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| Titel |
Diplodon shells from Northwest Patagonia as continental proxy archives: Oxygen isotopic results and sclerochronological analyses |
| VerfasserIn |
A. L. Soldati, L. Beierlein, D. E. Jacob |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250025978
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| Zusammenfassung |
| Freshwater mussels of the genus Diplodon (Bivalvia, Hyriidae) are the most abundant bivalve
(today and in the past) in freshwater bodies at both sides of the South-Andean Cordillera.
There are about 25 different Diplodon genera in Argentina and Chile that could be assigned
almost completely to the species Diplodon chilensis (Gray, 1828) and two subspecies: D. ch.
chilensis and D. ch. patagonicus; this latter species is found in Argentina between
Mendoza (32Ë 52’ S; 68Ë 51’ W) and Chubut (45Ë 51’ S; 67Ë 28’ W), including the
lakes and rivers of the target area, the Nahuel Huapi National Park (Castellanos,
1960).
Despite their wide geographic distribution, Diplodon species have only rarely
been used as climate archives in the southern hemisphere. Kaandorp et al. (2005)
demonstrated for Diplodon longulus (Conrad 1874) collected from the Peruvian Amazonas
that oxygen isotopic patterns in the shells could be used in order to reconstruct the
precipitation regime and dry/wet seasonal of the monsoonal system in Amazonia.
Although this study demonstrated the potential of Diplodon in climatological and
ecological reconstructions in the southern hemisphere, as of yet, no systematic
study of Diplodon as a multi-proxy archive has been undertaken for the Patagonian
region.
In this work we present sclerochronological analyses supported by δ18Oshell in recent
mussel of Diplodon chilensis patagonicus (D’Orbigny, 1835) collected at Laguna El Trébol
(42ºS-71ºW, Patagonia Argentina), one of the best studied water bodies in the region for
paleoclimate analysis. Water temperature was measured every six hours for one year using a
temperature sensor (Starmon mini®) placed at 5m depth in the lake, close to a mussel bank.
Additionally, δ18Owater was measured monthly for the same time range.gδ18Oshell values
obtained by micro-milling at high spatial resolution in the growth increments of three
Diplodon shells were compared to these records, and to air temperature and precipitation
records in the region (from the NOAA database, station: airport of S.C. de Bariloche:
41ºS-71ºW).
D. ch. patagonicus exhibit very well developed annual growth lines, which allow
calibrating a precise temporal scale with calendar years in the shell (Soldati et al., 2008).
Extremely wide increments (e.g. years 2000-2001 and 1978-1979), related to distinct periods
(so-called benchmark increments) are present in all specimens and can be used to anchor the
growth curves in order to create a master curve for the lake. δ18Oshell varies seasonally,
presenting minima during the warm season (November/March) and maxima in the austral
autumn/winter (April/October), reproducing the temperature fluctuations in the region. The
resolution of the δ18Oshell measurement varies for each year: samples obtained from
larger annual increments (>1 mm, generally mussels younger than 10 years old)
allow a resolution of ca. 2 months (5-7 samples per year), and sometimes even give
a 5 weeks resolution, while thinner annual increments (between 1 and 0.1 mm,
generally older than 10 years) allow only a 4-6 month resolution (2-3 points per
sampled year). Because of their long live span of ca. 100 years, Diplodon shells
are useful to construct an accurate climatological archive for Patagonia with time
windows of around a century, resolving the environmental signal annually and even
seasonally.
References:
CASTELLANOS Z.A. (1960). Almejas nacaríferas de la República Argentina. Género
Diplodon. Secretaría de Agricultura, Publicación Miscelánea, 421: 1–40.
KAANDORP R.J.G., VONHOF H.B., WESSELINGH F.P., PITTMAN L.R.,
KROON D. & HINTE J.E.V. (2005). Seasonal Amazonian rainfall variation in the
Miocene Climate Optimum. Palaeogeography, Palaeoclimatology, Palaeoecology, 221:
1-6.
SOLDATI A.L., JACOB D.E., SCHÖNE B.R., BIANCHI M.M., HAJDUK A. (2008).
Seasonal periodicity of growth and composition in valves of Diplodon chilensis patagonicus
(D’Orbigny, 1835). Journal of Molluscan Studies, doi:10.1093/mollus/eyn044. |
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