According to a recently published paper in the journal Science, (Cook et al., 2016, “Ocean forcing of glacier retreat in the western Antarctic Peninsula”), between 1945 and 2009 the mean ocean temperature warmed at depths of 150 to 400 meters for about 3/4ths of the waters surrounding the western Antarctic Peninsula (AP). The other 1/4th of the ocean waters at those depths (150 to 400 m) cooled (by -1¬∞C ) during those 65 years.
As the authors point out, and as the graph above shows, in the areas where the waters warmed (light red shaded), glacier retreat was observed to be most pronounced (blood red points). In the regions (Bransfield Strait) where the ocean waters cooled (blue shaded), glaciers were in balance and even advanced (blue points).
Citing this strong correlation between regional ocean warming/cooling and regional glacier retreat/advance, the authors concluded that the long-held assumption that atmospheric and surface warming (presumably driven by greenhouse gases) was what primarily caused Antarctic glaciers to recede is not supported by the evidence. Instead, it is the temperature of the ocean waters that “have been the predominant control on multidecadal glacier front behavior in the western AP.”
“Here, we identify a strong correspondence between mid-depth ocean temperatures and glacier-front changes along the ~1000-kilometer western coastline. In the south, glaciers that terminate in warm Circumpolar Deep Water have undergone considerable retreat, whereas those in the far northwest, which terminate in cooler waters, have not. Furthermore, a mid-ocean warming since the 1990s in the south is coincident with widespread acceleration of glacier retreat. We conclude that changes in ocean-induced melting are the primary cause of retreat for glaciers in this region. … [S]everal recent studies of Arctic glaciers have concluded that calving rates are strongly dependent on ocean temperatures. Until now, the role of the ocean (as opposed to the atmosphere) as the dominant driver of glacier frontal retreat on the western AP has not been considered…. We conclude that ocean temperatures below 100-m depth have been the predominant control on multidecadal glacier front behavior in the western AP.”
It should be pointed out that the decadal-scale changes in the heat content of the layers of abyssal vs. surface Southern Ocean are entirely consistent with what is expected with natural variability.