A hydrologically and biologically complex proglacial lake system at the margins of the collapsing Laurentide Ice Sheet



Graham H. Edwards 1, Gavin Piccione 2, Luke Moreton 1, Emma Rose Garrett 1, David Jones 3, Clara Danhof 3



1 Trinity University (San Antonio, TX), 2 Brown University (Providence, RI, U.S.A.), 3 Amherst College (Amherst, MA, U.S.A.)
IPCC, AR6, WG1, Fig. 9.18
IPCC, AR6, WG1, Fig. 9.17

Proglacial lakes & wetlands are/will be emergent, dynamic environments in the modern warming climate.

Glacial Lake Hitchcock (GLH)
Dalton+2023, Ridge+2012, McGann+2024, Springston+2024
Connecticut River Valley
G.H. Edwards

North American Varve Chronology

  • Precisely calibrated varve chronology of GLH, spanning 18.2–12.5 ka.
  • Well-established Laurentide Ice Sheet retreat and GLH residence Antevs 1922, Stone+2025
  • Lacustrine environment less well-described.
Ridge et al (2012), https://varves.as.tufts.edu/

Carbonate concretions / claybabies

Non-displacive, formed through oxidation of local org-C Wu+2021
Thanks to Sophie Shipman for polishing cross-section surfaces.

Carbonate concretions / claybabies

Non-displacive, formed through oxidation of local org-C Wu+2021

Reconstructing the hydrochemistry of the GLH proglacial lacustrine system.

Reconstructing the hydrochemistry of the GLH proglacial lacustrine system.

Field transect of the former GLH basin

Carbonate concretions

Isotope & trace element geochemistry

Bulk sediment

Ostracod and clay geochemistry

Sediment cores

Chronometric calibration with NAVC

Stable isotopes

Stable isotopes

Carbonate — concretions & ostracod valves

Stable isotopes

Carbonate — concretions & ostracod valves
↓T → ↓ δ18O

Stable isotopes

Carbonate — concretions & ostracod valves
  • Modern precipitation: -7 ≤ δ18O ≤ -10 ‰ Terzer-Wassmuth+2021
  • Similar δ18O for SN ostracods and concretions Danhof 2025
  • Concretion-forming waters ≈ lakewater
  • S→N transect of ↓δ18O (MVR, MB, WR)
    • Proximity to ice sheet margin?

Stable isotopes

Clays

Stable isotopes

Clays
  • Overestimate: δ18O ≤ 19 ‰ for T = 0°C
  • Clay formation in (sub)glacial waters
  • Basal LIS δ18O composition?
    • Barnes Ice Cap basal ice: δ18O≈−25 ‰ Zdanowicz+2002
    • N. Amer. fossil groundwaters: −12 ≤ δ18O ≤ −25 ‰ Ferguson & Jasechko 2015

Trace elements

Li, Na, Mg, Ca, Mn, Fe, Co, Ni, Cu, Zn, Sr, Ba, Pb, Th, U

Elevated Mn

Elevated Mn

Redox

  • Reducing conditions → high-Mn carbonate Wittkop+2020
  • Fe-Mn oxide formation Dean+1981
    • Reducing conditions → Mn2+
    • Oxidizing conditions → MnO2

Several reduction/oxidation cycles

↑ Mn → ↓ δ13C

Emerging story

  • Concretions form shortly after sediment deposition
  • Spatiotemporal variability → environmental diversity
  • Local/littoral processes dominate record
  • Complex shallow sediment biogeochemistry
  • Intense subglacial chemical weathering

Answers coming soon!

U-series ages (up to 10 ppm U)
Clumped carbonate isotopes

Conclusions

  • Carbonate concretions are a promising archive of proglacial environment
  • Forthcoming geochronology to better evaluate how
  • Robust evidence for complex (post)GLH biogeochemistry and hydrology

Poster 60-54

Modern Problems Require Ancient Lakes: The Chronology and Chemistry of Glacial Lake Hitchcock

gedward1@trinity.edu

Acknowledgements: Jack Ridge, Al Werner, and assorted (NE) Friends of the Pleistocene.