The “warm” Marine Isotope Stage 31 in the Labrador Sea: Low surface salinities and cold subsurface waters prevented winter convection

Abstract

Surface and subsurface conditions in the Labrador Sea during Marine Isotope Stage (MIS) 31 at the Integrated Ocean Drilling Program Site U1305 off southwest Greenland are reconstructed based on dinocyst and foraminifer assemblages. Isotopic compositions of planktonic (Neogloboquadrina pachyderma, Np) and benthic (Cibicides wuellerstorfi, Cw, and Oridorsalis umbonatus, Ou) foraminifera provide further information about water properties in the mesopelagic layer as well as at the seafloor. Dinocyst proxy reconstructions indicate low salinities (32-34.5), cool winters (3-6°C), and mild summers (10-15°C) in the surface water layer during the MIS 31 "optimum". However, planktonic foraminifer assemblages largely dominated by Np suggest relatively cold subsurface conditions in winter and summer (<4°C). Lower δ 13 C values in Np versus Cw further suggest either a lesser-ventilated mesopelagic layer than the bottom one or high organic matter oxidation rates at Np habitat depth. The dinocyst and planktonic foraminifer records together suggest a strong stratification between the surface and subsurface water layers. Isotopic and micropaleontological data thus converge toward paleoceanographical conditions unsuitable for convection and intermediate or deep water formation in the Labrador Sea during the warm MIS 31 interglacial, a situation comparable to the one that prevailed during the warm MIS 5e. the micropaleontological content of sediments from the Integrated Ocean Drilling Program (IODP) Site AUBRY ET AL. MIS 31 IN THE LABRADOR SEA 1206 PUBLICATIONS Paleoceanography

Climate response to drastically modified PDO, PNA and NAM in the superinterglacial MIS 31

“…Warmer conditions, with values as high as 5 °C are depicted in the NH polar region in agreement with palaeoreconstruction (Raymo et al 1996;Lawrence et al 2009;Melles et al 2012;Aubry et al 2016). This is supported by the reduced sea-ice extension and thickness due to the influence of the precessional cycle (Fig.…”

“…It should be noted that the Kurushio-Oyashio SST is an important source of heat contributing to the Northern Pacific climate variability and PDO magnitude (Trenberth et al 1998). A brief comparison with palaeoreconstruction shows that the seasonal temperature contrast in the NH was also reported by Aubry et al (2016). They claimed that cold subsurface and warm surface waters in the Labrador Sea associated with low salinity prevented winter oceanic convection (Fig.…”

Last Interglacial (MIS 5e) sea surface hydrographic conditions in coastal southern California based on dinoflagellate cysts

“…It was shown that multivariate statistical analyses performed with paleo and modern cyst assemblages could be used to reconstruct these parameters in the Late Quaternary [e.g. de Vernal et al, 2001de Vernal et al, , 2005de Vernal et al, , 2013Radi and de Vernal, 2008;Pospelova et al, 2015;Aubry et al, 2016;Hardy et al, 2018]. Most of these studies were focused on the LGM and the Holocene in the North Atlantic, and published data on dinoflagellate cysts during the LIG are less common in general and are again mainly located in the North Atlantic [e.g.…”