Fish Modify Calcium Carbonate

One of the great pleasures in reading science literature is the occasional bite at the unexpected. Here we learn that calcium carbonate is actively processed through the gut of a fish in copious amounts and in the process we conclude, is an active agent in converting calcium carbonate sources into immediately soluble forms.

Of course we get a little noise on the idea that human fishing is possibly depleting this resource. This is hardly true or ever likely to be true. Human fishing is selective and at worst removes competition from larger fish. Imagine what will happen to the population of ruminants if we hunted out all the big cats. Somewhere there is a population of little fish that is very happy we are knocking of their predators. And as this article makes very clear, the smaller fish are better at the conversion process.

http://www.terradaily.com/reports/Fishdunnit_Mystery_Solved_999.html

Fishdunnit! Mystery Solved

by Staff Writers
Virginia Key FL (SPX) Jan 20, 2009

An international team of scientists has solved a mystery that has puzzled marine chemists for decades. They have discovered that fish contribute a significant fraction of the oceans' calcium carbonate production, which affects the delicate pH balance of seawater.

The study gives a conservative estimate of three to 15 percent of marine calcium carbonate being produced by fish, but the researchers believe it could be up to three times higher.

Published January 16th in Science, their findings highlight how little is known about some aspects of the marine carbon cycle, which is undergoing rapid change as a result of global CO2 emissions.

Until now, scientists believed that the oceans' calcium carbonate, which dissolves in deep waters making seawater more alkaline, came from marine plankton. The recent findings published in Science explain how up to 15 percent of these carbonates are, in fact, excreted by fish that continuously drink calcium-rich seawater.

The ocean becomes more alkaline at much shallower depths than prior knowledge of carbonate chemistry would suggest which has puzzled oceanographers for decades. The new findings of fish-produced calcium carbonate provides an explanation: fish produce more soluble forms of calcium carbonate, which probably dissolve more rapidly, before they sink into the deep ocean.

Corresponding authors Drs. Frank Millero and Martin Grosell at the University of Miami's Rosenstiel School of Marine and Atmospheric Science and Dr. Rod Wilson of the University of Exeter note that given current concerns about the acidification of our seas through global CO2 emissions, it is more important than ever that we understand how the pH balance of the sea is maintained.

Although we know that fish carbonates differ considerably in their chemical make-up, the team has really only just scratched the surface regarding their chemical nature and ultimate fate in the ocean. Scientists clearly need to investigate this further to understand what this means for the future health of the world's oceans.

Millero, Grosell and Wilson, who was the recipient of the University of Miami's prestigious 2005 Rosenstiel Award, along with Rosenstiel School Marine Biology and Fisheries graduate student Josi Taylor collaborated with other British and Canadian scientists to reach the conclusion published in the current issue of Science.

The researchers suggest that fish carbonates dissolve much faster than those produced by plankton, and at depths of less than 1,000 m. Less soluble carbonates, produced by plankton, are more likely to sink further and become locked up in sediments and rocks for tens or hundreds of millions of years before being released. Fish carbonates, on the other hand, are likely to form part of the 'fast' carbonate system by more rapidly dissolving into seawater.

"As a marine chemist who has been studying the global carbon cycle and its impacts on the pH of the water and marine ecosystems for 40+ years, these results offer an important piece of the equation," said Millero, professor of Marine and Atmospheric Chemistry at the Rosenstiel School.

"By working with scientists in several disciplines we were able to come at this from different perspectives and combine data sets that hadn't been previously used together, to solve this problem. We can now employ the knowledge gained from this study to examine how ocean acidification due to the adsorption of CO2 from the burning of fossil fuels affects the ocean carbon system."

The combination of future increases in sea temperature and rising CO2 will cause fish to produce even more calcium carbonate, which is in sharp contrast to the response by most other calcium carbonate producing organisms.

Fish's metabolic rates are known to increase in warmer waters, and this study explains how this will also accelerate the rate of carbonate excretion. In addition, our existing knowledge of fish biology shows that blood CO2 levels rise as CO2 increases in seawater and that this in turn will further stimulate fish calcium carbonate production.

"Depletion of fish stocks due to overfishing will obviously influence global calcium carbonate production attributable to fish, but the prediction of the impact of overexploitation is complex. Smaller fish which often result from exploitation produce more calcium carbonate for the same unit of biomass than bigger fish, a simple consequence of higher mass-specific metabolic rates in the smaller animals.

In addition, the chemical nature of the calcium carbonate produced by fish, which determines solubility, almost certainly will depend on temperature, fish species, ambient pH and CO2 levels among other factors.

The influence of such factors on this newly recognized and significant contribution to oceanic carbon cycling offers an exciting challenge for further study" said Grosell, associate professor of Marine Biology and Fisheries at the Rosenstiel School.

Note:

Freshwater fish drink very little, while most marine fish ingest copious amounts of seawater to maintain salt and water balance. The European flounder is euryhaline and illustrates that no intestinal calcium carbonate is formed in freshwater (Figure A) and only a brief period in seawater results in the formation of x-ray opaque calcium carbonate precipitates in the intestinal lumen (Figure B). The calcium carbonate precipitates are formed regardless of feeding and are excreted to the surrounding seawater, where it impacts the pH balance

Glacial Silt

This article is a bit of a stretch but is a nice bit of information on the utility of ice in delivering nutrients to the Ocean.
I for one would like to see a workable strategy for getting nutrients into the oceanic biozone and ice does not leap to mind.
There is merit in the concept of a horizontal tube reaching deep into the ocean that I have toyed with for years. It is a bit of engineering still well beyond us I think. If it could work, the pressure and temperature gradients will sustain a massive continuing lift of nutrient rich waters to the surface such as happens around a sea mount.
The outflow would support a huge adjacent biomass.

http://www.guardian.co.uk/environment/2008/dec/07/melting-icebergs-slow-global-warming

Melting ice may slow global warming

Scientists discover that minerals found in collapsing ice sheets could feed plankton and cut C02 emissions

David Adam, environment correspondent
The Observer, Sunday December 7 2008

Collapsing antarctic ice sheets, which have become potent symbols of global warming, may actually turn out to help in the battle against climate change and soaring carbon emissions.

Professor Rob Raiswell, a geologist at the University of Leeds, says that as the sheets break off the ice covering the continent, floating icebergs are produced that gouge minerals from the bedrock as they make their way to the sea. Raiswell believes that the accumulated frozen mud could breathe life into the icy waters around Antarctica, triggering a large, natural removal of carbon dioxide from the atmosphere.

And as rising temperatures cause the ice sheets to break up faster, creating more icebergs, the amount of carbon dioxide removed will also rise. Raiswell says: ' It won't solve the problem, but it might buy us some time.'

As the icebergs drift northwards, they sprinkle the minerals through the ocean. Among these minerals, Raiswell's research shows, are iron compounds that can fertilise large-scale growth of photosynthetic plankton, which take in carbon dioxide from the air as they flourish.

According to his calculations, melting Antarctic icebergs already deposit up to 120,000 tonnes of this 'bioavailable' iron into the Southern Ocean each year, enough to grow sufficient plankton to remove some 2.6 billion tonnes of carbon dioxide, equivalent to the annual carbon pollution of India and Japan.

A 1 per cent increase in the number of icebergs in the Southern Ocean could remove an extra 26 million tonnes of CO2, equivalent to the annual emissions of Croatia.

Raiswell, a Leverhulme Emeritus Fellow, said: 'We see the rapid ice loss in Antarctica as one obvious sign of climate warming, but could it be the Earth's attempt to save us from global warming?' He added that the effect had not been discovered before because scientists assumed that the iron in the iceberg sediment was inert and could not be used by plankton.

In a paper published in the journal Geochemical Transactions, Raiswell and colleagues at the University of Bristol and the University of California describe how they chipped samples off four Antarctic icebergs blown ashore on Seymour island by a storm in the Weddell Sea.

They found that they contained grains of ferrihydrite and schwertmannite, two iron minerals that could boost plankton growth. 'These are the first measurements of potentially bioavailable iron on Antarctic ice-hosted sediments,' they write. 'Identifying icebergs as a significant source of bioavailable iron may shed new light on how the oceans respond to atmospheric warming.'

No rivers flow into the Southern Ocean and the only previously identified major source of iron for its anaemic waters is dust blown from South America. The team says that icebergs could deliver at least as much iron as the dust.

A key question is how much of the carbon soaked up by the growing plankton is returned to the atmosphere. 'We simply don't know the answer to that,' Raiswell said. Seeding the oceans with iron will only benefit the climate if the plankton sink to the bottom when they die, taking the carbon with them.

David Vaughan, a glaciologist with the British Antarctic Survey, said: 'It's a very interesting new line of research and one that should be looked at in more detail.'

He said the number of icebergs in the Antarctic was expected to rise by about 20 per cent by the end of the century, which could remove an extra 500 million tonnes of carbon dioxide each year, if they all seeded plankton growth.