Blog Archive

Saturday, April 30, 2011

Richard P. Allan & Brian J. Soden, Atmospheric warming and the amplification of precipitation extremes / 7 August 2008 / Page 2 / 10.1126/science.116078

Atmospheric Warming and the Amplification of Precipitation Extremes 

Richard P. Allan¹* and Brian J. Soden²

¹Environmental Systems Science Centre, University of Reading, Berkshire, RG6 6AL, U.K.

²Rosenstiel School of Marine and Atmospheric Sciences, University of Miami, FL 33149, USA. 


Climate models suggest that extreme precipitation events will become more common in an anthropogenically warmed climate. However observational limitations have hindered a direct evaluation of model projected changes in extreme precipitation. Here we use satellite observations and model simulations to examine the 
response of tropical precipitation events to naturally driven changes in surface temperature and atmospheric 
moisture content. These observations reveal a distinct link between rainfall extremes and temperature, with heavy rain events increasing during warm periods and decreasing during cold periods. Furthermore, the 
observed amplification of rainfall extremes is found to be larger than predicted by models, implying that 
projections of future changes in rainfall extremes due to anthropogenic global warming may be underestimated. 

*Correspondence e-mail:

K. E. Trenberth et al., J. Climate (2011), Atmospheric moisture transports from ocean to land and global energy flows in reanalyses

Atmospheric moisture transports from ocean to land and global energy flows in reanalyses

Kevin E. Trenberth, John T. Fasullo and Jessica Mackaro
National Center for Atmospheric Research 1, P. O. Box 3000, Boulder, CO 80307, email: , ph: (303) 497 1318, fax: (303) 497 1333


An assessment is made of the global energy and hydrological cycles from eight current atmospheric reanalyses and their depiction of changes over time. A brief evaluation of the water and energy cycles in the latest version of the NCAR climate model, CCSM4, is also given. The focus is on the mean ocean, land and global precipitation P, the corresponding evaporation E, their difference corresponding to the surface freshwater flux E-P, and the vertically integrated atmospheric moisture transports. Using the model-based P and E, the time and area average E-P for the oceans, P-E for land, and the moisture transport from ocean to land should all be identical but are not close in most reanalyses, and often differ significantly from observational estimates of the surface return flow based on net river discharge into the oceans. Their differences reveal outstanding issues with atmospheric models and their biases, which are manifested as analysis increments in the reanalyses. The NCAR CCSM4 model, along with most reanalysis models, the exception being MERRA, has too intense water cycling (P and E) over the ocean although ocean to land transports are very close to observed.

Precipitation from reanalyses that assimilate moisture from satellite observations exhibits large changes identified with the changes in the observing system, as new and improved temperature and water vapor channels are assimilated and, while Pimproves after about 2002, E-P does not. Discrepancies among hydrological cycle components arise from analysis increments that can add or subtract moisture. The large-scale moisture budget divergences are more stable in time and similar across reanalyses than model-based estimates of E-P. Results are consistent with the view that recycling of moisture is too large in most models and the lifetime of moisture is too short. For the energy cycle, most reanalyses have spurious imbalances ~10 W m−2 within the atmosphere, and ~5–10 W m−2 in net fluxes into the surface and to space. Major improvements are needed in model treatment and assimilation of moisture, and surface fluxes from reanalyses should only be used with great caution.
Received October 24, 2010; revised April 7, 2011

1The National Center for Atmospheric Research (NCAR) is sponsored by the National Science Foundation.

G. Svensson & J. Karlsson, J. Climate (2011), On the Arctic wintertime climate in global climate models

On the Arctic wintertime climate in global climate models

Gunilla Svensson*
Department of Meteorology, Stockholm University, Stockholm, Sweden
Johannes Karlsson
Jet Propulsion Laboratory, California Institute of Technology, USA


Energy fluxes important for determining the Arctic surface temperatures during winter in present-day simulations from the CMIP3 Multi-Model dataset are investigated. The model results are evaluated over different surfaces using satellite retrievals and ERA-Interim. The wintertime turbulent heat fluxes vary substantially between models and different surfaces. The monthly median net turbulent heat flux (upward) is in the range 100 to 200 Wm−2 and −15 to 15 Wm−2 over open ocean and sea-ice, respectively. The simulated net longwave radiative flux at the surface is biased high over both surfaces compared to observations, but for different reasons. Over open ocean, most models overestimate the outgoing longwave flux while over sea-ice it is rather the downwelling flux that is underestimated. Based on the downwelling longwave flux over sea-ice, two categories of models are found. One group of models which shows reasonable downwelling longwave fluxes, compared with observations and ERA-Interim, is also associated with relatively high amounts of precipitable water as well as surface skin temperatures. This group also shows more uniform air mass properties over the Arctic region possibly as result of more frequent events of warm-air intrusion from lower latitudes. The second group of models underestimates the downwelling longwave radiation and is associated with relatively low surface skin temperatures as well as low amounts of precipitable water. These models also exhibit larger decrease in the moisture and temperature profiles northward in the Arctic region which might be indicative of too stagnant conditions in these models.
*Corresponding author address: Gunilla Svensson, Department of Meteorology, Stockholm University, SE-106 91 Stockhholm, Sweden., E-mail: 

F. Giorgi et al., J. Climate (2011), Higher hydroclimatic intensity with global warming

Higher hydroclimatic intensity with global warming

F. Giorgi*, E-S. Im*, E. Coppola*, N. S. Diffenbaugh**, X. J. Gao***, L. Mariotti*, and Y. Shi***
* Earth System Physics Section, International Centre for Theoretical Physics, Trieste, Italy
** Department of Environmental Earth System Science and Woods Institute for the Environment, Stanford University, Stanford, CA, USA
*** National Climate Center, Chinese Meteorological Administration, Beijing, China


Because of their dependence on water, natural and human systems are highly sensitive to changes in the hydrologic cycle. We introduce a new measure of hydroclimatic intensity (HY-INT), which integrates metrics of precipitation intensity and dry spell length, viewing the response of these two metrics to global warming as deeply interconnected. Using a suite of global and regional climate model experiments, we find that increasing HY-INT is a consistent and ubiquitous signature of 21st century greenhouse gas-induced global warming. Depending on the region, the increase in HY-INT is due to an increase in precipitation intensity, dry spell length, or both. Late 20th century observations also exhibit dominant positive HY-INT trends, providing a hydroclimatic signature of late 20th century warming. We find that increasing HY-INT is physically consistent with the response of both precipitation intensity and dry spell length to global warming. Precipitation intensity increases due to increased atmospheric water holding capacity. Rather, increases in mean precipitation are tied to increases in surface evaporation rates, which are lower than for atmospheric moisture. This leads to a reduction in the number of wet days and an increase in dry spell length. Our analysis identifies increasing hydroclimatic intensity as a robust integrated response to global warming, implying increasing risks for systems that are sensitive to wet and dry extremes and providing a potential target for detection and attribution of hydroclimatic changes.

BREAKING: Anonymous Hits Chamber! by: Releases thousands of documents that contain content from the American Legislative Exchange Council, the U.S. Chamber of Commerce, and the ultra-right-wing, Koch-backed, union-killer Mackinac Center

by Muskegon Critic, Daily Kos, April 28, 2011
As we speak I'm sitting on a mile high pile of, I guess, unauthorized data released about the US Chamber of Commerce. Thousands and thousands of docs released a few hours ago. Wanna help read through the docs and see what horrific secret things the Chamber is up to? There's thousands of these docs.
This evening I came across a reference to a torrent on Twitter that caught my eyeball -- A "torrent" in this case is basically a document dump. Basically. The message intrigued me not only because it mentioned secret documents from the US Chamber of Commerce, but also....
A. It's a document dump from Anonymous
B. It contains documents from an organization that particularly makes my teeth curl, the Michigan based Mackinac Center for Public Policy. Those are the dudes who brought us the Overton Window. They're kind of nuts.
  This document release contains content from the American Legislative
Exchange Council, the U.S. Chamber of Commerce, and the Mackinac Center.

   The Chamber of Commerce came to our attention via the HBGary email
dump. Their connections to ALEC and the Mackinac Center are not entirely
clear, but the information we provide should help clarify things.
   Both files are encrypted using the system. We
don't feel a great need to protect this content since we're distributing
it, but we do feel a need to help you improve your tradecraft.
   The larger file,, is the content itself. The
password for this is "Barrett Brown".
   The smaller file,, contains clarifications that may
or may not be needed, depending on how wise those who download this
data prove to be. If the need becomes apparent we will provide the
password to Barrett Brown, with the expectation that he will release it
via and other channels.
   We are Anonymous.
   We are Legion.
   We do not forgive.
   We do not forget.

The torrent contains information about:

    - The US Chamber of Commerce
    - The ultraconservative think tank the Mackinac Center for Public Policy in Michigan
    - The American Legislative Exchange Council (ALEC)
All three, of course, are organizations that the Koch brothers are understood to have significant influence over, and all three HATE HATE HATE HATE HATE unions. And the middle class. And puppies. And probably popcorn.
It took a long time, but I managed to download the torrent and it's filled with thousands of documents. Mostly I'm poking through the Mackinac Center ones, which makes for filthy, nauseating reading at 3 AM.
But it could definitely use more people downloading the torrent and reviewing documents for weird, unethical, reprehensible behavior and unseemly connections and dealings.
Important: You'll also need a torrent client like utorrent or BitTorrent to receive the documents...and you'll need TrueCrypt to decode it
To open the file you will also need something called TrueCrypt which you can download here.
1.  Download TrueCrypt after you've finished loading the massive data dump to your computer.
2. Then open TrueCrypt (click the TrueCrypt icon)
3. Click Select File and locate the huge file from your local computer.
4. Select a directory in the top window...I used the Z directory
5. Click Dismount
6. Ignore the warning the system gives you about armageddon and system failure -- if it actually gives you a warning.
7. Enter the password Barrett Brown
8.'ll get a choice of which file you want to open...and from there on out it's pretty much millions and millions of pdf files.
Happy reading! Bring a barf bag.

Tas van Ommen: Warmer oceans release CO2 faster than thought

Warmer oceans release CO2 faster than thought

by Wendy Zukerman, New Scientist, April 25, 2011

As the world's oceans warm, their massive stores of dissolved carbon dioxide may be quick to bubble back out into the atmosphere and amplify the greenhouse effect, according to a new study.
The oceans capture around 30% of human carbon dioxide emissions and hide it in their depths. This slows the march of global warming somewhat. But climate records from the end of the last ice age show that as temperatures climb, the trend reverses and the oceans emit CO2, which exacerbates warming.
Previous studies have suggested that it takes between 400 and 1,300 years for this to happen. But now the most precise analysis to date has whittled that figure down.

Quick response

"We now think the delay is more like 200 years, possibly even less," says Tas van Ommen from the Australian Antarctic Division, in Hobart, who led the study.
The new results come from Siple and Byrd ice cores in western Antarctica. Van Ommen and colleagues dated CO2 bubbles trapped in the ice, and then compared their measurements with records of atmospheric temperatures from the same time period.
As expected, when temperature increased, carbon dioxide followed, but at both Siple and Byrd the time lag was around 200 years – much shorter than previous studies found.
Rising temperatures make carbon dioxide leak from the oceans for two main reasons. First, melting sea ice increases the rate that the ocean mixes, which dredges up CO2-rich deep ocean waters. Second, "when you warm the ocean up, just like warming up a Coke bottle, it drives the gas out," says van Ommen.
Previous estimates used cores from regions with low snowfall, van Ommen says, leading to a very gradual trapping of the carbon dioxide in the ice. This increased uncertainty in timing. Also, many previous studies used only one ice core site.

Worse warming?

And while more precise than the others, the team's study also comes with significant uncertainty: plus or minus 200 years, meaning there could actually be no lag time between rising temperatures and gases being released from the atmosphere.
"They've nailed it," says Paul Fraser, a greenhouse gas researcher at Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). He adds that despite the uncertainty, "this is a really good data set that they've got."
Van Ommen says climate modelling will be needed before we can speculate how the results relate to current warming.
The work was presented at the Greenhouse 2011 conference in Cairns earlier this month.

Friday, April 29, 2011

Top climate scientist, Kevin Trenberth, on the monster tornadoes: ‘It is irresponsible not to mention climate change’

Top Climate Scientist On The Monster Tornadoes: ‘It Is Irresponsible Not To Mention Climate Change’

by Brad Johnson, The Wonk Room, Think Progress, April 29, 2011

Throughout human history, the climate system has been a source of life and death, the sun and rain capable of feeding our crops and bringing us comfort, or unleashing terrible devastation in wind, fire, drought, storm, and flood. Each tragedy that occurs — such as the terrible outbreak of tornadoes and flooding storms this week in the South — reminds us of that awesome power, which is beyond our control and at the limits of our comprehension. We have also learned that humanity is meddling with that power, primarily through the burning of coal and oil that increases the amount of heat trapped in the atmosphere and oceans. Scientists have been warning our leaders for decades that this interference with the climate system is dangerous, and have worked tirelessly to explain how these threats are now coming to pass.

However, the Republican Party is now dominated by ideologues who deny the threat of polluting our climate, even when faced with direct evidence of what the climate system can do to the people they are sworn to protect.

Conservatives attack any discussion of climate policy within the context of the killer tornadoes as “grotesque,” saying that to do so is blaming the victims.

In an email interview with ThinkProgress, Dr. Kevin Trenberth, one of the world’s top climate scientists, who has been exploring for years how greenhouse pollution influences extreme weather, said he believes that it is “irresponsible not to mention climate change” in the context of these extreme tornadoes, adding that the scientific understanding of how polluting our atmosphere with billions of tons of greenhouse gases affects tornadic activity is still ongoing:
It is irresponsible not to mention climate change. … The environment in which all of these storms and the tornadoes are occurring has changed from human influences (global warming). Tornadoes come from thunderstorms in a wind shear environment. This occurs east of the Rockies more than anywhere else in the world. The wind shear is from southerly (SE, S or SW) flow from the Gulf overlaid by westerlies aloft that have come over the Rockies. That wind shear can be converted to rotation. The basic driver of thunderstorms is the instability in the atmosphere: warm moist air at low levels with drier air aloft. With global warming the low level air is warm and moister and there is more energy available to fuel all of these storms and increase the buoyancy of the air so that thunderstorms are strong. There is no clear research on changes in shear related to global warming. On average the low level air is 1 °F and 4% moister than in the 1970s.
Climate scientist Michael Mann explains further that “climate change is present in every single meteorological event”:
The fact remains that there is 4% more water vapor – and associated additional moist energy – available both to power individual storms and to produce intense rainfall from them. Climate change is present in every single meteorological event, in that these events are occurring within a baseline atmospheric environment that has shifted in favor of more intense weather events.
Climate scientist Gavin Schmidt concurred:
It is a truism to say that everything has been affected by climate change so far and therefore this latest outbreak must in some sense have been affected, but attribution is hard and the further down the chain the causality is supposed to go, the harder this is. For heat waves it is easier, for statistics on precipitation intensity it easier – there are multiple levels of good modelling, theory and observations to back it up. But we have much less to go on with tornadoes.
Those who deny the threat of polluting our climate system are not to blame for its fury — but none of us can shirk our responsibility to end our interference with the weather.

To find out if loved ones are okay, use Text REDCROSS to 90999 to donate $10 to relief efforts.

NOAA's National Weather Service: U.S. Tornadoes -- Daily Counts and Annual Running Trends*

NOAA: U.S. Tornadoes -- Daily Counts and Annual Running Trends*

Daily Counts and Annual Running Trend (Updated Frequently)
Click for full image --->    Tornado Reports       |       Hail Reports       |       Wind Reports
U.S. Annual Tornado Trends
Plot of the annual running total of U.S. tornadoes. (Click on image for a full resolution version.)
Annual Tornado Running Totals
Plot of the annual running total of tornado reports compared to inflation adjusted values. (Click on graph for a full description.)

Early Warning Signal for Ecosystem Collapse: Fluctuations Before the Fall

Early Warning Signal for Ecosystem Collapse: Fluctuations Before the Fall

ScienceDaily, April 28, 2011 — Researchers eavesdropping on complex signals emanating from a remote Wisconsin lake have detected what they say is an unmistakable warning -- a death knell -- of the impending collapse of the lake's aquatic ecosystem. Researchers have found that models used to assess catastrophic changes in economic and medical systems can also predict environmental collapse. Stock market crashes, epileptic seizures, and ecological breakdowns are all preceded by a measurable increase in variance—be it fluctuations in brain waves, the Dow Jones index, or, in the case of the Wisconsin lake, chlorophyll.
The finding, reported April 29, 2011, in the journal Science by a team of researchers led by Stephen Carpenter, a limnologist at the University of Wisconsin-Madison, is the first experimental evidence that radical change in an ecosystem can be detected in advance, possibly in time to prevent ecological catastrophe.
"For a long time, ecologists thought these changes couldn't be predicted," says Carpenter, a UW-Madison professor of zoology and one of the world's foremost ecologists. "But we've now shown that they can be foreseen. The early warning is clear. It is a strong signal."
The implications of the National Science Foundation-supported study are big, says Carpenter. They suggest that, with the right kind of monitoring, it may be possible to track the vital signs of any ecosystem and intervene in time to prevent what is often irreversible damage to the environment.
"With more work, this could revolutionize ecosystem management," Carpenter avers. "The concept has now been validated in a field experiment and the fact that it worked in this lake opens the door to testing it in rangelands, forests and marine ecosystems."
Ecosystems often change in radical ways. Lakes, forests, rangelands, coral reefs and many other ecosystems are often transformed by such things as overfishing, insect pests, chemical changes in the environment, overgrazing and shifting climate.
For humans, ecosystem change can impact economies and livelihoods such as when forests succumb to an insect pest, rangelands to overgrazing, or fisheries to overexploitation.
A vivid example of a collapsed resource is the Atlantic cod fishery. Once the most abundant and sought-after fish in the North Atlantic, cod stocks collapsed in the 1990s due to overfishing, causing widespread economic hardship in New England and Canada. Now, the ability to detect when an ecosystem is approaching the tipping point could help prevent such calamities.
In the new study, the Wisconsin researchers, collaborating with groups from the Cary Institute for Ecosystem Studies in Millbrook, N.Y., the University of Virginia in Charlottesville, and St. Norbert College in De Pere, Wis., focused their attention on Peter and Paul lakes, two isolated and undeveloped lakes in northern Wisconsin. Peter is a six-acre lake whose biota were manipulated for the study and nearby Paul served as a control.
The group led by Carpenter experimentally manipulated Peter Lake during a three-year period by gradually adding predatory largemouth bass to the lake, which was previously dominated by small fish that consumed water fleas, a type of zooplankton. The purpose, Carpenter notes, was to destabilize the lake's food web to the point where it would become an ecosystem dominated by large predators. In the process, the researchers expected to see a relatively rapid cascading change in the lake's biological community, one that would affect all of its plants and animals in significant ways.
"We started adding these big ferocious fish and almost immediately this instills fear in the other fish," Carpenter explains. "The small fish begin to sense there is trouble and they stop going into the open water and instead hang around the shore and structure, things like sunken logs. They become risk averse."
The biological upshot, according to the Wisconsin lake expert, is that the lake became "water flea heaven." The system becomes one where the phytoplankton, the preferred food of the lake's water fleas, becomes highly variable.
"The phytoplankton get hammered and at some point the system snaps into a new mode," says Carpenter.
Throughout the lake's three-year manipulation, all its chemical, biological and physical vital signs were continuously monitored to track even the smallest changes that would announce what ecologists call a "regime shift," where an ecosystem undergoes radical and rapid change from one type to another. It was in these massive sets of data that Carpenter and his colleagues were able to detect the signals of the ecosystem's impending collapse.
Ecologists first discovered the signals in computer simulations of spruce budworm outbreaks. Every few decades the insect's populations explode, causing widespread deforestation in boreal forests in Canada. Computer models of a virtual outbreak, however, seemed to undergo odd blips just before an outbreak.
The problem was solved by William "Buz" Brock, a UW-Madison professor of economics who for decades has worked on the mathematical connections of economics and ecology. Brock used a branch of applied mathematics known as bifurcation theory to show that the odd behavior was in fact an early warning of catastrophic change. In short, he devised a way to sense the transformation of an ecosystem by detecting subtle changes in the system's natural patterns of variability.
The upshot of the Peter Lake field experiment, says Carpenter, is a validated statistical early warning system for ecosystem collapse. The catch, however, is that for the early warning system to work, intense and continuous monitoring of an ecosystem's chemistry, physical properties and biota are required.
Such an approach may not be practical for every threatened ecosystem, says Carpenter, but he also cites the price of doing nothing: "These regime shifts tend to be hard to reverse. It is like a runaway train once it gets going and the costs -- both ecological and economic -- are high."

Record Number of Whales, Krill Found in Antarctic Bays

Record Number of Whales, Krill Found in Antarctic Bays

ScienceDaily, April 28, 2011 — Scientists have observed a "super-aggregation" of more than 300 humpback whales gorging on the largest swarm of Antarctic krill seen in more than 20 years in bays along the Western Antarctic Peninsula.

The sightings, made in waters still largely ice-free deep into austral autumn, suggest the previously little-studied bays are important late-season foraging grounds for the endangered whales. But they also highlight how rapid climate change is affecting the region.
The Duke University-led team tracked the super-aggregation of krill and whales during a six-week expedition to Wilhelmina Bay and surrounding waters in May 2009. They published their findings on April 27 in the online science journal PLoS ONE.
"Such an incredibly dense aggregation of whales and krill has never been seen before in this area at this time of year," says Duke marine biologist Douglas Nowacek. Most studies have focused on whale foraging habitats located in waters farther offshore in austral summer.
Nowacek and his colleagues observed 306 humpback whales -- or about 5.1 whales per square kilometer, the highest density ever recorded -- in Wilhelmina Bay. They measured the krill biomass at about 2 million tons. Small, floating fragments of brash ice covered less than 10 percent of the bay. The team returned in May 2010 and recorded similar numbers. Smaller but still higher-than-normal counts were also reported in neighboring Andvord Bay.
Advancing winter sea ice used to cover much of the peninsula's bays and fjords by May, protecting krill and forcing humpback whales to migrate elsewhere to find food, Nowacek says. But rapid climate change in the area over the last 50 years has significantly reduced the extent, and delayed the annual arrival, of the ice cover, says Nowacek, who is the Repass-Rodgers University Associate Professor of Conservation Technology.
"The lack of sea ice is good news for the whales in the short term, providing them with all-you-can-eat feasts as the krill migrate vertically toward the bay's surface each night. But it is bad news in the long term for both species, and for everything else in the Southern Ocean that depends on krill," says Ari S. Friedlaender, co-principal investigator on the project and a research scientist at Duke.
Antarctic krill are shrimp-like creatures that feed primarily on phytoplankton and live in large swarms in the Southern Ocean. Penguins, seals, seabirds and many whale species rely on the protein-rich, pinky-sized crustaceans as a source of food. Commercial fisheries are allowed to harvest up to 3 ½ tons of the krill a year as food for farm-raised salmon and for oil, rich in omega-3 acids, which is used in human dietary supplements.
Around the Western Antarctic Peninsula, krill migrate in austral autumn from open ocean waters to phytoplankton-rich bays and fjords, where juveniles feed and the population overwinters under the protective cover of ice. There is a strong correlation between the amount of sea ice and the amount of krill that survive the long, harsh Antarctic winter.
"If there are more areas with large aggregations of krill hanging out in waters where sea ice has diminished, you could see a big decrease in the standing krill stock, especially if we have a few years of back-to-back bad ice and the krill can't replenish themselves," Friedlaender says.
Scientists already have documented drops in krill abundance over the last 50 years related to reduced sea ice cover. Further drops could have far-reaching consequences. Seals and penguins have a relatively small foraging range, and some can't eat any prey other than krill or hunt without the presence of sea ice. Whales can migrate longer distances and might be able to find food elsewhere, but may be affected in other ways, as evidenced by snippets of unexpected sounds being transmitted by 11 whales the Duke team tagged in the study.
"We're starting to hear songs being produced by whales in the Antarctic -- sexual advertisements typically heard only in humpback breeding grounds that are located thousands of miles away from these bays," Friedlaender says.
Humpback whales typically reproduce once every three years, "so if a female doesn't have to go to the breeding grounds every year -- if she has access to food here and isn't being forced out by sea cover -- why should she leave?" Nowacek says. The presence of more females, coupled with access to a nightly krill feast, entices more males to stick around too. "So this may affect the timing and location of humpback breeding and other important lifecycle events."
Consideration of these factors, and the effects of rapid climate change, on krill dynamics will be critical to managing sustainable krill harvests and the continued recovery of baleen whales in the Southern Ocean, he says.

Douglas P. Nowacek et al., PLoS ONE, Super-Aggregations of Krill and Humpback Whales in Wilhelmina Bay, Antarctic Peninsula

PLoS ONE, 6(4) (2011) e19173; doi: 10.1371/journal.pone.0019173

Super-Aggregations of Krill and Humpback Whales in Wilhelmina Bay, Antarctic Peninsula

Douglas P. Nowacek1*Ari S. Friedlaender1Patrick N. Halpin1Elliott L. Hazen1,2David W. Johnston1Andrew J. Read1Boris Espinasse3Meng Zhou4, and Yiwu Zhu4
1 Nicholas School of the Environment and Pratt School of Engineering, Duke University Marine Laboratory, Beaufort, NC, U.S.A., 2 National Oceanic and Atmospheric Administration (NOAA) Pacific Fisheries Environmental Lab and University of Hawaii JIMAR, Pacific Grove, CA, U.S.A., 3 Laboratoire d'Océanographie Physique et Biogéochimique, Centre Océanologique de Marseille, CNRS, Université de la Méditerranée, Campus de Luminy, Marseille, France, 4 Department of Environment, Earth and Ocean Sciences, University of Massachusetts Boston, Boston, MA, U.S.A.


Ecological relationships of krill and whales have not been explored in the Western Antarctic Peninsula (WAP), and have only rarely been studied elsewhere in the Southern Ocean. In the austral autumn we observed an extremely high density (5.1 whales per km2) of humpback whales (Megaptera novaeangliae) feeding on a super-aggregation of Antarctic krill (Euphausia superba) in Wilhelmina Bay. The krill biomass was approximately 2 million tons, distributed over an area of 100 km2 at densities of up to 2000 individuals m−3; reports of such ‘super-aggregations’ of krill have been absent in the scientific literature for >20 years. Retentive circulation patterns in the Bay entrained phytoplankton and meso-zooplankton that were grazed by the krill. Tagged whales rested during daylight hours and fed intensively throughout the night as krill migrated toward the surface. We infer that the previously unstudied WAP embayments are important foraging areas for whales during autumn and, furthermore, that meso-scale variation in the distribution of whales and their prey are important features of this system. Recent decreases in the abundance of Antarctic krill around the WAP have been linked to reductions in sea ice, mediated by rapid climate change in this area. At the same time, baleen whale populations in the Southern Ocean, which feed primarily on krill, are recovering from past exploitation. Consideration of these features and the effects of climate change on krill dynamics are critical to managing both krill harvests and the recovery of baleen whales in the Southern Ocean.

Citation: Nowacek DP, Friedlaender AS, Halpin PN, Hazen EL, Johnston DW, et al. (2011) Super-Aggregations of Krill and Humpback Whales in Wilhelmina Bay, Antarctic Peninsula. PLoS ONE, 6(4) (2011) e19173; doi: 10.1371/journal.pone.0019173