Modeling oxygen isotopes in the Pliocene: Large-scale features over the land and ocean

Abstract

The first isotope-enabled general circulation model (GCM) simulations of the Pliocene are used to discuss the interpretation of 18 O measurements for a warm climate. The model suggests that spatial patterns of Pliocene ocean surface 18 O ( 18 O sw ) were similar to those of the preindustrial period; however, Arctic and coastal regions were relatively depleted, while South Atlantic and Mediterranean regions were relatively enriched. Modeled 18 O sw anomalies are closely related to modeled salinity anomalies, which supports using 18 O sw as a paleosalinity proxy. Modeled Pliocene precipitation 18 O ( 18 O p ) was enriched relative to the preindustrial values (but with depletion of < 2‰ over some tropical regions). While usually modest (<4‰), the enrichment can reach 25‰ over ice sheet regions. In the tropics 18 O p anomalies are related to precipitation amount anomalies, although there is usually a spatial offset between the two. This offset suggests that the location of precipitation change is more uncertain than the amplitude when interpreting 18 O p . At high latitudes 18 O p anomalies relate to temperature anomalies; however, the relationship is neither linear nor spatially coincident: a large 18 O p signal does not always translate to a large temperature signal. These results suggest that isotope modeling can lead to enhanced synergy between climate models and climate proxy data. The model can relate proxy data to climate in a physically based way even when the relationship is complex and nonlocal. The 18 O-climate relationships, identified here from a GCM, could not be determined from transfer functions or simple models.

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

“…Potential past changes in the seasonality of precipitation were also identified as highly important in these studies, especially for Greenland. A further study with the fully coupled isotope‐enabled GCM HadCM3 [ Tindall and Haywood , ], which is comparable to our coupled model setup, also concluded that the δ 18 O‐T relationship might have changed in time and space. However, this simulation was performed for the warm climate of the Pliocene, not the LIG.…”

Constraining past seawater δ 18 O and temperature records developed from foraminiferal geochemistry

“…PSU Solver can be suitably modified to address problems on timescales or foraminiferal species outside our example data sets, including important paleoclimate targets where seawater Mg/Ca was different from the modern ocean [ O ' Brien et al ., ; Ravelo et al ., ; Zhang et al ., ; Lear et al ., ]. The underlying code can also be suitably modified to address the nonstationarity of past δ 18 O sw ‐salinity relationships where modeling studies can provide important constraints on this problem [ Caley and Roche , ; Tindall and Haywood , ; Holloway et al ., ]. Such a temporal bias may be explicitly incorporated into PSU Solver by applying appropriate δ 18 O sw ‐salinity equations, furnished by paleoclimate simulations, in a piecewise manner.…”

A modeling study of the response of Asian summertime climate to the largest geologic forcings of the past 50 Ma

“…However, the overall pattern of forcing associated with CO 2 differences is quite uniform in both space and time. Because of this, the differences in atmospheric circulation and precipitation are relatively small (Figure b) and, therefore, the response is also fairly uniform: an enrichment of 1 to 2‰ over land (Figure c), consistent with increased specific humidity (not shown) and thus less Rayleigh fractionation over a warmer continent [e.g., Tindall and Haywood , ].…”