 |
| Titel |
{Carbon and oxygen isotope signals from marine ostracod calcite - results from present and past oceans} |
| VerfasserIn |
A. Bornemann, R. P. Speijer |
| Konferenz |
EGU General Assembly 2009
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027538
|
|
|
|
|
|
| Zusammenfassung |
| Systematic stable isotope studies on ostracod calcite are generally rare, in particular for
marine taxa only the work of DIDIÉ & BAUCH (2002) provides first clues towards an
improved understanding of ostracod stable isotope data in paleoceanography. Here we present
analyses from recent near surface sediments from the Gulf of Taranto, the Levantine Basin
(15 ka, both Mediterranean Sea) and the Paleocene of Tunisia (southern Tethyan margin).
Data are compared to those from selected benthic foraminiferal taxa from which the living
habitat and the isotopic disequilibria from ambient sea-water are well known. In addition,
size fractions of monospecific samples have been studied in order to test whether a size/mass
dependent change exists with respect to the isotopic composition of the carapace
calcite.
Calcification of ostracod carapaces is a very rapid process, which often takes place within
a few hours and the obtained signal provides only a snap-shot of the prevailing
paleoceanographic conditions. Multiple mono-specific measurements show therefore a much
higher variability than benthic foraminifera, but may give a more complete picture of the
seasonal changes. Our study confirms the findings of DIDIÉ & BAUCH (2002) and others
(for non-marine taxa) that ostracod calcite displays a positive species-specific deviation from
the sea-water δ18O composition between 0.5 and 1.5 per mil with an intra-specific variability
of less than 0.5 per mil. In contrast δ13C values cover a huge range with an off-set from
sea-water of up to -5 per mil and show a high intra-specific variability of up to 2 per
mil.
Size-fraction data show no systematic change, although a statistically significant positive
covariance between δ18O and δ13C has been observed. This covariance consists of a slope
similar to a kinetic controlled fractionation as has been described from asymbiotic planktic
foraminifera (Globigerina bulloides) and corals (MCCONNAUGHEY, 1989; SPERO &
LEA, 1996). This suggests that kinetic disequilibria control to a large extent isotope
fractionation in ostracod calcite.
While the δ13C values are probably also influenced by metabolic effects, previous studies
suggest that the δ18O of ostracod calcite correlates well with the δ18O of the ambient water
masses. However, this observation is not supported by our limited dataset from the
Levantine Basin. The ostracod data do not trace the prominent shift in sea-water δ18O
from 15 ka compared to today as it is apparent in the benthic foraminiferal data.
High-resolution time series data since the Last Glacial Maximum are desirable to
further explore the use of δ18O of marine ostracod calcite as a paleoenvironmental
proxy.
DIDIÉ, C. & BAUCH, H.A., 2002, Geophysical Monograph, v. 131, p. 279-299.
MCCONNAUGHEY, T., 1989, Geochimica et Cosmochimica Acta, v. 53, p.
151-162.
SPERO, H.J. & LEA, D.W., 1996, Marine Micropaleontology, v. 28, p. 231-246. |
|
|
|
|
|
|