Intensification of the hydrological cycle during Eocene `greenhouse' climates
Abstract
In the absence of strong dynamical changes, warmer climates are expected to be characterised by an intensified hydrological cycle, with a `wet-gets-wetter, dry-gets-drier' response predicted. However, considerable uncertainty exists in both the quantification and spatial distribution of precipitation in past warm climates. Here, we target several intervals during the early Eocene `greenhouse' (ca. 56-48 million years ago; Ma) to assess Earth's hydroclimate response to both gradual (Early Eocene Climatic Optimum; ~53-49 Ma) and transient (Paleocene-Eocene Thermal Maximum; ~56 Ma) warmth.
We have developed a comprehensive proxy `atlas' for the PETM and EECO comprising of both qualitative (e.g., leaf wax hydrogen isotopes, paired clumped isotopes of siderites) and quantitative (plant micro- and macrofossil-based) proxy records. Our plant-based proxies employ an ensemble probability density function approach that offers a consensus estimate across multiple proxies and climate variables. The quantitative proxy records from our atlas indicate enhanced mean annual precipitation (MAP) in the high-latitudes, including the Arctic, relative to modern. This is consistent with a range of qualitative proxy indicators. However, there are relatively few proxy estimates from the mid- and low-latitudes. To broaden our geographic coverage for the early Eocene `greenhouse', we include a reinterpretation of prior published plant proxy estimates, and analyse the hydrogen isotopic composition (δ2H) of leaf wax biomarkers in a suite of globally distributed sites. Preliminary leaf wax δ2H values indicate enhanced poleward moisture transport during the EECO, consistent with PETM-aged records. We will compare our new leaf wax δ2H dataset against isotope-enabled (atmospheric) general circulation models to assess the fidelity of our proxy estimates. Furthermore, we will compare our revised MAP compilation alongside state-of-the-art general circulation models carried out within the framework of DeepMIP (www.deepmip.org) to explore whether the Eocene was indeed characterised by a `wet-gets-wetter, dry-gets-drier' response.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMPP027..07C
- Keywords:
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- 3322 Land/atmosphere interactions;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 1655 Water cycles;
- GLOBAL CHANGE;
- 4914 Continental climate records;
- PALEOCEANOGRAPHY