Holocene black carbon in Antarctica paralleled Southern Hemisphere climate

Abstract

Black carbon (BC) and other biomass‐burning (BB) aerosols are critical components of climate forcing, but quantification, predictive climate modeling, and policy decisions have been hampered by limited understanding of the climate drivers of BB and by the lack of long‐term records. Prior modeling studies suggested that increased Northern Hemisphere anthropogenic BC emissions increased recent temperatures and regional precipitation, including a northward shift in the Intertropical Convergence Zone (ITCZ). Two Antarctic ice cores were analyzed for BC, and the longest record shows that the highest BC deposition during the Holocene occurred ~8–6 k years before present in a period of relatively high austral burning season and low growing season insolation. Atmospheric transport modeling suggests South America (SA) as the dominant source of modern Antarctic BC and, consistent with the ice core record, climate model experiments using mid‐Holocene and preindustrial insolation simulate comparable increases in carbon loss due to fires in SA during the mid‐Holocene. SA climate proxies document a northward shifted ITCZ and weakened SA Summer Monsoon (SASM) during this period, with associated impacts on hydroclimate and burning. A second Antarctic ice core spanning the last 2.5 k years documents similar linkages between hydroclimate and BC, with the lowest deposition during the Little Ice Age characterized by a southerly shifted ITCZ and strengthened SASM. These new results indicate that insolation‐driven changes in SA hydroclimate and BB, likely linked to the position of the ITCZ, modulated Antarctic BC deposition during most of the Holocene and suggests connections and feedbacks between future BC emissions and hydroclimate.

Refractory Black carbon (rBC) variability in a 47-year West Antarctic Snow and Firn core

“…We considered the new year to match the end of what we define as the dry season, as this is a reliable tie point in the record due to the abrupt drop in rBC concentrations based on the BC emission estimates from GFED4s and the fire spot databases from Australia and South America. This is also in agreement with Winstrup et al (2017) as the authors state that BC tends to peak a little earlier than New Year in their records (Roosevelt Island Ice Core -RICE) and to Arienzo et al (2017) as the WAIS Divide ice core presents rBC peaks in September. Also, the Pinatubo and Cerro Hudson eruptions (1991) identified in the record by Schwanck et al (2016) and Thoen et al (2018) were used as an absolute time horizon.…”

“…These initial studies used filter-based methods, which could under-or overestimate BC concentrations due to some analytical artifacts (Soto-García et al, 2011;Torres et al, 2014;Wang et al, 2012). Studies using the SP2 started appearing more than two decades later, aiming at recent snow rBC concentrations (Casey et al, 2017;Khan et al, 2019), near-surface air (Khan et al, 2018), recent-past ice cores (couple centuries - Bisiaux et al, 2012aBisiaux et al, , 2012b and the past millennia (Arienzo et al, 2017). From these, a few rBC records overlap temporally with the TT07 core presented in this work, and are presented in Table 4.…”

“…Although Southern Africa has the largest BC emissions in the SH, it is not considered to be a significant contributor to the aerosol load in Antarctica (Li et al, 2008;Neff and Bertler, 2015;Stohl and Sodemann, 2010). Both Australia (Bisiaux et al, 2012a) and South America (Arienzo et al, 2017) have been suggested as sources of BC to West Antarctica. Figure 6a shows the rBC monthly average values for TT07 and BC monthly-averaged BC emissions from GFED4s (1997GFED4s ( -2015 for the four SH emission regions (regions defined in GFED4s, see website).…”

“…Antarctica is a pristine environment far from the rest of the world, but black carbon can still be found in its atmosphere, snow and ice, as shown by early studies (Chýlek et al, 1987(Chýlek et al, , 1992Warren and Clarke, 1990). Although there are local emissions of BC due to scientific and touristic activities (Casey et al, 2017;Stohl and Sodemann, 2010), Antarctic ice also records Southern Hemisphere (SH) emissions and long-range transport of BC from low and mid-latitudes (Bisiaux et al, 2012a(Bisiaux et al, , 2012b, with BC concentrations in Antarctica being linked to biomass burning from South America, Africa and Australia (Arienzo et al, 2017;Koch et al, 2007;Stohl and Sodemann, 2010). Even tropical latitude emissions have a measurable influence on the continent (Fiebig et al, 2009).…”

“…Although there are several records of SH paleo-biomass burning, there are only a few publications on BC variability in ice cores from Antarctica. Some of those are focused on centennial-millennial timescales (Arienzo et al, 2017;Chýlek et al, 1992) and others on annual to decadal scales (Bisiaux et al, 2012a(Bisiaux et al, , 2012b. As more ice core records are needed to understand the spatial variability of BC transport and deposition to Antarctica, as well as to improve general circulation models (Bisiaux et al, 2012b), this work aims to add another high-temporal-resolution rBC record from a West Antarctic snow and firn core to the existing literature.…”