No two illustrations of THC are exactly the same, indicating the limits of our knowledge of the phenomenon. In fact, looking at Figure 6, (From “Stability of Southern Ocean Thermohaline Circulation”, marsland.ccs.110804.ppt), which illustrates THC subduction and upwelling points, very few of the upwelling areas agree with those shown in Figures 1, 2, 4 and 5.
Regardless, based on the upwelling areas in Figure 6, their coordinates were identified. Refer to Figure 7. The areas are coded with the same colors as the following graphs. The eastern equatorial Pacific has already been examined in this series, so it has been excluded from this post. Note: In a future post, I will look at the “mixing-driven” upwelling points identified in Figure 5.
Figures 8 and 9 show the SST and SST anomalies for four of the upwelling areas. Not shown is the area in the Southern Ocean, which would have skewed the SST graph. The SSTs (smoothed with an 85-month filter) vary from approximately 14 to 22 degrees C.
Figure 10: The areas off the U.S. West Coast (blue) and the Southwest Coast of Africa (purple), a hemisphere and an ocean away, have the same significant dip in temperature from the late 19th to the early 20th centuries. There is an approximate 5- to 6-year difference between their declines.
The upwelling areas off the South American West Coast (red) and the African Northwest Coast (green) have declines near the same period that are more rounded. Refer to Figure 11. In those areas, whatever caused the drops has either been muted with respect to the other two anomalies (Figure 10) or they are initiated by something entirely different or something on a different time scale.
The outlier is, of course, the SST of the Southern Ocean upwelling area, Figure 12. Its curve bears no resemblance to the others. Smoothed with an 85-month filter, its SST curve varies little from its SST anomaly curve, so I’ve used SST.
Sea Surface Temperature Data is Smith and Reynolds Extended Reconstructed SST (ERSST.v2) available through the NOAA National Operational Model Archive & Distribution System (NOMADS).