Greenland accumulation and its connection to the large-scale atmospheric circulation in ERA-Interim and paleoclimate simulations

Abstract

Abstract. Changes in Greenland accumulation and the stability in the relationship between accumulation variability and large-scale circulation are assessed by performing timeslice simulations for the present day, the preindustrial era, the early Holocene, and the Last Glacial Maximum (LGM) with a comprehensive climate model. The stability issue is an important prerequisite for reconstructions of Northern Hemisphere atmospheric circulation variability based on accumulation or precipitation proxy records from Greenland ice cores. The analysis reveals that the relationship between accumulation variability and large-scale circulation undergoes a significant seasonal cycle. As the contributions of the individual seasons to the annual signal change, annual mean accumulation variability is not necessarily related to the same atmospheric circulation patterns during the different climate states. Interestingly, within a season, local Greenland accumulation variability is indeed linked to a consistent circulation pattern, which is observed for all studied climate periods, even for the LGM. Hence, it would be possible to deduce a reliable reconstruction of seasonal atmospheric variability (e.g., for North Atlantic winters) if an accumulation or precipitation proxy were available that resolves single seasons. We further show that the simulated impacts of orbital forcing and changes in the ice sheet topography on Greenland accumulation exhibit strong spatial differences, emphasizing that accumulation records from different ice core sites regarding both interannual and long-term (centennial to millennial) variability cannot be expected to look alike since they include a distinct local signature. The only uniform signal to external forcing is the strong decrease in Greenland accumulation during glacial (LGM) conditions and an increase associated with the recent rise in greenhouse gas concentrations.

Dependence of Eemian Greenland temperature reconstructions on the ice sheet topography

“…A PI simulation with perpetual AD 1850 conditions is used as reference simulation for the paleosimulations since it describes the present climate without perturbation by human activities. This PI simulation has previously been used and described in Merz et al (2013). Moreover, five Eemian (referred to as EEM) sensitivity simulations with perpetual 125 ka conditions but different GrIS implementations are conducted: EEMpd with present-day GrIS, EEMr1 with a moderately retreated GrIS from Robinson et al (2011), EEMr2 with a strongly retreated GrIS from Robinson et al (2011), EEMr3 with the same GrIS mask as EEMr2 but without the South Dome, and EEMr4 with the simulated Eemian GrIS from Born and Nisancioglu (2012).…”

Warm Greenland during the last interglacial: the role of regional changes in sea ice cover

“…In the successor model, CCSM4, these biases have been substantially improved through changes in sea ice albedo and ocean overflow parameterizations (Gent et al, 2011). Further, CCSM4 shows in general good skill in simulating the present-day surface climate and atmospheric circulation in and around Greenland (Vizcaino et al, 2013;Merz et al, 2013Merz et al, , 2014b. Hence, we have good confidence in CCSM4's capability in representing the components of the North Atlantic and Greenland climate system that are of importance for this study, e.g., SAT, surface energy fluxes, surface winds, or precipitation.…”

An ice sheet model of reduced complexity for paleoclimate studies

“…We employ simulations of both preindustrial (PI) and glacial (LGM) climates (Table 2, Fig. 2), which have been analyzed and validated earlier by Hofer et al (2012) and Merz et al (2013). The lower boundary conditions for the sea surface are derived from fully coupled simulations with the preceding model version, CCSM3, as outlined in detail in the original publications.…”

“…This is an important mechanism because it influences the melt-400 B. Neff et al: An ice sheet model of reduced complexity for paleoclimate studies Table 2. List of CCSM4 simulations of preindustrial (PI) and Last Glacial Maximum (LGM) climates (Hofer et al, 2012;Merz et al, 2013) which are used as climate forcing in the ice model. Orbital parameters are calculated according to Berger (1978).…”

“…Similarly, meridional water transport from the tropics to high latitudes, arguably controlled by insolation gradients instead of absolute values, has been suggested as a limiting factor of ice sheet growth (Raymo and Nisancioglu, 2003). Changes in topography due to the accumulation of ice alter the atmospheric circulation on local (Merz et al, 2014a, b) and hemispheric scales (Li and Battisti, 2008;Pausata et al, 2011;Merz et al, 2013). As ice sheets are usually brighter than the surface they replace, they impact the planetary radiation balance in the short-wavelength part of the spectrum (Cess et al, 1991).…”