Because this is a huge expanse that takes up heat from the atmosphere, understanding how it does so is critical to seasonal weather patterns, El Nino, and to global climate change.
In temperate latitudes, the atmosphere heats the ocean in summer and cools it in winter. This causes a clear seasonal cycle in sea surface temperature, at least in the middle of the ocean. At low latitudes near the equator, the atmosphere heats the sea surface throughout the year. Yet a strong seasonal cycle in sea surface temperature is present here, as well. This has puzzled oceanographers for decades who have suspected mixing may be the cause but have not been able to prove this.
Moum, Nash and their colleagues began their effort in 2005 to document mixing at various depths on an annual basis, which previously had been a near-impossible task.
"This is a very important area scientifically, but it's also quite remote," Moum said. "From a ship it's impossible to get the kinds of record lengths needed to resolve seasonal cycles, let alone processes with longer-term cycles like El Nino and La Nina. But for the first time in 2005, we were able to deploy instrumentation to measure mixing on a NOAA mooring and monitor the processes on a year-round basis."
The researchers found clear evidence that mixing alone cools the sea surface in the cold tongue, and that the magnitude of mixing is influenced by equatorial currents that flow from east to west at the surface, and from west to east in deeper waters 100 meters beneath the surface.
"There is a hint although it is too early to tell that increased mixing may lead, or have a correlation to the development of La Nia," Moum said. "Conversely, less mixing may be associated with El Nio. But we only have a six-year record we'll need
|Contact: Jim Moum|
Oregon State University