While BP obviously has reasons to minimize the estimate, the small estimates were erroneously given credit by the US government when NOAA released its first estimate based on satellite photographs of the Gulf.
As we all know, oil floats on top of water and, based on that idea, NOAA thought they could estimate the magnitude of the spill by measuring the size of the oil slick that the satellite photographed.
In making that assumption, NOAA estimators overlooked the findings of a 2004 NRC report which predicted that the oil in a deepwater blowout could break into fine droplets, forming plumes of oil mixed with water that would not quickly rise to the surface.
That is precisely what has happened. Last week a research ship documented the existence of a massive underwater plume the existence of which totally invalidates the assumption on which the NOAA estimate was based.
The possibility that the oil would not rise to the surface is explained by fluid dynamics, as shown in the video below. The main factors involved are a) whether a spill is released in the form of a turbulent jet, or is under less pressure and b) the density of the surrounding water, due to temperature and salinity. In the first experiment the spill is released in the form of a turbulent jet and forms an underwater plume. In the second experiment the spill is not a jet and rises to the surface.
And, as the recently released video of the leaking Deep Horizon well shows, the leak is a highly pressurized jet. Precisely the situation one would expect to create an underwater plume. Serious geeks can read the explanation by Robert Faulkner, a polymer scientist, who has been at the forefront of theorizing the behaviour of the plumes from the Deep Horizon accident.
The location of the oil in the water column is important not only because it affects estimates of the total spill but, more crucially, because it suggests that the environmental legacy of the Deep Horizon spill may be different than expected. Rather than the goo-slathered birds and animals that washed ashore after the Exxon Valdez spill, the greatest impact of BP's spill will be out of sight and more insidious — what biologists call "sublethal effects."
According to an article by Craig Welsh, the Seattle Times Environmental reporter who won a Pulitzer Prize for his reporting on the Exxon Valdez accident,
The Exxon Valdez spill became a sort of wetlab for marine toxicologists, and researchers spent years learning how the complex suite of chemicals that make up oil — particularly polycyclic aromatic hydrocarbons (PAHs) — can affect ocean creatures. Most visible were the birds and otters that died from hypothermia when oil coated their fur or feathers, or were poisoned after ingesting petroleum while grooming.
But equally hard hit was a transient pod of killer whales. Several of the whales died later, presumably from inhaling toxic vapors or eating oiled seals. More troubling still: No whale from the pod has reproduced since.
Other disturbing things happened below the surface. Pink salmon and herring could swim away, but the eggs they deposited in nearby streams or on algae didn't survive because oil caused embryos to fill with fluid.
Later, scientists studying zebrafish learned that was because PAHs damage a fish's developing heart. The results have been repeated with fish in all types of oceans — minnows, flounder, Japanese sea bass, an Australian rainbow fish.
"The heart in a fish is one of the first organs to become functional," said John Incardona, a marine toxicologist with NOAA's Northwest Fisheries Science Center in Seattle. "It starts beating early, and if it doesn't get built right, it disrupts their ability to feed."
In recent years, scientists in Alaska have taken the research further, exposing the embryos of migrating salmon to ever smaller doses of oil. At minuscule doses, the fish survived and swam out to sea normally, but 40 percent fewer fish came back. Results were the same each time they tried the experiment.
"In the Gulf you have all those deepwater fish that produce free-floating embryos," Incardona said. "And you also have massive oil plumes moving around."
Scientists after Exxon Valdez also marveled at oil's ability to work through the food chain. Some clams and mussels metabolize hydrocarbons slowly, and oil showed up in them at chronically elevated levels for years. Those shellfish were eaten regularly by Harlequin and Barrow's goldeneye ducks and sea otters, all of which saw dramatic population declines in oiled areas a decade later. Even otters born after the Valdez spill lived shorter lives in areas that had been heavily oiled.
Dynamic time in Gulf
Ron Kendall, director of the Institute of Environmental and Human Health at Texas Tech University, toured the tide flats along the Gulf Coast last week. Far offshore, bluefin and yellowfin tuna were migrating beneath floating mats of seaweed. Nearshore, herons and terns and pelicans fluttered among the grasses.
"This is a very dynamic time in the Gulf — everything is nesting or laying eggs or reproducing," Kendall said. "People don't realize how fragile it is. You take out the shellfish or the wetlands or the floating seagrasses, there goes the base of the food chain."
And oil can do damage in many ways. It can smother grasses and algae and alter the oxygen content of marine waters. Fish can inhale it through their gills. In animals of all types it can affect neurological systems, livers and kidneys. The ingestion of oil by warm-blooded animals can even change their metabolism.
Scientists soon will get test results back from samples of crabs, shrimp and oysters, some of which feed off the bottom or by filtering water. Many Gulf birds are plunge-divers that eat these invertebrates, but other fish and mammals eat them, too.
"As a scientist, it's just so hard to get your head around it," Kendall said. "You get oil on a pelican, and it's hard for them to fly or survive. But what about the reproductive cycle of a tuna? What happens to sperm whales that swim through those plumes?"
Endangered Kemps Ridley, loggerhead and leatherback sea turtles already are washing up dead on beaches in larger-than-normal numbers, but Barbara Schroeder, an ecologist with NOAA Fisheries, has other worries, too. PAHs can burn turtles' skin, eyes, nose and lungs, increasing the odds of life-threatening infections later. Turtles also tend to feed on anything that might resemble food, including tar balls. That can cause ulcers, bleeding and malnutrition.
"Will females be able to make eggs? Will they develop properly?" Schroeder asked.
For now, these questions remain mysteries that not even Nuka the sea otter can help answer.
At the Seattle Aquarium, Nuka receives special care. Biologists help her fight off mites. She is fed a bounty of crab and clam brought to her from clean waters. Handlers lay out mats of algae so she doesn't have to haul herself onto chilly rocks.
But the Gulf's creatures have to fend for themselves in an environment no one really understands.
On the upside, the higher metabolic rate of oil eating bacteria in the warm waters of the Gulf compared to the cold waters of Alaska could decrease the length of time the oil remains in the water. But that is small comfort.