Understanding the temporal slope of the temperature‐water isotope relation during the deglaciation using isoCAM3: The slope equation

Abstract

The temporal and spatial slopes of water isotope‐temperature relations are studied for the last 21,000 years over the middle and high latitudes using a series of snapshot simulations of global climate and water isotopes in the isotope‐enabled atmospheric model isoCAM3. Our model simulation suggests that both the temporal slope and spatial slope remain largely stable throughout the last deglaciation. Furthermore, the temporal slope can vary substantially across regions. Nevertheless, on average, and most likely, the temporal slope is about 0.3‰ °C−1 and is about half of the spatial slope. Finally, the relation between temporal and spatial slopes is understood using a semiempirical equation that is derived based on both the Rayleigh distillation and a fixed spatial slope. The slope equation quantifies the Boyle's mechanism and suggests that the temporal slope is usually smaller than the spatial slope in the extratropics mainly because of the polar amplification feature in global climate change, such that the response in local temperature at middle and high latitudes is usually greater than that in the total equivalent source temperature.

Impact of abrupt sea ice loss on Greenland water isotopes during the last glacial period

“…2 B ) (i.e., we find a strong systematic relationship between the size of the abrupt warming and the paleothermometer coefficient at all Greenland ice core sites). This finding also provides support for the idea that the paleothermometer is fundamentally dependent on the change in temperature at high latitude ( 32 ). The pattern varies over Greenland: small decreases occur in the paleothermometer coefficient with warming event size at DYE3 compared with large decreases in the coefficient at NEEM.…”

The Connected Isotopic Water Cycle in the Community Earth System Model Version 1

“…This is particularly true for locations with annual average temperatures less than 5 °C, where the iCESM1 slope is substantially shallower than the GNIP observations (not shown). This overly shallow slope in iCESM1 appears larger than was the case in iCAM3 (Guan et al, ), and may be related to biases in extratropical moisture transport in iCAM5, as discussed in Nusbaumer et al (). Further, the precipitation rate versus δ 18 O slope, which can be thought of as representing the “amount effect” (Dansgaard, ), is too strong in iCESM1 relative to observations (Figure c).…”

“…The CESM is one of the most widely used climate models in the world, owing to its unique open‐source nature and the availability of publicly hosted community ensemble simulations (Kay et al, ; Otto‐Bliesner et al, ). However, although some components of the previous model versions (e.g., CCM3, CAM2, Community Atmosphere Model, version 3 (CAM3)) have included isotopic simulation capacity (e.g., Guan et al, ; Tharammal et al, ), to date no isotopic processes had been included in the fully coupled CESM. This new model version (hereafter “iCESM1”) thus represents a significant technical advance, as the isotopic simulation capabilities will be retained through successive model generations.…”

Antarctic surface temperature and elevation during the Last Glacial Maximum

“…in the 0.1 to 0.6 ‰ K -1 range, and thus considerably lower than the spatial slope (6,8,11,135) in the 0.6 to 0.9 ‰ K -1 range and thus comparable to the spatial slope (5,6,8,12,136) in the 0.9 to 1.6 ‰ K -1 range and thus considerably larger than the spatial slope (12, 137) (this study) Note that it is not trivial to compile the temporal slopes consistently, given that papers report values at different locations and time intervals, and the fact that the simulated temporal slopes tend to be highly variable between nearby location (8,138). A systematic iGCM intercomparison would be highly valuable to the field.…”