No direct link between North Atlantic currents and sea level along the New England coast



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No direct link between North Atlantic currents and sea level along the New England coast

As the North Atlantic Oscillation (NAO) evolves, it affects the trade winds, which blow from the east to the tropical Atlantic. When the NAO is high, the trade winds are stronger than normal, which strengthens the Southern Rollover Circulation System (AMOC). But at the same time, the westerly winds over New England are also stronger than usual. With the unusually high atmospheric pressure on the northeast coast, this lowers the average sea level. It is the wind and the pressure that feed the two phenomena. Credit: Natalie Renier, Woods Hole Oceanographic Institution

A new study by the Woods Hole Oceanographic Institution (WHOI) outlines the influence of major North Atlantic currents on sea level in the northeastern United States. The study, published June 13 in the journal Geophysical Research Letters, examined both the Amoc force (AMOC) – a conveyor belt of currents that move warmer waters northward and colder waters southward into the Atlantic – and historical records of the level of the sea on the shores of New England.

"Scientists had already noticed that if AMOC was stronger in a given season or year, the sea level fell in the northeastern United States. Was weakening, the average sea level was increasing considerably, "says Chris Piecuch, physical oceanographer to the WHO author on paper. "During the winter of 2009-2010, for example, we saw the AMOC weaken by 30%." Meanwhile, the sea level in our region has increased by six inches. does not seem much, but half a foot The rise in sea level, maintained for months, can have serious repercussions on the coast. "

"But we do not know if these two things – the coastal sea level and AMOC – are linked by cause and effect," Piecuch adds. Although the study confirmed that AMOC intensity and sea level appeared to be changing at the same time, it revealed that none of them led to a direct change in the behavior of the other. Instead, both appear to be simultaneously controlled by the variability of major weather patterns on the North Atlantic, such as the North Atlantic Oscillation (NAO).

"The changes in the NAO are altering AMOC level and sea level separately," says Piecuch. "The changes in the NAO affect the trade winds, which blow from the east over the tropical Atlantic.When the NAO is high, the trade winds are stronger than normal, which strengthens the AMOC. But at the same time, the west The winds over New England are also stronger than usual.With exceptionally high air pressure on the northeast coast, this lowers the average sea level It is the winds and the pressures that are at the origin of both phenomena. "

According to Piecuch, a study of this type was not even possible until recently. In recent decades, satellite imagery has allowed scientists to record ocean surface displacements, but has not been able to detect subsurface currents. However, starting in 2004, an international team of scientists began maintaining an instrument chain that extends from the Atlantic to Florida, between Florida and Morocco. The instruments, collectively referred to as the RAPID network, contain a variety of sensors that measure currents, salinity, and temperature. "RAPID does not solve the details of each individual current along the way, but it gives us the full sum of the ocean 's behavior, which is what AMOC stands for," notes Piecuch.

These discoveries are particularly important for residents of the northeastern coast of the United States, he adds. Existing climate models suggest that sea levels will rise globally over the next century as a result of climate change, but that sea-level rise on the New England coast will be above the global average . Scientists have traditionally assumed that future sea-level rise in the northeastern United States is inextricably linked to a weakening of AMOC, which is also predicted by climate models. But, considering the results of the study, this hypothesis may need to be re-examined, says Piecuch. "The current problem is that we only have about 13 years of AMOC data, so to get a better idea of ​​the relationship between these two elements in the long run, we will have to wait longer." Observation records become available, "he says.


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More information:
Christopher G. Piecuch et al, How is New England's coastal sea level related to the southern overturning circulation of the Atlantic at 26 ° north latitude? Geophysical Research Letters (2019). DOI: 10.1029 / 2019GL083073

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Woods Hole Oceanographic Institution


Quote:
No direct link between North Atlantic currents and sea level along the New England coast (June 14, 2019)
recovered on June 15, 2019
from https://phys.org/news/2019-06-link-north-atlantic-currents-sea.html

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