Oxygen Isotopic Signatures of Major Climate Modes and Implications for Detectability in Speleothems
Creators: name: Midhun, M.
name: Stevenson, S.
name: Cole, J. E.
Publisher: name: NOAA National Centers for Environmental Information
Year: 2021
Subjects: subject: AMO
subject: speleothem
subject: stable isotope
subject: PDO
subject: paleoclimate
subject: ENSO
subject: Geological Sciences
subject: Science

description: Natural and social systems worldwide are impacted by climate modes such as the El Niño/Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO), making it imperative to understand their sensitivity to climate change. Paleoclimate studies extend the observational climate baseline, and speleothem records (δ18Ospel) are a common data source. However, relationships between δ18Ospel and climate modes are uncertain; climate models provide a way to test the strength and stability of these relationships. Here, we use the isotope‐enabled Community Earth System Model’s Last Millennium Ensemble combined with a forward proxy model to delineate the global expression of modal variability in “pseudo‐stalagmite” (δ18Ospel) records worldwide. The modeled δ18Ospel spatially correlates with modal signatures. However, substantial changes in modal variance only modestly affect individual δ18Ospel variance. A network of δ18Ospel records, particularly one that straddles the Pacific, significantly improves the reconstructability of ENSO variance.Plain Language SummaryClimate variability on interannual‐decadal timescales often takes the form of coherent patterns (“modes”), such as the El Niño/Southern Oscillation (ENSO) phenomenon of the tropical Pacific. These patterns strongly impact global climate, and how they will change as the world warms remains uncertain. Although instrumental climate records are relatively short, paleoclimate records reveal past changes in these modes, allowing us to document their ranges of natural variability. A common approach is to use records of oxygen isotopic variations preserved in, for example, cave formations. To interpret these data, we must understand how climate modes impact the local isotopic content of precipitation and account for how paleoclimate data record this signal. Here, we use a climate model that includes isotope physics in the hydrologic cycle to show that although the oxygen isotope record in cave formations is influenced by different climate modes, the magnitude of the signal at any individual site appears relatively small. However, in the model, combining cave records from multiple regions can reconstruct past changes in the strength of ENSO. Multidecadal modes are more challenging to reconstruct from modeled cave records, perhaps reflecting model biases toward too‐weak multidecadal variability and too‐strong ENSO.Key PointsCoherent δ18O patterns are associated with the El Niño Southern Oscillation/Pacific Decadal Oscillation/Atlantic Multidecadal OscillationChanges in the strength of major climate modes lead to relatively small changes in the speleothem δ18O variability at individual sitesUsing a well‐distributed network of speleothem δ18O greatly increases the fidelity of modal variance reconstructions