Brazilian researchers make discovery in Antarctica

A University of São Paulo group discovers a glacial structure that proves the existence of climatic variations on the Antarctic continent roughly 15 million years ago.

By Elton Alisson

Agência FAPESP –  Universidade de São Paulo (USP) researchers have identified the fundamental glacial structure that clarifies the paleoclimatic history of Antarctica during the Miocene period (approximately 15 million years ago).

The structure – known as a glacial clast pavement – proves that there was a period of expansion in the ice mantle in Eastern Antarctica after a period of warming known as the Miocene Climatic Optimum, when it is estimated that the Antarctic ice mantle began to expand.

The details of the study will be presented in July during the biannual conference of the Scientific Committee on Antarctic Research (Scar), which will be held in Portland, Oregon, in the United States.

“The pavement documents an important paleoclimatic event for the Eastern Antarctic during the Miocene,” states Antonio Carlos Rocha Campos, professor of the USP Geosciences Institute and project coordinator, in an interview with Agência FAPESP. Rocha Campos conducted projects funded by FAPESP, including the Thematic Project “Tectonic, climatic and paleogeographic characteristics, genesis and preservation of pre-cenozoic glacial deposits in Brazil.”

According to the researcher, the structure found provides complete and irrefutable evidence that the continent underwent a phase of glaciation roughly 10 million years ago, after a warming period over 15 million years ago.

Glacial clast pavements (rock fragments) are produced by glaciers as they slide across the surfaces over which they move, taking with them rocks of various forms and sizes, which are then absorbed into the ice. When the rock fragments are released, they are re-embedded subglacially and eroded during the advance of the glaciers, resulting in a type of rock pavement.

In 2011, during a study on Seymour Island (Marambio Base) on the eastern part of the Weddel Sea in Eastern Antarctica, a team of researchers from the Brazilian Antarctic Program (Pronantar), which includes Rocha Campos, found and identified this type of glacial structure for the first time on that part of the Antarctic continent.

According to Rocha Campos, the presence of clast pavement indicates that the ice mantle of Eastern Antarctica reached Seymour Island during the Upper Miocene (approximately 10 million years ago). The mantle moved quickly, probably across land. 

“The history of glaciation in Antarctica during the Miocene was told based on evidence that still left doubts. The existence of clast pavements clarified the question of why structures are known to be associated with the action of glaciers,” he affirmed.

The researchers now intend to analyze other phases of the paleoclimatic history of Eastern Antarctica, about which there are still doubts regarding the identification of evidence that characterizes and proves climatic changes occurred on the continent.

Among the stages is a passage from the Eocene (roughly 36 million years ago) to the Oligocene (30 million years ago), when there was notable climate change in almost all of Antarctica in conjunction with the formation of the ice mantle that covered the continent.

In this geological interval, Antarctica also experiences changes in the warming phase, followed by glaciation, similar to the climatic changes that occurred in the Miocene.

“The history of the formation of the Antarctic ice mantle is full of irregularities. Not only was there a gradual reduction in temperature and a progressive increase in Antarctica’s ice mass, but alternating stages of milder climate followed by phases of warmer climate,” explains Rocha Campos.

Some of the evidence used to characterize this climatic change includes deposits of glacial origin. Nevertheless, according to the researcher, the identification of this type of sediment or rock is highly complex and often inconclusive.

On Seymour Island, for example, where Brazilian researchers are conducting studies, several climatic intervals are based on the presence of glacial sediments. Still, identification cannot always be made with absolute certainty. “Diagnostic glacial structures, like glacial clast pavements, are rare,” says Rocha Campos.

Fire at the Brazilian base

Rocha Campos and the colleagues in his USP group were housed at the Argentine Marambio Base, and many of them had already returned to Brazil when a fire broke out at the Commander Ferraz Brazilian Antarctic Base (EACF) – Proantar’s base on the continent – in late February.

According to Rocha Campos, the study they conducted does not rely on the Brazilian base. “But we clearly and deeply regret the loss of EACF, given its symbolic and scientific importance, as well as the loss of human life,” he stresses.

As the majority of the rocks around the base are volcanic and Rocha Campos’ research group is dedicated to studying glacial rock, the researchers set up a campsite or requested housing in a base near the region where they would conduct their studies, such as Argentina’s base on Seymour Island.