By Andy May
Something interesting PNAS thing discusses the deepest part of the Camp Century Greenland ice core. It has no fee wall. Researchers, led by Andrew Christ (Department of Geology, University of Vermont) found evidence of an ice-free vegetation environment at the base of the Camp Century ice core about a million years ago. This means that the glaciers, now 1.4 kilometers (0.9 mi) thick, at the Camp Century site completely melted and reformed between 0.7 and 1.4 million years ago. The Camp Century location, along with other deep ice core locations, is shown in Figure 1.
The Greenland ice sheet was completed 7.5 million years ago and grew significantly from 3.3 to 2.7 million years ago. So in general we are discussing a time period where Greenland is often very similar to today.
Sediments beneath the ice, containing well-preserved fossil plants and other paleontological evidence of an ice-free environment at the Camp Century site. Macrofossils are also found at NGRIP, but in ice. Images of the macrofossils found in the Camp Century core are shown in Figure 2.
The base sediments of the Camp Century core are 3.4 meters thick. The researchers divided it into three units. Evidence suggests that the most recent sedimentary has undergone melting and coagulation between 0.7 and 1.4 Ma. In Figure 3, we show Javier’s illustration of the past million years.
Figure 4 shows the full possible time horizon for the Camp Century melt event from Tzedakis et al. (2017).
The earlier part of the melting time was near the “Middle Pleistocene Transition”, about 1.25 Ma. The mid-Pleistocene transition (MPT) is the time defined by the total energy required for an interglacial period to begin and succeed. Before 1.5 Ma, less total energy was needed to melt the ice and enter the interphase like today. The amount of energy required increases over time until it levels off around 0.6 Ma, see Figure 5. Possible time period for total melting in the Camp Century core, at 77°N and 61°W , which is essentially the width of the Middle Pleistocene Transition.
During the MPT transition, the stability of the northern ice sheet is changing. As Figures 3 and 4 show, MIS 31 (1.7 Ma) and MIS 25 (9.6 Ma) were unusually warm and occurred during a period of very little ice. In fact, the glacial periods 600K years ago were not as cold as the ice ages 600K years ago. The Dye ice core shows it to be ice-free from 424 to 374 ka (MIS-11), but Dye lies further south than Camp Century (see Figure 1). MIS 11 is just after the end of the MPT.
The golden curve in figure 4 is18O, an oxygen isotope ratio that varies linearly with surface temperature. It peaks during the MIS period. The other curve in Figure 4 is the isolation of 65°N. These curves are also shown in Figure 3, where they are easier to read.
The current elevation of the underlying sediment at Camp Century is 500 meters above mean sea level, removing 1.4 km. of the upper ice would lead to a recovery of about 950 meters in about 10,000 years. So if the conditions were the same when the ice melted, the final altitude would be about 1,400 meters.
It’s hard to draw any firm conclusions from the data shown in this article, but I found it very interesting, and it’s a well-written article you should read. It is amazing that the Greenland ice sheet completely melted to 77°N. However, it happened during the MPT which is less surprising, since this is clearly a time of unstable climate. This geological event does not affect the current climate debate, but it does show that natural forces can cause extreme changes in climate.
Figures 3, 4, and 5 show how much colder ice ages have been over the past 600 million years, compared with two million years ago. We are now living in a cold part of Earth’s history. Something to think about, when governments are trying to force us back Little Ice Age (approximately 1300 to 1850) by limiting CO2 emissions.