HR: 08:30h
AN: PP11A-03    [Abstracts]
TI: Sedimentary Regimes in the Northern Mendeleev Ridge During the Last Climatic Cycles
AU: * Not, C
EM: not.christelle@courrier.uqam.ca
AF: GEOTOP UQAM-McGill, CP 8888 Succ Centre Ville, Montréal, QC H3C 3P8, Canada
AU: Hillaire-Marcel, C
EM: hillaire-marcel.claude@uqam.ca
AF: Département des sciences de la terre et de l'atmosphère, CP 8888 Succ Centre Ville, Montréal, QC H3C 3P8, Canada
AU: Hillaire-Marcel, C
EM: hillaire-marcel.claude@uqam.ca
AF: GEOTOP UQAM-McGill, CP 8888 Succ Centre Ville, Montréal, QC H3C 3P8, Canada
AU: Preda, M
EM: preda.michel@uqam.ca
AF: Département des sciences de la terre et de l'atmosphère, CP 8888 Succ Centre Ville, Montréal, QC H3C 3P8, Canada
AU: de Vernal, A
EM: devernal.anne@uqam.ca
AF: Département des sciences de la terre et de l'atmosphère, CP 8888 Succ Centre Ville, Montréal, QC H3C 3P8, Canada
AU: de Vernal, A
EM: devernal.anne@uqam.ca
AF: GEOTOP UQAM-McGill, CP 8888 Succ Centre Ville, Montréal, QC H3C 3P8, Canada
AB: Due to low productivity and low sedimentation rates in the central Arctic Ocean, the setting of chronostratigraphy in deep sea-cores is a challenge. ¹⁴C stratigraphies are limited to the upper few centimeters, whereas oxygen isotopes in foraminifera are inconclusive due to both gaps in their records and the impact of isotopically light brines linked to sea-ice formation on their oxygen composition. To document further this issue, we use cores raise from two sites, with water depth of ∼1600 m (site 12) and ∼2500 m (site 11) respectively, in the northern Mendeleev Ridge area, during the 2005 HOTRAX cruise in the Arctic. Grain size, mineralogical (dolomite vs. calcite contents, clay minerals), geochemical (C_org, C_inorg, ¹³C_org, C_org/N_total ratios) and isotopic (²¹⁰Pb, ²³⁸U, ²³⁴U, ²³²Th, ²³⁰Th, ²³¹Pa, ¹³⁷Cs) measurements were made on grounded bulk sediment, whereas when present, foraminifera were analyzed for their ¹³C and ¹⁸O contents. The first striking feature depicted is the remarkable similarity of sedimentological and geochemical profiles at both sites despite their bathymetric difference. ²¹⁰Pb and ¹³⁷Cs data indicate a mixed layer restricted to the top cm. Foraminifera from this layer yielded a ¹⁴C age of 8500 a (Libby's years) suggesting high fluxes during the early Holocene thermal optimum. Below this layer, scattered foraminiferal shells down to about 12 cm, yielded Libby's ages ranging 27-33 ka with reversals suggesting that this section likely incorporates reworked material. By combining all information available, two drastically distinct sedimentary regimes may be inferred in this area. One corresponds mostly to ice-rafted deposition (IRD), as indicated by high sand, but low carbon contents, and the absence of foraminifer shells. The second regime is characterized by high contents in foraminifer shells, clays, Corg. and Cinorg, as well as high excesses in ²³¹Pa and ²³⁰Th linked to high scavenging rates in the overlying water column. From this information, a rough stratigraphic frame has been set in these cores. A discrete interglacial interval assigned to MIS (Marine Isotopic Stage) is found at about 16 to 19 cm in both multicores and a more pronounced MIS 7 interglacial is seen below, from 26 to about 37 cm. Both yielded high ¹³C-foraminiferal calcite expected under interglacial conditions. Sedimentation rates varying between appr. 1 to 3 mm/ka are proposed in this sector of the Mendeleev Ridge.
DE: 0473 Paleoclimatology and paleoceanography (3344, 4900)
DE: 4207 Arctic and Antarctic oceanography (9310, 9315)
DE: 4924 Geochemical tracers
DE: 9315 Arctic region (0718, 4207)
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2009 Joint Assembly