Millennial-scale changes in ventilation of the thermocline, intermediate, and deep waters of the glacial North Atlantic

Insights into North Atlantic deep water formation during the peak interglacial interval of Marine Isotope Stage 9 (MIS 9)

“…The modern hydrographic properties of NADW (Dickson and Brown 1994) may be subdivided into UNADW and LNADW, and have been proposed to be similar to that of previous interglacial periods (Duplessy et al 1984;Oppo and Fairbanks 1990;Raymo et al 1990Raymo et al , 2004Venz et al 1999). In contrast, abundant benthic δ 13 C evidence has emerged indicating that the hydrographic settings of deep and intermediate-depth ocean layers were quite different during glacial stages (i.e., Duplessy et al 1988, Oppo andLehman 1993;Curry et al 1999;Raymo et al 2004;Curry and Oppo 2005;Lynch-Stieglitz et al 2007;Gebbie 2014, Oppo et al 2015.…”

“…4). Although a few factors may affect the δ 13 C signal (i.e., Grossman 1987;Curry et al 1988), the variability at each site and gradients between sites may largely be interpreted as reflecting the influence of different hydrologic properties of the water masses involved (Oppo and Lehman 1993;Curry et al 1998Curry et al , 1999McManus et al 1999;Venz et al 1999;Raymo et al 2006). One prominent factor that influences variations in the local benthic δ 13 C is the mixing of water masses that have different isotopic compositions (Curry et al 1988, Oppo andHorowitz 2000).…”

The impacts of deglacial meltwater forcing on the South Atlantic Ocean deep circulation since the Last Glacial Maximum

“…Their results show a rather linear response of the NADW decrease relative to the amount of input of freshwater. Rind et al (2001) also point out that other studies discuss changes in the NADW associated with the millennial-scale cooling events (Charles et al, 1996;Manabe and Stouffer, 1997;Zahn et al, 1997;Curry et al, 1999). Proxy records of 231 Pa / 230 Th ratios recorded in a Bermuda Rise sediment core (Stanford et al, 2006), for example, suggest a weak AMOC at H1 (McManus et al, 2004), which resulted from a decreased NADW production.…”

“…These conditions led to increased sea ice formation (Liu et al, 2005) and extensive associated brine injection into the Southern Ocean (Shin et al, 2003). A salty (and therefore denser) version of the Antarctic Bottom Water (AABW) was present then (Adkins et al, 2002;Marchitto et al, 2002;Curry and Oppo, 2005), which acted as a subsurface salinity barrier, i.e., a strong vertical stratification that prevented other water masses from entering the AABW domain. Adkins (2013) points out that the LGM ocean had a much lower vertical mixing rate than the modern one.…”

“…Adkins (2013) points out that the LGM ocean had a much lower vertical mixing rate than the modern one. According to chemical proxy evidence, AABW filled most of the Atlantic Ocean basin at the LGM, while the North Atlantic produced a water mass that penetrated only to the mid-depths of the Atlantic (Duplessy et al, 1988;Boyle and Leach, 1995;Yu et al, 1996;Curry and Oppo, 2005;Lynch-Stieglitz et al, 2006;Marchitto and Broecker, 2006). This water mass was much shallower than the modern North Atlantic Deep Water (NADW) and can be referred as the Glacial North Atlantic Intermediate Water -GNAIW (e.g., Duplessy et al, 1988).…”