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| Titel |
Modern Amundsen Sea Circumpolar Deep Water Nd isotope composition and its evolution since the Antarctic Cold Reversal |
| VerfasserIn |
Marcus Gutjahr, Derek Vance, Claus-Dieter Hillenbrand, Gerhard Kuhn |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250052158
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| Zusammenfassung |
| The Amundsen Sea in the Pacific sector of the Southern Ocean is one of the most remote and
least explored ocean basins on Earth. To date, for example, there are only a few water
column Nd concentration and isotopic data predominantly from seawater samples
of water masses bathing the shelf that were collected during cruises JR141 and
JR179 with RRS James Clark Ross in 2006 and 2008, respectively. In spring 2010
additional water column samples were taken in this area during RV Polarstern cruise
ANT-XXVI/3, in order to cross-calibrate deep-sea coral derived fossil Nd isotope
compositions collected during this and an earlier RV Polarstern cruise in 2006. The
aim of our study is to evaluate the Nd concentration and isotopic budget of this
sector of the Southern Ocean today, and to reconstruct the Circumpolar Deep Water
(CDW) Nd isotopic variability in intermediate water depth back into the last glacial
period. Fossil corals were dredged from water depths ranging from 2500 m to 1400
m.
Over most of the water column in the vicinity of the Marie Byrd Seamounts (~123Ë W,
~69Ë S), the Nd isotope composition (expressed in ÉNd) displays typical CDW compositions
ranging from ÉNdof -9.0 in 500 m water depth to values of -7.9 in 3000 m (n=6). These
compositions are in excellent agreement with late Holocene fossil coral-derived ÉNd that
scatter around values of ~-8.4. However, seawater ÉNd values 160 m above the seafloor are
almost three ÉNd, and those 1.5 m above the seabed almost five ÉNd more radiogenic than the
ÉNd compositions seen throughout the upper 3 km of the water column. Given that the
hydrographic data (potential temperature and density, salinity) in these water depths are still
characteristic for CDW, the radiogenic ÉNd values above the sediment-bottom water
interface suggest that solute fluxes and exchange processes, referred to as “boundary
exchange” by Lacan and Jeandel (2005), are also evident from the abyssal Southern
Ocean.
Past CDW ÉNd, as recorded in our radiocarbon-dated calcitic scleraxonian octocorals,
show only minor variability throughout the Holocene and the latest stage of the last
deglaciation, though mimicking trends seen in Holocene deep-sea corals as distant as the
intermediate North Atlantic (Colin et al., 2010). Conversely, several Amundsen Sea corals
dating back to approximately the Antarctic Cold Reversal (ca. 14.5-12.5 ka BP) and the
middle Marine Isotope Stage 3, respectively, show considerable variability towards more
radiogenic ÉNd, in agreement with Fe-Mn oxyhydroxide-derived bottom water Nd
isotope reconstructions from the Cape Basin in the Atlantic sector of the Southern
Ocean (Piotrowski et al., 2005). Overall our data suggest a strong connection of
North Atlantic Deep Water (NADW) contributions to the Antarctic Circumpolar
Current on the one hand and Amundsen Sea CDW ÉNd on the other for a given time.
This finding is in agreement with suggestions brought forward by Piepgras and
Wasserburg (1982) for a strong influence of Atlantic-derived Nd in setting an ACC
ÉNd.
References
Colin, C., Frank, N., Copard, K., Douville, E., 2010. Neodymium isotopic composition of
deep-sea corals from the NE Atlantic: implications for past hydrological changes during the
Holocene. Quaternary Science Reviews, 29 (19-20): 2509-2517.
Lacan, F., Jeandel, C., 2005. Neodymium isotopes as a new tool for quantifying exchange
fluxes at the continent-ocean interface. Earth and Planetary Science Letters, 232 (3-4):
245-257.
Piepgras, D. J., and G. J. Wasserburg (1982), Isotopic composition of neodymium in
waters from the Drake Passage, Science, 217 (4556), 207-214.
Piotrowski, A.M., Goldstein, S.L., Hemming, S.R., Fairbanks, R.G., 2005. Temporal
relationships of carbon cycling and ocean circulation at glacial boundaries. Science, 307
(5717): 1933-1938. |
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