Glacial–interglacial changes in H<sub>2</sub><sup>18</sup>O, HDO and deuterium excess – results from the fully coupled ECHAM5/MPI-OM Earth system model

Abstract

Abstract. In this study we present the first results of a new isotope-enabled general circulation model set-up. The model consists of the fully coupled ECHAM5/MPI-OM atmosphere-ocean model, enhanced by the JSBACH interactive land surface scheme and an explicit hydrological discharge scheme to close the global water budget. Stable water isotopes H 2 18 O and HDO have been incorporated into all relevant model components. Results of two equilibrium simulations under pre-industrial and Last Glacial Maximum conditions are analysed and compared to observational data and paleoclimate records for evaluating the model's performance in simulating spatial and temporal variations in the isotopic composition of the Earth's water cycle. For the pre-industrial climate, many aspects of the simulation results of meteoric waters are in good to very good agreement with both observations and earlier atmosphere-only simulations. The model is capable of adequately simulating the large spread in the isotopic composition of precipitation between low and high latitudes. A comparison to available ocean data also shows a good model-data agreement; however, a strong bias of overly depleted ocean surface waters is detected for the Arctic region. Simulation results under Last Glacial Maximum boundary conditions also fit to the wealth of available isotope records from polar ice cores, speleothems, as well as marine calcite data. Data-model evaluation of the isotopic composition in precipitation reveals a good match of the model results and indicates that the temporal glacial-interglacial isotopetemperature relation was substantially lower than the present spatial gradient for most mid-to high-latitudinal regions. As compared to older atmosphere-only simulations, a remarkable improvement is achieved for the modelling of the deuterium excess signal in Antarctic ice cores. Our simulation results indicate that cool sub-tropical and mid-latitudinal sea surface temperatures are key for this progress. A recently discussed revised interpretation of the deuterium excess record of Antarctic ice cores in terms of marine relative humidity changes on glacial-interglacial timescales is not supported by our model results.

Stable water isotopes in the MITgcm

“…Despite these sources of error, the simulated pattern of δ 18 O w both at the sea surface as well as in the deep ocean agrees fairly well with other recent studies such as the study by Xu et al (2012) with an OGCM as well as the studies by Roche and Caley (2013) and Werner et al (2016) with fully coupled models.…”

The PMIP4 contribution to CMIP6 – Part 4: Scientific objectives and experimental design of the PMIP4-CMIP6 Last Glacial Maximum experiments and PMIP4 sensitivity experiments

“…with well-stratified glacial ocean states), to minimize spin-up duration. Such ocean states, such as described in Werner et al (2016), which provide 3-D fields of sea temperature, salinity, and associated stable water isotopes on a regular 1 • × 1 • grid, are available on the PMIP4 website and from the PMIP2 and PMIP3 databases.…”

“…Both the change in ice sheets and in GHG concentrations are negative radiative forcings and contribute, with impacts of similar orders of magnitude, to a climate much colder than today (e.g. Yoshimori et al, 2009;Brady et al, 2013). They are the main drivers of differences in the LGM atmosphere compared to present or pre-industrial conditions.…”

“…Analysis of the processes involved in the temperature response to the forcings (i.e. GHG for current-to-future warming, and ice sheets and GHG for the LGM-to-pre-industrial warming) are essential for this investigation, because while some feedbacks appear to work in a similar manner for LGM-to-pre-industrial and for future warming, feedbacks such as the cloud radiative feedback do not (Yoshimori et al, 2009). The relative magnitudes of the different feedbacks also vary between those two climates, so that the relationship with climate sensitivity is not straightforward .…”

FAME (v1.0): a simple module to simulate the effect of planktonic foraminifer species-specific habitat on their oxygen isotopic content

“…The equilibrium 15 calcite oxygen-18 in that case is computed from annual averaged seawater temperatures and oxygen-18 taken either at surface or averaged over the upper 50 to 100 meters of the water column (e.g. Caley et al, 2014;Werner et al, 2016). To go one step further, it is necessary to account for species-specific habitat when computing calcite oxygen-18.…”