Microbial biomass, photosynthesis and chlorophyll a related pigments in the ponds of the McMurdo Ice Shelf, Antarctica

Abstract

Abstract:The extensive ablation zone on the McMurdo Ice Shelf (78"S, 165'30E) contains numerous ponds that are lined with benthic mats of cyanobacteria and associated micro-organisms. The photoautotrophic biomass content of these mats was examined in six contrasting ponds. Particulate carbon contributed only 3.2% of the mat dry weight, with C:N ratios generally less than 20:l. The chlorophyll a content was low relative to carbon (chlorophyll a : C < 0.01). Analysis of the mats by high performance liquid chromatography [HPLC] showed that the pigment fraction assayed spectrophotometrically as chlorophyll a contained large quantities (up to 70%) of the degradation product chlorophyllide u and the epimer chlorophyll a'. Photosynthetic rates per unit chlorophyll a [HPLC] were extremely slow: <O. 1 mg C (mg Chlu)-' h-', less than one tenth the rates recorded in the overlying phytoplankton community. These analyses indicate that in the ice pond benthic mats most of the dry weight is inorganic, most of the organic carbon is non-chlorophyllcontaining material, and much of the chlorophyll a is not photosynthetically active. Cold temperatures and the associated low activity of herbivores anddetritivores may contribute towards this preservation of inactive chlorophyll a on the McMurdo Ice Shelf, and perhaps in similar benthic mats in the lakes and streams of southern Victoria Land.

Influences of Pond Geochemistry, Temperature, and Freeze-Thaw on Terminal Anaerobic Processes Occurring in Sediments of Six Ponds of the McMurdo Ice Shelf, near Bratina Island, Antarctica

“…The study ponds were discrete and were designated with the unofficial names, Fresh, Skua, P-70, Brack, Salt, and Orange. The water chemistry and algal mats in the ponds have been previously described (9,10,17). Underlying the cyanobacterial mat at the bottom of each pond was a layer of anaerobic sediment, which varied in depth depending on the pond, reaching a depth maximum of about 18 to 20 cm.…”

“…The bottoms of these ponds are covered with thick mats consisting of cyanobacteria, diatoms, and green algae (9,10), below which is often a layer of anoxic sediment. Variations in chemical and physical conditions between the ponds leads to community differentiation within and between the mats and to differences in mat morphology, thus creating in a small area a variety of modern unlithified stromatolites unique on Earth (19).…”

Toxin production in cyanobacterial mats from ponds on the McMurdo Ice Shelf, Antarctica

“…The hollows are frequently occupied by ponds and lakes ranging in size from 1 to 30,000 m 2 . Pond chemistry is varied due to dierent ages of the ponds and due to sea water intrusions and lenses of mirabilite (Na 2 SO 4 +10H 2 O; Howard-Williams et al, 1989). A second type of environment found in this region is an estuary, ā at area of interconnected ponds exposed to the tide (one per day) of McMurdo Sound and thus to sea water.…”

“…A second type of environment found in this region is an estuary, ā at area of interconnected ponds exposed to the tide (one per day) of McMurdo Sound and thus to sea water. Algal mats dominated by cyanobacteria, but also containing diatoms and planktonic¯agellates, make up a large part of the biomass in these summer meltwater ponds (Howard-Williams et al, 1989). While the environment of the``undulating ice'' is characterized by a broad range in salinities and a greater diversity of taxa, the estuary shows less variation in salinities and less taxa in the algal mats.…”

Photosynthesis in Extreme Environments

“…In the coastal areas, microbial mats are usually restricted to the shore and bottom of the streams as the flat lowlands are covered by extensive carpets of mosses and in some areas by the vascular plants Deschampsia antarctica and Colobanthus quitensis. The photosynthetic rates per unit of chlorophyll a of the mats analyzed were low compared with other cyanobacterial communities of more temperate environments (Ariosa et al, 2006), but are in the range of other Antarctic microbial mats (Howard-Williams et al, 1989;Davey, 1993;Vincent et al, 1993). It is possible that the depth layers where photosynthesis reached its maximal values and the overcast weather conditions of this region are conducive to a low P max and , which were lower and higher, respectively, than in other cyanobacterial communities.…”