Homogeneous sulfur isotope signature in East Antarctica and implication for sulfur source shifts through the last glacial-interglacial cycle

Abstract

Sulfate aerosol (SO 4 2− ) preserved in Antarctic ice cores is discussed in the light of interactions between marine biological activity and climate since it is mainly sourced from biogenic emissions from the surface ocean and scatters solar radiation during traveling in the atmosphere. However, there has been a paradox between the ice core record and the marine sediment record; the former shows constant non-sea-salt (nss-) SO 4 2− flux throughout the glacial-interglacial changes, and the latter shows a decrease in biogenic productivity during glacial periods compared to interglacial periods. Here, by ensuring the homogeneity of sulfur isotopic compositions of atmospheric nss-SO 4 2− (δ 34 S nss ) over East Antarctica, we established the applicability of the signature as a robust tool for distinguishing marine biogenic and nonmarine biogenic SO 4 2− . Our findings, in conjunction with existing records of nss-SO 4 2− flux and δ 34 S nss in Antarctic ice cores, provide an estimate of the relative importance of marine biogenic SO 4 2− during the last glacial period to be 48 ± 10% of nss-SO 4 2− , slightly lower than 59 ± 11% during the interglacial periods. Thus, our results tend to reconcile the ice core and sediment records, with both suggesting the decrease in marine productivity around Southern Ocean under the cold climate.

Regional Characteristics of Atmospheric Sulfate Formation in East Antarctica Imprinted on 17O‐Excess Signature

“…nss at Dome C throughout 2011 in comparison to those previously reported for DDU (Ishino et al, 2017). Note that the concentration data are presented in Ishino et al (2019) ] nss is enhanced during austral summer and reduced during winter, a seasonality that is driven by marine biogenic emission of DMS Preunkert et al, 2007Preunkert et al, , 2008. This seasonal cycle in [SO 4 2− ] nss is partially intensified by atmospheric dynamics due to enhanced efficiency of meridional long-range transport and the weakened inversion layer on the Antarctic Plateau during summer, as previously suggested by the similar seasonal cycle with 210 Pb (Elsässer et al, 2011;.…”

“…The procedures for extraction and quantification of soluble species concentrations in aerosols are detailed in Ishino et al. (2019). Some anions (NO 3 − and SO 4 2− ) and cations (K + , Mg 2+ , and Ca 2+ ) were measured at Tokyo Tech using ion chromatograph ICS2100, DIONEX with a guard column (Dionex IonPac AG19) and a separation column (Dionex IonPac AS19) for anions, and 881 Compact IC Pro, Metrohm with a guard column (Metrosep C4 S‐Guard/4.0) and a separation column (Metrosep C 4‐150/4.0) for cations.…”

“…Additionally, to explore other possible processes influencing the Δ 17 O(SO 4 2− ) nss values, we investigated the relationship of Δ DC–DDU to various chemical species observed at both sites. They include ion concentrations and acidity in aerosols ([H + ]), ratios of respective sulfur components, [SO 4 2− ] ss /[SO 4 2− ] total ratio (=1 – [SO 4 2− ] nss /[SO 4 2− ] total , cf., Equation ), and sulfur isotopic composition of non‐sea‐salt sulfate ( δ 34 S nss ) (Ishino et al., 2019). [H + ], estimated by using the following equation, was used to consider the contribution of aqueous‐phase S(IV) + O 3 pathway, which is highly dependent on pH of liquid water in the atmosphere (Seinfeld & Pandis, 2006): …”

“…Also [SO 4 2− ] ss /[SO 4 2− ] total was used to consider the potential importance of aqueous‐phase S(IV) + O 3 reaction, since it has been recognized that S(IV) + O 3 proceeds rapidly in alkaline (pH ∼ 8) deliquescent solution in fresh sea‐salt particles, subsequently shutting off due to acidification of sea‐salt aerosol by the produced sulfate as well as by uptake of acidic gases such as SO 2 , HNO 3 , and H 2 SO 4 (Alexander et al., 2005). δ 34 S nss was used to test the impact of sulfur sources on Δ 17 O(SO 4 2− ) nss , since it reflects the relative contributions of marine biogenic (i.e., DMS‐sourced) sulfate and nonmarine sulfate (nmb‐SO 4 2− ) including volcanic and continental sulfur sources (Ishino et al., 2019; Patris et al., 2000; Pruett et al., 2004). Additionally, 210 Pb was used to trace the contribution of long‐range transport of continental submicron aerosols (Elsasser et al., 2011; Legrand, Preunkert, Weller, et al., 2017).…”

“…Chen et al (2018) reported that GEOS-Chem model run with DMS concentration in seawater from Lana et al (2011) and without DMS oxidation by BrO, the condition used in this study, overestimates mixing ratio of DMS by a factor of 5 and 21 during summer and winter at DDU, respectively. This is likely a main reason for the overestimate of [SO 4 2− ] nss at DDU and Dome C, as DMS oxidation is thought to be the main source of sulfate in these locations (e.g., Ishino et al, 2019;Minikin et al, 1998) ) nss in the model as we discuss in Section 4.…”