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The Oil Spill in the Gulf of Mexico

The facts

On April 20, 2010 the Deepwater Horizon offshore oil drilling platform that was situated about 40 miles (64 km) southeast of the Louisiana coast had an important explosion, attributed to lapses in safety and maintenance by BP staff.

 What is it?  Crude oil
Composition by weight
Element Percent range
Carbon 83 to 87%
Hydrogen 10 to 14%
Nitrogen 0.1 to 2%
Oxygen 0.1 to 1.5%
Sulfur 0.5 to 6%
Metals < 0.1%

Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil.

Composition by weight
Hydrocarbon Average Range
Paraffins 30% 15 to 60%
Naphthenes 49% 30 to 60%
Aromatics 15% 3 to 30%
Asphaltics 6% remainder
An oil spill can produce five types of ‘sheen’, depending on whether it comprises light or heavy oil. In the Gulf of Mexico before dispersants, the slick was made up of light, volatile oil, no thicker than a human hair and, therefore, does not appear as the dark, black area, often seen in images of spills. Instead, around 97% of the area is made up of a thin layer of oil, around 0.0001 millimetres thick. Since Sulfonic Acid Salt (Corexit EC9500A & EC9527A, Dispersit SPC 1000) dispersants has been used, the nature and distribution of the spill has changed, what used to be mostly on the surface is now on the whole water column and sunk at the bottom. Collecting oil sheens is increasingly difficult as time goes.
 How much Oil is there?

Comparing Estimates:
NOAA | 795'000 Liters/day
USGS (Added May 27) | 1'908'000 to 3'020'758 Liters/day
Outside Estimates | 3,974,682 Liters/day
BP (Worst Case as of May 5) | 9,539,237 Liters/day
Experts' Worst Case | 15,898,729 Liters/day 

April 20 - June 2 : 39 days.
Minimum : 30'810'000 liters of crude oil
Maximum : 624'000'000 liters of crude oil
This is the largest oil spill in US history. 

35 percent of crude oil evaporates in 15 days, between 50 percent and 60 percent of the oil would remain in or on the water, and the rest would be dispersed in the ocean.
 Where is it? The spill originated from 28.73667°N 88.38716°W
1,524 meters below the ocean surface
April 25 - 1,500 km2 (NASA Picture)
April 28 -  74874 km2 (308km diameter)
April 30 - 10,000 km2 - Hits the coast
Recent reports also mention a major part of the spill being underwater and not observable from the surface. See next page.

The is moving a lot, and some plumes may be caught by the gulf stream up to Florida. Observing or collecting those underwater plumes has proven very complicated. 

The NOAA response provide extensive documentation of the spill progression, day after day as pdf.

 Environmental effect Immediate effects
- Petroleum toxicity
- Oxygen depletion
- temperature change (oil film transculent)

The water is covered with a thin film of oil [source].
- human health
- fishing industry
- tourism
- biodiversity
• Fish: open-water species, such as tuna, sailfish and Jacks
• Birds: pelagic birds, such as shearwaters and frigate birds
• Mammals: fin whales, sperm whales and bottlenose dolphins
• Turtles: loggerheads and Kemp's ridleys 

 Responsible, cost  BP, 

BP has refused to allow independent scientists to perform accurate measurements – and is a matter of ongoing debate. On the other hand individuals have been performing many local reports providing interesting crowd-source datasets. 

Another good way to make your own opinion is to look at the images of what is really happening there, we assembled a great galery of the images that are most explanatory here.

Via <Etienne Gernez>
"Pollutions des côtes par les hydrocarbures", 2008, Paul Fattal