A new study by Woods Hole Oceanographic Institution (WHOI) clarifies the influence of large currents in the North Atlantic at sea level along the northeastern United States. The study, published June 13 in the journal Geophysical research letters, investigated both the strength of the Atlantic Meridian Overpass Circulation (AMOC) – a conveyor belt of currents that move warmer waters north and colder waters south of the Atlantic – and historic sea level records in the New England coast.
"Researchers have previously noted that if AMOC is stronger during a particular season or year, sea levels in the Northeast US will decrease. If AMOC deteriorates, average sea levels will increase significantly," said Chris Piecuch, a physical oceanographer at WHOI and lead author on paper. For example, in 2010 we saw AMOC weakening by 30 percent. At the same time, the sea level in our region rose by six inches. It doesn't sound like much, but half a foot of the sea level rise, which is held for several months, can have serious coastal consequences. "
"But it has been unclear whether the two things – the coastal level and AMOC – are linked to cause and effect", Piecuch adds. Although the study confirmed that AMOC intensity and sea level seem to change at the same time, it found that it does not directly cause changes in the second behavior. Instead, both appear to be controlled simultaneously by variations in large weather patterns across the North Atlantic, such as North Atlantic oscillation (NAO).
"Changes in the NAO change both the AMOC and the sea level separately," says Piecuch. "When the NAO changes, it affects the trade winds blowing from the east across the tropical Atlantic. When the NAO is high, the trade winds are stronger than normal, which in turn strengthens the AMOC. But at the same time, the western winds over New England are stronger than usual. high air pressure on the north-east coast lowers the average sea level. It is wind and pressure that drives both phenomena. "
According to Piecuch, a study like this was not even possible until recently. In recent decades, satellite images have given researchers a list of ocean surface movements, but have not been able to detect currents beneath the surface. As of 2004, an international team of scientists began to maintain a chain of instruments spanning the Atlantic between Florida and Morocco. Instruments, collectively called the RAPID matrix, hold a variety of sensors that measure currents, salinity, and temperature. "RAPID does not solve the details of each individual stream along the way, but it gives us the sum of the ocean's behavior, which is what AMOC represents," Piecuch notes.
These results are particularly important for residents along the northeastern coast of the United States, he adds. Existing climate models suggest that sea levels will rise globally over the next century due to climate change, but the rising sea level on the New England coast will be greater than the global average. Researchers have traditionally assumed that the increased future sea level in the northeastern United States is inextricably linked to a weakening of AMOC, which the climate models also predict. But, considering the findings, it can be assumed that the audit, Piecuch says. "The problem right now is that we only have about 13 years of AMOC data to work with. To get a better sense of how these two things are related to each other in the long run, we must wait for a longer stretch of observation records to become available , he says.
Cooperation on the study was also Glen G. Gawarkiewicz and Jiayan Yang of WHOI; Sank Dangendorf of the University Siegen in Germany; and Christopher M. Little and Rui M. Ponte of Atmospheric and Environmental Research, Inc.
The work was supported by the National Science Foundation Awards OCE-1558966, OCE-1834739 and OCE-1805029; NASA contract NNH16CT01C; and J. Lamar Worzel Assistant Scientist Fund and Penzance Endowed Fund in support of Assistant Researchers at Woods Hole Oceanographic Institution.