A research team from the University of Galway has captured a rarely observed ocean mixing process during an expedition to the Greenland Sea.
The findings published in the Journal of Geophysical Research: Oceans suggest it could improve our understanding of Arctic climate change.
The research team spent several weeks at sea during the summer of 2023 aboard the Marine Institute’s research vessel RV Celtic Explorer, carrying out surface ocean measurements in one of the most remote and climate sensitive parts of the world.
The team focused on a phenomenon known as “cabbeling”.
The Air‐Sea Interaction Profiler (ASIP) undergoing tests on the deck of the R/V Celtic Explorer. Due to the movement of the ship, the instrument needs to be strapped to the deck, although the weather conditions were optimal as can be seen from the calm seas. Photo: Professor Brian Ward, University of Galway
This process involves the temperature and salinity (concentration of salt) in the ocean, which together make up the ocean density.
“Cabbeling” occurs when two water masses with different temperatures and salinities, but the same density, are mixed together. The result is a denser mixture than either of the original water masses, a consequence of the non-linear behaviour of seawater.
This denser mixture then sinks, triggering turbulence and vertical mixing. “Cabbeling” has important implications for melting Arctic sea ice as it can increase the amount of heat from below to the ocean surface, the researchers state.
The team deployed a robotic instrument known as the Air-Sea Interaction Profiler (ASIP), which is a unique instrument specifically designed to study small-scale processes at the ocean surface.
The ASIP is 2.8 metres in length, weighs about 90 kilograms, and is completely autonomous.
An illustration of the cabbeling process. The interaction between a warm water intrusion beneath a cold fresh water cap of similar density resulting from ice melt at the surface gives rise to cabbeling densification and sinking‐induced turbulence. Also depicted is the Air‐Sea Interaction Profiler (ASIP) autonomous profiling instrument. Photo credit: Kevin McGraw, University of Galway
Repeated dives and ascents by the robotic instrument carry its sensors through the upper 100 meters of the upper ocean, making fine-scale physical measurements including turbulence, temperature, and salinity.
The results have implications for improving scientists’ understanding of “cabbeling” and its potential role in models of sea surface warming and Arctic ice loss, particularly as climate patterns shift, the researchers say.
The Greenland Sea is expected to experience increased freshwater outflow from melting ice in a warmer climate, altering the regional dynamics. Understanding and incorporating the effects of “cabbeling” will enhance the accuracy of predictions of ocean heat transport, especially in polar regions where warming is accelerating and sea ice is in decline, they say.
The study was led by PhD candidate Kevin McGraw, Professor Audrey Morley and Professor Brian Ward from University of Galway, and took place along the East Greenland Polar Front, an area where cold, fresh Arctic water meets warmer, saltier Atlantic water.
The full study is available to read here
