[1] We simulate a suite of aerosols in the new GISS ModelE GCM: present-day sulfur species and the natural species sea salt, radionuclides 7 Be (stratospheric source), and 210 Pb (derived from 222 Rn from soils). The natural species are used to test the model and to help diagnose the anthropogenic sulfur species. Model improvements over previous versions include increased vertical resolution, addition of a stratiform dissolved species budget (DSB), better tracer coupling to the boundary layer, and an improved relative humidity-dependent radiative scheme. The DSB reduces the loads of most soluble species since it increases stratiform precipitation scavenging. We compare the model with extensive surface and aircraft concentration measurements in the troposphere and stratosphere. We compare three different formulations of the 222 Rn emissions and find that a scheme with reduced radon flux at high latitudes of the Northern Hemisphere for all seasons gives the best 210 Pb results. Although the 222 Rn emissions appear to be approximately the right order of magnitude, model 210 Pb is too large. Conversely, our 7 Be source is too small (since concentrations in the upper troposphere and stratosphere are deficient), while the 7 Be surface concentrations are as observed. These radionuclide results suggests that model scavenging (by moist convection) is deficient. Our new model uses increased natural sulfur emissions; however, the DSB causes sulfate to be generally less than observed and indicates a need for additional sulfur oxidation mechanisms. Model radiative forcing for sulfate and sea salt are À0.54 and À1.1 W m À2 , respectively. The anthropogenic sulfate forcing is À0.25 W m À2 , less than the À0.68 W m À2 in our previous model mainly owing to an 18% decrease in industrial emissions.

Isotope, aerosol, and methane records document an abrupt cooling event across the Northern Hemisphere at 8.2 kiloyears before present (kyr), while separate geologic lines of evidence document the catastrophic drainage of the glacial Lakes Agassiz and Ojibway into the Hudson Bay at approximately the same time. This melt water pulse may have been the catalyst for a decrease in North Atlantic Deep Water formation and subsequent cooling around the Northern Hemisphere. However, lack of direct evidence for ocean cooling has lead to speculation that this abrupt event was purely local to Greenland and called into question this proposed mechanism. We simulate the response to this melt water pulse using a coupled general circulation model that explicitly tracks water isotopes and with atmosphere-only experiments that calculate changes in atmospheric aerosol deposition (specifically 10 Be and dust) and wetland methane emissions. The simulations produce a short period of significantly diminished North Atlantic Deep Water and are able to quantitatively match paleoclimate observations, including the lack of isotopic signal in the North Atlantic. This direct comparison with multiple proxy records provides compelling evidence that changes in ocean circulation played a major role in this abrupt climate change event.

The connection between the production of the cosmogenic isotope 10Be and changes in heliomagnetic activity makes ice core 10Be an attractive proxy for studying changes in solar output. However, interpreting 10Be ice core records on centennial timescales is complicated by potential climate‐related deposition changes that could obscure the 10Be production signal. By using the Goddard Institute for Space Studies ModelE general circulation model to selectively vary climate and production functions, we model 10Be flux at key ice‐coring sites. We vary geomagnetic field strength and the solar activity modulation parameter (ϕ), CO2, sea surface temperatures, and volcanic aerosols to assess impacts on 10Be. Specifically, we find significant latitudinal differences in the response of 10Be fluxes to changes in the production function. In the climate experiments the 10Be deposition changes simulated over ice sheets in both hemispheres are comparable to those seen in the production experiments. This altered deposition combined with changes of snow accumulation results in significant climate‐related 10Be concentration variation in both Greenland and Antarctica. Over the Holocene our results suggest that the 10Be response to climate change should not be neglected when inferring production changes.