Intra-interglacial climate variability in the North Atlantic during MIS 11

• Main Authors: Kandiano, Evgeniya S., Van der Meer, M. T. J., Schouten, S., Bauch, Henning A., Sinninghe Damste, J. S.
• Format: Conference Object
• Language: unknown
• Published: GeoUnion Alfred-Wegener-Stiftung 2014
• Subjects: Ice Sheet; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/27669/

A pronounced intra-interglacial MIS 11 cold event was revealed in the North Atlantic by sea surface temperature (SST) and salinity (SSS) reconstructions. SSTs were established using TEX86-indices derived from relative abundances of glycerol dialkyl glycerol tetraethers (GDGTs) of Thaumarcheota and alkenone-based Uk’37 indices. To assess variations in palaeo-SSS, the hydrogen isotopic (δD) compositions of long chain alkenones were determined. For further interpretation, the obtained SST and SSS reconstructions were compared to relative planktic foraminiferal abundances, ice rafted debris (IRD) counts and δ18O records from benthic and planktic foraminifera. According to our data, the temperature amplitude of the aforementioned cold event reached 7 °C. We assume that this value might combine the actual cooling with an additional effect of a vertical migration of the Thaumarchaeota to deeper and, therefore, colder water layers, which might occur due to an enhanced intensity of open ocean upwelling which is generally characteristic for this location during cooling episodes. This explanation is also supported by changes in stable oxygen isotopes of deep-living planktic foraminiferal species G. truncatulinoides (s) and (d). A pronounced increase of δ18O values contemporaneous with the cold event might indicate a change of habitat conditions of these species towards colder temperatures. Another evidence of enhanced upwelling intensity during this episode might be derived from increased relative abundance of planktic foraminiferal species G. bulloides, whose geographical distribution is related to upwelling zones. A salinity drop was registered before the SST decrease. Because the intra-interglacial MIS 11 cold event occurred during the phase of slowly decreasing benthic δ18O values, we assume that it might be related to the late phase of the circum-North Atlantic ice sheet decay. Therefore, its nature might resemble the one of the 8.2 ka Holocene event.