Looking Into the Past to Predict the Future

Dear readers,

Now that I've sufficiently convinced you that ocean acidification is something that you should be actively concerned about, you may be wondering what we can expect if things continue on as normal. In fact, the geological record provides several clues about what a more acidic ocean may look like. Approximately 56 million years ago, the Earth underwent a period known as the Paleocene-Eocene Thermal Maximum (or PETM), which was characterized by intense warming and a rapid rise in carbon dioxide (CO2) levels. Similar to today, the increased CO2 in the atmosphere led to an acidification of the oceans. When examining the fossil record through sediment cores, the evidence is starkly obvious. For 40,000 years bottom-dwelling shelled creatures entirely disappeared from the fossil record! Furthermore, after the PETM ended, it took 60,000 years before the oceans returned to their "normal" state and showed a new layer of fossilized shells in the sediment cores.

What this tells us is two things. First, that increasing the acidity of the oceans really does lead to an extinction of bottom-dwelling marine shelled organisms. Second, that biological systems take a LONG time to recover. Even more alarming is that the rate at which carbon dioxide (CO2) levels are currently rising greatly overtakes the rate at which they were rising to cause the PETM. Researchers who study the PETM found that a release of 4.5 million tons of CO2 over a period of 1,000-10,000 years caused the PETM climate change. In contrast, the rate at which we burn fossil fuels will release the same amount in 300 years. As a result, we can expect that the recovery period for anthropogenic climate change will also be quite long. 


- N. Gallo

The data about the PETM comes from a large sediment core that was extracted from Spitsbergen Island in Norway. (Photo credit: http://c1.planetsave.com/files/2011/06/263373616_bf3a8a01c1.jpg)

This image is slightly confusing because you have to look at it from right to left, with the oldest sediments being on the far right. The obvious change in color from light brown to dark red/brown shows the extinction of small shelled marine organisms. On the left, you can see the long gradual recovery time before the return of shelled marine organisms in the fossil record. (Photo credit: http://www.ecord.org/images/booths/replica208a.jpg)

A close-up of the obvious change in sediment composition caused by the extinction of shelled marine organisms during the PETM. The dark red/brown sediments show a lack of any calcium carbonate presence. (Photo credit: http://www.geol.umd.edu/~jmerck/geol100/images/37/petmcore70909s.jpg)

A Wake Up Call - The Biological Ramifications of Ocean Acidification

“We found that mere absorption of CO2 from the atmosphere into the ocean was enough to harm marine creatures,” - Ken Caldeira, chemical oceanographer at the Carnegie Institution of Washington in Stanford, California, and author of the first major publication on ocean acidification.

Dear readers,

As I was researching ocean acidification, I was struck with how immediate and serious the biological ramifications were. All of a sudden, the climate change conversation switched from that of an abstract problem, to an immediate problem. I found myself wondering not about shifting coastlines or more severe summers, but instead about witnessing the next major marine extinction in my lifetime and wondering what would substitute the 100 million tons of seafood that we consume every year. For the first time while writing this blog, the game had changed to considerations of survival.

To put it in perspective, here's why I'm concerned. The biological ramifications of ocean acidification will probably be more profound than the consequences of global and oceanic temperature rise. First of all, consider the myriad of marine species that have some form of hard outer shell. Ocean acidification changes the fundamental chemistry of the oceans, stripping the carbonate ions from those shells. This translates to the weakening and dissolving of existing shells, and the decreased ability of organisms to build their shells or skeletons and calcify at the necessary rate. While the species that we commonly think of, such as coral reefs and oysters, will be severely affected by this, it is the less popular species, such as calcareous plankton and minuscule clams, which will profoundly change the marine food web.

The point to take away is that these less popular species form the base of the marine food chain. While they may not be large and vibrant (like reef systems), they fuel our fisheries. If the base of the food chain takes a hit, then our already weakened fisheries will collapse. All of this gives me great reason to be gravely concerned.

-N. Gallo

A marine pteropod. These small snails are planktonic, free swimming organisms with calcium carbonate shells, that are a main food source for juvenile salmon, mackerel, herring, and cod. Just one example of the many shelled planktonic organisms that will be affected by ocean acidification. Photo credit: http://www.nopp.org/wp-content/uploads/2010/06/pteropod.jpg

Anthropogenic Ocean Osteoporosis I - The Chemistry

Dear readers,

Now that you know what causes ocean acidification, this entry will focus on one of the consequences of ocean acidification. In nature, there are many delicate equilibriums. For example, in the oceans, there is a balance between the addition of minerals, such as calcium carbonate, to the oceans, which occurs through the slow weathering of land and stone, and the absorption of carbon dioxide (CO2) into the water. Today, the oceans are absorbing CO2 at a rate of 22 million tons a day, which is overloading this delicate balance and changing the chemistry of the marine system.

Due to the important chemical equilibrium in the oceans between CO2, carbonate ions (CO₃^2-), water, and carbonic acid (H2CO3), an increase in CO2 means a decrease in the available carbonate ions in a marine system. Basically, the available carbonate ions get used up to decrease the elevated concentration of CO2 and form carbonic acid. This process returns the system to a chemical equilibrium. However, on a biological level this has two profoundly negative consequences. One we have already touched on: ocean acidification. As the concentration of carbonic acid increases, the oceans become more acidic. The second consequence is that the availability of carbonate ions decreases.

Carbonate ions are extremely important because, when they react with calcium ions (Ca+2), they form calcium carbonate (CaCO3). Calcium carbonate is the substance of every single shell and coral skeleton in the ocean. As the concentration of carbonate ions decreases, so does the ability of a plethora of marine organisms to build their skeletons and shells. Basically, the anthropogenic input of CO2 into the atmosphere is inadvertently causing a case of ocean osteoporosis.

-N. Gallo

Over thousands of years, the ocean reclaims sediments and minerals by weathering the land. The ions from this weathering process naturally balance the amount of CO2 the oceans absorb. However, the rate of industrial CO2 production has overwhelmed this delicate balance, leading to ocean acidification and decreased carbonate availability. (Photo credit: http://www.alaska-in-pictures.com/data/media/6/crashing-waves_4710.jpg)

For a longer explanation about the chemistry of carbonate loss, check out this great blog entry: http://www.realclimate.org/index.php/archives/2005/07/the-acid-ocean-the-other-problem-with-cosub2sub-emission/

The Irrefutable Link: CO2 and Ocean Acidification

 “It is very complicated to pin the heating of the planet on a single gas, but ocean acidification involves straightforward chemistry” - Robert B. Dunbar, professor of geological and environmental sciences at Stanford University

Dear readers,

Hope you've all been having a great weekend! In the last post, we talked about how rising atmospheric carbon dioxide (CO2) levels have contributed to the increased acidification of the oceans. For a quick review, when CO2 comes into contact with salt water, it reacts to form several chemical species. One of these is carbonic acid (H2CO3), which, when it dissociates in water, produces free hydrogen (H+) ions. The concentration of hydrogen ions in a solution (H+) determines the solution's acidity.

The oceans have been acting as a giant sponge for CO2, absorbing more than 50% of human emitted CO2. As a result, rising CO2 levels, caused by the burning of fossil fuels, have directly caused the ocean's pH (acidity measure) to drop from 8.179 during the 1700s to 8.069 right now. While this decrease of 0.11 pH units may not seem large, since pH is calculated on a logarithmic scale, this actually translates to a 30% increase in acidity*!! Furthermore, projections for year 2100, which are based on current CO2 emissions levels, predict that ocean pH will drop by an additional 0.3-0.5 units, becoming approximately 150% more acidic! A drop in pH that large hasn't been seen in 20 million years and will have profound effects on marine flora and fauna.

So, while it may be difficult to pinpoint whether the exact cause of global warming is the increased CO2 emissions of the 20th and 21st century, the case of ocean acidification is directly and cleanly linked to increased anthropogenic CO2 emissions. Thus, in the oceans we can most clearly see our impact on the global environment.

-N. Gallo

The Dissolving Truth: A pteropod shell placed for 45 days in ocean water under 2100 projections. The next entry will more specifically address how ocean acidification affects calcification. (photo credit: http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F)

*(To avoid confusion, I should note that the oceans are not actually acidic. On the pH scale, anything that is below 7 pH units is considered acidic, so the oceans are still alkaline at a pH of 8.069. However, most marine organisms are extremely sensitive to pH changes, and the oceans are rapidly becoming more acidic/less basic).

Good links for further reading
1. "What Is Ocean Acidification?" -  http://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F
2. "Ocean Acidification: A Global Case of Osteoporosis" - http://discovermagazine.com/2008/jul/16-ocean-acidification-a-global-case-of-osteoporosis/article_view?b_start:int=0&-C=
3. "Covering Ocean Acidification: Chemistry and Considerations" - http://www.yaleclimatemediaforum.org/2008/06/covering-ocean-acidification-chemistry-and-considerations/
4. "The Acid Ocean - The Other Problem with CO2 Emission" - http://www.realclimate.org/index.php/archives/2005/07/the-acid-ocean-the-other-problem-with-cosub2sub-emission/

Atmospheric CO2 Levels and An Introduction to Ocean Acidification

 Dear readers,

As mentioned before, the second most common greenhouse gas is carbon dioxide, making up 9-26% of atmospheric greenhouse gases. There is hard data available from a myriad of sources that confirms that CO2 levels have been rising over the last century, primarily as a result of the increased burning of fossil fuels during and after the Industrial Revolution. According to a report by the Intergovernmental Panel on Climate Change (IPCC), since 1750, the concentration of CO2 has increased by 108ppm (parts per million), an increase of 38.6%, bringing us to a current concentration of 388ppm. While several other greenhouse gases have increased during this time period, such as methane (CH4), nitrous oxide (N2O), and CFCs (chlorofluorocarbons, chemical compounds that deplete the ozone), we will focus on CO2 levels because they have the greatest impact on the oceans.

CO2 levels are extremely important from the oceanic perspective because the oceans play a key role in the planet's carbon cycle. In fact, the oceans tend to act like a carbon sink for both bound carbon (in living and dead materials) and for CO2. This means that the oceans can actually buffer global CO2 concentrations, but this can only go on for so long before the ocean's chemistry gets profoundly changed as a result of the increased CO2 being taken up. The ocean is able to buffer gaseous CO2 by chemically converting it to carbonic acid (H2CO3). Unfortunately, an increase in carbonic acid in the oceans results in a lowering of the pH level and an increase in acidity. In future entries, we will talk about the importance of rising ocean acidity on the marine flora and fauna that call the oceans home.

As you can see by the graph, since pre-industrial times the average oceanic sea surface pH has decreased from between 0.06 to 0.11 pH units, with the greatest pH changes in the Atlantic. Since pH is calculated on a logarithmic scale, this translates into a substantial change in pH levels. (photo credit: http://images-mediawiki-sites.thefullwiki.org/02/2/6/4/88391784058062717.png)

Getting a Bad Rep. Frequently, when greenhouse gases are discussed, they are discussed negatively as climate change indicators, and overall, get a bad reputation. But everything is needed in moderation, and the greenhouse gases in our atmosphere play an extremely important role in determining our planet's climate. Do you know what temperature our planet would be right now if we had absolutely no greenhouse gases?

Temperature, the Ocean, and the Water Cycle

Dear readers,

While the last entry introduced you to the temperature-CO2 debate that is still raging, this entry and the next will focus on why CO2 levels and rising temperatures are extremely important independent of past geological climate data. And, as promised, this will take us right back to the oceans:) While it is entirely likely that our planet is warming due to both natural (changing solar intensity) and anthropogenic causes (increased greenhouse gases), the fact that it is warming is significantly changing the oceans and the water cycle.

As the USGS reports, the ocean is the world's greatest storehouse of water, containing about 96.5% of all the water on earth. As the ocean surface temperatures rise, the water cycle will be affected, leading to more evaporation and water vapor entering the atmosphere. Since water vapor is the most abundant greenhouse gas, making up 36-72% of our atmospheric greenhouse gases, increased atmospheric water vapor can amplify the warming effect by increasing the absorption and trapping of thermal radiation. This is called a positive feedback loop. Increased temperatures increase the atmospheric water vapor concentration, which in turn raises temperatures. Positive feedback loops are extremely common in biological systems and may significantly amplify the effects of climate change. Therefore, if pushed by increasing temperatures, the oceans may inadvertently help drive climate change through the water cycle, leading to the next mass extinction event. 

But temperature and water vapor aren't the only culprits. Come back next time to discuss the effect of the second most abundant greenhouse gas, CO2, on the oceans.

-N. Gallo

Cool fact. The Amazon River is the largest river in the world by water volume, containing about 1/5 of the world's total river flow. However, of the total water on Earth, it makes up < 0.4%. In comparison, the oceans make up 96.5% of the Earth's water, thus playing a very important part in the water cycle.
(photo credit: http://www.eltourismo.com/wp-content/uploads/2010/07/Amazon-River.jpg)

For more information on the ocean's role in the water cycle, check out this USGS article title "The Water Cycle: Water Storage in Oceans," which can be accessed here: http://ga.water.usgs.gov/edu/watercycleoceans.html

The Geological History of Climate Change

 Dear readers,

For this entry I will not discuss my favorite topic (the oceans), but will focus on geological climate change. My reasoning is that to discuss current climate change, you must understand the past. This geological data is also what frequently gets cited in arguments against anthropogenic climate change. For this reason alone, I think it's very important that we all understand the data. So, I apologize for leaving the oceans, but I can promise a big ocean perspective payoff in the next entry, because, as I said before, it all leads back to the oceans.

The topic of anthropogenic climate change is particularly controversial in the field of paleoclimatology. Paleoclimatologists are scientists who study the climate over the geological history of the Earth, and can therefore compare current climate changes with those in the distant past. They are able to do this by correlating the temperature of the earth with data from ancient microfossils, sediment layers, and gas bubbles trapped in ice sheets.

One thing all paleoclimatologists agree on is that Earth's climate is variable. The graph below shows the variation in temperature over 542 million years, with the current rise in temperatures on the far right. What paleoclimatologists do not agree on is if increasing carbon dioxide (CO2) levels can be indicted with the temperature rise, because, in the past, natural temperature rise led to increased CO2 levels (not the other way around). This conclusion, however, does not take into account positive feedback loops in the biosphere or the Industrial Revolution. 

(Image credit: http://upload.wikimedia.org/wikipedia/commons/f/f5/All_palaeotemps.png - copy and paste link into browser to increase image size)  

Come back next time to see how this debate ties back into our oceans! 

-N. Gallo