he melting of large icebergs is a key stage in the evolution
of ice ages
Date:
February 19, 2021
Source:
University of Granada
Summary:
A new study, in which the Andalusian Earth Sciences Institute (IACT) (CSIC-UGR)
participated, has described for the first time a key stage in the beginning of the great
glaciations and indicates that it can happen to our planet in the future. The study claims to
have found a new connection that could explain the beginning of the ice ages on Earth.
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A new study, in which the Andalusian Earth Sciences Institute (IACT) (CSIC-
UGR) participated, has described for the first time a key stage in the
beginning of the great glaciations and indicates that it can happen to our
planet in the future. The findings were recently published in the scientific
journal Nature.
The study claims to have found a new connection that could explain the beginning of the ice ages on
Earth.
Antarctic iceberg melt could hold the key to the activation of a series of mechanisms that cause the
Earth to suffer prolonged periods of global cooling, according to Francisco J. Jiménez-Espejo, a
researcher at the Andalusian Earth Sciences Institute (CSIC-UGR), whose discoveries were recently
published in the journal Nature.
It has long been known that changes in the Earth's orbit, as it moves around the Sun, trigger the
beginning or end of glacial periods by affecting the amount of solar radiation that reaches the
planet's surface. However, until now, the question of how small variations in the solar energy that
reaches us can lead to such dramatic shifts in the planet's climate has remained a mystery.
In this new study, a multinational group of researchers proposes that, when the Earth's orbit around
the sun is just right, the Antarctic icebergs begin to melt further and further away from the continent,
moving huge volumes of freshwater from the Antarctic Ocean into the Atlantic.
This process causes the Antarctic Ocean to become increasingly salty, while the Atlantic Ocean
becomes fresher, affecting overall ocean circulation patterns, drawing CO 2 from the atmosphere and
reducing the so-called greenhouse effect. These are the initial stages that mark the beginning of an
ice age on the planet.
Within this study, the scientists used several techniques to reconstruct oceanic conditions in the
past, including by identifying tiny fragments of rock that had broken away from Antarctic icebergs as
they melted into the ocean. These deposits were obtained from marine sediment cores recovered by
the International Ocean Discovery Program (IODP) during Expedition 361 off the sea-margins of
South Africa. These sediment cores enabled the scientists to reconstruct the history of the icebergs
that reached these latitudes in the last million and a half years, this being one of the most continuous
records known.
Climate simulations
The study describes how these rocky deposits appear to be consistently associated with variations
in deep ocean circulation, which was reconstructed from chemical variations in minute deep-sea
fossils known as foraminifera. The team also used new climate simulations to test the proposed
hypotheses, finding that huge volumes of fresh water are carried northward by icebergs.
The first author of the article, PhD student Aidan Starr from the University of Cardiff, notes that the
researchers are "surprised to have discovered that this teleconnection is present in each of the
different ice ages of the last 1.6 million years. This indicates that the Antarctic Ocean plays a major
role in the global climate, something that scientists have long sensed, but that we have now clearly
demonstrated."
Francisco J. Jiménez Espejo, a researcher with the IACT, participated in his capacity as a specialist
in inorganic geochemistry and physical properties during the IODP 361 expedition aboard the
JOIDES Resolution research vessel. For two months, between January and March 2016, the
research team sailed between Mauritius and Cape Town, collecting deep-sea sediment cores.
Jiménez Espejo's main contribution to the study focused on identifying the geochemical variations
associated with glacial and interglacial periods, which has made it possible to estimate with greater
accuracy the age of the sediment and its sensitivity to the different environmental changes
associated with those periods.
Over the course of the last 3 million years, the Earth began to experience periodic glacial cooling.
During the most recent episode, about 20,000 years ago, icebergs continuously reached the Atlantic
coasts of the Iberian Peninsula from the Arctic. Currently, the Earth is in a warm interglacial period
known as the Holocene.
However, the progressive increase in global temperature associated with CO 2 emissions from
industrial activities could affect the natural rhythm of glacial cycles. Ultimately, the Antarctic Ocean
could become too warm for Antarctic icebergs to be able to carry freshwater north, and therefore a
fundamental stage in the beginning of the ice ages -- the variations in thermohaline circulation --
would not take place.
Ian Hall, also of Cardiff University, who co-directed the scientific expedition, indicates that the resu
