A new study by the Woods Hole Oceanographic Institution (WHOI) explains the impact of major currents in the North Atlantic at sea level along the North-East United States.
Study published in the journal Geophysical Research Letters, he examined both the Atlantic Atlantic Recourse (AMOC) power – a conveyor belt of currents that moves warmer waters north and cooler waters south in the Atlantic – and historical records of sea level in coastal New England.
"Scientists have noted earlier that if AMOC is stronger in
in a given season or year the sea level in the north-eastern part of the USA is falling. If
AMOC weakens, average sea level increases significantly – says Chris Piecuch,
physical oceanographer in WHOI and the main author of the article. "During
for example, in the winter of 2009-2010 we saw AMOC weakening by 30
percent. At the same time, the sea level in our region has increased by six inches.
It does not sound very often, but it's rising half a meter high
for many months can have serious coastal effects. "
"But it is not clear whether these two things – coastal sea level and AMOC – are related to cause and effect" – adds Piecuch.
Although the study confirmed that the intensity of AMOC and sea level seem to change at the same time, it turned out that none of them directly changes the behavior of the other. Instead, both seem to be controlled simultaneously by the variability of major weather patterns over the North Atlantic, such as the North Atlantic Oscillation (NAO).
"Changes in NAOs change AMOC and sea level separately," he says
Cissy. "As the NAO changes, it affects trade winds that blow
from the east through the tropical Atlantic. When the NAO is high,
commercial winds are stronger than normal, which in turn strengthens AMOC.
But at the same time, the western winds over New England are also
stronger than usual. Along with extremely high air pressure on
on the north-east coast this reduces the average sea level. It's the wind and
pressure, which drives both phenomena. "
According to Piecuch, until recently such a study was not even possible. For several dozen years, satellite images have been giving scientists a record of ocean surface motion, but they are unable to detect currents below the surface. However, since 2004, an international team of scientists has started to maintain the chain of instruments extending across the Atlantic between Florida and Morocco. The instruments, collectively called the RAPID table, contain various 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 sum of the ocean's behavior, which is represented by AMOC," notes Piecuch.
These findings are especially important for residents along the north-east coast of the USA, he adds. Existing climate models suggest that sea levels will increase globally in the next century due to climate change, but the sea level rise on the New England coast will be larger than the global average. Researchers traditionally assume that the increase in the future sea level in the north-east US is inextricably linked to the weakening of AMOC, which also predict climate models. However, considering the findings of the study, this assumption may require re-examination, says Piecuch.
"The problem is that we have only 13 years of AMOC data to work. To better understand how these two things relate to each other in the long run, we will have to wait for a longer period of observational records to become available, "he says.
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