arXiv subjects

Marcel Babin

Publications and source records attributed to Marcel Babin.

5 recordsLinked to original sources

arXiv2026

Tara Polaris expeditions: Sustained decadal observations of the coupled Arctic system in rapid transition

The coupled Arctic system is in rapid transition and is set to undergo further dramatic changes over the coming decades. These changes will lead most likely to an ice-free ocean in summer, expected before mid-century. The Arctic will become more strongly influenced by atmospheric and oceanographic processes characteristic of mid-latitudes, increasing the prevalence of contaminants and new biological species. This ongoing transition of the Arctic to a new state necessitates systematic monitoring of all sentinels (variables that make an essential contribution to characterizing the Earth's state) to improve our understanding of the system, enhance forecasting and support knowledge-based decisions. Here, we describe a sustained multi-decadal observation program to be implemented on the Tara Polar Station between 2026 and 2046. The monitoring program is designed as a series of year-long drift expeditions, called Tara Polaris, in the central Arctic Ocean, covering all seasons. The multidisciplinary data will bridge ecological, geochemical, biological, and physical parameters and processes in the atmosphere, sea ice and ocean. In addition, data collected with consistent methodologies over a 20-year period will make it possible to distinguish long-term trends from seasonal and interannual variability. In this paper, we discuss specific measurement challenges in each compartment (i.e., atmosphere, sea ice and ocean) along key sentinels and the most pressing scientific questions to be addressed. The expected outcomes of the Tara Polaris program will enable us to understand and quantify the main feedbacks of the coupled Arctic system, with their seasonal and interannual trends and spatial variability.

q-bio.PE↗

arXiv2026

Inversion of Sea Ice Spectral Albedo to Estimate Under-Ice Transmittance

Sunlight radiation under snow-covered sea ice obtained from remote sensing could help assess under-ice primary production at pan-Arctic scale. Yet, the current remote sensing methods to estimate sunlight transmittance under sea ice is limited by its reliance on imprecise snow depth products and its inability to sense microstructure-driven variations in snow and ice light scattering properties. Based on Monte-Carlo simulations of radiative transfer, we developed an inversion method relying solely on spectral albedo to estimate transmittance under snow-covered sea ice. The method analyses albedo spectral information to derive the vertically resolved scattering properties of snow and sea ice above the freeboard. Assuming fixed columnar ice physical and optical properties, transmittance is then estimated. At ground level, our spectral albedo inversion method is more precise than the current approaches. We argue this is because it implicitly accounts for the variability in snow scattering properties. This method could significantly improve the satellite estimation of photosynthetically available radiation under sea ice, especially because it does not need snow depth.

physics.ao-ph↗

arXiv2026

The Tara Polaris scientific vision: Advancing our understanding of the central Arctic Ocean to better address life in the Earth System

The Arctic Ocean is currently experiencing, at the forefront of global concerns, the pressures of climate change and global pollution. To boost our ability to understand the state of this ecosystem, its evolution in this context and its resilience, the Tara Ocean Foundation has built the Tara Polar Station (TPS), intended to become a permanent observatory of the central Arctic Ocean. The objective of this initiative is threefold: to deepen our knowledge of the foundations of life in an ice-covered polar ocean, to better understand the dynamics of the coupled ocean-ice-atmosphere system and the role of living organisms, and to identify long-term trends in the main characteristics of the Central Arctic Ocean ecosystem resulting from global change. In this article, we describe the vision that guided the development of the Tara Polaris scientific programme, and more specifically the first of ten transpolar drifts that will be undertaken over the next 20 years aboard the TPS (Tara Polaris I, II, III, etc.). The research activities of the Tara Polaris I expedition will be grouped under four specific but interrelated themes: biosphere-atmosphere interactions, epi- and mesopelagic life in an ice-covered ocean, life in sea ice, and pollution. In addition, a theme that cuts across all environmental compartments and disciplines, and is implemented on all Tara Polaris expeditions, is the establishment of an observatory that will monitor the main sentinels of this ecosystem. This umbrella article introduces these different themes, which are then described in more detail in four other articles in this Special Feature, in addition to an article describing the technical characteristics of the TPS.

physics.ao-ph↗

arXiv2026

Microscopy system for in situ sea ice structure and biology observations

Sea ice harbours a rich community of well-adapted microorganisms that inhabit liquid micro-spaces where extreme conditions prevail. Currently at risk under climate change, the sea-ice microbiome holds mysteries about evolution of life on Earth and possibly elsewhere, which require methodological innovation to be unravelled. Gaining microscopic insight into the internal structure and biology of sea ice has traditionally been limited to destructive and extrusive ice core sampling methods. Here we present an in situ microscopic imaging system to observe undisturbed living microorganisms directly within sea the ice matrix. The complex and heterogeneous nature of sea ice, including its water crystal lattice, brine channels, air bubbles, and various impurities, presents engineering challenges for the development of this imaging system. Despite the fragile nature of the sea-ice matrix, we could successfully deploy, test and use the new in situ microscope during a recent expedition on the icepack in Arctic. We collected numerous images of live and intact single-celled and colony-forming diatoms, and documented for the first time at such a high resolution some microphysical features of sea ice. The hardware and software design of the endoscope is presented along with acquisition results of the microstructure and diatom images. These findings collectively demonstrate the potential for this new in situ microscopic imaging system to transform the way we study sea ice and to allow a deeper understanding of its complex microstructure and living microorganisms.

physics.ao-ph↗

arXiv2023

On the use of a consumer-grade 360-degree camera as a radiometer for scientific applications

Improved miniaturization capabilities for complex fisheye camera systems have recently led to the introduction of many compact 360-degree cameras on the consumer technology market. Designed primarily for recreational photography, several manufacturers have decided to allow users access to raw imagery for further editing flexibility, thereby offering data at sensor level that can be directly exploited for absolute-light quantification. In this study, we demonstrate methodologies to carefully calibrate a consumer-grade 360-degree camera for radiometry use. The methods include linearity analysis, geometric calibration, assessment of the illumination fall-off across the image plane, spectral-response determination, absolute spectral-radiance calibration, immersion factor determination and dark-frame analysis. Accuracy of the calibration was validated by a real-world experiment comparing sky radiance measurements with a co-localized Compact Optical Profiling System (C-OPS, Biospherical Instruments Inc.), which gave mean unbiased percentage differences of less than 21.1 %. Using the photon-transfer technique, we calculated that this camera consisting of two fisheyes with a 182$^\circ$ field of view in air (152$^\circ$ in water) has a limit of detection of at least $4.6 \times 10^{-7}$ $\mathrm{W \cdot sr^{-1} \cdot m^{-2} \cdot nm^{-1}}$ in its three spectral channels. This technology, with properly stored calibration data, may benefit researchers from multiple scientific areas interested in radiometric geometric light-field study. While some of these radiometric calibration methods are complex or costly, this work opens up possibilities for easy-to-use, inexpensive, and accessible radiance cameras.

physics.optics↗