Big thaw projected for Antarctic sea ice: Ross Sea will reverse current trend, be largely ice free in summer by 2100

Emperor Penguins: Changes in the extent and duration of Ross Sea ice will significantly impact marine life in what is one of the world’s most productive and unspoiled marine ecosystems, where rich blooms of phytoplankton feed krill, fish, and higher predators such as penguins.

Credit: Photo courtesy of Walker Smith

Date:

February 27, 2014

Source:

Virginia Institute of Marine Science

Summary:  A new modeling study suggests that a recent observed increase in summer sea-ice cover in Antarctica's Ross Sea is likely short-lived, with the area projected to lose more than half its summer sea ice by 2050 and more than three quarters by 2100. These changes will significantly impact marine life in what is one of the world's most productive and unspoiled marine ecosystems.

Antarctica's Ross Sea is one of the few polar regions where summer sea-ice coverage has increased during the last few decades, bucking a global trend of drastic declines in summer sea ice across the Arctic Ocean and in two adjacent embayments of the Southern Ocean around Antarctica.
 

Now, a modeling study led by Professor Walker Smith of the Virginia Institute of Marine Science suggests that the Ross Sea's recent observed increase in summer sea-ice cover is likely short-lived, with the area projected to lose more than half its summer sea ice by 2050 and more than three quarters by 2100.

These changes, says Smith, will significantly impact marine life in what is one of the world's most productive and unspoiled marine ecosystems, where rich blooms of phytoplankton feed krill, fish, and higher predators such as whales, penguins, and seals.

Smith, who has been conducting ship-based fieldwork in the Ross Sea since the 1980s, collaborated on the study with colleagues at Old Dominion University. Their paper, "The effects of changing winds and temperatures on the oceanography of the Ross Sea in the 21^st century," appears in the Feb. 26 issue of Geophysical Research Letters. Smith's co-authors are Mike Dinniman, Eileen Hofmann, and John Klinck.

Smith says "The Ross Sea is critically important in regulating the production of Antarctica's sea ice overall and is biologically very productive, which makes changes in its physical environment of global concern. Our study predicts that it will soon reverse its present trend and experience major drops in ice cover in summer, which, along with decreased mixing of the vertical column, will extend the season of phytoplankton growth. These changes will substantially alter the area's pristine food web."

Researchers attribute the observed increase in summertime sea ice in the Ross Sea -- where the number of days with ice cover has grown by more two months over the past three decades -- to a complex interplay of factors, including changes in wind speed, precipitation, salinity, ocean currents, and air and water temperature.

But global climate models agree that air temperatures in Antarctica will increase substantially in the coming decades, with corresponding changes in the speed and direction of winds and ocean currents. When Smith and his colleagues fed these global projections into a high-resolution computer model of air-sea-ice dynamics in the Ross Sea, they saw a drastic reduction in the extent and duration of summer sea ice.

The modeled summer sea ice concentrations decreased by 56% by 2050 and 78% by 2100. The ice-free season also grew much longer, with the mean day of retreat in 2100 occurring 11 days earlier and the advance occurring 16 days later than now.

Also changed was the duration and depth of the "shallow mixed layer," the zone where most phytoplankton live. "Our model projects that the shallow mixed layer will persist for about a week longer in 2050, and almost three weeks longer in 2100 than now," says Smith. "The depth of the shallow mixed layer will also decrease significantly, with its bottom 12% shallower in 2050, and 44% shallower in 2100 than now."

For Smith, these changes in ice, atmosphere, and ocean dynamics portend major changes in the Antarctic food web. On the bright side, the decrease in ice cover will bring more light to surface waters, while a more persistent and shallower mixed layer will concentrate phytoplankton and nutrients in this sunlit zone. These changes will combine to encourage phytoplankton growth, particularly for single-celled organisms called diatoms, with ripples of added energy potentially moving up the food web.

But, Smith warns, the drop in ice cover will negatively affect several other important species that are ice-dependent, including crystal krill and Antarctic silverfish. A decrease in krill would be particularly troublesome, as these are the major food source for the Ross Sea's top predators -- minke whales, Adélie and Emperor penguins, and crabeater seals.

Overall, says Smith, "our results suggest that phytoplankton production will increase and become more diatomaceous. Other components of the Ross Sea food web will likely be severely disrupted, creating significant but unpredictable impacts on the ocean's most pristine ecosystem."

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Story Source:
The above story is based on materials provided by Virginia Institute of Marine Science. The original article was written by David Malmquist. Note: Materials may be edited for content and length.

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Journal Reference:

1. Walker O. Smith, Michael S. Dinniman, Eileen E. Hofmann, John M. Klinck. The effects of changing winds and temperatures on the oceanography of the Ross Sea in the 21stcentury. Geophysical Research Letters, 2014; DOI: 10.1002/2014GL059311

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Virginia Institute of Marine Science. "Big thaw projected for Antarctic sea ice: Ross Sea will reverse current trend, be largely ice free in summer by 2100." ScienceDaily. ScienceDaily, 27 February 2014. <www.sciencedaily.com/releases/2014/02/140227115512.htm>.

Waterbirds' hunt aided by specialized tail: Swimming birds evolved rudder-like tail to dive for food

Date:

February 26, 2014

Source:

PLOS

Summary:

The convergent evolution of tail shapes in diving birds may be driven by foraging style. Birds use their wings and specialized tail to maneuver through the air while flying. It turns out that the purpose of a bird's tail may have also aided in their diversification by allowing them to use a greater variety of foraging strategies. To better understand the relationship between bird tail shape and foraging strategy, researchers examined the tail skeletal structure of over 50 species of waterbirds, like storks, pelicans, and penguins, and shorebirds, like gulls and puffins. They first categorized each species by foraging strategy, such as aerial, terrestrial, and pursuit diving, and then compared the shape and structure of different tails.

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This is a contrast of the typical elongate pygostyle of a diving bird (A), the Adélie Penguin (Pygoscelis adeliae, specimen AMNH 623439) to the typical short, dorsally deflected pygostyle of a non-diving bird (B), the Northern Fulmar (Fulmarus glacialis, specimen AMNH 20697).

Credit: Ryan Felice; CC-BY

The convergent evolution of tail shapes in diving birds may be driven by foraging style, according to a paper published in PLOS ONE on February 26, 2014 by Ryan Felice and Patrick O'Connor from Ohio University.

Birds use their wings and specialized tail to maneuver through the air while flying. It turns out that the purpose of a bird's tail may have also aided in their diversification by allowing them to use a greater variety of foraging strategies. To better understand the relationship between bird tail shape and foraging strategy, researchers examined the tail skeletal structure of over 50 species of waterbirds, like storks, pelicans, and penguins, and shorebirds, like gulls and puffins. They first categorized each species by foraging strategy, such as aerial, terrestrial, and pursuit diving, and then compared the shape and structure of different tails.

Scientists found that foraging style groups differed significantly in tail skeletal shape, and that shape could accurately "predict" foraging style with only a small amount of mismatch. In particular, underwater foraging birds, such as cormorants, penguins, puffins, gannets, and tropicbirds, have separately evolved a similarly specialized elongated tail structure, whereas aerial and terrestrial birds have a short, dorsally deflected tail structure. Moreover, each underwater foraging group, such as foot propelled, wing propelled, or plunge diving, had a distinctive tail-supporting vertebrae shape. 
According to the authors, the probable separate evolution of the specialized tail in underwater-diving birds may suggest that body structure adapted to the demand, or the need to move the tail as a rudder during underwater foraging. In contrast, the authors found no conclusive results when looking at the relationship between tail shape and flight style.

Mr. Felice adds, "Previous research has shown that diving birds evolve specializations in wing and leg morphology to facilitate underwater locomotion. This study puts a necessary focus on the tail, finding that this region of the body also evolves in response to the demands of underwater movement."

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Story Source:
The above story is based on materials provided by PLOS. Note: Materials may be edited for content and length.

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Journal Reference:

1. Ryan N. Felice, Patrick M. O’Connor. Ecology and Caudal Skeletal Morphology in Birds: The Convergent Evolution of Pygostyle Shape in Underwater Foraging Taxa. PLoS ONE, 2014; 9 (2): e89737 DOI: 10.1371/journal.pone.0089737

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PLOS. "Waterbirds' hunt aided by specialized tail: Swimming birds evolved rudder-like tail to dive for food." ScienceDaily. ScienceDaily, 26 February 2014. <www.sciencedaily.com/releases/2014/02/140226174546.htm>.

New insights into origin of birds focuses on key characteristics that preceded flight: Body size, forelimb length

Date:

February 23, 2014

Source:

University of Bristol

Summary:

The key characteristics of birds which allow them to fly -- their wings and their small size -- arose much earlier than previously thought, according to new research that examined closely the Paraves, the first birds, and their closest dinosaurian relatives which lived 160 to 120 million years ago. Researchers investigated the rates of evolution of the two key characteristics that preceded flight: body size and forelimb length. In order to fly, hulking meat-eating dinosaurs had to shrink in size and grow much longer arms to support their feathered wings.

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Ruby Throated Hummingbird in flight. Being small and light is important for a flyer, and it now seems a whole group of dozens of little dinosaurs were lightweight and had wings of one sort or another. Most were gliders or parachutists, spreading their feathered wings, but not flapping them.

Credit: © gregg williams / Fotolia

The key characteristics of birds which allow them to fly -- their wings and their small size -- arose much earlier than previously thought, according to new research from the Universities of Bristol and Sheffield into the Paraves, the first birds and their closest dinosaurian relatives which lived 160 to 120 million years ago.

Mark Puttick and colleagues investigated the rates of evolution of the two key characteristics that preceded flight: body size and forelimb length. In order to fly, hulking meat-eating dinosaurs had to shrink in size and grow much longer arms to support their feathered wings. "We were really surprised to discover that the key size shifts happened at the same time, at the origin of Paraves," said Mr Puttick of Bristol's School of Earth Sciences. "This was at least 20 million years before the first bird, the famous Archaeopteryx, and it shows that flight in birds arose through several evolutionary steps."

Being small and light is important for a flyer, and it now seems a whole group of dozens of little dinosaurs were lightweight and had wings of one sort or another. Most were gliders or parachutists, spreading their feathered wings, but not flapping them. "Out of all these flappers and gliders, only the birds seem to have been capable of powered flight," said co-author Mike Benton, Professor of Vertebrate Palaeontology at Bristol. "But you wouldn't have picked out Archaeopteryx as the founder of a remarkable new group."

The study applied new numerical methods that calculate the rate of evolution of different characteristics across a whole evolutionary tree, and identify where bursts of fast evolution occurred. "Up to now you could only have guessed roughly where the major evolutionary transitions occurred," said Dr Gavin Thomas of the University of Sheffield, "but the new methods pinpoint the size changes. The small size of birds and their long wings originated long before birds themselves did."

Birds owe their success to their flight, wings and feathers. Until the 1990s, when the first feathered dinosaurs were found in China, birds were thought to have originated rapidly, marking a major transition from dinosaurs. Now, we know that Archaeopteryx was only one of a large number of small, flying dinosaurs. "The origin of birds used to be seen as a rapid transition," said Mark Puttick, "but now we know that the key characteristics we associate with them arose much earlier."

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Story Source:
The above story is based on materials provided by University of Bristol. Note: Materials may be edited for content and length.

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Journal Reference:

1. Mark N. Puttick, Gavin H. Thomas, Michael J. Benton. HIGH RATES OF EVOLUTION PRECEDED THE ORIGIN OF BIRDS. Evolution, 2014; DOI: 10.1111/evo.12363

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University of Bristol. "New insights into origin of birds focuses on key characteristics that preceded flight: Body size, forelimb length." ScienceDaily. ScienceDaily, 23 February 2014. <www.sciencedaily.com/releases/2014/02/140223215134.htm>.

Yellow-eyed penguins forage in trawlers' wake

Wednesday Feb 12, 2014

A yellow-eyed penguin. Photo / Thinkstock

 

New Zealand's endangered yellow-eyed penguin have been found to follow the line of swooping seabirds - literally - when it comes to reaping the food stirred up by trawlers.

An Otago University research team have discovered the penguins, of which there were around 500 estimated pairs left on mainland New Zealand, forage in straight lines for several kilometres by following furrows in the seafloor scoured out by fishing trawlers.

Using GPS dive loggers the researchers monitored the penguins' movements over three years showing the birds use furrows scoured on the seabed by otter boards from trawl nets to find food, particularly blue cod. "This research is unique as it shows for the first time that not only do flying seabirds follow fishing vessels, but also penguins, with the latter foraging after a trawler has gone through a particular area," lead research Professor Philip Seddon said.

The researchers said blue cod and other bottom feeders were likely to forage around the seafloor lines because they were attracted to the marine life stirred up and exposed by the action of the nets being dragged behind fishing trawlers. The lines made by the otter boards, which keep the mouth of the trawl net open, are up to 15cms wide and two centimetres in depth on a north-east to south-west axis.

They can remain on the sea floor for a year or more and are clearly visible. GPS dive loggers were attached to the back of the birds to determine the depth the penguins dive, their locations and line of travel and how far they swim in one foraging trip. Lines on the seafloor were located by using video footage taken by a remote operated vehicle launched from the university's research vessel Polaris II.

Many penguins swim to a depth of between 60 and 70 metres to feed during multiple dives - up to 80 - over several hours before returning to shore. The penguins can travel up to 120 kilometres in one trip, while foraging in the mid-shelf fishing grounds some 20 kilometres off the Otago Peninsula.

The study shows that the birds also revisit the lines on subsequent occasions and might develop a visual memory of the area, researchers say. "It appears that using the lines for foraging is particularly related to bad breeding years when penguins are more likely to go further out to sea to find blue cod and other bottom feeders. This might also be due to the individual preference of some birds though," said Dr Thomas Mattern, the first author of the paper reporting the results. But the researchers say that one of the downsides of foraging around the trawl lines might be that an exclusive diet of blue cod, which tends to be low in nutritional value, could affect breeding.

As yet, there was no confirmation of this hypothesis and further research was needed to determine if there is any relationship between foraging patterns, diet quality and breeding success in the penguin population.

The research was published in the journal PloS ONE and supported by the Yellow-Eyed Penguin Trust.

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