MATISHOV G.G., DZHENYUK S.L., DAHLE S.
Murmansk Marine Biological Institute RAS
AKVAPLAN-NIVA

Sea ice is the most important natural factor, determining ecological security of oil-gas excavation on the Arctic shelf.

Exploration of the Barents Kara oil-gas bearing province demands development of qualitatively new approaches to the ecological accompany of the industrial activity and its information provision. Several aspects of this problem is reflected in the MMBI publications (Scientific methodical approaches..., 1997; Modem technologies..., 1999; Matishov et al., 2001). But nowadays a unified set of requirements to the information on the ice cover and connected with natural phenomena necessary for the EIA fulfillment in the freezing seas lacks.

For the fields on the West Arctic seas the following types of ice situation are typical:

- ice cover is absent in field area directly but impacts the field of currents and wind generated waves, migration routes of fishes, sea birds and mammals (Norwegian shelf, south-western Barents Sea):
- episodic invasions of drifting ices or prolonged presence of the area of work in the near edge zone which is accompanied with a significant variability of the majority of the ecosystem parameters (central and eastern parts of the Barents Sea, including Stockman field);
- ice cover is formed annually and remains in the period from 3-4 up to 12 months, determining completely oceanological and ecological situation during this period (Pechora and Kara Seas).

Depending on the ice regime type the requirements to the information on the sea ices differ significantly. In the first case it is sufficient to have the data on the large scale variability of the degree of ice cover and ice edge. These parameters are well studied in the climatic aspect and usually easily accessible by the remote sensing data.

For those shelf areas where ice appears episodically, approximate estimations of such invasions are of the priority character. Traditional approaches accepted in the climathology of sea ices are in this case insufficient. Thus, in some Russian issues similar series maps of the Barents sea ice conditions (average, maximal and minimal location of the ice edge by months) are presented. G.K. Zubakin (1987) obtained approximate estimations of the ice edge applying the theory of crossings. This approach considers inter-annual variability of ice cover but, but fluctuations of synoptic scale are not taken into consideration. A more correct way for obtaining such estimations is formation of sets of observations for the availability and cohesion of ice according to the satellite data with periodicity not rarer that 5 days. Optimal duration of the sets is 30 years, minimal allowable - approximately 10 years (this requirement is also obligatory for other types of ice cover data). If such information is available long- term estimations might be received not only with monthly but also with decade resolution.

Over the greater part of the Barents Sea area freezing or invasion of the drifting ices is observed not annually. The most actual example is the Stockman field area, where a probability of ices occurrence in a concrete year is approximately 50 %, and these events are possible from December till July (Scientific and methodical approaches..., 1997). For such areas standard parameters of ice phases accepted in oceanology - duration of the ice period, average, early and late periods of formation and disappearance of ice should not be used. Instead the ice conditions description should contain the following characteristics: probability of availability of ices on the pointed out date or during a definite interval of the annual cycle (monthly, decade); the earliest periods of ices appearance and the latest periods of its disappearance (a guaranteed duration of the iceless period is determined simultaneously by this); probability characteristics of the ices cohesion referred to the periods of its presence. Statistic estimations of the average and maximal movements of ice edge are also obligatory. All these data might be also received by the remote sensing data with high temporal-spatial resolution.

It should be noted that this group of parameters to the largest degree depends on the variability of the climatic background. Under conditions of global shortening of Arctic ice cover any estimations obtained by long-term data might turn out unsound. It is necessary to verify continuously this information by monitoring data and to reveal the newest trends at the temporal intervals of 3-5 years.

In the areas of the Barents Sea shelf with unstable ice regime 200-300 in depths prevail, hi this depth range depth sea does not produce direct affect the dynamics and morpho-metric characteristics of ice cover, thus, that is why to connect correspondent observation and the points of shelf platform installation is not necessary. Such parameters as velocity and direction of drifting ice, thickness, hummocking, average and maximal dimensions of ices in the off-sea areas are sufficiently unified. This allows attracting for the statistic processing the data, obtained in different sea areas. But their grouping in respect to the age stages of ice is necessary at that. The latter distinguished by a significant inter-annual variability, thus connection of the data and definite calendar intervals in this case might be ineffective.

The fullest data on the dynamics and geometric characteristics of ice cover in the off-sea areas of the Barents Sea are presented in the monograph (Hydrometeorology..., 1990). Later investigations were earned out mainly by the oil-gas companies orders, and their results were not published, hi spite of this a current level of knowledge on ices in these areas considering the thoughts forwarded might be admitted satisfactory.

Among natural factors creating technological and ecological risks in the northern, central and eastern Barents Sea areas icebergs are to be noted. They might be distributed to the south till 72° N. According to the summary data published (Abramov, 1992) there might be obtained risks estimations of meeting with icebergs for concrete areas and seasons, but the priority task is tracing icebergs during satellite monitoring of ice situation.

The third type of ice regime typical of the Pechora and Kara Seas, demands principally different approaches to the collection and analysis of data. Ice cover parameters here depend significantly on the distribution of depths, distance from the coast and configuration of the coastal line. Two states of ice cover are revealed there: drifting and fast (land-fast) ice. For them phase characteristics are determined separately: average and extreme periods of appearance and disappearance, duration of ice period. For the description of the drifting ices the same set of parameters like that in the deep water seas areas is used, but at the ice cohesion almost constantly close to 10 the degree of hummocking acquires especially important value. For its detailed description an independent integrity of parameters is necessary, that is: degree of hummocking, forms, dimensions- prevailing orientation of hummocks.

On small depths this description should be added by characteristics of submarine bottom relief, and probability estimations of stamukhas and submarine furrows appearance. Land-fast ice is characterized by the breadth of the land-fast stretch, thickness, degree of hummocking, availability of tidal cracks.
Investigations of the Pechora and the Kara Seas ices become especially active during last 20 years in connection with geological reconnaissance and trial drilling on the shelf Review of these works is published (Mironov et al., 2001). But together with this a large amount of materials on these areas is obtained on the commerce basis, thus, it is not accessible for usage. As on the shallow-water shelf each area demands individual investigation and description, insufficiency of natural data has to be replenished by mathematical modeling of ice processes, and in case of lack of adequate models or initial data for the models calculations - development of the typical schemes of ice cover evolution on the basis of climatic analogues. And it is quite sufficient to select analogues on air temperature and atmospheric circulation, as hydrometeorological conditions on the Arctic shelf are distinguished by stability in winter period.

To fulfill biological chapters of environmental impact assessment there is no need to use detailed description of ice cover during its stable existence. Leading ecological factors are variability of ice edge in the off-sea area and phases of ice processes in the coastal areas. Ice conditions to a great extent determine natural variability of the ecosystem processes, on the background of which summary contribution of anthropogenic impacts and its constituent connected with oil-gas complex are to be revealed. Another group of EIA tasks is connected with estimation of impact the marine environment at the accidental situations, especially oil and gas- condensate spills. For these purposes ice information on any not pointed out earlier sea areas with a high degree of the component and spatial- temporal resolution might be necessary.

References

Abramov V.A. Russian iceberg observations in The Barents Sea. 1933-1990 // Polar Research. 1992. V. 11, N. 2. P. 93-97.
Hydrometeorology and hydrochemistrv of USSR Seas. V. 1. The Barents Sea. Iss. 1. Hydometeorological regime / Ed. by F.S. Terziev et al. L.: Hydrometeoizdat. 1990. 280 pp. (in Russian)
Matishov G G, Denisov V. V., Dzhenyuk S. L., Znev A. N., Sochnev O. Ya. Application of modem information technologies in the ecological accompany of the marine oil gas excavation in the Arctic // Papers RAO 01. 5 International Conference RAO-01 «Exploration of the Russia Arctic Seas shelf». SPb. 2001. P. 315-318. (in Russian)
Mironov E.U., Lebedev A. A , Spichkin V. A., Tymyakov A. B. Degree of investigations of shelf ice- conditions in the south- eastern Barents Sea and south-west Kara Sea // Papers AARII2001. V. 444. P. 59-72 (in Russian)
Modem technologies and forecast in polar oceanology and biology / Ed. by G. G. Matishov. Apatity: KSC RAS. 1999. 446 pp. (in Russian)
Scientific-methodical approaches to the estimation of impact assessment of oil- gas excavation on the Arctic Seas ecosystems (on the example of the Stockman project) / Ed. by G. G. Matishov and B. A. Nikitin. Apatity: KSC RAS. 1997. 394 pp. (in Russian)
Zubakin G. K. Large scale variability of the North -European basin seas ice cover. L.:
Hydrometeoizdat. 1987. 160 pp. (in Russian)

ARCTIC SHELF OIL AND GAS CONFERENCE 2004