Rare Amber Fragment Uncovers Ancient Forest Beneath Antarctic Ice

Recently, scientists discovered an amber deposit in Antarctica, calling into question our vision of this polar region nearly 90 million years ago. Published in the journal Antarctic Science, this study carried out by the Alfred Wegener Institute and the TU Bergakademie Freiberg reveals that Antarctica, now covered in ice, was once home to a temperate forest.

The amber found in the underwater sediments of Pine Island Bay is direct evidence of the presence of coniferous conifers and humid forests at extreme latitudes, adapted to periods of prolonged polar nights and frequent fires. This discovery adds to knowledge about ancient ecosystems in polar regions and raises crucial questions about the resilience of these forests to the changing climate conditions of the Cretaceous Era.

The hope of finding a forest

Since the early 19th century, scientists have discovered wood and leaf fossils in Antarctica, revealing that a rich plant past existed long before the continent was plunged into a frigid climate. However, the majority of these remains date from several hundred million years ago, to a time when Antarctica was part of the supercontinent Gondwana.

As this supercontinent fragmented, Antarctica drifted toward the South Pole, moving away from Australia and South America. This process of geological separation has raised questions about the fate of its ancient forests, and the impacts of these movements and the climate change that accompanied them.

The drill sample from Antarctica contained remnants of amber and possible bark intrusions, visible in the red square. © Klages et al., 2024

However, in 2017, a team of researchers carried out an underwater drilling off the coast of West Antarctica, in the bay of Pine Island, at 73.57° South, 107.09° West, a remote region of the Embayment of the Amundsen Sea. In particular, it used the MARUM-MeBo70 underwater drill to extract deep sediments almost a kilometer below the water surface. They then discovered in 2020 a network of fossilized roots dating from the Middle Cretaceous, accompanied by pollen and spores preserved on a microscopic scale.

The southernmost amber in the world, buried in Antarctic mud

This same drilling recently made it possible to find tiny fragments of translucent amber at precisely 946 m. They measure between 0.5 and 1 millimeter, placed on a layer of lignite approximately 5 cm thick, itself in a layer of mudstone (solidified mud) 3 meters thick. These fragments present varying shades of yellow to orange and festoon-shaped fractures, typical signs of resinous flow from ancient conifers. They named this discovery “Amber from the Isle of Pines”. Some fragments show intriguing micro-inclusions, potentially pieces of bark. They provide valuable clues about the types of vegetation that existed in this polar region during the Cretaceous.

For scientists, this discovery is crucial. Effectively, it fills a gap in the mapping of amber deposits on a global scale. Until then, the southernmost deposits of amber had been observed in basins in Australia and New Zealand. This find demonstrates that at a time when the earth's climate was particularly hot and humid, coniferous forests were present in Antarctica. According to Dr. Klages, these forests thrived in favorable climatic conditions, characterized by mild temperatures and high humidity, similar to those of today's temperate forests. The amber discovered thus proves the existence of coniferous forests on all continents, even in areas that are now polar.

Amber, witness to a resilient forest facing extreme conditions

Amber fragments discovered in Antarctica display remarkable characteristics that reveal not only their age, but also the environmental conditions of the time. In fact, these fragments, of exceptional transparency, show signs of pathological resin flow. This is a phenomenon where the tree produces resin in response to injury or pest attacks. This process of “traumatic resinosis” plays a key role in the defense of trees. It forms a physical and chemical barrier against infections and insect attacks. The amber thus preserved retains the solidified resin, which seals the wounds in the bark. Its translucent quality and almost intact composition suggest rapid fossilization.

Indeed, the fragments found were quickly covered by sediments under shallow water, in an environment where the water created a protective barrier against degradation agents such as atmospheric oxygen and ultraviolet radiation. UV rays, in particular, degrade the resin by changing its chemical composition, which alters its structure and appearance.

A slice of Antarctic amber, showing signs of bark intrusion from a Cretaceous era tree. © Klages et al., 2024

According to Dr. Henny Gerschel, the study of these fossil fragments provides direct insight into the climatic conditions that prevailed in this region around 90 million years ago. At this time, Antarctica was home to a temperate forest, rich in conifers as previously mentioned. It managed to survive despite prolonged periods of polar night and the frequent fires of the Cretaceous era. This resilience of these forests in the face of environmental disturbances is visible in the inclusions of bark and pathological resin present in the amber.

Implications for understanding ancient ecosystems

The amber samples, although tiny, could therefore contain a wealth of information on the complex and rich ecosystem that populated Antarctica during the Cretaceous. Fossilized resin is known to capture and preserve microscopic items from the past, such as spores, pollen, and in some cases, microorganisms like fungi or bacteria. These inclusions, if present, could provide scientists with direct clues about the biodiversity of this era and the ecological interactions within this now extinct temperate forest.

Such microscopic elements would help to determine the plant composition on the one hand. It was undoubtedly dominated mainly by conifers close to the species of the modern temperate forests of New Zealand and Patagonia. On the other hand, we could understand more precisely the climatic conditions allowing this vegetation to thrive in warm and humid, although polar, environments.

As Dr. Johann Klages explains, the researchers' goal is to go beyond simply identifying amber. They hope to reconstruct the functioning of this forest ecosystem by studying its fossilized residue. Scientists are looking to determine which major events, such as forest fires or insect infestations, marked this environment by leaving specific traces in the amber fragments. “It was very exciting to realize that at some point in their history, all seven continents had climatic conditions that allowed resin-producing trees to survive,” concludes Johann Klages.

Source: Klages JP, Gerschel H, Salzmann U, et al., “First discovery of Antarctic amber. Antarctic Science”. Published online 2024:1-2. doi:10.1017/S0954102024000208