Abstract
Abstract. Pleistocene benthic δ18O records exhibit strong spectral power at ~41 kyr, indicating that global ice volume has been modulated by Earth's axial tilt. This feature, and weak spectral power in the precessional band, has been attributed to the influence of obliquity on mean annual and seasonal insolation gradients at high latitudes. In this study, we use a coupled ocean-atmosphere general circulation model to quantify changes in continental snowfall associated with mean annual and seasonal insolation forcing due to a change in obliquity. Our model results indicate that insolation changes associated with a decrease in obliquity amplify continental snowfall in three ways: (1) Local reductions in air temperature enhance precipitation as snowfall. (2) An intensification of the winter meridional insolation gradient strengthens zonal circulation (e.g. the Aleutian low), promoting greater vapor transport from ocean to land and snow precipitation. (3) An increase in the summer meridional insolation gradient enhances summer eddy activity, increasing vapor transport to high-latitude regions. In our experiments, a decrease in obliquity leads to an annual snowfall increase of 25.0 cm; just over one-half of this response (14.1 cm) is attributed to seasonal changes in insolation. Our results indicate that the role of insolation gradients is important in amplifying the relatively weak insolation forcing due to a change in obliquity. Nonetheless, the total snowfall response to obliquity is similar to that due to a shift in Earth's precession, suggesting that obliquity forcing alone can not account for the spectral characteristics of the ice-volume record.
Highlights
It has long been known that the Quaternary global icevolume record, archived in benthic δ18O, varies at orbital frequencies (Hays et al, 1976; Imbrie, 1980, 1985, 1993)
Though precession has a large influence on high-latitude summer insolation intensity, this influence is counteracted by a change in the duration of summer due to variations in Earth’s angular speed as it revolves around the Sun
Raymo et al (2006) proposes that the change in benthic δ18O due to the increase in the NH ice volume was offset by the melting of the West Antarctic Ice Sheet due to out-of-phase precessional insolation forcing between the two hemispheres
Summary
It has long been known that the Quaternary global icevolume record, archived in benthic δ18O, varies at orbital frequencies (Hays et al, 1976; Imbrie, 1980, 1985, 1993). A number of studies have suggested that an increase in the seasonal equator-to-pole insolation gradient might have enhanced snowfall over ice sheets due to greater latent heat transport and internal climate processes (e.g. ENSO-like oscillation) (Johnson, 1991; Khodri et al, 2001; Vettoretti and Peltier, 2003, 2004; Kukla and Gavin, 2004). In support of these ideas, Raymo and Nisancioglu (2003) show that the summer equator-to-pole insolation gradient is in-phase with benthic δ18O during the early Pleistocene.
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