A new aquatic gastropod stable isotopic continental paleoclimate proxy for New Zealand systems
Abstract
Endemic to New Zealand, the aquatic gastropod Potamopyrgus antipodarum (i.e. New Zealand Mud Snail), is extremely common in modern aqueous environments and is an abundant subfossil preserved in Quaternary sediments throughout the country. This ubiquity presents unprecedented opportunities to explore stable isotope based paleoclimatic and paleoenvironmental research across New Zealand’s diverse natural systems through time. In an effort to evaluate the utility of New Zealand Mud Snail shells as isotopic proxies, approximately 10 modern snails were collected at each of 18 freshwater systems located throughout New Zealand and analyzed for stable carbon and oxygen isotopic compositions. Results indicate: 1) the oxygen isotope composition of P. antipodarum shells collected from through-flowing lakes and streams exhibit a significant positive correlation with mean annual catchment temperature; 2) shell isotopic compositions typically vary over an approximately 2 permil range for both carbon and oxygen within a single site; 3) inter-site variability is also relatively high with each site defining an isotopically distinct population; 4) shells collected from closed-basin lakes showed markedly more positive delta-values than geographically similar through-flowing systems most likely due to evaporative effects. These results suggest P. antipodarum represents an important new continental climate change proxy for New Zealand systems. However, the modern snail shell results indicate there are also several weaknesses associated with this new proxy. Most importantly, the relatively high degree of natural variability within individual sites indicates multiple contemporaneous shells are needed when performing paleo-research. Additionally, the modern results indicate, as expected, the oxygen isotope composition of snails shells is sensitive to both changes in temperature and hydrologic balance, making it difficult to differentiate between paleo-hydrologic and thermal signals. In an effort to potentially overcome this challenge, the hydrogen isotope composition of shell carbonate was also determined for individual shells. Enough hydrogen, presumably derived from water trapped within shell carbonate, was liberated from 1-2 mg of crushed shell through thermal decomposition followed by continuous flow pyrolysis isotopic analysis. This new technique suggests a multi-proxy method applied to individual aquatic carbonate subfossil specimens is possible.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP31B1345H
- Keywords:
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- 0454 BIOGEOSCIENCES / Isotopic composition and chemistry