141-9 Water in unexpected places

Session: New Advances in Geobiology

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With climate change worsening, understanding how animals adapt to water scarcity is becoming increasingly important. Triple oxygen isotope analysis is an incredibly powerful tool to trace water sources in animals by distinguishing from contributions like pre-formed water, food-oxygen, and atmospheric O₂. Some of these models use general assumptions about animal physiology and leaf water evaporation to predict environmental conditions. Because of this, paleoclimatologists have created ¹⁷O-based body water models for paleoclimate reconstruction.  To ground truth these models in modern systems we have developed an equilibration method using CO₂–H₂O oxygen exchange allowing us to measure δ^’18O and Δ^’17O values via tunable infrared laser direct absorption spectroscopy (TILDAS). Validated against traditional cryogenically distilled water methods, this technique enables streamlined analysis of whole blood and plant samples. Applied to desert-dwelling rodents (Heteromyidae), our method revealed seasonal shifts in water use, with free water contribution closely tracking precipitation events. This was unexpected because kangaroo rats (Dipodomys sp.) eat water poor seeds and do not drink water, so this increase in free water contribution must come from seed rehydration and/or vapor uptake in high relative humidity burrows. This usage of water via seed rehydration or water vapor uptake in burrows shows the critical role burrowing plays in water conservation for survival in desert ecosystems and underscores the need to consider how animal lifestyle history and behavior can contribute non-conventional water sources. With desert plants, our method revealed limitations in modeling leaf water and validated a ϴ value of 0.511 for leaf water evaporation, instead of the generally accepted ϴ value of 0.518. This lower theta value allows the model to predict Δ^’17O values down to around -600 per meg, matching measured values of heavily enriched desert leaf water in this study. The diurnal enrichment in leaf water also challenges the hypothesis of using relative humidity as the major defining factor of leaf water enrichment and instead shows that a sliding-scale approach may be more effective when predicting leaf water δ^’18O and Δ^’17O values. These deviations from previously made assumptions underscores the need for further ground truthing of body water models with modern systems across ecosystems and species.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9408

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