Les données issues de deux campagnes de mesures in situ de l’initiative Green Edge dans l'océan Arctique viennent d’être publiées.
In the oceans, we differentiate sea ice (ice pack) formed from sea water (salt water) and icebergs, formed from inland waters (fresh water).
Sea ice forms when ocean water temperatures reach freezing point, about -1.8°C, depending on the salinity of the water. Sea ice grows both in size and thickness to form ice floes in late fall and winter. Multi-year ice, which does not melt from one season to the next, can reach a thickness of about 3 m.
This drifting ice sometimes collides, deforms and cracks. These cracked areas open up ice-free areas called leads and polynyas. Through these holes in the ice, which are darker in colour than the ice, or in other words, have a smaller albedo than on ice-covered areas, solar radiation reflects less. As a result, through these "holes" in the ice, the ocean absorbs more energy, which accelerates their warming. The melting of the ice pack does not bring water to the ocean and therefore does not contribute to the direct rise in its level. However, the increased melting of the ice increases the solar radiation absorbed at the ocean surface, which amplifies their warming.
Icebergs are formed from continental ice, which flows to the ocean as floating ice shelves. Blocks of ice break up (icebergs) from these platforms and leave the continent to drift with the currents and winds. The largest icebergs reaching up to several tens of kilometres can drift for several years on trajectories of several thousand kilometres.
Monitoring sea ice and melting continental ice are essential indicators for assessing the extent of climate change.
Une conférence-atelier sur le rôle de la glace de mer dans le Système Terre : une approche multidisciplinaire est organisée les 4-5-6 juin 2019 à…
The physical characteristics of sea ice and icebergs and their spatial and temporal variability are well described by spatial remote sensing, whether using imaging, altimeter or optical radar techniques.
A quick look at the satellite sensors behind the "ice" products in the ODATIS catalogue:
SAR imagery sensors, in C-band on the Sentinel-1 satellite for example, systematically map sea ice and are able to measure ice extent. The passive microwave sensors of the SSM/I and SSMIS radiometer are also used to calculate sea ice concentration.
Radar altimeters for satellite missions with a very steep orbit capable of reaching high latitudes (Envisat, Saral, Cryosat) determine the extent, thickness and volume of sea ice (corrected for snow depth at their surface). These sensors are also used to detect "holes" in the ice pack (polynyas, leads) and are able to follow the deformation dynamics of the ice pack. Altimeter radars are also used for iceberg detection, their monthly ice volume, the probability of icebergs being present and the average iceberg area.
The backscatter properties of scatterometers (AMI WIND on ERS satellites, ASCAT on METOP satellites for example) allow to monitor the extent and edges of sea ice (distinguishing open waters from sea ice), but also the age of sea ice.
- On the AVISO+ website, a video produced by CNES in 2015, on sea ice monitoring in the Arctic.
- Animation of the A56 iceberg drift in the South Atlantic Ocean, between March and October 2016 depending on surface temperature.
- On the ESA website, Space in Videos section, Hidden ice canyons in the making, genesis of an iceberg
- Frappart, F, Benoit Legresy, Fernando Niño, Fabien Blarel, Nicolas Fuller, Sara Fleury, Florence Birol, and S. Calmant. 2016. An ERS-2 Altimetry Reprocessing Compatible with ENVISAT for Long- Term Land and Ice Sheets Studies. Remote Sensing of Environment, no. 184: 558–81. doi:10.1016/j.rse.2016.07.037.
- Girard-Ardhuin, F., and R. Ezraty, 2012 : Enhanced Arctic sea ice drift estimation merging radiometer and scatterometer data. IEEE Trans. Geosci. Remote Sensing, vol. 50, n. 7, pp 2639-2648. doi : 10.1109/TGRS.2012.2184124.
- Guerreiro K., Fleury S., Zakharova E., Rémy F., Kouraev A., 2016. Potential for Estimation of Snow Depth on Arctic Sea Ice from CryoSat-2 and SARAL/AltiKa Missions. Remote Sensing of Environment 186 (December): 339–49. doi:10.1016/j.rse.2016.07.013.
- Krumpen, T., M. Janout, K.I. Hodges, R. Gerdes, F. Girard-Ardhuin, J.A.H. Hölemann, S. Willmes, 2013 : Variability and trends in Laptev sea ice outflow between 1992-2011. The Cryosphere, vol. 7, pp 349-363. DOI : 10.5194/tcd-7-349-2013.
- Hippert A. 2016, Diminution du volume de la glace de mer de l’Océan Arctique : étude des incertitudes de mesures de l’épaisseur de glace liées à la neige, rapport de stage de fin d'études, pdf
- Krumpen, T., M. Janout, K.I. Hodges, R. Gerdes, F. Girard-Ardhuin, J.A.H. Hölemann, S. Willmes, 2013 : Variability and trends in Laptev sea ice outflow between 1992-2011. The Cryosphere, vol. 7, pp 349-363. doi : 10.5194/tcd-7-349-2013, (pdf)
- Rozman, P., J. Hölemann, T. Krumpen, R. Gerdes, C. Köberle, T. Lavergne, S. Adams, F. Girard-Ardhuin, 2011 : Validating satellite derived and modeled sea ice drift in the Laptev sea with In Situ measurements of winter 2007/08. Polar Research, vol. 30 (7218). DOI : 10.3402/polar.v30i0.7218
- Sumata, H., T. Lavergne, F. Girard-Ardhuin, N. Kimura, M.A. Tschudi, F. Kauker, M. Karcher, R. Gerdes, 2014 : An intercomparison of Arctic ice drift products to deduce uncertainties estimates, J. Geophys. Res., vol. 119, pp 4887-4921, doi: 10.1002/2013JC009724.
- Télédétection satellitaire des surfaces enneigées et englacées, Télédétection satellitaire des surfaces enneigées et englacées, page web externe.
- Zakharova E.A., Fleury S., Guerreiro K., Willmes S., Rémy R., Kouraev A ., Heinemann G., 2015. Sea iceleads detection using SARAL/AltiKa altimeter. Marine Geodesy, 38(S1), 522-533, doi 10.1080/01490419.2015.1019655
- Merino Nacho M., Le Sommer J., Durand G., Jourdain N., Madec G., Mathiot P., Tournadre J., 2016, Antarctic icebergs melt over the Southern Ocean : climatology and impact on sea ice, Ocean Modelling, August 2016, Volume 104, Pages 99-110, DOI: 10.1016/j.ocemod.2016.05.001, pdf
- Tournadre J., Accensi M., Girard-Ardhuin F., 2013, The ALTIBERG iceberg data base, Doc. Tech. LOS, pdf
- Tournadre, J. N. Bouhier, F. Girard-Ardhuin, F. Rémy, 2015 : Large icebergs caracteristics from altimeter waveforms analysis. Journal of Geophys. Res., vol 120, pp 1954-1974. DOI : 10.1002/2014JC010502.
- Tournadre, J., N. Bouhier, F. Girard-Ardhuin, F. Rémy, 2016: Antarctic icebergs distributions 1992-2014. Journal of Geophys. Res., vol 121, pp 327-349. DOI : 10.1002/2015JC011178