Concept information
Preferred term
CRAC-ICE
Definition
- Short Title: CRAC-ICE Project URL: http://www.annee-polaire.fr/api/la_recherche_francaise_et_l_api/81_collaborative_research_into_antarctic_calving_and_iceberg_evolution Proposal URL: http://classic.ipy.org/development/eoi/proposal-details.php?id=81 CRAC-ICE will be a coordinated investigation into calving processes on three major Antarctic ice shelves, and a (long-term) monitoring of icebergs in the Southern Ocean, including the study of the physical processes related to iceberg drift and decay. The processes leading to a calving event include the initiation and propagation of through-cutting rifts. Iceberg calving can result in a significant loss of mass from the Antarctic ice sheet, and represents ~ 65% of the total ice sheet ablation. Therefore, it is critical to understand the processes which precede and lead up to a major calving event in order to realistically assess how future climate changes might affect the Antarctic Ice Sheet. Post-calving, iceberg drift is influenced by the shape of the coastline, bottom topography, and a combination of tides, currents, wind, and sea ice. Monitoring the evolution of icebergs as they drift into warmer waters provides a valuable experiment in how rapid climate change influences ice shelves - especially such components as firn compaction, the impact of surface meltwater, ponding, and iceberg break-up. Grounded icebergs cause a severe devastation of the sea floor, forcing benthic communities to re-colonise. Iceberg melting and decay represents a significant source of freshwater (and mineral dust) primarily into the upper layers of the Southern Ocean's northern fringe. A stabilisation of the weakly stratified water column has important and poorly understood consequences for sea ice and water masses involved in deep and bottom water formation, and the biology of the euphotic zone. CRAC-ICE's first objective is to develop an understanding of the mechanics of ice shelf rift initiation and propagation via three complementary components: 1. Fieldwork: Networks of autonomous observation stations (GPS, seismometers, webcams and AWS) will be deployed around selected rift tips on each ice shelf for one year. The measurements will be combined with oceanographic measurements of currents, temperature and salinity, and significant wave heights. These mirror campaigns will provide a continuous time series of rift widening (GPS) as well as rupture locations and source mechanisms (seismic), which can be compared with environmental effects such as large storms. Ground penetrating radar profiles will be collected, to probe the subsurface structure of the rift. Cores will be taken of the mélange inside each rift to determine its composition. On the Ross Ice Shelf, autonomous vertical profilers will be installed beneath a rift to monitor ocean currents and mixing, and to take depth profiles of salinity and temperature on a daily basis for one year. 2. Satellite data analysis: Satellite images (e.g. MODIS, MISR, ASTER, RADARSAT) provide "snapshot" observations of the surface expression of the rift at discrete time intervals. Image pairs provide estimates of velocity, ice strain rates, and rift widening rates on much larger spatial and temporal scales than the ground-based measurements. InSAR analysis using Radarsat will provide rift deformation rates. ICESat/CryoSat laser and radar altimeter data will be used to provide surface profile information for each rift and estimate mélange thickness. 3. Modeling: Physical modelling, using a large ice tank, will be used to simulate ice shelf behaviour over a range of conditions. The results from these experiments, along with data collected in (1) and (2), will be used to construct realistic suites of numerical models of ice shelves which explicitly include fracture physics. This will enable careful hypothesis testing of the mechanisms and processes which occur during ice shelf break up - including the effect of mélange within rifts. CRAC-ICE's second objective is the monitoring of iceberg evolution as they drift away from their calving sites, based on: 1. Shipbased observations near drifting bergs, including the deployment of autonomous observation stations on icebergs of various sizes equipped with sensors for position, air pressure, strain and tilt, reporting via the ARGOS system. 2. Satellite data analysis using imagery (e.g. Envisat, Radarsat, ALOS) with different spatial resolution. A pattern-recognition algorithm will be applied to identify and track icebergs with minimum lengths between 200 - 500 m (depending on pixel size). Radar imagery will be used to monitor the physical changes in icebergs (surface melting, firn compaction, ponding, etc.) from their sites of calving through to their final break-up. Estimates of the total mass loss (and related freshwater flux) will be made by combining size information from satellite imagery with freeboard elevation from satellite altimetry (ICESat, CryoSat, Envisat), both compared with modeled melt rates. 3. Modeling of iceberg drift to guide image acquisition. The simulated track will be used to bridge the interval between a pair of images. Modeled side wall (including wave erosion) and basal melting will be used to verify the observed mass losses due to size and freeboard reductions. (en)
Broader concept
- A - C (en)
URI
https://gcmd.earthdata.nasa.gov/kms/concept/69966e64-9135-4d58-a1f5-85db86edb20b
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