The heart of Greenland has recently been green. A two-mile-deep ice core from the very center of Greenland's ice sheet in Summit, Greenland, produced a fossil assemblage containing an insect's compound eye, an arctic poppy seed, willow wood matter, fungi, and spike moss. The discovery, made by scientists at the University of Vermont, supports a previously controversial hypothesis that Greenland has not been frozen solid for millions of years. Instead, some 416,000 years ago, the arctic island emerged from its perpetual winter, exhibiting a milder arctic ecosystem long enough to sustain plants, small trees, flowers, and insects.
The evidence suggests that Greenland remained thawed for thousands of years in between phases of sustained freezing and ice accumulation, called glaciation periods. The discovery also implies that the two miles of ice covering Greenland today had to have accumulated over an estimated 416,000 years. Greenland's ice sheet can no longer be considered a stable component of the Pleistocene Ice Age, but instead as a dynamic landscape and ecosystem that experienced inter-glacial periods and biological revival of the island.
Fossil identification and soil analysis revealed that central Greenland hosted an open, arid, and green landscape at least once during the last 1.1 million years, most likely 416,000 years ago. The vegetation in the ice core samples necessitates a surface temperature range from 1 to 10 degrees Celsius -- a tolerable, albeit cold environment at which the organisms could survive. The closest living relatives of the fossilized plants and insects thrive in short artic winters, where even the summers are snowy.
As reported in PNAS on August 5, 2024, scientists analyzed glacial till and soil from the base of the impressive ice core collected in 1993 during the Greenland Ice Sheet Project 2. The rock and ice of the core have been extensively studied, but the three inches of glacial till at the bottom of the core had been previously overlooked. The subglacial rock contained cosmogenic nucleotides that prove that Summit's surface was exposed to the elements for an extended period. The organic carbon, nitrogen, and the presence of meteoric Beryllium-10 indicate the development of soil, which takes some time. Meteoric 10Be falls from the skies in rain drops and then binds tightly to surface sediments. The concentration of 10Be in soil samples serves as a marker of soil erosion. This means the ice sheet had completely receded long enough for this particular soil chemistry to develop, for poppies to spring up, moss to cover the ground, and insects to proliferate, and pollinate the vegetation. Small trees were even given enough time to populate the rocky landscape. This revelation constrains modern understanding of the Pleistocene sea level fluctuations during an epoch of lower carbon dioxide concentrations, the cyclic glaciation and deglaciation periods, ecosystem recovery, and the transition between warming and cooling periods.
When considering these drastic changes in Greenland's ice sheet volumes, it is interesting to note that the extreme global glaciation in the Pleistocene caused a staggering 390-foot sea level drop, relative to today's mean sea level, that exposed the land bridge from Alaska to Russia. The variation in Greenland's environment through the last Ice Age indicated by this particular study is one example of the extreme swings in temperature and terrain experienced on Earth during the 2.5 Ma of the Pleistocene Epoch.
The complete melting of an ice sheet should correlate to an incremental rise in sea level. Greenland is the canary in the coal mines of climate change, and scientists have focused innumerable research dollars and intellectual efforts on reconstructing the history of its ice sheets as it correlates to the global mean sea level curve. Ice cores provide a valuable history of isotopic geochemistry that dates back only as long as the ice has been continually frozen. Isotopic analysis of the elements that make up the ice can give an inexact but useful indication of the temperature at which the ice was formed. Interestingly, oxygen isotopes from ice cores, coral skeletons, and tree rings can be calibrated and used as proxy records of past temperatures.
These datasets are the foundation of the global temperature reconstructions. The results from this study have underscored the utility of a critical database that is stored at the bottom of existng ice sheets, the basal ice-sediment interface, where fossils of the most recent warm period can refine our understanding of the cyclic ice ages and warming periods Earth has experienced in recent history, pre-dating human civilization.