LARISSA - LARsen Ice Shelf System, Antarctica, a NSF-funded project.

LARISSA - LARsen Ice Shelf System, Antarctica, a NSF-funded project.
We are conducting an integrated, multi-disciplinary field program to address the rapid and fundamental changes occurring in the Antarctic Peninsula region as a consequence of the abrupt collapse of the Larsen B Ice Shelf in the fall of 2002. A profound transformation in ecosystem structure and function is occurring in coastal waters of the western Weddell Sea. This transformation appears to be yielding a redistribution of energy flow between chemoautotrophic and photosynthetic production, and to be causing the rapid demise of the extraordinary seep ecosystem discovered beneath the ice shelf, providing an ideal opportunity to test fundamental paradigms in ecosystem evolution.

Thursday, March 4, 2010

Time to pack

15 – 26 Feb Following our ROV dive in the Antarctic Sound, we headed
 around the Trinity Peninsula into the Bransfield Strait (see above map of
 the Antarctic Peninsula). Along the way, we dropped another whale bone 
lander after many hours of rigging this malodorous free-vehicle package
 (rotting whale bones smell very bad!!). Following the bone lander
 deployment, there was extensive debate among the scientists on board
 concerning where to focus our research efforts on the west side of the
 Antarctic Peninsula to optimize the scientific outputs from the remainder 
of the cruise. The members of the Marine Ecosystems project urged strongly
 to conduct a comparative study of fjord ecosystems differentially affected 
by climate warming from north to south along the Antarctic Peninsula,
 beginning with Admiralty Bay on King George Island. However, we were 
overruled by the chief scientist, who insisted on revisiting former study
 sites in Hughes Bay in the Gerlache Strait. The Marine Ecosystems group 
made the best of the situation, collecting opportunistic multiple cores,
 yoyo camera transects and an otter trawl in Hughes Bay from Feb 15-18. The
 seafloor fauna in Hughes Bay was very depauperate, apparently heavily 
disturbed by large inputs of glacial till (i.e., sediments) from the
 numerous glaciers emptying into the bay. In contrast to the
 fjord systems we sampled earlier, this site had very little drift
 macroalgae on the seafloor, presumably because the open bay has little
 subtidal area to support kelps and other macroalgae.

Glaciers calving icebergs into Hughes Bays. Large volumes of 
meltwater and sediments are carried into the bay with these icebergs, 
causing massive burial disturbance at the seafloor.

At the end of our stay in Hughes Bay, we went ashore in rubber zodiac boats 
to collect kelp (for food-web analyses) and to do a bit of site seeing. We
 encountered icebergs seeming designed by Gaudi, gentoo
 penguins and a large leopard seal dozing on an ice flow

Gentoo penguins on the shoreline of Hughes Bay. 

A large leopard seal lazily eyeing us from its napping spot on
an ice floe. I think we look like lunch!

On the night of Feb 18, we transited south to Andvord Bay, the fjord just
 south of Cape Renaud (see map). There, we completed the earlier work within initiated in this fascinating fjord, using megacore and Blake trawl samples
 to document the remarkably rich fauna in the fjord basins. The trawl
 brought up huge numbers of giant polychaete worms. These
 worms are four inches long, one inch in diameter and stuffed to the
 bursting point with eggs and sperm. The biomass and diversity of these
 large worms in Andvord Bay are truly remarkable, indicating the seafloor at
 500 m depths in the fjord is receiving much more food than the open 
continental shelf at similar depths. Most of the seafloor animals we
re covered were filled with reproductive products and appeared ready to
 spawn, suggesting this has been a summer of high productivity. It appears
 that the fjords like Andvord Bay, because of their food-rich conditions,
 could be providing larvae to seed seafloor populations far beyond the fjord
 bounds. Because fjord conditions are being altered by climate warming
 (i.e., by increasing glacier melting and glacial sediment loading), the
 Andvord seafloor ecosystems are likely to be very climate sensitive, and
 may be transitioning to the depauperate conditions we observed in Hughes
Bay. Clearly, the Antarctic Peninsula fjord communities merit much 
further to study to elucidate their patterns of causes of high 
biodiversity, and the sensitivity of these unusually rich communities to
 climate warming.

Sausage sized (4-inch long) polychaete worm from the floor of 
Andvord Bay. This ampharetid worm is white because it is bulging with 
sperm ready to be released into the water column during mass spawning. 

Our final day in Andvord Bay was punctuated by a helicopter ride for the 
benthic ecologists (Laura, Craig and David). We flew from the ship to the 
desolate top of the Antarctic Peninsula, getting a view of the massive ice
 fields straddling the Peninsula. As we descended down a
 glacier back to the ship, the views were astounding, leaving impressions of
 stark beauty that we will retain for a life time. 

The ice sheet atop the Antarctic Peninsula. This sheet extends 
unbroken for 1000 miles along the Peninsula to the main part of the
 Antarctic Continent. 

View from the Helicopter as we fly down from the top of the
 Antarctic Peninsula into Andvord Bay.

On 24 Feb we completed our seafloor ecosystem studies along the west
 Antarctic Peninsula by deploying another whale bone lander south of Anvers 
Island, and then conducting an ROV dive in the Palmer Deep, a 1440 m deep 
basin off the southeast tip of Anvers Island. To our surprise, we found a 
large number of king crabs in the basin at depths below 1000 m, indicating 
that these invasive marauders have already penetrated deep onto the
 Antarctic shelf. As mentioned earlier, king crabs have been
 excluded from Antarctic ecosystems for possibly millions of years due to
 very low water temperatures on the Antarctic shelf. Climate warming in 
this region apparently is allowing these species to move shallower,
 threatening the vulnerable unique Antarctic seafloor communities. Where we
 found abundant crabs on the Palmer deep floor, we only found sea anemonies,
 suggesting that the brittle stars and crinoids had been consumed by the 
voracious, skeleton crushing crabs. This discovery of crabs in the Palmer 
deep is a sobering reminder of the vulnerability of Antarctic marine 
ecosystems to climate change. 

Marauding king crabs marching across the floor of the Palmer
 Deep. These crabs are bad news for the endemic Antarctic benthic fauna!

After spending 25 Feb packing and stowing gear in the hold and on the upper
 decks of the NP Palmer, we are now heading north across the Drake Passage
 towards Punta Arenas (to be reached in four days time). The forecasts are 
for rough weather in the Drake -- nothing unusual in this part of the
 ocean! Our last views of the ice bound continent and islands were of
 Smith Island in the Bransfield Strait in the wee hours of the 26th. While
 we are all eager to get home after two long months at sea, we will miss the 
scenery and ecosystems of Antarctica! 

Non-programmed camping in James Ross Island

10 - 14 Feb With heavy hearts we have headed northward from Lockyer Station
and out through the Antarctic Sound to the west side of the Antarctic
 Peninsula. Unusually heavy sea ice, including floes (or floating ice slabs)
 several years old and meters thick have forced us to abandon our plan to
 work in the Larsen B area. Although our vessel, the NB Palmer, is an 
icebreaker, it cannot safely smash its way through multiyear sea ice
 because of high pressure ridges (compressed areas of sea ice 3-4 meters 
high). It is clearly unsafe to linger longer on the eastern side of the 
Antarctic Peninsula this high ice year, and even our offshore oceanographic
 sites are now covered solidly with the pack ice. 

Satellite image showing heavy sea-ice cover throughout our
 desired study area in the Larsen B vicinity (dashed circle). Flat whit areas are sea ice and ice shelves; ruffled areas throwing shadow are
 clouds. In most years, the circled area is clear of sea ice by the end of
 January. The heavy sea conditions this year illustrate the high
 interannual variability in weather conditions in the Antarctic – even
 though climate warming continues at a very fast rate in this region, during 
some years, sea ice may still persist throughout the summer due to
 stochastic weather processes.

Before leaving Lockyer Station, we had a bit of a scare, and a reminder 
that the Antarctic is still a remote and potentially dangerous environment.
 Two of our party, a geologist and writer for National Geographic, were
 flown by helicopter to a site on the Antarctic Peninsula 25 miles away to
 collect glacial erratics (rocks dropped by glaciers far from their site of 
origin). As they were working, the weather began to close in so they
 helicopter flew out the pick them up and return them to the ship. During
 the return flight (only about 15 minutes), the weather closed in even 
further, and whiteout conditions forced the helicopter, with three aboard,
 to land on a beach on James Ross Island only 6 miles from the ship. A snow 
storm ensued for the next three days, grounding the scientist,
 writer and helicopter pilot in two small tents for three days. The
 helicopters always travel with emergency rations for 6 days, sleeping bag s
and tents, so the stranded party was is in no immediate danger. However,
 it was sobering to realize that while they were only 6 miles from us, there
 was nothing we or anyone else on earth could do for them until the snow
 storm abated. After 3 days, we finally had a patch of blue sky in which to 
recover our now smelly shore party. They had spent their time digging a
 latrine, building snow walls to protect the tents from the 30 inches of 
snow fall, and reading and dozing in their sleeping bags. The National 
Geographic writer now has quite a story to tell about forced camping in the
 Antarctic wilderness, an experience somewhat reminiscent of the stranding
 of Shackleton’s shore party on Elephant Island, 180 miles north of here.

The snow storm that stranded three of our expedition members on 
James Ross Island for three days.

Following recovery of our wayward three, the NB Palmer crashed northward
 through very thick sea ice, making only 2-4 knots for 26 hours. 
As we entered the Antarctic Sound, the strait between the Weddell and
 Scotia Seas at the north end of the Antarctic Peninsula, the sea ice 
thinned and we were able to make much better time. By evening of the 13th 
we were in position for an ROV dive on a recently discovered submerged
 volcano in the Antarctic Sound, to search for hydrothermal vents to provide 
study organisms for David Honig and Mike McCormick. The ROV dive found no
 vents, but did reveal dense communities of sponges, crinoids (see lilies),
 brittle stars and other suspension feeders characteristic of
 the Antarctic seafloor. It is thought that such communities can thrive in
 the Antarctic only because large crushing predators, such as king crabs and
 bottom feeding sharks, are excluded by the very cold Antarctic waters 
(below 0 centigrade). Such communities of exposed suspension feeders 
occurred worldwide in the ancient ocean, but apparently were eliminated
 with the evolution of large crabs and bottom-feeding sharks. The lack of
 these large, skeleton-crushing (or duraphagous) predators in the Antarctic 
has allowed the radiation of a diverse assemblage of suspension feeders 
unique to Antarctic waters. As climate change brings warmer waters to the
 Antarctic, skeleton-crushing predators, especially king crabs, threaten to
 invade shallow waters around the Antarctic Peninsula, potentially leading
 to the extinction of many unique Antarctic species. During the dive we 
also observed giant “barrel” sea anemones that apparently roll along
 the seafloor without a permanent attachment. This may be an 
adaptation to utilize habitats newly exposed by the bulldozing of the
 seafloor by grounding icebergs, a major source of disturbance for seafloor 
habitats at depths less than 300 m in Antarctica.

The NB Palmer breaking its way though multi-year sea ice south
 of the Antarctic Sound.

A dense assemblage of suspension feeding sea lilies (crinoids, 
plumose yellow animals), brittle stars, sponges (white blobs and shapes),
 and octocorals (pink trees) on the seafloor at 500 m depths on the
 submerged volcano in the Antarctic Sound. This is classic, high-biomass,
 exposed Antarctic benthic assemblage is likely to be very susceptible to
 predation from invading king crabs. 

Barrell anemone approximately 30 cm (12 inches) long rolling 
along the seafloor on the Antarctic Sound submerged volcano.

Monday, March 1, 2010

Lockyer Station

3 – 9 Feb The last few days of have been a flurry of oceanographic
sampling activity, during which we have collected two kasten cores, 6
megacores, one Blake trawl, numerous CTD’s, and conducted 6 yoyo camera
transects. This sampling is to characterize our first oceanography station
near Lockyer Island (dubbed “Lockyer Station”) to provide insights into
seafloor and water-column ecological processes and community structure on
the inner continental shelf site not recently influenced by an Antarctic
ice sheet. The seafloor at Lockyer Station lies 505 m below the sea
surface and is a plain covered with mud intermixed with gravel from iceberg
rafted material. Our yoyo camera transects and trawl sample reveal a
relatively rich community of megafauna (animals large enough to be
identified in photographs), including large “sea pigs” (sea cucumbers
in the genus Protelpidia, picture 38), very large brittles stars
(Ophiostarte gigas, picture 39), and an occasional giant basket glass
sponge with crinoids (sea lilies, picture 40). Many of the megafauna are
unusually large, including the 20 cm long sea pigs and meter high basket
sponges, suggesting that this is a stable sedimentary environment (low
flow, little disturbance ice bergs, and slow sediment accumulation). The
station looks very much like our continental shelf stations at similar
depths on the other side of the Antarctic Peninsula, west of Anvers Island.
 Our trawl sample also recovered a diversity of large benthic (seafloor
species) including a large icefish (picture 41) . These fish are unique to
Antarctica and have no hemoglobin in their blood; oxygen concentrations are
high enough in the cold Antarctic waters that these sluggish fish do not
need hemoglobin in their blood to carry oxygen. Their gills and blood are
translucent white.

Large sea pig 20 cm (8 inches) long. This animal is a
 “deposit feeder" and uses that tentactles at left to ingest mud particles.
It then digests off the organic matter for food. This is the most common 
feeding mode on Earth!

The large, mucus cover brittle star Ophiostarte gigas. This is
a predator that feeds on other brittle stars, polychaete worms, and

A giant filter feeding basket sponge about 1 meter tall and
 half a meter wide (this is a downward view from the Yoyo Camera). Clinging
to the sides of the sponge are yellow crinoids, or sea lilies. Both the
sponge and crinoids are suspension feeders that removed food particles as
they drift by in the water column.

An ice fish caught in the trawl. These are called ice fish
because their blood is transparent due to an absence of hemoglobin. Their
gills are translucent.

After three grueling 18-hr work days, our intrepid benthic team of Laura,
David and Craig (me) are now nearly finished with sampling of the seafloor
biota at Station Lockyer. Our samples have been excellent in quality and
we are confident we will be able to characterize biodiversity and ecosystem
function at this station (including foodweb structure and rates of sediment
mixing by mud-eating animals like sea cucumbers). It will provide an
excellent baseline to compare to the Larsen B stations recently exposed
from beneath ice shelves. Unfortunately, the sea ice is thickening around
us and further south in the Larsen B area, so it now seems unlikely that
we will be able to get to Larsen B for the rest of the cruise. Time to
develop plan B!

Hill Island

30 Jan – 2 Feb We are now a halted in the sea ice a few miles west of
 Snow Hill Island, unable to break our way any close than 60 miles to the 
entrance of the Larsen B region, around the tip of Robertson Island
 (map below). Quite appropriately, we can see Cape Longing in the 
distance, reflecting our desire to get further south into our primary study
area. Our satellite images of sea ice indicate that the leads are closing
in the Larsen B area, reducing the changes of getting there. We are within 
helicopter range of several or our terrestrial sites for GPS stations that 
will evaluate the rebound, or rise, of land masses as a result of the
 breakup of the Larsen B shelf; a vast weight of ice has been lifted from
the the coast in this region, and the Antarctic peninsula is likely to be
rising at a few millimeters a year as a consequence. Thus, the terrestrial
 components of our program may not be set back too heavily from lack of ship 
access to the Larsen B region.

Map of East Antarctic Peninsula including Larsen B Area, and
 showing Lockyer Island Station location near Snow Hill Island.

The oceanographers on board the vessel have discussed how to modify our
 sampling program to best advance our goals of studying the effects of
ice-shelf loss on Antarctic marine ecosystems, while working in waters in 
which sea-ice conditions will allow the ship to work. A number of smaller 
ice shelves have collapsed on this eastern side of the Antarctic Peninsula 
in the last few decades, including one covering the southern Gustav Channel
 (see map). We now plan to sample the Gustav Channel as a post-ice shelf
 system (with ice shelf loss in about 1992), and then to sample the mid- and
 outer-continental shelf stations east of James Ross Island, to provide a
 comparison with the open sea-ice zone. We will also sample an inner shelf
 site just west of Snow Hill Island, very close to our current location. 
These latter three sites will provide a necessary context to evaluate
 colonization patterns in the Gustav Channel, and in the Larsen B area, when
 we finally are able to get south of Robertson Island (most likely not until
 2012, during our next LARISSA cruise). Thus, even though we are currently 
barred from the Larsen B area by sea ice, we will be able to conduct
 ecosystem studies on this cruise that advance or understanding of the
effects of rapid climate warming and loss of ice shelves on Antarctic
 marine ecosystems. Now that we have a workable plan, we are eager to 
press forward with our sampling!