New research provides the first direct proof for the Gulf Stream blender impact, identifying a new mechanism of mixing water throughout the swift-moving current. Because ocean mixing plays a role in these processes the results have implications for fisheries, climate and weather. The Gulf Stream is one of the drivers of climate and biological growth in Florida to Newfoundland and along the shore of Europe.
The multi-institutional study led by a University of Maryland researcher revealed that churning along the edges of the Gulf Stream across regions as small as a kilometer could be a leading source of sea mixing involving the waters on both sides of the current. The study was published in the Proceedings of the National Academy of Sciences on July 6, 2020.
“This long-standing debate about whether the Gulf Stream functions as a blender or a barrier to sea mixing has largely considered big ocean eddies, tens of kilometers to some hundred km across,” said Jacob Wenegrat, an assistant professor in UMD’s Department of Atmospheric and Oceanic Science and also the lead author of this analysis. “What we are adding to the argument is that this new proof that variability at the kilometer scale seems to be doing a lot of mixing. And those scales are really difficult to monitor and version.”
Since the Gulf Stream classes its way up the east coast of the U.S. and Canada, it attracts hot salty water from the tropics to the north Atlantic. But the present also generates an invisible walls of water that divides two distinct ocean regions: the colder, fresher waters across the northern border of the Gulf Stream which swirl in a counterclockwise direction, along with the warmer, saltier waters in the southern edge of the present that circulate in a clockwise direction.
Just how much ocean mixing happens across the Gulf Stream is a topic of scientific discussion. As a result have not fully accounted for the contribution of blending on each side of the current.
To conduct the study, the researchers had to take their tools to the source: the border of the Gulf Stream. Two teams of scientists aboard two global-class research vessels braved winter storms on the Atlantic Ocean to release a fluorescent dye along the northern front of the Gulf Stream and track its path over the subsequent days.
The first team released the dye alongside a float comprising an acoustic beacon. Downstream, the next team monitored the float and monitored the concentration of dye combined with water temperature, salinity, chemistry and other capabilities.
Back on shore, Wenegrat and his coauthors developed high-resolution simulations of these physiological processes that may result in the dye to spread throughout the water in the manner the area teams recorded. Their results showed that turbulence across regions as a kilometer exerted an important influence on the path of the dye and resulted in mixing of water properties like temperature and salinity.
“These results emphasize the use of variability at tiny scales that are presently hard to observe using standard procedures, such as satellite observations,” Wenegrat said. “Variability at this scale is not currently resolved in global climate models and won’t be for decades to come, so it leads us to wonder, what have we been missing?”
By showing that modest mixing round the Gulf Stream may have a significant effect, the new study shows an important, under-recognized contributor to sea circulation, biology and potentially climate.
For example, the Gulf Stream has a significant part in what is called the sea biological pump–a method that traps surplus carbon dioxide, buffering the planet from global warming. In the Gulf Stream region’s surface waters, ocean mixing influences the increase of phytoplankton–the foundation of the ocean food web. All these phytoplankton sink taking carbon with them trapping it and absorb carbon dioxide around the surface. Current versions of the sea biological pump don’t account for the large effect small mixing across the Gulf Stream could have on phytoplankton growth.
“To make progress with this we need to find methods to quantify these processes on a finer scale using theory, innovative numerical versions and new observational methods,” Wenegrat said. “We need to be able to comprehend their impact on large-scale flow and biogeochemistry of the sea.”
The research paper,”Increased mixing across the gyre boundary at the Gulf Stream front,” Jacob O. Wenegrat, Leif N. Thomas, Miles A. Sundermeyer, John R. Taylor, Eric A. D’Asaro, Jody M. Klymak, R. Kipp Shearman, and Craig M. Lee, has been printed in the July 6, 2020 dilemma of the Proceedings of the National Academy of Sciences.
Jacob O. Wenegrat el al.,”Increased mixing round the gyre boundary at the Gulf Stream front,” PNAS (2020). www.pnas.org/cgi/doi/10. 1073/pnas. 2005558117
First direct evidence of ocean mixing across the Gulf Stream (2020, July 6)
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