§  Arctic sea ice is getting thinner, younger, and more seasonal

Increasing  solar  radia.on  under   Arc.c  sea  ice  –     Seasonality  and  spa.al  distribu.on    

10 March 2014

Stefanie Arndt, Marcel Nicolaus

Motivation

§  Arctic sea ice is getting thinner, younger, and more seasonal

§  Observed decrease in surface albedo [Perovich et al., 2011] , earlier melt onset, and longer melt season [Markus et al., 2009]

>  Increase in sea ice/snow melt,

and light absorption and transmission

>  Changes affect the ice-

associated ecosystem

Motivation

§  First up-scaling of transmitted heat fluxes through Arctic sea ice in summer by Nicolaus et al.

[2012,2013]

>  Extending and generalizing the method by new a parameterization to quantify

large-scale,

multi-seasonal, and interannual changes

in the radiation transfer through Arctic sea ice [Arndt&Nicolaus, subm. in JGR]

Solar heat input into the

Arctic Ocean through

sea ice in August 2011

[Nicolaus et al., 2013].

Method

New up-scaling method for calculation of under-ice radiation

01#

Jan# EMO# MO# MO+14d# EFO# FO# FO+60d# Dec# ^31#

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Transmittance

FYI

melting FYI new FYI new MYI melting MYI MYI

I" II" III" IV" V" VI" I"

Pond"

covered"

sea"ice"

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Transmittance

FYI

melting FYI new FYI new MYI melting MYI MYI

I Winter II Early melt

III Continuous melt IV Summer

V Fall freeze-up

VI Continuous freeze

Total transmittance of pond covered sea ice.

Parameterization

Method

New up-scaling method for calculation of under-ice radiation

Data sets

§  Sea ice concentration [OSI SAF]

§  Sea ice age [Maslanik et al., 2007, 2011]

§  Downward surface solar radiation [ECMWF]

§  Melt/ Freeze onset dates [Markus et al., 2009]

§  Melt pond fraction [Rösel et al., 2012]

01#

Jan#

EMO# MO# MO+14d# EFO# FO# FO+60d#

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Transmittance

FYI melting FYI new FYI new MYI melting MYI MYI

I" II" III" IV" V" VI" I"

Pond"

covered"

sea"ice"

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2

Transmittance

FYI melting FYI new FYI new MYI melting MYI MYI

I Winter II Early melt

III Continuous melt IV Summer

V Fall freeze-up VI Continuous freeze

Total transmittance of pond covered sea ice.

Parameterization

Seasonality of transmitted heat fluxes

Apr May Jun

Jul Aug Sep

§  96 % of the annual under-ice radiation are transmitted in only 4 months (May to August)

≙ 51.2×10 ¹⁹ J

§  Highest fluxes in June (20.9×10 ¹⁹ J)

Monthly mean of transmitted heat fluxes through Arctic sea ice in 2011.

Annual and monthly trends

(a)$ (b)$

Trend in annual total solar heat input through Arctic sea ice from 1979 to 2011.

§  Light transmission

increases by 1.5% per year Arctic-wide since 1979

Annual trends

[Arndt&Nicolaus, subm. in JGR]

Annual and monthly trends

Monthly trends

(a)$

60 65 70 75 80 85 90

Solar heat flux [10 19 J]

Total annual 2011

(b)$

1979 0 1983 1987 1991 1995 1999 2003 2007 2011

10 20 30 40

Solar heat flux [10 19 J]

May June July August 60

65 70 75 80 85 90

Solar heat flux [10 19 J]

Total annual

(a)$

60 65 70 75 80 85 90

Solar heat flux [10 19 J]

Total annual 2011

(b)$

1979 0 1983 1987 1991 1995 1999 2003 2007 2011

10 20 30 40

Solar heat flux [10 19 J]

May June July August 60

65 70 75 80 85 90

Solar heat flux [10 19 J]

Total annual

Monthly Arctic-wide solar heat input through Arctic sea ice from 1979 to 2011.

§  Strongest increase in June by 2.3% per year

Sensitivity studies

Melt onset – 14 days

(a)$ (b)$

Freeze onset + 14 days

Changes in total solar heat input through sea ice in 2011.

Increase of 24 % of

transmitted under-ice radiation

Increase of 1 % of transmitted under-ice radiation

(c) Assuming only FYI in the entire Arctic in 2011, transmitted under-ice radiation increases by another 18 %.

(a)$ (b)$

[Arndt&Nicolaus, subm. in JGR]

Conclusions

§  Changes in sea ice properties have a large impact on the energy budget

§  The additional energy input into the sea ice and upper ocean impacts e.g.

§  Heat storage in the ocean mixed layer

§  Melt season duration/ timing

§  Melting processes

§  Bio-geo-chemical processes

§  Comparison with surface radiation trends [Perovich et al., 2011]:

§  Larger trend in light transmission than absorption

>  Additional transmittance-melt

Outlook

§  How big are the effects of a changing physical environment on the ecosystem and coupled climate system exactly?

(paper in prep. by Fernandez et al.)

§  How does the data product change with an improved Arctic-wide snow depth and sea ice thickness data product?

!!

Stefanie Arndt^1,2*, Marcel Nicolaus¹, Wolfgang Dierking¹, Sascha Willmes³

BREMERHAVEN Am Handelshafen 12 27570 Bremerhaven Telefon 0471 4831-0 www.awi.de

! Persistent snow cover throughout the summer

! Snow evaporation dominates the snow thinning, whereas sea-ice melt is characterized by lateral and bottom melt

! Strong metamorphosis of snow causes increasing formation of superimposed ice and ice-layers in the snow pack

! Summer melt defined through enhanced diurnal freeze-thaw cycles in snow wetness, emissivity ε, brightness temperature TB

1 Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung Bremerhaven, Germany 2 Universität Bremen, Germany 3 Universität Trier, Germany

* stefanie.arndt@awi.de

References

Arndt, S. and Nicolaus, M. (subm.), Increasing solar radiation under Arctic sea ice – Sesonality and spatiial distribution, submitted in Journal of Geophysical Research, 2014.

Markus, T., J. C. Stroeve, and J. A. Miller (2009), Recent changes in Arctic sea ice melt onset, freezeup, and melt season length, Journal of Geophysical Research, 114(C12), C12024.

Willmes,!S.,!C.!Haas,!M.!Nicolaus,!and!J.!Bareiss!(2009),!Satellite!microwave!observaAons!of!the!interannual!variability!of!snowmelt!on!sea!ice!in!the!Southern!Ocean,!Journal(of(

Geophysical(Research3Oceans,!114.!

Detection and quantification of sea-ice melt

The mass and energy balance of sea ice are strongly connected through the transfer of solar radiation from the atmosphere through snow and sea ice into the ocean. Recent studies show that a major uncertainty in quantification of the sea ice mass balance is related to the timing and duration of the melt season as well as the very limited knowledge of the characteristics of the snow layer on top.

Therefore, we are working on (1) improving our understanding of radiative transfer into and through Arctic and Antarctic sea ice

and its impacts on sea-ice melt, and (2) improving existing and developing new remote sensing tools and data products. This allows for estimates of sea-ice melt and freeze rates, and large- scale estimates of heat fluxes in and under sea ice. Here we show established methods for melt onset detection on sea ice based on passive microwave data, and we present first new ideas for future improvements for onset detection methods.

Introduction

! Snow melts completely during summer – resulting in a melt pond covered surface

! Almost simultaneous snow-melt onset in the entire Arctic

! During melt onset: Formation of liquid water within the snow pack

> Increasing surface emissivity ε and brightness temperature TB,

decreasing backscatter coefficient σ⁰ (for MYI)

> Melt onset detection based on the sensitivity of TB to liquid

water content in the snow pack

Surface properties and melt onset detection

May Jun

Jul Aug

Figure 1: Early melt onset (EMO) and early freeze onset (EFO) from 2009 onwards [Markus et al.,2009 updated].

Early melt onset

Early freeze onset

2009 2010 2011 2012

Early melt onset

2008/2009 2009/2010 2010/2011 2011/2012

Figure 3: Solar heat fluxes under Arctic sea ice from May to August 2011 [Arndt&Nicolaus, subm.].

ARCTIC ANTARCTIC

(a)$(a)$ (b)$(b)$

Annual trend from 1979 to 2011

Figure 4: Annual solar heat input through Arctic sea ice.

(a) Average and (b) trend from 1979 to 2011.

The trend is corrected for the trend in sea ice concentration.

Purple shaded areas were not covered with sea ice during the maximum extent in all years [Arndt&Nicolaus, subm.].

! Light transmission increases by 1.5%

per year Arctic-wide since 1979

! The strongest trend is derived for June (4.8×10¹⁹ J per year)

! How do snow cover properties change during an annual cycle?

! Which sea ice and snow cover classification is reasonable for Antarctic sea ice?

! How can the stronger Antarctic sea ice drift be included in the transmittance parameterization?

Key questions for light transmittance in the Antarctic

! 4 months account for 96 % of the total annual solar heat input through sea ice

InternaAonal!Symposium!on!Sea!Ice!in!a!Changing!Environment,!Hobart!(Tasmania,!Australia),!

9!–!14!March!2014!

> Detection limits through weak diurnal cycles, strong ice drift, …

First ideas of data improvements

Applying melt onset routine by Markus et al.

[2009] in areas of…

Applying MeDeA [Willmes et al., 2009] in areas of …

Seasonality in 2011

Application for energy balance calculations

! Strong diurnal freeze-thaw cycles

! Low summer temperatures (T2m< 0°C)

! Weak melt pond coverage

> Comparable surface conditions as on

Antarctic sea ice

! Weak diurnal freeze-thaw cycles

! Strong surface snow melt

> Comparable surface conditions as on Arctic sea ice

! How to handle sea ice drift/ deformation, polynias, … ?

> Deriving and estimating seasonality and trends of light transmission through Antarctic sea ice

!!!?!!!?!

!?!!!!!!!?!

!!!!?!!!!?!

Figure 2: Early melt onset (EMO) and early freeze onset (EFO, only for perennial sea ice) from 2008/2009 onwards detected by a Melt Detection Algorithm MeDeA [Willmes et al.,2009, updated].

The white area represents the maximum sea ice extent in the given season.

20!Mar!

01!May!

01!Jul!

Early freeze onset

18!Jul!

01!Sep!

01!Nov!

01!Jan!

01!Oct!

01!Dec!

01!Jan!

01!Nov!

01!Oct!

01!Dec!

01!Feb!

01!Mar!

§  How can the developed Arctic-based method be transferred to Antarctic surface processes?

(see Poster Session A, location number 008)

Thanks  for  your  a;en.on!