Sal wrote:Oceans ....
The oceans are excellent carbon sinks.
http://en.wikipedia.org/w/index.php?title=Paleocene%E2%80%93Eocene_Thermal_Maximum
PETM is probably the only example within the Cenozoic Era (approximately the last 65 million years) wherein a mass of carbon comparable to projected anthropogenic emissions (>2000 Gt or Pg) rapidly entered these reservoirs. The source of the CO 2 , and whether it was oxidized CH 4 , remain open issues; nonetheless, abundant evidence indicates nearly coeval changes in global warming and global carbon cycling, strongly suggesting a link between the two.
Numerous other changes can be observed in stratigraphic sections containing the PETM. [5]
Fossil records for many organisms show major turnovers. For example, in the marine realm, a mass extinction of benthic foraminifera, a global expansion of subtropical dinoflagellates, and an appearance of excursion planktic foraminifera and calcareous nannofossils all occurred during the beginning stages of PETM. On land, there was a sudden appearance of modern mammal orders (including primates) in Europe and North America. Sediment deposition changed significantly at many outcrops and in many drill cores spanning this time interval.
Although now widely accepted that the PETM represents a “case study” for global warming and massive carbon input to Earth’s surface, the cause, details and overall significance of the event remain perplexing.
Life [edit]
The PETM is accompanied by a mass extinction of 35-50% of benthic foraminifera (especially in deeper waters) over the course of ~1,000 years – the group suffering more than during the dinosaur-slaying K-T extinction. Contrarily, planktonic foraminifera diversified, and dinoflagellates bloomed. Success was also enjoyed by the mammals, who radiated extensively around this time.
The deep-sea extinctions are difficult to explain, as many were regional in extent. General hypotheses such as a temperature-related reduction in oxygen availability, or increased corrosion due to carbonate undersaturated deep waters, are insufficient as explanations. The only factor global in extent was an increase in temperature. Regional extinctions in the North Atlantic can be attributed to increased deep-sea anoxia, which could be due to the slowdown of overturning ocean currents, [18] or the release and rapid oxidation of large amounts of methane.
In shallower waters, it's undeniable that increased CO 2 levels result in a decreased oceanic pH, which has a profound negative effect on corals. [27] Experiments suggest it is also very harmful to calcifying plankton. [28] However, the strong acids used to simulate the natural increase in acidity which would result from elevated CO 2 concentrations may have given misleading results, and the most recent evidence is that coccolithophores (E. huxleyi at least) become more, not less, calcified and abundant in acidic waters. [29] Interestingly, no change in the distribution of calcareous nanoplankton such as the coccolithophores can be attributed to acidification during the PETM. [29] Acidification did lead to an abundance of heavily calcified algae [30] and weakly calcified forams. [31]
The increase in mammalian abundance is intriguing. There is no evidence of any increased extinction rate among the terrestrial biota. Increased CO 2 levels may have promoted dwarfing [32][33] – which may have encouraged speciation. Many major mammalian orders –including the Artiodactyla, horses, and primates – appeared and spread across the globe 13,000 to 22,000 years after the initiation of the PETM. [32]
Orbital forcing [edit]
The presence of later (smaller) warming events of a global scale, such as the Elmo horizon (aka ETM2), has led to the hypothesis that the events repeat on a regular basis, driven by maxima in the 400,000 and 100,000 year eccentricity cycles in the Earth's orbit. The current warming period is believed to last another 50,000 years due to a minimum in the eccentricity of the Earth's orbit. Orbital increase in insolation (and thus temperature) would force the system over a threshold and unleash positive feedbacks.
Recovery [edit]
The δ 13 C record records a duration of around 120,000 [22] to 170,000 [1][53] years, slightly faster than the residence time of carbon in the modern atmosphere (100,000 to 200,000 years). A feedback system [54] would explain this slightly more rapid recovery time.
The most likely method of recovery involves an increase in biological productivity, transporting carbon to the deep ocean. This would be assisted by higher global temperatures and CO 2 levels, as well as an increased nutrient supply (which would result from higher continental weathering due to higher temperatures and rainfall; volcanics may have provided further nutrients). Evidence for higher biological productivity comes in the form of bio-concentrated barium. [54] However, this proxy may instead reflect the addition of barium dissolved in methane. [55] Diversifications suggest that productivity increased in near-shore environments, which would have been warm and fertilized by run-off, outweighing the reduction in productivity in the deep oceans.
http://en.wikipedia.org/wiki/Carbonate_rock
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