Millennial Scale Climate Variability

• In general millennial-scale cycles occur in high-resolution Antarctic ice cores, particularly in methane and temperature records (e.g. Byrd, EPICA Dome C). However, they appear lower amplitude and their timing may differ from their NH counterparts (D-O events).

• The pattern of millennial-scale variability superimposed on G-I climate cycles in Antarctic ice cores occurs both during and prior to the last 100 kyr.

• The millennial-scale climate cycles labelled as 'A-events' in Antarctic temperature records suggest that Antarctica and the Southern Ocean may be out-of-phase with Greenland warming events (Blunier and Brook, 2001). It has been suggested that this was the pattern expected from simple models involving changes in ocean heat transport (Stocker and Johnsen, 2003), with Antarctica and the Southern Ocean able to accumulate heat when ocean heat transport to the north was weak.

• Although uncertainties between the age of the gas (methane) and the ice enclosing it in Antarctic ice cores makes evaluation of the precise timing of inter-hemispheric millennial-scale cycles difficult, in some D-O cycles the temperature maxima in the north and south appear to be synchronous (e.g. EPICA Community Members, 2006).

• In this case, methane concentrations are most likely controlled by changing wetland extents in the northern high latitudes and tropics, along with changes in sinks (Valdes et al., 2005), and thus are relevant to Antarctic climate only as a relatively minor amplifier. However, a Pacific Basin ocean clathrate source for the methane has also been proposed (Kennett et al., 2000).

• Millennial-scale Antarctic warm periods (A1-A7; Blunier and Brook, 2001) are well expressed in SST, thermohaline circulation (sortable silt) and 818O records from the southern mid-latitude ocean (Barrows et al., 2007; Carter et al., 2008). One of these events, ACR, at -14.2-12.4 ka, is associated with an abrupt cooling of -2°C in the Southern Ocean and an expansion of ice shelves and sea ice (Shemesh et al., 2002), modest intensification of winds (Stenni et al., 2001; Rothlisberger et al., 2002) and intensification in deep abyssal inflow along eastern New Zealand through the Pacific gateway (Carter et al., 2008).

• Thus, millennial-scale climate variability in Antarctica and Southern Ocean appears to display many similar characteristics and processes (perhaps with reduced amplitude) to those observed at the orbital scale (e.g. SSTs, sea ice, water masses and circulation).

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