 |
| Titel |
Ocean ventilation rates during the last deglaciation: paired radiocarbon and Nd isotope compositions in deep-water corals from the NW Atlantic |
| VerfasserIn |
Kirsty C. Crocket, Tina van de Flierdt, Laura F. Robinson, Jess F. Adkins |
| Konferenz |
EGU General Assembly 2011
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250050870
|
|
|
|
|
|
| Zusammenfassung |
| Atmospheric CO2 has varied systematically during mid-Pleistocene glacial/interglacial
cycles. Despite intense investigation, the exact causal mechanisms remain unknown.
Sequestration of carbon in the deep ocean during glacials and its subsequent release during
deglaciation undoubtedly play a role, given the much larger size of the ocean carbon reservoir
compared to that of the atmosphere, thus allowing small changes in ocean circulation to have
a large impact on atmospheric CO2. However, concrete evidence of the ocean’s
role has yet to be established. One route of investigation is to determine ocean
ventilation rates. To do so requires combining dynamic tracer data, such as radiocarbon,
with a conservative tracer to identify the water masses involved and their mixing
ratios.
We describe the novel use of deep sea coral species D. dianthus as an archive material
providing both radiocarbon and conservative water mass tracer data in the form of Nd isotope
compositions. The majority of corals in this study are deglacial in age and span a water depth
of 1000 to 2600 m in the NW Atlantic, where changes in the water column structure were
pronounced across the last glacial/interglacial cycle (1). Additional coral samples are located
in the NE Atlantic and the northernmost parts of the North Atlantic to provide a broader
picture of change. Corals with existing radiocarbon data and U/Th ages (1-4) were
subsampled before undergoing extensive physical and chemical cleaning (5). Purification of
coral Nd was achieved using an initial Fe co-precipitation step followed by separation of
coral REE from matrix, and finally Nd separation by α-HIBA column chromatography. The
low concentrations of coral Nd (3 to 29 ppb; 5) required analysis of the isotope composition
by TIMS as NdO+, which ionises Nd more efficiently compared to Nd+ analysis
(6).
This study builds on existing work using D. dianthus, which has identified radiocarbon
age reversals within single specimens (4) and rapid changes in radiocarbon content of the
NW Atlantic water column (1). By pairing the Nd isotope data to the radiocarbon data, we are
able to identify the water masses present in the NW Atlantic during the deglaciation, the
extent of mixing between these, and ultimately to translate the radiocarbon data into ocean
ventilation rates.
L. F. Robinson et al., Science 310, 1469 (Dec, 2005).
L. F. Robinson et al., Bulletin of Marine Science 81, 371 (Nov, 2007).
S. F. Eltgroth et al., Paleoceanography 21, PA4207 (Nov, 2006).
J. F. Adkins et al., Science 280, 725 (May, 1998).
T. van de Flierdt et al., Geochimica Et Cosmochimica Acta 74, 6014 (Nov, 2010).
M. F. Thirlwall, Chemical Geology: Isotope Geoscience section 94, 13 (1991). |
|
|
|
|
|
|