Lake sediments preserve an extraordinary archive of environmental change. Among the most rapidly advancing tools for accessing these archives are lipid biomarkers. The application of lipid biomarkers to paleolimnology has seen significant methodological and interpretive developments over the past decade, establishing them as central tools in the reconstruction of past climate and ecological dynamics.

This session invites contributions that explore the use of lipid biomarkers in lake sediment records to reconstruct past environmental conditions, with a particular emphasis on recent advances in analytical approaches, proxy calibration, and integrative interpretation. Innovations such as expanded calibrations of branched GDGTs for continental temperature reconstructions, compound-specific isotope analysis (e.g., δ¹³C, δ²H) of long-chain n-alkyl lipids such as plant waxes, and the development proxies such as stanols and bile acids have significantly improved the spatial and temporal resolution of paleoclimatic and paleoecological reconstructions. These approaches offer refined insights into changes in vegetation and hydrological regimes, as well as paleoecological responses, across time.

We welcome studies demonstrating the utility of lipid biomarkers for reconstructing a broad range of environmental parameters and ecological response. These molecular proxies have been deployed in diverse settings—from tropical crater lakes sensitive to hydroclimate variability, to Arctic and alpine lakes recording rapid deglacial transitions, to temperate systems documenting anthropogenic land-use and eutrophication histories. As a result, the spatial reach and thematic breadth of lipid biomarker applications have expanded substantially, and their integration with other proxy systems has become increasingly common. This session aims to foster dialogue across disciplinary boundaries—bringing together organic geochemists, paleolimnologists, paleoecologists, archaeologists, and climate scientists—to discuss the future of lipid biomarker proxies. Contributions are encouraged that address new biomarker applications, multiproxy reconstructions, challenges in compound interpretation, or methodological advances in quantification and calibration. Comparative studies and regional syntheses that link molecular data with ecological and climatic processes are especially welcome.

Lead Organizer: Benjamin Gwinneth, Université de Montréal (benjamin.gwinneth@umontreal.ca)

Co-organizers:

Jules Blais, University of Ottawa (Jules.Blais@uottawa.ca)

Presentations

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09:00 AM

SEDIMENT BIOMARKERS TRACK A SEABIRD COLONY RESPONSE TO PAST CHANGES IN CLIMATE (10835)

Primary Presenter: Jules Blais, University of Ottawa (jules.blais@uottawa.ca)

Jules M. Blais¹, Raphael Siegel¹, David C. Eickmeyer¹, Linda E. Kimpe¹, Arnaud Huguet²¹University of Ottawa, Ottawa, ON, Canada, K1N 6N5² Sorbonne Universite, Paris, France Lake sediments track a history of long-term environmental changes.  Environmental monitoring often extends back no more than a few decades, and is lacking in remote places like the Arctic, which is currently experiencing some of the most rapid environmental change on Earth. Archival sediment records in the form of dated sediment cores can greatly enhance our knowledge of past environmental change because they can extend the time scales of studies by thousands of years and they are broadly distributed in the environment. Here we summarize the results from a dated sediment core from Cape Vera Devon Island that tracks inputs from a large northern fulmar (Fulmarus glacialis) colony via d15N, sterols, stanols, and biogenic elements known to be enriched near seabird colonies. We compare these records with emerging techniques in paleoclimate studies, notably the microbial membrane lipids called glycerol dialkyl glycerol tetraethers (GDGTs) that track recent temperature records to show how northern fulmar populations have responded to past climate.

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09:15 AM

LONG CHAIN N-ALKANES IN LAKE SEDIMENT TRACK DIFFERENCES IN ADJACENT LAND VEGETATION (10244)

Primary Presenter: Bowen Xiao, University of Ottawa (bxiao049@uottawa.ca)

We analyzed n-alkanes, lignin-derived phenols, and other sediment markers from 19 lakes across four Saskatchewan ecoregions, from Prairie Grassland to Boreal Upland, to establish ecoregion-specific signatures and assess their correlation with catchment land cover (trees vs. herbaceous plants). Significant correlations were found between the n-alkane ratios C₃₁/(C₂₇ + C₃₁) and C₃₁/(C₂₇ + C₂₉ + C₃₁) and the herbaceous-to-tree ratio in catchments, indicating their potential for reconstructing historical land cover from sediment records. The C₃₁/(C₂₇ + C₃₁) ratio also varied significantly among ecoregions, particularly distinguishing Prairie Grassland from forested regions. No correlations were observed between sediment n-alkane ratios and chlorophyll-a in lake water, confirming these ratios reflect terrestrial land cover rather than algal production. The C/N ratio and δ¹³C were not effective for distinguishing ecoregions or land cover, likely due to confounding influences from algal production and agricultural activities. In contrast, lignin-derived phenols appeared to be influenced by other factors such as mean annual temperature, soil type, and decomposition processes before depositing into the lake. Overall, our research highlights the potential of n-alkanes as biomarkers for tracking distinct land cover types and enhancing the accuracy of estimating surface vegetation composition, due to their positive correlation with the proportion of grasses and trees.

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09:30 AM

Compound-Specific Isotope Analyses of n-Alkane Biomarkers Reveals Source-Dependent and Persistent Priming Effects in Incubated Sediments (10805)

Primary Presenter: Yeganeh Mirzaei, Concordia University and Geotop Research Center (yeganeh.mirzaei@concordia.ca)

The introduction of new bioavailable carbon into natural systems can awaken existing old carbon stocks, not only posing threats to the ecosystem’s health, but also increasing CO₂ fluxes to the atmosphere. The freshly discharged labile organic carbon (OC) can fuel microbial communities to decompose recalcitrant and previously stable native pools, a process known as positive priming effect (PE). While patterns of PE are well investigated in soils and terrestrial systems, it remains insufficiently studied in aquatic environments. In particular, it is not well understood that to what extent and for how long the inputs of labile OC from different origins can trigger distinct PE responses in sediments. Hydrocarbon biomarkers, particularly n-alkanes of different chain lengths, have been wildly used as molecular tracers of different OC sources. In this study, by applying n-alkanes’ stable carbon isotope values and concentrations (C₁₅–C₃₀) in isotopic mass balance equations, we quantified the contributions of fresh labile OC and old sedimentary OC to the remineralized pool and tracked the induced PE and its variation during incubation experiments. Spiking coastal sediments (δ¹³C = −25.26 ± 0.06 ‰) with isotopically distinct marine OC (protein-rich Nannochloropsis phytoplankton, δ¹³C = −43.18 ± 0.31 ‰) and terrestrial OC (polysaccharide-rich C₄ corn leaves, δ¹³C = −13.90 ± 0.09 ‰) across 30 microcosms respectively resulted in 10.3 ± 1.5 % and 30.4 ± 3.6 % stimulation of sedimentary OC decomposition in molecular level that last during the course of incubation (32 days). Moreover, we detected synergistic enhancement of the PE in sediments when receiving 1:1 mixtures of marine and terrestrial OC inputs. These amplified, persistent, and source-specific priming responses of sediments to fresh OC discharges show that the mobilization and degradation of previously stabilized native stocks can potentially turn long-term and major sinks of carbon into sources under different perturbed states, having serious implications during ongoing climatic changes.

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09:45 AM

REFINING THE USE OF GLYCEROL DIALKYL GLYCEROL TETRAETHERS (GDGTS) AS PALEOCLIMATE PROXIES IN EASTERN AND WESTERN CANADA. (11238)

Primary Presenter: Adriana Raats, University of Ottawa (adriana.raats.11@gmail.com)

Glycerol dialkyl glycerol tetraethers are a class of lipid biomarkers that in recent decades have been shown to serve as paleoclimate indicators in lake sediment. New research and recent methodological advances have shown that the 5’ methyl branched tetraether index (MBT^5’­­_Me ), among other indices, correlates well with synoptic temperatures, including months above freezing and mean summer temperature. However, the use of the MBT^5’­­_Me as a paleoclimate marker requires the development of calibration estimates for the areas under investigation. Efforts are underway to generate global, regional, and lake-specific temperature calibrations for the MBT^5’_Me index, but to date only two have been generated for Canadian regions. The Arctic, where climate warming is particularly pronounced and relatively understudied, remains particularly under-represented in these global GDGT-temperature calibrations.  This study analyzed two lake sediment transects in Canada, one using lacustrine surface sediment from lakes in Western Canada running parallel to the Rocky Mountains, and the other in Eastern Canada from southern to northern Quebec to create two separate temperature calibrations for use in Canadian ecozones. Preliminary modelling of the transects demonstrate that the MBT^5’_Me index is inversely correlated with latitude, and principal component analyses indicate lipid structure trends consistent with previous studies, showing promising results for its use as a paleoclimate indicator in lake sediments from these regions.

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10:00 AM

NORTH PACIFIC CLIMATE VARIABILITY INFERRED FROM A 600-YEAR SEDIMENTARY LIPID BIOMARKER RECORD AND ECOSYSTEM RESPONSES IN CULTUS LAKE, BRITISH COLUMBIA, CANADA (11173)

Primary Presenter: Daniel Dagodzo, University of Ottawa (ddago070@uottawa.ca)

Branched glycerol dialkyl glycerol tetraethers (brGDGT) are bacterial membrane lipids widely used as indicators of past temperature. We developed a lake-specific brGDGT temperature calibration for Cultus Lake, British Columbia, using seasonally resolved suspended particulate matter and in situ measurements. Among all compounds, brGDGT Ib showed the strongest thermal sensitivity, and multivariate modelling identified two-predictor regression (including Cal1(brGDGT Ib and IIa') and Cal2 (brGDGT Ib and IIb')) that substantially improved temperature prediction compared with the commonly used MBT'5Me index and existing regional or global models. Applying Cal2 to a ~600-year sediment record (since ~1400 CE) reconstructs pronounced multi-centennial temperature variability consistent with independent regional proxies, including tree-ring indices and Na⁺ from Mt. Logan ice core records. This multi-centennial temperature variability tracks sedimentary δ¹⁵N, a proxy for Pacific salmon escapement, until the late nineteenth century, when a sustained δ¹⁵N enrichment reflected increasing anthropogenic nitrogen loading and a decoupling from Pacific salmon escapement dynamics. These results demonstrated that lake-specific brGDGT calibrations capture both long-term regional climate variability and decadal Pacific forcing while highlighting the growing influence of anthropogenic nutrient inputs on modern lake biogeochemistry.

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10:15 AM

GLYCEROL DIALKYL GLYCEROL TETRAETHERS (GDGTs) AS PROXIES TO TRACK URANIUM MILL RELATED ACID ROCK DRAINAGE IN WHISKEY LAKE, ON (11054)

Primary Presenter: Kayla Lerette, University of Ottawa (klere057@uottawa.ca)

As the threat of climate change continues to grow, nuclear energy has risen to prominence as an alternative to fossil fuels; in Canada, it is expected to play a key role in achieving net-zero emissions by 2050. As a result, a more comprehensive understanding of the environmental consequences of uranium mining and milling is essential, particularly as the industry plans to expand into traditional Indigenous lands. Here, we investigate the impacts of uranium mining and milling in sediment cores taken from Whiskey Lake, which was exposed to two episodes of acidic loading from the uranium mines and mills operating in Elliot Lake for approximately 40 years (~1955-1996). We focus on glycerol dialkyl glycerol tetraethers (GDGTs), membrane lipids synthesized by archaea and bacteria, as a novel tool to track acid mine drainage resulting from uranium mining and milling. These lipid structures are sensitive to changes in environmental conditions, and while GDGT-temperature relationships have been widely used for paleoclimatic reconstruction, the GDGT-pH relationship – where increasing cyclization corresponds generally to increasing pH – is relatively less explored. We predicted increased GDGT cyclization in sediments deposited during the release of acid rock drainage associated with intensified mining and milling activity. Results show the utility of GDGTs in tracking periods of acid rock drainage in lake sediments.

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