If the jazz rhythm of cold climate is defined by North Atlantic iceberg activity, then New Zealand’s glaciers accent the back beat.
That is the finding of Peter Strand and collaborators as described in their recent paper in Quaternary Science Reviews.
The signature beat of Northern Hemisphere cold periods during the last glacial period (since about 90,000 years ago) are known as Heinrich events.
Hartmut Heinrich found layering of rock sediment on the bed of the Atlantic that wasn’t local. It had arrived by iceberg transport. Dating when each of these layers of foreign rocks were deposited provided a good indication of when the Northern Hemisphere was cold. Other efforts to date Northern Hemisphere cold periods aligned well to Heinrich’s rock layer dates, so his name has been associated with these cold Northern Hemisphere events.
When considering the current rapid change in global temperatures, it is not unreasonable to look to the past to see how temperature changes were manifest.
One point of interest is whether there is synchronisation of Northern and Southern Hemisphere temperatures.
The lines of rock on the hillsides above New Zealand’s Lake Pukaki represent past extents of a former glacier. Peter Strand and his colleagues found that each rock-line was deposited by the glacier at different times during the last glacial period.
If the Northern and Southern hemisphere temperatures were synchronised, then the dates of these moraines should align with the Heinrich events.
The dates of these moraines fall between the Heinrich events. It seems that when the Northern Hemisphere was cold, The Pukaki glacier was in retreat, and when the Northern Hemisphere was warm, the Pukaki glacier advanced to build these moraines.