South American Paleoclimate from Peruvian Lake Cores

My dissertation objective was to reconstruct changes in South American paleoclimate and paleohydrology over the Late Pleistocene glacial-interglacial cycles. I accomplished this using stable isotope proxies (clumped isotopes and triple oxygen isotopes) of lake sediment cores collected from Lake Junín in the central Peruvian Andes. The Junín record is a high elevation record (>4500 meters) which extends back an impressive 700,000 years.

My PhD work has been published in three studies. The first was designed as a modern analog study to document the relationship between carbonate clumped isotopes of lake sediments and environmental (i.e., lake water) temperature and carbonate triple oxygen isotopes and evaporative water balance of lake systems across a range of hydrologic configurations (Katz et al., 2023). My second and third chapters applied these new tools to the Holocene and Marine Isotope State 15 (MIS 15), respectively (Katz et al., 2024; 2025). Through this work, we determined that links between orbital forcing and the South American Monsoon are a first-order control on local water balance in the central Peruvian Andes during interglacial periods for at least the last 500,000 years.

Following my success with interglacial lake carbonates, I also began exploring the glacial intervals. Carbonate isotope stratigraphy during these intervals is impeded by high influxes of detrital carbonate (in the from of glacial flour) from the catchment. Detrital carbonates have severely hampered paleoclimate research on the glacial carbonates. Using clumped isotopes, I show we can screen for the presence of detrital cabonates within lake sediments, thereby improving the paleoclimate data we can recover from the 6 glacial intervals(!) represented in the Junín core. The manuscript associated with this work is currently in preparation.

Related publications:

Katz, S.A., Levin, N.E., Abbott, M.B., Rodbell, D.T., Passey, B.H., Katz, S.A. (2025) "Orbital forcing drives both the South American monsoon and local water balance in the central Andes during interglacials." Geophysical Research Letters, 52 (10.1029/2025GL116249).

Katz, S.A., Levin, N.E, Abbott, M.B, Rodbell, D.T., Passey, B.H., DeLuca, N.M., Larsen, D.J., Woods, A. (2024) “Holocene temperature and water stress in the Peruvian Andes: insights from lake carbonate clumped and triple oxygen isotopes.” Paleoceanography and Paleoclimatology, 39 (10.1029/2023PA004827).

Katz, S.A., Levin, N.E, Rodbell, D.T., Gillikin D.P., Aron, P.G., Passey, B.H., Tapia, P.M., Serrepe, A.R., and Abbott, M.B. (2023) “Detecting hydrologic distinctions among Andean lakes using clumped and triple oxygen isotopes” Earth and Planetary Science Letters, Vol 602 (doi.org/10.1016/j.epsl.2022.117927).

More detailed descriptions of these projects are included below.

Michigan Postdoctoral Research on Glacial Carbonates

Example mixing model between authigenic and detrital carbonate in the Junin catchment (blue curve). A glacial sample with a clumped isotope temperature of 40C is projected onto the mixing model (orange square) to establish a detrital estimate.

During my short postdoc at Michigan, I developed a framework for using clumped isotopes to screen lake sediment samples for detrital carbonate, using samples from the Junin core as a case study. High concentrations of clastic material within the the glacial intervals has inhibited prior carbonate isotope analysis, but I show that clumped isotope data and mixing models have the potential to improve the accuracy of paleoclimate interpretations during these intervals.

This work is currently in prep.

PhD Dissertation Chapters

Chapter 1 Detecting hydrologic distinctions among Andean lakes using clumped and triple oxygen isotopes

In this study, I analyzed triple oxygen isotopes and clumped isotopes from modern surface waters and lacustrine carbonates from four lakes. We showed that clumped isotopes track environmental temperatures and triple oxygen isotopes track hydrology (i.e., evaporation) in each lake. Furthermore, the combination of clumped and triple oxygen isotopes allows us to faithfully reconstruct local precipitation δ18O from carbonates formed from evaporated lake waters. This modern calibration study provides critical context for burgeoning triple oxygen isotope paleoclimate work in lake systems.

Publication: doi.org/10.1016/j.epsl.2022.117927

AGU 2020 Abstract

Fieldwork in the Lake Junin Region, Peru, 2019

Chapter 2 Holocene temperature and water stress in the Peruvian Andes: insights from lake carbonate clumped and triple oxygen isotopes

Global climate during the Holocene is considered to have been relatively stable compared to the late Pleistocene. However, evidence from lacustrine records in South America suggests the tropical latitudes experienced significant water balance variability during the Holocene, rather than quiescence. In this study, we use clumped and triple oxygen isotopes to develop Holocene temperature and evaporation records from Lakes Junín, Pumacocha, and Mehcocha to build a more complete picture of paleo-hydroclimate, specifically changes in water balance (P–E), in this region.

Publication: 10.1029/2023PA004827

AGU 2021 Abstract

Selected Holocene climate records from South America.

Core image credit: Junin working group

Chapter 3 Orbital forcing drives both the South American monsoon and local water balance in the central Andes during interglacials

South American summer monsoon (SASM) strength tracks insolation on orbital timescales, linking global climate and continental hydrology. However, whether local water availability also responds to global climate forcings is unclear. Here, we present water balance records from Lake Junín, an Andean lake within the SASM domain. Local water balance and SASM strength is inferred from triple oxygen isotopes of lake carbonates during two interglacial periods (MIS 15, 621–563 ka; the Holocene, 11.7–0 ka). We find SASM strength and water balance both follow the precession-pacing of local summer insolation, with the driest conditions occurring at Lake Junín under weakened SASM (and vice versa). Further, the largest variations occur during MIS 15, when insolation was more variable than the Holocene. These results suggest that global climate influences South American hydrology on both the local and continental scales, with implications for tropical water resources, the atmospheric greenhouse effect, and ecosystem dynamics.

Publication DOI: 10.1029/2025GL116249

DOIs for supplemental data available: 10.7302/wzbz-v060 (all data; University of Michigan Deep Blue Repository) and 10.60520/IEDA/113718 (clumped and triple oxygen isotope data; Earth Chem Repository)

Text copyright of Sarah Katz 2026.NO AI TRAINING: Without in any way limiting the author’s exclusive rights under copyright, any use of this publication to “train” generative artificial intelligence (AI) technologies to generate text or images is expressly prohibited. The authors reserve all rights to license uses of this work for generative AI training and development of machine learning language models.

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