Remember those tarballs that washed ashore during Isaac – that's nothing compared to Natural oil pollution

I’m sure you’ve seen the picture of tarballs on the beach splashed all over the MSM after hurricane Isaac came ashore in Louisiana. The left leaning website Think Progress (parent of Joe Romm’s Climate Progress) framed it this way:

A Greenpeace research team took samples from beaches along the Alabama coast on September 2, including from an area with hundreds of tar balls in the Bon Secour National Wildlife Refuge.

Hundreds of tar balls on the beach at Bon Secour National Wildlife Refuge, Alabama on September 2, 2012

Reuters was still pushing the story yesterday. CBS News says:

Tests run by Louisiana State University for state wildlife officials confirmed that oil found on Elmer’s Island and Grand Isle matched the biological fingerprint of the hundreds of millions of gallons of oil that spewed from BP’s Macondo well.

Old oil washes up on La. beaches after Isaac

On Wednesday, BP PLC said oil from its spill had been exposed by Isaac’s waves and that the company would work to clean it up.

What’s interesting is that this isn’t anything new. Tarballs wash up on the Gulf beaches with regularity.

You can learn a lot searching though old articles, for example this one from NASA Earth Observatory

Twice an Exxon Valdez spill worth of oil seeps into the Gulf of Mexico every year, according to a new study that will be presented January 27 at the Ocean Sciences Meeting in San Antonio, Texas.

But the oil isn’t destroying habitats or wiping out ocean life. The ooze is a natural phenomena that’s been going on for many thousands of years, according to Roger Mitchell, Vice President of Program Development at the Earth Satellite Corporation (EarthSat) in Rockville Md. “The wildlife have adapted and evolved and have no problem dealing with the oil,” he said.

Science Daily also covered it: Scientists Find That Tons Of Oil Seep Into The Gulf Of Mexico Each Year

Here’s a peer reviewed paper on the subject from 2002,

Transfer of hydrocarbons from natural seeps to the water

column and atmosphere

I. R. MACDONALD1, I. LEIFER2, R. SASSEN1, P. STINE1, R. MITCHELL3 AND N. GUINASSO JR1 1Texas A&M University—GERG, College Station, TX, USA; 2University of California, Chemistry Department, Santa Barbara, CA, USA; 3Earth Satellite Corp., Rockville, MD, USA

From the abstract:

The northern Gulf of Mexico contains hundreds of active seeps that can be studied experimentally with the use of submarines and Remotely Operated Vehicles (ROV).Hydrocarbon flux through surface sediments profoundly alters benthic ecology and seafloor geology at seeps. In water depths of 500–2000 m, rapid gas flux results in shallow, metastable deposits of gas hydrate, which reduce sediment porosity and affect seepage rates. This paper details the processes that occur during the final, brief transition — as oil and gas escape from the seafloor, rise through the water and dissolve, are consumed by microbial processes, or disperse into the atmosphere.

Here’s another back to 1988:

Leakage of deep, reservoired petroleum to the near surface on the gulf of Mexico Continental slope

Kennicutt, M.C.; Brooks, J.M.; Denoux, G.J.

Marine Chemistry, Volume 24, issue 1 (May, 1988), p. 39-59.

ISSN: 0304-4203 DOI: 10.1016/0304-4203(88)90005-9

Elsevier Science

Where they say in the abstract:

Reservoired oils, shallow sediment cores (2m), sea slicks and tar balls were collected in the Green Canyon Lease area of the northern Gulf of Mexico continental slope. The gaseous and liquid hydrocarbons associated with near surface sediments and water have migrated from deep (2000-3000 m) subsurface reservoirs and/or source rocks. This conclusion is based on molecular (GC/FID, GC/FPD, GC/MS) and carbon isotopic evidence. Visual observations at two locations on the continental slope confirm the presence of massive amounts of active liquid as well as gas seepage. Hydrate gas recovered in sediment cores originates from deep, oil-associated gas. This gas has migrated to shallow sediments with little or no isotopic fractionation. In contrast, near surface hydrocarbon liquids (shallow bitumens and sea slicks) are depleted in aliphatics, 4-ring or larger aromatics, naphthalene, C1-naphthalenes and C2-naphthalenes as compared to the reservoired fluids. These near-surface fluids are extensively altered by the concurrent processes of migration, dissolution and microbial degradation. However, the distributions of highly alkylated (> C2) naphthalenes, phenanthrenes and dibenzothiophenes, triterpanes, steranes and triaromatized steranes are similar to the precursor reservoired oil. This study documents, for the first time, a direct link between natural seepage in a deep water marine setting and sea slick and tar ball formation. This and other studies suggest that the natural seepage of oil and gas can be a significant process in the deep ocean.

Combine that with this story yesterday:

Inconvenient bacteria eats a good portion Deepwater Horizon oil spill

At least 200,000 tons of oil and gas from Deepwater Horizon spill consumed by gulf bacteria

Researchers from the University of Rochester and Texas A&M University have found that, over a period of five months following the disastrous 2010 Deepwater Horizon explosion and oil spill, naturally-occurring bacteria that exist in the Gulf of Mexico consumed and within five months removed at least 200,000 tons of oil and natural gas that spewed into the deep Gulf from the ruptured well head.

And I just can’t get too worried about things like this. Nature seems to deal with it effectively.

California has the same natural tarball feature: California oil seeps

As pointed out by the National Research Council (NRC) of the U.S. National Academy of Sciences, “natural oil seeps contribute the highest amount of oil to the marine environment, accounting for 46 per cent of the annual load to the world’s oceans.

But that sort of factual reporting doesn’t sit well with the current alarmism, so you won’t find it in the recent barrage of news articles.

h/t to reader Jimbo


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So what it boils down to is, as long as we don’t spill more than 2 tankers worth a year on average, we’re doing long-term good by pumping the stuff out and safely burning it where it can’t cause harm to the bottom of the food chain 😉


Anyone who has spent time on the TX or LA gulf coast can tell you about tar. When we complained about how crappy our beaches were as children, we were chided by our parents and reminded that the tar put the clothes on our backs and food on our tables. It’s ever-present, spill or no spill.


One has to assume that BP is aware of all this.
REPLY: I’m sure they are, but they’ll be excoriated if they don’t do something, even if some of the oil isn’t theirs. – Anthony


My father was a seventh generation Floridian, and I spent many of my formative years on the beaches of Florida. Tar Balls are as common as seashells in some areas and have been there for millions of years, Petroleum, like CO2, is a natural product and part of our ecosystem, and should never be considered pollution. Early explorers to the west coast of America wrote of asphalt islands and volcanoes, obviously these were larger ‘spills’ than man has ever caused.
We do not now, and never have lived in Eden.

“California is blessed with interesting place names from its multicultural past. Pismo Beach is named for the Chumah Indain word for ‘globs of tar’ due to the natural Hydrocarbon outflow. The Spanish Portola Expedition in 1769 discovered “molten geysers of tar” at the present day La Brea tar pits in downtown Los Angeles. La Brea is the Spanish word for tar.
Tar still oozes from the ground at La Brea, down now to about 10 gallons per day. Globs of tar still wash up at Pismo Beach, but are now blamed on mans failed drilling or shipping efforts. While Earth’s Hydrocarbon production does not appear finite in the near term, there is one thing that is FINITE. The Earth only has a finite storage capacity for this daily production.”
from “Fossil Fuel is Nuclear Waste”….Canada Free Press, Sept 26, 2010


An interesting question is how much this seepage has varied over time. The impression I had from the articles on bacteria suggest that they basically convert the oil to CO_2, ditto the methane. This in turn means that the ocean isn’t just a passive, thermally regulated reservoir for CO_2, but is itself a conduit for carbon to enter as well as leave the reservoir from the Earth itself (carbon rains down onto the ocean floor, is buried perhaps in the form of clathrates or dense oils, and eventually is subducted at plate boundaries, carbon that was subducted long ago is released in the form of gas or oil seepage and is in turn at least partially converted to CO_2 in the reservoir).
So, is it a significant source or not? One Exxon Valdez a year in the gulf isn’t a lot, not really. One Exxon Valdez in every Gulf-sized patch of ocean floor is a lot of Exxon Valdez’s. And what are the error bars on that estimate? Could it be two EVs of seepages? Ten? A half? Is it a function of time, and if so is it increasing?
I was aware of this problem way back when the spill was still ongoing. A Duke vessel went to the Gulf to look for the methane that was supposed to be spewing out of the well at the surface. Surprisingly, there wasn’t very much. Way back then it was proposed that it was being converted to clathrates and being eaten by bacteria on the way to the surface. I was looking at it because there was an odd pattern of hot weather across the US that year that I thought (and still think) might be explained by a “plume” of methane from the spill locally boosting the GHE for a time. But perhaps it was a CO_2 plume, being emitted by all of those hungry bacteria!


BP are well aware and have been since before the second world war; and the spills in the Arabian Gulf during the recent wars there have been cleaned up by nature just as efficiently as the ones in the Gulf of Mexico.
But these facts don’t make exciting news stories in MSM.

Richard111 says:
September 12, 2012 at 9:16 am
One has to assume that BP is aware of all this.
Yup. And what the environmental lobby doesn’t tell us is that OF COURSE the oil will have a similar ‘biological’ [sic] fingerprint, man-made or natural, because it seeps from the same source. It’s like global warming: There is warming, but can you figure out what proportion is man-made? Uh, no.


Which is why the gulf is home to swarms of petroleum ingesting bacteria.

Les Johnson

Oil leaking from natural seeps accounts for about 60% of oil spills in North America. This is over 1 million bbls every year. Most of the rest of the oil in the seas, is from boating, especially recreational boating.
Less than 5% of North American oil in the seas is from oil extraction and transport.


I know the moment anyone from an oil company gets involved it’s “Big Oil”, but c’mon everyone, this has been going on since the big turtle that carries the earth (see: Bryson, Bill, 199anything) stepped upon the subsequent turtle down… and so on. Oil is less dense then almost everything else in the subsurface, gas even more so (by which I mean lees so, dense that is). So unless it comes across the rare convex downward subsurface bump in the ground it’s gonna end up bubbling out at the ocean bottom, or creek bed – which is how we discovered the stuff in the first place, just ask you local Greek… its simple physics and it’s about 90% of every hydrocarbon molecule ever generated by nature… yep, nature, pesky brat that nature…
I promise you, every single one of us evil cronies in big oil wish it were less than 90 %, but the next time I tell management that we expect to trap more than 10% (miss out on only 80%) I swear it’ll be the last time I tell management anythng in this industry…. There are known knowns people (See: Rumsfeld, teh evil years)
Oil goes up… sorry about that!
… and sorry for the obscure Bill Bruson reference.

Tim Walker

I enjoy Wattsupwiththat and agree that MSM folks don’t want to talk about the natural oil seeps and blow out of proportion the tar balls and many other stories, but some might take away from this story: the idea that petroleum is a substance that nature, including wildlife and us, doesn’t have a problem with. The concentrated amount of oil from a tanker spill or large well leak does cause some serious, local and relatively short term problems. Plus when it gets into drinking water through underground tank leaks or spills into watersheds the carcinogens it contains does pose a problem for people’s health.

Kip Hansen

Dr. LEIFER of the University of California, Chemistry Department, Santa Barbara, one of the authors of the 2002 paper, should have personal experience with this. One can not walk the beach there without getting tarballs on one’s feet or shows. When I attended UCSB in the late 1960’s, tarballs on the campus beach were so pervasive that the college dorms placed gallon cans of mineral spirits in the bathrooms so that the tar could be removed and not tracked throughout the buildings.


The Gulf of Mexico has active asphalt volcanoes, and other parts of the world also, it’s completely natural. The coast of California has extinct asphalt volcanoes. As a kid (20 something years ago) I visited the La Brea Tar Pits and was fascinated by them.


Is it beyond the wit of some not to comprehend that if oil and seeps exist on land above sea level then they must also occur below sea level which is 71% of the Earth’s surface.


Oil/tar seeps have been around as long as the planet has. Cripes, some folk really need to go outdoors. People have been using these seeps to the best of their ability for as long as people have been around too. Not only that, plants release volatile hydrocarbon compounds by the ton. Heck, ethylene is a plant stress hormone and causes fruit to ripen.

Julian Flood

Re Joe’s comment about spilling tankers of oil:
On the WUWT ice page there’s a graph of arctic temperature anomalies: 8 deg C off Alaska, two similar hotspots off Siberia. I can’t find how much oil comes from the North Slope, but there’s a UN estimate of oil coming down the Siberian rivers. These are the rough notes I’ve made about the matter :-
UN via, the amount of oil coming down the Siberian rivers is
Lena 25,000 tons
Ob 125,000 tons
Yenisei 225,000 tons
(total spill down the rivers is 500,000 tons, 150 million US gallons, A m^3 weighs .9 tonne, ish, so total spill from Siberian rivers is 500,000/.9. Call it 600,000 m^3 in round figures.)
Benjamin Franklin’s experiment on a Clapham lake shows that 5 ml of light oil can smooth a hectare. 1 hectare per 5ml. The area smoothed by the river outflow is 6*10^5 * 10^6 ml total, call it 10^11 hectares if all were light oil. Let’s call it 10% light oil (pessimistic because the oil will already have been spilled and is likely to be predominately light oil) so 10^10 hectares can be smoothed.
What would the outcry be if every five weeks an Exxon Valdez piled into the Siberian coast? And what would it do to the sea surface?
Prediction: oil polluted Arctic seas will warm. Oil will freeze into the ice in the winter and be released on melting, increasing the concentration around the edge of the ice.
This can’t be right: the pollution is so high it’s unbelievable. Could someone show me where I’ve not divided by 100 or something?

Julian Flood

Oh, yes, the Siberian seas:
Laptev, Kara and Barents seas area is about 3*10^6 km^2. East Siberian 1. Total 4 * 10^6 km^2 which is 4* 10^8 hectares. Let’s call it 10^9 hectares.

Steve C

“A Greenpeace research team took samples …”
That’s right, guys, the tarball is an old Unix archive file format. Try putting them in your computers and see what’s in them.
(Offered in the hope that they’ll try it, which would at least reduce the damage they do … 🙂


Natural oil seepage in the Gulf-

Gerry Parker

My experience since the mid-1960’s on Florida beaches is the same as described by previous posts. Once or twice a year tar balls on the beach (Careful kids! Don’t get it on your feet!).
We sometimes wondered if it was from a tanker ourt parents told us had been torpedoed by the Germans in WW2, but have since learned about the seeps. You can observe slicks from these on commercial flights as you fly up or down the state when the sun is in the west and you are looking out at the Gulf. There is a lot of it when you see it from the air, although I’ve never encountered a slick while out on a boat.
Gerry Parker


Shortly after the 1971 San Fernando Earthquake I was walking along Arroyo Simi in Simi Valley. I had walked there many times before, but this time I noticed fresh seeps of crude oil from cracks in the exposed bedrock. The geological event 25 miles away had triggered the release of near-surface crude oil deposits. If a moderate earthquake can trigger a release this far away, one can only imagine what happens with earthquakes occurring offshore where the oil-bearing strata are even closer to the surface.


This thread is about natural seepage of oil and gas. Of course, these seeps either burn or are converted by microorganisms so they enter the carbon cycle as fossil fuels also enter the carbon cycle when people burn them for use.
And coalfield fires have always also existed, too. These release about the same amount of CO2 as all human activity.
Of course, CO2 which results from seeped oil and gas and from coal field fires has the carbon isotope ratios of fossil fuels.
But people who don’t know about natural fossil fuel emissions often claim the changes to the carbon isotope ratio in the air prove humans are responsible for the recent rise in atmospheric CO2. We may – or may not – be responsible but the carbon isotope ratio changes don’t prove it.


Deepwater Horizon spilled crude oil coming out had more C9 – C16 hydrocarbons than C17 – C30 hydrocarbons. I think analysis of shore tar balls will clearly show weathering as evidenced by rising % concentration of long chain alkanes & the short chain alkanes disappearing.
A tar ball is not a mass of constant composition like some Dung bettle’s roll up. There are probably bio-remediation scientists working on augmenting treatment bacteria with enhanced alkane/alkyne/cycloalkine degrading genes such as alkB, alkH, alkJ, BMO, chnB, chnE & Xamo.

Ryan says:
September 12, 2012 at 9:54 am
Methinks that would be conCAVE downward.

“Petroleum….the OTHER renewable energy”
Once again the green meanies have lied to humanity….the reason there is Methane under every rock you frack is that is is being constantly produced. And NO Dr Brown….a giant BP Methane cloud did NOT drive regional temperatures that summer….the SUN did.


I wonder if BP is just looking at this as a cleanup or if they think they can recover some of the oil from the tar balls?


I remember standing on a tar ball on the beach in Byron Bay in Oz took me half an hour with sand to get the bloody stuff off with a nice red foot.
Although my mate stood on a jelly fish and I’m sure most of you know what we had to do, luckily we where 20 somethings and had been drinking all day.


In the ’50’s and ’60’s I would regularly have to clean the tar off of my feet after spending a day at the beaches in So. California… Beaches like Hermosa, Redondo, Manhattan.. even up to Malibu and Leo Carillo. If tar balls accumulate and there is no natural remediation, then why aren’t the beaches today covered in tar??
It certainly wasn’t little kids like me collecting them on our feet in the summertime and taking them home for our parents to dissolve with kerosene…

In the world of hazardous materials response, we don’t usually speak of pollution but of “contamination,” which is different from exposure. Exposure is coming into personal contact with something nasty (like the fine aroma of a former road-warrior skunk along the highway).
Contamination, on the other had, we often note is just something where it should not be, like chewing gum stuck to the sole of your shoe… That would appear to be the case here…


“I’m sure they are, but they’ll be excoriated if they don’t do something, even if some of the oil isn’t theirs. – Anthony”
“And I just can’t get too worried about things like this. Nature seems to deal with it effectively.”
Name a place on Earth where this takes place naturally (see picture)? Name one? It happens every year according to you. Please tell me where?

D Boehm
Berényi Péter

But, but, if we remove all the foodstuff from the bottom of the Gulf and burn it in cars, an entire ecosystem will be starved to death for the lack of natural oil seeps. It is certainly worse than we thought, just think of what it would do to biodiversity. The upshot is natural tarballs, as all things natural, is a blessing, only artificial ones hurt birdies.


The drift of your comments seems to validate or even excuse BP’s culpability for the criminal negligence related to the blowout in the Gulf spill. Dumping millions of tons of crude on the floor of the Gulf has had serious consequences, as might be expected. In all honesty, the impact has yet to be fully quantified. It is known that in the harvesting and trapping sites associated with the spill, the catch is off 30-40%. Other factors are in play so the situation is not completely clear cut. But the early signs point to the toxic gunk that covers large tracks of the seabed as being a key factor in the drop off.
I’m not in favor of dragging in ideological chestnuts to the otherwise indispensable WUWT website. There are plenty of other sites where people can spout off on politics and economics. That kind of tub-thumping, does not, in my opinion, enhance the prime mission and credibility of WUWT . Once you start importing your own brand of bromides to the site, the scientific credibility becomes vitiated. Your judgments on matters of climate science start to come into question.
Some restraint in matters not related to climate and atmospheric science probably serves best, the prime mission of WUWT. Just a friendly suggestion.

Why would BP argue if they are being given it all and it is valuable?
Surely they are working on ways to collect, sell and profit from it as oil extraction continues to decrease natural oil seeps. They must be laughing frequently at how they can be causing a major reduction in the pressure behind natural oil seeps and a reduction in all the life forms that depend upon it while being blamed for the opposite.

Robbie says:
September 12, 2012 at 12:33 pm
“Name a place on Earth where this takes place naturally (see picture)? Name one?”
“When Marco Polo in 1264 visited the Azerbaijani city of Baku, on the shores of the Caspian Sea, he saw oil being collected from seeps. He wrote that “on the confines toward Geirgine there is a fountain from which oil springs in great abundance, in as much as a hundred shiploads might be taken from it at one time.”
From Wiki
Perhaps thanks to Big oil it does seem to happen less often now. So the birds live on until that terrible wind turbine day comes along.

Gunga Din

It seems that just about anything and everything that happens in nature is now blamed on Mankind … and, of course, with enough money and authority some members of Mankind claim they can fix it.

Luther Wu

siliggy says:
September 12, 2012 at 1:42 pm
Robbie says:
September 12, 2012 at 12:33 pm
“Name a place on Earth where this takes place naturally (see picture)? Name one?”
“When Marco Polo in 1264 visited the Azerbaijani city of Baku, on the shores of the Caspian Sea, he saw oil being collected from seeps. He wrote that “on the confines toward Geirgine there is a fountain from which oil springs in great abundance, in as much as a hundred shiploads might be taken from it at one time.”
From Wiki
Perhaps thanks to Big oil it does seem to happen less often now. So the birds live on until that terrible wind turbine day comes along.
That gets you a Gold Star pasted next to your name.

JD Ohio

Coal Oil Point off the coast of Santa Barbara is the second largest natural oil seep in the world. It releases a large amount of methane, and I believe it is a very substantial contributor to air pollution in Santa Barbara.


Robbie you might want to rain in your indignation as Greenpeace says ‘hundreds of tar balls’ so it is probably easily remedy with a bucket and a pair of gloves.


Argh. A chemical is a chemical is a chemical. It does not matter if it came from a green plant or a Monsanto plant. Toxicity is determined by dose and route of administration. Everything and nothing is toxic without specifying what and how much and how it is delivered. The earth is 6 quintillion tons of chemicals. Puleeze give me a break.


Or is it sextillion, I forget ;(


Robbie says:
September 12, 2012 at 12:33 pm
Name a place on Earth where this takes place naturally (see picture)? Name one? It happens every year according to you. Please tell me where?

Will this do?
It seems the answer to the naturally oiled birds is………………………………………….allow more drilling off the coast.
I hope this does not count as a vicious put down. 😉


Robbie, check this out:

The reduction in natural seepage pollution as a result of offshore oil drilling has been established by long-term UCSB studies. What many residents don’t realize is local natural oil seepage kills wildlife. Far more birds have died from these seeps than from all California offshore oil spills combined over the last 50 years.
Just last month, the Long Beach-based International Bird Rescue Research Center reported, “Natural Seep Oil Prompts Bird Rescue in California” with more than 50 birds oiled in January. In March 2011, the IBRRC headline was, “Natural Seep Oiled Birds Continue to Flood IBRRC.” Santa Barbara Wildlife Care Network routinely sees dead seep-oiled birds. A local 2005 natural oil seepage event killed more birds than the 1969 oil spill in the Santa Barbara

Robbie, please don’t read this as a vicious put down. I just want to get at facts and truth. That’s all. Have a nice evening.

Louis Hooffstetter

I learn something new everyday. From Wikipedia:
“The petroleum fly, Helaeomyia petrolei, is a species of fly from California, USA. The larvae feed on dead insects that become trapped in naturally occurring petroleum pools, making this the only known insect species that develops in crude oil, a substance which is normally highly toxic to insects.”
OMG! If all the oil seeps are cleaned up, these cute little buggers will become extinct! I certainly hope Lisa Jackson will do as much to protect this endangered species as she has done to protect the Polar Bears!


Most oil fields have been discovered by finding the sources of seeps, so much of the oil we’re taking out of the ground was the same stuff which was leaking out anyway.


Tar balls are definitely caused naturally, and occur even in the remote Seychelles Islands, stuck in the middle of the Indian Ocean. For as long as anyone can remember, tar balls have washed up onto the pristine white beaches of the Seychelles during the north-west monsoon period between November to February.


“And I just can’t get too worried about things like this. Nature seems to deal with it effectively.” … tell that to fishermen in Alaska!

Bilkadi writes: “In a true sense then, the politics of oil in the ancient Middle East sealed the fate of Antony and Cleopatra” (
He relates how the Arabs were involved in the first known oil wars, Nabateans in the bitumen battles to be precise. 2500 years ago they or their predecessors waited on the shores of the Dead Sea for great blobs of tar to surface, and they would race out in reed boats to claim them (the boats, like the Yahwist Noah’s ark, were probably sealed with the pitch). Genesis 14 tells of an army being bogged down in slime pits in the same area, one element of the story which we must admit smacks of authenticity.
Sea level has probably an insignificant effect on oil seeps, but this is not the case for endorrheic lakes, like the Caspian and Dead Sea, where fluctuations can be drastic. We would expect some relation between recent climate and tar/oil commerce in the regions of these lakes: dry conditions lead to falling surface elevation, reducing pressure on the seeps. That’s why things like that don’t happen no more nowadays. –AGF


Julian Flood says:
September 12, 2012 at 10:17 am
Oh, yes, the Siberian seas:
Laptev, Kara and Barents seas area is about 3*10^6 km^2. East Siberian 1. Total 4 * 10^6 km^2 which is 4* 10^8 hectares. Let’s call it 10^9 hectares.

The arctic is not a good comparison with the Gulf of Mexico in regard to bacterial degradation of oil, since temperature plays a big role on the rate of bacterial (or any other) metabolism.
Thus for instance some very large oil discharges in the Arabian sea have dissipated very rapidly, vanishing after just a year or two, while discharges in temperate or Arctic oceans linger for longer since bacterial action is much slower.