Oceanoxia, revisited.

So in my opening statement, I discussed the risks involved in an ocean drained of dissolved oxygen. Seas devoid of any life that needs dissolved oxygen to live, and massive colonies of anaerobic bacteria on the sea floor, breathing out plumes of hydrogen sulfide, which, in the past, has been linked to the near-death experience of multicellular life on earth. Well, now we have an update on the progress of that scenario.

This is, I know, a bit much to swallow. The oceans as toxic soups? Clouds of deadly, flammable gas drifting across the landscape like fog on a spring morning? A future of acid-proof buildings and gas masks, eking out a living on the highest mountains and plateaus where the gas rarely comes? Could that really happen?

As I mentioned before, the process is underway on a small scale in New York already (has been for some time, so no fear that New York is about to be gassed by Green Lake in the immediate future), but creating similar conditions in the ocean is a bit different. What are the factors that would lead to that? To begin with, the ocean’s surface is where the bulk of its oxygen is produced – photosynthetic algae produce massive amounts of oxygen (and fix massive amounts of CO2), making the water around them rich with the life-giving stuff. Waves churn some of that downward in large storms, but really the big oxygen transfer system is the various places where the currents that run along the surface of the oceans hit a cold area. The cold water becomes denser, and sinks, pulling oxygen into the depths, and churning the deep oceans into something that’s livable. As sea surfaces warm, that pattern becomes less stable, but the REAL kicker is the north pole. All that sea ice we keep hearing about, plus the conditions that maintain it – they cool the water and send it to the depths, this happens in the north Atlantic AND the northern Pacific oceans:

from forces.sci.edu

Take away the ocean conveyor, and that water just moves around the globe on the surface allowing the oxygen depletion of the depths.

Another way can be seen in every state in the continental US – go find a pond near a cow barn, or a horse barn, or an agricultural field. You’re looking for the one that has murky green water and smells bad. What that is, is eutrophication – the influx of hard-to-get nutrients into the water from all the animals and fertilizers means that life BOOMS, for a time. Eventually, though, what you get is a pond or even a river where a brief boom of life brought about by the influx of chemical food has pulled the oxygen out of the water, and the sudden growth of algae and duckweed on the surface has blocked out light to plants growing on the bottom, and suddenly you’re left with a pond that has frogs, some bugs, and nothing that requires oxygen in the water to breathe.  THAT process is happening now, all over the world.

And so we come to the update.

In a NOAA report titled “Ocean scale hypoxia-based habitat compression of Atlantic istiophorid billfishes” (reported here in Science Daily), scientists have found that some fish are starting to move away from their typical ranges as growing areas of the ocean are becoming oxygen-deprived. To be clear – these areas still have dissolved oxygen, but it is no longer sufficient for fish that used to live there. From the article:

An expanding zone of low oxygen, known as a hypoxic zone, in the Atlantic Ocean is encroaching upon these species’ preferred oxygen-abundant habitat, forcing them into shallower waters where they are more likely to be caught.

During the study, published recently in the journal Fisheries Oceanography, scientists tagged 79 sailfish and blue marlin with satellite tracking devices in the western North Atlantic, off south Florida and the Caribbean; and eastern tropical Atlantic, off the coast of West Africa. The pop off archival satellite tags monitored horizontal and vertical movement patterns. Researchers confirmed that billfish prefer oxygen rich waters closer to the surface and will actively avoid waters low in oxygen.

While these hypoxic zones occur naturally in many areas of the world’s tropical and equatorial oceans, scientists are concerned because these zones are expanding and occurring closer to the sea surface, and are expected to continue to grow as sea temperatures rise.

“The hypoxic zone off West Africa, which covers virtually all the equatorial waters in the Atlantic Ocean, is roughly the size of the continental United States, and it’s growing,” said Dr. Eric D. Prince, NOAA’s Fisheries Service research fishery biologist. “With the current cycle of climate change and accelerated global warming, we expect the size of this zone to increase, further reducing the available habitat for these fish.”

This is not the beginning of the end, and you don’t need to run out and buy yourself a gas mask, but it is one of many signs that things are changing, and not in a way that will be good for us. It’s all very well to talk about hurricanes and floods and droughts, and those are all very very important to pay attention to. We cannot, however, afford to ignore the oceans themselves, and the life in them that keeps us alive.