Little Biology Essay Assignment

Little Biology Essay

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I n 1956 Roger Revelle and Hans Suess, geochemists at the Scripps Institution of Oceanography in California, pointed out the need to measure carbon dioxide in the air and ocean so as to obtain “a clearer understanding

of the probable climatic effects of the predicted great indus- trial production of carbon-dioxide over the next 50 years.” In other words, they wanted to fi gure out how dire the situ- ation would be today. That they had to argue the importance of such observations now seems astonishing, but at the time scientists did not know for certain whether the carbon diox- ide spewing out of tailpipes and smokestacks would indeed accumulate in the atmosphere. Some believed that it would all be absorbed benignly by the sea or be happily taken up by growing plants on land.

Revelle and the young researcher he hired for this project, the late Charles David Keeling, realized that they had to set up equipment at remote locations, far from local sources and sinks of carbon dioxide, which would cause the measure- ments to vary erratically. One spot they chose was about as far from industrial activity and vegetation as anyone could get: the South Pole. Another was at a newly established weather station atop Mauna Loa in Hawaii.

Little Biology Essay

The Mauna Loa monitoring has continued (with just one brief interruption) from 1958 to this day. Being not so remote as Antarctica, Hawaii sees carbon dioxide levels rise and fall sharply in step with the Northern Hemisphere’s growing sea- son, but at the end of each and every year, the concentration of this heat-trapping gas always ends up higher than it was 12

Much of the carbon dioxide given off from the burning of fossil fuels goes into the ocean, where it changes the acid balance of seawater. The repercussions for marine life may be enormous B Y S C O T T C . D O N E Y

Little Biology Essay

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COPYRIGHT 2006 SCIENTIFIC AMERICAN, INC.

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months before. So it did not take long for the scientifi c com- munity to realize that Revelle was right—much of the carbon dioxide released into the atmosphere was destined to remain there. But his calculations were also correct in showing that a substantial fraction would end up in the sea. And it was clear to Revelle long ago that the part that went into the ocean would fundamentally alter the chemistry of seawater. Unlike some aspects of climate change, the reality of this effect—essentially the acidifi cation of the ocean—is not much debated, although its full implications are just now being revealed.

How Unnatural? the h alf-century r ecord that Keeling produced is extremely valuable, but it is too short to place the current

situation in context. Scientists have, however, been able to obtain a longer-term perspective by measuring air bubbles trapped in ice cores. From this natural archive they have learned that the atmospheric concentration of carbon dioxide was approximately constant for several thousand years and then began to grow rapidly with the onset of industrialization

Little Biology Essay

COR AL REEFS —and the extraordinary biodiversity they support—are under siege from many forces, including exposure to toxic chemicals and direct physical destruction. A less known but perhaps greater threat is the change in ocean chemistry caused by the burning of fossil fuels. Today one third of the carbon dioxide given off in that process enters the ocean, reducing its naturally alkaline pH. This shift toward more acidic conditions diminishes the ability of corals (and many other marine organisms) to grow.

Much of the carbon dioxide given off from the burning of fossil fuels goes into the ocean, where it changes the acid balance of seawater. The repercussions for marine life may be enormous B Y S C O T T C . D O N E Y

COPYRIGHT 2006 SCIENTIFIC AMERICAN, INC.

60 S C I E N T I F I C A M E R I C A N M A R C H 2 0 0 6

in the 1800s. This gas is now about 30 percent more abundant than it was a few hundred years ago, and it is expected to double or triple its former level by the end of this century.

This burgeoning supply of carbon comes largely from the burning of fossil fuels—coal, oil and natural gas. (Cement production and the burning of tropical forests add some, too, but to simplify things, let me gloss over such secondary con- tributions for the sake of clarity.) Unlike the constituents of living organisms, fossil fuels contain little or none of the ra- dioactive form of carbon: the carbon 14 isotope, which has eight neutrons in the nucleus rather than the usual six. Fossil fuels also display a unique ratio of the two stable isotopes of carbon (carbon 12 and 13). The combustion of these fuels thus leaves a distinctive isotopic signature in the atmosphere. So no one can question where the growing surplus of carbon dioxide comes from.

Little Biology Essay

Absorption rates can vary, but today about 40 percent of the carbon dioxide derived from fossil fuel remains in the at- mosphere; the rest is taken up by vegetation on land or by the ocean, currently in about equal proportions. The injection of fossil-fuel carbon into the sea is, as of yet, a relatively small addition to the ocean’s huge natural reservoir of this element. Detecting and quantifying the uptake, therefore, requires es- pecially precise measurements, ones good to at least one part in 1,000. And because the amounts vary substantially from place to place, the task also demands the resources and perse- verance to map carbon concentrations throughout the world.

Oceanographers did exactly that in the late 1980s and 1990s, as part of a global assessment that went by two acronyms: JGOFS (for Joint Global Ocean Flux Study) and WOCE (for World Ocean Circulation Experiment).

Those surveys, however, did not in themselves identify what part of the carbon measured is natural and what part derives from the carbon dioxide that people have dumped into the air. In 1996 Nicolas Gruber, now at the University of California, Los Angeles, and two of his colleagues developed an innovative technique for doing so. The application of Gru- ber’s method to all the JGOFS and WOCE data, an exercise completed in 2004, suggests that the ocean has absorbed ful- ly half of all the fossil carbon released to the atmosphere since the beginning of the Industrial Revolution.

Another way to document this process is to make repeated measurements of carbon on the same piece of ocean. One must

be careful to distinguish the fossil car- bon from the various biological sources of this element in the sea. And the obser- vations need to span a decade or more to reveal the overall trend brought on by the burning of fossil fuels against the background of natural variability. Last year Rik Wanninkhof of the National Oceanic and Atmospheric Administra-

Little Biology Essay

tion’s Atlantic Oceanographic and Meteorological Laboratory and I led a research expedition to do just such an experiment.

With a party of 31 scientists, technicians and students onboard our research vessel, we spent almost two months sampling the physical and chemical properties of the western South Atlantic, from top to bottom, starting near Antarctica and ending near the equator. This is the very same slice of ocean that I and other scientists had fi rst measured in 1989, when I was a graduate student.

When we compared our observations from 2005 with those made 16 years earlier, we found that the upper few hun- dred meters of the South Atlantic in general have higher car- bon concentrations today than in the recent past, which is consistent with the notion that the sea is taking in atmospher- ic carbon dioxide. Other oceanographers have found similar trends in the Pacifi c and Indian oceans as well. But what ex- actly does this change portend for the marine environment?

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