Abstract. This paper presents a first implementation of the Maxwell-EB model on geophysical scales. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover in floes, the strong spatial localization of the thickest, ridged ice and the opening of polynyas downstream of the Strait are all represented. The model represents different dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.

Abstract. This paper presents a first implementation of a new rheological model for sea ice on geophysical scales. This continuum model, called Maxwell elasto-brittle (Maxwell-EB), is based on a Maxwell constitutive law, a progressive damage mechanism that is coupled to both the elastic modulus and apparent viscosity of the ice cover and a MohrCoulomb damage criterion that allows for pure (uniaxial and biaxial) tensile strength. The model is tested on the basis of its capability to reproduce the complex mechanical and dynamical behaviour of sea ice drifting through a narrow passage. Idealized as well as realistic simulations of the flow of ice through Nares Strait are presented. These demonstrate that the model reproduces the formation of stable ice bridges as well as the stoppage of the flow, a phenomenon occurring within numerous channels of the Arctic. In agreement with observations, the model captures the propagation of damage along narrow arch-like kinematic features, the discontinuities in the velocity field across these features dividing the ice cover into floes, the strong spatial localization of the thickest, ridged ice, the presence of landfast ice in bays and fjords and the opening of polynyas downstream of the strait. The model represents various dynamical behaviours linked to an overall weakening of the ice cover and to the shorter lifespan of ice bridges, with implications in terms of increased ice export through narrow outflow pathways of the Arctic.

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The Shtokman gas condensate field lies in the centre of the shelf zone of the Russian sector of the Barents Sea about 600 kilometers northeast from Murmansk. Shtokman Development AG (SDAG, 51% Gazprom, 25% Total and 24% Statoil) is in charge of the integrated development of the phase 1 of the Shtokman Gas condensate field. Exploitation of the gas field will be done through a floating platform that will export gas and condensate to the shore via pipeline. Significant sea ice invasions occur at Shtokman in approximately 3 out of 10 years, on average. Icebergs may also occur in the SCGF area. Ice and iceberg management activities have been planned to support the operations. The ice and iceberg management activities include surveillance, threat assessment and physical management. At this stage, definitions of strategy and philosophies for ice and iceberg management have been developed and preliminary plans for the main tasks have been outlined. The present paper describes the different components of the ice and iceberg management system and the rationales for the main technical choices. 1 INTRODUCTION The Barents Sea is bordered by the cold and icy waters of the Arctic Ocean and the Kara Sea on the North and East sides and by the warm water of the Norwegian Sea on the west side. The Gulf Stream enters the Barents Sea as the North Cape and Spitsbergen branches of the Norwegian current, bringing warm water into the region. The border between warm and cold water varies in location, depending on the oceanographic and meteorological conditions; this change is more sensitive in the Eastern part of the Barents Sea and especially at the Shtokman field. Sea ice does not form at Shtokman (except very thin ice in very cold years) but is exported from the North - Northeast by persistent winds. Thus, the origin of ice which can arrive at Shtokman is North-Eastern Barents Sea and possibly Kara Sea. The presence of drifting sea ice is observed in approximately 40% of the years on the Shtokman field, based on satellite observations from 1974 to 2007. This means that sea ice in the Shtokman area occurs approximately once every 2.6 years. Sea ice arrives rapidly at the Shtokman area and ice concentration may increase from 2/10th to above 8/10th within a few hours. Furthermore, ice may not be continually present at Shtokman throughout any one ice season. Historically, icebergs have been observed near Shtokman (within 75 nm) about once every five years on average. 10% of icebergs observed within 25 nm circle around Shtokman were in ice while 40% of icebergs observed within up to 100 nm north of Shtokman were in ice. With regard to seasonal variation it must be assumed that the probability of encountering icebergs at Shtokman during spring is higher than during late summer / early autumn.

The exploration and production of polar oil and gas fields, which are technologically challenging due to extreme weather conditions, are also constrained by strong environmental issues. Safe and economical activities in such hostile and fragile regions require very insightful engineering. The presence of sea ice is representing a triple challenge: economical, technological and environmental. This makes the Arctic exploration and production activities complex. Ice Management (IM) is one of the tools that could efficiently assist to develop Arctic reserves. However, for each project that uses IM operations, a preliminary study is required to evaluate the efficiency of these support operations and to estimate the possible extension in the season of operation of a field. Efficiency of an IM philosophy can be estimated in a global view based on the extension in the operability window. In a more detailed view, it can be assessed taking into account the optimal number of icebreakers, the IM patterns, the available time for eventual disconnection, and the floe size reduction (leading to ice load reduction). For this study, we will focus on the ice floe size and loads reduction. The most common approach for physical management of sea ice is the one where icebreakers reduce floe size of the drifting ice upstream the floating platform (ref. Moran et al. [1], Coche et al. [2]). This paper describes this philosophy and demonstrates based on real-time simulation that its benefit is limited to mild ice scenarios such as unidirectional ice drift. A more efficient way to manage sea ice is (1) to identify the most hazardous events (e.g. big ridges); (2) prioritize these events; and (3) deal with them starting by the most hazardous one.