“We immediately saw that something special was going on,” said Johann Klages, describing the moment a dark, organic-rich layer appeared in a seafloor core lifted from the Amundsen Sea off West Antarctica. It was not an ice valley but a laboratory table on a ship in 2017, the RV Polarstern. The seafarer exercise of days had yielded only sterile sandstone. In what was supposed to be the last try then came a three metre stretch that resembled ground and not seabed. The same visual indication was a glimpse into a South Pole that was previously bearing thick vegetation.
The core, which was found in the present day Pine Island Glacier, consisted of fossil forest ground: a fine clay, silt weaving through networks of roots, and rich with pollen and spores. Later CT scanning revealed roots that had been well preserved to the extent that they contained individual cell structures, which makes a geological puzzle into a practical climate record. More importantly, the material was viewed as a layer of land which was deposited approximately at 2730 metres beneath the bottom of the ocean and ice meaning that sediments that are present in the ocean and ice were previously piled up in a coastal terrain. The vegetation assemblage in that landscape consisted of conifers, ferns and flowering plants, with the earliest records of flowering plants at such high Latitude in the Antarctic.
It is not the botany that is awkward about the reconstruction but the astronomy. The site was close to 82 degrees south which was close enough to the pole that would have been in about four months of winter darkness. However, there are several pieces of evidence which point to a cool, marshy rainforest ca. 90 million years ago, towards the middle of the Cretaceous. Both soil temperature indicators and the biological traces point at an average annual temperature of about 12C with Summer values around 19C (and in some reconstructions even more so). Rainfall was said to be similar to the present-day maritime conditions, and river or swamp waters might go up to approximately 20 o C. It is not only warmth, but long-term warmth in a location where the annual budget of energy sources should have been chastising.
When he explains that paradox, he makes readers focus on those feedbacks that are normally encountered by people living in modern times separately: greenhouse gases, albedo, and the very presence of ice as a physical object. The model experiments reported together with the main research demonstrated that the recreated conditions could not be achieved unless Antarctica had no large ice sheet, the ground had a dense vegetation, and the carbon dioxide in the atmosphere was considerably greater than previously contemplated in the middle of the Cretaceous. A range of 1,120 to 1,680 parts per million has been quoted by Klages, as opposed to a background assumption of about 1000 ppm of that period and a contemporary atmosphere of just over 400 ppm. Such difference is important since an ice sheet is not merely frozen water, but a sun-reflecting surface which makes the cold even stronger. Plants do just the reverse making the surface dark and consume heat.
It is difficult to discern the engineering narrative found within the science. These deep-time archives are available remotely, through drilling off an icebreaker, with rigs that are built to drill the continental shelves. That capacity is supplemented by a second archive of Antarctic that is directed at a different question: not ancient forest, but ancient air.
In some isolated “blue ice areas,” where overlying snow and ice cover has been blown off by the wind and older ice has been exposed by the flow, scientists have excavated ice fragments as old as 6 million years old in the Allan Hills. Those samples serve as climate records, not an ongoing record but a sort of a snapshot, even more than scientists forecast the Antarctic ice cores to date. The quality is methodological, just as historical: they preserve “ancient precipitation and, more importantly, ancient air,” in order to be able to measure gas-isotopes that tie age propositions, as well as to be able to place time-temperature limits in the past.
The buried soil of a polar rainforest and the open fragments of old ice together serve to point out a single practical fact: Antarctica is not just an archive but it is a collection of many archives, all with various resolution and various blind spots. When those records concur on such matters as the temperatures, the significance of the ice cover, the extent of the carbon dioxide they do not just bring the past to life. They increase the role of the climate models to meet the boundary conditions particularly in the high latitudes where small changes in reflectivity and circulation can determine whether ice survives.
