Abstract. This paper presents the analysis of floe-size distribution (FSD) data obtained in laboratory experiments of ice breaking by waves. The experiments, performed at the Large Ice Model Basin (LIMB) of the Hamburg Ship Model Basin (Hamburgische Schiffbau-Versuchsanstalt, HSVA), consisted of a number of tests in which an initially continuous, uniform ice sheet was broken by regular waves with prescribed characteristics. The floes' characteristics (surface area; minor and major axis, and orientation of equivalent ellipse) were obtained from digital images of the ice sheets after five tests. The analysis shows that although the floe sizes cover a wide range of values (up to 5 orders of magnitude in the case of floe surface area), their probability density functions (PDFs) do not have heavy tails, but exhibit a clear cut-off at large floe sizes. Moreover, the PDFs have a maximum that can be attributed to wave-induced flexural strain, producing preferred floe sizes. It is demonstrated that the observed FSD data can be described by theoretical PDFs expressed as a weighted sum of two components, a tapered power law and a Gaussian, reflecting multiple fracture mechanisms contributing to the FSD as it evolves in time. The results are discussed in the context of theoretical and numerical research on fragmentation of sea ice and other brittle materials.

Renewed political and commercial interest in the resources of the Arctic, the reduction in the extent and thickness of sea ice, and the recent failings that led to the Deepwater Horizon oil spill, have prompted industry and its regulatory agencies, governments, local communities and NGOs to look at all aspects of Arctic oil spill countermeasures with fresh eyes. This paper provides an overview of present oil spill response capabilities and technologies for ice-covered waters, as well as under potential future conditions driven by a changing climate. Though not an exhaustive review, we provide the key research results for oil spill response from knowledge accumulated over many decades, including significant review papers that have been prepared as well as results from recent laboratory tests, field programmes and modelling work. The three main areas covered by the review are as follows: oil weathering and modelling; oil detection and monitoring; and oil spill response techniques.

a b s t r a c t a r t i c l e i n f oWe investigated how physical incorporation, brine dynamics and bacterial activity regulate the distribution of inorganic nutrients and dissolved organic carbon (DOC) in artificial sea ice during a 19-day experiment that included periods of both ice growth and decay. The experiment was performed using two series of mesocosms: the first consisted of seawater and the second consisted of seawater enriched with humic-rich river water. We grew ice by freezing the water at an air temperature of −14°C for 14 days after which ice decay was induced by increasing the air temperature to −1°C. Using the ice temperatures and bulk ice salinities, we derived the brine volume fractions, brine salinities and Rayleigh numbers. The temporal evolution of these physical parameters indicates that there was two main stages in the brine dynamics: bottom convection during ice growth, and brine stratification during ice decay. The major findings are: (1) the incorporation of dissolved compounds (nitrate, nitrite, ammonium, phosphate, silicate, and DOC) into the sea ice was not conservative (relative to salinity) during ice growth. Brine convection clearly influenced the incorporation of the dissolved compounds, since the non-conservative behavior of the dissolved compounds was particularly pronounced in the absence of brine convection. (2) Bacterial activity further regulated nutrient availability in the ice: ammonium and nitrite accumulated as a result of remineralization processes, although bacterial production was too low to induce major changes in DOC concentrations. (3) Different forms of DOC have different properties and hence incorporation efficiencies. In particular, the terrestrially-derived DOC from the river water was less efficiently incorporated into sea ice than the DOC in the seawater. Therefore the main factors regulating the distribution of the dissolved compounds within sea ice are clearly a complex interaction of brine dynamics, biological activity and in the case of dissolved organic matter, the physico-chemical properties of the dissolved constituents themselves.

When modeling gravity wave propagation through an array of discrete ice floes, considered as a homogenous elastic continuum, the equivalent elasticity is less than the intrinsic material elasticity of ice. The array behaves increasingly like a collection of rigid floating masses when the floe sizes decrease. Extending a former wave flume experiment with polyethylene plates (Sakai & Hanai, 2002, https://web2.clarkson.edu/projects/iahrice/IAHR%202002/Volume%202/189.pdf), we conducted an experiment with saline ice floes at the Hamburg Ship Model Basin (HSVA). Using the measured wave number and the dispersion relation from a continuous elastic plate theory, we determine the equivalent elasticity. Parallel theoretical solutions are obtained using the matched eigenfunction expansion method (Kohout et al., 2007, https://doi.org/10.1016/j.jfluidstructs.2006.10.012), assuming ice floes as an array of thin elastic plates floating over inviscid water. Despite data scatter in laboratory tests, the celerity (phase speed) from the laboratory and theoretical results both show a decreasing trend when the floe size reduces. The corresponding equivalent elastic modulus decreases from the intrinsic modulus to zero. The matched eigenfunction expansion method is then applied to investigate cases under field conditions. Using all the theoretical results, an empirical relation is proposed for the equivalent elasticity in terms of wavelength, floe size, and length scale from the intrinsic elasticity of the floes. In addition to celerity, wave amplitude along the ice cover is compared with the theoretical results. Large discrepancies of wave attenuation from laboratory and theoretical solutions are found, indicating that attenuation mechanisms other than wave scattering need to be considered.Plain Language Summary Ocean wave forecasts in the ice-covered seas require reliable modeling of ice effect on wave propagation. The wave dispersion and damping rate due to the ice cover are different from the propagation in open water. One way is to consider the total effect of a field of fragmented ice floes as one continuous elastic sheet. However, the elasticity of the sheet is not measurable directly, which could be much lower than the intrinsic elasticity of ice. In this study, we examine a single-period wave propagating through an array of ice floes using both physical measurement and a theoretical approach. We analyze data from two laboratory experiments and the parallel theoretical studies. The theoretical studies are also extended into field scales using parameters collected from two field experiments. By assimilating all results, we determine the dependence of the equivalent elasticity of the sheet on the floe size. Furthermore, the surface undulation due to free edges makes the attenuation measurement challenging. Despite this difficulty, extra damping beyond wave scattering is observed.

Given rapid sea ice changes in the Arctic Ocean in the context of climate warming, better constraints on the role of sea ice in CO 2 cycling are needed to assess the capacity of polar oceans to buffer the rise of atmospheric CO 2 concentration. Air-ice CO 2 fluxes were measured continuously using automated chambers from the initial freezing of a sea ice cover until its decay during the INTERICE V experiment at the Hamburg Ship Model Basin. Cooling seawater prior to sea ice formation acted as a sink for atmospheric CO 2 , but as soon as the first ice crystals started to form, sea ice turned to a source of CO 2 , which lasted throughout the whole ice growth phase. Once ice decay was initiated by warming the atmosphere, the sea ice shifted back again to a sink of CO 2. Direct measurements of outward ice-atmosphere CO 2 fluxes were consistent with the depletion of dissolved inorganic carbon in the upper half of sea ice. Combining measured air-ice CO 2 fluxes with the partial pressure of CO 2 in sea ice, we determined strongly different gas transfer coefficients of CO 2 at the air-ice interface between the growth and the decay phases (from 2.5 to 0.4 mol m −2 d −1 atm −1). A 1D sea ice carbon cycle model including gas physics and carbon biogeochemistry was used in various configurations in order to interpret the observations. All model simulations correctly predicted the sign of the air-ice flux. By contrast, the amplitude of the flux was much more variable between the different simulations. In none of the simulations was the dissolved gas pathway strong enough to explain the large fluxes during ice growth. This pathway weakness is due to an intrinsic limitation of ice-air fluxes of dissolved CO 2 by the slow transport of dissolved inorganic carbon in the ice. The best means we found to explain the high air-ice carbon fluxes during ice growth is an intense yet uncertain gas bubble efflux, requiring sufficient bubble nucleation and upwards rise. We therefore call for further investigation of gas bubble nucleation and transport in sea ice.