[ad_1]
Researchers have discovered that water in the North Atlantic has "dramatically weakened."
The study shows that levels are at the lowest level of 1,500 years – and climate change is to blame.
Researchers warn that currents will have a "profound effect" on both the North American and European climates.
Scroll down to the video
The Ocean Weakened: This is a scheme of circulation in the western North Atlantic during the episode of strong (left) and weak (right) transport west of the Labrador Current (LC). The oceanography of this region is characterized by the interaction of water masses formed in the Labrador and moving to the west (LC and Labrador Sea Slope Water (LSSW)) and the eastward flowing water bodies originating from the Gulf Stream (GS ) and its Temperate Atlantic Slope. Water (ATSW). The exact location where these two water mass systems meet (yellow dashed lines) is determined by the force of the northern recirculation spin (white arrows), which controls the temperature.
Researchers studied the Transverse Southern Atlantic Circulation (AMOC), the branch of the North Atlantic circulation that carries warm water to the surface of the Arctic and cold water toward the equator.
The research, co-led by Drs. Christelle Not and Benoit Thibodeau of the Department of Earth Sciences and the Swire Institute of Marine Sciences at the University of Hong Kong are interpreted as a direct consequence of global warming and the associated melting of the Greenland ice sheet.
Slower circulation in the North Atlantic can produce profound changes in both North American and European weather, but also in African and Asian summer monsoon rains.
The AMOC plays a crucial role in regulating global climate, but scientists are struggling to find reliable indicators of their intensity in the past.
"The discovery of this new AMOC registry will increase our understanding of its drivers and ultimately help us better understand the possible change in the near future under global warming," Thibodeau said.
The research team also encountered a weak signal during a period called the Little Ice Age (a cold period observed between about 1600 and 1850 AD).
WHAT WAS THE LITTLE ICE AGE?
The reconstructed depth of the Little Ice Age varies between different studies
The Little Ice Age occurred between 1300 and 1850 AD
There were two phases of the Little Ice Age, the first beginning around 1290 and continuing through the late 1400s.
There was a slightly warmer period in the 1500s, after which the weather deteriorated substantially, with the colder period between 1645 and 1715.
During this colder phase of the Little Ice Age, there are indications that average winter temperatures in Europe and North America were 2 ° C lower than currently.
The Baltic Sea has frozen, as do many of Europe's rivers and lakes.
The Frozen Thames, 1677, an original painting in the London Museum collection
The winters were very cold and the summers were often cold and humid.
These conditions led to widespread crop failure, famine and population decline.
There was an increase in levels of social unrest as large portions of the population were reduced to hunger and poverty.
Although not as pronounced as the twentieth-century trend, the signal can confirm that this period was also characterized by a weaker circulation in the North Atlantic, which implies a decrease in the heat transfer to Europe, contributing to the cold temperature of this period .
However, more work is needed to validate this hypothesis.
"Although we can reconstruct the temperature in the twentieth century against instrumental measurement, it is not possible to do so during the period of the Little Ice Age.
"So we need to conduct more analysis to consolidate this hypothesis," said Dr. Not.
The results were recently published in the prestigious journal Geophysical Research Letters.
The Southern Atlantic Transverse Circulation (AMOC) is the branch of the North Atlantic circulation that brings warm surface waters towards the Arctic and cold deep waters towards the equator.
This transfer of heat and energy not only has a direct influence on the climate in Europe and North America, but can affect the African and Asian monsoon system through its effect on sea surface temperature, hydrological cycle, atmospheric circulation and variation in the zone of intertropical convergence.
Drs. No and Thibodeau used microfossils, called foraminifer, found in a sediment core to estimate the past temperature of the ocean. In the photo, the foraminifera species used in this study
Many climate models have predicted a weakening, or even collapse, of this branch of circulation under global warming, in part due to the release of fresh water from the Greenland Ice Sheet.
This freshwater has lower density than salt water and thus prevents the formation of deep water, slowing down the entire circulation.
However, this weakening is still vigorously debated because of the shortage of AMOC's long-term record.
Drs. No and Thibodeau used microfossils, called foraminifer, found in a sediment core to estimate the past temperature of the ocean.
The sediment core used is the Laurentian Channel, on the Canadian coast, where two major currents meet.
The force of these currents will control the temperature of the water at the core site, which implies that the temperature reconstructed from that core is indicative of the force of the North Atlantic circulation.
With their collaborators from the United States of America, they validated their results using instrumental data and two numerical models that can simulate the climate and the ocean.
[ad_2]
Source link