Abrupt changes in Antarctic Intermediate Water circulation over the past 25,000 years

A boundary exchange influence on deglacial neodymium isotope records from the deep western Indian Ocean

“…Figure 6: WIND 28K uncleaned foraminifera ε Nd record compared to sediment leachate ε Nd records from RC11-83 (Piotrowski et al, 2005) and V19-188 (Pahnke et al, 2008). The RC11-83 and V19-188 records are plotted on their original published age models, with representative error bars (2σ external) from those studies, while the age model for WIND 28K is from Yu et al (2010), after Kiefer et al (2006).…”

“…Table 1 for core depths). Also shown are the locations of water column ε Nd profiles from Bertram and Elderfield (1993;sites CD1502-1507; diamonds labelled with their numeric identifier and colour coded according to their location; see Figure 5), ferromanganese crust 109D-C (28 °S, 61 °E, 5200-5700 m water depth; white square; O'Nions et al, 1998) and sediment core V19-188 (6.87 °S, 60.67 °E, 3356 m water depth; pink circle; Pahnke et al, 2008). Schematic deep water flow paths of CDW and NIDW are shown by dark blue and light blue arrows, respectively (redrawn from McCave et al, 2005); for more detailed hydrography, including the detailed flow paths of NIDW and AAIW at shallower depths, see McCave et al (2005).…”

“…Controls by local buffering might also explain the discrepancy between WIND 5K and an existing ε Nd record from V19-188 at 3356 m water depth on the north-eastern margin of the Mascarene Plateau (Pahnke et al, 2008; Figures 1 and 6). Late Glacial ε Nd values of -4.2 in V19-188 appear surprisingly radiogenic and, if these are to be explained by a boundary exchange control, this requires a different temporal evolution of boundary exchange on the eastern flank of the Mascarene Plateau to that observed on the Madagascan margin (Table 4).…”

“…Such conservative behaviour in the Antarctic Circumpolar Current has recently been demonstrated in modern seawater studies (Carter et al, 2012;Stichel et al, 2012) and we show that this was apparently true during both the Holocene and Late Glacial periods. The implication is that evidence on the ε Nd evolution of the Southern Ocean end member through time may be obtained from WIND 5K or RC11-83 (Piotrowski et al, 2005), but not from WIND 28K or V19-188 (Pahnke et al, 2008).…”

“…Rutberg et al, 2000;Piotrowski et al, 2005;Gutjahr et al, 2008;Pahnke et al, 2008;Roberts et al, 2010). If ε Nd is treated as a conservative tracer, comparison with non-conservative tracers may also be valuable; for example, its coupling or decoupling with carbon isotope changes through time may provide evidence on productivity, nutrient regeneration or other carbon cycle changes (e.g.…”