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The view from the south is, more than ever, dominated by ominous signs of change. Antarctica and the Southern Ocean are intrinsic to the Earth system, and their evolution is intertwined with and influences the course of the Anthropocene. In turn, changes in the Antarctic affect and presage humanity's future. Growing understanding is countering popular beliefs that Antarctica is pristine, stable, isolated, and reliably frozen. An aspirational roadmap for Antarctic science has facilitated research since 2014. A renewed commitment to gathering further knowledge will quicken the pace of understanding of Earth systems and beyond. Progress is already evident, such as addressing uncertainties in the causes and pace of ice loss and global sea-level rise. However, much remains to be learned. As an iconic global “commons,” the rapidity of Antarctic change will provoke further political action. Antarctic research is more vital than ever to a sustainable future for this One Earth.

Improved waste management at McMurdo Station, Antarctica beginning in the 1980s has been followed by decreases in polycyclic aromatic hydrocarbon (PAH) and metal contamination in the adjacent marine sediments. However, determining the effect of the decreased contamination on marine ecological indicators (macrobenthic fauna) is confounded by concurrent changes in climate cycles and other physical forces. Between 2000 and 2013, there was a decrease in concentrations of some contaminants including mercury, copper, organochlorines, and PAHs in marine sediments adjacent to McMurdo Station. PAH concentrations in Winter Quarters Bay decreased an order of magnitude from 2000/2003 to 2012/2013 and were within an order of magnitude of reference area concentrations by 2013. Macrobenthic communities did not indicate any sign of recovery and have not become more similar to reference communities over this same period of time. Temporal changes in macrobenthic community composition during the study period had higher correlations with climatic and sea ice dynamics than with changes in contaminant concentrations. The Interdecadal Pacific Oscillation climatic index had the highest correlation with macrobenthic community composition. The Antarctic Oscillation climatic index, maximum ice extent and other natural environmental factors also appear to influence macrobenthic community composition. Despite large improvements in environmental management at McMurdo Station, continuing environmental vigilance is necessary before any noticeable improvement in ecological systems is likely to occur. The effects of climate must be considered when determining temporal changes in anthropogenic effects in Antarctica. Maintaining long-term monitoring of both contaminants and ecological indicators is important for determining the localized and global influences of humans on Antarctica, which will have implications for the whole planet.

Oil and gas seeps are common worldwide; occur on land and beneath the ocean; are numerous in the Gulf of Mexico; and are biogenic, thermogenic, or mixed in origin. Seeps occur as gases, liquids, asphalts, and tars. Seeps are estimated to account for about 95 % of oil annually discharged to the Gulf of Mexico waters. Biogenic gas seeps have a microbial metabolic origin. Thermogenic hydrocarbons rise to the surface from more deeply buried source rock horizons or accumulations. The seepage of oil and gas into marine sediments initiates a complex biogeochemical cycle. A unique ecology has evolved in association with oil and gas seeps based on chemosynthesis and symbioses. Consortia of microbial species mediate the geological and biogeochemical processes that are essential for supporting what are commonly referred to as cold-seep communities. At these locations, bacteria oxidize hydrocarbons to carbon dioxide or bicarbonate ions, which favor the formation of hard ground substrate in otherwise mostly muddy environments. Thermogenic oil and gas seeps and biogenic gas seeps are pervasive and intrinsic features of the Gulf of Mexico. Thermogenic seeps will persist as long as oil and gas continue to migrate to the seafloor.

Contaminants in coastal sediments are compared with continental shelf/slope and abyssal sediments. Early introductions of contaminants to sediments were due to agricultural pesticide use, increased populations in, and industrialization of, coastal areas, and oil and gas exploration and production post-World War II. Coastal estuaries were judged to be in good to poor condition with concentrations of metals and pesticides in more than 40 % and concentrations of PAHs and PCBs in less than 1 % of coastal sediments exceeding levels suspected of causing biological effects. Within bay systems, steep gradients in contaminant concentrations were observed near population centers, agricultural activities, and industrial complexes. Highest concentrations of DDT, PCBs, PAHs, Ag, As, Cd, Hg, Pb, Sn, and Zn were found in sediments near population centers, agricultural lands, and industrial/military complexes. Natural petroleum seepage is the major source of hydrocarbons in north central Gulf of Mexico continental shelf/slope sediments.

Water quality is determined by the interaction of physiographic setting with human activities and is measured as the degree of eutrophication—the clarity of water—and the levels of contaminants. The patterns and trends in the Gulf of Mexico water quality are highly variable in space and through time. Assessments conclude that water quality in the Gulf of Mexico coastal environments is highly influenced by human activities, and the primary cause of degraded water quality is excess nutrients. The resulting eutrophication has led to low dissolved oxygen and increased chlorophyll a concentrations, diminished water clarity, and other secondary effects including toxic/nuisance algal blooms and loss of submerged aquatic vegetation. Overall, the ecological condition of the coastal northern Gulf of Mexico was judged as fair to poor, water quality was fair, and expressions of eutrophication were high.

Kennicutt, M.C. et. al.-- 17 pages, 3 figures, The Antarctic Roadmap Challenges (ARC) project identified critical requirements to deliver high priority Antarctic research in the 21st century. The ARC project addressed the challenges of enabling technologies, facilitating access, providing logistics and infrastructure, and capitalizing on international co-operation. Technological requirements include: i) innovative automated in situ observing systems, sensors and interoperable platforms (including power demands), ii) realistic and holistic numerical models, iii) enhanced remote sensing and sensors, iv) expanded sample collection and retrieval technologies, and v) greater cyber-infrastructure to process ‘big data’ collection, transmission and analyses while promoting data accessibility. These technologies must be widely available, performance and reliability must be improved and technologies used elsewhere must be applied to the Antarctic. Considerable Antarctic research is field-based, making access to vital geographical targets essential. Future research will require continent- and ocean-wide environmentally responsible access to coastal and interior Antarctica and the Southern Ocean. Year-round access is indispensable. The cost of future Antarctic science is great but there are opportunities for all to participate commensurate with national resources, expertise and interests. The scope of future Antarctic research will necessitate enhanced and inventive interdisciplinary and international collaborations. The full promise of Antarctic science will only be realized if nations act together, The authors recognize the financial support that made the Scan and ARC possible. The Council of Managers of National Antarctic Programs (COMNAP), the Tinker Foundation and the Scientific Committee on Antarctic Research (SCAR) provided the majority of the funding for this project including the costs of travel and participation of invited, non-COMNAP workshop attendees. In-kind support was provided by many COMNAP-Member national Antarctic programmes including Dirección Nacional del Antártico (DNA, Argentina), Australian Antarctic Division (AAD, Australia), Programa Antártico Brasileiro (PROANTAR, Brazil), Instituto Antártico Chileno (INACH, Chile), Polar Research Institute of China (PRIC, China), Instituto Antártico Ecuatoriano (INAE, Ecuador), Institut Polaire Français Paul Emile Victor (IPEV, France), Alfred Wegener Institute (AWI, Germany), National Institute of Polar Research (NIPR, Japan), Korea Polar Research Institute (KOPRI, Republic of Korea), Antarctica New Zealand (New Zealand), Arctic and Antarctic Research Institute (AARI, Russia), Spanish Polar Committee (CPE, Spain), British Antarctic Survey (BAS, UK), and the US National Science Foundation (NSF, USA)

International audience; The Southern Ocean is experiencing relentless change. The Antarctic and Southern Ocean community, represented by 75 scientists and policy-makers from 22 countries, recently met to formulate a collective vision on the priorities for Antarctic research for the next two decades and beyond. Here, we assess high-interest research areas related specifically to Southern Ocean life and ecology that, although not all retained as the 80 top priorities among the addressed scientific domains, are of considerable relevance to the biology and ecology of the Southern Ocean. As certain regions of the Southern Ocean ecosystems have witnessed abiotic and biotic changes in the last decades (e.g., warming, climate variability, changes in sea ice, and abundance of marine organisms), such an exercise was urgently needed. We concluded that basic biological information on the taxonomy of numerous organisms is still lacking in areas, such as the deep-ocean floor or the under-ice environments. Furthermore, there is a need for knowledge about the response and resilience of Antarctic marine ecosystems to change. The continuation of a long-term commitment and the development and use of innovative technology to adequately monitor the Southern Ocean ecosystems is required. Highlighting the most important Southern Ocean research topics allow the identification of the challenges and future requirements in technological development, and both research and funding strategies for the various stakeholders.

Fossil fuels are used throughout the United States Antarctic Program. Accidental releases of petroleum hydrocarbons are the leading source of environmental contamination. Since 1999 McMurdo Station has been the site of the most extensive environmental monitoring programme in Antarctica. Nearly 2500 surface soil samples were collected from 1999–2007 to determine the spatial “footprint” of petroleum hydrocarbons. Total petroleum hydrocarbons (TPH) concentrations were measured using a high-resolution capillary gas chromatographic method with flame ionization detection. Three distinct TPH patterns were detected: low molecular weight gasoline/JP5/AN8, residual weathered petroleum and an unresolved complex mixture of high molecular weight material. Overall TPH concentrations were low with 38% of the samples having TPH concentrations below 30 ppm and 58% below 100 ppm. Total petroleum hydrocarbon concentrations above 30 ppm are largely confined to the central portions of the station, along roads and in other areas where elevated TPH would be expected. Peripheral areas typically have TPH concentrations below 15 ppm. Areas of elevated TPH concentrations are patchy and of limited spatial extent, seldom extending over distances of 100 m. This environmental monitoring programme is ongoing and can serve as an example to other Antarctic programmes concerned with monitoring environmental impacts.

McMurdo Station is the logistics hub of the United States Antarctic Program, and localized environmental impacts have accompanied its nearly 50 years of continuous operation. An extensive collection of aerial photographs were used to map changes in the buildings, fuel storage tanks, roads, and physically disturbed areas at McMurdo Station since its establishment in 1956. From 1956 and continuing through the 1960s, rapid expansion of the station occurred. From 1970 until present, the area impacted by human activities has increased but at a much decreased rate. Current station operations are largely confined to areas that had already been impacted in the first 10–15 years of the station operations. The spatio-temporal perspective on McMurdo Station's growth provides a baseline from which future changes in the spatial extent of areas impacted by human activities can be monitored as required by the Protocol on Environmental Protection to the Antarctic Treaty.

Fixed-point and probabilistic sampling designs were compared to investigate which design best detected known contamination gradients in the marine ecosystem adjacent to McMurdo Station, Antarctica. The fixed-point sampling design included transects along historical contamination and physical disturbance gradients. The probabilistic sampling design used randomly selected hexagons spaced at 50 m intervals. In both designs, 15 stations were sampled over a small area (~1 km2) that extended from Winter Quarters Bay to Cape Armitage. Sediment quality triad components (sediment chemical contaminants, sediment toxicity, and a benthic index of biotic integrity) were measured to indicate chemical, toxicological, and biological effects. There were higher correlations between sediment quality triad components for the fixed-point sampling design than for the probabilistic design. The fixed-point design was better at detecting the intensity of alteration because disturbance of the marine ecosystem at McMurdo Station is localized within a small area. Based on these results, a limited fixed-point design with nine stations detected no significant change in macrofaunal community structure over a four year period from 2000–2004. However, the macrofaunal assemblages present in the contaminated portions of Winter Quarters Bay are indicative of a disturbed benthic community that has been subject to organic enrichment and toxic chemical exposure.

The early national expeditions to Antarctica were short-term, with science usually driven by the interests and opportunities of those scientists who were taken along. Some expeditions made important collections of both data and specimens that proved crucial in establishing why more research should be funded. However, in those early days, there was little coordination other than attempts to use similar instruments and protocols for collecting physical data such as magnetic and meteorological records. With our present-day sophisticated communications, aerial and oceanic surveys, regular access to scientific stations and ships across Antarctica and the Southern Ocean, and research on and around the continent by many nations, collaboration is essential to make the most of the resources. Establishing the Scientific Committee on Antarctic Research (SCAR) in 1958 proved to be a crucial step in developing the Antarctic scientific community and maximising the value of research across all scientific fields. In parallel to this, SCAR has also developed a major role as the primary scientific advisor to the Antarctic Treaty Parties on scientific and environmental matters.

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.

The molecular and stable carbon isotopic compositions of contaminant polycyclic aromatic hydrocarbons (PAHs) at McMurdo Station, Antarctica were analyzed in samples collected from land and sub-tidal area. PAHs in the study areas were characterized by high amounts of naphthalene and alkylated naphthalenes from petroleum products introduced by human activities in the area. Principal component analysis (PCA) of PAH composition data identified multiple sources of PAH contamination in the study area. Compositional assignments of origins were confirmed using compound specific stable carbon isotopic analysis.

Purification and isotope analysis methods were developed to accurately measure the stable carbon isotope ratio of individual PAHs in environmental samples. Sample extracts were separated into several fractions by column chromatography and were purified by high-performance liquid chromatographic and thin-layer chromatographic techniques. The mean recovery of the purification method for all compounds was approximately 80%. The purity of isolates was verified by GC/MS in the full scan mode. The accuracy and precision of the method were verified using authentic standards of known isotopic compositions. The standard deviation for multiple analyses ranged between 0.1 and 0.4%o for standard material and between 0.1 and 0.7%o for environmental extracts after purification. The purification and isotope analysis methods were used to discern the sources of PAHs in environmental samples using variations in stable carbon isotopic compositions of individual compounds. Itwas confirmed thatthe purification method effectively purifies environmental samples while retaining original isotopic signatures so that PAH content and stable isotopic compositions can be used to infer contaminant sources in complex environmental settings.

Molecular geochemical properties of crude oils and surface petroleum seeps from the southern part of the Gulf of Suez were evaluated. The characterizations of individual aliphatic, aromatic, and biomarker compounds were based on gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS) analyses. The results provided strong evidence for a close genetic association of these samples. The geochemical characteristics suggest an origin from Tertiary source rocks deposited in a normal marine environment that received continental runoff. The molecular signatures of the investigated samples were very similar to those of the Lower Miocene Rudeis Formation source rock in the southern Gulf of Suez. Further, biomarker fingerprints of the investigated oil seeps were compared with those of the Dead Sea asphalt, as well as the bitumen from some Egyptian mummies reported in the literature. The results demonstrate that oil seeps from the southern end of Gebel El Zeit were used by ancient Egyptians for embalming. © 2005 Wiley Periodicals, Inc.

Reported here are results of the compound specific carbon isotopic analysis (CSIA) of individual PCB congeners. This investigation was designed to determine the suitability of CSIA on this class of compounds in natural materials. Samples of duck tissue, duck liver, duck egg and grass carp were collected from the Housatonic River, Massachusetts, and compared with samples of fresh Aroclor® 1242, 1254,1260, and 1262. Twenty congeners were selected for isotopic analysis based on their ability to be separated chromatographically and their expected abundance in tissue samples. Animal tissue samples showed variable PCB patterns and abundances although all animals were expected to have been exposed to Aroclor® 1260. These characteristics are thought to be related to the structure of the food web or metabolic and physiological features of the individual animals. Grass carp samples had excellent correlation in the isotopic compositions of the congeners. Although the correspondence of δ 13 C in congeners from fresh Aroclor 1260 to congeners from tissue samples may not be expected to be identical, the patterns of similarity were very supportive of the maintenance of the isotopic signal into the food chain. The patterns observed in these and other samples suggest a fractionation process where residual congener pools can become progressively enriched while the congeners produced from degradation are more depleted. The isotopic patterns provide insight to degradation processes and into relative metabolic stability of the various congeners in different animals. The results of this study suggest that CSIA analysis of PCBs at natural abundance can provide significant insight into tracing these compounds through the natural environment. The data also suggest that tracking PCB mixtures may be possible using CSIA techniques after standard chromatographic matching or other fingerprinting techniques become blurred.

Compound specific isotope analysis (CSIA) has been used to measure the δ13C of selected individual polycyclic aromatic hydrocarbons (PAHs) from a crude oil that was exposed to enhanced microbial biodegradation. Twenty-one liters of a crude oil were introduced to series of separate 5 m×5 m wetland plots along the San Jacinto River, Texas. Smaller grids were established within each area to serve as control plots, plots for addition with nitrogen fertilizer, or as plots for addition with petroleum degrading microbes. Samples of randomly selected, oil impacted soils were collected at 4, 28, and 56 days after oil inoculation. These samples initially were analyzed using GC/MS for identification of PAH compounds. The initial results on the soils indicated a tendency for samples to shift from low and high molecular weight PAH compounds to eventually predominantly high molecular weight compounds. Fifteen specific PAH compounds, including two containing sulfur, were selected for compound specific isotope analysis based on chromatography and expected abundance in the soils. Five alkylated components, a dimethylnaphthalene, two trimethylnaphthalenes, a methyldibenzothiophene, and a dimethylphenanthrene, were seen to be best resolved and are suggested to be the most reliable for observations of isotopic changes during biodegradation. Isotopic variability during the treatment period follows patterns with an overall trend toward enrichment in the residual PAH pool of 2–8‰. All treatment grids, including the control, underwent isotopic alteration throughout the duration of the experiments. ANOVA testing of the isotopic results indicated that the control grids showed the smallest amount of changes over time, whereas the nutrient and microbe amended grids were not significantly different from each other. Although the trends on isotopic enrichments were predictable, the magnitude of changes was not. One additional finding indicated that time trials beyond 2-month periods were needed to determine if nutrient or microbial additions are advantageous for PAH biodegradation in wetland soils. The results of these tests highlight the importance of understanding the magnitude and direction of isotopic variations in PAH compounds as part of investigations aimed at tracing these compounds from potential sources.

Discovery of at least 100 subglacial lakes beneath the vast East Antarctic Ice Sheet has focused international attention on the challenges presented by the way we conduct science in such unique and inhospitable settings in an atmosphere of increasingly stringent environmental concerns. Exploration of subglacial environments will require careful and detailed planning, organization, and international cooperation. To this end, the Scientific Committee on Antarctic Research (SCAR) convened an international Group of Specialists (Subglacial Antarctic Lake Exploration Group of Specialists?SALEGOS) to develop a detailed assessment of the needs and critical milestones to be accomplished during the implementation of a subglacial exploration and research program. This paper surveys the progress and recommendations made by SALEGOS since its inception regarding the current state of knowledge of subglacial environments, technological needs and challenges, international management, the portfolio of scientific projects, and "clean" requirements for entry, observatory deployment, and sample retrieval.

Chlorophyll and carotenoid pigment distributions are used to describe spatial and temporal variations in phytoplankton biomass in the water column of the northeastern Gulf of Mexico (NEGOM) between the Mississippi River Delta in Louisiana and Tampa Bay in Florida from November 1997 through August 2000 and to infer seasonal changes in phytoplankton taxonomic composition. Chlorophyll a concentration in the water averaged 0.4 μg/l but ranged as high as 12 μg/l on nine cruises in this region during the 3 year period. The spatial distribution of chlorophyll a appeared to be controlled by riverine and estuarine input of nutrient-enriched freshwater. The Mississippi and Apalachicola River systems were the two main controlling features for the spatial distribution of chlorophyll in the NEGOM area. On average, the near-surface as well as subsurface waters near the Mississippi River–Mobile Bay outflow regions had the highest chlorophyll a concentrations of the study area during the 3 years. Subsurface waters near the Apalachicola River outflow region also had consistently high chlorophyll a concentrations during the nine cruises, even though the near-surface waters in this region did not. Algorithmic analyses of pigment composition indicated that prymnesiophytes, prokaryotes, cyanobacteria, diatoms, and pelagophytes were the major phytoplankton taxa on the NEGOM continental margin. On average, prymnesiophytes accounted for 25–40% of total chlorophyll in the water column over this continental margin during the 3 year period. Prokaryotes averaged 14–38% of chlorophyll a in the water column. Diatoms, which contributed 6–13% of chlorophyll a, were primarily found in inner shelf coastal waters. In contrast, prymnesiophytes and pelagophytes reached highest abundances in outer shelf and slope waters. Phytoplankton communities also differed vertically. Pelagophytes occurred in higher abundance in subsurface water, while dinoflagellates reached greater concentrations in near-surface waters.

In an attempt to examine the suitability of chemical fingerprinting methods in oil spill investigations, multiple parameters sensitive to both sources and degree of weathering were used to characterize spilled oil samples and to distinguish spilled hydrocarbons from sources unrelated to the spill in shoreline of the Gulf of Suez, Egypt. The characterizations of individual aliphatic and aromatic compounds were based on gas chromatography and gas chromatography/mass spectrometry analyses. The distribution of n-alkanes, polynuclear aromatic hydrocarbons (PAHs) and alkyl PAHs in the source oil and an oil slick collected 72 h after the spill were very similar. Major compositional changes observed in a weathered oiled sediment collected nine months after the spill from the shoreline at the spill location were consistent with previous studies. Molecular parameters of hopane and sterane biomarkers were very similar in the source oil, the spilled oil and the highly weathered oiled sediment. The similarity in biomarker compositions provided a strong evidence for a close genetic association of these samples. Ratios of C2-chrysenes/C2-phenanthrenes and C2-chrysenes/C2-dibenzothiophenes, the pregnane index (sum of the concentrations of C21 and C22 steranes over total concentration of steranes×100), and the tricyclic terpane index (sum of the concentrations of C19 and C30 tricyclic terpanes over total concentration of terpanes×100) clearly differentiated the refined oil products from crude oils. The composition of bilge oil indicated enrichment of late eluting steranes and terpanes and showed biomarker distributions similar to natural petroleum. The results further support that sterane and terpane biomarker analyses could differentiate oil samples of different sources even though they were sometimes indistinguishable in PAH and alkane compositions.

Offshore hydrocarbon production effects are localized in the Gulf of Mexico extending only 200 m from platforms. Effects are caused by the contaminant gradient or the fouling community on platform legs. To distinguish between contaminant and reef effects, meiofauna were sampled at production platforms (reef and contaminant effects), artificial reefs (reef, but no contaminant effects), platform removal sites (contaminant, but no reef effects), and controls (no contaminants or reef effects), and replicated in three blocks. The removal sites had higher concentrations of many contaminants than reef or control sites, but lower concentrations than platform sites. Reduced meiobenthic abundances and altered Harpacticoida community structure were primarily a function of reef effects, not contaminant effects. The habitat influence is likely a result of complex ecological interactions near platforms. The reef effect appears to be important in controlling meiofauna near platforms where contaminants are low because of drilling and production techniques used in the Gulf of Mexico. The finding that contaminants alone do not explain faunal patterns around offshore platforms indicates that future studies should include appropriate artificial reef control sites.

Evolving short-term (less than 5 yr) compositional changes in hydrocarbon charge from some Eugene Island Block 330 (EI-330) wells are demonstrated. Storage, analytical, and production artifacts are shown to be minimal. In some wells, compositions remain constant from 1985 to 1993, whereas in others in the same reservoir, significant changes are observed. In some cases, temporal variability is greater than spatial variability. Maximum temporal change is strongest for specific compounds: toluene and C 6 to C 9 normal alkanes, but is also observed to a lesser extent for higher-molecular-weight components (up to n -C 32 ). Principal coordinate analysis shows the highest degree of overall temporal compositional change over an 8-yr period in the shallowest wells where there is also evidence of biodegradation. Small temporal compositional changes are also observed in two deeper wells that are below the thermal window favorable for biodegradation. An exception is an unusual oil, where a very large increase in toluene, as well as smaller changes in a number of n -alkanes, was observed in 1993. The δ 13 C compound-specific isotopic signature of toluene, in addition to several other C 7 -C 8 compounds in this oil, yields convincing evidence that it is related to the same family as other EI-330 oils and unlikely to be due to a drilling or laboratory contaminant. Minor isotopic differences in other C 7 compounds (1.5‰) are consistent with extensive gas washing of this oil. The short-term compositional changes in EI-330 oils are attributed to gas washing, which causes overprinting of biodegraded oils with light n -alkanes in shallower GA and HB reservoirs where oils are currently being biodegraded in situ. Patterns of smaller changes in heavier compounds in both shallower and deeper wells are also consistent with this interpretation.

To determine the quality of sediments and extent of contaminant impacts, a Sediment Quality Triad (SQT) study was conducted at 36 sites in the Corpus Christi Bay, Texas, USA, system. Fifteen of the 36 sites were located near storm-water outfalls, but 13 other sites (i.e., industrial and domestic outfalls, oil field–produced water discharges, and dredging activity) and eight reference sites were also evaluated. Sediment samples were collected and analyzed for physical–chemical characteristics, contaminant concentrations (metals, polycyclic aromatic hydrocarbons [PAHs], polychlorinated biphenyls [PCBs], and pesticides), toxicity (amphipod and mysid solid phase and sea urchin pore-water fertilization and embryological development tests), and a benthic index of biotic integrity (BIBI) composed of 10 independent metrics calculated for each site. This large data matrix was reduced using multivariate analysis to create new variables for each component representing overall means and containing most of the variance in the larger data set. The new variables were used to conduct the correlation analysis. Toxicity was significantly correlated with both chemistry and ecological responses, whereas no correlations between the benthic metrics and sediment chemistry were observed. Using the combined information from the SQT, four of the five most degraded sites were storm-water outfall sites. Although estuaries are naturally stressful environments because of salinity and temperature fluctuations, this ecosystem appears to have been compromised by anthropogenic influences similar to what has been observed for other heavily urbanized bay systems along the Texas and Gulf coast.

Petroleum seep mussels are often exposed to high hydrocarbon concentrations in their natural habitat and, thus, offer the opportunity to examine the relationship between parasitism, disease and contaminant exposure under natural conditions. This is the first report on the histopathology of cold-seep mussels. Seep mussels were collected by submersible from four primary sites in the Gulf of Mexico, lease blocks Green Canyon (GC) 184, GC-234, GC-233, and Garden Banks 425 in 550–650 m water depth. Five types of parasites were identified in section: (1) gill “rosettes” of unknown affinity associated with the gill bacteriocytes, (2) gill “inclusions” similar to chlamydia/rickettsia inclusions, (3) extracellular gill ciliates, (4) body “inclusions” that also resemble chlamydial/rickettsial inclusions, and (5) Bucephalus-like trematodes. Comparison to shallow-water mytilids demonstrates that: (1) both have similar parasite faunas; (2) seep mytilids are relatively heavily parasitized; and (3) infection intensities are extremely high in comparison to shallow-water mytilids for Bucephalus and chlamydia/rickettsia. In this study, the lowest prevalence for chlamydia/rickettsia was 67%. Prevalences of 100% were recorded from three populations. Bucephalus prevalence was ⩾70% in three of 10 populations. The parasite fauna was highly variable between populations. Some important parasites were not observed in some primary sites. Even within primary sites, some important parasites were not observed in some populations. Bucephalus may exert a significant influence on seep mussel population dynamics. Forty percent of the populations in this study are severely reproductively compromised by Bucephalus infection. Only a fraction of petroleum seep mussel populations are maintaining the entire beta-level population structure of this species. Variation in two parasites, gill ciliates and Bucephalus, explained most of the variation in PAH body burden between mussel populations. PAHs are known to be sequestered preferentially in gametic tissue. Bucephalus would be expected to reduce overall body burden, at high infection intensities, by replacing gametic tissue. PAH concentrations exceeded 1 ppm in 4 of 9 populations, a ratio significantly higher than the 8 of 30 mussel locales in the NOAA Mussel Watch Program. Only five Mussel Watch locales exceeded the highest value for a petroleum seep population. Digestive gland and gill tissue atrophy were not significantly correlated with PAH body burden, even though some populations were characterized by body burdens exceeding 1 ppm, suggesting that seep mussels may not be as sensitive to PAH exposure as are some shallow-water mytilid populations.

The largest of the three scientific bases operated by the United States Antarctic Program (USAP), McMurdo Station has experienced numerous localised environmental impacts over its fifty-plus years of occupation. Since 1999 a long-term environmental monitoring programme has examined human impacts in the terrestrial and marine environments in proximity to the station. The programme was developed from an assessment of system attributes amenable to monitoring, an understanding of the nature of historical and ongoing environmental impacts and a consideration of the spatial scales over which impacts would be expected. While station operations continue to impact the local environment, the ‘footprint’ of human disturbance observed at McMurdo Station today primarily represents vestiges of historical practices. In the terrestrial environment, the impact of human activities is typically confined to within a few hundred meters of the station and contamination by petroleum hydrocarbons and metals are found where expected. This ongoing monitoring programme represents an important step in understanding how a legacy of human activities can affect the local environment surrounding an Antarctic scientific base. The developed framework is suitable for adaptation to other Antarctic research stations with similar physical settings and mix of human activities. The programme has provided, and will continue to provide, crucial baseline environmental information which can serve as the scientific basis for future assessments of the impact of human activities at McMurdo Station over the next 50 years.

Thermogenic (structure II) gas hydrate is abundant on the Gulf of Mexico continental slope because hydrocarbon gases from a deep, hot subsurface petroleum system vent prolifically to the sea floor in regions of low temperatures and high pressures that are within the gas hydrate stability zone (GHSZ). The distribution of gas hydrate is controlled by geologic structure. Molecular distributions of gases venting from hydrate-bearing sediments show that gas hydrate decomposition is not significant in comparison to flux from the subsurface petroleum system. Structure II gas hydrate is commonly encountered, and contains C 1 -C 5 hydrocarbons that crystallize from relatively unaltered vent gases. Most surficial structure II gas hydrate sites (0-6 m) studied from the ∼540-1930 m water depth range are stable, and gas hydrate is thought to be accumulating to considerable depth in sediment because of the prolific, ongoing venting of gas. Bacterial methane hydrate is also abundant in the Gulf of Mexico. A leaky petroleum system is the larger contributor of thermogenic greenhouse gases to the ocean and atmosphere from the Gulf of Mexico, not gas hydrate decomposition. Gas hydrate crystallization in the Gulf of Mexico sequesters large volumes of greenhouse gases in sediments, deforming soft sediments, and is proposed as an agent that stabilizes or dampens climatic change under the present climatic regime.

Various biomarkers were used to determine the exposure of fish (Arius felis and Micropogon undulatus) from Galveston Bay (GB), Texas, USA to organic contaminants. Sediment levels of polynuclear aromatic hydrocarbons (PAHs) in GB ranged from 81 to >1000 ng/g and polychlorinated biphenyls (PCBs) were

Une synthese des articles portant sur la reponse du benthos a la pollution des mers parait indiquer que les communautes constituees de l'endofaune macroscopique et de la meiofaune ont des profils repetables de reponse a la contamination des sediments qui sont generalement observables a des niveaux taxonomiques eleves (meme a celui du phylum). Ces reponses semblent etre alimentees a la fois par des caracteristiques ecologiques et physiologiques intrinseques des taxons superieurs : p. ex., les crustaces (particulierement les amphipodes et les harpacticoides) et les echinodermes sont sensibles aux substances toxiques tandis que les polychetes, les oligochetes et les nematodes (particulierement les depositivores non selectifs) tirent parti de l'enrichissement en matieres organiques. L'application de ce modele aux resultats obtenus dans le cadre du projet GOOMEX fait intervenir la toxicite et l'enrichissement en matieres organiques comme facteurs. Les resultats des tests de toxicite et les rapprochements entre des concentrations observees de contaminants et des niveaux d'effets connus paraissent indiquer que les metaux sont les principaux agents de la toxicite. Nous parvenons aux conclusions suivantes : 1) les forages produisent des effets durables dans l'environnement sedimentaire autour des plates-formes de production gaziere, 2) les effets combines de la toxicite et de l'enrichissement en matieres organiques sont probablement a l'origine des reponses facilement detectables de la meiofaune benthique et de l'endofaune macroscopique jusqu'a 100-200 m et 3) le fait de ne pas detecter de signes d'exposition ou d'effets subletaux chez le poisson et la plupart des grands invertebres est le resultat de leur grande mobilite par rapport a l'echelle des changements dans l'environnement et de leur exposition negligeable aux hydrocarbures et a d'autres contaminants.

Les caracteristiques geochimiques des sediments adjacents a trois plates-formes de production (par 22 a 150, d'eau) dans le nord-ouest du golfe du Mexique ont ete determinees a partir de la presence de l'ouvrage, de la quantite et du type de materiaux liberes par l'ouvrage, et du contexte hydrographique local. Les sediments proches des plates-formes ( 80 m), les concentrations des metaux a l'etat de traces dans les sediments n'ont pas varie pendant des annees. Il s'est avere que quelques metaux (Pb, Cd) se sont constamment accumules dans les sediments depuis la mise a l'eau de la plate-forme.

The Gulf of Mexico Offshore Operations Monitoring Experiment (GOOMEX) is a three-phase study to test and evaluate a range of biological, biochemical, and chemical methodologies to detect and assess chronic sublethal biological impacts in the vicinity of long-duration activities associated with oil and gas exploration and production. A chronic impact is defined as an effect on the biota caused by exposure to the long-term accumulation of chemicals in the environment. The basic program, comprising four field activities over a 2-yr period, was designed to detect nearfield impacts and contaminant gradients extending out from each site. Five test sites were evaluated and three selected as most appropriate for long-term study: MU-A85, MAI-686, and HI-A389. The sampling design included a radial pattern with stations at 30-50, 100, 200, 500, and 3000 m distance and employed a dose-response model to test the hypotheses that biological, chemical, and biochemical variations are due to platform-derived contaminants. Study components included contaminant (trace metals and hydrocarbons) analysis in sediments, pore waters, and biological tissues; assemblage analysis of benthic meiofauna, infauna, and epifauna, assessment of community health based on life history and reproduction studies; and the induction of detoxification responses. Resume : L'Experience de surveillance des operations extracotieres dans le golfe du Mexique, dite « GOOMEX », est une etude en trois etapes visant a verifier et a evaluer une gamme de methodes biologiques, biochimiques et chimiques de detection et d'evaluation des effets biologiques subletaux chroniques au voisinage d'activites de longue duree, associees a la prospection et a la production de petrole et de gaz. Un effet chronique s'entend d'un effet sur le biote d'une exposition a l'accumulation prolongee de produits chimiques dans l'environnement. Le programme de base, comportant quatre activites sur le terrain en 2 ans, vise a detecter les effets des contaminants a proximite de chaque site et leurs gradients en s'en eloignant. Cinq sites d'essai ontete evalues, et trois ont ete choisis comme les plus appropries pour une etude a long terme : MU-A85, MAI-686 et HI-A389. Dans le plan d'echantillonnage de geometrie radiale, ou les stations etaient reparties a des distances de 30-50, 100, 200, 500 et 3 000 m, le modele dose-reponse retenu visait a verifier les hypotheses selon lesquelles les variations biologiques, chimiques et biochimiques tiennent aux contaminants de plate-forme. Les volets de l'etude comprenaient l'analyse des contaminants (hydrocarbures et metaux a l'etat de traces) dans les sediments, les eaux interstitielles et les tissus biologiques, l'analyse d'assemblages de la meiofaune, de l'endofaune et de l'epifaune benthiques, l'evaluation de la sante du milieu d'apres des etudes du cycle biologique et de la reproduction et l'induction de reponses de detoxification. (Traduit par la Redaction)

Whole oil GC-MS was used to characterize selected polynuclear aromatic hydrocarbons (PAH) in a suite of marine crude oils derived from source rocks deposited under different conditions. The selected PAH consist primarily of 2- and 3-ring aromatic hydrocarbons, including naphthalenes (to C 4 ), fluorenes (to C 3 ), phenanthrenes (to C 4 ) and dibenzothiophenes (to C 3 ), as well as several 4- and 5-ring compounds. Concentrations of the selected PAH range from 2294 to 129,170 ppm and typically comprise between 1% and 20% of the total C 12+ aromatic fraction. PAH compositions in all source types are dominated by naphthalenes. These compounds comprise between 41.9% and 88.9% of the total PAH measured. The greatest difference between oils lies in the relative abundance of dibenzothiophenes. Their abundance rivals that of naphthalenes in the carbonate oils (up to 41.7% of total PAH) but is exceedingly low in the paralic oils ( < 2.1% of total PAH). These differences, which reflect differences in clastic content, Eh-pH, and availability of reduced sulfur in the source rock depositional environment, are captured in the ratio DBT/P, calculated as the sum of all dibenzothiophenes relative to phenanthrenes. DBT/P is greater than 1.0 in most carbonate-sourced oils but ranges between 0.08 and 0.18 in the paralic-sourced oils. Siliciclastic-sourced oils are intermediate, with values ranging from 0.14 to 0.87 (average 0.40). All oils show a predominance of alkylated PAH homologues over the unsubstituted parent, however, the maximum degree of alkylation (the most abundant alkylated homologues within any given PAH series) varies. Carbonate-sourced oils show a high degree of alkylation, often maximizing at C 3 or C 4 , while paralic-sourced oils generally exhibit a lower degree of alkylation in which the C 1 or C 2 isomers predominate. Siliciclastic-sourced oils are intermediate. with alkylation maximizing between the C 2 and C3 isomers. We propose that these alkylation trends reflect differences in the PAH precursor moieties in source kerogens and/or variations in the thermal history of the source types, i.e., milder thermal history for the carbonate oils relative to paralic and siliciclastic oils.

Pigment and stable isotopic compositions of suspended particulate organic matter (SPOM) were determined in several estuaries along the Texas coast of the Gulf of Mexico. Analysis of the composition of accessory pigments suggested that the phytoplankton taxa varied among these bays. The δ 13 C values of SPOM, lipids, and chlorophylls in these bays varied from − 18 to − 27, − 20 to − 31, and − 18 to − 31‰, respectively. The δ 13 C values of SPOM, lipids, and chlorophylls, and the pigment composition together suggest that the 13 C-depleted organic matter in Corpus Christi Bay in June 1992 resulted from the fixation of 13 C-depleted CO 2 derived from riverine water or in situ remineralization of organic matter. The lipids and chlorophyll a isolated from the nearly freshwater system of Aransas Bay in 1992 were 13 C-enriched and most likely derived from local phytoplankton production. The δ 13 C values of SPOM, lipids and chlorophylls in the bays where salinities were closest to that of seawater were in the range expected for marine phytoplankton, i.e., − 18 to − 24‰. The δ 15 N values for SPOM, lipids, and chlorophyll a ranged from + 4 to + 14‰ with most between + 6 to + 10‰. These values are similar to the SPOM of marine systems and indicate a common source of nitrogen throughout the estuaries.

Data from a regional surface geochemistry survey in the North Viking Graben have been studied using principal components analysis, which allows process-specific fingerprints from extremely small amounts of thermogenic hydrocarbons in sea-bed sediments to be isolated and separated from data noise. Although the North Viking Grahem has thick, unfaulted Tertiary sediments with no obvious seepage conduits, the detected signals correlate with proved hydrocarbon accumulations in the area.

Pure individual and mixed pigment standards were distributed among Joint Global Ocean Flux Study (JGOFS) pigment analysts to estimate the variability of their spectrophotometric and chromatographic systems. To monitor the integrity of the pigments during the comparison exercise, chlorophyll and carotenoid standards were archived and periodically analyzed by high-performance liquid chromatography (HPLC). Pigment standards stored in the dark under nitrogen at − 20 °C were found to be stable for periods of at least one year. Results from three separate intercalibration exercises document a better agreement for spectrophotometric analyses than for HPLC. For the spectrophotometric comparisons, 90% of the pigments analyzed by participant laboratories were within ± 6% of the mean “consensus” values. By contrast, 65 and 85% of the laboratories agreed to within ± 10 and ± 20%, respectively, when chromatographic analyses were compared. Chlorophyll absorption measurements obtained with a diode array-type spectrophotometer were 6–9% lower than those obtained with monochromator-type spectrophotometers. These underestimates probably result from chlorophyll fluorescence contamination associated with the optical configuration of the diode array spectrophotometer. It was also determined that HPLC methods which are not capable of separating monovinyl chlorophyll a from divinyl chlorophyll a can produce 15–25% overestimates of total chlorophyll a concentration in Prochlorococcus -dominated oceanic waters. A simple dichromatic approach is described for eliminating this variable source of error caused by co-elution of these structurally-related pigments. The use of internal standards and periodic calibration checks with external standards is highly recommended for improving analytical performance.

Organic geochemistry played a major role in the environmental assessments conducted following the Exxon Valdez oil spill, which occurred on March 24, 1989, and released about 258,000 bbls (41 million liters) of Alaska North Slope crude oil into Prince William Sound. Geochemical analyses of more than 15,000 sediment, tar, and biological samples and about 5000 water samples provide the largest database yet collected on oil-spill chemistry, and we review the results here. The marine environment of the Sound has a complex background of petrogenic, pyrogenic, and biogenic hydrocarbons from natural and anthropogenic sources. Geochemical evaluation of the fate and effects of the spilled oil required that this oil and its residues be distinguished from the background. A variety of molecular and isotopic techniques were employed to identify various hydrocarbon sources and to distinguish quantitatively among mixed sources in the samples. Although the specific criteria used to distinguish multiple sources in the region affected by the Exxon Valdez spill are not necessarily applicable to all spill situations, the principles that governed their selection are. Distributions of polycyclic aromatic hydrocarbons (PAH) and dibenzothiophenes distinguish Exxon Valdez oil and its weathered residues from background hydrocarbons in benthic sediments. Ratios of C 2 -dibenzothiophene C 2 -phenanthrene and C 3 -dibenzothiophene C 3 -phenanthrene were particularly useful. Carbon isotopes and terpane distributions distinguished Exxon Valdez residues found on shorelines from tars from other sources. Diesel and diesel soot were identified by the absence of alkylated chrysenes and a narrow distribution of n-alkanes, whereas pyrogenic products were distinguished by the dominance of 4- to 6-ring PAH over 2- to 3-ring PAH and by the dominance of non-alkylated over alkylated homologues of each PAH series. The presence of 18α(H)-oleanane in benthic sediments, coupled with its absence in Exxon Valdez oil and its residues, confirm another petrogenic source. Results of geochemical studies suggest that the petrogenic component in the background of benthic sediments is derived from oil seeps in the eastern Gulf of Alaska. In 1990 and 1991, Exxon Valdez residues, generally forming a small increment to the pre-spill background, were found to be only sporadically distributed in some shallow, near shore sediments adjacent to shorelines that had been heavily oiled in 1989. In 1994, occurrences of Exxon Valdez tars on shoreline surfaces were rare, although residues could be found buried in shoreline sediments at some isolated locations along the spill path where they were protected from wave action. Spilled oil residues collected 16 months after the spill were degraded, on average, by nearly 50%. Shoreline residues from sources other than the spill were also identified and are widespread throughout the Sound. These residues include (1) geochemically distinct tars and oils imported from California oil fields to Alaska for fuel and construction purposes prior to the discovery of the Cook Inlet and North Slope oil fields, (2) diesel and diesel soot, and (3) more highly refined products. Of the more than 2700 chemical analyses of biological samples of higher life forms (fish, birds, and mammals) about 150 (6%) indicate recognizable residues of Exxon Valdez oil, which were identified by their distribution of polycyclic aromatic hydrocarbons (PAH). Most of these samples (138) were collected in 1989 and most were associated with external surfaces or the gastrointestinal tract. Rarely do internal tissues or fluids contain recognizable fingerprints of spilled oil. This observation includes samples from marine mammals that were visibly oiled externally. Other hydrocarbon sources, including diesel and a non-petroleum artifact that occurs when concentrations of individual PAH are at or near their method detection limit, are also identified in biological samples.

Benzo[a]pyrene (BaP) elicited a dose-response induction of hepatic CYP1A1 gene expression in killifish characterized by increased CYP1A1 mRNA levels, ethoxyresorufin O-deethylase (EROD) and aryl hydrocarbon hydroxylase (AHH) activities. There were marked differences in the maximally-induced EROD (1529 pmol mg−1min−1) and AHH (377 pmol mg−1 min−1) activities and these differences were observed at all ume points and at concentrations of BaP from 1 to 50 mg/kg. Treatment of killifish with BaP did not significantly affect binding of [125I]epidermal growth factor (EGF) to hepatic plasma membranes containing the EGF receptor. There was a dose-dependent increase in formation of DNA adducts in killifish treated with 1-50 mg/kg of BaP. Two-dimensional thin-layer chromatographic analysis of the [32P] labeled adducted nucleoudes revealed one major spot. In a time course study over a period of 2–14 days, the relative DNA adduct levels in fish treated with 5 mg/kg BaP were constant. The most sensitive indicator of exposure to BaP was the dose-dependent formation of biliary metabolites in which there was a > 40-fold increase (compared to untreated animals) in fluorescent metabolites formed at the lowest dose of BaP (1 mg/kg) used in this study. Killifish expressed relatively high levels (203 fmol/mg) of the nuclear aryl hydrocarbon (Ah) receptor which was isolated from nuclear extracts of fish treated with [3H]-2,3,7,8-tetrachlorodibenzo p-dioxin. The nuclear Ah receptor complex sedimented at 6.0 S which was similar to that observed in other animal species. Based on their CYPIA1 induction response to BaP and Ah receptor levels, the results of this study indicate that killifish are highly Ah-responsive.

Polycyclic aromatic hydrocarbons (PAH), polychlorinated biphenyls (PCBs), pesticides, and trace metal concentrations in McMurdo Sound and Arthur Harbor, Antarctica, sediments and marine biota are reported. Biomarkers of contaminant exposure, biliary metabolites and EROD assays, were also measured. Hydrocarbon and trace metal contamination are generally limited to within hundreds of meters of human settlements. Local releases of fossil fuels, disposal of waste materials, and aging of ship and station structures contribute to contamination. High concentrations of PCBs were detected in sediments (250-4200 ng g{sup -1}) and organisms (up to 420 ng g{sup -1}) from Winter Quarters Bay (WQB). Trace metal and PAH sediment concentrations rarely exceed levels known to cause toxic effects in marine organisms, whereas PCBs in WQB often do. Biological responses to exposure include the formation of PAH metabolites and the inducement of the P4501A detoxification system in fish. Induction of EROD activity in in vitro rat hepatoma H4IIE cell bioassays by tissue extracts correlated with known levels of PCB contamination in invertebrate tissues. Local sources of contaminants greatly exceed those attributable to long-distance atmospheric transport. 31 refs., 4 figs.

A geochemical study of 36 oils from the northern Timan-Pechora Basin indicates four oil types. Two types of sulfur-rich oils (range 1.4–2.5% sulfur) can be identified on the basis of both gross and molecular properties. These oils are found primarily in the Toravey, South Toravey and Roman Trebs fields. They are also present in the offshore Prirazlom field, thereby extending the geographic range of sulfur-rich oils into the Pechora Sea. Another oil type exhibits a distinctive odd predominance of n -alkanes in the range n -C 11 through n -C 19 and a diminished abundance of n -alkanes greater than C 19 . These oils, which occur primarily in the A. Titov and Labogan fields, show striking similarities to Ordovician-sourced oils from other Paleozoic basins throughout the world. Their biomarker and isotopic compositions, for example, bear a strong resemblance to oils generated from the Ordovician Viola Limestone of the Anadarko Basin. The fourth oil type occurs in the northwestern portion of the basin in the Khylchuyu field. Some mixing between the various types is evident. Light oils and condensates of the Peschano-ozyor, Shtokman, Rusanov and Vasilkovo fields cannot be readily assigned to any of these four types. The Upper Devonian Domanik Formation is generally thought to be the major oil source in the Timan-Pechora Basin. However, geochemical characteristics of Timan-Pechora oils analyzed do not closely resemble those of other Upper Devonian-source oils, such as those generated from the Duvernay Formation of Western Canada. These differences might reflect variations in the organic matter preserved in the two basins during the late Devonian or may indicate that the Upper Devonian is not an important hydrocarbon source in the northern Timan-Pechora region. The results suggest that the Timan-Pechora oils analyzed are generated from Paleozoic carbonate or calcareous shale source rocks, at least one of which appears to be of Ordovician age.

The carbon isotopic composition of the marine diatom Phaeodactylum tricornutum (δ13Cp) was measured over a series of growth rates (μ) in a continuous culture system in which both δ133CCO2 and [CO2]aq were determined. In accord with theory, a linear relationship was found to exist between μ/ [CO2]aq and ɛp (≡1000(δ13CCO2 − δ13Cp)/1000 + d δ13Cp), the biological fractionation associated with carbon fixation. The range of [CO2]aq in the continuous culture system was 13–31 μmol kg−1. Measurements of δ13CCO2 and [CO2]aq in the mixed layer of the equatorial Pacific and estimates of δ13Cp obtained from the δ13C of chlorophyll a combined with the regression line fit to the P. tricornutum data give phytoplankton growth rates that are in excellent agreement with those estimated via other techniques. Measurement of ɛp and [CO2]aq in the field can provide an estimate of in situ phytoplankton growth rates without the potential artifacts associated with incubation methodologies. These findings also suggest that accurate estimations of ancient CO2(aq) concentrations will require knowledge of both ɛp and phytoplankton growth rate.

Sediment characteristics on the Mississippi-Alabama shelf are dynamic and change in time scales varying from less than 6 months to more than 2 years. Some sediment properties varied by more than an order of magnitude over the 2, years of study. Individual sediment components vary independently and can be described as cyclic, steadily increasing, random, or unchanging. Many of the variations are linked to influxes of terrestrial material associated with river discharge, non-point terrestrial run-off and/or outflow from coastal environments during storm events. Carbonate content and grain size varied from clay-rich fine-grained sediments associated with the Mississippi River delta complex to coarse-grained shell hash on the eastern shelf. Organic carbon content, extractable organic matter and hydrocarbons were elevated in sediments near the Mississippi River delta complex and in a band of sediments between the 100 and 200 m isobaths. TOC values in excess of 2% were observed, however, average TOC concentrations were 0.8%. Hydrocarbons in sediments were present at low concentrations and are a mixture of biological and petroleum hydrocarbons. Terrestrial plant biowaxes were ubiquitous and, when present, petroleum hydrocarbons were associated with elevated barium concentrations. Aromatic hydrocarbon compositions were indicative of unprocessed petroleum and were dissimilar to combustion PAH detected in adjacent bays. PAH concentrations were as much as six times lower than adjacent coastal sediment concentrations. Spatial and temporal heterogeneity in sediments is due to variations in inputs, preservation, diagenetic alteration and oceanographic setting.

The Antarctic Treaty System, acknowledged as a successful model of cooperative regulation of one of the globe's 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 region's 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.