Figure 8: Climate anomaly pattern that drove New Zealand glacier advances.

Lower-to-middle troposphere (a) and surface (b,c) climate anomalies for the South Pacific region. The anomalies depict the spatial patterns for the average mass balance gain composite minus the average mass balance loss composite, and hence represent the atmospheric and oceanic conditions that promoted glacier advances in New Zealand. SPCZ refers to the South Pacific Convergence Zone. Geopotential height contours are shown every 10 m (positive=solid; negative=dashed). Zonal wind (u-wind) anomaly is at the 500 hPa geopotential height level shown in a and the solid (dashed) line represents the location where there is a zone of maximum (minimum) westerly anomalous flow. Arrows in b show surface wind anomalies. All anomalies (except sea ice) are shown relative to climatology for the 1981–2010 period. Low temperatures at 850 hPa geopotential height (t850; ∼1,500 m above the sea level) extend over most of the South Pacific from southern Australia to South America. This pattern is also associated with increased sea ice concentration (%), and advancing outlet glaciers in East Antarctica directly south of New Zealand. In the Amundsen Sea sector of West Antarctica on the opposite side of this atmospheric and oceanic dipole, this climate pattern is associated with warmer air and higher SSTs and reduced sea ice concentration, and likely increases in sub-ice shelf melt rates at Pine Island Glacier.