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| Titel |
Strontium/lithium ratios in shells of Cerastoderma edule – A potential temperature proxy for brackish environments |
| VerfasserIn |
Christoph S. Füllenbach, Bernd R. Schöne, Regina Mertz-Kraus |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109173
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| Publikation (Nr.) |
 EGU/EGU2015-9056.pdf |
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| Zusammenfassung |
| Bivalve shells provide high-resolution records of climate variability. However, the number of
suitable proxies to quantify environmental variables is still limited. The most frequently used
and well-accepted tool for environmental reconstructions from shell carbonate,
δ18Oshell, is a dual proxy that simultaneously informs about water temperature and
the oxygen isotope signature of the water. Reconstruction of water temperature
requires knowledge of δ18Owater and reconstruction of the latter requires knowledge
of salinity. Element-to-calcium ratios that are frequently used in other biological
carbonates as tools for temperature reconstructions such as Sr/Cashell or Mg/Cashell are
strongly biologically controlled in bivalves and show only a weak correlation to
temperature.
Here, we present Sr/Lishell ratios as a new temperature proxy that can complement
δ18Oshell-based environmental reconstructions. In seawater, strontium and lithium have long
residence times of 1.5Ma and 2Ma, respectively. Furthermore, salinity changes do not appear
to affect the incorporation of Sr2+ and Li+ into the shells. Sr and Li concentrations
were determined via LA-ICP-MS (line-scan method) in aragonitic shells of four
Cerastoderma edule specimens collected alive from the intertidal zone of the North
Sea. Geochemical data from the ontogenetic year three (growing season: April –
September) were placed in precise temporal context by using tidal growth patterns
and then compared to instrumental water temperature and water chemistry data.
Sr/Lishell values (15 to 287 mmol/mmol) are significantly above Sr/Liwater (1.9 to 3.3
mmol/mmol) suggesting the presence of vital effects. However, all shells revealed
similar Sr/Lishell patterns that are strongly negatively correlated to water temperature
(r^2 = 0.65 to 0.74; p < 0.01; T = -0.056 (±0.005) * (Sr/Lishell) [mmol/mmol] +
23.188 (±0.92)). To test the robustness of the presented proxy, we applied the new
paleothermometry equation (Sr/Lishell vs. temperature) to a fourth specimen of C.
edule. Instrumental temperatures were perfectly resembled with an average absolute
difference of 1.9°C. Considering that Sr2+ and Li+ can substitute Ca2+ in the crystal
lattice of aragonite, the Sr/Lishell ratio is a measure of which of the two elements is
preferably incorporated into the shell. For currently unknown reasons, this ratio
seems to be temperature-dependent. At higher water temperature, an increased
amount of Li+ in incorporated into the shells. Sr/Lishell values may function as a
new temperature proxy in bivalves from brackish environments. Future studies are
required to test if the Sr/Lishell vs. temperature-relationship remains unchanged
through lifetime and if this proxy can be applied to other environments and species. |
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