Everything old is new again, and today’s example is the so called Bipolar Seesaw freshly discovered. The bipolar seesaw is the swing in temperatures between the two poles of earth, where if its up in one pole its down in the other. But how freshly discovered is it? Well, here’s an article from 1998 about — ta da — the bipolar seesaw, complete with polar ice cores showing temperature fluctuations.
Even more interesting is this 2001 article by Wallace S. Broecker that ties it all together:
Geologists are now investigating whether these groupings correspond to another new source of evidence of cyclic patterns in Earth’s recent history. This evidence comes from studies of sediment in the deep waters of the North Atlantic. The rock fragments in these sediments are much too large to have been transported there by ocean currents; they could have reached their present location only by having been frozen into large icebergs that floated long distances from their point of origin before melting. During the past decade, Gerard Bond, my colleague at Columbia University’s Lamont-Doherty Earth Observatory, has studied the makeup of such ice-rafted debris. Noticing that some of the sediment grains were stained with iron oxide, he reasoned that they must have come from locales where glaciers had overrun outcrops of red sandstone. Bond concluded that a detailed analysis of deep sediment cores would reveal changes in the mix of sediment sources over time. This proved to be an excellent strategy, for Bond found something so unexpected that it stunned all of us who study climate history. The proportion of these red-stained grains fluctuated back and forth over time from lows of 5 percent to highs of about 17 percent, and these fluctuations had a pattern: a nearly regular, 1,500-year cycle. Even more amazing, he found that the cycles ran virtually unchanged, in both amplitude and duration, through both ice-age and non-ice-age periods during the last 100,000 years.
Bond puzzled over what might be pacing this cycle. As a geologist, he knew that the sources of the red-stained grains were generally closer to the North Pole than were the places yielding a high proportion of “clean” grains. At certain times, apparently, more icebergs from the far north were making their way well to the south before finally melting and shedding their sediment. Bond hypothesized that the alternating cycles might be evidence of changes in ocean-water circulation.
Ocean waters are constantly on the move, and water temperature is both a cause and an effect. As water cools, it gets denser and sinks to the bottom. In one part of what I like to call the “bipolar seesaw,” the bottom layer of the world’s oceans comes from cold, dense water sinking in the far North Atlantic. This causes the warm surface waters of the Gulf Stream to be pulled northward, as they are today. Bond realized that during this part of the ocean cycle, a large proportion of the icebergs that bear red grains would melt while still fairly far north. But sometimes the ocean reorganizes itself, and the Southern Hemisphere holds sway in driving ocean circulation. At such times, surface waters in the North Atlantic would generally be colder, permitting icebergs bearing red-stained grains to travel farther south before melting and depositing their sediment.
So what we have is just more confirmation, not anything new with the latest announcement of findings. Although I can’t complain too much, because it was new to me.
