Cryptic photosynthesis, Extrasolar planetary oxygen without a surface biological signature

On the Earth, photosynthetic organisms are responsible for the production of virtually all of the oxygen in the atmosphere. On the land, vegetation reflects in the visible, leading to a red edge that developed about 450 Myr ago and has been proposed as a biosignature for life on extrasolar planets. However, in many regions of the Earth, and particularly where surface conditions are extreme, for example in hot and cold deserts, photosynthetic organisms can be driven into and under substrates where light is still sufficient for photosynthesis. These communities exhibit no detectable surface spectral signature to indicate life. The same is true of the assemblages of photosynthetic organisms at more than a few metres depth in water bodies. These communities are widespread and dominate local photosynthetic productivity. We review known cryptic photosynthetic communities and their productivity. We link geomicrobiology with observational astronomy by calculating the disk-averaged spectra of cryptic habitats and identifying detectable features on an exoplanet dominated by such a biota. The hypothetical cryptic photosynthesis worlds discussed here are Earth-analogs that show detectable atmospheric biomarkers like our own planet, but do not exhibit a discernable biological surface feature in the disc-averaged spectrum.Comment: 23 pages, 2 figures, Astrobiology (TBP) - updated Table 1, typo in detectable O2 correcte

Spring phytoplankton onset after the ice break-up and sea-ice signature (Adélie Land, East Antarctica)

The phytoplankton onset following the spring ice break-up in Adélie Land, East Antarctica, was studied along a short transect, from 400 m off the continent to 5 km offshore, during the austral summer of 2002. Eight days after the ice break-up, some large colonial and solitary diatom cells, known to be associated with land-fast ice and present in downward fluxes, were unable to adapt in ice-free waters, while some other solitary and short-colony forming taxa (e.g., Fragilariopsis curta, F. cylindrus) did develop. Pelagic species were becoming more abundant offshore, replacing the typical sympagic (ice-associated) taxa. Archaeomonad cysts, usually associated with sea ice, were recorded in the surface waters nearshore. Rough weather restricted the data set, but we were able to confirm that some microalgae may be reliable sea-ice indicators and that seeding by sea ice only concerns a few taxa in this coastal area of East Antarctica. Keywords: Ice break-up; phytoplankton; sea-ice signature; East Antarctica (Published: 10 January 2011) Citation: Polar Research 2011, 30, 5910, doi: 10.3402/polar.v30i0.591

Trophic interactions within the Ross Sea continental shelf ecosystem

The continental shelf of the Ross Sea is one of the Antarctic's most intensively studied regions. We review the available data on the region's physical characteristics (currents and ice concentrations) and their spatial variations, as well as components of the neritic food web, including lower and middle levels (phytoplankton, zooplankton, krill, fishes), the upper trophic levels (seals, penguins, pelagic birds, whales) and benthic fauna. A hypothetical food web is presented. Biotic interactions, such as the role of Euphausia crystallorophias and Pleuragramma antarcticum as grazers of lower levels and food for higher trophic levels, are suggested as being critical. The neritic food web contrasts dramatically with others in the Antarctic that appear to be structured around the keystone species Euphausia superba. Similarly, we suggest that benthic–pelagic coupling is stronger in the Ross Sea than in most other Antarctic regions. We also highlight many of the unknowns within the food web, and discuss the impacts of a changing Ross Sea habitat on the ecosystem

Algal biomass and pigments along a latitudinal gradient in Victoria Land lakes, East Antarctica

It is generally accepted that Antarctic terrestrial diversity decreases as latitude increases, but latitudinal patterns of several organisms are not always as clear as expected. The Victoria Land region is rich in lakes and ponds and spans 8 degrees of latitude that encompasses gradients in factors such as solar radiation, temperature, ice cover and day length. An understanding of the links between latitudinally driven environmental and biodiversity changes is essential to the understanding of the ecology and evolution of Antarctic biota and the formulation of hypotheses about likely future changes in biodiversity. As several studies have demonstrated that photosynthetic pigments are an excellent, although underused, tool for the study of lacustrine algal communities, the aim of the present study was to investigate variations in algal biomass and biodiversity across the latitudinal gradient of Victoria Land using sedimentary pigments. We test the hypothesis that the biodiversity of freshwater environments decreases as latitude increases. On the basis of our results, we propose using the number of sedimentary pigments as a proxy for algal diversity and the sum of chlorophyll a and bacteriochlorophyll a with their degradation derivatives as an index of biomass. Overall, our data show that biomass and diversity decrease as latitude increases but local environmental conditions, in particular, natural levels of eutrophy, can affect both productivity and diversity

Biogeographic trends in Antarctic lake communities

The basic biogeographic zones proposed many years ago – the Subantarctic islands, Maritime Antarctica and Continental Antarctica – continue to hold up, though they cannot be seen as absolute dividers of biodiversity. For example, subantarctic Macquarie Island appears to be biogeographically separate from the islands of the Kerguelen Province, and on the continent there are species that are present in lakes of more than one zone. Furthermore, there are numerous lake environments that have yet to be investigated, and it is probable that some of these lakes could turn up surprises that will bring into question these basic divisions. An important question to be answered is whether these biogeographic zones reflect climate attributes, or whether they were moulded long ago by barriers to dispersal. Again, our imperfect knowledge of Antarctic lacustrine biogeography means that this question cannot at present be answered. However, as discussed elsewhere in this volume (Chown and Convey), there are indications of a strong biogeographical boundary for terrestrial species between the Maritime and Continental Antarctic zones. A palaeolimnological approach will assist in answering this question: understanding how Antarctic biogeography has developed through time will provide necessary insights into current distributions. A prime example is the occurrence of the copepod Boeckella poppei in Beaver Lake. Pugh et al. (2002) initially concluded that this species was an anthropogenic introduction, then Bayly et al. (2003) provided morphological evidence for long habitation in the area of Beaver Lake. Recent palaeolimnological work has shown that the species has been present in nearby Lake Terrasovoje for at least 9000 yrs (L. Cromer, A. Bissett, J. Gibson and K. Swadling, unpublished data). Even though this lake has only existed in the Holocene, cosmogenic exposure dates in the same area of exposed rock can exceed 106 years (D. Gore and D. White, personal communication). From these observations it can be concluded that Boeckella poppei has been associated with the Beaver Lake area for at least the entire Holocene and probably well back into the Pleistocene, and that its occurrence outside its ‘preferred’ biogeographical zone (Maritime Antarctica) is not a reflection of current climate, rather of history. The majority of our knowledge regarding Antarctic lacustrine biodiversity and biogeography has come from classic taxonomic studies, where the morphology (or biochemistry for bacteria) has been of greatest importance. In many cases this has led to questionable identification, correct identification of species is paramount if the true biodiversity and biogeography of Antarctica is to be deduced. It is only in the last few years that the more objective approach of molecular genetics has been applied to Antarctic lacustrine organisms, and then only for more cryptic groups, such as bacteria and cyanobacteria. As more samples and organisms are studied by these methods it is likely that new relationships between species distributions will be found. Due to the limited number of species in Antarctica (compared to more temperate zones), it may be possible in the future to record the make-up of selected genes of most, if not all, of the biota, which will allow more precise analysis. There is increasing evidence for endemism amongst the inhabitants of lakes both on the Antarctic continent and the subantarctic islands, from bacteria to crustacea. Use of molecular genetic techniques to identify more cryptic species will most likely add to the list of putative endemics. It is clear, however, that recent colonisation and current climate also play important roles in the distribution of the biota, as most of the lakes in Antarctica are of relatively recent (Holocene) origin. Colonising species have to be adapted to transport from source areas, which can either involve inter- or intra-continental movement, as well as survival on arrival at potential habitat. Flexibility in nutritional and habitat requirements is an important factor in determining whether a species will be a successful coloniser. The buffering to environmental extremes provided by the liquid water habitat means that conditions further south will not be as harsh as those experienced by their terrestrial counterparts. As the climate changes in the future, it will be interesting to note the effects of these changes on the lacustrine biota. Will new species colonise the Antarctic Peninsula where temperatures are warming? In the longer term, the biogeography of Antarctic lakes will continue to be dynamic. New species will arrive, others will become extinct. The biogeographic zones long-proposed may continue to hold, though more precise knowledge of current distributions and responses to climate change may refine our view.MICROMAT, LAQUA