The Continental Margins Program in Georgia

From 1984 to 1993, the Georgia Geologic Survey (GGS) participated in the Minerals Management Service-funded Continental Margins Program. Geological and geophysical data acquisition focused on offshore stratigraphic framework stud ies, phosphate-bearing Miocene-age strata, distribution of heavy minerals, nearsurface alternative sources of groundwater, and development of a PC-based Coastal Geographic Information System (GIS). Seven GGS publications document results of those investigations. In addition to those publications, direct benefits of the GGS's participation include an impetus to the GGS's investigations of economic minerals on the Georgia coast, establishment of a GIS that includes computer hardware and software, and seeds for additional investigations through the information and training acquired as a result of the Continental Margins Program. These additional investigations are quite varied in scope, and many were made possible because of GIS expertise gained as a result of the Continental Margins Program. Future investigations will also reap the benefits of the Continental Margins Program.     

Restoration of oiled mussel beds in Prince William Sound, Alaska

Natural loss of hydrocarbons was often low from mussel (Mytilus trossulus) beds (which were typically not cleaned after the Exxon Valdez oil spill), thus this habitat remained a long-term source of oil. Consequently, experimental restoration of nine contaminated beds was attempted in 1994; mussels were removed, contaminated surface sediment was replaced (33 metric tons), and original mussels were returned. Hydrocarbon concentrations and mussel populations were monitored for 5 years thereafter. Post-restoration mussel population fluctuations were indistinguishable from regional changes. Increased short-term oil loss was apparent, but long-term (5 year) improvement was equivocal and difficult to distinguish from natural losses. By 1999, oil concentrations in mussels were typically at baseline levels in restored and oiled reference beds; concentrations in replaced sediment were elevated in one third of restored beds, indicating recontamination from underlying or surrounding sediment. Our results suggest mussel relocation is feasible but suggest oil might more effectively be removed from sediment mechanically or chemically than manually.     

Ecosystem management bioindicators: the ECOMAN project – a multi-biomarker approach to ecosystem management

The ECOMAN project was initiated from an awareness of the complexity of the functioning of coastal marine systems and the clear need for more pragmatic environmental assessment techniques linking environmental degradation with its causes. The aim of the project is to develop a suite of easy to use, cost effective and environmentally valid biological responses (biomarkers) to assess the general health of coastal systems, including estuaries. To achieve this aim, various sublethal endpoints are being measured and evaluated from a range of common coastal organisms showing different feeding types (filter feeding, grazing and predation) and habitat requirements (estuary and rocky shore) and at different levels of biological response (cellular, physiological and behavioural). This holistic integrated approach is essential to identify the full impact of chemical contamination on organisms, and enables the sensitivity of organisms to be ranked and key sentinel species for specific habitats to be identified.     

Quantitative relationships between uplift and relief parameters for the Southern Alps,New Zealand,as determined by fission track analysis

The Southern Alps mountain chain, New Zealand, has formed as a consequence of late Cenozoic collision of the continental parts of the Pacific and Australia plates. Fission track analysis has yielded estimates of the amount, age of initiation, and rate of late Cenozoic rock uplift for 82 surface samples taken from transects across the Southern Alps. The mean surface, summit and valley elevations in the vicinity of each of the rock sample sites have also been measured. Regression of the geomorphic variables on the uplift variables has been used to establish quantitative relationships between uplift and geomorphology. There are strong and consistent linear associations between uplift and the elevations of the mean surface, summits and valleys. The preferred regression models have uniform slope but varying elevation response between transects. Substitution of space for time has allowed the evolution of landforms to be studied. To the east of the Main Divide, elevation and relief are proportional to, and closely related to, the age of initiation of rock uplift (‘uplift age’) and the amount of rock uplift (r² > 0·8). Mean surface uplift was delayed for ～2 Ma after the start of rock uplift, a result of the stripping of a soft cover rock succession that, prior to rock uplift, overlaid the harder greywacke basement. Inter-transect variations in regression response and x-intercept are inferred, therefore, to reflect the variable preuplift thickness of cover rocks. However, the regular regression slope for the transects reflects the consistent nature of the interaction between uplift and the erodibility of greywacke basement. Uplift of the mean surface proceeded at 0·4 km/km and 0·4 km/Ma of rock uplift, while the rock uplift rate was 0·8 km/Ma. Summit elevations have increased at a rate of 0·6 km/Ma and valley elevations have increased at 0·2 km/Ma. Regression lines relating mean surface, summit and valley elevations to rock uplift and uplift age diverge from common intercepts; it is concluded, therefore, that the mountains east of the Main Divide have continued to increase in elevation and relief and change in form over time since the start of mean surface uplift. Mountain elevation has little relationship with late Cenozoic mean rock uplift rates of 0·8–1·0 km/Ma or inferred contemporary rock uplift rates (r² ～ 0·3). In contrast, to the west of the Main Divide, elevation is shown to be closely related to rock uplift rate (r² > 0·3). In contrast, to the west of the Main Divide, elevation is shown to be closely related to rock uplift rate (r² > 0·8). Transects with higher rock uplift rates support higher topography. Landforms are therefore in a stable equilibrium with rock uplift rate, and the landscape contains no residual evidence of the total amount of rock uplift, or the age of uplift. Lithological variation appears to have no relationship with elevation.     

Retrospective analysis: bile hydrocarbons and histopathology of demersal rockfish in Prince William Sound,Alaska, after the Exxon Valdez oil spill

Demersal rockfish are the only fish species that have been found dead in significant numbers after major oil spills, but the link between oil exposure and effect has not been well established. After the 1989 Exxon Valdez oil spill in Prince William Sound, Alaska, several species of rockfish (Sebastes spp.) from oiled and reference sites were analyzed for hydrocarbon metabolites in bile (1989-1991) and for microscopic lesions (1990 and 1991). Biliary hydrocarbons consistent with exposure to Exxon Valdez oil were elevated in 1989, but not in 1990 or 1991. Significant microscopic findings included pigmented macrophage aggregates and hepatic megalocytosis, fibrosis, and lipid accumulation. Site differences in microscopic findings were significant with respect to previous oil exposure in 1991 (P=0.038), but not in 1990. However, differences in microscopic findings were highly significant with respect to age and species in both years (P<0.001). We conclude that demersal rockfish were exposed to Exxon Valdez oil in 1989, but differences in microscopic changes in 1990 and 1991 were related more to age and species differences than to previous oil exposure.