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| Titel |
Assessing linkages between ice sheet calving, subpolar gyre density and deep water ventilation during the last glaciation |
| VerfasserIn |
Sunniva Rutledal, Ulysses S. Ninnemann, Helga (Kikki) F. Kleiven, Nil Irvali |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250150029
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| Publikation (Nr.) |
 EGU/EGU2017-14450.pdf |
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| Zusammenfassung |
| Deep ocean circulation plays an important role in the Earth’s climate system and is postulated
to be closely linked to ice sheet dynamics and abrupt climate oscillations. However, the
nature of this coupling remains unclear. Iceberg and freshwater pulses have been
hypothesized as both the trigger for, and the response to, reduced Atlantic meridional
overturning circulation (AMOC). Differentiating between these two hypotheses requires
high-resolution records constraining the relative timing of ice sheet, freshwater, and ocean
circulation changes.
Here we assess the relative timing and linkages between iceberg discharge, surface water
physical properties in the subpolar gyre, and North Atlantic deep water ventilation using
proxy records co-registered in the same sediment sequence. High-resolution stable
isotope analysis (δ18O & δ13C ) of planktonic (N. pachyderma (s)) and benthic
(C. wuellerstorfi) foraminifera and ice-rafted debris (IRD) records from the core
GS15-196-02GC taken in the Irminger basin (59o37.1 N, 40o44.25 W, 2468 water
depth) document a clear relationship between increasing freshwater fluxes (IRD and
planktonic δ18O), decreasing deep water ventilation (benthic δ13C), and temperature and
salinity changes in the subpolar gyre surface waters (planktonic δ18O). Our benthic
(C. wuellerstorfi) carbon isotope record documents clear variability in deep ocean
ventilation throughout the last glacial and deglacial periods. Notably, periods of high
iceberg discharge and freshening of the subpolar gyre surface waters are preceded by
decreases in deep water ventilation (benthic δ13C); consistent with the hypothesis that
reduced AMOC is important for triggering ice sheet melting/collapse. However,
ventilation decreases of similar scale occur without accompanying peaks in IRD,
suggesting circulation changes do not always trigger ice sheet collapse. In addition, the
periods of weakest ventilation (low benthic δ13C ) are clearly coincident with the
largest IRD peaks and planktonic δ18O decreases, consistent with a feedback of
ice sheet melting and subpolar freshening on deep water circulation. Indeed, the
largest IRD and lowest planktonic δ18O values are associated with Heinrich event
1 and the onset of this anomaly is marked by the period of weakest deep water
ventilation (lowest benthic δ13C) observed in our record. Taken together we find support
for ice sheet melting and increased freshwater supply as both a trigger for, and a
feedback on, ocean circulation changes during the late glacial and deglacial period. |
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