M. C. Kennicutt

A Methanotrophic Marine Molluscan (Bivalvia, Mytilidae) Symbiosis: Mussels Fueled by Gas

An undescribed mussel (family Mytilidae), which lives in the vicinity of hydrocarbon seeps in the Gulf of Mexico, consumes methane (the principal component of natural gas) at a high rate. The methane consumption is limited to the gills of these animals and is apparently due to the abundant intracellular bacteria found there. This demonstrates a methane-based symbiosis between an animal and intracellular bacteria. Methane consumption is dependent on the availability of oxygen and is inhibited by acetylene. The consumption of methane by these mussels is associated with a dramatic increase in oxygen consumption and carbon dioxide production. As the methane consumption of the bivalve can exceed its carbon dioxide production, the symbiosis may be able to entirely satisfy its carbon needs from methane uptake. The very light (δ13C = -51 to -57 per mil) stable carbon isotope ratios found in this animal support methane (δ13C = -45 per mil at this site) as the primary carbon source for both the mussels and their symbionts.

Antarctic climate change and the environment: an update

We present an update of the ‘key points’ from the Antarctic Climate Change and the Environment (ACCE) report that was published by the Scientific Committee on Antarctic Research (SCAR) in 2009. We summarise subsequent advances in knowledge concerning how the climates of the Antarctic and Southern Ocean have changed in the past, how they might change in the future, and examine the associated impacts on the marine and terrestrial biota. We also incorporate relevant material presented by SCAR to the Antarctic Treaty Consultative Meetings, and make use of emerging results that will form part of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report

Challenges to the Future Conservation of the Antarctic

Changing environments and resource demands present challenges to Antarctic conservation. The Antarctic Treaty System, acknowledged as a successful model of cooperative regulation of one of the globes largest commons (1), is under substantial pressure. Concerns have been raised about increased stress on Antarctic systems from global environmental change and growing interest in the regions resources (2, 3). Although policy-makers may recognize these challenges, failure to respond in a timely way can have substantial negative consequences. We provide a horizon scan, a systematic means for identifying emerging trends and assisting decision-makers in identifying policies that address future challenges (2, 3). Previous analyses of conservation threats in the Antarctic have been restricted to matters for which available evidence is compelling (4). We reconsider these concerns because they might escalate quickly, judging from recent rapid environmental change in parts of Antarctica and increasing human interest in the region (see the map). We then focus on a more distant time horizon.

A roadmap for Antarctic and Southern Ocean science for the next two decades and beyond

Abstract Antarctic and Southern Ocean science is vital to understanding natural variability, the processes that govern global change and the role of humans in the Earth and climate system. The potential for new knowledge to be gained from future Antarctic science is substantial. Therefore, the international Antarctic community came together to ‘scan the horizon’ to identify the highest priority scientific questions that researchers should aspire to answer in the next two decades and beyond. Wide consultation was a fundamental principle for the development of a collective, international view of the most important future directions in Antarctic science. From the many possibilities, the horizon scan identified 80 key scientific questions through structured debate, discussion, revision and voting. Questions were clustered into seven topics: i) Antarctic atmosphere and global connections, ii) Southern Ocean and sea ice in a warming world, iii) ice sheet and sea level, iv) the dynamic Earth, v) life on the precipice, vi) near-Earth space and beyond, and vii) human presence in Antarctica. Answering the questions identified by the horizon scan will require innovative experimental designs, novel applications of technology, invention of next-generation field and laboratory approaches, and expanded observing systems and networks. Unbiased, non-contaminating procedures will be required to retrieve the requisite air, biota, sediment, rock, ice and water samples. Sustained year-round access to Antarctica and the Southern Ocean will be essential to increase winter-time measurements. Improved models are needed that represent Antarctica and the Southern Ocean in the Earth System, and provide predictions at spatial and temporal resolutions useful for decision making. A co-ordinated portfolio of cross-disciplinary science, based on new models of international collaboration, will be essential as no scientist, programme or nation can realize these aspirations alone.

Stable Carbon Isotopic Evidence for Carbon Limitation in Hydrothermal Vent Vestimentiferans

Stable carbon isotope composition (δ13C values) can be used to evaluate an animals source of nutritional carbon. Most animals with chemoautotrophic endosymbionts have quite negative tissue δ13C values due to discrimination against 13C associated with chemoautotrophic assimilation of inorganic carbon. However, the δ13C values of hydrothermal vent (HTV) vestimentiferans are significantly higher than the values reported for non-HTV vestimentiferans or other invertebrates with chemoautotrophic endosymbionts. Tissue δ13C values of two species of HTV vestimentiferans increase with increasing size of the animals. This relation supports the hypothesis that the relatively high δ13C values are the result of inorganic carbon limitation during carbon fixation. A more favorable relation between gas exchange and carbon fixation in the smaller individuals is expected, due to differences in the geometric scaling of gas-exchange surfaces and trophosome volume.

The regional patterns of hydrocarbon alteration in the Gulf of Mexico area

More than 600 oils from Texas, Alabama, Louisiana, Mississippi, Florida, and adjacent offshore areas were analyzed for gasoline and C{sub 10+} compounds. The following parameters were evaluated geographically: heptane and isoheptane values (paraffincity indices), toluene/n-heptane (aromaticity index) and n-heptadecane/pristane. Isoheptane value is defined as the ratio of {approximately}methylhexanes to dimethylcyclopentanes; heptane value is defined as the percentage of n-heptane in the chromatographic suite between, and including cyclohexane through methylcyclohexane. The maturity trends defined by heptane and isoheptane values form coherent groupings that mimic the regional geologic structure. Thermal maturity is consistently higher when determined from isoheptane ratios than from heptane ratios. The heptane ratio, which is more sensitive to biodegradation then the isoheptane ratio, often spuriously indicates suppressed maturity levels due to alteration. Nevertheless, maturity levels defined by gasoline-range compositions appear to be higher than those defined by a higher molecular weight biomarkers (i.e., steranes, triterpanes). A possible explanation is that hydrocarbon fluids in the Gulf Coast are often a combination of fractions derived from organic matter at different stages of thermal evolution, implying progressive expulsion of hydrocarbons of increasing maturity from one or more sources, mixing, and multiple episodes of reservoir filling.