Seasonal and interannual variability of the mineral dust cycle under present and glacial climate conditions

Abstract

[1] We present simulations of the dust cycle during present and glacial climate states, using a model, which explicitly simulates the control of dust emissions as a function of seasonal and interannual changes in vegetation cover. The model produces lower absolute amounts of dust emissions and deposition than previous simulations of the Last Glacial Maximum (LGM) dust cycle. However, the simulated 2-to 3-fold increase in emissions and deposition at the LGM compared to today, is in agreement with marine-and ice-core observations, and consistent with previous simulations. The mean changes are accompanied by a prolongation of the length of the season of dust emissions in most source regions. The increase is most pronounced in Asia, where LGM dust emissions are high throughout the winter, spring and summer rather than occurring primarily in spring as they do today. Changes in the seasonality of dust emissions, and hence atmospheric loading, interact with changes in the seasonality of precipitation, and hence of the relative importance of wet and dry deposition processes at high northern latitudes. As a result, simulated dust deposition rates in the high northern latitudes show high interannual variability. Our results suggest that the high dust concentration variability shown by the Greenland ice core records during the LGM is a consequence of changes in atmospheric circulation and precipitation locally rather than a result of changes in the variability of dust emissions.

A simulation of the global distribution and radiative forcing of soil dust aerosols at the Last Glacial Maximum

“…Werner et al (2002) estimated a 2.2-fold higher dust emission flux at LGM compared to PRE, which is close to this study, though their estimation of the total LGM flux was smaller (2383 Tg/yr). The dust emission flux under the present climate condition is estimated to be 2594 Tg/yr in this study, which is in agreement with most past studies, ranging about from 1500 to 3000 Tg/yr (e.g., Tegen and Fung, 1994;Dentener et al, 1996;Chin et al, 2002;Tanaka and Chiba, 2005), while Werner et al (2002) estimated it to be 1060 Tg/yr. Reasons for the high dust emission flux at LGM could be due not only to expansion of emission sources but also to stronger winds during this period.…”

“…The simulation suggests that about 60% of the increase in the global total dust emission at LGM relative to PRE is due to a difference in the meteorological conditions, especially the strong winds and less precipitation, and the other is due to a difference in vegetation. These contributions to the increase in LGM dust emissions are close to the ones computed by Werner et al (2002). Figure 3c and d shows simulated global distributions of the annual mean dust column loading at LGM and PRE, respectively, and Table 3 shows zonal column loading and deposition flux of soil dust aerosols.…”

“…They showed that changes in source areas are required to predict any substantial increase in the dust deposition over the polar regions. Werner et al (2002) suggested from their simulation that one third of the increase in the total global dust emission flux in the LGM is related to source-region changes, while two thirds is caused by glacial wind speed changes over modern dust emission regions. Mahowald et al (2006) indicated that low CO 2 concentration at the LGM resulted in expanding dust sources through less fertilization of vegetation.…”

Links between Patagonian Ice Sheet fluctuations and Antarctic dust variability during the last glacial period (MIS 4-2)

“…Studies based on nssCa 2þ and sea-salt Na þ fluxes of EDC and EDML ice cores provide evidences that the transport time for dust from Patagonia to Antarctica has not changed strongly between the last glacial and the Holocene (Fischer et al, 2007b). As well, most of general circulation models suggest modest changes in atmospheric transport (Mahowald et al, 1999;Werner et al, 2002;Krinner and Genthon, 2003), or changes which are too small to account for the large dust variability as recorded in ice cores (Röthlisberger et al, 2002). However, the northward expansion of Antarctic seaice (Crosta et al, 2004;Gersonde et al, 2005) and evidences from paleoenvironmental reconstructions in southern South America (Markgraf et al, 1992;Lamy et al, 1999;Moreno et al, 1999 2008) suggest a northward extension of the SWW during the last glacial period.…”

Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core

“…We interpret this as progressive coupling of the climates of Antarctic and lower latitudes. Limited changes in glacial2interglacial atmospheric transport time 4,9,10 suggest that the sources and lifetime of dust are the main factors controlling the high glacial dust input. We propose that the observed 25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.…”