One of the main objectives of this cruise was to compare food concentration and availability in the water column in the Weddell Sea with the previously recorded autumn data. Furthermore, short-time changes in these variables in the surface (beneath the ice) and in the near-bottom water layers was considered essential to understand benthic community trophic dynamics.
Food analyses of benthic suspension feeders (mostly cnidarians) revealed limited connection between the rain of larger particles sinking to the seafloor during the short Antarctic summer and the food of these organisms, and incubation experiments presented evidence for the use of the fine seston fraction by certain suspension feeders. The potential food analyses i n the water column will be continued and refined, putting major emphasis o n the quality of the food offer and the processes that make the food available t o the benthos. A multidisciplinary approach will be undertaken considering seston quality analysis and processes above and at the seafloor. The three main questions were: 1) Are the biochemical characteristics (i.e. chlorophyll a, organic carbon, carbohydrate, protein and lipid concentrations) different i n the Same Weddell sea transect comparing data collected in two short time series? 2) Can we quantify food concentration (seston concentration and quality) differences between seston sampled near the ice sheet and i n the water column near the seafloor? 3) Which are the main fractionate lipid contributors within the seston total lipids? Do these macromolecules reveal short-time changes in spring at the surface and in the bottom water?
Work at sea
Water was collected in Niskin bottles with the Bio-Rosette at 4 different depths at each station of the 6-7 and 19-20 December 2003 transects, picking up two samples (two Niskin bottles) from each depth to have two replicates of each depth point. Water was filtered using triplicates of each parameter and each depth with a 150mmHg pressure pump, using GFIF precombusted (450 ¡C 5h) filters (0.4 um porus) for the different parameters.
These parameters were a) Chlorophyll a (500mllfilter), b) Organic Carbon and Nitrogen (1 OOOmlIfilter), C) Proteins (1 500 mllfilter), d) Carbohydrates (1 500 mllfilter), e) Lipids (5000 rnllfilter), and f) Fractionate Lipids (5000 mllfilter).
Filters were then immediately frozen at -27 'C to be processed on the ship or in the lab. Water samples very close to the bottom (0.5 metres above the surface) were taken with the Giant Water Sampler at the same stations of the transect.
Chlorophyll a and Phaeophytin a were extracted in the dark at 4 'C with 90%
acetone and measured fluorometrically. Organic Carbon and Nitrogen content were determined with an Elemental Analyser (Carlo Erba). Proteins will be processed with the Lowry method. Total particulate carbohydrate concentration was measured according to Dubois et al. (1956). Extraction and quantification of the total lipids were performed according to the method of Barnes and Blastock (1973). Fractionate lipid extraction will be carried out according to Grimalt et al (1992) and Yruela et al (1990).
Preliminary results
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6-7 December 2003 TransectCarbohydrates: Seston carbohydrates were higher near the surface (5 and 25 meters depth) than in the mid column and in the near-bottom water samples, except at the last sampling point (Fig. 30). Concentrations were up to 5 times higher at these surface points, except at the first sampling station where the carbohydrate seston concentration was close to the 25m depth point.
Station 1 (6112103)
W - - .. -. .... . % H'..---
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0 10 20 30 40 50
Carbohydrate concentration pg I
'
Station 3 [ 7 / 1 2 / 0 3 )
Station 2 (7112103)
.. .- - - ~B
Carbohydrate Concentration pg F'
Station 4 (711 2103)
Carbohydrate Concentration pg I'' Carbohydrate Concentration ug 1.'
Station 5 (7112103)
0 10 20 30 40 50
Carbohydrate Concentration ug I '
Fig. 30 Seston carbohydrate profiles at transect stations during Dec 6-7 (transect location See Fig. 24)
Lipids: Seston lipid concentration was almost undetectable near the bottom in the transect points three and five, while in the other transect points the distribution seemed to be more regular (Fig. 31). Except for the sampling point three, lipid concentration was higher near the surface (beneath the ice) than at 25 m depth.
Results 52
Station 1(6/12/03)
0 10 20 30 40 50 60 Lipid Concentration pg 1.'
Station 3(7/12/03)
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E 200V
5 $ 300
Station 2(7/12/03)
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E 200 ;V
0 10 20 30 40 50 60 Lipid Concentration {ig 1"
Station 4(7/12/03)
Lipid Concentration ~g 1'. Lipid Concentration pg I"
Station 5(7/12/03)
0 L
100
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E 200U
-C 300 0
400
500
0 10 20 30 40 50 60 Lipid Concentration pg I"'
Fig. 31 Seston lipid profiles at transect Stations during Dec 6-7 (transect location see Fig. 24)
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19-20 December 2003 TransectCarbohydrates: The more irregular situation detected in the carbohydrate concentration in the first transect completely changed in the second transect (Fig. 32). Concentrations near the surface (beneath the ice and 25 m depth)
were up to 15 times higher than near the bottom samples (Bio-Rosette samples), and up to 4-5 times greater comparing the Same points with the previous transect.
Station 1 (1911 2/03) Station 2 (19/12/03)
Carbohydrate Concentration yg I" Carbohydrate concentration pg I"
Station 3 (19/12/03) Station 4 (20/12/03)
0 50 100 150 200 0 50 100 150 200
Carbohydrate Concentration ng I'' Carbohydrate Concentration pg I"
Station 5 (2011 2/03)
& 300 n
400
500
50 100 150 200
Carbohydrate Concentration ug I '
Fig. 32 Seston carbohydrate profiles at transect stations during Dec 19-20 (transect location See Fig. 24)
Lipids: Seston lipid concentration followed the Same trends as carbohydrates in this second transect (Fig. 33). Near the surface, lipids were up to 8 times higher than near the bottom, and midwater sample values (100m depth) were close to the near bottom ones. All seston values (carbohydrates and lipids) were higher in the second transect compared with the first one.
Station 1(19/12/03) Station 2(19/12/03)
0 20 40 60 80 WO 0 20 40 60 80 100
Lipid Conceniration pg 1.' Lipid Concentration pg I"'
Station 3(19/12/03) Station 4(20/12/03)
Lipid Concentration !ig 1.' Lipid Concentration ng 1"
Station 5(20/12/03)
Lipid Concentration pg 1.'
Fig. 33 Seston lipid profiles at transect stations during Dec 19-20 (transect location See Fig. 24)
Results 5 5
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Giant Water SamplerCarbohydrates and lipids were analyzed in the water samples of the Giant Water Sampler (GWS) (Fig. 34). Unfortunately, carbohydrates were not analyzed on board at point 3 (Fig. 34). Carbohydrates were higher very close to the bottom in the second transect compared to the first one. On the other hand, lipids were slightly lower in the second transect compared to the first one, but clearly higher in the bloom transect points analyzed (up to 4 times higher compared with the second transect).
Fig. 34 Seston carbohydrate and lipid concentrations in giant water samples at transect stations ("I": Dec 6-7, "2": Dec 19-20, "3": "bloom transect" at Dec 22- 23).
Considering both transects (6-7 December and 19-20 December 2003), carbohydrate and lipid seston were more abundant in near surface waters after the Wo weeks of primary production process. Near the bottom, the GWS showed a similar trend, although it seems that in the second transect lipid concentrations of the seston were slightly lower than in the first one. It s e e m s that the phytoplankton rain from the ice sheet began after the 6-7 December transect, increasing significantly the material available for the benthic suspension feeders towards the end of the transect.
C: Biochemistry of Antarctic benthic organisms