JR161: Food webs in the Antarctic


 

JR161


Cruise Diary


Monday 20 November
Scotia Sea: Lat 55.32.34S, Long 44.46.56 W
01.04GMT

Day 27 of the cruise JR161 aboard the British Antarctic Research Ship RSS James Clark Ross
Conditions: Moderate Swell, Overcast/Snowing


Tom writes:

"Two weeks of science to go and its going to be busy.  Having lost quite a large chunk of time at Signy Island, scientists are working round the clock to finish the science program before we depart for the Falklands around 1 December. So far we have completed one 4-day process station in a low-productivity (biological activity) area and three 2-day condensed stations on a transect line north from the ice edge towards South Georgia.  We are set for two more process stations close to the island of South Georgia, which should have higher productivity.

Review of station summaries:

Process Station 1:
North of the Antarctic Circumpolar Front, high nutrient levels and low chlorophyll levels characterised this classic HNLC region. Phytoplankton populations are limited by the amount of available iron, which is low in this region.  If there isn’t much phytoplankton there isn’t much of anything else.  This station acts as the control for the remainder of the cruise.

 

Transect of Condensed Stations 2:
We are at the start of the summer season in the southern hemisphere and the winter sea ice is rapidly retreating.  Our line of condensed 2-day stations measured the biology throughout the water column from the edge of the melting ice into the open ocean.  Layers of snow coat the sea ice and are nutrient-rich and contain high levels of iron.  As these rapidly melt in the summer season, these nutrients are released into the surface waters of the ocean and, combined with the ever increasing day length; provide excellent conditions for phytoplankton to grow.  In addition, communities of phytoplankton survive in the ice and are also released upon melting, providing a productive base to the food chain that supports higher tropical levels.  As you travel away from the ice edge, you travel from waters in which phytoplankton are yet to bloom, through waters where phytoplankton are blooming, and to waters where phytoplankton populations have been consumed by predators as larger animals are abundant."

Satellite image of surface chlorophyll concentrations (Courtesy of Beki Korb, BAS). 
The yellow and green colours indicate high chlorophyll concentrations. 
Clouds and sea ice show up as black – much of the bottom right corner is sea-ice.

 

Phytoplankton concentrations in the water column in the condensed stations. 
Station 2 is dominated by large diatom species; an excellent food source for the rest of the food chain.

 


More soon - please visit us again in a few days' time for the next installment....



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October 2006
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