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! 

1 comment:

  1. Antarctica tour is such a good traveling experience for any people. The mount climbing and wildlife of Antarctica is very unique and amazing.
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