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Although great progress has been made to advance the scientific understanding of oil spills, tools for integrated assessment modeling of the long-term impacts on ecosystems, socioeconomics and human health are lacking. The objective of this study was to develop a conceptual framework that could be used to answer stakeholder questions about oil spill impacts and to identify knowledge gaps and future integration priorities. The framework was initially separated into four knowledge domains (ocean environment, biological ecosystems, socioeconomics, and human health) whose interactions were explored by gathering stakeholder questions through public engagement, assimilating expert input about existing models, and consolidating information through a system dynamics approach. This synthesis resulted in a causal loop diagram from which the interconnectivity of the system could be visualized. Results of this analysis indicate that the system naturally separates into two tiers, ocean environment and biological ecosystems versus socioeconomics and human health. As a result, ocean environment and ecosystem models could be used to provide input to explore human health and socioeconomic variables in hypothetical scenarios. At decadal-plus time scales, the analysis emphasized that human domains influence the natural domains through changes in oil-spill related laws and regulations. Although data gaps were identified in all four model domains, the socioeconomics and human health domains are the least established. Considerable future work is needed to address research gaps and to create fully coupled quantitative integrative assessment models that can be used in strategic decision-making that will optimize recoveries from future large oil spills.

The northwest (NW) Gulf of Mexico is marked by strong seasonal patterns in regional and mesoscale circulation and variable effects of riverine/estuarine discharge, which influence distributions of nutrients, phytoplankton biomass and primary production. During a series of five cruises in the NW Gulf of Mexico in 1993 and 1994, an extensive data set was collected including nutrients, phytoplankton biomass (chlorophyll a), and photosynthesis–irradiance (P–E) parameters. Primary production was estimated using P–E parameters in conjunction with profiles of biomass and irradiance. Relatively high biomass and primary production were observed in inner shelf waters during spring conditions of high river discharge. This was attributed to the retention of biomass and nutrients on the shelf by the combination of high river outflow and a westward flow along the inner shelf with consequent onshore Ekman component. During summer, when surface currents shifted towards the north and east, values of nutrients, biomass and primary production were relatively high east of Galveston Bay and decreased outward from the coast. This pattern was apparently a consequence of nutrient inputs from riverine, upwelling and benthic sources. Nutrients, biomass and productivity in the western portion of the study area in summer were generally lower as a result of the upcoast flow of oligotrophic offshore water. Inter-annual variability was observed between November 1993 and 1994 with higher biomass and productivity occurring in November 1993. This was partially attributed to higher river discharge prior to November 1993, retention of biomass and nutrients by the downcoast flow along the inner shelf, and possibly, injection of nutrients onto the shelf at the shelf break. Our findings demonstrate that the interaction of circulation and availability of light and nutrients are largely responsible for variations in primary production. Nitrogen appeared to be the primary limiting nutrient, however, a potential for phosphate limitation was also observed particularly during periods of higher river discharge. Light availability was a critical variable during the fall and winter months, when higher primary production was restricted to shallow waters where vertical mixing was constrained by bottom topography. In deep waters, counteractive changes in nutrient and light availability apparently resulted in minor temporal variation between seasons. The annual carbon production in the Louisiana–Texas (LATEX) continental shelf region was estimated to be 159 g C m−2 year−1, which is within the range of prior estimates for this region. Given that the area of the study region was approximately 140,000 km2, this would be equivalent to an areal carbon production of about 22.2 million metric tons.

During April and May 1993, the typical south and southwestward directed flow over the Texas shelf interacted with current rings located just off the Texas shelf in the Gulf of Mexico. The rings, a cyclone/anticyclone eddy pair, were oriented such that water was transported onto the shelf between the rings and water was drawn from the shelf on the rings' offshore-directed limbs. A shelf convergence zone transported water to the shelf edge where some of the water became entrained between the cyclone/anticyclone pair. Active shelf-slope exchange such as that seen in the April-May 1993 episode may be a more typical example of synoptic shelf circulation than the general circulation pattern suggested by averaging multiannual observations. Nutrient and particle distributions were influenced by the interactions of the shelf current with the rings. Where the cyclonic and anticyclonic eddies directed flow off the shelf, particles were transported off the shelf. Additionally, particles in the bottom nepheloid layer were transported off the shelf in the shoreward limb of the cyclone, even though currents in this limb were directed along the isobaths. Nutrient concentrations, hence nutrient fluxes, were generally low in near-surface waters every-where in the study area. At mid-depth and in near-bottom waters, nutrient fluxes were highest near the cyclone because of higher current speeds in this feature and higher nutrient concentrations at depth.

In May 1986, we investigated processes contributing to the unique characteristics of oceanic fronts in the western Mediterranean Sea. Simulated in situ measurements of 14C-based primary production were made in conjunction with precise chemical, physical and optical analyses coordinated with remote sensing. Eight transects consisting of 4–7 vertical stations were made across density fronts associated with the Almeria Gyre and the Algerian Current. A model was developed to describe the relationship between chlorophyll-specific primary production (mg C mg Chl−1h−1) and depth in the water column. Model regressions for Modified Atlantic Water (MAW, salinity = 36.5–36.8), Mediterranean water (37.6–38.0), and intermediate frontal water were not significantly different, and a single equation based on the pooled data was used to estimate regional production. East of 0° longitude, primary production integrated over the upper 100 m (ΣP) in Mediterranean water was 0.47 g C m−2 d−1 (range0.33–0.60) and 0.88 g C m−2 d−1 (range 0.50–1.30) in MAW and frontal regions. higher ΣP in MAW and frontal regions could be attributed partially to higher integrated chlorophyll, although locationof the chlorophyll maximum higher in the water column was also an important contributing factor. The chlorophyll maximum was shallower in MAW than in Mediterranean-type water. The depth of chlorophyll maxima generally coincided with the nitracline rahter than isopycnal surfaces, supporting the view that chlorophyll distributions and primary production were primarily influenced by nutrient supply.

Analysis of sulfur and oxygen isotopic compositions of dissolved sulfate from a vertical water profile in the anoxic, hypersaline Orca Basin provides important constraints upon the provenance of the sulfate. Results support a dissolution origin of the brine from a Jurassic evaporitic salt. However, mass balance considerations and the observed minima in the vertical δ18O-sulfate profile at the brine-seawater interface are not reconcilable with only a simple two box brine-seawater mixing model. Instead, the data imply contributions from the oxidation of sulfides.

Hydrogen peroxide, micronutrients, chlorophyll, primary production and light were measured at a series of stations in the western Mediterranean Sea. Hydrogen peroxide concentrations greater than 100 nmol 1−1 were found in this region. There was a significant relationship between hydrogen peroxide and primary production rates near the surface where the light intensity was high. This link between hydrogen peroxide and biological activity may have resulted from photochemically reactive organic compounds that were excreted during photosynthesis or from the direct biological production of hydrogen peroxide. Elevated concentrations were not found in the deep chlorophyll maximum however, which indicates that high light intensities are necessary for biogenic hydrogen peroxide production in this area. Hydrogen peroxide concentrations decreased much more slowly with depth than did light. The decoupling of light and hydrogen peroxide must have been due to a combination of a slow decay rate and rapid vertical transport. However, simple calculations indicate that eddy diffusion alone could not have transported enough hydrogen peroxide to produce the effects that were seen. Large anomalies in the concentration profiles that were detected in frontal regions indicate that hydrogen peroxide can be a useful tracer of vertical transport in the upper ocean. The size of the anomalies appears to be coupled to the salinity gradient across the front, which drives the frontal circulation.

The composition of light hydrocarbon gases in the Orca Basin, an anoxic, hypersaline intraslope depression on the continental slope of the northern Gulf of Mexico, indicates that both methane and ethane are biogenic in nature with a C1(C2 + C3) ratio of 730 and a δ13C of methane of −73%. relative to the PDB standard. The concentrations of methane (750 mM) and ethane (1300 mM) in the Orca Basin brine are higher than any other marine anoxic basin. These high levels result not from high rates of productivity, but from the long residence time of the brine in the basin, due to its high stability toward mixing with overlying seawater (Δσ1ΔZ = 3.2m). Both methane and ethane show well mixed distributions in the brine. These distributions probably result from convective mixing of the isohaline brine pool due to normal heat flow from the basin sediments. Methane and ethane maxima above the pycnocline at the brine/seawater interface reflect in situ production and/or consumption in the aerobic water column. Concurrent maxima in suspended particulate material distributions in this region suggest methane may be produced there in anaerobic microenvironments associated with the suspended matter. Reduced rates of anaerobic decomposition (including sulfate reduction) in the brine sediments are inferred from preserved Sargassum fronds in the sediments, vertical sulfate profiles in most cores, and the sediment organic carbon content which is two to three times higher in sediments below the high salinity brine than in the normal Gulf sediments nearby.