The Northern Hemisphere experienced dramatic changes during the last glacial, featuring vast ice sheets and abrupt climate events, while high northern latitudes during the last interglacial (Eemian) were warmer than today. Here we use high-resolution aerosol records from the Greenland NEEM ice core to reconstruct the environmental alterations in aerosol source regions accompanying these changes. Separating source and transport effects, we find strongly reduced terrestrial biogenic emissions during glacial times reflecting net loss of vegetated area in North America. Rapid climate changes during the glacial have little effect on terrestrial biogenic aerosol emissions. A strong increase in terrestrial dust emissions during the coldest intervals indicates higher aridity and dust storm activity in East Asian deserts. Glacial sea salt aerosol emissions in the North Atlantic region increase only moderately (50%), likely due to sea ice expansion. Lower aerosol concentrations in Eemian ice compared to the Holocene are mainly due to shortened atmospheric residence time, while emissions changed little.

Abstract. The seasonal and annual representativeness of ionic aerosol proxies (among others, calcium, sodium, ammonium and nitrate) in various firn cores in the vicinity of the NEEM drill site in northwest Greenland have been assessed. Seasonal representativeness is very high as one core explains more than 60 % of the variability within the area. The inter-annual representativeness, however, can be substantially lower (depending on the species) making replicate coring indispensable to derive the atmospheric variability of aerosol species. A single core at the NEEM site records only 30 % of the inter-annual atmospheric variability in some species, while five replicate cores are already needed to cover approximately 70 % of the inter-annual atmospheric variability in all species.The spatial representativeness is very high within 60 cm, rapidly decorrelates within 10 m but does not diminish further within 3 km. We attribute this to wind reworking of the snow pack leading to sastrugi formation.Due to the high resolution and seasonal representativeness of the records we can derive accurate seasonalities of the measured species for modern (AD 1990(AD -2010 times as well as for pre-industrial (AD 1623-1750) times. Sodium and calcium show similar seasonality (peaking in February and March respectively) for modern and pre-industrial times, whereas ammonium and nitrate are influenced by anthropogenic activities. Nitrate and ammonium both peak in May during modern times, whereas during pre-industrial times ammonium peaked during July-August and nitrate during June-July.

Climate changes in the NorthWildfires represent an important driver in ecosystem development 1 and pyrogenic emissions of trace gases, black carbon and other aerosol components have a strong regional effect on the radiation balance and atmospheric chemistry 2 . A detailed understanding of the response of vegetation and wildfire activity to climate change is hampered by the relatively long timescales of ecosystem change and fire recurrence.Paleoclimate information can help in this regard, documenting a wide range of climate and environmental changes on orbital, millennial and decadal timescales.During the last glacial cycle, the climate of the northern hemisphere was fundamentally altered as ice cover and sea level varied 3 , impacting the areal extent of vegetation and its composition. On top of these slow changes, the North Atlantic region was characterized by rapid DO warmings, where temperatures in Greenland increased by 10--15°C in a few decades 4,5 . These events also had strong, far--field effects on boreal and tropical methane emissions 6 , monsoon intensity 7 and dust emissions in Chinese desert areas 8,9 . However, there is little paleoclimate information available from North America (NA), especially at a resolution allowing the identification of DO events in continental, ice--free regions 10--14 .In particular, the continent--wide reconstruction of wildfire activity based on charcoal records does not extend beyond the last glacial/interglacial transition 1,15 . 3 North American soil and wildfire signal in Greenland ice coresGreenland ice cores can fill this gap because aerosol--transported NH4 + in the ice comes from NA soil emissions but (together with other pyrogenic aerosol tracers 16,17 ) also from NA wildfire events 17,18 . Background NH4 + concentrations in Greenland are derived mainly from bacterial decomposition of nitrogen in NA soils 19 , leading to a broad NH4 + summer maximum in Greenland ice 18,20 . On top of this mean annual cycle, very large peaks are detected during individual summers, caused by NA biomass burning events 21,22 , also characterised by co--occurring peaks in fire--specific organic aerosol compounds 17,23 . These events exceed the NH4 + background by more than an order of magnitude and dominate the Greenland NH4 + budget in those years 18,20 . The imprint of these events is strongly dependent on atmospheric circulation at the time of the fire, which must be favourable for long--range transport from NA to Greenland. Accordingly, not all fire events are recorded in Greenland ice. However, averaged over a sufficient time period, ice core records can provide a reliable picture of relative changes in NA wildfire frequency 18 . When measured at high resolution, the NH4 + ice core record can provide the change in average background NH4 + from soil emissions, concentrations of fire events above this background and fire peak frequency (FPF).In this study, Greenland NH4 + concentrations were measured in cm--resolution on the NGRIP ice core with our Continuous Flow Analysis 24,25 sys...