ALBERT

Description: While there is a general sense that lakes can act as sentinels of climate change, their efficacy has not been thoroughly analyzed. We identified the key response variables within a lake that act as indicators of the effects of climate change on both the lake and the catchment. These variables reflect a wide range of physical, chemical, and biological responses to climate. However, the efficacy of the different indicators is affected by regional response to climate change, characteristics of the catchment, and lake mixing regimes. Thus, particular indicators or combinations of indicators are more effective for different lake types and geographic regions. The extraction of climate signals can be further complicated by the influence of other environmental changes, such as eutrophication or acidification, and the equivalent reverse phenomena, in addition to other land-use influences. In many cases, however, confounding factors can be addressed through analytical tools such as detrending or filtering. Lakes are effective sentinels for climate change because they are sensitive to climate, respond rapidly to change, and integrate information about changes in the catchment.

Description: A two day workshop on Southern Ocean cephalopods was held in Hobart, Tasmania, Australia prior to the triennial 2006 Cephalopod International Advisory Council (CIAC) symposium. The workshop provided a second international forum to present the current state of research and new directions since the last Southern Ocean cephalopod meeting held in 1993. A major focus of the workshop was trophic ecology and the use of a variety of tools that can be applied in Southern Ocean trophic studies for both cephalopod and predator researchers. New tools that are being used as trophic indicators and tracers in food chain pathways include stable isotope, heavy metal and fatty acid signature analysis. Progress is also being made on understanding squid population dynamics in relation to other key components of the ecosystem by incorporating squid data in ecosystem models. Genetic barcoding is now of great value to fish taxonomy as well as other groups and it is expected that a cephalopod barcoding initiative will be an important tool for cephalopod taxonomy. There is a current initiative to produce a new cephalopod beak identification guide to assist predator biologists in identifying cephalopod prey items. There were also general discussions on specific taxonomic issues, Southern Ocean Cephalopod paralarvae and parasites, and suggestions for future CIAC workshop topics.

Description: Cephalopods are highly sensitive to environmental conditions and changes at a range of spatial and temporal scales. Relationships documented between cephalopod stock dynamics and environmental conditions are of two main types: those concerning the geographic distribution of abundance, for which the mechanism is often unknown, and those relating to biological processes such as egg survival, growth, recruitment and migration, where mechanisms are sometimes known and in a very few cases demonstrated by experimental evidence. Cephalopods seem to respond to environmental variation both ‘actively’ (e.g. migrating to areas with more favoured environmental conditions for feeding or spawning) and ‘passively’ (growth and survival vary according to conditions experienced, passive migration with prevailing currents). Environmental effects on early life stages can affect life history characteristics (growth and maturation rates) as well as distribution and abundance. Both large-scale atmospheric and oceanic processes and local environmental variation appear to play important roles in species–environment interactions. While oceanographic conditions are of particular significance for mobile pelagic species such as the ommastrephid squids, the less widely ranging demersal and benthic species may be more dependent on other physical habitat characteristics (e.g. substrate and bathymetry). Coastal species may be impacted by variations in water quality and salinity (related to rainfall and river flow). Gaps in current knowledge and future research priorities are discussed. Key research goals include linking distribution and abundance to environmental effects on biological processes, and using such knowledge to provide environmental indicators and to underpin fishery management.

Description: We examined the physiological responses of steady-state iron (Fe)-replete and Fe-limited cultures of the biogeochemically critical marine unicellular diazotrophic cyanobacterium Crocosphaera at glacial (19 Pa; 190 ppm), current (39 Pa; 380 ppm), and projected year 2100 (76 Pa; 750 ppm) CO2 levels. Rates of N2 and CO2 fixation and growth increased in step with increasing partial pressure of CO2 (pCO2), but only under Fe-replete conditions. N2 and carbon fixation rates at 75 Pa CO2 were 1.4-1.8-fold and 1.2-2.0-fold higher, respectively, relative to those at present day and glacial pCO2 levels. In Fe-replete cultures, cellular Fe and molybdenum quotas varied threefold and were linearly related to N2 fixation rates and to external pCO2. However, N2 fixation and trace metal quotas were decoupled from pCO2 in Fe-limited Crocosphaera. Higher CO2 and Fe concentrations both resulted in increased cellular pigment contents and affected photosynthesis vs. irradiance parameters. If these results also apply to natural Crocosphaera populations, anthropogenic CO2 enrichment could substantially increase global oceanic N2 and CO2 fixation, but this effect may be tempered by Fe availability. Possible biogeochemical consequences may include elevated inputs of new nitrogen to the ocean and increased potential for Fe and/or phosphorus limitation in the future high-CO2 ocean, and feedbacks to atmospheric pCO2 in both the near future and over glacial to interglacial timescales.

Description: Live-collected samples of four common reefbuilding coral genera (Acropora, Pocillopora, Goniastrea, Porites) from subtidal and intertidal settings of Heron Reef, Great Barrier Reef, show extensive early marine diagenesis where parts of the coralla less than 3 years old contain abundant macro- and microborings and aragonite, high-Mg calcite, low-Mg calcite, and brucite cements. Many types of cement are associated directly with microendoliths and endobionts that inhabit parts of the corallum recently abandoned by coral polyps. The occurrence of cements that generally do not precipitate in normal shallow seawater (e.g., brucite, low-Mg calcite) highlights the importance of microenvironments in coral diagenesis. Cements precipitated in microenvironments may not reXect ambient seawater chemistry. Hence, geochemical sampling of these cements will contaminate trace-element and stable-isotope inventories used for palaeoclimate and dating analysis. Thus, great care must be taken in vetting samples for both bulk and microanalysis of geochemistry. Visual inspection using scanning electron microscopy may be required for vetting in many cases.

Description: Mombacho is a deeply dissected volcano belonging to the Quaternary volcanic chain of Nicaragua. The southern, historic collapse crater (El Crater) currently hosts a fumarolic field with a maximum temperature of 121°C. Chemical and isotopic data from five gas-sampling field campaigns carried out in 2002, 2003 and 2005 highlight the presence of high-temperature gas components (e.g. SO2, HCl and HF), which indicate a significant contribution of juvenile magmatic fluids to the hydrothermal system feeding the gas discharges. This is strongly supported by the mantle-derived helium and carbon isotopic signatures, although the latter is partly masked by either a sedimentary subduction-related or a shallow carbonate component. The observed chemical and isotopic composition of the Mombacho fluids seems to indicate that this volcanic system, although it has not experienced eruptive events during the last centuries, can be considered active and possibly dangerous, in agreement with the geophysical data recorded in the region. Systematic geochemical monitoring of the fumarolic gas discharges, coupled with a seismic and ground deformation network, is highly recommended in order to monitor a possible new eruptive phase.

Description: The published mean δ34S values of ore-related pyrites from orogenic gold deposits of the Eastern Goldfields Province, Yilgarn Craton lie between −4‰ and +4‰. As for orogenic gold deposits worldwide, most deposits have positive means and a restricted range of δ34S values, but some have negative means and wider ranges of δ34S values. Wall-rock carbonation and back-mixing of similar-source fluids with different fluid pathways can explain some of the more negative δ34S signatures. However, structural setting appears to be the most important factor controlling ore-fluid oxidation state and hence the distribution of δ34S values in gold-related pyrites. Shear-hosted deposits appear to have experienced fluid-dominated processes such as phase separation, whereas stockwork, vein-hosted or disseminated deposits formed under conditions of greater rock buffering. At Victory-Defiance, in particular, negative δ34S values are more common in gently dipping dilational structures, compared to more compressional steeply dipping structures. It appears most likely that fluid-pressure fluctuations during fault-valve cycles establish different fluid-flow regimes in structures with different orientations. Rapid fluid-pressure fluctuations in dilational structures during seismic activity can cause partitioning of reduced gas phases from the ore fluid during extreme phase separation and hence are an effective method of ore-fluid oxidation, leading to large, local fluctuations in oxidation state. It is thus not necessary to invoke mixing with oxidised magmatic fluids to explain δ34S signatures indicative of oxidation. In any case, available, robust geochronology in the Eastern Goldfields Province does not support the direct involvement of oxidised magmatic fluids from adjacent granitic intrusions in orogenic gold genesis. Thus, negative mean δ34S values and large variations in δ34S values of ore-related pyrites in world-class orogenic gold deposits are interpreted to result from multiple mechanisms of gold precipitation from a single, ubiquitous ore fluid in varying structural settings, rather than from the involvement of oxidised ore fluids from a different source. Such signatures are indicative, but not diagnostic, of anomalously large orogenic gold systems.

Description: Todayrsquos Wadden Sea is a heavily human-altered ecosystem. Shaped by natural forces since its origin 7,500 years ago, humans gradually gained dominance in influencing ecosystem structure and functioning. Here, we reconstruct the timeline of human impacts and the history of ecological changes in the Wadden Sea. We then discuss the ecosystem and societal consequences of observed changes, and conclude with management implications. Human influences have intensified and multiplied over time. Large-scale habitat transformation over the last 1,000 years has eliminated diverse terrestrial, freshwater, brackish and marine habitats. Intensive exploitation of everything from oysters to whales has depleted most large predators and habitat-building species since medieval times. In the twentieth century, pollution, eutrophication, species invasions and, presumably, climate change have had marked impacts on the Wadden Sea flora and fauna. Yet habitat loss and overexploitation were the two main causes for the extinction or severe depletion of 144 species (~20% of total macrobiota). The loss of biodiversity, large predators, special habitats, filter and storage capacity, and degradation in water quality have led to a simplification and homogenisation of the food web structure and ecosystem functioning that has affected the Wadden Sea ecosystem and coastal societies alike. Recent conservation efforts have reversed some negative trends by enabling some birds and mammals to recover and by creating new economic options for society. The Wadden Sea history provides a unique long-term perspective on ecological change, new objectives for conservation, restoration and management, and an ecological baseline that allows us to envision a rich, productive and diverse Wadden Sea ecosystem and coastal society.

Description: Sea ice brines were collected from a single floe composed of different ice types in the western Weddell Sea in December 2004. The chemical composition of the brines (temperature: 23.4°C to 22.1°C; salinity: 40–63) was examined on seven occasions over 25 days with measurements of dissolved oxygen, dissolved inorganic macronutrients (nitrate plus nitrite, ammonium, phosphorus [DIP], and silicic acid), pH, total alkalinity (AT), dissolved organic carbon (DOC) and nitrogen (DON), total dissolved inorganic carbon (CT), and the stable isotopic composition of CT (δ13CT). The in situ pH ranged from 8.41-8.82 on the seawater scale, dissolved oxygen from 212-604 µmol kg−1, nitrate from 0.1-3.1 µmol kg−1, ammonium 0.1-2.4 µmol kg−1, DIP 0.4- 2.0 µmol kg−1, silicic acid 4-80 µmol kg−1, AT 2,690-4,620 µeq kg−1, DOC 115-359 µmol kg−1, DON 8-26 µmol kg−1, CT 2,090-3,550 µmol kg−1, and δ13CT +2.9‰ - +6.4‰. Compared with the chemical composition of surface oceanic water (salinity of 34), the brines had elevated pH, reduced concentrations of dissolved inorganic macronutrients (including carbon), especially dissolved inorganic nitrogen, and were mostly supersaturated with dissolved oxygen with respect to equilibrium with air, whereas the CT was considerably enriched in 13C. The chemical composition of the brines was consistent with internal biological productivity, but there was a lack of a distinctive and uniform relationship among the major dissolved inorganic nutrients typically used for describing biological activity. This was interpreted as the result of varying stoichiometry of biological activity within a very small spatial scale. Modification by abiotic processes was a potential contributing factor, such as degassing acting on the dissolved oxygen concentration. Carbonate mineral formation, acting on AT and CT, was not evident in brines from first-year ice but was apparent in brine from second-year ice.