Altimetric observation of wave attenuation through the Antarctic marginal ice zone using ICESat-2

Abstract

Abstract. The Antarctic marginal ice zone (MIZ) is a highly dynamic region where sea ice interacts with ocean surface waves generated in ice-free areas of the Southern Ocean. Improved large-scale (satellite-based) estimates of MIZ width and variability are crucial for understanding atmosphere-ice-ocean interactions and biological processes, and detection of change therein. Legacy methods for defining the MIZ width are typically based on sea ice concentration thresholds, and do not directly relate to the fundamental physical processes driving MIZ variability. To address this, new techniques have been developed to determine MIZ width based on the detection of waves and calculation of significant wave height attenuation from variations in ICESat-2 surface heights. The poleward MIZ limit (boundary) is defined as the location where significant wave height attenuation equals the estimated satellite height error. Extensive automated and manual acceptance/rejection criteria are employed to ensure confidence in MIZ width estimates, due to significant cloud contamination of ICESat-2 data or where wave attenuation was not observed. Analysis of 304 MIZ width estimates retrieved from four months of 2019 (February, May, September and December) revealed that sea ice concentration-derived MIZ width estimates were far narrower (by a factor of ~7) than those from the new techniques presented here. These results suggest that indirect methods of MIZ estimation based on sea ice concentration are insufficient for representing physical processes that define the MIZ. Improved measurements of MIZ width based on wave attenuation will play an important role in increasing our understanding of this complex sea ice zone.

Directional Surface Wave Spectra And Sea Ice Structure from ICEsat-2 Altimetry

“…The provided algorithm has particular use when applied at scale. We expect 10 − 15% of the IS-2 tracks in polar regions to be dominated by waves (Brouwer et al, 2021). That implies roughly 3 − 4.5 × 10 3 cases of diverse wave observation in the MIZ (as of June 2022) to sample the large space of wave-ice interaction, which is likely enough to better constrain seaice wave interactions.…”

The Antarctic Marginal Ice Zone and Pack Ice Area in CMEMS GREP Ensemble Reanalysis Product

“…In fact, the properties of Antarctic ice cover do not directly depend on the degree of coverage. In-situ measurements carried out in the Southern Ocean showed that close pack ice with SIC up to 100% do have the dynamical properties of the MIZ (Alberello et al, 2019;Vichi et al, 2019;Brouwer et al, 2021), which discredits the reliability of thresholdbased definition. Vichi (2021) proposed an alternative MIZ definition that is based on statistical properties of the SIC and its spatial and temporal variability.…”

Floes, the marginal ice zone and coupled wave-sea-ice feedbacks

“…At any instant, the area of ice-covered regions with energetic ocean surface waves can be much smaller than that ‘influenced’ by waves more generally. In global measurements with the ICESat-2 altimeter, the MIZ was defined as those regions where waves were identified at least 7.5% of the time [ 6 ]—and of 4402 individual observations of sea ice heights in the Southern Ocean, just 304 (7.0%) were identified visually as having waves in them [ 15 ]. The MIZ is dynamic, and ICESat-2 overflights inconsistently sample the constantly varying sea ice surface.…”

“…The influence of ocean surface waves is also used to define the MIZ [10]. Waves can be observed propagating long distances within the sea ice [8,9,[11][12][13][14][15]. A companion review in this special issue discusses the theory and observation of waves in the MIZ [16].…”

“…A companion review in this special issue discusses the theory and observation of waves in the MIZ [16]. Recently, new satellite platforms have allowed the observation of waves in sea ice at high resolution and at global scales, making it feasible to quantify global MIZ extent [13,15,17]. Yet as sea ice is an efficient damper of high-frequency wave energy, waves in sea ice are often long-period swell waves, episodically generated by storms or mesoscale weather events [12,[18][19][20].…”