The U.S. Northeast continental shelf's "cold pool," an essential habitat for diverse marine life, faces increasing seasonal changes due to shifting oceanic conditions. In a significant breakthrough, researchers at the Massachusetts Institute of Technology (MIT) and the Woods Hole Oceanographic Institution (WHOI) have harnessed the power of salinity as a tracer to investigate these changes, offering new insights that could aid in sustainable fisheries management.
"This paper provides first evidence for a seasonal salinification of the cold pool on the US Northeast continental shelf, as consistently observed in the multi-year mooring record of the [Ocean Observatories Initiative] Coastal Pioneer Array," lead author Lukas Taenzer, a recent doctoral graduate from the MIT-WHOI Joint Program, said in a news release.
Published in the Journal of Geophysical Research: Oceans, the study introduces a novel methodology deploying salinity measurements to track the influx and exit of ocean water in the cold pool. The research shows that this technique can reveal the physical processes impacting coastal ecosystems.
"We follow the signatures of the ocean's salinity, rather than temperature, to identify the physical processes that are responsible for the observed changes of coastal ecosystem conditions," added Taenzer. "Our results demonstrate the value of salinity measurements to highlight how the interplay between air-sea interactions, offshore forcing and upstream conditions influence coastal ecosystem conditions in the sheltered cold pool on the timescales of weeks to years."
This exploration into salinity's role proves especially significant considering the limitations of temperature data.
"That's really hard to determine when using temperature as a tracer, because with temperature you can't really distinguish why the pool gets warmer. By tracking salt, we can actually pinpoint why the cold pool changes throughout the year," Taenzer added.
The study's implications extend beyond academic curiosity, emphasizing practical applications for fisheries management.
"This understanding is important to help NOAA Fisheries manage U.S. fish stocks sustainably," added Taenzer.
Svenja Ryan, an assistant scientist in WHOI's physical oceanography department, highlighted the impact of continuous subsurface measurements.
"We didn't see the salinification of the cold pool previously because we didn't have continuous subsurface measurements," she said in the news release. "The fact that salinity is a valuable tracer enables us to advance our dynamic understanding of the seasonal cycle and the processes in the ocean."
Complementing this current study, Ryan and colleagues' 2024 companion paper focused on surface salinity variations using historical data.
"Continuous, global sea surface salinity observations from satellites, such as the NASA Soil Moisture Active Passive satellite mission, are critical for tracking surface ocean conditions in near-real time. They enabled our novel findings about the seasonal evolution of freshwater signals across the Northeast U.S. shelf over the past decade," added Caroline Ummenhofer, a senior scientist in WHOI's physical oceanography department and lead principal investigator on the NASA project that co-funded both papers. "Also, they are increasingly used by the fishing community, for example, in their decision-making."