Biological oceanography

The Hitchhiker’s Guide to Marine Snow

Article: Durkin CA, Cetinić I, Estapa M, Ljubešić Z, Mucko M, Neeley A, Omand M (2022) Tracing the path of carbon export in the ocean though DNA sequencing of individual sinking particles. ISME J:1–11. https://doi.org/10.1038/s41396-022-01239-2

Snow in the ocean?

Image 1. Marine snow particles (white specs) sinking below the ocean’s surface. Image: rawpixel.

Did you know that it snows in the ocean? There are particles that sink in the ocean that look just like the snow that falls from the sky. Termed ‘Marine Snow,’ these ocean particles are composed of poop, dead and decaying animals, and other tiny pieces of organic matter. Marine snow has important implications for climate change because marine snow is primarily composed of carbon. When it sinks, or is exported, to the deep ocean, these carbon particles can remain sequestered away from the atmosphere, and not be respired as carbon dioxide (CO2), a greenhouse gas, for hundreds to thousands of years.

Image 2. Different types of ocean particles that form marine snow. These particles were all produced as fecal pellets from a zooplankton called a copepod. Image: wikimedia commons.

While we generally know marine snow is made of tiny particles of carbon in the form of poop, dead animals, and organic matter, it is hard to know exactly what they are made of because the particles are very small and located in the middle of the ocean, where they can be difficult to collect and sample. However, improvements in satellite technology, imaging equipment, and DNA sequencing enables better determination of the components in marine snow. An international group of scientists recently utilized this suite of technology to identify what types of dead organisms compose marine snow particles and how much carbon they are actually exporting.

Measuring marine snow

Image 3. A sediment trap that will be deployed in the ocean to collect marine snow particles. Image: NASA.

Marine snow particles were collected using a sediment trap deployed at locations in the North Pacific and the California Current. A sediment trap is a large, tube-shaped device that is moored at thousands of feet below the ocean’s surface to trap particles as they sink. Once the particles were collected, images were taken of the different particles and the DNA in those particles was sequenced to identify who composed them.

The scientists found that the most influential factor for how a particle was exported was its size and how it was packaged. Marine snow comes in many different shapes and sizes based on how it was produced (see image 2). When marine snow sinks, it can also be eaten by other animals, breaking it down into smaller particles. It was also found that larger (>300 μm) particles were primarily composed of small (<50 μm) photosynthetic organisms, known as chlorophytes.

Marine snow and climate

The results of this research are important because it shows that not all marine snow is created equal. Depending on who produced, pooped, or decayed the carbon particles has important implications for how efficiently those particles are exported to the deep ocean, and how effectively marine snow can sequester carbon away from the atmosphere to limit the amount of greenhouse gases. Continuing to image and quantify marine snow particles in other regions of the global ocean will be important for accurately predicting the effects of climate change in the future.

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