Abstract
Deriving the snow depth on Antarctic sea ice is a key factor in estimating sea-ice thickness distributions from space or airborne altimeters. Using a linear regression to model snow depth from observed ‘total freeboard’, or the snow/ice surface elevation relative to sea level is an efficient and promising method for the estimation of snow depth for instruments which only detect the uppermost surface of the sea-ice conglomerate (e.g. laser altimetry). However the Antarctic pack-ice zone is subject to substantial variability due to synoptic-scale weather forcing. Ice formation, motion and melt undergo large spatio-temporal variability throughout the year. In this paper we estimate snow depth from total freeboard for the ARISE (2003), SIPEX (2007) and SIPEX-II (2012) research voyages to the East Antarctic pack-ice zone. Using in situ data we investigate variability in snow depth and show that for East Antarctica, relationships between snow depth and total freeboard vary between each voyage. At a resolution of metres to tens of metres, we show how regression-based snow-depth models track total freeboard and generally over-estimate snow depth, especially on highly deformed sea ice and at sites where ice freeboard makes a substantial contribution to total freeboard. For a set of 3192 records we obtain an in situ mean snow depth of 0.21 m (σ=0.19m). Using a regression model derived from all in situ points we obtain the same mean, with a slightly lower variability (σ=0.16m). Using voyage-specific subsets of the data to derive regression models and estimate snow depth, mean snow depths ranged from 0.19 m (model derived from SIPEX observations) to 0.25 m (model derived from SIPEX-II observations). While small, these discrepancies impact ice thickness estimation using the assumption of hydrostatic equilibrium. Mean in situ ice thickness for all samples is 1.44 m (σ=1.19m). Using empirical models for snow depth, ice thickness varies from 1.0 to 1.8 m with the best match to the in situ mean given when snow depth is derived using a snow depth model from all observations (1.53 m, σ=1.55m). However, mean values only tell part of the story when investigating the sea-ice thickness distribution. Here we explicitly show how modelling snow depth and ice thickness based on a total freeboard signal compares with in situ observations. This provides insight into the confidence we place in ice thickness distributions derived using a total freeboard signal and empirically-derived models for snow depth.
Original language | English |
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Pages (from-to) | 41-52 |
Number of pages | 12 |
Journal | Deep-Sea Research Part II: Topical Studies in Oceanography |
Volume | 131 |
DOIs | |
Publication status | Published - 1 Sept 2016 |
Bibliographical note
Publisher Copyright:© 2016 Elsevier Ltd
Funding
This research was supported by the Australian Government׳s Cooperative Research Centres Programme through the Antarctic Climate and Ecosystems Cooperative Research Centre; and AAS projects 2298 , 2901 , 4073 . We thank the crew of RSV Aurora Australis , AAD voyage management, science technical support and all field support personnel for assistance with in situ data collection. We thank the reviewers for their assistance in clarifying and strengthening this work.
Funders | Funder number |
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Australian Government׳s Cooperative Research Centres Programme |
Keywords
- East Antarctica
- Empirical modelling
- Ice-thickness estimate
- Sea ice
- Snow depth
- Total freeboard