This SciShow video was made in partnership with the Monterey Bay Aquarium and their research and technology partner MBARI. [♪ INTRO] Carbon is fundamental to life on Earth.

And it goes through a complex cycle, from the atmosphere, to plants and animals, to the deep ocean. After that… scientists’ understanding gets a little fuzzy.

It’s a pretty important cycle to both life and the climate crisis, so scientists and engineers have been working together to monitor it in its entirety. But when carbon hits the depths of the ocean, the trail gets harder to follow. Or at least it was that way until 2011, when a robot called the Benthic Rover II started roaming the ocean floor and keeping an eye, or a sensor, on things down there.

That little rover, as well as its predecessor, have helped researchers discover how organisms at the bottom of the ocean participate in the carbon cycle. Which means they’re filling in some missing pieces of the carbon puzzle to help researchers figure out the climate crisis. Carbon makes up the basic structure of every living thing we know of.

But it doesn’t only exist in living things. It goes through a complicated cycle across living and nonliving forms. Carbon dioxide from the air gets incorporated into plants and other photosynthesizers in a variety of chemical forms.

Then, that carbon makes its way up the food web. Sooner or later it’s released into the air or soil, where it can stay tucked away or begin the cycle again. Of course, humans put a bit of a thumb on the scale by burning fossil fuels, which releases carbon that’s been locked up for hundreds of millions of years into the atmosphere.

But more than 25% of the excess carbon dioxide that humans have added to the atmosphere is absorbed by the ocean. The carbon in the atmosphere, from humans or otherwise, can dissolve directly into the oceans or enter through photosynthesis. Then, the carbon stored in old body parts, poop, and mucus from the ocean surface falls to the deep ocean in what’s called marine snow.

And that becomes the base of the deep ocean food web. But researchers knew that they were missing something about this process. By all accounts, the amount of marine snow known to drift down to the ocean floor was not enough to provide all of the energy that the food web needs.

So to figure out what they were missing, in 2011, a team of scientists and engineers backed by the Monterey Bay Aquarium Research Institute put the Benthic Rover II on the case. This deep ocean robot was the successor to the first Benthic Rover, which was the first of its kind in the 1990’s. The first Benthic Rover started this mission but was lost at sea, so the Benthic Rover II picked up where it left off and became the longest running fully autonomous deep-sea rover in the world.

The Benthic Rover II is a car-sized rover made of titanium and plastic that can collect data on its own for a year. It’s been roaming around the Northeast Pacific Ocean, 4000 meters below sea level, taking pictures of the ocean floor, and measuring how much oxygen is taken up by the critters down there. It also takes readings of the temperature, currents, and even light signatures of chlorophyll to tell researchers where the freshest, most nutrient rich marine snow, or carbon food, can be concentrated.

Measuring benthic oxygen tells researchers how active deep ocean organisms are. It’s an indication of how much carbon is used, compared to the carbon that’s falling down in marine snow. By taking these readings, the rover has given researchers an idea of how much carbon is being eaten in the deep ocean.

In the long term, researchers found, there’s still a deficit. But the rover detected short periods when enough carbon food fell to the ocean floor to sustain the organisms down there for months – or maybe even longer. Which, I mean, of course they found that, or these organisms wouldn’t be there.

But that finding let researchers reframe the question. What’s happening to all that carbon? And it takes a village to answer a question like that.

Decades before the Benthic Rover II was monitoring all those critters consuming ocean floor carbon, scientists and engineers were using other tools to assess the carbon input on the North Atlantic ocean floor. A time-lapse camera situated on the ocean floor showed them when big clumps of fresh marine snow settled to the seafloor, and which animals ate it. And sediment traps, which collect the bits and pieces of sea stuff falling from above, like marine snow, helped them figure out how much carbon was in particulates that settled on the floor.

Together, these tools helped them understand how ocean floor communities respond to events where there’s a lot of carbon. If the junk drifting to the ocean floor is “snow,” then the cameras and traps found blizzards. Knowing that marine blizzards can happen, the Benthic Rover team kept an eye on both the ocean surface and floor in the Pacific Ocean to detect these blizzards and find some of their causes.

The data indicated eight events when there was way more marine snow than usual in a six year period. On some of those occasions, a ton of algae bloomed all at once and sank at different speeds to the depths of the ocean. Those algae blooms produced a huge amount of marine snow.

And within days of those blizzards hitting the seafloor, the Benthic Rover II measured that ocean floor organisms were using up a lot of organic carbon from the sudden influx of food, because they consumed more oxygen than usual. This told scientists that usually, a steady drift of marine snow feeds the deep ocean organisms, but every now and then, when winds are high, marine blizzards bring carbon feasts. But they didn’t eat all of it.

Some was left over. So the excess carbon remained in the sediment, where it could still be eaten in leaner times. But marine blizzards aren’t just algae remnants.

They can also come from things like salp carcasses. And by filling in more unknowns about the carbon cycle, the Benthic Rover II may have helped researchers understand the climate crisis in general. See, before the rover started searching the ocean floor for carbon, there were arguments to be made that changes in ocean temperatures could either increase or decrease marine snow.

So there was no real consensus. But a paper published in 2013 incorporating data from the Benthic Rover II showed an increase in marine snow… at least in the North Pacific where it hung out. The winds stirred up more nutrients from deeper waters, which supplied more marine snow to the ocean floor along the California coast.

Now, understanding how carbon is transported to the ocean floor is important not just for knowing how organisms down there eat. It’s important to how we understand our own future, thanks to the climate crisis. Carbon that gets transported that far down often stays there for a long time.

And this might sound obvious, but carbon that’s down there isn’t in the atmosphere. Knowing where the world’s carbon is going, and when, helps us create more accurate models of how the climate crisis is going to unfold in the future. Because in order to say how many degrees warmer things are going to get, we need to know how much carbon is doing the warming… and how much is tucked away.

So knowing what’s going on down at the bottom of the ocean can help us understand what’s going on up here too. All thanks to one intrepid autonomous robot. Thanks to MBARI and the Monterey Bay Aquarium for SEA-porting this SciShow video!

They’re a research institute and aquarium smack CRAB in the middle of the coastline in California, USA. And if the California coast is good enough for the Benthic Rover II, then by JELLY it’s good enough for us. But to keep it safe in this climate crisis, the Monterey Bay Aquarium is taking action.

And they have resources on their website to enCORAL you to join in the effort and turn the tide. The aquarium itself is powered by 100% renewable energy and outfitted with electric car charging stations. Through active efforts to reduce their FINprint, they’ve been carbon neutral since 2017!

So you can feel good about giving them a visit in person or at their website: montereybayaquarium.org. And learn more about MBARI’s work to understand our changing ocean at mbari.org. Because we don’t have to leave it all up to the Benthic Rover. [♪ OUTRO]