 |
| Titel |
High-resolution elemental records of Glycymeris glycymeris (Bivalvia) shells from the Iberian upwelling system: Ontogeny and environmental control |
| VerfasserIn |
Pedro Freitas, Christopher Richardson, Simon Chenery, Paul Butler, David Reynolds, Miguel Gaspar, James Scourse |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250111069
|
| Publikation (Nr.) |
 EGU/EGU2015-11134.pdf |
|
|
|
|
|
| Zusammenfassung |
| The great potential of bivalve shells as a high-resolution geochemical proxy archive of
environmental conditions at the time of growth has been known for several decades. The
elemental composition of bivalve shells has been studied with the purpose of reconstructing
environmental conditions: e.g. seawater temperature (Sr and Mg), primary productivity (Li,
Mn, Mo and Ba), redox conditions (Mn and Mo), terrigenous inputs (Li) and pollution (Cu,
Zn, Cd and Pb). However, the interpretation of such records remains extremely challenging
and complex, with processes affecting element incorporation in the shell (e.g. crystal
fabrics, organic matrix, shell formation mechanisms and physiological processes)
and the influence of more than one environmental parameter affecting elemental
composition of bivalve shells. Nevertheless, bivalve shells remain an underused
source of information on environmental conditions, with the potential to record
high-resolution (sub-weekly to annually), multi-centennial time series of geochemical proxy
data.
The relatively long-lived bivalve (>100 years) Glycymeris glycymeris occurs in
coastal shelf seas of Europe and North West Africa and is a valid annually resolved
sclerochronological archive for palaeonvironmental reconstructions. The temporal framework
provided by absolute annually dated shell material makes Glycymeris glycymeris a valuable,
albeit unexplored, resource for investigating sub-annually resolved geochemical proxies. We
present a first evaluation on the potential of Ba, P and U, the latter two elements rarely
studied in bivalves, in Glycymeris glycymeris shells to record variations in the environmental
conditions, respectively primary productivity, dissolved inorganic phosphorus and carbonate
ion concentration/pH.
High-resolution (31 to 77 samples per year) profiles of elemental/Ca ratios
(E/Ca) over four years of growth (2001 to 2004) were obtained by LA-ICP-MS on
two shells (13 and 16 years old) live-collected in 2010 at 30 m water depth on the
Iberia upwelling system. In both shells, clear E/Ca annual cycles with significant
higher-frequency variability (weekly to sub-monthly) were observed over the four years of
growth analysed. However, E/Ca ratios and the amplitude of the annual E/Ca cycles
were lower in the older shell and showed decreasing trends with age (ontogenetic
effects). E/Ca ratios were age-detrended using statistical techniques derived from
dendrochronology, resulting in similar and coherent profiles in both shells. It seems unlikely
that enough variability in E/Ca ratios will be recorded in the shell after 15 to 20 years
of age to allow the retrieval of an environmental signal by age-detrending E/Ca
ratios. Detrended P/Ca, Ba/Ca and U/Ca in Glycymeris glycymeris shells showed
coherent variations with coeval modelled and instrumental oceanographic series
from the Iberia upwelling system that suggest a robust potential as an archive of
environmental conditions in the first 15 to 20 years of growth. Nevertheless a robust
calibration is required to distinguish between the influences of multiple environmental
parameters.
This study was financed and conducted in the frame of the Portuguese FCT GLYCY
Project (contract PTDC/AAC-CLI/118003/2010). |
|
|
|
|
|
|