Changes in black carbon deposition to Antarctica from two high-resolution ice core records, 1850–2000 AD

Abstract

Refractory black carbon aerosols (rBC) emitted by biomass burning (fires) and fossil fuel combustion, affect global climate and atmospheric chemistry. In the Southern Hemisphere (SH), rBC is transported in the atmosphere from low- and mid-latitudes to Antarctica and deposited to the polar ice sheet preserving a history of emissions and atmospheric transport. Here, we present two high-resolution Antarctic rBC ice core records drilled from the West Antarctic Ice Sheet divide and Law Dome on the periphery of the East Antarctic ice sheet. Separated by ~3500 km, the records span calendar years 1850–2001 and reflect the rBC distribution over the Indian and Pacific ocean sectors of the Southern Ocean. Concentrations of rBC in the ice cores displayed significant variability at annual to decadal time scales, notably in ENSO-QBO and AAO frequency bands. The delay observed between rBC and ENSO variability suggested that ENSO does not directly affect rBC transport, but rather continental hydrology, subsequent fire regimes, and aerosol emissions. From 1850 to 1950, the two ice core records were uncorrelated but were highly correlated from 1950 to 2002 (cross-correlation coefficient at annual resolution: <i>r</i> = 0.54, <i>p</i> < 0.01) due to a common decrease in rBC variability. The decrease in ice-core rBC from the 1950s to late 1980s displays similarities with inventories of SH rBC grass fires and biofuel emissions, which show reduced emission estimates over that period

Characterizing black carbon in rain and ice cores using coupled tangential flow filtration and transmission electron microscopy

“…While post-deposition processes within the glacier cannot be ruled out, volume equivalent diameters of BC particles found in the ice (Bisiaux et al, 2012) are similar to those determined over the remote Southern Ocean by the HIPPO project (Schwarz et al, 2010). Snow densification and ice metamorphosis are more likely to aggregate BC particles into crystal junctions.…”

“…Using an average BC concentration of 0.08 µg kg −1 from the same Law Dome location in Antarctica (Bisiaux et al, 2012) and a concentration ratio of 2 L to 1.5 mL, the final BC concentration of the ice core samples was ∼ 100 µg kg −1 .…”

“…Ice and snow from this site have been the subjects of a large number of studies (Burn-Nunes et al, 2011;Curran et al, 1998;Etheridge et al, 1996;Palmer et al, 2001;Pedro et al, 2012;Vallelonga et al, 2002;Morgan, 1996, 2010). The flux of BC deposition at the same sampling site in Law Dome, East Antarctica has been quantified using an SP2 (Bisiaux et al, 2012). The ice core used in this study was cut longitudinally into two parallel sections, 1 m long with a 5 cm by 5 cm cross-section.…”

“…Murr et al (2004) analyzed particles in ice cores from the Greenland ice cap by melting the ice and depositing 180 mL of sample on a 5 mm TEM grid, a few microliters at a time. As made evident by this process, isolating these particles for characterization is technically challenging, especially in ultra-clean Antarctic ice, where their abundance is often less than 0.1 µg kg −1 (Bisiaux et al, 2012). As Antarctic ice cores have substantially lower BC concentrations than that observed in Greenland ice, larger sample volumes (> 1 L melt water) are necessary to acquire sufficient particles for characterization, making this drop-by-drop method impractical.…”

“…Previous studies have investigated BC mass concentrations in rainwater (Ohata et al, 2011;Torres et al, 2013), snow packs (Hegg et al, 2009;Warren and Clarke, 1990), and ice cores (Bisiaux et al, 2012;McConnell et al, 2007), but little data exists regarding the morphology, chemical composition, and insoluble coatings of BC particles in rain and snow. This is particularly true of aged, long-range transported particles that have been deposited at the polar ice caps.…”