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| Titel |
Variability in ISOW Vigor Over the Last two Millennia and its Relationship to Climate |
| VerfasserIn |
Tor Lien Mjell, Ulysses Silas Ninnemann, Helga Flesche Kleiven, Ian Hall |
| 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 |
250054237
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| Zusammenfassung |
| Low frequency variability in the Atlantic Meridional Overturning Circulation (AMOC)
constitutes a key uncertainty in predictions of future climate, ocean, and atmospheric CO2
changes. Although AMOC variability is commonly invoked to explain low frequency climate
variability observed on millennial to multidecadal timescales during the Holocene,
there is very little observational or paleoclimatic evidence available to test these
hypotheses. In short, empirical constraints on the nature and magnitude of ocean
variability (under a range of boundary conditions) are sorely needed before we can hope
to evaluate and understand the role of the ocean in either past or future climate
changes.
Here we use well dated (210Pb and AMS 14C), high sedimentation rate, multi and gravity
cores taken on the Gardar Sediment Drift (60Ë 19’N, 23Ë 58’W, 2081 m water depth) to
reconstruct decadal to centennial variability in the properties and vigor of the eastern
branch of the Nordic Seas overflows over the past two millennia. The Gardar drift
accumulates on the eastern flank of the Reykjanes Ridge due to the supply of sediments
provided by the overlying Iceland Scotland Overflow Water (ISOW)—an important
constituent of North Atlantic Deep Water (NADW). We reconstruct the bottom water
physical and chemical properties of ISOW using the oxygen and carbon isotopes of
benthic foraminifera (C. wuellerstorfi), while changes in the vigor of near bottom
flow are inferred from size variations in the sediment proxy mean sortable silt.
In addition, changes in surface hydrography are reconstructed using the δ18O of
several planktonic foraminifer species G. bulloides, G. inflata, and N. pachyderma
(d).
Our records provide a sub-decadally sampled history of ISOW variability spanning the
last ~2000 years. Our results reveal that AMOC variability is tightly coupled to low
frequency variations in basin-wide climate (Atlantic Multidecadal Oscillation-AMO). In
particular, that the eastern branch of the Nordic Seas overflows (ISOW) covaried with
AMO over the past ~350 years on both inter-decadal and centennial timescales,
with increased (decreased) ISOW vigor during warm (cold) AMO phases. The
similarities suggest that key components of AMOC are linked to basin wide temperature
perturbations. Furthermore, our finding of a correlation between high medieval temperatures
in Western Europe (800-850 AD) and a vigorous ISOW, as well as a correlation
between low summer temperatures in Iceland and a markedly more sluggish ISOW
(990-1050 AD), indicates that this coupling is representative for the past ~2000
years and may have played a role in historically important climate perturbations. |
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