Icebergs in Antarctica are gradually melting farther and farther away from the frozen continent, may be the trigger that plunges the earth into a new ice age, the study shows.
Researchers from Cardiff University reconstructed past climatic conditions and identified small fragments of Antarctic rock that fell into the high seas as part of a study designed to understand how ice ages begin.
The cycles of the ice age over the last 1.6 million years have been the pace of periodic changes in the Earth’s orbit around the sun – changing how much solar radiation reaches the surface.
Prior to this study, however, little was known about how changes in solar energy from small changes in orbit could so dramatically change the Earth̵
They found that melting icebergs gradually move fresh water from the south to the Atlantic Ocean by melting further from Antarctica – causing a change in ocean circulation and throwing the planet into a cold period – triggering an ice age.
The impact of man-made CO2 emissions could make the southern Ocean too hot for the Antarctic ice sheets to reach, bringing an end to this 1.6-year cycle of ice ages starting with melting icebergs, the study authors warned.
Icebergs in Antarctica are gradually melting farther and farther away from the frozen continent, may be the trigger that plunges the earth into a new ice age, the study shows. Stock image
The team found that icebergs from Antarctica gradually remain unmelted further north during certain changes in the Earth’s orbit around the sun – reducing solar energy that reaches the surface.
In their study, the team suggests that when the Earth’s orbit around the sun is just right, icebergs in Antarctica begin to melt further and further away from Antarctica.
This results in huge amounts of fresh water being moved away from the South Seas and into the Atlantic Ocean.
As the Southern Ocean becomes saltier and the North Atlantic Ocean becomes fresher, large circulation patterns in the ocean begin to change dramatically, pulling CO2 out of the atmosphere and reducing the so-called greenhouse effect.
This, in turn, pushes the Earth into ice age conditions, according to the team, which reconstructed previous climatic conditions, including finding small fragments of Antarctic rock that fell into the open ocean by melting icebergs.
The rock fragments were obtained from sediments recovered by the International Ocean Discovery Program (IODP), which represents 1.6 million years of history.
The study showed that these deposits, known as Ice-Rafted Debris, apparently consistently led to changes in the deep-sea circulation, reconstructed from the chemistry of small deep-sea fossils called foraminifera.
The team identified small fragments of Antarctic rock that had been deposited in the high seas by melting icebergs to track changes in salt and fresh water over time.
The team also used new climate model simulations to test their hypothesis and found that huge amounts of fresh water could be moved by the icebergs.
Lead author of the study Aidan Starr said they were amazed to find that the link between iceberg melting and ocean circulation was present during the beginning of each ice age in the last 1.6 million years.
‘Such a leading role for the Southern Ocean and Antarctica in the global climate has been speculated, but it was very exciting to see it so clearly in geological evidence,’ he said.
Professor Ian Hall, co-author of the study and co-lead researcher for the IODP expedition from Cardiff, said the results provide a ‘missing link’ in the history of the ice age.
Antarctic icebergs move into the southern ocean without melting and move fresh water from this ocean to the Atlantic Ocean, triggering changes in ocean circulation and cooler periods
Over the last three million years, the earth has regularly plunged into ice age conditions, but is currently within an interglacial period where temperatures are warmer.
However, it cannot happen again in the same way due to the impact of man-made CO2 emissions that are warming the world.
Researchers suggest that the natural rhythm of ice age cycles may be disrupted, as the southern ocean is likely to become too hot for Antarctic icebergs to travel far enough to trigger the changes in ocean circulation required for an ice age to begin.
Professor Hall believes that the results can be used to understand how our climate can respond to man-made climate change in the future.
‘In the same way that we are observing an increase in mass loss from the Antarctic continent and iceberg activity in the Southern Ocean as a result of warming associated with the current human greenhouse gas emissions,’ Hall said.
‘Our study underscores the importance of understanding icebergs and melting patterns in the development of the most robust predictions of their future impact on ocean circulation and climate,’ he said.
Professor Grant Bigg of the University of Sheffield’s Department of Geography, who contributed to the iceberg model simulations, said this was a groundbreaking modeling in climate models.
Adding it was crucial to ‘identifying and supporting the ice-rafted waste hypothesis of Antarctic iceberg meltwater impacts leading to ice cycle eruptions.’
The results are published in the journal Nature.
ATLANTIC OCEAN CIRCULATION PLAYS A KEY ROLE IN REGULATING THE GLOBAL CLIMATE
When it comes to regulating the global climate, the circulation of the Atlantic Ocean plays a key role.
This is due to a constantly moving system of deep water circulation, often referred to as the global sea conveyor belt, which sends hot, salty Gulf Stream water to the North Atlantic, where it releases heat into the atmosphere and warms Western Europe.
The cooler water then sinks to great depths and travels all the way to Antarctica and eventually circulates back up to the Gulf Stream.
When it comes to regulating the global climate, the circulation of the Atlantic Ocean plays a key role
This movement is driven by thermohaline flows – a combination of temperature and salt.
It takes 1000 years for water to complete a continuous journey around the world.
Researchers believe that when the North Atlantic began to warm up towards the end of the Little Ice Age, freshwater disrupted the system, called the Atlantic Meridional Overturning Circulation (AMOC).
Arctic sea ice and ice sheets and glaciers surrounding the Arctic began to melt, forming a huge natural faucet that flowed into the North Atlantic.
This huge influx of fresh water diluted the surface seawater, making it easier and less able to sink deep and slowing down the AMOC system.
Researchers have found that the AMOC has weakened more rapidly since 1950 in response to the recent global warming.