Abstract
Sulfate aerosol (SO42−) 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-) SO42− 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-SO42− (δ34Snss) over East Antarctica, we established the applicability of the signature as a robust tool for distinguishing marine biogenic and nonmarine biogenic SO42−. Our findings, in conjunction with existing records of nss-SO42− flux and δ34Snss in Antarctic ice cores, provide an estimate of the relative importance of marine biogenic SO42− during the last glacial period to be 48 ± 10% of nss-SO42−, 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.
Highlights
Secondary sulfate plays an important role in aerosol and cloud interactions and influences solar radiation[1]
Nss-SO42− concentrations ([SO42−]nss) show well-marked seasonality with maxima of up to ca. 300 ng m−3 in late austral summer (February), with minima less than 20 ng m−3 during winter (August) (Fig. 1b). These trends are consistent with continuous observations at Dome C13,14 and DDU15,16, which are known as a result of enhanced production of biogenic dimethyl sulfide (DMS) over the Southern Ocean during the austral summer and its subsequent oxidation into SO42−
The δ34Snss values increase during August–December, with a considerable decrease in November at Dome C, in contrast to the gradual change observed at Dumont d’Urville Station (DDU)
Summary
Secondary sulfate plays an important role in aerosol and cloud interactions and influences solar radiation[1]. It has been shown that nss-SO42− flux recorded in Antarctic ice cores has not significantly changed throughout the last eight glacial cycles, which is concluded to indicate a nonsignificant change in marine biogenic activity[3]. This conclusion is inconsistent with the implication derived from marine sediment cores that shows lower productivity at latitudes higher than 50°S during the last glacial period than during the current warm period[6]. To address the above discussion, we performed a year-round observation of δ34Snss values of atmospheric SO42− at Dome C (75°06′S, 123°12′E; 3233 m a.s.l.) and Dumont d’Urville Station (DDU) (66°40′S, 140°01′E; 40 m a.s.l.), inland and coastal sites in East Antarctica, respectively, by utilizing continuous aerosol samples at those sites. We utilized δ34Snss values to estimate changes in sulfur sources in both the present and the past Antarctic atmosphere to infer the major nonmarine sulfur sources that remain to be identified
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