Millennial changes in North American wildfire and soil activity over the last glacial cycle

Abstract

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...

Chemical compositions of solid particles present in the Greenland NEEM ice core over the last 110,000 years

“…Biomass burning plumes also represent a significant source of aerosol (e.g., KNO 3 , K 2 SO 4 , and KCl) [e.g., Popovicheva et al ., ]. Soluble aerosol of the Arctic region is also secondarily produced from several sources, including NH 3 emitted by bacterial decomposition in soils and biomass burning [e.g., Fuhrer et al , ; Silvente and Legrand , ; Hansson and Holmén , ; Fischer et al , ], sulfur species emitted by marine biological activity (dimethyl sulfide (DMS)) and volcanoes (SO 2 ) [e.g., Legrand and Delmas , ; Hansson and Saltzman , ; Legrand et al , ; Legrand and Mayewski , ], and nitrogen oxides emitted from the surface soil by microorganisms and biomass burning or produced within the troposphere (lightning) and stratosphere (N 2 O oxidation) [e.g., Fuhrer and Legrand , ; Legrand and Mayewski , ; Röthlisberger et al , ]. Secondary aerosol contains salts such as NH 4 NO 3 , NH 4 HSO 4 , and (NH 4 ) 2 SO 4 .…”

“…A useful technique for reconstructing past soluble aerosols from ice cores is the determination of the anions and cations, and this can be done either by ion chromatography [e.g., Legrand et al , , ; Littot et al , ] or fluorescence and absorbance methods [ Röthlisberger et al , ; Kaufmann et al , ; Bigler et al , ]. Using ion concentrations, long‐term aerosol studies have been done on Greenland ice cores from Dye 3 [ Hammer et al , ], Renland [ Hansson , ], Greenland Ice Core Project (GRIP) [ Fuhrer et al , ; De Angelis et al , ; Legrand et al , ], Greenland Ice Sheet Project 2 (GISP2) [ Mayewski et al , ], and North Greenland Ice Core Project (NGRIP) [ Jonsell et al , ; Ruth et al , ; Bigler et al , ; Fischer et al , ]. Concerning specific ions, the concentration of Ca 2+ , a terrestrial proxy, decreases from cold to warm periods up to a factor of 80 between the Last Glacial Maximum (LGM; 15.0–26.9 kyr B.P.)…”

Boreal fire records in Northern Hemisphere ice cores: a review

“…Although again it is not easy to compare this low-resolution Greenland levoglucosan record with high-resolution ammonium Greenland records, we note that the Greenland ammonium records indicate a different picture. Fischer et al (2015) on the basis of the high-resolution (10-110 kyr BP) ammonium record obtained from the North GRIP deep ice core indicated an increase of fire activity at the onset of BA, followed by a weak decrease during the YD, and a second increase toward the beginning of the Holocene. For the Holocene, on the basis of the ammonium record at Summit, Fuhrer et al (1996) Figure 12.…”

“…To investigate the change in fire frequency during the last 1000 years we deployed a similar peak detection technique as in Fischer et al (2015) based on a robust outlier detection method (Fischer et al, 1998). The only difference was that, using singular spectrum analysis, we subtracted small background variations (on the order of 2-5 ppb) from the annual mean NH + 4 data sets before peak detection (Fischer et al, 1998).…”

Historic global biomass burning emissions for CMIP6 (BB4CMIP) based on merging satellite observations with proxies and fire models (1750–2015)

“…Excess ammonium in ice cores has been used as a fire proxy on very long timescales (Fischer et al, 2015), and in rare cases multi-proxy fire reconstructions have also been developed from ice cores (Eichler et al, 2011;Legrand et al, 2016).…”