A research team from University of Galway has captured a rarely observed ocean mixing process during an expedition to the Greenland Sea, a finding that 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. 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.
To observe the cabbeling process, the team deployed a robotic instrument known as the Air-Sea Interaction Profiler (ASIP ), which is specifically designed to study small-scale processes at the ocean surface. Repeated dives and ascents by the robotic instrument carry its sensors through the upper 100 metres of the upper ocean, making fine-scale physical measurements including turbulence, temperature, and salinity.
The study has been published in the Journal of Geophysical Research: Oceans.
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 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.
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.
“These observations are a good example of the subtle processes associated with climate change and how small-scale processes can have broader implications,” said Professor Brian Ward, Professor of Ocean Physics at the School of Natural Sciences, University of Galway. “New methods of detection, such as the Air-Sea Interaction Profiler instrument, are required to fully understand the coupled ocean-atmosphere system.”
The research highlights the importance of combining innovative ocean technology with field observations to improve our understanding of fine scale mixing processes that shapes regional and global climate patterns.
