Posted by: Dr Churchill | April 22, 2012

Ocean’s Eleventh Hour — Have a Happy Earth Day

On this Earth Day is good to remember the oceans, our primordial home and the place where all Life came from…

And in order to respect the origins of our Life we ought to respect the oceans and treat them still as part of our Mother-Home. Even though we feel we have matured, we still depend on the oceans for our survival in ways that are far more complex than enjoying the seas, eating fish and bathing… Our umbilical cord to the seas has never been severed and it still is our feeding tube and the regulator of our oxygen supply.

Do you get this?

Now our Oceans are in a deep crisis as they are rapidly warming up and are entering a state of famine and because of that we need to become aware of the science behind all this and make efforts to remediate it soonest.

Because as the oceans get warmer overall, some cold-water regions are shifting towards the “longer-food-chain” regime. In the North Atlantic, for instance, the boundary between the two types of food chain has already shifted 1000 kilometres northward in recent decades.

Add to this our toxic oil spills, our agricultural runoff of pesticides, fertilizers and chemicals, our overfishing, our pollution, human caused ocean acidification due to rising CO2 levels, and  ocean deoxygenation due to warmer water, you can see the vicious cycle forming and then is really difficult to predict the fate of the world’s oceans and oceanic life.

To have any chance, to understand the fecundity and vitality of the oceans, the fate of all species of life it supports and even of the fisheries — we really need to start from the basics. Plankton. How much plankton exists out there and what are the significant long term trends for this basic building block in the life, food and energy chain.  And since it seems that plankton is in a state of famine right about now, we need to hassle.

Because plankton is the basic ingredient of life in the oceans. To that end we need to observe it’s trends. And still observe and note the very long-term, reliable monitoring of phytoplankton’s ebb and flows and it’s relative state of existence. Is the ocean in a state of phytoplankton abundance, in a state of poverty or in a state of famine?

And maybe we can answer this question clearly yet only relative to the years since 1997, but not before. Because that’s when we started having satellite observations of how green are our oceans. And still we do this but some of the satellites scheduled to do just that, were never sent to orbit, some have fallen off or gone silent, and even the ones that do the job right now, are coming to the end of their lives, with no replacements on sight.

The bottom line is that while the debate about ocean’s famine results continues, we really could have missed a massive decline in phytoplankton – and if we are not careful, we won’t be able to spot future declines either.

We know that these tiny marine plants produce half the planet’s food – and there are signs that their numbers are plummeting massively as the seas warm up. Let’s make an experiment: Fill a jar with seawater and peer at it, and you probably won’t see much. Filter some through a very fine net and take a look with a microscope, though, and a whole world of plants and animals appears. This invisible world is absolutely vital to life on Earth.

Most of the oxygen you are breathing was made by minuscule algae and bacteria. These plants, known as phytoplankton, provide half of the food on which all the animals on this planet depend. From the puniest shrimp to the mightiest whale, almost every creature living in the oceans ultimately relies on phytoplankton, as do many land-dwellers – including us. Three billion people depend in part on seafood for protein, and the livelihoods of nearly a tenth of the world’s population are linked to fisheries.

Phytoplankton, in short, help make the world go round. “It’s a big part of the planet’s life-support system. If phytoplankton decline, it threatens the food base of a vast part of the biosphere,” says marine biologist Boris Worm. “There’s less fuel in the tank of the machinery of life, and you just don’t get as far.”

This is dramatically illustrated during El Niño events, when plankton levels plummet in the eastern Pacific, with huge consequences for the rest of the ecosystem. “When you go to the Galapagos during an El Niño, it’s a totally different place,” says Worm. “All the fur seals are skinny and there are a lot of dead birds.”

That’s why many people were stunned when a team led by Dr Worm, announced in 2010 that the same thing is occurring on a global scale, albeit far more gradually. Phytoplankton levels have dropped by almost 40 per cent since the 1940s, they concluded.

Some researchers weren’t just dubious about the claim, they were incredulous. After all, Worm was saying that phytoplankton levels had crashed without anybody noticing. In this age of satellite observations, could we really have missed such a huge change for so long? And if phytoplankton levels really have plummeted, what has caused this decline – and will it continue?

You might think it would be easy to tell how productive the oceans are, but the question is surprisingly hard to answer. It is not like studying rainforests or grasslands, where plant growth is relatively easy to measure. Many phytoplankton species are so small they are hard to see even under a microscope. Instead, everyone relies on the fact that the stuff inside them that actually captures the sun’s energy – chlorophyll – is green. The greener the water, the more tiny plants there are in it.

Nowadays, satellites can measure the ocean’s greenness directly. But the first satellite that could do this went into orbit in 1979, and there is an uninterrupted satellite record only from 1997. This is not nearly enough time to spot a long-term trend. The only way to look further into the past is to turn to data collected the old-fashioned way, from a ship. From the 1940s onward, that has usually meant taking water samples and measuring their greenness with a spectrophotometer.

Before that, oceanographers mostly relied on one of the lowest-tech scientific devices ever invented, the Secchi disc: a weighted disc on a string, usually painted black and white. Dropping the disc over the side and recording the depth at which it vanishes from view reveals how murky the water is. Away from muddy coastal waters, this depends on how much phytoplankton there is. “It’s a really good measurement. Surprisingly so,” says Marlon Lewis, a colleague of Worm’s at Dalhousie University in Halifax, Canada, and part of his team.

Another team member, graduate student Daniel Boyce, delved into the archives to compile as much of the colour and Secchi data as he could. “He’s a new generation of oceanographer,” says Lewis. “Halfway through the study, I said ‘Dan, have you ever actually been on a boat?’ And he said no. He’s mining the rich data sets that we have accumulated over the years.” Altogether, Boyce found nearly half a million observations spanning the world’s oceans.

Then the team had to make sense of it. First they tossed out near-shore measurements, where the Secchi disc readings would be affected by sediment. Then they controlled for the fact that phytoplankton are much more common in some parts of the ocean, and during some seasons, than in others. Only after they had stripped out all this noise would any long-term trend appear.

And there it was: in 8 out of 10 ocean regions, phytoplankton levels have been falling (Nature, vol 466, p 591). Sure, numbers were up in some places and down in others, but on average, the decline was about 1 per cent per year over the last 40 years. “It’s very shocking,” says Boyce. “If I hadn’t seen the results, I wouldn’t have believed it.” In fact, at first he didn’t believe it. He and his colleagues checked and rechecked their analysis, but couldn’t find a flaw.

What could be causing this decline? Phytoplankton levels are determined by the balance between how fast these cells grow and divide, and how quickly they get eaten by tiny animals or killed by viruses. Changes higher up in the food chain can cascade down. Fewer small fish, for instance, will lead to more phytoplankton-gobbling zooplankton. In theory, then, fishing could be affecting phytoplankton, but these kinds of ecological effects are very difficult to study in the ocean.

What we do know is that in many parts of the oceans, phytoplankton growth is limited by a lack of vital nutrients such as nitrate, phosphate and iron. Rivers and dust-laden winds supply some, and life itself may also play a big role in fertilising surface waters. In most oceans, however, the upwelling of deeper water is the main source. Big storms that stir up the sea and bring lots of nutrient-rich water to the sunlit surface layer, for instance, lead to bumper catches of fish in later years, while the reduced upwelling during El Niño events causes plankton levels to plummet.

These factors explain why phytoplankton growth varies so wildly from year to year in any given area. Across the planet these fluctuations tend to balance out, so overall phytoplankton productivity doesn’t change that much. What makes Worm’s decline so scary is that it seems to be happening worldwide at the same time.

The obvious suspect is global warming. More than 90 per cent of the heat retained by Earth as a result of rising greenhouse gases ends up in the sea. Plankton do grow faster in warmer conditions, but warming has a far less desirable effect, too. As surface waters warm, they become less dense and this makes it harder for cold, nutrient-rich water to rise to the surface. Less mixing means less fertiliser, and if phytoplankton run out of nutrients they cannot grow however warm the water is. So on balance, warmer waters are expected to reduce phytoplankton growth, and this is just what Worm’s team found. Apart from in the Arctic and Southern oceans, there was a strong link between higher sea surface temperatures and lower phytoplankton levels.

Oceanographers almost all agree that warming will lead to a decline in phytoplankton, but most expected only a small fall over the coming decades. And while there have already been dramatic falls in fish catches in many parts of the world, these have been attributed to overfishing rather than falling phytoplankton.

Of course Worm’s study suffers from problems, not least because it combines Secchi disc readings with spectrophotometer measurements. Secchi readings tend to slightly overestimate phytoplankton concentrations, so since Secchi observations predominate early in the 20th century and colour estimates predominate later, this could give the appearance of decline where none exists (Nature, vol 472, p E5). “The amount of bias they show is as large as the trend they report over time,” says Ryan Rykaczewski of Princeton University.

To iron out these issues, Worm and his team went back to their original data, carefully cross-calibrating Secchi, satellite and shipboard colour measurements, and correcting statistically for any differences. They also broadened their sweep to include Forel-Ule observations, and plan to add the Continuous Plankton Recorder data as well. They hope this improved, enlarged data set will help settle the controversy. The initial results still point to a worldwide decline of somewhere between 20 and 70 per cent.

“From everything we have done so far, we’re seeing a decline,” says Worm. “No matter what we include or exclude, we are always seeing a decline. The magnitude of the decline, and the regional detail, is still in question – but that there is a decline, I have very little doubt.”

Scott Doney of Woods Hole Oceanographic Institution in Massachusetts, for instance, says that several climate models predict declines in phytoplankton. “Worm’s results are certainly in line with what some of the models are suggesting,” he says.

David Siegel of the University of California at Santa Barbara agrees that the effect may be real, but thinks more work needs to be done to confirm its magnitude. His unpublished analysis of 13 years of satellite colour data suggests warming leads to clear declines in phytoplankton in the tropics, with a more mixed response in temperate waters.

A similar study in 2006 came to much the same conclusions. “What we see in the satellite record, very clearly, is there is a very strong relation between climate-driven changes in the surface temperature and the plankton,” says team member Michael Behrenfeld of Oregon State University in Corvallis.

Ocean acidification is the other major Oceanic problem, besides warming and it also has it’s own set of devastating conditions, because Ocean Acidification, is the term given to the chemical changes in the ocean as a result of carbon dioxide emissions. Fundamental changes in seawater chemistry are occurring throughout the world’s oceans. Since the beginning of the industrial revolution, the release of carbon dioxide (CO2) from humankind’s industrial and agricultural activities has increased the amount of CO2 in the atmosphere. The ocean absorbs about a quarter of the CO2 we release into the atmosphere every year, so as atmospheric CO2 levels increase, so do the levels in the ocean. Initially, many scientists focused on the benefits of the ocean removing this greenhouse gas from the atmosphere.  However, decades of ocean observations now show that there is also a downside — the CO2 absorbed by the ocean is changing the chemistry of the seawater.

Ocean Acidification Illustration

  • The huge amounts of atmospheric CO2 being absorbed by the world’s oceans is making them more acidic than they have been for tens of millions of years.
  • Coral Reefs provide habitat for at least a quarter of all marine species. Many of these face extinction if reefs disappear.
  • The biodiversity and splendour of coral reefs are at risk of disappearing for thousands of years. This places in jeopardy an estimated 500 million people who depend on coral reefs for their daily food and income.
  • The Great Barrier Reef will die off at this rate of acidification within thirty years.
  • If atmospheric CO2 can be stabilised at 450 ppm, (one possible target that has been discussed by politicians) only 8% of existing tropical and subtropical coral reefs will still be in waters of the right pH level to support their growth.
  • Within decades, Ocean Acidification will also start to have major impacts on temperate and polar water ecosystems. In fact, colder water absorbs higher levels of CO2 than warmer water. Our polar seas are already so acidic that they are starting to dissolve some shells.
World map showing varying change to pH across different parts of different oceans

Change in sea water pH caused by human created CO2between the 1700s and the 1990s

As the amount of carbon has risen in the atmosphere there has been a corresponding rise of carbon going into the ocean. Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.25 to 8.14, representing an increase of almost 30% in “acidity” (H+ ion concentration) in the world’s oceans.

This ongoing acidification of the oceans along with the warming, pose the most significant threat to the food chains connected with the oceans, to the human species and to our environment.




And keep in mind that we are part of that ecology and a definite part of that particular food chain…

So while the debate about whether phytoplankton levels have fallen already is far from settled, there is strong evidence that they have fallen sharply and will continue falling in the future as the oceans warm further due to anthropogenic global warming caused by our CO2 emissions.

What does this mean for us?

Well, for starters, there are big regional differences and there will be winners as well as losers. Although Worm’s team found a steep overall decline, their results still suggest phytoplankton levels rose in small areas of the ocean.

The bad news is that even in those areas where the productivity of phytoplankton rises, there will be less fish in the sea.

Because in temperate regions, the phytoplankton tends to consist of large cells that are eaten by large zooplankton, such as copepods, and then by fish. Phytoplankton in the tropics, in contrast, tend to be tiny cyanobacteria, which are eaten by tiny zooplankton, which are eaten by slightly larger ones and so on.

There are several more links in the food chain before we get to the fish — and an incredible 90 % per cent of the energy is lost at the crossing towards each link — and all the way to the human mouth.

This is part of the reason why warmer and even tropical waters tend to support far fewer fish, and thus less vigorous fisheries, than cold waters.

Otherwise, Happy Earth Day everybody

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