comparing & contrasting regional sea ice changes · pdf filecomparing & contrasting...
TRANSCRIPT
Sharon Stammerjohn
Institute of Arctic & Alpine Research
University of Colorado Boulder
(& many esteemed and cited colleagues)
Comparing & Contrasting Regional Sea
Ice Changes
Photo taken by author, Oden 2007, southern Bellingshausen Sea
Sea Ice Challenges Workshop
Hobart, Tasmania 12-13 May 2015
Outline
Photo: Maria Stenzel, Amundsen Sea (NBP0901)
1. The Mean Seasonal & Regional Picture
sea ice, winds, ice motion, ice thickness
2. Regional Atmosphere-Ocean-Ice Changes
wind/waves, ice motion, ice edge location, ice
concentration, ice thickness
3. Seasonal Atmosphere-Ocean-Ice
Feedbacks
Simpkins et al (2012), Fig 2
Seasonal Sea Ice Concentration (SIC) & Variability S
tan
da
rd D
evia
tio
n
(Contours mark 25%, 50% & 75% SIC)
Summer
(1980-2008)
Autumn
Winter
Spring
Stammerjohn et al (2012), updated
Mean Ice Season Duration & Variability
1979-2014
Mean Ice Season Duration
Autumn Ice Edge Advance (STD)
Spring Ice Edge Retreat (STD)
Holland and Kwok (2012), Fig 1
Mean Sea-Level Pressure & Ice Motion
Apr-Oct (1992-
2010)
Correlation between Winds & Ice Motion
Apr-Oct (1992-
2010)
Summer (JFM)
Autumn (AMJ)
Winter (JAS)
Spring (OND)
Mean Seasonal Sea Ice Thickness Holland et al (2014) Fig 3
2003-2008
Antarctic ice edge changes are
largely wind-driven, especially
during spring & autumn
Photo: Maria Stenzel, Amundsen Sea (NBP0901)
But what appears on the surface
is very different from what
appears below…
Photo: Langdon Quetin, Western Antarctic Peninsula (beset during NBP0107)
Seasonal pack ice thickening > ~1 m is largely
due to wind-forced rafting and ridging
Wind/Waves & Ice Drift Lead to Changes in:
• Timing of ice edge advance/retreat
• Ice concentration
• Ice thickness
Ice Season Duration Trend
Stammerjohn et al (2012), Fig 1f
Now ~3 months
shorter
Now ~2 months longer
(1979-2013) Now ~1
months
shorter
Now ~1
months
longer
Wind-Driven Trends in Sea-Ice Motion Holland & Kwok (2012), Fig 3
Ice Motion & Concentration Trends
Ice Motion (vectors)
(black, sig >90%)
Ice Concentration
Apr-Jun
(1992-2010)
Wind (vectors)
(black, sig >90%)
Sea-level pressure
Apr-Jun
(1992-2010)
Wind & Sea-Level Pressure Trends
Kohout et al (2014), Fig 4
Trends in Ice Edge Latitude & Significant Wave Heights
(1997-2009)
(Sep-Feb)
(Mar-Aug)
Ob
serv
ed Mod
eled
Holland et al. (2014), Fig 9
Modeled Ice Thickness & Ice Velocity Trends
Autumn (AMJ) Winter (JAS) (1992-2010) (1992-2010)
Massonnet et al (2013), Fig 2d
Modeled Ice Thickness Trends (1980-2008)
With assimilated
sea ice
concentration
Stammerjohn et al (2012), Fig 4
Ice-Ocean Feedbacks
See also Nihashi & Ohshima (2001) & Holland (2014)
Bellingshausen Sea
Amundsen Sea
Weddell gyre
Ross gyre
Figure: Doug Martinson (adapted from Orsi et al, 1995)
The Regional Proximity of warm Circumpolar Deep Water
(CDW) to Continental Shelves
Paolo et al (2015), Fig 1
Ice shelf
thickness &
volume changes
Volume losses increased
by 70% in last decade
Upwelled ocean
heat a factor?
Summary
Photo: Palmer LTER, Avian Island, west Antarctic Peninsula
• Regional differences in sea ice changes largely reflect regional differences in
atmospheric circulation patterns, that in turn can lead to differences in wind-
and wave-forcing
• Continental shelf regions also differ in their coastal icescapes (e.g., polynyas, ice
tongues, fast ice), which in turn contributes to regional differences in sea ice
• Continental shelf regions differ in their bathymetry and proximity to the ACC,
thus differ with respect to shelf currents and in the degree to which they may be
influenced by warm CDW
• Seasonal sea ice changes exhibit strong feedbacks between spring and the
subsequent autumn, consistent with ice-albedo/ocean feedbacks, accentuating
regions of strong sea ice changes
Extra Slides
(Holland & Kwok, 2012)
Fig 1b
Sfig 4c
Apr-Oct 1992-2010 Correlations
Vector correlation
(ice motion & winds)
% explained
Smoothed fraction of autumn ice diff
trend explained by flux divergence
Key Findings
• Wind and ice motion strongly coupled
in Pacific and Atlantic sectors
• Weakly coupled around East
Antarctica, where coastal current
dominates
• Flux divergence (advection + divergence)
explains large fraction of concentration
difference around West Antarctica
• Wind-driven thermodynamic changes
dominate elsewhere
Stammerjohn et al (2012), GRL, Fig 1
2.9 months
shorter ice
season
3.3 months
shorter
2.6 months
longer
Mean Timing in Spring Sea Ice Retreat & Autumn Advance
Stammerjohn et al (2008), Fig 2
(1979-2006)
Holland (2014), Fig 2
Trends in Ice Concentration, 1979-2012
Wind (vectors)
(black, sig >90%)
Sea-level pressure
(Apr-Jun)
Trends in Sea-Level Pressure & Winds, 1992-2010 (Holland & Kwok, 2012, Nature Geoscience, Fig 3b)
(e.g., Stammerjohn et al, 2008; Turner et al, 2009)
The trends in winds are
consistent with the
trends in sea ice Warm northerlies: less sea ice
Cold southerlies: more sea ice
(Meredith et al, 2010, Prog Oc, Fig 3)
High latitude response
to SAM & ENSO
Variability
SLP vs
SAM
Atmospheric Low deepens
…during +SAM
SLP vs
ENSO
…and during La Nina
(e.g., Stammerjohn et al, 2008; Turner et al, 2009)
SAM/ENSO
partially explains
regional trends
(Meredith et al., 2010, Prog. Oceanog, Fig 3)
But there are other tropical
linkages & feedbacks too SLP vs
SAM
For example, Atmospheric Low
deepens during…
+SAM (summer-autumn trend) (e.g., Turner et al, 2009)
SLP
vs ENSO
La Nina (spring) (e.g., Fogt & Bromwich, 2006)
Central Tropical Pacific warming
(spring trend) (e.g., Schneider et al, 2012;
Ding et al, 2011)
Ice feedback (autumn trend) (e.g., Raphael et al, 2011)
Tropical & North Atlantic warming
(winter trend) (Li et al, 2014)
Annual Hydrographic Survey
(CTD-Rosette, Net Tows)
4 Thermistor Moorings
Palmer Long-Term Ecological Research (LTER) Study Region
(1993 - ongoing)
Rothera Base (UK)
Avian Island
Adélie Penguin Colonies
Charcot Island
Palmer Station (US)
Satellite remote sensing
ocean color (chlorophyll)
surface temperature
sea ice, 1978-present Process Studies
SLOCUM Glider Base
Canyons & Deeps
LTER local Time series
Semi-weekly, Oct -April
BAS RaTS Local Time Series
Weekly, year-round
Anvers Island
Antarctic Peninsula
Sediment Trap
Ice Season 90 days shorter;
Ice Advance 60 days later
(Martinson et al, 2008, DSRII, Fig 10)
Heat content of sub-
pycnocline waters has
increased
Wind & Ice Motion
Correlation (Apr-Oct)
MODIS Terra, 2 Jan 2011
Amundsen
Sea Polynya
Pine Island
Polynya
Amundsen Sea Polynya International Research Expedition
Stammerjohn et al (submitted), Elementa
Randall-Goodwin et al (submitted), Elementa
(ASPIRE, Dec 2010 to Jan 2011)
Intensive ocean obs…
…indicate high
meteoric content
Wind & Ice Motion
Correlation (Apr-Oct)
Polynyas, Ice Production & seasonal
Evolution in the Ross Sea (PIPERS)
(Jacobs & Giulivi, 2010, J Clim, Fig 3)
Sub-Surface Ross
Sea Freshening
Ice Season 80
days longer
Wind & Ice Motion
Correlation (Apr-Oct)
Inbound Stations
Outbound Stations
Buoy Array Deployments
Polynya Stations
Terra Nova Bay
Polynya
Ross Sea Polynya
PIPERS Field Campaign:
April-May 2017
(Maksym et al, 2012, Oceanography, Fig 5)
Challenges of Obtaining Sea Ice Thickness Measurements
IceSAT data courtesy of Ron Kwok
Oct-Nov 2003 Mean Sea Ice Thickness
ICESat Satellite Altimetry Ship-based Visual Observations
ASPeCt ICESat
Nihashi & Ohshima (2015), Fig 5:
Frequency of fast ice & polynya
occurrence during the freezing period
(March October) for the period 2003-
2011
Measurements from Ice Mass Balance (IMB)
buoys
Dep
th (
cm)
Dep
th (
cm)
Sea ice thickness: the balance between snow
accumulation and ocean heat
Amundsen Sea
•Warm ice regime
•Rapid snow accumulation
•Flooding, minimal freezing
•Ice rots within, overwhelming
‘conveyor belt’ growth
mechanism (snow-ice formation
top, melt bottom)
Weddell Sea
•Cold ice regime
•Thin snow cover
•Minimal surface melt in
summer
(Maksym et al, 2012, Oceanography, Fig 4)