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| Titel |
Holocene Evolution of the Irminger Current: a Perspective from the Southwest Iceland Shelf |
| VerfasserIn |
Ursula Quillmann, Anne E. Jennings, Tom M. Marchitto, Vivian Underhill, John T. Andrews |
| 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 |
250047842
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| Zusammenfassung |
| The Irminger Current (IC), a branch of the North Atlantic Current (NAC), transports heat and
nutrients to the Icelandic shelf. Variations in the water masses of the IC have been recently
linked to variations in the water mass properties of the NAC, which in turn are affected by
North Atlantic subpolar gyre (SPG) dynamics. Modern observations yield that the SPG
oscillates between two modes: an extended and a contracted mode. In the extended mode, the
SPG entrains more relatively cold and fresh polar waters, and in the contracted
mode more relatively warm and saline subtropical waters. We use variability in
temperature, the isotopic composition of seawater (δ18Osw), and the nutrient content of
the IC to reconstruct the Holocene evolution of the IC as it enters the Icelandic
shelf.
We present preliminary results of Mg/Ca ratios measured on Globigerina bulloides, a planktic
foraminifer, and Cassidulina laevigata, a benthic foraminifer, from core MD99-2259 (54°
37.0’ N, 24° 26.58’ W, 520 m water depth) from the southwest Iceland shelf. Core
MD99-2259 lies in the flow path of the IC and therefore should monitor changes in the
North Atlantic water mass characteristics, which we hypothesize originated from
changes in SPG dynamics. The temperature is calculated from the measured Mg/Ca
ratios and the calculated temperature is used to separate the δ18Osw contribution to
the oxygen isotopic composition of G. bulloides and C. laevigata. We reconstruct
paleonutrients from the Cd/Ca ratios in G. bulloides and C. laevigata. Cd/Ca ratios have
been used to reconstruct paleonutrients because in modern sediments they correlate
well with dissolved Cd in seawater, which resembles the nutrient PO4. However, a
potential temperature-dependence of the Cd/Ca of G. bulloides has been suggested. We
present the Cd/Ca record and the calculated PO4 record, which is corrected for
temperature.
To test our hypothesis that changes in the water mass characteristics in the IC are linked to
SPG dynamics, we compare our results with our SPG dynamic reconstruction of core
NEAP4K from Björn Drift in the northern Iceland Basin south of Iceland (61° 29.91’ N,
24°10.33’ W, 1627 m water depth). NEAP4K lies near the present-day position of the eastern
boundary of the SPG and thus likely monitors variations in SPG dynamics and the nutrient
content of the Atlantic water masses. The NEAP4K results suggest that the SPG went
generally from more extended modes in the early Holocene to more contracted modes
towards the present with some millennial scale oscillations superimposed. The Cd/Ca record
shows in general anticorrelations between temperature and nutrients. Higher nutrients
generally are associated with an extended SPG mode, which is consistent with
modern climatologial observations that the SPG has higher [PO4] than the subtropical
gyre. |
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