Ocean Tech
A new way to track marine snow ‘blizzards’
Deep beneath the surface of the worlds’ oceans, a massive blizzard is swirling in slow motion. This storm of “marine snow” consists of tiny particles of organic matter; carbon-rich fragments of dead tissue and feces from plankton, fish, and other animals. Its significance goes far beyond just being waste material: as these particles sink down from the sunlit surface waters, they become an essential source of food for other marine creatures—and in the process, play a crucial role in the regulation of global climate. Their gradual descent through the ocean serves as a giant conveyor belt for carbon, moving it from the surface to the deep sea where it can remain sequestered for hundreds to thousands of years.
Scientists have known about the importance of marine snow for decades, but actually quantifying that snow—determining its source, its sinking speed, and its carbon content to figure out its ecological and climate impact—has remained an elusive challenge.
A new device designed at WHOI, called the Twilight Zone Explorer (TZEx), may provide a solution. It’s designed to hover in the twilight zone, a region of dark water roughly 200-1000 meters down, and as it drifts through that realm, it’s able to capture sinking particles, measure their speed using onboard cameras, and preserve their contents for study at the surface—something few other devices have been able to do.
“TZEx will let us tackle some really basic scientific questions about marine snow that have yet to be answered. Namely, how much falls in a given location? How do those levels change over time? What role do certain animals play in creating it or consuming it?” says Ken Buesseler, a marine radiochemist who works with WHOI’s Ocean Twilight Zone project, or OTZ.
Frame: A carbon fiber frame contains all of the instruments aboard the float, and aids in deployment and recovery.
Strobe and Radio antennaStrobe and Radio antenna: provides instrument remotely. visual and radio direction-finding cues that help crews recover TZEx.
Collection tubesCollection tubes: These hollow cylinders guide marine snow into collection cups below.
Syntactic FoamSyntactic Foam: A dense foam made of hollow ceramic spheres that provide buoyancy needed to keep TZEx upright.
Underwater Vision ProfilerUnderwater Vision Profiler: This onboard camera and strobe light let TZEx measure the abundance and size of marine snow particles as they fall through its field of view.
Iridium AntennaIridium Antenna: When TZEx returns to the surface, this satellite antenna provides its precise location and lets scientists reprogram the instrument remotely.
CarouselCarousel: A rotating section containing twelve sample cups. As TZEx moves from one depth to another, the carousel can rotate to reveal fresh cups, letting the instrument capture multiple samples in a single deployment.
Sample CupsSample Cups (obscured): Each sample cup collects marine snow as it falls through the collection tubes above.
Argo-style floatArgo-style float: The heart of TZEx. This cylinder houses batteries, an electronic control system, and an adjustable oil-filled bladder that controls its depth.
A CAD representation of the TZEx. While submerged, the device records marine snow abundance and size, captures sinking particles, and preserves their contents for further study at the surface. (Drawing by Kaitlyn Tradd, © Woods Hole Oceanographic Institution)
Buesseler calls these basic measurements of marine snow the “holy grail” of his field. They’re essential for figuring out how long carbon stays in the deep ocean, and what the precise impact of that sequestration may be for global climate. Using onboard collection tubes to catch the snow fall, he’s able to gather data on the total amount of marine snow that falls at a particular place and time, which will help him figure out why a blizzard in one area can slow to a light flurry in others. The samples also contain genetic and biochemical material that Buesseler and his colleagues can use to determine the particles’ original source.
In addition to capturing marine snow, TZEx is also able to measure the size and speed of individual particles using specialized cameras called Underwater Vision Profilers (UVPs). These are side-facing camera that can record the time it takes for a particle to drift past. In order to determine that speed accurately, TZEx is designed to remain at a precise depth, making it a rock-solid platform that doesn’t move in relation to the snow around it. Instead, the device is able to stay at a particular depth for days at a time while it collects data and samples.
This kind of information will also help to determine how the behavior of fish and plankton affects the movement of carbon through the twilight zone. As animals from the zone migrate up to the surface and back again each day, they eat bits of marine snow, defecate, and eat once more, altering both the quantity, carbon content and the size of the particles that drift through the water. This dynamic behavior contributes to a remarkable recycling process in the twilight zone, where on average 90% of carbon that sinks through is constantly consumed, defecated, and recycled before it reaches the deep ocean. Data from TZEx, Buessler says, will provide valuable insights on how this process works, improving our understanding of not only how carbon cycles through the mid-ocean, but also how that process affects global climate.
"Closing the gap between what we know and what we don't know will help us better understand the complex processes occurring both at the surface and in the twilight zone. Ultimately, this knowledge will refine our calculations on how these waters affect the greenhouse gas carbon dioxide in the atmosphere and contribute to global climate change—an issue of paramount urgency as atmospheric CO2 levels continue to rise."
MEET THE AUTHOR David Levin
While swimming as a child, David Levin spent as much time as possible under the surface, inspecting the bottom with a mask and flippers. Today,...
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