Modeling the Impact of Wind Intensification on Antarctic Sea Ice Volume

Abstract

A global sea ice-ocean model is used to examine the impact of wind intensification on Antarctic sea ice volume. Based on the NCEP-NCAR reanalysis data, there are increases in surface wind speed (0.13% yr 21 ) and convergence (0.66% yr 21 ) over the ice-covered areas of the Southern Ocean during the period 1979-2010.Driven by the intensifying winds, the model simulates an increase in sea ice speed, convergence, and shear deformation rate, which produces an increase in ridge ice production in the Southern Ocean (1.1% yr 21). The increased ridged ice production is mostly in the Weddell, Bellingshausen, Amundsen, and Ross Seas where an increase in wind convergence dominates. The increase in ridging production contributes to an increase in the volume of thick ice (thickness . 2 m) in the Southern Ocean, while the volumes of thin ice (thickness # 1 m) and medium thick ice (1 m , thickness # 2 m) remain unchanged over the period 1979-2010. The increase in thick ice leads to an increase in ice volume in the Southern Ocean, particularly in the southern Weddell Sea where a significant increase in ice concentration is observed. The simulated increase in either the thick ice volume (0.91% yr 21 ) or total ice volume (0.46% yr 21 ) is significantly greater than other ice parameters (simulated or observed) such as ice extent (0.14-0.21% yr 21 ) or ice area fraction (0.24%-0.28% yr 21 ), suggesting that ice volume is a potentially strong measure of change.

Sources of heterogeneous variability and trends in Antarctic sea-ice

“…This behaviour is consistent with winds being the main driver of Antarctic sea-ice increases 17 . The WALL simulation is also more consistent with the observed increase in Antarctic sea-ice area between 1979 and 2007 than the CORE2 ARTICLE simulation.…”

“…Recently, observations and modelling have highlighted the importance of wind variability in accounting for the behaviour of Southern Hemisphere sea-ice 10,[15][16][17][18][19] . Originally, it was argued that trends in dynamics and thermodynamics linked to local winds were responsible for producing the regional sea-ice trends in most sectors of the Southern Ocean 16 .…”

Recent changes in Antarctic Sea Ice

“…A modelling study [50] has suggested that the recent increase of wind speed and convergence in the sea ice zone may have increased ridging production, leading to an increase in volume of thick ice, although it is not possibly to verify this at present. Hopefully, future developments will allow sea ice thickness to be routinely monitored allowing the investigation of changes in ice volume.…”

Aspects of intraseasonal variability of Antarctic sea ice in austral winter related to ENSO and SAM events

“…Atmospheric reanalysis daily data were taken from the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim gridded data product over 1995-2014(Dee and others, 2011. We used mean sea-level pressure (MSLP), geopotential height (1000,975,950,925,900,850,800,750,700,650,600,550, 500 hPa), 2 m temperature (T2m), and meridional component of 10 m wind (V10m) at 2°× 2°latitude/longitude resolution, for ease of computation and acknowledging that features of interest are of large spatial scale, from meso-α to synoptic scale.…”

“…Indices were averaged for the 3 months of July, August and September, with the threshold ±0.5°C (ENSO)/standard deviations (SAM) take as the cutoff for positive and negative 'events' according to NOAA/NWSCPC (Table 1). Based on the above index values, four El Niño years (1997,2002,2004, 2009), seven La Niña years (1995( , 1998( , 1999( , 2000( , 2007( , 2010( ), nine ENSO-neutral years (1996( , 2003( , 2005( , 2006( , 2012( , 2013( , 2014, six SAM positive years (1997,1998,2004,2008,2010,2012), eight SAM negative years (1995,1996,2000,2002,2007,2009,2011,2013) and six SAM-neutral years (1999,2001,2003,2005,2006,2104) were selected for analyses in this study.…”