A first-of-its-kind study of marine heat waves in the Chesapeake Bay revealed that the events are more expansive than previously known and follow seasonal patterns.
What's happening?
It marked the first analysis of marine heat waves below the first meter of water in an estuary, as the Chesapeake Bay Journal reported. The paper covered data from three monitoring programs between 1986 and 2021, according to a news release, and was published in the Journal of Geophysical Research: Oceans in February.
It examined the climatological aspects of these heat waves in the Chesapeake Bay and showed they last longer than was known, wax and wane with the seasons, and coincide with the expansion of hypoxic zones.
"The only reason that we are able to do [that kind of study] is because of all of the monitoring programs in the Chesapeake Bay," lead author Nathan Shunk of William & Mary's Virginia Institute of Marine Science said, per the Bay Journal. "Everybody really cares about the health of the bay."
The study showed that water temperatures rise days, weeks, and even months before and after marine heat waves. These changes last longer at the surface but are present for as long as weeks in the subsurface.
It also documented that the water in fall and winter was more homogeneous, allowing the heat to penetrate to the bottom. In spring and summer, lighter freshwater on its way to the Atlantic Ocean trapped heat, creating a kind of buffer atop the denser saltwater and possibly protecting organisms at the bottom of the estuary.
Why are these heat waves concerning?
The study highlighted that dissolved oxygen levels decreased during the heat waves, with the biggest declines in winter and spring. This change related mostly to the deep channel of the bay's main stem, per the release.
"It would probably be more like going to a higher elevation," Shunk told the Bay Journal. "There's less oxygen in the water, but it's nowhere near lethal levels."
From April through October, the decreases aligned with an expanded hypoxic region, or dead zone. "Hypoxia has a significant, negative impact on marine life in the Bay," according to the release, and the combination could "squeeze" fish and other organisms into a smaller usable habitat.
"On the edges of the border of the hypoxic region, the dissolved oxygen is so low that just small changes kind of push it into levels that are potentially lethal for fishes and whatnot," Shunk said in the Bay Journal report.
For the region's famous blue crabs, it may change migration and reproductive patterns. The study noted seasonal temperatures guide the species and that marine heat waves could disrupt that, as they have also been shown to affect fisheries.
What's being done about marine heat waves?
The baseline for marine heat waves is rising as temperatures around the world spike, in part because Earth is about 71% ocean, and that water absorbs 91% of the planet's excess heat. In the Chesapeake Bay, temperatures have risen about 0.2 degrees Celsius (about 0.36 degrees Fahrenheit) per decade over the last 50 years, per the study,
Continued study of the bay and its wildlife can help raise awareness about the resulting problems and aid conservation efforts.
In the big picture, governments and corporations must match the efforts of individuals to reduce reliance on dirty energy. Using dirty energy is the root cause of warming temperatures, which are exacerbating extreme weather events such as floods, droughts, and, yes, heat waves.
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