HR: 11:50h
AN: PP12A-07    [Abstracts]
TI: Multi-Proxy Evidence for Reduced North Atlantic Deep Water Flux Across the 8.2 kyr B.P. Event From Core MD03-2665 at the Eirik Drift
AU: Kleiven, H F
EM: kikki@uib.no
AF: Bjerknes Centre of Climate research, Univ. of Bergen, Allegaten 55, Bergen, 5007 Norway
AU: * Kissel, C
EM: kissel@lsce.cnrs-gif.fr
AF: LSCE, Ave. de la Terrasse, Gif-sur-Yvette, 91198 France
AU: Laj, C
PP12A-07 AF: LSCE, Ave. de la Terrasse, Gif-sur-Yvette, 91198 France
AU: Ninneman, U S
PP12A-07 AF: Dept. Earth Sci., Univ. of bergen, Allegaten 55, Bergen, 5007 Norway
AU: Richter, T
PP12A-07 AF: Royal NIOZ, P.O.Box 59, Den Burg, 1790 AN Netherlands
AU: Cortijo, E
PP12A-07 AF: LSCE, Ave. de la Terrasse, Gif-sur-Yvette, 91198 France
AB: The cause of the cooling event culminating at 8.2 kyr B.P. in the Summit ice records, and in particular the role of ocean dynamics in this event, is a matter of considerable debate. Only a few marine records of suitable quality for monitoring North Atlantic Deep Water (NADW) properties during this climatic anomaly are available-making it difficult to assess how, or even if, deep ocean ventilation changed at this time. Here we report on multi-proxy evidence for deep-water changes across the 8.2 kyr event in the IMAGES core MD03-2665, which was taken from 3440m, water depth on the Erik drift , within the western boundary flow path of newly formed NADW. Here we report on benthic stable isotope records, magnetic properties and X-ray fluorescence (XRF) logging data through the Holocene. The Holocene in this core is represented by about 5.6 m of sediment (since 10.5 kyr B.P.). Based on 13 AMS 14C dates the average sedimentation rate is 103 cm/kyr between 10.5 kyr and 8.3 kyr and 38 cm/kyr from 8.3 kyr to the present. The benthic carbon isotope record (C. wuellerstorfi), our proxy for deep water chemistry, shows two pronounced depletions around, and just prior to, the 8.2 kyr event. These carbon isotopic excursions are twice as large as any other observed within the Holocene at this location. The first and largest excursion occurs between 3.45 and 3.25 mbsf where the carbon isotopic values decrease from average Holocene values of about 1 per mil to below 0 per mil. With the presently available radiocarbon ages, the event occurred between 8.5 and 8.7 kyr B.P. (calib5). After a brief recovery, a second carbon isotopic excursion of about 0.8 per mil occurs beginning at about 8.2 kyr on our current age model. Our sedimentological proxies show clear evidence for an excursion associated with the first carbon isotopic minimum between 8.5-8.7 kyr. Magnetic properties indicate that magnetite is the main magnetic carrier. Its average grain size is fining abruptly in this interval, in contrast to uniform magnetic grain sizes throughout the Holocene. XRF logging data show a sudden drop in the Sr and Ca contents, while Fe, Ti, K and Al all increase by about 60%. Likewise, CaCO3 percentages abruptly decrease from 17% to 0.6% subsequently recovering to values of about 20% after the event. Changes in chemical composition at the beginning of the event are very abrupt (within a few cm), whereas the return to "normal" values (comparable to those prior to 8.7 kyr B.P.) is distinctly more gradual. The inferred increase in bottom water nutrients, decreasing sediment biogenic content, weaker bottom current activity with decrease in magnetic grain size and concentration are all consistent with a sudden and significant decrease of NADW influence at this site just prior to 8.2 kyr B.P.. The extremely low carbon isotopic values associated with this event suggest a stronger influence of southern source bottom waters in the sub-polar Northwest Atlantic at this time. Our evidence for deep-water variations will be compared to published records across this interval to elucidate the relationship between ocean dynamics and climate across the 8.2 kyr B.P. event.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4936 Interglacial
DE: 4962 Thermohaline
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005