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Cape Adare

> 2.5 xlO6 barrels

(350,000 tonnes)

Possession Island

< 1 x 106 barrels

(130,000 tonnes)

Cape Hallett

> 1.3 x 106 barrels

(170,000 tonnes)

Franklin Island

> 2.0 xlO6 barrels

(275,000 tonnes)

Beaufort Island

> 1.5 x 106 barrels

(215,000 tonnes)

Cape Bird

» 6.0 x 106 barrels

(863,000 tonnes)

Penguins are particularly vulnerable to oil fouling (Kerley and Erasmus, 1987) and it seems likely that in the event of a major spill impacting the site of a rookery (e.g., Fig. 11.15), mortality would be greatest during the period the beach was protected by an ice-foot. At that time, the birds coming on shore would be herded through narrow leads and passages where congealing oil would concentrate. This risk to individuals would be lessened if the beach were open to the sea.

Oil-ice Interaction

The behaviour of oil released in a frozen sea or under ice is schematically illustrated in Fig. 11.16. Ice will tend to limit the rapid spread of the oil. Biodégradation and mechanical dispersal of oil trapped in leads between flows, pumped on to the ice surface, or held in oil-slush-ice mixtures is likely to be slow. Wind, wave, tidal action or broad oceanic circulation could spread this contamination far from its place of origin (e.g., Fig. 11.11). Oil, seasonally entrained and encapsulated in ice, would migrate to the surface ponding in summer melt pools (Martin, 1979; Wadhams, 1981) to be released back into the sea. It has been argued that release of large quantities of oil on to the Antarctic pack ice surface could significantly lower its albedo and consequentially trigger a rise in sea level (cf. Mitchell, 1982). However, dilution effects over the vastness of the Southern Ocean, and seasonal variations in the extent of sea ice cover suggest that oil-induced melting in this manner should not significantly effect either local or global climate.

Polynyas

A polynya centred on Terra Nova Bay and induced by strong westerly katabatic winds is a persistent wintertime feature of the western Ross Sea (Kurtz and

Fig. 11.16. Schematic illustration of interactions between sea ice and water (after Wadhams, 1981; Bobra and Fingas, 1986). Oil can be trapped in pools beneath pack ice or amongst leads between flows. It can be pumped under or on to the ice surface to be covered and/or absorbed by drifting snow. Oil is lost to the atmosphere through evaporation, and dispersed in sea water through droplet formation, solution and emulsification (mousse formation). Encapsulated oil migrates upwards during winter through brine channels in first year sea ice to pond at the surface in the following summer (inset, right).

Fig. 11.16. Schematic illustration of interactions between sea ice and water (after Wadhams, 1981; Bobra and Fingas, 1986). Oil can be trapped in pools beneath pack ice or amongst leads between flows. It can be pumped under or on to the ice surface to be covered and/or absorbed by drifting snow. Oil is lost to the atmosphere through evaporation, and dispersed in sea water through droplet formation, solution and emulsification (mousse formation). Encapsulated oil migrates upwards during winter through brine channels in first year sea ice to pond at the surface in the following summer (inset, right).

Bromwich, 1983). The open water area averages 1,000 km2 over most years and reaches a maximum of 5,000 km2. Other polynyas in this region are reported from McMurdo Sound and off the Ross Ice Shelf (cf. Knapp, 1972).

The extent to which the Ross Sea polynyas are winter refuges for seals, penguins and other animals has not been established. However, Arctic studies suggest they are likely to be regions of high productivity and considerable ecological importance, where an oil spill or blowout could be environmentally devastating (Stirling et al., 1981). Oil from a spill in Terra Nova Bay would probably be held offshore by strong westerly winds and seldom directly threaten the penguin colony of Inexpressible Island. On the other hand, oil would be dispersed to the eastern margin of the polynya where it would be driven against the pack ice margin, and also into leads through the ice, and where it could imperil marine mammals and birds.

Subsea Blowout

Water depths over postulated exploitable hydrocarbon prospects around the Ross Sea, and in particular over the Victoria Land Basin (cf. Cook and Davey, 1984, this volume) are generally greater than 350 m and may exceed 1,000 m.

From such depths, it is unlikely that a constricted conical or cylindrical, rapidly ascending column of oil and expanding gas bubbles as illustrated by Lewis (1979, fig. 2) would ever reach the surface to form a gas boil in open water (Westergaard, 1980), or interact with an ice cover (Lewis, 1970, fig. 3). In water within a few degrees of freezing and at depths of 300 m or more, formation of gas hydrates having densities and appearance similar to ice is likely (Topham and Bishnoi,

1980). Slowly ascending oil droplets and decomposing hydrates would be dispersed widely by even weak currents, reaching the surface over a much wider area than in the case of a shallow-water blowout, and perhaps spreading many unpredictable kilometres downdrift from the release point (cf. Lewis, 1979, fig. 4).

Iceberg scour and furrow marks have yet to be reported from the floor of the Ross Sea. Occasional icebergs in this region may have drafts greater than 400 m, but in general most are unlikely to greatly exceed 300 m (Keys, 1984). Elsewhere around the continent, side-scan sonar surveys have reported modern iceberg scouring from water depths of at least 300 m in the Weddell Sea (Lien, 1981) and over 500 m off Wilkes Land to the west of the Ross Sea, although the age of the latter remain uncertain (Eittreim et al., 1984). It is likely that scour features in water depths of 400-600 m or more are relict (Lien, 1981; Orheim and Elverhoi,

1981). Thus, the potentially most favourable sites for subsea well head completions, and pipelines over most of their length along possible routes to shore facilities, will be at depths more or less safely beyond iceberg scour limits. Only near the coast, where water depths shoal abruptly would pipelines be at risk to ice scour and need to be buried for protection. Here also, pipeline landfalls and onshore facilities face the threat of ice-piling and ride-up (e.g., Kovacs and Sodhi, 1981).

Hydrocarbon Spills and the Marine Biota

The marine biota of the Southern Ocean and Ross Sea are described elsewhere in this volume. Extrapolation from Arctic studies (cf. Dunbar, 1985), predicting the possible effects that a major oil/condensate/gas spill would have on the local and regional biota, needs to be approached with caution (Knox, 1982). The central and key role that krill plays in Southern Ocean and Ross Sea ecosystems is often emphasized (e.g., Knox, 1984). Crustacea are widely recognized as being particularly sensitive to oil fouling and large spills could jeopardize krill concentrations of the Ross Sea. The short, simple food webs of lower species diversity that characterize high latitudes are often considered vulnerable to man-induced perturbations, but to term these ecosystems "fragile" may be a misconception (e.g., Weller, 1980; Dunbar, 1985). Adaptation to seasonal extremes of light, temperature and other environmental parameters indicates a resilience that popular opinion seldom acknowledges. Regionally separated and isolated dense populations (e.g., penguin rookeries, krill swarms) scattered but widely distributed, suggest that local extirpations through pollution could be repaired by immigration from adjacent areas (e.g., Dunbar, 1985). It must also be noted that the impact of even the most massive imaginable spills would be mitigated by the dilution properties of the very vastness of the Southern Ocean (Zumberge, 1979).

The importance of the unique and specialized sea-ice microbial community has been reviewed by Bradford (1978). Like ice-margin phytoplankton blooms (e.g., Smith and Nelson, 1985), it is a highly significant part of the productive Ross Sea ecosystem (Palmisano and Sullivan, 1983; El-Sayed, this volume). Zooplankton biomass is lower inshore than it is offshore (see Foster, 1987). The vulnerability of the sea-ice microbial community to oil contamination is substantially greater than that of either zoo- or phytoplankton, where effects would probably be both local and transient (Keys, 1984). It has been emphasized that hydrocarbon-degrading and -utilizing bacteria are absent from Antarctic waters (Keys, 1984). However, Piatt's (1979) observations near Grytviken, South Georgia, and Konlechner's (1985) study at Cape Bird, Ross Island, attest to the presence of hydrocarbon-degrading micro-organisms. Decomposition rates at these high latitudes would be much lower than at mid to low latitudes.

The deeper-water benthos of possible well sites is unlikely to be imperilled through seafloor dumping or accidental release of oil contaminated drill cuttings and drilling muds, although some local environmental deterioration may be evident (cf. Macdonald, 1982).

The shallow benthos below the abrasion limit of sea ice (0-c. 30 m) is abundant and diverse. Sensitivity of this community to hydrocarbon pollution has been demonstrated by Robilliard and Busdosh (1981). They described a depleted biota, including a bed of dead clam shells, over a small area of petroliferous-smelling sediment, alongside the wharf in Winter Quarters Bay, McMurdo Sound, at a depth of 25 m.

There is popular perception that larger marine mammals (whales, sea elephants, sea lions, seals) of the region would be at risk in a large oil spill. This scenario may be correct for Mysticeti (baleen whales) where vulnerability is likely to be through a contaminated food vector, rather than in direct oiling. On the other hand, there is evidence that Odontoceti (toothed whales) and Phocidae (seals) can detect and hence avoid oil slicks (e.g. Smith et al., 1983), although it must be noted that many years ago Lillie (1954) reported oil-fouled seals in Antarctic waters. These animals would be more susceptible to oiling when sea-ice cover was extensive and congealing oil was imprisoned in the leads through which they were forced to surface. The relative defenselessness of penguins to oil-fouling has been briefly discussed elsewhere in this review. Harper (1983) and Harper et al. (1984) have commented on the prospect of a large spill in the Ross Sea decimating neighbourhood penguin populations and detrimentally affecting other local seabird species.

Pesticides and Other Persistent Compounds

Polychlorinated biphenyls (PCBs) and several other persistent synthetic organic compounds (DDT, DDE and TDE) are stable contaminants that have global distribution and are an acknowledged environmental hazard. Such residues are widespread around Antarctica (Risebrough et al., 1976) and have been detected in Adelie Penguins and Crabeater Seals from Cape Crozier, Ross Island (Sladen et al., 1966). Wildlife from mainland New Zealand and offshore Subantarctic islands are also known to be contaminated (Bennington et al., 1975;

Solly and Shanks, 1976), as they are from elsewhere in the region (e.g., Kerguelen Islands — Abarnou et al., 1986). PCBs and pesticide residues have been detected in the atmosphere and surface waters across the Southern Ocean between Australia and Antarctica, with higher concentrations noted in the vicinity of the Balleny Islands and off the Sabrina Coast (Tanabe et al., 1983).

In general, contamination levels determined in both wildlife (Bennington et al., 1975) and oceanic waters (Tanabe et al., 1983) become progressively less with increasing distance from local Australian and New Zealand sources. These levels are substantially lower than those reported from lower latitudes and the Northern Hemisphere. Other than some slight evidence from Syowa Station (Hidaka et al., 1984), Antarctic scientific bases do not appear to be significant point sources of chlorinated hydrocarbon contamination (Riseborough, 1977). The dominant pathway for the transfer of PCB and DDT residues to these remote southern regions is through atmospheric circulation, ocean currents and seasonal migrants from the north (Risebrough et al., 1976; Risebrough, 1977; Tanabe et al., 1983). However, a recently available report (Manheim, 1988) reveals that waters off McMurdo base are grossly contaminated with PCBs. A local source through indiscriminate waste disposal is indicated with reported PCB levels (18-340 ppb) significantly greater than those of polluted United States estuaries. Although established by conservative measurement techniques, these results need to be verified.

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