How The Human Footprint Is Trampling Over Our Oceans

There’s a lot more than just salt in the sea. The oceans play a major role in the cycling of critical elements and nutrients, such as carbon, nitrogen, and phosphorus, around the globe.

Now a new report in the journal Science today hits home just how large a stamp humans already have had on our planet's fundamental churnings: We are threatening the very composition of seawater itself.

And take note, messing with the oceans on this fundamental scale may screw us landlubbers as much as it does aquatic life.

The problem stems from the same big three human activities we already hear a lot about: fossil-fuel combustion, industrial agriculture, and climate change. And while the interactions are complex, there are some simple take-home points.

One of the most important is that these effects are, in fact, documented. We’re not just talking about theoretical changes here, and these are more than warning signs. These are signals that have been measured.

The second message is this: The ocean may be big, but our industries are bigger. And the changes noted here are likely just the beginning. The oceans remain “woefully under-sampled for most compounds," the scientists write.

Here’s the basic breakdown of what we're doing to our oceans, as summarized today by some of the world's leading ocean experts:

Warming: The oceans have absorbed between 25 to 30 percent of all human-generated CO2 emissions since the industrial revolution. But as seas warm, this rate of CO2 uptake slows down. This means more CO2 stays in the skies. In the future, global warming will happen faster and faster.

Acid: All that extra CO2 its turning the oceans more acidic, making it much harder for marine species to build carbonate shells. Today, ocean acidification is happening 30 to 100 times faster than ever in the recent geological past. Left unchecked, coral reefs and shelled animals, such as clams, will start literally dissolving by the end of the century. Some plankton -- the base of the marine food chain -- may also be wiped out.

Dead Zones: Fertilizer run-off and fossil fuel burning are creating dead zones in coastal seas. Humans are the source of about half of all nitrogen carried by rivers to the seas. Too many of these nutrients fuel oxygen-sucking algae and microbe blooms. Life up the food chain, from shrimp and oysters to fish and fisherman, suffer for it.

Toxic Blooms: This excess flood of nutrients also spur a toxic form of these algal blooms, which kill fish and make coastal residents really sick.

Suffocating Fish: There are increasingly more and much larger open ocean zones where fish struggle to catch their breath. That's because the ocean is like a giant layer cake, where warm, fresh layers sit atop colder, saltier ones. But as surface waters warm, this stratification is becoming more pronounced, and less oxygen is moving from the rich deep waters to the oxygen-deprived ocean surface.

Seafood Threats: We are creating an acronym soup of pollutants in our oceans: POPs, DDT, and PCBs, not to mention methyl mercury. Human activities are moving unprecedented levels of these pollutants around the globe, and these accumulate in seafood we eat.

Lead: The one bright spot on this list. Since leaded gasoline was phased out in the 1970s, lead concentrations have decreased in the North Atlantic back down to early 20th century levels.

This Is All Too Complicated To Predict: These effects can all interact, sometimes making the situation more hazardous. For example, corals are able to tolerate some temperature rise. But they can tolerate a lot less heat when they are also bathed in more acidic seas.

We have barely scratched the surface in understanding how these impacts will affect marine life, climate, and humans. One thing we do know is that we are all part of the Life Aquatic—and the sooner we stop contaminating our waters, the sooner the oceans can go back to providing the life support systems we all depend upon.

Here are a few ways to help: support organic farming; stop subsidies to fossil fuels; and support efforts for the EPA to regulate CO2 as a pollutant. Please chime in with other suggestions.

Photo credit: ratamahatta