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| Titel |
Northern Hemisphere Cryospheric Connections during Deglaciation: Expected and Unexpected Responses. |
| VerfasserIn |
Ingrid Hendy, Alice Chang |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250038341
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| Zusammenfassung |
| We present a high-resolution glaciomarine record for MD02-2496 (48-58.5N; 127-02.1W;
1243m water depth), collected from the Vancouver Island continental slope. 46 AMS 14C
dates have been generated from both planktonic foraminifera carbonate and bulk sedimentary
organic carbon. The presence of two 14C plateaus during deglaciation (~13.3 and ~14.8 14C
kyr BP) provide a potential stratigraphic marker allowing for correlation with other deglacial
paleoclimate records as the 14C plateaus should be geologically instantaneous due to rapid
atmospheric mixing. After correcting for the estimated local surface ocean 14C reservoir age
(>807 years), these plateaus coincide with global 14C plateaus (12.2 and 13.3 14C kyr
BP).
The resulting chronology enables correlation of glaciomarine sedimentary sequences within
MD02-2496, to well known terrestrial units associated with Cordilleran Ice Sheet (CIS)
advance and retreat in the Pacific Northwest over the last 50 ka and provides new insight into
ice sheet processes. Of significance is the previously unknown ice-rafted debris events
identified in the >250μm grains g-1 record at ~42, 17.2 to 16.1 and 14.8 ka. These are
interpreted to represent catastrophic retreats of the western marine margin of the CIS that are
co-incident with North Atlantic ice rafting events – Heinrich Events 1 and 5. Elemental
analysis of bulk sediments reveals the provenance of glacial sediment discharged before and
after these catastrophic events shifted between granitic and basaltic sources. These
glaciomarine sedimentary sequences may reflect a shift from proglacial lake outburst flooding
(i.e. Lake Missoula flood events) to meltwater associated with a downwasting ice sheet, with
the catastrophic iceberg calving providing the transition between these two ice ablation
states.
The planktonic foraminiferal δ18O record from MD02-2496 suggests rapid warming and
cooling (i.e. Bølling and Younger Dryas) in the local marine realm may have had little impact
on the CIS as the ice sheet response generally preceded these climatic events by ~100
years. However, the near co-incidence of ice sheet retreat/advance with climate
events does suggest an intriguing connection between rapid climate change and ice
sheets. Disruption of meriodional overturning circulation (MOC) via rapid ice sheet
melting has received much attention in the North Atlantic but not in the Pacific. The
climatic consequences of meltwater discharge to an already stratified North Pacific
Ocean have previously been considered to have been limited when compared to
similar events in the Atlantic. Recent observations of the Cascadia Basin where
glaciomarine sediments from the CIS were deposited during the last glacial/deglaciation
suggest that the basin contributes to the upwelling limb of thermohaline circulation.
Could CIS activity provide a mechanism for NE Pacific Ocean destabilization during
deglaciation that needs to be considered alongside the impact of Heinrich Events on
MOC? |
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