (2005) Factors controlling d13C values of sedimentary carbon in hypertrophic Baldeggersee, Switzerland, and implications for interpreting isotope excursions in lake sedimentary records. Limnology Oceanography 50, 914-922.

Varekamp, J. C., G. B. Pasternack, and G. L. Rowe Jr. 2000. “Volcanic Lake Systematics II. Chemical Constraints.” Journal of Volcanology and Geothermal Research. https://www.sciencedirect.com/science/article/pii/S0377027399001821.

Wilkinson, Bruce H., and Brandon J. McElroy. 2007. “The Impact of Humans on Continental Erosion and Sedimentation.” GSA Bulletin 119 (1-2): 140–56.

Witze, Alexandra. 2023. “This Quiet Lake Could Mark the Start of a New Anthropocene Epoch.” Nature Publishing Group UK. July 11, 2023. https://doi.org/10.1038/d41586-023-02234-z.

Woodruff, Jonathan D., Anna P. Martini, Emhmed Z. H. Elzidani, Thomas J. Naughton, Daniel J. Kekacs, and Daniel G. MacDonald. 2013. “Off-River Waterbodies on Tidal Rivers: Human Impact on Rates of Infilling and the Accumulation of Pollutants.” Geomorphology 184 (February): 38–50.