Post on 02-Jan-2016
Assessing the Ecological Impact of the Antarctic Ozone Hole
Using Multi-sensor Satellite DataDan Lubin, Scripps Institution of OceanographyKevin Arrigo, Dept. of Geophysics, Stanford UniversityOsmund Holm-Hansen, Scripps Institution of Oceanography
Enhancement of UV Flux at Antarctic Surface
•Measured since 1988•NSF UV Monitoring Program
Palmer StationMcMurdo StationUshuaia, ArgentinaBarrow, AKSan Diego, CAhttp://www.biospherical.com
10-4
10-3
10-2
10-1
100
101
102
290 300 310 320 330 340 350 360
Palmer Station UV Solar Spectra
Day 296 16:00 Z (210 DU, ovc)Day 326 13:00 Z (334 DU, clear)Day 296 Theoretical Clear Sky
spec
tral
irra
dian
e (m
icro
wat
ts c
m-2
nm
-1)
wavelength (nm)
The Antarctic Marine Food Web
Primary Production
Grazing by Krill (Euphausia superba)
Higher Predators(leopard seals, orcas)
Field Work on Ecological Effects•Began in late 1980s, primarily at Palmer Station, west of Antarctic Peninsula
•Smith et al. (Science, 1990) ICECOLORS: 2-4% reduction in primary production in marginal ice zone (MIZ)
•Holm-Hansen et al. (Photochem. Photobiol., 1993), reduction < 1% integrated over entire Southern Ocean
Need for Satellite-Based Assessment•Comprehensive field work is expensive, limited in time and place.
•Previous estimates of total impact on Southern Ocean primary production are rough extrapolations from point measurements to larger areas.
•Satellite data now offer complete coverage of the Southern Ocean for evaluating key forcing factors.
Surface UVR Algorithm Developmentco-locating TOMS, AVHRR, SSM/I in 3 regions
•Sea ice more influential than clouds on TOA UV radiance.•Parameterization of UV sea ice albedo as function of sea ice concentration.•Method developed to use TOMS and SSM/I alone.•see Lubin and Morrow, JGRd (2001).
Seasonal variability in sea ice concentration
1 Sep1992
1 Oct1992
1 Aug1992
1 Nov1992
1 Dec1992
1 Jan1992
10010 20 30 40 50 60 70 80 900Sea ice concentration (%)
A B
C D
E F
10 -8
10 -7
10 -6
10 -5
10 -4
10 -3
10 -2
280 300 320 340 360 380 400 420
Action Spectra
bio
log
ica
l we
igh
ting
fu
nct
ion
wavelength (nm)
Photoinhibtion in AntarcticPhytoplankton (Neale et al., 1998)
Erythema(McKinlay & Diffey, 1987)
Comparison with Palmer Station UV Monitor Data
y = 1.005x - 10.354
R2 = 0.88
0
300
600
900
1200
0 300 600 900 1200
Measured 305 nm daily dose (J m -2 nm-1)
0
200
400
600
800
1000
1200
Dec 1992
Date
MeasuredModeled
Nov 1992Oct 1992
A B
Geographic Assessment of Enhanced UV Fluxes
• Spectral flux weighted by action spectrum for photoinhibition in Antarctic phytoplankton
• Define climatological UVR:– in terms of mean cloud attenuation, sea ice, 1979 total ozone
– evaluate 20-year standard deviation
• Enhancement: where photoinhibition flux exceeds climatological mean by 2 or more
• Geographically significant enhancement: where the enhanced fluxes intersect biomass as determined by SeaWiFS
• Lubin et al., GRL 2004
UVR Enhancement at Palmer Station, Spring 1992
0
0.01
0.02
0.03
0.04
0.05
0.06
240 260 280 300 320 340 360
A. Comparison with NSF UV Monitor
satellitemeasured
305
nm fl
ux (
W m
-2 n
m-1
)
day number of 19920.0002
0.0004
0.0006
0.0008
0.0010
0.0012
0.0014
0.0016
240 260 280 300 320 340 360
B. Criteria for Enhanced UVR
1992 satellite doseclimatological satellite doseclimatological dose + 1.96 sigmaclear sky dose
dose
ra
te (
wei
ght
ed
W m
-2)
day number of 1992
100
150
200
250
300
350
400
450
240 260 280 300 320 340 360
C. Total Column Ozone
19921979
Dob
son
units
day number of 1992
0
20
40
60
80
100
240 260 280 300 320 340 360
D. Sea Ice Concentration
1992climatological
day number of 1992
conc
entr
atio
n (%
)
0
5
10
15
20
25
30
35
80 85 90 95
Fraction of Southern Ocean BiomassUnder Enhanced UV Photoinhibition Flux
SeptemberOctoberNovemberDecember
mon
thly
ave
rage
bio
mas
s fr
actio
n
year
UVR Enhancements by Southern Ocean SectorLubin et al., GRL 2004
0
10
20
30
40
50
60
70
-180 -120 -60 0 60 120 180
1979198119831985
surf
ace
biom
ass
frac
tion
(%)
bin center longitude
A. Pre-Discovery Years
0
10
20
30
40
50
60
70
-180 -120 -60 0 60 120 180
1987198819891990
surf
ace
biom
ass
frac
tion
(%)
bin center longitude
B. Post-Discovery Years
0
10
20
30
40
50
60
70
-180 -120 -60 0 60 120 180
199219941996
surf
ace
biom
ass
frac
tion
(%)
bin center longitude
C. Early-Mid 1990s
0
10
20
30
40
50
60
70
-180 -120 -60 0 60 120 180
199719981999
surf
ace
biom
ass
frac
tion
(%)
bin center longitude
D. Late 1990s
Spectral Flux at the Sea Surface
• Edd and Edi are direct and diffuse components• surface reflection divided into direct and diffuse components,
both of which are sum of specular reflection and reflectance from sea foam
• sea foam reflectance a function of wind stress• Fresnel’s law for specular reflection
Ed (,0, t) 1 d Edd (,0 , t) 1 i Edi( ,0 ,t)
dr 0.5sin2( w )
sin2( w )
tan 2( w )
tan 2( w )
In-Water Optics
• Beer’s law for spectral flux penetration
• Diffuse attenuation coefficient Kd(z) partitioned into components describing attenuation by pure water, phytoplankton, detritus, and chromophoric dissolved organic matter.
Ed (z ) Ed (0 )e K (z)z
Kd (z) Kdw Kdp(z) KdDet(z) KdCDOM (z)
In-Water Optics - Components
Kdw(z) bbw(z) aw(z)
Kdp(z) bbp(z) ap
* (z)Chla(z)
KdDet(z) aDet (440, z)eS1( 400)
KdCDOM(z) aCDOM(400,z)eS2 ( 400)
•Pure Water: coefficents from Smith & Baker (1981)
•Plankton (chlorophyll) from Sathyendranath et al. (1989)
•Detritus from work by Arrigo et al. (1998)
•CDOM from work by Mitchell and Holm-Hansen (1991); Arrigo et al. (1998)
Phytoplankton Production
• G is phytoplankton growth rate (d-1) calculated from temperature and light availability
• C/Chl a is the phytoplankton C:Chl a mass ratio (50)
• Beff is effective phytoplankton concentration
• G is modeled in terms of a temperature-dependent maximum rate and a light limitation term
PP(z, t) G(z, t) CChla Beff (z, t)
G(z, t) G0ekT( z) 1 exp
PUR(z, t)
Ek
Cumulative Exposure to UVR
• Throughout the day, the physiological inactivation of algal biomass (effective biomass Beff) is expressed by reducing Beff with increasing UVR exposure.
• At dawn, Beff(z,t) is set = Chl a (z,t)
• Vertical mixing: simulated by averaging Beff over MLD, then applying this average to each layer within MLD
Beff (z, t) Beff (z, t t)e Hinh (z,t )
Hihn(z, t) A()Ed (, z, t)ddt280nm
700nm
t 0
t
Comparison with Field Observations:% decrease in C-fixation relative to no UVR
64 S, 72 W MODEL ICECOLORS
1979 1992 ozone hole 1990
Surface
+UVA+UVB 55 59 4 56-77+UVA 48 48 0 45-65+UVB 21 30 9 8-20
5 m depth
+UVA+UVB 40 43 3 35-80+UVA 36 36 0 15-42+UVB 11 16 5 21-60
Station A59.19 S, 56.89 E
04 October
1992, UVA+B1979, UVA+B1992, UVA1979, UVA1992, UVB1979, UVB
12:0012:3013:0013:3014:0014:3015:00
1992, UVA+B1979, UVA+B1992, UVA1979, UVA1992, UVB1979, UVB1992, No UV1979, No UV
12:0012:3013:0013:3014:0014:3015:00
0 0.05 0.10 0.15 0.20
0 0.05 0.10 0.15 0.200 0.05 0.10 0.15
Hinh Beff (mg Chl a m-3)
0
5
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25
30
0
5
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25
30
0
5
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25
30
Beff (mg Chl a m-3)
0 0.5 1.0 1.5 2.0 2.5 3.0
Daily production (mg C m-3)
0
10
20
30
40
50
60
70
80
90
100
A B
DC
•Photoinhibition dose Hinh varies with time and depth, 30% greater in exp. run than control at surface
•Assess individual contributions of UV-B and UV-A
•Substantial UV-A contribution to Hinh and Beff
•Panel B: 1979 (control)
•Panel C: 1992 (exp.)
Temporal Variation in Primary Production Loss
over Southern Ocean
-0.1
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
5
10
15
20
25
% loss in production
% decrease in ozone
R = 0.85
Aug Sep Oct Nov Dec
Date
0
50
100
150
200
250
300
350
1979
1992
A
B
Major Conclusion of Small Impact• Surface UVR-induced losses of primary production can be several percent,
with large UV-B component• When integrated to 0.1% light depth, loss of primary production throughout
Southern Ocean, due to enhanced UV-B, is < 0.25%• Major reasons: strong UV-B attenuation with depth, location of most ozone
depletion over Antarctic continent, temporal mismatch between maximum ozone loss and maximum phytoplankton abundance
• Several sensitivity analyses did not alter this conclusion:– changing MLD and mixing time– temperature dependence of primary production– Photoacclimation parameter Ek, specifying saturation of photosynthesis– detrital and CDOM absorption– phytoplankton absorption– variability in Action Spectrum– Instantaneous versus cumulative exposure to UVR