HR: 1340h
AN: PP43A-0654    [Abstracts]
TI: Highly Variable Holocene Climate in the Subpolar North Atlantic
AU: * Berner, K
EM: kari@npolar.no
AF: Norwegian Polar Institute, Polar Environmental Centre, Tromso, 9296 Norway
AU: * Berner, K
EM: kari@npolar.no
AF: The Faculty of Sience, University of Tromso, Tromso, 9037 Norway
AU: Koc, N
EM: nalan.koc@npolar.no
AF: Norwegian Polar Institute, Polar Environmental Centre, Tromso, 9296 Norway
AU: Divin, D
EM: dima@npolar.no
AF: Norwegian Polar Institute, Polar Environmental Centre, Tromso, 9296 Norway
AU: Divin, D
EM: dima@npolar.no
AF: The Faculty of Sience, University of Tromso, Tromso, 9037 Norway
AB: A composite record of four sediment cores (LO09-14) from the sub-polar North Atlantic, the Reykjanes Ridge, was investigated with decadal time resolution in order to assess surface ocean variability during the last 11 kyr (the Holocene period). Today, the core site is under the influence of the Irminger Current, which is a branch of the North Atlantic Drift continuing northwestward around Iceland. The sub-arctic front is proximal to the investigated area resulting in dynamic hydrographic conditions. The composite core consist of ca. 6.5 m Holocene sediments, and the age model is based on 40 AMS 14C dates of the foraminifera Globigerina bulloides. Detailed analyses of diatom species are transferred to quantitative reconstruction of past sea surface temperatures (SSTs) in order to quantify surface stability in this sensitive region. Results from the diatom transfer functions, using statistical methods as Imbrie & Kipp (IK), Weighted Averaging Partial Least Square (WA-PLS) and Maximum Likelihood (ML), show low (8-13.5°C) and highly variable temperatures in the early Holocene (11 - 7 kyr). Episodes of temperature fluctuation, with amplitudes of 3 to 5°C within 150 years characterize this period. We infer a weak Irminger Current and frequent advection of sub-polar water over the site during the early Holocene. This unstable period is followed by a mid-Holocene thermal optimum (12-16 °C) between 7 and 5 kyr characterized by episodes of temperature fluctuation amplitudes of 1 to 4 °C within 300-150 years. The final interval from 5 kyr to the present reveals cooler (11-13 °C) surface conditions and somewhat more stable conditions compared to the period between 11 to 7 kyr. The sub-polar North Atlantic seems to have experienced highly variable surface conditions throughout the Holocene. Over the investigated site the Holocene thermal optimum is not reach until 7-5 kyr, lagging the northern hemisphere insolation maximum by 4000 years. The waning Laurentide ice sheet and its effect on the ocean and atmosphere circulation might cause the delayed response in the sub-polar North Atlantic. Holocene climate variability of the North Atlantic and the Nordic Seas has shown to experience a series of millennial-scale shifts in the surface circulation. The LO09-14 record shows significant features with a periodicity between 640-960 years and 1400-2500 years, and the cycles are more frequent in early and mid-Holocene than in late Holocene. In mid-Holocene thermal optimum the cycles show some correlation to 1500 years IRD pulses (Bond et al., 1997), but early Holocene is in opposite phase. The cooling events in the area correlates to d13C record from ODP site 980, and therefore indicate a surface-deepwater linkage through the Holocene.
DE: 1616 Climate variability (1635, 3305, 3309, 4215, 4513)
DE: 1635 Oceans (1616, 3305, 4215, 4513)
DE: 4901 Abrupt/rapid climate change (1605)
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005