T202 Lakes of the World through Time and Space II: Archives of Climate Variability, Paleoenvironment, Geohazards, and Economic Resources

Tuesday, 17 October 2023
1:30 PM - 5:30 PM
334

LAKE SEDIMENT INSIGHTS INTO BIOGEOCHEMICAL CYCLING UNDER DIFFERENT REDOX ENVIRONMENTS

Paper number: T202-3
Program: Technical Sessions
Time: 1:50 PM – 2:05 PM

Authors

Abstract

With rising surface water temperatures due to climate change, lakes are expected to experience widespread, prolonged periods of seasonal stratification and low-oxygen conditions. Changes to hypolimnetic oxygen levels will affect the composition and preservation of organic matter. The organic carbon (δ13Corg) and bulk nitrogen (δ15N) isotope composition of sedimentary organic matter has been widely used to trace biogeochemical cycling in lacustrine environments. This study aims to determine associations between water column oxygenation and lake sediment isotope composition by compiling a global dataset of 217 lakes with 43 anoxic and 174 oxic lakes. Anoxic and oxic lake sediments form a dataspace ranging from δ15N: +10 to -10‰ and δ13Corg: -31 to -20‰. Anoxic lakes contain more positive and negative values for δ13Corg likely reflective of a diversity of microbial metabolisms under anaerobic waters. Oxic lakes contain more negative values for δ15N potentially indicating atmospheric or anthropogenic influences. Based on a subset of anoxic (n = 13) and oxic (n = 21) lakes containing a wider array of physiographic parameters, anoxic lakes show a negative correlation between lake elevation and δ13Corg as well as δ15N, meanwhile, oxic lakes exhibit a positive correlation between δ15N and lake elevation. Therefore, while C and N cycles are typically considered to be tightly coupled, we find important differences related to oxygenation that have implications for understanding future biogeochemical cycling as well as for interpreting the rock record. Paleolake formations (n = 11) often plot within the modern data array, but lakes reconstructed as alkaline (pH > 9) can have more extreme δ15N and δ13Corg values than any modern lakes, and typically have δ15N values values in excess of 10‰, supporting previous studies that have suggested this threshold for alkaline paleolake deposits. Future work will focus on using this dataset to identify geochemical and lake morphological variables that drive isotopic trends under different lake oxygen conditions.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-395480

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