A Laurentide outburst flooding event during the last interglacial period

Abstract

(Fig. 1). The red layer is ∼10 cm thick at Site U1305 and ∼20 cm thick at U1302 (Figs 2-4). The base of the layer is very sharp at both sites, suggesting rapid onset of deposition with little bioturbation. At Site U1305, the top of the layer is well defined, whereas at Site U1302 the top of the layer is more diffuse with a distinct tail, probably the result of mixing by bioturbation. The bright red colour of the layer is distinctive and marked by anomalously high values of a * (red-green colour parameter) at both sites. A peak in the first derivative of the reflectance spectrum at 565 nm suggests that the red colour is primarily imparted by haematite in the sediment 6 (see Supplementary Information).Core scanning X-ray fluorescence (XRF) measurements show high values of Ca/Sr in the red layer interval at both sites (Figs 3 and 4), indicating an increase in the proportion of strontium-poor detrital carbonate relative to strontium-rich biogenic carbonate 7 . The peak carbonate content of the sediment within the layer is ∼30% at Site U1305 and ∼40% at Site U1302. At Site U1305, the carbonate peak corresponds to a significant increase above background levels whereas at Site U1302 the increase is less pronounced, most likely owing to relatively higher deposition rates of synsedimentary biogenic carbonate during the interval.Bulk carbonate δ 18 O shows a strong decrease to values of about −5 (versus Vienna PeeDee Belemnite) within the red layer at both sites, which is typical of detrital carbonate from Hudson Bay 8 . Organic biomarkers provide further evidence of the source of the red layer. At both sites the red layer contains high abundances of a suite of organic compounds normally absent in recent sediments. These petrogenic compounds include carotenoid-derived aromatic hydrocarbons (for example, isorenieratane and palaerenieratane), aromatic steroids and secohopanoids (see Supplementary Information). The relative abundances of these compounds are approximately three times higher at Site U1302 than at Site

Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

“…Indeed, the smaller size of the LIS is consistent with changes in large-scale atmospheric circulation that facilitated the development of a larger Eurasian Ice Sheet during MIS 6 (Colleoni et al, 2016). Little is known about the deglaciation of the LIS at the end of MIS 6, but a major glacial lake outburst flood has been reported from a proximal marine core in the Labrador Sea around 124 ka (Nicholl et al, 2012), which may be analogous to the widely reported drainage of glacial Lake Agassiz during the final deglaciation of the LIS around 8.2 ka (e.g. Barber et al, 1999).…”

Biogenic magnetite, detrital hematite, and relative paleointensity in Quaternary sediments from the Southwest Iberian Margin

“…Hysteresis ratios: M r /M s and H cr /H c where M r is saturation remanence, M s is saturation magnetization, H cr is coercivity of remanence, and H c is coercive force, can be used to delineate single domain (SD), pseudo- single domain (PSD) and multidomain (MD) magnetite and to assign "mean" magnetite grain sizes through empirical and theoretical calibrations of the so-called Day plot (Day et al, 1977;Carter-Stiglitz et al, 2001;Dunlop, 2002;Dunlop and CarterStiglitz, 2006). Magnetic hysteresis properties were also analyzed through First-Order Reversal Curves (FORCs) that provide enhanced mineral and domain state discrimination (Pike et al, 1999;Roberts et al, 2000;Muxworthy and Roberts, 2007). FORCs are carried out by progressively saturating a small (few hundred mg) sample in a field (H sat ), decreasing the field to a value H a , reversing the field and sweeping it back to H sat in a series of regular field steps (H b ).…”

Deep Atlantic variability during the last interglacial period

“…2). The last and most prominent of the NADW anomalies during the early LIG (at ~124 ka) was also associated with an outburst flood analogous to the one believed to have triggered the 8.2 ka event, when large amounts of freshwater entered the North Atlantic through the Labrador Sea (Nicholl et al 2012;Galaasen et al 2014). Taken together, this highlights buoyancy gain from a generally warm Galaasen et al (2014).…”