Simulating climate and stable water isotopes during the Last Interglacial using a coupled climate‐isotope model

Abstract

Understanding the dynamics of warm climate states has gained increasing importance in the face of anthropogenic climate change, and while it is possible to simulate warm interglacial climates, these simulated results cannot be evaluated without the aid of geochemical proxies. One such proxy is δ18O, which allows for inference about both a climate state's hydrology and temperature. We utilize a stable water isotope equipped climate model to simulate three stages during the Last Interglacial (LIG), corresponding to 130, 125, and 120 kyr before present, using forcings for orbital configuration as well as greenhouse gases. We discover heterogeneous responses in the mean δ18O signal to the climate forcing, with large areas of depletion in the LIG δ18O signal over the tropical Atlantic, the Sahel, and the Indian subcontinent, and with enrichment over the Pacific and Arctic Oceans. While we find that the climatology mean relationship between δ18O and temperature remains stable during the LIG, we also discover that this relationship is not spatially consistent. Our results suggest that great care must be taken when comparing δ18O records of different paleoclimate archives with the results of climate models as both the qualitative and quantitative interpretation of δ18O variations as a proxy for past temperature changes may be problematic due to the complexity of the signals.

Water isotopes – climate relationships for the mid-Holocene and preindustrial period simulated with an isotope-enabled version of MPI-ESM

“…For the first case, the small difference between the modeled 6k and PI annual mean temperatures (less than 1 • C; Fig. 5a) and a strong seasonality of precipitation can probably lead to meaningless δ 18 O p -T gradients (Gierz et al, 2017). For the second case, changes in the monsoon strength can explain the very high δ 18 O p -T gradients (more precipitation combined with lower temperatures).…”

“…Using the ECHAM5/MPIOM model, Werner et al (2016) have examined the changes in δ 18 O and d-excess between the LGM and the modern period. This same model has been exploited to examine the δ 18 O-temperature temporal relationship between the LIG and the modern period (Gierz et al, 2017).…”

“…In this paper, we present the first results of a new isotopeenhanced version of the fully coupled Max Planck Institute for Meteorology Earth System Model (MPI-ESM) (Giorgetta et al, 2013;Mauritsen et al, 2019), called hereafter MPI-ESM-wiso. It follows the efforts of Werner et al (2016), who developed the previous model version.…”

Water isotopes – climate relationships for the mid-Holocene and pre-industrial period simulated with an isotope-enabled version of MPI-ESM

“…This result has to be taken in caution, especially for the East Antarctic area where only the EDC site satisfies the required conditions for 0.7 0.5 0.3 0.1 0.1 0.3 0.5 0.7 0.9 1.1 1.3 The δ 18 O p values in polar regions grid boxes might be biased by strong changes of seasonality or intermittency of the precipitation rate (Sime et al, 2009). So, in the same way as Gierz et al (2017), we replace the arithmetic annual mean temperatures by the precipitation-weighted annual mean temperatures in the calculation of the δ 18 O p -T gradients (Fig. 11).…”

“…Using the ECHAM5/MPIOM model, Werner et al (2016) have examined the changes in δ 18 O and dex between the LGM and the modern period. This same model has been exploited to examine the δ 18 O-temperature temporal relationship between the LIG and the modern period (Gierz et al, 2017).…”