Southern Hemisphere Water Mass Conversion Linked with North Atlantic Climate Variability

Abstract

Intermediate water variability at multicentennial scales is documented by 340,000-year-long isotope time series from bottom-dwelling foraminifers at a mid-depth core site in the southwest Pacific. Periods of sudden increases in intermediate water production are linked with transient Southern Hemisphere warm episodes, which implies direct control of climate warming on intermediate water conversion at high southern latitudes. Coincidence with episodes of climate cooling and minimum or halted deepwater convection in the North Atlantic provides striking evidence for interdependence of water mass conversion in both hemispheres, with implications for interhemispheric forcing of ocean thermohaline circulation and climate instability.

Deep water variability on the southern Agulhas Plateau: Interhemispheric links over the past 170 ka

“…The few highresolution paleoceanographic records from the Southern Hemisphere oceans confirm this suggestion [Charles et al, 1996;Pahnke et al, 2003;Pahnke and Zahn, 2005], although such records are sparse and do not allow us to draw a conclusive picture for the wider Southern Hemisphere oceans. It has been suggested by early studies [Hays et al, 1976;Imbrie et al, 1989;Howard and Prell, 1992;Labeyrie et al, 1996] that on orbital timescales, Southern Ocean sea surface temperatures (SST) respond early to changes in the orbital parameters and might actually lead global ice volume [Charles et al, 1996].…”

“…For this comparison we have chosen deep South Atlantic cores RC11-83 [Charles et al, 1996] and TN057-21 (Table 2 [ Ninnemann and Charles, 2002]), which remained strongly influenced by SCW (i.e., AABW) over both glacial and interglacial periods. We also use core MD97-2120 (Table 2 [ Pahnke and Zahn, 2005]) from the Chatham Rise, southwest Pacific, as an alternative Southern Ocean record documenting AAIW variability. Finally, core MD95-2042 (Table 2 [ Shackleton et al, 2000]) from the Iberian Margin was chosen as a North Atlantic reference as it is high resolution, has a timescale that has been tied to both Vostok and Greenland Ice Core Project (GRIP) and reflects changing northern versus southern water sources in the North Atlantic during glacial periods.…”

Coupling of millennial‐scale changes in sea surface temperature and precipitation off northeastern Brazil with high‐latitude climate shifts during the last glacial period

“…Subsequently, short-term climatic changes were also found in high-resolution climate archives from the tropics Schulz et al, 1998;Peterson et al, 2000;Jennerjahn et al, 2004;Wang et al, 2004] and the Southern Hemisphere [Pahnke and Zahn, 2005;Sachs and Anderson, 2005]. In the North Atlantic, large abrupt shifts in temperature, so-called Dansgaard-Oeschger events, were part of longer-term cooling trends (Bond cycles) that culminated in massive iceberg surges, known as Heinrich events [Heinrich, 1988;Broecker et al, 1992;Bond et al, 1993].…”

Dominant Northern Hemisphere climate control over millennial-scale glacial sea-level variability

“…Further back in the glacial, the coral-based data set becomes more incomplete and the reliably dated sea-level points, though showing the general amplitude of sea-level changes, are insufficient to establish the exact pattern and timing of millennial-scale changes (Chappell, 2002;Cutler et al, 2003). Alternatively, sea-level information can be derived from oxygen isotope (d 18 O) records of benthic foraminifera that appear to show a global signal as a similar style of variability has been observed in different ocean basins (Shackleton et al, 2000;Pahnke and Zahn, 2005). However, the benthic records may be substantially biased by local hydrographic changes (Skinner et al, 2003) limiting their use as a global sea-level proxy.…”