Antarctic Sea Ice Extent (Observations)

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Antarctic Sea Ice Extent (Observations) Rob Massom (Australian

What does the satellite record tell us about variability & trends? 1.

trend, but considerable Inter-annual & Regi

, Bootstrap SB2 SIE monthly anomalies (courtesy J Comiso, NASA) S

Nishio, 2008) Weddell Sea Extent, x10 6 km 2 1.7 ±0.

6 %/dec 0 o Weddell Bell- Amundsen Indian Extent, x10 6 km 2 1.7 ±0.

4 %/dec Ross Sea Ross W Pacific W Pacific Ocean 4.1 ±0.5 %/dec 1.

1 Antarctic Sea Ice Extent (Observations) Rob Massom (Australian Antarctic Division + ACE CRC, Tasmania, Australia) 1. What does the satellite record tell us about variability & trends? 1.A Passive microwave SIE & SIC (from 1979): Overall slight positive trend, but considerable Inter-annual & Regional Variability e.g., Bootstrap SB2 SIE monthly anomalies (courtesy J Comiso, NASA) S Hemisphere SB2 new enhanced version version of BT2/SBA (Comiso & Nishio, 2008) Weddell Sea Extent, x10 6 km ±0.2 %/dec Bell-Amundsen -3.5 ±0.6 %/dec 0 o Weddell Bell- Amundsen Indian Extent, x10 6 km ±0.4 %/dec Indian Ocean 2.8 ±0.4 %/dec Ross Sea Ross W Pacific W Pacific Ocean 4.1 ±0.5 %/dec 1.9 ±0.6 %/dec NB Data inconsistency problem (Eisenmann et al., 2014) only w/ BT1 i.e., fixed prior to AR5. - Different algorithms but similar trends & variability (e.g. Parkinson & Cavalieri, 2012; IPCC, 2013 Chapter 4, Suppl. Mat.)

SIE Trend, x10 6 km 2 / dec Trends have strong spatial &

trends (1979-2013) Courtesy J. Comiso (NASA), J.

(2015) Weddell Autumn Winter Bell-Amundsen Spring Summer

2 SIE Trend, x10 6 km 2 / dec Trends have strong spatial & temporal dependence - Trends in monthly mean SIE - SI Conc trends ( ) Courtesy J. Comiso (NASA), J. Turner (BAS) e.g., Turner et al. (2015) Weddell Autumn Winter Bell-Amundsen Spring Summer Trend, % / dec - Strong seasonal dependency in Weddell & Bell-Amundsen sectors e.g., Holland (2014)

trend (1979/80-2010/11) Spatially consistent with trend in annual mean SI concentration 1979-2013 Turner et al. (2015) -3.

3 1.B Change in Sea Ice Seasonality Stammerjohn et al. (2008, 2012) - Timings of annual advance & retreat, & coverage duration a key factor (Parkinson, 1998; Massom & Stammerjohn, 2010) Duration trend (1979/ /11) Spatially consistent with trend in annual mean SI concentration Turner et al. (2015) -3.3 Months Signif at <5% level Months Trend, % / dec Ross Sea: >60% of overall net increase - NB Considerable decadal variability in observed trends (Simpkins et al., 2013) - Need for longer time series (continuation of PMW record)

1.C Pre-1979 (pre-nimbus 7 SMMR) Satellite Observations Reprocessed ESMR data (1973-76) (+ digitised NIC charts) affect the long-term trend (Cavalieri et al.

, 2013) Extent Anomaly Early visible & IR imagery suggests higher overall extents in 1960s: - Late 1960s (Sissala et al., 1972; Streten, 1973; Zwally et al., 1983) - Sept 1964 extent of 19.7 ±0.

4 1.C Pre-1979 (pre-nimbus 7 SMMR) Satellite Observations Reprocessed ESMR data ( ) (+ digitised NIC charts) affect the long-term trend (Cavalieri et al., 2003) Extent NB An unknown bias in ESMR data (IPCC, 2013) Trend: ±0.08 x 10 6 km 2 /dec Nimbus 1 AVCS composite Sept (Meier et al., 2013) Extent Anomaly Early visible & IR imagery suggests higher overall extents in 1960s: - Late 1960s (Sissala et al., 1972; Streten, 1973; Zwally et al., 1983) - Sept 1964 extent of 19.7 ±0.03 x 10 6 km 2 higher than any maximum in (Meier et al., 2013) - SIEs in May July 1966 (10.7, 14.3 & 16.4 x 10 6 km 2 ) similar to the 1980s (Gallaher et al., 2014) - Apparent strong inter-annual variability Aug 1966 = 15.9 ±0.04 x 10 6 km 2 may be unreliable due to uneven sampling Invaluable data mining, but uncertainties: navigation & cloud-ice discrimination errors may introduce bias compared to PMW estimates + difficult to quantify & compare.

1.C Coastal Fast Ice Narrow but key element & interface between ice sheet & ocean/pack ice (Massom et al.

To date: 10 o W 170 o E, 2000-2008 (Fraser et al.

3 % / yr Syowa Ice Sheet 100 km Amery Ice Shelf Davis - But again regional contrasts: W Pacific SE Indian Ocean -0.40 ± 0.

5 1.C Coastal Fast Ice Narrow but key element & interface between ice sheet & ocean/pack ice (Massom et al., 2010) Sensitive to (change in) winds (Massom et al., 2009) & waves (Langhorne et al., 2001) MODIS mapping at 2 km res. To date: 10 o W 170 o E, (Fraser et al., 2012) 20 day composites - Short time series but upturn overall after 2004: Pack Ice Mawson Overall Extent Anomaly ± 0.3 % / yr Syowa Ice Sheet 100 km Amery Ice Shelf Davis - But again regional contrasts: W Pacific SE Indian Ocean ± 0.37 %/yr +4.7 ± 0.42 %/yr - Extending to circumpolar, and in time - Greater variability - Increase in summer persistence since 2004 winds & iceberg groundings (under investigation) Short time series - extending in time & to circum-polar (in progress)

6 2. Other observations and how they inform our understanding 2.A Proxy estimates: Also indicate more extensive ice prior to the early 1970s: Whale catch locations (de la Mare, 1997, 2009): Oct-March decline from s to 1970s-1980s (of o lat) largest in S Atlantic, but also across Indian Ocean-Ross Sea. - Challenged by Ackley et al. (2003) ship-satellite bias in estimates of summer ice edge. - See also Cotté & Guinet (2007) large SIE reduction in 1960s in Weddell Sea. Ice core Methanesulphonic acid (MSA) records (Sarah Das talk): - Late-winter maximum SIE declines of 1.5 o in E Antarctic since 1950s (Curran et al., 2010). ~20% decline but not uniform: ~10-yr cyclical variation - Also 0.7 o decline in Bellingshausen Sea during 20 th C (Abram et al., 2010). Ice core deuterium excess data - 2-5% reduction in Ross Sea SI Area from mid-1950s to early-1990s (Sinclair et al., 2014) S Orkney Islands fast ice duration (from 1903) (Murphy et al., 1995; 2014): - Change in the 1950s - Proxy for longer-term SIC & SIE in N Weddell Sea & regional atmospheric forcing. Issue re proxy reconstructed time series high observational uncertainty (difficult to quantify & validate) But invaluable & consistency in results/findings. MORE Sarah Das talk

7 2.B Ship logbook records - largely from summer UK Ship (Discovery) Reports from 1920s & 1930s (Mackintish, 1972) digitised by Ackley et al. (2003) Early expeditions (Parkinson, 1990) Cook (1772-4) Bellingshausen ( ) Wilkes ( ) Courtesy Leanne Armand - Parkinson (1990) - no compelling evidence of a substantial difference compared to 1970s - Reports of more extensive ice in Weddell & Amundsen Seas - isolated outer bands? (Worby and Comiso, 2004) Patchy record, high uncertainty (no validation + other factors)

8 3. What are the key uncertainties in the observational record? PMW SIC/SIE record accuracy (bias) & precision (SD) affected by data, algorithm & physical factors: - Mismatches in calibration (Meier et al., 2011), resolution & scanning geometry between sensors (Comiso & Nishio, 2008) uncertainties minimised by recent reprocessing - NB Spurious trend identified by Eisenman et al. (2014) rectified. - Different main algorithms (i.e., Bootstrap, NT) yield different absolute values (Parkinson & Comiso, 2008) but generally similar trends e.g., IPCC (2013) - Absolute differences caused by differences in: 1) choice/utilization of channels; 2) tie-points; 3) sensitivities to changes in surface physical temp & emissivity; & 4) weather filters (Comiso et al., 1997; - Accuracies: ±5% to ±15% - errors largest in summer, & in marginal ice zone (MIZ) year round (& thin/new ice to ±30%) (Brucker et al., 2014; Comiso et al., 2011) - See also ESA algorithm comparison report (2013): Ivanova et al. (2015): Uncertainties not fully known, but estimates are maturing. Need further cal/val (Brucker et al., 2014)

Resolution dependent e.g., AMSR v SSM/I (Comiso & Nishio, 2008) Melt season bias (Nov-Feb) PMW edge 1-1.

9 What does the PMW sensor see as the ice edge (at 15% conc)? MIZ - typically low conc & diffuse? Typical banding 100 km 10 m Overlap in emissivities of ice & ocean + weather effects SIC/SIE errors increase in MIZ Resolution dependent e.g., AMSR v SSM/I (Comiso & Nishio, 2008) Melt season bias (Nov-Feb) PMW edge o latitude S of observations (Worby & Comiso, 2004) Reasonable agreement during growth season (March-Oct) MODIS 18 Oct., 2001 (res. 250 m), ~ o E

Sea Ice Extent an incomplete descriptor of sea ice state e.g.

, 2006) Sustained NW ly winds Extreme ice compaction against Antarctic Pen.

83m - BUT immense dynamic compaction & thickening - to ~20 m N.B. Coincided with extensive melt!

10 Sea Ice Extent an incomplete descriptor of sea ice state e.g., Bellingshausen Sea, Sept 2001-Feb 2002 (Massom et al., 2006) Sustained NW ly winds Extreme ice compaction against Antarctic Pen. - Anomalously low regional ice extent Sea Ice Ant Pen Ice conc, % Diver Tim = 1.83m - BUT immense dynamic compaction & thickening - to ~20 m N.B. Coincided with extensive melt!! Air temps to >0 o C CRUCIAL NEED additional info on sea ice thickness/volume ALSO importance of extreme events Photo courtesy Lang Quetin (UCSD) Courtesy: Lang Quetin, UCSB

11 4. What additional observations are critical? Large-scale ice thickness & volume, snow depth (+ validation) Precipitation & snow accumulation/loss (Leonard & Maksym, 2011) Zs:Zi, flooding & snow ice formation/contribution (Maksym & Markus, 2008) Large-scale motion & dynamics/deformation at high-resolution, satellite w/ more buoys (IMB etc.) Independent data for determining satellite SIC/SIE algorithm & data accuracy/bias & precision i.e., in MIZ & covering seasons & regions Process studies what is driving observed patterns (including waves), & regional & seasonal/temporal dependence & variability - MIZ, interior pack, polynyas/coastal, dynamics v thermodynamics - Ice-ocean-atmosphere (interaction/flux) measurements Cross-cryosphere interactions Thank You!

Trends in the sea ice cover using enhanced and compatible AMSR-E, SSM/I, and SMMR data

Click Here for Full Article JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113,, doi:10.1029/2007jc004257, 2008 Trends in the sea ice cover using enhanced and compatible AMSR-E, SSM/I, and SMMR data Josefino C.