Should We Be Worried the Oceans Are Getting Darker?

 Before 1968, the public had never seen the Earth in color. They'd seen parts -- close-ups taken in orbit -- but not the iconic, round, blue image we take for granted today.

Color photos of Earth began arriving en masse with the 1967 Apollo 7 mission, all taken from low Earth orbit. People saw the curvature of the planet, the swirling cloud cover, and of course, the massive oceans. But they only got pieces of the whole. It wasn't until Apollo 8, when humans left Earth's orbit for the first time, that ordinary people could see their world in color, in its entirety. All because astronaut Bill Anders had the good sense to bring along a 70 mm Hasselblad camera loaded with color film.

The actual Apollo 8 mission must have been terrifying to contemplate at the time. Three astronauts were literally going where no man had gone before. They would leave Earth's protective gravity, travel through deep space, and enter orbit around the Moon. But the fact they pulled it off isn't the most-remembered thing about the mission.

The "flight" to the Moon took them three days and nights. Then came the unexpected moment. As Anders and his crewmates orbited the Moon -- the first humans ever to do so -- they were busy carrying out technical observations. Then, as they rounded the far side of the Moon, a vision appeared on the lunar horizon. Earth came into view -- not a partial glimpse, but a fully illuminated world floating in the blackness of space. Anders quickly grabbed his camera.

The photo he captured is now called _Earthrise_. It became one of the most iconic images of the 20th century. For the first time, the public saw their home planet and faced the truth it was just a fragile, glowing ball floating in the void. The image generated a seismic shift in global consciousness, and our sense of our place in the universe.

Anders later put it best: "We came all this way to explore the Moon, and the most important thing is that we discovered the Earth."

Of course, seeing Earth from space is now commonplace. The brilliant blue of the oceans -- covering 71% of the surface -- is a familiar sight. But recently, something disturbing began happening: the colors started changing. The oceans are no longer so blue. They're getting darker.

Scientists at the Plymouth Marine Laboratory first noticed it while studying how artificial light from cities affects the ocean at night.

It's a kind of pollution, artificial light at night. And it can be surprisingly harmful to marine life. For example, when sea turtles hatch, they instinctively know to crawl to the brightest light. Why? Because on a beach at night, the brightest thing is the ocean because the moon reflects on the water. But that's no longer true when there are nearby street lamps and hotels. The hatchlings get confused and walk to the wrong light, heading inland. They end up exhausted and dehydrated and often killed by cars. Entire nests can be destroyed this way.

There are many more examples. But researchers began asking a bigger question about sunlight penetrating the oceans: they couldn't judge how bad things were getting until they knew what was normal. This led them to look more closely at overall data, not just at night. They analyzed a decade of water clarity records and satellite optical measurements. The study covered 2003 - 2022.

What they found is disturbing. There is no "normal". In fact, there is a trend in one direction. The oceans are getting darker. 

Turns out there is a bigger issue than too much artificial light. It's too little natural light. The amount of sunlight reaching the upper layer of the ocean is decreasing. That upper layer is important -- it's what we think of, when we imagine what the ocean is, with schools of fish and sharks swimming by. The upper layer -- called the photic zone -- is home to the vast majority of marine life. 

The amount of light absorbed in the photic zone helps determine the ocean's color. In healthy waters, the ocean takes in sunlight, absorbs the red and yellows, and scatters the blue. Thus, healthy oceans are blue. 

But the oceans are getting murky from agricultural and industrial waste, increased sediment -- runoff from heavier rainfall, and overgrown algae. As a result, more light is absorbed, less reflected back into the photic zone. Thee oceans are trending brown or even gray. The phenomenon is called "ocean darkening". And the Plymouth researchers found it in over one-fifth of the global ocean. The photic zone depth had decreased as much as 50 meters in some places, over 100 meters in others.

If the trend continues, the consequences will be deadly. 

If the photic zone disappears, we will face a global ecological catastrophe. Marine photosynthesis will end, killing phytoplankton, then zooplankton, then down the food chain: fish, whales, sharks, seabirds--nearly all ocean life would face famine or asphyxiation.

You might think, well, humans don't live in the oceans, so, we'd find a way to survive. But 3 billion people rely on seafood as a major protein source. Without global fisheries, we'd have widespread starvation, food wars, and economic collapse in coastal regions.

And it gets worse. 

Oceans produce nearly 80% of the Earth's oxygen. Without sunlight penetrating the oceans, oxygen production will plummet. Earth's breathable atmosphere will thin. We'd be facing a human survival crisis.

Turns out, as the ocean's color fades to black, so does life on Earth.

Well . . . some kind of life might survive. Plenty of bizarre creatures thrive in the extreme environments and pitch black depths at the bottom of the ocean. 

You just don't want to be forced to live with them.