Ammonium and non-sea salt sulfate in the EPICA ice cores as indicator of biological activity in the Southern Ocean

Abstract

a b s t r a c tSulfate (SO 4 2À ) and ammonium (NH 4 þ ) flux records over the last 150,000 years from both Antarctic EPICA ice cores (European Project for Ice Coring in Antarctica) are presented. The ice core record from Dome C is influenced by the Indian sector of the Southern Ocean (SO), whereas Dronning Maud Land is facing the Atlantic sector. Generally, they reflect the past atmospheric aerosol load and, thus, potentially reveal the fingerprint of marine biogenic sources from the SO. The most important feature of both, the nssSO 4 2À as well as NH 4 þ flux records, is the absence of any significant glacial cycles, in contrary to the distinct transitions for mineral dust and sea salt aerosol over the last 150,000 years. This finding challenges the iron fertilization hypothesis on long time scales, as the significant changes in dust, e.g. from the last glacial maximum toward the Holocene have neither an impact on nssSO 4 2À nor on NH 4 þ fluxes found in interior Antarctica. The inter-site correlation of both species is weak, r 2 ¼ 0.42 for the nssSO 4 2À flux and r 2 ¼ 0.12 for the NH 4 þ flux respectively, emphasizing the local source characteristics of biogenic aerosol from the SO.Millennial variability in NH 4 þ and nssSO 4 2À is within the uncertainty of our flux estimates. Correlation with mineral dust and sea ice derived sodium shows only a very weak influence of dust deposition on those insignificant changes in nssSO 4 2À flux for the Atlantic sector of the Southern Ocean, but also small transport changes or terrigeneous sulfate contributions may contribute to those variations at EDML.

Seasonal variations and vertical features of aerosol particles in the Antarctic troposphere

“…Recent works suggested that black carbon, derived mostly from biomass burning, was transported to Antarctic coasts (Fiebig et al, 2009;Hara et al, 2010). Significant increase of anthropogenic species, however, have not been identified in the Antarctic ice core records (e.g., Legrand and Mayewski, 1997;Watanabe et al, 2003;Kaufmann et al, 2010) and snow pit record (Iizuka et al, 2004). Furthermore, our previous investigation showed the occasional occurrence of Antarctic haze at Syowa Station during winter-spring .…”

Ice sheets and nitrogen

“…They are also unusual among measured chemicals in that the concentration recorded over a full glacial cycle in two cores [55] is inversely proportional to the snow accumulation rate, such that the flux is almost constant. Only non-sea-salt sulfate shows a similarly flat flux over such major climate shifts.…”

Spatial and temporal variability of snow chemical composition and accumulation rate at Talos Dome site (East Antarctica)

“…Hence, ammonia is supposed to be the major neutralizer agent for acidic species, especially sulfuric and nitric acids, and it plays a relevant role as pH-regulator in the marine boundary layer (MBL), as first proposed by Bouwman et al (1997). Indeed, NH 4 + and sulfate are often associated in the atmospheric aerosol because they arise from marine activity (Kaufmann et al, 2010). In off-shore oceanic areas, NH 4 + mainly originates from the biological decomposition of organic matter, with a highly variable contribution of zooplankton, as well (Johnson (2008) recently developed the concept of "co-emission", suggesting interaction processes between nssSO 4 2− and NH 4 + in the MBL.…”