Clays in Antarctica from millions of years ago reveal past climate changes

Members of the TASMANDRAKE research group of the Andalusian Earth Sciences Institute (IACT), which pertains to the University of Granada and CSIC, have published a research paper in the prestigious international journal Scientific Reports describing their analysis of clays from Antarctica dating back 35.5 million years, to reconstruct past climate changes.

Glaucony grains observed under an electron microscope
[Credit: University of Granada]

Their study was conducted in the area known as Drake Passage—the body of water that separates South America from Antarctica, between Cape Horn (Chile) and the South Shetland Islands (Antarctica). The results help to better understand the climatic conditions prior to the formation of the Antarctic Circumpolar Current, thus evaluating possible links between the development of the ice sheet in Antarctica and the changes in the tectonic and paleoceanographic configuration. Such questions constitute key facets of past climate functioning that provide boundary conditions for today's climate models, which predict a general rise in sea levels over the coming centuries.

The article analyses the relevance as a climatic indicator of the mineral commonly known as 'glauconite', which is more properly termed 'the glauconia facies' or 'glauconia'. This is a type of green clay, formed mainly in shallow marine environments (<500 m) with temperatures below 15° C, under very specific oxygenation conditions.

The existence of this clay formation in the Antarctic region has received little scholarly attention to date compared to other geological records on the planet. The characteristic green-coloured mineral has been observed around Antarctica and the Antarctic Ocean in sedimentary sequences of the Terminal Eocene Event—that is, before one of the main climatic transitions in Earth's history. The Eocene–Oligocene climate transition took place approximately 34–33.6 million years ago.

Northwest region of the Antarctic Peninsula (South Shetland Islands)
[Credit: University of Granada]

This scientific contribution describes, for the first time in the Antarctic Ocean, a glauconitisation event (in which glauconia was formed) approximately 35.5 million years ago in the Weddell Sea, northeast of the Antarctic Peninsula between South America and Antarctica.

The formation of glauconia 35.5 million years ago marks the onset of progressive sea level rise in the north Weddell Sea during the Terminal Eocene. The results of this scientific study thus provide new insights regarding changes in paleoceanographic conditions just prior to the Eocene–Oligocene climate transition and the controversial opening and deepening of Drake Passage.

Studying the weather of the past to predict the future

The separation of the Antarctic continent from South America and Oceania allowed bodies of water to transfer freely between the Pacific and Atlantic Oceans. This new circulation of bodies of water resulted in the Circumpolar Current and, with it, the thermal insulation of the Antarctic and the formation of the ice cap on a continental scale.

Map of Antarctica showing the location of the Antarctic Circumpolar Current (ACC), which flows from west to east.
The ACC is a fundamental element in the deep global circulation connecting the Pacific, Atlantic, and Indian
Oceans. It is therefore an important part of the global ocean circulation network that distributes
 heat around the Earth [Credit: University of Granada]

The opening of Drake Passage between South America and the Antarctic Peninsula is therefore considered one of the most important events in the history of the Earth's oceanic and atmospheric circulation. However, in the absence of dating for the formation of the sedimentary basins of Drake Passage, it is difficult to specify the precise age when the Passage began to open up and the Circumpolar Current started to form. The glauconia analysis conducted by the TASMANDRAKE research group contributes to progress in this area of study.

To put these changes into perspective, Adrian Lopez Quiros, the principal author of the research, notes that "it is necessary to study the past to understand the present and help predict the future," by better understanding the tectonic, climatic, and paleoceanographic conditions that led to the onset and subsequent evolution of this important ocean current.

The United Nations' Intergovernmental Panel on Climate Change (IPCC), a major reference source for climate forecasts, established several possible future climate scenarios in 2014. However, the new data, when comparing simulations with real-world data, predict even greater impacts than those previously foreseen in the IPCC climate scenarios. Therefore, climate change is developing faster than previously thought. With its research, the TASMANDRAKE group aims to provide new variables for these models—focusing on sediments and geophysics—to ensure that its results reflect real-life events even more accurately, especially in terms of the transoceanic currents, global warming, and rising sea levels.

Source: University of Granada [January 23, 2020]

Arctic sea ice can't 'bounce back'

A team of scientists led by the University of Exeter used the shells of quahog clams, which can live for hundreds of years, and climate models to discover how Arctic sea ice has changed over the last 1,000 years.

Quahog clams [Credit: Paul Butler]

They found sea ice coverage shifts over timescales of decades to centuries - so shrinking ice cannot be expected to return rapidly if climate change is slowed or reversed.

The study examined whether past ice changes north of Iceland were "forced" (caused by events such as volcanic eruptions and variations in the sun's output) or "unforced" (part of a natural pattern).

At least a third of past variation was found to be "forced" - showing the climate system is "very sensitive" to such driving factors, according to lead author Dr Paul Halloran, of the University of Exeter.

"There is increasing evidence that many aspects of our changing climate aren't caused by natural variation, but are instead 'forced' by certain events," he said.

"Our study shows the large effect that climate drivers can have on Arctic sea ice, even when those drivers are weak as is the case with volcanic eruptions or solar changes.

"Today, the climate driver isn't weak volcanic or solar changes - it's human activity, and we are now massively forcing the system."

Co-author of the study Professor Ian Hall, from Cardiff University, said: "Our results suggest that climate models are able to correctly reproduce the long-term pattern of sea ice change.

"This gives us increased confidence in what climate models are telling us about current and future sea ice loss."

When there is lots of sea ice, some of this drifts southwards and, by releasing fresh water, can slow the North Atlantic Ocean circulation, otherwise known as the Atlantic Meridional Overturning Circulation (AMOC).

The AMOC brings warm water from the tropics towards the Arctic, so slowing it down cools this region and allows sea ice to grow further.

So, with less ice the AMOC can bring in more warm water - a so-called "positive feedback" where climate change drives further warming and sea ice loss.

Quahog clams are thought to be the longest-living non-colonial animal on Earth, and their shells produce growth rings which can be examined to measure past environmental changes.

Dr Halloran is part of the Global Systems Institute, which brings together experts from a wide range of fields to find solutions to global challenges.

The findings are published in the journal Scientific Reports.

Source: University of Exeter [January 21, 2020]

Climate (not humans) shaped early forests of New England

A new study in the journal Nature Sustainability overturns long-held interpretations of the role humans played in shaping the American landscape before European colonization. The findings give new insight into the rationale and approaches for managing some of the most biodiverse landscapes in the eastern U.S.

Archaeologists Dianna Doucette, Deena Duranleau, and Randy Jardin conducting investigations at the Lucy Vincent Beach
 Site, Martha's Vineyard. The long-held belief that native people used fire to create a diverse landscape of woodlands,
grasslands, heathlands, and shrublands in New England has led to a widespread use of prescribed fire as a conservation
tool. Research by Oswald and colleagues indicates that these openlands actually arose following European contact,
deforestation, and agricultural expansion [Credit: Elizabeth Chilton, Binghamton University]

The study, led by archaeologists, ecologists, and paleoclimatologists at Harvard, Emerson College and elsewhere, focuses on the coast from Long Island to Cape Cod and the nearby islands of Nantucket, Martha's Vineyard, Block Island, and Naushon--areas that historically supported the greatest densities of Native people in New England and today are home to the highest concentrations of rare habitats in the region, including sandplain grasslands, heathlands, and pitch pine and scrub oak forests.

"For decades, there's been a growing popularization of the interpretation that, for millennia, Native people actively managed landscapes - clearing and burning forests, for example - to support horticulture, improve habitat for important plant and animal resources, and procure wood resources," says study co-author David Foster, Director of the Harvard Forest at Harvard University. This active management is said to have created an array of open-land habitats and enhanced regional biodiversity.

But, Foster says, the data reveal a new story. "Our data show a landscape that was dominated by intact, old-growth forests that were shaped largely by regional climate for thousands of years before European arrival."

Fires were uncommon, the study shows, and Native people foraged, hunted, and fished natural resources without actively clearing much land.

The long-held belief that native people used fire to create a diverse landscape of woodlands, grasslands,
heathlands, and shrublands in New England has led to a widespread use of prescribed fire as a
conservation tool. Research by Oswald and colleagues indicates that these openlands actually
 arose following European contact, deforestation, and agricultural expansion. These landscapes
and their critical habitats and species are best maintained through agricultural practices like
 grazing, as seen here on conservation land on the Elizabeth Islands, Massachusetts
[Credit: David Foster]

"Forest clearance and open grasslands and shrublands only appeared with widespread agriculture during the European colonial period, within the last few hundred years," says Wyatt Oswald, a professor at Emerson College and lead author of the study.

The authors say the findings transform thinking about how landscapes have been shaped in the past - and therefore how they should be managed in the future.

"Ancient Native people thrived under changing forest conditions not by intensively managing them but by adapting to them and the changing environment," notes Elizabeth Chilton, archaeologist, co-author of the study, and Dean of the Harpur College of Arts and Sciences at Binghamton University.

To reconstruct historical changes to the land, the research team combined archaeological records with more than two dozen intensive studies of vegetation, climate, and fire history spanning ten thousand years. They found that old-growth forests were predominant for millennia but are extremely uncommon today.

Conservationists have employed prescribed fire in an attempt to maintain openland habitats such
 as the Katama sandplain grassland on the island of Martha's Vineyard. Research by Oswald and
colleagues indicates that, despite a large human population for thousands of years, fire was
uncommon and landscapes across southern New England were heavily forested until
European contact and deforestation for agriculture. Grazing and other agricultural
practices can be used to maintain these uncommon habitats today
 [Credit: David Foster, Harvard University]

"Today, New England's species and habitat biodiversity are globally unique, and this research transforms our thinking and rationale for the best ways to maintain it," says Oswald. "It also points to the importance of historical research to help us interpret modern landscapes and conserve them effectively into the future."

The authors also note the unique role that colonial agriculture played in shaping landscapes and habitat. "European agriculture, especially the highly varied activity of sheep and cattle grazing, hay production, and orchard and vegetable cultivation in the 18th and 19th centuries, made it possible for open-land wildlife species and habitats that are now rare or endangered - such as the New England cottontail - to thrive," says Foster. Open-land species have declined dramatically as forests regrow on abandoned farmland, and housing and commercial development of both forests and farms have reduced their habitat.

Foster notes that the unique elements of biodiversity initiated through historical activities can be encouraged through analogous management practices today.

"Protected wildland reserves would preserve interior forest species that were abundant before European settlement," he says. "Lands managed through the diversified farming and forestry practices that created openlands and young forests during the colonial period would support another important suite of rare plants and animals."

The long-held belief that native people used fire to create a diverse landscape of woodlands, grasslands,
 heathlands, and shrublands in New England has led to a widespread use of prescribed fire as a
 conservation tool. Research by Oswald and colleagues indicates that these openlands actually
arose following European contact, deforestation, and agricultural expansion. These landscapes
 and their critical habitats and species are best maintained through agricultural practices like
grazing, as seen here on a hillside in Chilmark, Martha's Vineyard, MA.
[Credit: David Foster, Harvard University]

For successful conservation models that leverage this historical perspective, the authors point to efforts by The Trustees of Reservations, the oldest land trust in the world, which manages more than 25,000 acres in Massachusetts embracing old and young forests, farms, and many cultural resources. The organization uses livestock grazing to keep lands open for birds like bobolinks and meadowlarks, which in turn supports local farmers and produces food for local communities.

Jocelyn Forbush, Executive Vice President for the Trustees, says, "Maintaining the legacy of our conserved openlands in Massachusetts is an important goal for The Trustees and we are increasingly looking to agricultural practices to yield a range of outcomes. In particular, we are employing grazing practices to support the habitats of our open and early successional lands in addition to the scenic and cultural landscapes that shape the character of our communities."

Source: Harvard University [January 20, 2020]