32 years of sea ice physics and biogeochemistry
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32 Years of Sea Ice Physics and Biogeochemistry. S.F. Ackley. Sea Ice Scales. Antarctic Sea Ice Profile. Antarctic Sea Ice Freeboards. Conclusions through Halftime ~1994. Algal incorporation in Frazil Ice exceeded incorporation in Columnar Ice

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Conclusions through halftime 1994
Conclusions through Halftime ~1994

  • Algal incorporation in Frazil Ice exceeded incorporation in Columnar Ice

  • Nearly all Antarctic sea ice contains measurable Chl content but low concentrations

  • Primary mechanism of incorporation is wave pumping in frazil-pancake ice

  • Concentrations in ice exceeded that in underlying water column by 10x to 100x


Conclusions through halftime 19941
Conclusions through Halftime (~1994)

  • Algal growth led to nutrient drawdown, so high algal concentrations required renewal of nutrients from surface sea water

  • Top surface freezing in autumn led to convective overturning and fueled a fall bloom of algae (Fritsen et al 1994 from ISW)

  • Warming leads to porous sea ice, while cooling can cause brine rejection and upwelling (Golden et al 1997)


Krill under sea ice
Krill under Sea Ice

Credit: Klaus Meiners


Krill swarms

Krill under sea ice

First evidence of extensive krill swarms under ice


2 nd half 2007 to present
2nd Half (2007 to Present)

  • SIPEX-E.Antarctic Ice—A Seasonal Progression

  • SIMBA-Bellingshausen Sea Ice—Temperature Cycling

  • DMS and DMSP Production

  • A Sea Ice CO2 Pump


ICESat 1290

ICESat 1305

ICESat 0166

ICESat 0025

ICESat 0055

ICESat 1297

Background: AMSR-E ice conc. 10 Oct. 2007; courtesy of G. Spreen


SIPEX Ice temperature and salinity (iron site)

Figure: Delphine Lannuzel

Photo: Mats Granskog


SIPEX - Ice algal biomass

Chlorophyll a (mg m-2)

Relative ice core depth (%)

Time →

Most of the algal biomass was at the bottom of the cores,

except towards the end of the experiment


Time Series Sampling, How does the sea ice at one site change with time? Occupied one floe for 27 days.


Mixture of Ice Types at Ice Station Belgica change with time? Occupied one floe for 27 days.

Icebergs

open water lead

Liege Site

(off photo)

Brussels Site - level first year ice- no flooding

Deformed thick ice with snow cover- Fabra Site (60 to 80% neg. freeboard)


Brussels site- level ice, thin snow change with time? Occupied one floe for 27 days.

Liege site- mod. roughness, thicker snow

Brussels site-smooth, thin snow

Fabra site

highly deformed, thick snow cover


C. Fritsen change with time? Occupied one floe for 27 days.

C. Fritsen

SIMBA Brussels Site

Texture

G = granular

C = columnar

FS = froz. snow

f = fine

m = medium

c = coarse

s = small

l = large

M. Lewis


SIMBA Liège Site change with time? Occupied one floe for 27 days.

Texture

G = granular

C = columnar

FS = froz. snow

f = fine

m = medium

c = coarse

s = small

l = large

M. Lewis


Brussels Site IMB change with time? Occupied one floe for 27 days.

Radiometer Buoy (Brussels 1)

Thinner snow cover allows cold pulse

to penetrate sea ice

No flooding at snow/ice interface

Ice thickness loss


Thermodynamics at Brussels Site ( change with time? Occupied one floe for 27 days. unflooded)


DMS(P) and change with time? Occupied one floe for 27 days. Chla evolution at Brussels Site

[Chla] measurements by I. Dumont, C. Fritsen, B. Saunders


Liège Site IMB change with time? Occupied one floe for 27 days.

Colder Air Temperatures don’t

penetrate thick snow cover

Snow/Ice Interface continuously

flooded with sea water

Sea Ice relatively isothermal

Irregular ice bottom affects sonar

returns. Bottom pinger reset when

CTD removed for repairs.


DMS(P) and change with time? Occupied one floe for 27 days. Chla evolution at Liège Site

[Chla] measurements by I. Dumont, C. Fritsen, B. Saunders


Radiometer indicates change with time? Occupied one floe for 27 days.

changes in irradiance,

snow cover thickness, biological growth

Opening and closing of

Leads in the ice

Breakup of the

ice floe where IMBs

separate and drift

independently


Simba accomplishments
SIMBA Accomplishments change with time? Occupied one floe for 27 days.

Antarctic sea ice is a springtime “Biogeochemical Reactor” Driven by Physical Feedback, where thermal changes drive porosity and convection, leading to:

  • Nutrient Flux =>Enhanced Biological Productivity

  • Biological Degradation=>DMSP+DMS Flux

  • Porosity Changes=>CO2 Exchanges

  • Shelf Sediments and Iceberg Melting as Iron sources


The sea ice co2 pump
The Sea Ice CO2 Pump change with time? Occupied one floe for 27 days.


A long lived dogma… change with time? Occupied one floe for 27 days.

  • Weiss et al 1979, Gordon et al 1984, Poisson and Chen 1987

    • « Weddell Sea pack ice effectively blocks the air-sea exchange of gases »

    • No evidence of marked ventilation is found in deep waters of the Weddel Sea. Thus sea ice appears to prevent air-sea exchange.


A long lived dogma challenged

A long lived dogma challenged?… change with time? Occupied one floe for 27 days.

Science 282: 2238

  • Kelley & Gosink 1970s-80s

    • « unlike ices from pure freshwater, sea ice is a highly permeable medium for gases »

    • They found rate of CO2 penetration about 60 cm h-1 at -7°C

    • « gas migration through sea ice is an important factor in ocean-atmosphere winter communication particularly when the surface temperature is > -10° » (Gosink et al., 1976. Nature 263: 41)

Golden et al., 1998

  • Theoretical and experimental evidence that sea ice permeability increases considerably above -5°C, the so-called “law of fives”(Golden et al., 1998. Science 282: 2238)


Sea ice phase diagram
Sea Ice Phase Diagram change with time? Occupied one floe for 27 days.


Caco 3 dissolution precipitation

CaCO change with time? Occupied one floe for 27 days. 3 dissolution/precipitation

2HCO3- + Ca2+ CaCO3 + CO2

  • Thompson and Nelson 1956 showed that at a temperature just below the freezing point calcium carbonate begins to precipate from the entrained brines in sea ice and remains in the ice.

  • Weiss et al 1979 observed alkalinity anomalies in the surface water of the Weddell Sea

  • Jones et al. 1983 observed a transfer of CaCO3 from the ice to surface waters in the Arctic Ocean

  • Papadimitriou et al. 2004 and Dieckmann et al. observed CaCO3 precipitation in artificial and natural sea ice and identified it as Ikaite

  • Rysgaard et al. 2007 suggested that CaCO3 precipitation in sea ice might act as a sink for CO2.


45 change with time? Occupied one floe for 27 days.

SEA ICE PUMP

Is CO2 released to the atmosphere anytime new ice forms?

(Answer on Next Slide)

D. Nomura, 2006

A potential abiotic CaCO3 Carbon source

fall/winter

In winter, precipitation of CaCO3 occurs within sea ice.

Produced CO2 is expelled with brine, while CaCO3 is trapped within brine channels

Brine sink rapidly carrying CO2 (see Brine Drainage Slide)

Part of CO2 which passes below the pycnocline is « removed » from the system.

2HCO3- + Ca2+

CaCO3 + CO2

CO2

Rysgaard et al., 2007, Delille et al., in prep.


Upward co2 flux over new ice at the simba site
Upward CO2 Flux over New Ice at the SIMBA site change with time? Occupied one floe for 27 days.

Figure 17:Temperature at the ice interface and CO2 fluxes over ice and snow (positive fluxes correspond to efflux to the atmosphere) at 5 sites of the second "frost flowers" station.


Brine drainage at simba
Brine Drainage at SIMBA change with time? Occupied one floe for 27 days.


GAS COMPOSITION IN SEA ICE change with time? Occupied one floe for 27 days.

46

A potential abiotic CaCO3 Carbon pump

fall/winter

spring

In spring, CaCO3 trapped within sea ice dissolves. This process consumes CO2.

Budget of winter and spring processes is a net sink of CO2. It depends on:

ratio of CaCO3 trapped vs CO2 expelled (?)

quantity of CO2 which pass below the pycnocline during the autumn-winter (?)

CaCO3 + CO2

2HCO3- + Ca2+

2HCO3- + Ca2+

CaCO3 + CO2

CO2

CO2

Rysgaard et al., 2007, Delille et al., in prep.


Conclusions change with time? Occupied one floe for 27 days.

Sea ice exhibits marked CO2 dynamics controlled by (i) salinity (ii) precipitation/dissolution of CaCO3 and (iii) primary production

CaCO3 precipitation occurs within sea ice and can be a very efficient pathway for atmsopheric CO2 uptake

Sea ice in spring exchanges CO2 with the atmosphere. Sea ice acts first as a source of CO2 to the atmosphere then as a sink.

This spring sink of the antarctic sea ice is about -0.025 PgC yr. It would represent an additional sink of 50% to the CO2 sink of the Southern Ocean

Taking into account CaCO3 precipitation and particular sea-ice processes especially discrepency in salt:gas rejection (loose et al. 2009) and possible artefacts in the transcient hallogen tracers, it might deserve to revisite C anthropogenic computation in sea ice covered waters


Where are we
Where are we? change with time? Occupied one floe for 27 days.

  • Strong Coupling between the biogeochemistry and physics of the ice, related to growth, thermal driving, snow

  • Climatically active gases, DMS and CO2, are important new developments

  • Time series from IMBs with additional sensors like radiometers, oxygen, pCO2 look important

  • Modeling of fluid flow looks critical

  • Subtle differences in conditions can lead to big differences in the biogeochemistry


It s been fun

It’s been fun change with time? Occupied one floe for 27 days.

Thanks to Elizabeth for the invite.


48 change with time? Occupied one floe for 27 days.

GAS COMPOSITION IN SEA ICE

CO2 : the ”trouble maker”

Summary

  • pCO2 is a difficult variable to measure in the sea ice environment

  • a suite of measurement techniques are still in development and in the need of proper validation

  • pCO2 is generally supersaturated in most of the sea ice cover during the winter

  • pCO2 is highly undersaturated in the whole sea ice cover during spring and summer

  • Potential and concurrent mechanisms for the pCO2 drawdown during the summer are:

    • Dilution of brines

    • Dissolution of calcium carbonate

    • Primary Production

  • There is a potential inorganic CaCO3 CO2 pump associated to sea ice growth and decay


From land fast sea ice to multiyear pack ice change with time? Occupied one floe for 27 days.

Ispol drift experiment

R.V. Polarstern

Nov-Dec 2004

First and multi-year pack ice

AA03-V1 cruise

R.V. Aurora Australis

Sep-Oct 2003

First year pack ice

Simba drift experiment

R.V. N.B. Palmer

Oct 2007

First year pack ice


47 change with time? Occupied one floe for 27 days.

GAS COMPOSITION IN SEA ICE

66°38’ S

66°38‘30 S

66°39' S

(from Solubility equations)

(from Oxygen production)

(from Total alcalinity anomaly)

CO2 : the ”trouble maker”

Balancing the effects…

Dumont d’Urville, 1999

It works!...and all three processes contribute!

Delille al. , 2007


Key processes sal brine sal seawater

Key processes ? (Sal brine > sal seawater) change with time? Occupied one floe for 27 days.


Key processes sal brine sal seawater1

Key processes ? (Sal brine > sal seawater) change with time? Occupied one floe for 27 days.


Air ice gas transfer

Air-ice gas transfer change with time? Occupied one floe for 27 days.

Permeable

Impermermeable


Scaled using sea ice temperature derived from the nemo lim model

Scaled using sea ice temperature derived from change with time? Occupied one floe for 27 days. the NEMO-LIM model

mmol m² d-1

Spring air-ice fluxes of CO2 for the Antarcticseaicecoverisassessed to -0.025 PgCfromOctober to December


Co 2 fluxes

CO change with time? Occupied one floe for 27 days. 2 fluxes

Air-ice fluxes:

-0.025 Pg

Air-sea fluxes south of 50°S:

-0.05 Pgyr-1

Springantarcticseaicecoverwouldrepresent an additionalsink of about 50% of the overall CO2sink of the SouthernOcean


Independent assessment

Independent assessment change with time? Occupied one floe for 27 days.

Estimates of potential air-ice CO2 fluxes related to spring and summer physical and biogeochemical processes observed during the 2003/V1 and ISPOL cruises. Flux representative of a 4 months period.

The overall CO2 fluxes reach 142 mmol m-2.

Taking into account a mean value for the Antarctic sea ice edge surface area of 16×106 km2, the corresponding overall CO2 fluxes account for 0.029 PgC.

This compares favourably with our previous estimate of an additional sink of 0.025 PgC.


Sea ice exchanges CO change with time? Occupied one floe for 27 days. 2 with the atmosphere

Semiletov

et al. 2007

Semiletov

et al. 2004

Nomura et al.

Heinesch

et al.

T2-017

Zemelink et al. 2006

This study

Semiletov et al. 2004

Zemelink et al. 2006

Semiletov et al. 2007

Nomura et al. T2-017

Heinesch et al.

This study


Back of the envelope computation change with time? Occupied one floe for 27 days.

Semiletov

et al. 2007

Semiletov

et al. 2004

Nomura et al.

Heinesch

et al.

T2-017

Zemelink et al. 2006

This study

Semiletov et al. 2004

Zemelink et al. 2006

-1 gC m-2 month-1

Semiletov et al. 2007

Nomura et al. T2-017

Heinesch et al.

This study


Back of the envelope computation change with time? Occupied one floe for 27 days.

Rawmean of spring air-ice CO2 fluxes

-1 gC m-2month-1

Spring surface of antarcticseaicecover

20* 106 km²

Time length of fluxes

2 months

Overallspringantarctic

air-ice CO2 fluxes

- 0.04 PgCyr-1

Overall S.O. open water fluxes (Takahashi et al. 2009)

- 0.05 PgCyr-1


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