Microphytobenthos (MPB) communities are responsible for most primary production in shallow intertidal mudflats. The effects of short-term changes in temperature and light (1200, 500 and 0 μmol photons m−2 s−1) on the photosynthetic activity of intertidal MPB communities of Browns River, Tasmania, during winter (0, 5, 10 and 15°C) and summer (20, 25, 30, 35 and 40°C) were examined using a Pulse Amplitude Modulated (Water PAM) fluorometer. The MPB communities were primarily dominated by the diatom genera Navicula, Cocconeis and Amphora, with a difference in species dominance during seasons. During summer, Amphora coffeaeformis dominated communities were significantly impacted by temperatures above 30°C regardless of light intensities. The MPB was able to photosynthesize at temperatures only up to 25°C. The rETRmax at 25°C, ranged from 39.18 ± 3.42 (500 μmol photons m−2 s−1) to 22.83 ± 1.05 (0 μmol photons m−2 s−1), which was lower than the values recorded at an equivalent irradiance in in-situ summer. However, if ambient temperature exceeds 25°C in summer, it is likely that the photosynthetic capabilities of the MPB will be diminished and it will cause irreversible photoinhibition.

Ice algae are a key component in polar marine food webs and have an active role in large-scale biogeochemical cycles. They remain extremely under-sampled due to the coarse nature of traditional point sampling methods compounded by the general logistical limitations of surveying in polar regions. This study provides a first assessment of hyperspectral imaging as an under-ice remote-sensing method to capture sea-ice algae biomass spatial variability at the ice/water interface. Ice-algal cultures were inoculated in a unique inverted sea-ice simulation tank at increasing concentrations over designated cylinder enclosures and sparsely across the ice/water interface. Hyperspectral images of the sea ice were acquired with a pushbroom sensor attaining 0.9 mm square pixel spatial resolution for three different spectral resolutions (1.7, 3.4, 6.7 nm). Image analysis revealed biomass distribution matching the inoculated chlorophyll a concentrations within each cylinder. While spectral resolutions >6 nm hindered biomass differentiation, 1.7 and 3.4 nm were able to resolve spatial variation in ice algal biomass implying a coherent sensor selection. The inverted ice tank provided a suitable sea-ice analogue platform for testing key parameters of the methodology. The results highlight the potential of hyperspectral imaging to capture sea-ice algal biomass variability at unprecedented scales in a non-invasive way.

The primary aim of this review is to highlight that sea-ice microbes would be capable of occupying ice-associated biological niches on Europa and Enceladus. These moons are compelling targets for astrobiological exploration because of the inferred presence of subsurface oceans that have persisted over geological timescales. Although potentially hostile to life in general, Europa and Enceladus may still harbour biologically permissive domains associated with the ice, ocean and seafloor environments. However, validating sources of free energy is challenging, as is qualifying possible metabolic processes or ecosystem dynamics. Here, the capacity for biological adaptation exhibited by microorganisms that inhabit sea ice is reviewed. These ecosystems are among the most relevant Earth-based analogues for considering life on ocean worlds because microorganisms must adapt to multiple physicochemical extremes. In future, these organisms will likely play a significant role in defining the constraints on habitability beyond Earth and developing a mechanistic framework that contrasts the limits of Earth's biosphere with extra-terrestrial environments of interest.

The Richmond River Valley of northern N.S.W. contains a late Pleistocene succession dating back to approximately 250,000 yr B.P. Dinoflagellate and spore-pollen assemblages from the lowest interval, the lower “Dungarubba Clay” of Drury (1982), indicate deposition in a restricted estuarine environment at approximately 250,000 yr. Deposition in the overlying interval, the upper “Dungarubba Clay” and “Gundurimba Clay”, at approximately 120,000 yr B.P., began in a restricted estuary, but rising sea level caused inundation and deposition in a more open, marine-dominated environment. Dinoflagellate cyst assemblages from the last interglaciation (stage 5) are interpreted by analogy with those from the morphologically similar, modern Broken Bay, N.S.W. They are indicative of an open, marine-dominated environment and imply that barrier formation in the Richmond River Valley, and possibly elsewhere in northern N.S.W., did not commence until after the initial postglacial transgression. Synchronous changes in sea level and rainforest development suggest that there was no significant time lag between climate and sea-level change.

The paleo-depositional environment of inner Prydz Bay, East Antarctica, has been reconstructed for the past 21,320 14C yr B.P., using diatom assemblages and sediment facies from a short, 352-cm-long gravity core. Between 21,320 and 11,650 14C yr B.P., compact tillite and diamicton are present in the core, and diatom frustules are rare to absent. These data suggest that an ice sheet grounded over the site during the last glacial maximum. Following glacial retreat, siliceous muddy ooze was deposited, from 11,650 to 2600 14C yr B.P., in an open marine setting. During this stage, diatom frustules are abundant and well preserved, and Thalassiosira antarctica resting spores and Fragilariopsis curta dominate the assemblage. This assemblage suggests open marine deposition in an environment where the spatial and temporal distribution of sea ice is less than today. Since 2600 14C yr B.P., sea-ice and ice-edge diatom species have become more abundant, and neoglacial cooling is inferred. The assemblage is similar to that forming currently in Prydz Bay, where sea ice is absent (<10% cover) for 2–3 months of the year and permanent ice edge and/or multiyear sea ice remains in close proximity to the site.

Microphytobenthos (MPB) contributes up to half the primary production of estuaries. These microorganisms are sensitive to changes in sediment temperatures, particularly the extreme temperatures during exposure periods. This study investigates the physiological responses of MPB to freezing temperatures at two locations near Hobart, Tasmania during winter. Photosynthetic parameters were measured at 2 mm intervals to a depth of 10 mm. FV/FM values at three different distances from the shoreline at Kings Beach and Browns River in winter were between 0.584 and 0.617. rETRmax values were between 24.696 and 20.773. Maximum α values peaked in the subsurface rather than at the sediment surface. In vitro laboratory experiments (down to −5°C) showed little difference in response between the control and treatment groups, indicating no apparent effects of short term freezing on the MPB. Little change in photosynthetic parameters in response to freezing was probably associated with the resistance of light-harvesting reactions to freezing temperatures, recovery of the plasmalemma integrity or cryoprotection. Sediment composition and species composition were similar at both sampling sites. Therefore, responses of MPB were not due to species and grain size composition.

Sea ice microalgae actively contribute to the pool of dissolved organic matter (DOM) available for bacterial metabolism, but this link has historically relied on bulk correlations between chlorophyll a (a surrogate for algal biomass) and bacterial abundance. We incubated microbes from both the bottom (congelation layer) and surface brine region of Antarctic fast ice for nine days. Algal-derived DOM was manipulated by varying the duration of irradiance, restricting photosynthesis with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) or incubating in the dark. The bacterial response to changes in DOM availability was examined by performing cell counts, quantifying bacterial metabolic activity and examining community composition with denaturing gradient gel electrophoresis. The percentage of metabolically active bacteria was relatively low in the surface brine microcosm (10–20% of the bacterial community), the treatment with DCMU indirectly restricted bacterial growth and there was some evidence for changes in community structure. Metabolic activity was higher (35–69%) in the bottom ice microcosm, and while there was no variation in community structure, bacterial growth was restricted in the treatment with DCMU compared to the light/dark treatment. These results are considered preliminary, but provide a useful illustration of sea ice microbial dynamics beyond the use of ‘snapshot’ biomass correlations.

Polar lakes respond quickly to climate-induced environmental changes. We studied the chemical limnological variability in 127 lakes and ponds from eight ice-free regions along the East Antarctic coastline, and compared repeat specific conductance measurements from lakes in the Larsemann Hills and Skarvsnes covering the periods 1987–2009 and 1997–2008, respectively. Specific conductance, the concentration of the major ions, pH and the concentration of the major nutrients underlie the variation in limnology between and within the regions. This limnological variability is probably related to differences in the time of deglaciation, lake origin and evolution, geology and geomorphology of the lake basins and their catchment areas, sub-regional climate patterns, the distance of the lakes and the lake districts to the ice sheet and the Southern Ocean, and the presence of particular biota in the lakes and their catchment areas. In regions where repeat surveys were available, inter-annual and inter-decadal variability in specific conductance was relatively large and most pronounced in the non-dilute lakes with a low lake depth to surface area ratio. We conclude that long-term specific conductance measurements in these lakes are complementary to snow accumulation data from ice cores, inexpensive, easy to obtain, and should thus be part of long-term limnological and biological monitoring programmes.

Microphytobenthos need photoadaptive strategies to survive the highly dynamic light environment in which they reside. Xanthophyll pigments can provide photoprotection by cycling electrons between epoxide and de-epoxide forms, dissipating excess light energy as heat. This study examined the xanthophyll cycle in microphytobenthos on a tidally exposed substrate at Browns River, Tasmania. Fv/Fm decreased from 0.52±0.01 to 0.47±0.01 at noon in surface samples and a decrease in the diadinoxanthin:chlorophyll-a ratio from 0.022±0.003 to 0.015±0.005 also suggests that the microphytobenthos was under physiological stress at noon. The results indicate that the cells exposed to light at the surface migrated deeper into the sediments and replenished the epoxide form of their xanthophylls. The results suggest that micrphytobenthos utilizes both behavioural and physiological strategies to survive in the dynamic intertidal environment.

This study is the first published survey of diatom-environment relationships on sub-Antarctic Macquarie Island. Fifty-eight sites in 50 coastal and inland lakes were sampled for benthic diatoms and water chemistry. 208 diatom species from 34 genera were identified. Multivariate analyses indicated that the lakes were distributed along nutrient and conductivity gradients. Conductivity, pH, phosphate (SRP), silicate and temperature all explained independent portions of the variance in the diatom data. Transfer functions provide a quantitative basis for palaeolimnological studies of past climate change and human impacts, and can be used to establish baseline conditions for assessing the impacts of recent climate change and the introduction of non-native plants and animals. Statistically robust diatom transfer functions for conductivity, phosphate and silicate were developed, while pH and temperature transfer functions performed less well. The lower predictive abilities of the pH and temperature transfer functions probably reflect the broad pH tolerance range of diatoms on Macquarie Island and uneven distribution of lakes along the temperature gradient. This study contributes to understanding the current ecological distribution of Macquarie Island diatoms and provides transfer functions that will be applied in studies of diatoms in lake sediment cores to quantitatively reconstruct past environmental changes.

Fossil marine diatom assemblages from the Sørsdal Formation, a deposit of diatomaceous sand from Marine Plain in the Vestfold Hills, provide age and palaeoenvironmental information from a Pliocene coastal setting in East Antarctica. Benthic and meroplanktic diatom taxa suggest deposition in a shallow coastal embayment with water depths of 20–25 m. Diatom biostratigraphy indicates that the Sørsdal Formation belongs to the Fragilariopsis barronii Zone (4.5 to 4.1 Ma), through correlation to reference sections in the Ross Sea and Southern Ocean. Features of the other biota suggest higher sea-surface temperatures and reduced sea-ice cover, consistent with global records of higher sea level.

We have determined the base composition (percentage of guanine-cytosine base pairs, GC%) of total DNA from Euphausia superba to be 32% ± 0.5%. This is the lowest GC% recorded for a metazoan. Low GC% DNA has high concentrations of thymine (T) residues and consequently a greater abundance of adjacent T residues [T(n) arrays]. Ultraviolet B (280–320 nm, UV-B) radiation damages DNA primarily at (T)n arrays, so we suggest that krill DNA may be more susceptible to damage from increased levels of UV-B radiation over the Southern Ocean than the DNA of other Antarctic organisms.

Sediment cores from Abel and Platcha Bays, in the Vestfold Hills, east Antarctica, contain evidence for a local late Holocene increase in fast ice extent and a possible ice cap retreat at approximately 1750 yr BP, a similar time to the Chelnock Glaciation. Prior to this time both bays experienced periods of isolation that lead to changes in their diatom flora, C:N ratio, percentage of biogenic silica and total organic carbon. Three new diatom indices are proposed; the fast ice index, based on the proportion of fast ice taxa present, the benthic index, based on the proportion of benthic taxa and the snow index, based on the proportion Berkelaya adeliense and Thalassiosira ausiralis. These indices show strong relationships with the percentage of biogenic silica, total organic carbon and percentage sand. A weak relationship exists between the fast ice index and ∂13C and no relationship with the C:N ratio.