Atmospheric decadal variability from high-resolution Dome C ice core records of aerosol constituents beyond the Last Interglacial

Abstract

Along the EPICA Dome C ice core, we measured concentrations of different water-soluble aerosol constituents and deduced total depositional flux records. Here we present high-resolution sodium, calcium, ammonium and nitrate data covering the last 173,000 years. The first three of these species are passive tracers and reveal source and long-range transport changes whereas nitrate is deposited reversibly. However, it can be used to check isotope-derived accumulation rate estimates, a prerequisite to calculate total depositional fluxes. During the last two transitions from glacial to interglacial periods, changes in the total depositional flux differ strongly for different aerosol species. The largest changes are observed in the terrestrial aerosol proxy non-sea salt calcium, only moderate changes occur in the marine sea salt indicator sodium, while ammonium, a proxy for marine bioproductivity, remains rather constant. In agreement with previous studies, we find that only considerable glacial–interglacial changes at both, the terrestrial and the marine sea salt aerosol source can explain the observed pronounced changes. The unprecedented high-resolution of our data allows for the first time the examination of decadal variability back to the penultimate glacial period. On the one hand, we find occasional fast shifts occurring within a few years; here we present such an event in the calcium record from the penultimate glacial period. On the other hand, we examine variation coefficients and pairwise correlation coefficients, both determined in 200-year windows. They generally reveal only moderate changes. During glacial periods, slightly lower variation coefficients are found, concurrent with slightly higher correlation coefficients, which points to a more uniform and stronger coupled atmospheric long-range transport of the different aerosol species to the East Antarctic Plateau and less influence of cyclonic activities during cold periods. The opposite is observed for interglacial periods with probably even reinforced importance of cyclonic influences during the Last Interglacial period, the Marine Isotope Stage 5.5. This period reveals no evidence for abrupt climatic changes in any of the species, however, the marine sea salt aerosol indicator sodium shows a distinct minimum followed by a pronounced increase. This pattern is explained by significantly reduced sea ice production in the Indian Southern Ocean sector, which is believed to be the dominant source of sodium deposited in Dome C during warm periods.