New tools for optical measurements in sea ice

The quantity and quality of sunlight transmitted into and through sea ice is a crucial key necessary to understand the thermodynamic development of the ice cover, upper ocean heat and freshwater budget, as well as the associated primary production. Due to its solid impenetrable nature, most optical measurements so far have been conducted above and underneath the sea ice covering our polar oceans. Only very limited measurements have been carried out inside the ice cover itself. This strongly limits our current knowledge of the vertically varying inherent optical properties (IOP) of sea ice, as well as the geometric shape of the in-ice light field. Both factors currently limit our abilities to reliably model radiative transfer in sea ice. Here we present multiple new tools that can fill this observational gap and provide comprehensive optical measurements within the ice: This includes a chain of multispectral light sensors for seasonal long-term monitoring. It is derived from the proven design of the newest generation of ice-mass-balance buoys with digital thermistor strings and enables a non-destructive measurement with flexible geometry. We present data from a first prototype deployed together with an array of drifting ice observatories at the North Pole in September 2018. These vertically resolved in-ice light profiles are compared to in-ice measurements with a newly designed in-ice optical profiler system based on the well-proven TriOS Ramses hyperspectral radiometers. Combining expertise from photonics, medical and sea-ice science enables the ongoing development of a set of endoscopic probes allowing optical studies in sea ice with minimum disturbance of the ice. This includes in-ice microscopy for in-situ ice algal investigations, a UV-spectrometer to observe brine nitrate concentration in situ, a reflectance probe for high-resolution direct determination of inherent optical properties, as well as a radiance camera for quantification of the angular radiance distribution. Here we present data from the first field tests during the Arctic field season 2018. First ruggedized prototypes could be available to the scientific community soon

A multimodal endoscopic approach for characterizing sea-ice optics, physics, biology and biogeochemistry at small scale

Sea ice is a complex and heterogeneous medium that hosts a rich community of microbial organisms and small invertebrates. This ecosystem is shaped by a network of inhabitable spaces where the upward and downward fluxes of solutes and light support primary production, and ultimately the whole sea-ice trophic network. Describing the optical, physical, biological and biogeochemical processes that drive the functioning of the sea-ice ecosystem at the appropriate, i.e. small scale (micro- to centimeter), is very challenging. This medium is solid, fragile and highly heterogeneous. Traditional sea-ice sampling methods based on coring are most often coarse and destructive. Not only do they not allow the small scale to be explored, they generally alter the material to be analyzed. Here, we present a new approach for measuring relevant variables of the sea-ice ecosystem at small scale and, as much as possible, non-destructively. Inspired by medical endoscopes, the custom-built platform is intended to carry various types of miniaturized optical sensors for radiometry, chemistry and high-resolution imaging of the sea-ice interior. In this presentation, we will describe the concept and present the progress made to date