Geochemistry Pop Quiz 2 - 20/3/2013
Niall Smith - SF Earth Science
1) On what evidence is the statement “If current carbon dioxide emission trends continue, shells of marine organisms will start dissolving in some parts of the ocean sometime around mid-century” supported? Provide a short explanation and what you think are the two most relevant literature references illustrating your point.
The scientific evidence which supports this statement originates from two distinct categorical sources - historical scientific evidence, and present day observations and corresponding scientific projections or estimates.
The historical scientific evidence in question consists of observations of ...view middle of the document...
Any species with a carbonate shell or skeleton did not survive - the ocean acidity passed a point where calcium carbonate shells begin to dissolve. Although this ocean acidification was intense, had a rapid onset and lasted only 1-2 years, every species of plankton became entirely extinct, and it took an enormous 500,000 years for them to re appear in the fossil record, and furthermore many millions of years to re-evolve and regain the levels of species diversity which existed pre-extinction (Caldeira, 2007). Clearly this brief but powerful stint of ocean acidification had profound biological impacts and detrimental effects on marine ecosystems.
The global implications of the bolide impact 65 million years ago have startled scientists in many areas, but the manner in which this mass extinction affected the ocean is perhaps the most frightening. The series of marine extinctions has been described as a 'Cautionary tale for the future' (Caldeira, 2007), a statement with which I fully agree. The sudden shift in the ocean acidity at this time was unexpected, and although the acidification probably subsided in 1-2 years, it took millions of years for the marine species and ecosystems to recover. What if this event is comparable to a compact, concise version of what has been gradually happening over time since the beginning of the industrial era, right up to the present day?
We are all familiar, if not over familiar with the present day 'carbon crisis', but it is nearly always applied or linked to global climate change. Carbon dioxide has for millions of years, acted as the greenhouse gas which we know today that contributes to our earths surface temperature by trapping heat in our atmosphere. The carbon cycle on our planet, however is both delicate and pivotal to our survival. Carbon is added to the earths atmosphere primarily through geological degassing, and removed primarily through weathering and the consequential production of carbonate shells and skeletons in our oceans. It is this balanced cycle which has kept out planets surface temperature in the 'goldilocks zone' - the optimal temperature in which life can thrive. Today however, the carbon balance in our atmosphere has been rapidly upset purely through anthropological actions.
We are burning fossil fuels on a massive global scale, and adding 100 times the natural output of carbon dioxide to our atmosphere (Caldeira, 2007). In the Cretaceous period the earth experienced an imbalance in the carbon cycle, as a result of widespread increases in volcanism which contributed huge amounts of greenhouse gases to the atmosphere. However, this was only twice the amount of the baseline natural output - and it was small enough for the earth to recover through the natural uptake of carbon, through weathering and deposition of carbonate shells. The ocean prevented our planet from producing a runaway greenhouse effect. In stark contrast, anthropological...