Extreme Monsoon Rainfall Signatures Preserved in the Invasive Terrestrial Gastropod Lissachatina fulica

Abstract

Indian summer monsoon (ISM) rainfall lasts for a period of 4 months with large variations recorded in terms of rainfall intensity during its period between June and September. Proxy reconstructions of past ISM rainfall variability are required due to the paucity of long instrumental records. However, reconstructing subseasonal rainfall is extremely difficult using conventional hydroclimate proxies due to inadequate sample resolution. Here, we demonstrate the utility of the stable oxygen isotope composition of gastropod shells in reconstructing past rainfall on subseasonal timescales. We present a comparative isotopic study on present day rainwater and stable isotope ratios of precipitate found in the incremental growth bands of giant African land snail Lissachatina fulica (Bowdich) from modern day (2009) and in the historical past (1918). Isotopic signatures present in the growth bands allowed for the identification of ISM rainfall variability in terms of its active and dry spells in the modern as well as past gastropod record. Our results demonstrate the utility of gastropod growth band stable isotope ratios in semiquantitative reconstructions of seasonal rainfall patterns. High resolution climate records extracted from gastropod growth band stable isotopes (museum and archived specimens) can expand the scope for understanding past subseasonal‐to‐seasonal climate variability.

Holocene cultural and climate shifts in NW Africa as inferred from stable isotopes of archeological land snail shells

“…Shells collected in Algeria during 1973 track the highest δ 18 O values of the entire snail isotope record (Figure 4(a)), pointing to severely dry conditions, in agreement with instrument records in the area. The coherence between historic shell δ 18 O values presented here and rainfall records from N Africa reinforces the sensitivity of snails to shifts in dry/wet conditions and further supports snail shell validity as historic climatic proxies (see also Ghosh et al, 2017).…”

“…These shells, all else being equal, should have grown at times when RH was very high, between 97% (Figure 6(a)) and even 99% (Figure 6(b)). If these hypothetical scenarios are true, then snails from Algeria appear to be highly sensitive to moisture changes and can track variations in humidity and rainfall at historical, decadal scales, as previously shown by Ghosh et al (2017). Future research in the study area will expand isotopic analyses of historical shells to further test and verify these humidity fluctuations of the 20th century.…”

“…Thus, oxygen and carbon stable isotopes extracted from archeological and historical shells have been widely used as proxies for paleoclimatic and paleoenvironmental reconstructions (e.g. Balakrishnan et al, 2005;Colonese et al, 2010Colonese et al, , 2011Colonese et al, , 2013aColonese et al, , 2013bFaber, 2012;Ghosh et al, 2017;Prendergast et al, 2016;Rangarajan et al, 2013;Yanes et al, 2011Yanes et al, , 2012Yanes et al, , 2013. Lubell et al, 1976).…”

Floating boat method for carbonate stable isotopic ratio determination in a GasBench II peripheral

“…The GasBench II peripheral of an isotope ratio mass spectrometer is commonly used for preparation of samples of water and carbonate, for stable isotope ratio measurements. 1,2 Stable isotopic investigations of carbonates for paleo-climate research 3,4 demand a highly precise 5 automated method for consistent performance in sample preparation, and high sensitivity of the mass spectrometer to detect signals from small CO 2 gas samples. The advantages of this peripheral for carbonate stable isotopic ratio determination includes ease of sample preparation without evacuation, an automated sampler for helium flushing, a controlled temperature bath for acid digestion reaction, and withdrawal of CO 2 from a reaction vial for isotopic analysis by isotope ratio mass spectrometry.…”

Overview of the oxygen isotope systematics of land snails from North America

“…The vast majority of snail isotope studies worldwide have analyzed δ 18 O values of entire shells rather than employing a time-series approach (Supplementary Table 1), although eight published articles have explored high-resolution oxygen isotope time series along shell growth direction (Goodfriend, 1992; Leng et al, 1998; Baldini et al, 2007; Yanes et al, 2011b, 2012, 2014; Rangarajan et al, 2013; Ghosh et al, 2017). In addition, one study focused on shell margin or last growth episode oxygen isotope values (Yanes and Fernandez-Lopez-de-Pablo, 2017), and two have analyzed snail body fluid δ 18 O values in conjunction with shell δ 18 O (Goodfriend et al, 1989; Prendergast et al, 2015).…”