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Recent Changes in Phytoplankton Communities Associated with Rapid Regional Climate Change Along the Western Antarctic Peninsula

Authors:
  • 1.Science Systems and Applications, Inc., 2.NASA, GSFC, 3.Florida Atlantic University, HBOI

Abstract and Figures

The climate of the western shelf of the Antarctic Peninsula (WAP) is undergoing a transition from a cold-dry polar-type climate to a warm-humid sub-Antarctic-type climate. Using three decades of satellite and field data, we document that ocean biological productivity, inferred from chlorophyll a concentration (Chl a), has significantly changed along the WAP shelf. Summertime surface Chl a (summer integrated Chl a approximately 63% of annually integrated Chl a) declined by 12% along the WAP over the past 30 years, with the largest decreases equatorward of 63 degrees S and with substantial increases in Chl a occurring farther south. The latitudinal variation in Chl a trends reflects shifting patterns of ice cover, cloud formation, and windiness affecting water-column mixing. Regional changes in phytoplankton coincide with observed changes in krill (Euphausia superba) and penguin populations.
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DOI: 10.1126/science.1164533
, 1470 (2009); 323Science et al.Martin Montes-Hugo,
Along the Western Antarctic Peninsula
Associated with Rapid Regional Climate Change
Recent Changes in Phytoplankton Communities
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, 6 of which can be accessed for free: cites 26 articlesThis article
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increased in Europe after 1990, in agreement with
the AOD changes seen in Figs. 1 and 2. However,
many more stations have measured visibility and
many have longer histories. The use of emis-
sions to infer aerosols introduces considerable
uncertainty in the estimation of aerosol impacts
on radiation (16).
The ViI AOD over land is a complementary
constraint to satellite-derived AOD (4,5)thatis
most readily obtained over oceans. The latter in-
cludes volcanic and high-level dust contributions
that are necessarily excluded by the ViI approach.
The AOD estimated from the Advanced Very
High Resolution Radiometer (AVHRR) instru-
ment (1719) for the period 1991 to 2005, averaged
globally over the oceans, indicates a change com-
parable in magnitude but opposite in sign to that
indicated by Fig. 1. Changes seen in regional analy-
ses of these data (18,19), however, appear to be
entirely consistent with those found here, showing
decreases in Europe and increases in industrializing
Asia. In particular, the strongest decreases (greater
than 0.003 year
1
) indicated in Fig. 2 are over a belt
north of the Mediterranean extending into Asia,
matching the analyses over the Mediterranean,
Black, and Caspian seas (19), and the strongest
increases (greater than 0.003 year
1
) are in near-
coast industrializing Asia, thereby matching these
analyses (19). Thus, it would appear that estimates
of change over these regions for the period since
1991 might be improved by combining the ViI and
AVHRR estimates.
Although increases in the concentrations of
many types of aerosols may have contributed to
the AOD increase, by far the largest documented
changes in aerosols and their precursors are those
from the increased use of fossil fuels, in particular
SO
2
. If so, the changes reported here appear to be
inconsistent with the conclusions of the Inter-
governmental Panel on Climate Change (IPCC)
[(20), chapter 2, p. 160], which cited studies con-
cluding that global emissions of sulfate aerosol
decreased by 10 to 20 Tg year
1
from 1980 to
2000. Those estimates may not have adequately
accounted for the 20 Tg year
1
increase of sulfate
emission over Asia during that period (21). Increases
in biomass burning of tropical forest and agri-
culture (22,23) may also have contributed to in-
creases in AOD. The decrease of AOD in Europe
is a consequence of near-constant fossil fuel use
coupled with a large decrease in sulfur content as
required by air quality regulations.
Current descriptions of AOD as provided by
satellite data (6) have been used as a major con-
straint on the aerosol radiative forcing used as part
of the IPCC modeling of climate change (4,5).
However, the objective of simulating the 20th-
century climate as a means of validating the models
has been limited by an absence of observational
information on the time history of AOD, a short-
coming that is remedied by the data set de-
scribed here.
References and Notes
1. M. Wild et al., Science 308, 847 (2005).
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Int. J. Climatol. 27, 1505 (2007).
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Lett. 33, L01812 (2006).
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11. C. Ruckstuhl et al., Geophys. Res. Lett. 35, L12708 (2008).
12. V. Vestreng, M. Adams, J. Goodwin, Inventory Review
2004: Emission Data Reported to CLRTAP and the NEC
Directive. EMEP/EEA Joint Review Report (Norwegian
Meteorological Institute, Oslo, 2004).
13. D. G. Streets et al., J. Geophys. Res. 108, 8809 (2003).
14. A. Ito, J. E. Penner, Global Biogeochem. Cycles 19,
GB2028 (2005).
15. T. Novakov et al., Geophys. Res. Lett. 30, 1324 (2003).
16. J. M. Haywood, O. Boucher, Rev. Geophys. 38, 513 (2000).
17. M. I. Mishchenko et al., Science 315, 1543 (2007).
18. M. I. Mishchenko, I. V. Geogdzhayev, Opt. Express 15,
7423 (2007).
19. T. X.-P. Zhao et al., J. Geophys. Res. 113, D07201 (2008).
20. Intergovernmental Panel on Climate Change, Climate
Change 2007: The Physical Science Basis. Contribution of
Working Group I to the Fourth Assessment Report of the
Intergovernmental Panel on Climate Change, S. Solomon
et al., Eds. (Cambridge Univ. Press, Cambridge, 2007).
21. T. Ohara et al., Atmos. Chem. Phys. 7, 4419 (2007).
22. C. Venkataraman, G. Habib, A. Eiguren-Fernandez,
A. H. Miguel, S. K. Friedlander, Science 307, 1454 (2005).
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T. W. Swetnam, Science 313, 940 (2006); published
online 5 July 2006 (10.1126/science.1128834).
24. We thank A. Riter for her editing and proofreading
of the manuscript. GSOD data are available at
ftp://ftp.ncdc.noaa.gov/pub/data/gsod.
Supporting Online Material
www.sciencemag.org/cgi/content/full/323/5920/1468/DC1
Materials and Methods
Figs. S1 to S7
Table S1
References
22 October 2008; accepted 23 January 2009
10.1126/science.1167549
Recent Changes in Phytoplankton
Communities Associated with Rapid
Regional Climate Change Along the
Western Antarctic Peninsula
Martin Montes-Hugo,
1
Scott C. Doney,
2
Hugh W. Ducklow,
3
William Fraser,
4
Douglas Martinson,
5
Sharon E. Stammerjohn,
6
Oscar Schofield
1
The climate of the western shelf of the Antarctic Peninsula (WAP) is undergoing a transition from a
cold-dry polar-type climate to a warm-humid sub-Antarctictype climate. Using three decades of
satellite and field data, we document that ocean biological productivity, inferred from chlorophyll a
concentration (Chl a), has significantly changed along the WAP shelf. Summertime surface Chl a
(summer integrated Chl a ~63% of annually integrated Chl a) declined by 12% along the WAP over
the past 30 years, with the largest decreases equatorward of 63°S and with substantial increases in Chl
a occurring farther south. The latitudinal variation in Chl a trends reflects shifting patterns of ice cover,
cloud formation, and windiness affecting water-column mixing. Regional changes in phytoplankton
coincide with observed changes in krill (Euphausia superba) and penguin populations.
Over the past several decades, the marine
ecosystem along the western continental
shelf of the Antarctic Peninsula (WAP)
(62° to 69°S, 59° to 78°W, ~1000 by 200 km) has
undergone rapid physical climate change (1).
Compared with conditions in 1979 at the be-
ginning of satellite data coverage, seasonal sea
ice during 2004 arrived 54 T9 (1 SE) days later in
autumn and departed 31 T10 days earlier in
spring (2). Winter air temperatures, measured
between 62.2°S, 57.0°W and 65.3°S, 64.3°W,
warmed at up to 4.8 times the global average rate
during the past half-century (35). This warming
is the most rapid of the past 500 years and stands
in contrast to a marked cooling between 2700
and 100 years before the present (57). As the
once-perennial sea ice and glaciers retreat (6,8),
maritime conditions are expanding southward to
displace the continental, polar system of the
southern WAP (9).
As a result, populations of sea icedependent
species of lower and higher trophic levels are
being demographically displaced poleward and
are being replaced by ice-avoiding species (e.g.,
1
Coastal Ocean Observation Lab, Institute of Marine and
Coastal Sciences, School of Environmental and Biological
Sciences, Rutgers University, New Brunswick, NJ 08901, USA.
2
Department of Marine Chemistry and Geochemistry, Woods
Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
3
The Ecosystems Center, Marine Biological Laboratory, Woods
Hole, MA 02543, USA.
4
Polar Oceans Research Group, Post
Office Box 368, Sheridan, MT 59749, USA.
5
Lamont-Doherty
EarthInstitute,Palisades,NY10964,USA.
6
Ocean Sciences,
University of California, Santa Cruz, CA 95064, USA.
*To whom correspondence should be addressed. E-mail:
montes@marine.rutgers.edu
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krill are being replaced by salps, and Adélie
penguins by Chinstrap penguins) (1,10,11). Do
these biogeographic modifications originate
from changes at the base of the food web?
In the short term (monthly-interannual scale)
and during spring and summer, variations in
latitudinal gradients in phytoplankton biomass
as a function of time have been associated with
sea ice timing and extent (12,13). However, this
mechanism has not been investigated over a
longer time scale of decades. Further, the rela-
tive importance of subregional differences in cli-
mate variables other than sea ice (e.g., cloudiness
and currents) in determining WAP alongshore
phytoplankton dynamics is not known. In con-
trast to previous work, we suggest that along-
shore phytoplankton distribution in this region
has been adjusting to the ongoing, long-term sea
ice decline and spatial modifications of other
physical climate factors. Short-term evidence
from seasonal cruises (1315) suggests an inverse
relationship between phytoplankton biomass in
surface waters (0- to 50-m depth) and the depth
of the upper mixed layer (UML). As the UML
becomes less stratified, mean light levels for phyto-
plankton photosynthesis decrease, and phyto-
plankton growth is not large enough compared
with Chl a loss (e.g., grazing and sinking) to
support Chl a accumulation in surface waters
(14). Because deepening of UML is mainly de-
termined by greater surface wind stress (14),
particularly during ice-free conditions, the expec-
tation is for a general decrease (increase) of phyto-
plankton biomass at <64°S (>64°S) due to deeper
(shallower) UML given a shorter (longer) sea ice
season and greater (smaller) influence of wind in
determining UML depth and, therefore, mean
light levels.
Based on Chl a concentration derived from
satellites [Coastal Zone Color Scanner (CZCS)
and Sea-Viewing Wide Field-of-View Sensor
(SeaWiFS)] (Chl
S
) and in situ shipboard mea-
surements (Chl
in situ
)(16), we report a two-decadal
(19781986 to 19982006) increase (decrease) of
biomass in summer (December to February) phyto-
plankton populations in the continental shelf
waters situated south (north) with respect to the
central part of the WAP region (Palmer Archipel-
ago, 64.6°S, 63.6°W). These spatial trends were
mainly associated with geographic differences in
receding sea ice cover and solar illumination of
the sea surface.
Since the 1970s, there has been a 7.5% areal
decline in summer sea ice throughout the WAP,
with the declines varying regionally (Fig. 1, blue
bars, and fig. S5, A and E). Cloudiness (Fig. 1,
pink bars, and fig. S5, B and F) and wind patterns
(Fig.1,blackbars,andfig.S5,CandG)have
also changed during the past decade. In the
1970s, overcast skies tended to be positively
associated with windy conditions, but in the past
10 years this covariation has weakened consid-
erably (fig. S5, B, C, F, and G). Surface winds
have become more intense (up to 60% increase)
during mid to late summer (January and February)
(Fig. 1 and fig. S5, C to G). Overall, these climate
variations were associated with a 12% decline in
Chl
S
over the entire study region (Table 1) that
resembles Chl
S
declines reported in northern
Monthly change of recent climatology (1998-2006)
with respect to the past (1978-1986)
-6
-3
0
3
6
Northern sub-region Southern sub-region
1
4
2
3
5
B
Sea ice
extent
Cloud
cover
Wind
speed
Chls
A
Sea ice
extent
Cloud
cover
Wind
speed
BC
*
**
Chls
*** *
**
**
**
*
** **
*
**
**
**
** **
**
**
solid (Dec)
horizontal (Jan)
oblique (Feb)
**
1978-1986
1998-2006
Sea ice
edge
66° S
62° S A
70° W 60° W
40° W
60° E
120° E
80° W
50° S
70° S
Southern Ocean
Antarctic Peninsula
Bellingshausen Sea
Fig. 1. Decadal variation of phytoplankton biomass and environmental factors along the
WAP in (A) the northern WAP subregion and (B) the southern WAP subregion. Chl
S
is
chlorophyll a concentration data derived from satellites (1978 to 1986 and 1998 to 2006).
Decadal variations (present past) of mean Chl
S
during December (solid bar), January
(horizontal stripes), and February (oblique stripes) were evaluated for 1998 to 2006 with
respect to the 1978 to 1986 baseline using a Student ttest. For each variable (xaxis), the
absolute value of the ttest statistic was multiplied by the sign of the trend (1, decrease; +1,
increase) of the present monthly mean with respect to the mean of the historical period (yaxis). For January and February, Student tof Chl
S
was divided by 5.
Significant differences between the periods at 95% (*) and 99% (**) confidence levels are indicated. (C) Spatial domains A (northern subregion) and B (southern
subregion) overlap the original transects of the Palmer-LTER regional grid, where ship-based stations are denoted by blue crosses and red circles, respectively. 1,
Bransfield Strait; 2, Gerlache Strait; 3, Anvers Island; 4, Adelaide Island; 5, Marguerite Bay. Average January sea ice extent during 1978 to 1986 (solid green line)
and 1998 to 2006 (broken dotted green line) is indicated.
Table 1. Field validation satellite-based chlorophyll a concentration changes between the summers of
1978 to 1986 (past period) and 1998 to 2006 (present period), calculated for the northern and southern
WAP subregions. Chl
spast
is the monthly average of satellite-derived Chl a (mg m
3
) from 1978 to 1986;
dChl
s(presentpast)
is the arithmetic average of pixel-by-pixel differences in satellite-derived Chl a between
the 1978 to 1986 period and the 1998 to 2006 period; dChl
s
% and dChl
in situ
% are relative changes in
monthly averaged Chl a [100 (Chl a
1998-2006
Chl a
1978-1986
)/Chl a
1978-1986
] based on satellite-derived
and shipboard Chl a measurements, respectively. Significant increase (+) or decrease ()ofChlaindicated
with a confidence limit of 95% (*) and 99% (**); two SE shown in parentheses.
Subregion Chl
spast
dChl
s(presentpast)
dChl
s
% dChl
in situ
%
Northern December 1.39 (0.11) 1.36 (0.26)** 97.8**
January 5.59 (0.20) 5.43 (0.26)** 97.1** 25.2*
February 2.96 (0.18) 2.12 (0.49)** 71.6** 74.0**
Southern December 0.89 (0.03) +1.25 (0.08)** +140.4**
January 0.89 (0.02) +0.49 (0.03)** +55.1** +228.6**
February 0.94 (0.03) +0.02 (0.14) +2.1 13.6
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high latitudes (>40°N) between 19791986 and
19972000 (17).
In the northern subregion of the WAP (61.8°
to 64.5°S, 59.0° to 65.8°W), the skies have
become cloudier, winds persistently stronger
(monthly mean up to 8 m s
1
), and summer
sea ice extent less, conditions favoring deeper
wind-mixing during the months most critical for
phytoplankton growth (December and January)
(Fig. 1 and fig. S5, A to D). Hence, phyto-
plankton cells inhabiting these waters have been
exposed to a deeper mixed layer and overall less
light for photosynthesis (14) that may explain
the dramatic Chl
S
decrease (seasonal average,
89%) detected in recent years (Fig. 1, Fig. 2A,
and fig. S5D). Additionally, recent declines of
Chl a over the northern WAP subregion might
also be partially related to a greater advection of
relatively poorChl a waters coming from the
Weddell Sea into the Bellingshausen Sea through
the Bransfield and Gerlache Straits (18). A Chl
a decrease was less evident during February
(Table 1), which suggests that increased mixing
early in the growth season caused a lag in phyto-
plankton bloom initiation but did not influence
Chl a levels as strongly later in the growth sea-
son. Two possible trigger mechanisms for such a
delay are stronger winds [up to 5.4% increase,
January (table S5)] and an insufficient volume of
fresh water from melting sea ice [up to 79% less
sea ice, December (table S5)] that otherwise
would create a favorable, strongly stratified, shal-
low UML (1315).
In the southern subregion of the WAP (63.8°
to 67.8°S, 64.4° to 73.0°W), remotely sensed Chl
a has undergone a remarkable increase (66% on
average) from 19781986 to 19982006 (Fig. 1,
fig. S5H, Fig. 2A, and Table 1) that can be
attributed mainly to high Chl
S
values (monthly
mean up to 6.58 mg m
3
) during 2005 and 2006.
These years were characterized by a substantial
decrease in sea ice extent (~17.4 × 10
3
km
2
,
~80% with respect to the 1978 to 1986 average,
December), cloud cover (~11.1%, January), and
wind intensity (up to 19%, December and
January) (Fig. 1, fig. S5, E to G, and table S5).
Unlike the northern WAP, the decrease in sum-
mer sea ice extent in the southern WAP has
occurred in areas that were previously sea ice
covered most of the year. Therefore, the increase
in ice-free summer days translates into more fa-
vorable conditions in the UML (e.g., increased
light) for phytoplankton growth. Together these
environmental changes are expected to enhance
photosynthesis and favor Chl a accumulation due
to lower light limitation.
Regions with high Chl a levels in the WAP
are characterized by a larger fraction of phyto-
plankton with fucoxanthin, a pigment marker for
diatoms, and a larger fraction of relatively large
cells (>20 mm) (contribution of cells >20 mmto
total Chl a 0.5) (Fig. 2B). Therefore, the
observed trends of decreasing Chl a in the north-
ern subregion and increasing Chl a in the south-
ern subregion are likely accompanied by shifts in
community composition with a greater (lesser)
fraction of diatoms and large cells in the southern
(northern) region. This restructuring of the phyto-
plankton community has major implications for
biogeochemical cycles of the WAP region. Large
(>5 mm) phytoplankton contribute 80% of the
particulate organic carbon export at high lat-
itudes, with diatoms making up the majority of
large phytoplankton export in the Southern
Ocean (19).
Historical shipboard measurements of Chl a
within the study area confirmed the general
north-south transitions seen in the satellite data
with higher (lower) phytoplankton biomass in the
southern (northern) WAP subregion in the past
decade compared with 1978 to 1986 (Table 1 and
tables S3 and S4). In fact, available field mea-
surements during January and February evidenced
a greater occurrence of phytoplankton blooms
(Chl a > 5 mg m
3
) in the northern (southern)
WAP subregion from 1978 to 1986 (1987 to
2006) (SOM Text, S6D) (16).
In the northern WAP, the maximum chloro-
phyll values measured by satellite (up to 40 mg m
3
,
January) or in situ (up to 38 mg m
3
, February)
were larger in the past (1978 to 1986) compared
with the present (1997 to 2006). Conversely, in
the southern WAP this pattern was reversed, and
spaceborne and shipborne observations consist-
ently showed higher pigment values in the last
decade (satellite, up to 33 mg m
3
; ship, up to
25 mg m
3
, January) (tables S4 and S5). Monthly
Chl a differences between northern and southern
WAP locations were also statistically coherent
63° S
66° S
Nbin /N
mode
Nbin /N
mode
Nbin /N
mode
Chlin situ
bin
(mg m-3)(mg m
-3)
0.0
0.3
0.6
0.9
Large cells
(157)
Small cells
(72)
Fucoxanthin bin
70° W 65° W 60° W -10 -5 0 5 10
0.0
0.3
0.6
0.9
-30 -20 -10 0 10 20 30
0.0
0.3
0.6
0.9
dChls (mg m-3)
dChls (mg m-3)
Northern
sub-region
Southern
sub-region
Change on satellite-derived chlorophyll a
(dChls(present-past), mg m-3)
00303-
B
-6 6
Antarctic Peninsula
A
0.5
1
5
10
>10
0.05
1
2
>2
0.02
0.1
Fig. 2. Variation of phytoplankton biomass, composition,
and cell size distribution over the WAP region. (A)Averageof
pixel-by-pixel absolute difference (t
f
t
o
) in satellite-derived
chlorophyll a concentration [dChl
s(presentpast)
(t
f
-t
o
)=Chl
s
(t
f
)
Chl
s
(t
o
)] between the mean January observations for 1978 to
1986 (t
o
) and mean January observations for 1998 to 2006
(t
f
). Positive (negative) dChl
s
corresponds to an increase
(decrease) of Chl
s
with respect to the 1970s. Negative (by a factor of ~2, northern subregion, upper histogram) and positive (by a factor of ~1.5, southern
subregion, lower histogram) trends in Chl
s
are evident in the satellite data. N
bin
/N
mode
is the relative frequency of observations per bin, normalized by the mode.
Gray pixels indicate areas without data or without valid geophysical retrieval due to cloud and sea ice contamination; black pixels indicate land. (B)Histogramsof
contribution of diatoms (fucoxanthin marker) and phytoplankton communities dominated by large (20 mm) versus small (<20 mm) cell diameter to total in situ
chlorophyll a concentration (Chl
in situ
). Phytoplankton cell size spectra were computed from satellite imagery (1998 to 2006) (16), and phytoplankton pigments
were measured over the northern and southern WAP subregions and during 1993 to 2006 Palmer-LTER cruises. Number of samples used to construct each
histogram shown in parentheses.
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with satellite-derived and field Chl a trends,
and in both cases latitudinal phytoplankton bio-
mass gradients were greater during January
compared with February (Fig. 1 and tables S4
and S5).
Our study provides evidence for the occur-
rence of substantial and statistically significant
latitudinal shifts at the base of the Antarctic
Peninsula marine food web that may be con-
tributing to observations of an apparent reorga-
nization of northern WAP biota during the past
decade [e.g., Euphausia superba (Antarctic krill),
Pleuragramma antarcticum (Antarctic silver-
fish), and Pygoscelis Adeliae (Adélie penguin)]
that rely on ice-edge diatom blooms (20, 21). The
southward relocation of phytoplankton patches
with abundant and large cells (>20 mm) due to
local alterations in environmental variables is ex-
pected to exacerbate the reduction of krill abun-
dance in the northern WAP. This represents a
setback for the survival of fish (silverfish) and
birds (Adélie penguins) that depend on krill but
favors other species, including Electrona antarc-
tica (Lanternfish), Pygoscelis papua (Gentoo
penguin), and Pygoscelis antarcticus (Chinstrap
penguin) (21,22).
The observed latitudinal response of phy-
toplankton communities along the WAP with
respect to historical sea ice variability can be
compared with that estimated from geological
proxies for similar paleo-oscillations in sea ice
extent and rate of change identified during the
Holocene (5,23,24). Paleo-records show that
analogous climate variations have occurred in the
past 200 to 300 years, and over longer 2500-year
cycles, with rapid (decadal) transitions between
warm and cool phases in the WAP (5,25,26).
In this study (~30 years), the Chl a trend evi-
denced in the southern subregion of the WAP
presented similar characteristics to those trends
detected during typical interneoglacial periods
(~200 to 300 years) (i.e., high phytoplankton
biomass, and presumably productivity, due to
less area covered by permanent sea ice) (26).
Since the 1970s, Chl a trends over the whole
WAP were also attributed to other factors not
necessarily ice-related (e.g., spatial differences
in cloud cover) (27) or coupled with the length
of the ice-free season (e.g., wind-driven changes
in mixed layer depth) (14,15,28)thatwere
equally important in determining phytoplankton
blooms.
This work suggests that a combination of
atmosphere-, ice-, and ocean-mediated processes
have been shaping the along-shelf distribution of
phytoplankton biomass over the WAP region
since the 1970s. The shift toward higher Chl a to
the south was first detected using ocean color
imagery and subsequently confirmed with in situ
historical measurements. The spatial asymmetry
of decadal changes in Chl a reported here may
explain the ongoing latitudinal compositional
changes in fish, zooplankton, and marine bird
species over the WAP, a testimonial to which
may be the recent success of krill recruitment and
the bonanza of krill feeders in nearby Marguerite
Bay (68.3°S, 68.3°W) (29).
References and Notes
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(2001).
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Oceanogr. 55, 1949 (2008).
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(1991).
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Oceanogr. 55, 2068 (2008).
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material on Science Online.
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1730 (2002).
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Oceanogr. 49, 935 (2002).
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(2006).
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(2008).
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Boca Raton, FL, ed. 2, 2006).
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1 (2003).
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437 (1965).
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29. M. Marrari et al., Deep-Sea Res. 55, 377 (2008).
30. This research is part of the Palmer Antarctica Long-Term
Ecological Research (LTER) project (http://pal.lternet.edu).
It was supported by NSF Office of Polar Programs grants
0217282 to H.W.D. and the Virginia Institute of Marine
Science and 0823101 to H.W.D. at the Marine Biological
Laboratory.
Supporting Online Material
www.sciencemag.org/cgi/content/full/323/5920/1470/DC1
Materials and Methods
SOM Text
Figs. S1 to S5
Tables S1 to S9
References
11 August 2008; accepted 12 January 2009
10.1126/science.1164533
A Recessive Mutation in the APP
Gene with Dominant-Negative Effect
on Amyloidogenesis
Giuseppe Di Fede,
1
Marcella Catania,
1
Michela Morbin,
1
Giacomina Rossi,
1
Silvia Suardi,
1
Giulia Mazzoleni,
1
Marco Merlin,
1
Anna Rita Giovagnoli,
1
Sara Prioni,
1
Alessandra Erbetta,
2
Chiara Falcone,
3
Marco Gobbi,
4
Laura Colombo,
4
Antonio Bastone,
4
Marten Beeg,
4
Claudia Manzoni,
4
Bruna Francescucci,
5
Alberto Spagnoli,
5
Laura Cantù,
6
Elena Del Favero,
6
Efrat Levy,
7
Mario Salmona,
4
Fabrizio Tagliavini
1
*
b-Amyloid precursor protein (APP) mutations cause familial Alzheimers disease with nearly
complete penetrance. We found an APP mutation [alanine-673valine-673 (A673V)] that causes
disease only in the homozygous state, whereas heterozygous carriers were unaffected, consistent
with a recessive Mendelian trait of inheritance. The A673V mutation affected APP processing,
resulting in enhanced b-amyloid (Ab) production and formation of amyloid fibrils in vitro. Co-
incubation of mutated and wild-type peptides conferred instability on Abaggregates and inhibited
amyloidogenesis and neurotoxicity. The highly amyloidogenic effect of the A673V mutation in the
homozygous state and its anti-amyloidogenic effect in the heterozygous state account for the
autosomal recessive pattern of inheritance and have implications for genetic screening and the
potential treatment of Alzheimers disease.
Acentral pathological feature of Alzheimers
disease (AD) is the accumulation of b-Ab
in the form of oligomers and amyloid
fibrils in the brain (1). Abis generated by sequen-
tial cleavage of the APP by b-andg-secretases
and exists as short and long isoforms, Ab1-40 and
Ab1-42 (2). Ab1- 42 is especially prone to mis-
folding and builds up aggregates that are thought
to be the primary neurotoxic species involved in
AD pathogenesis (2,3). AD is usually sporadic,
but a small fraction of cases is familial (4). The
familial forms show an autosomal dominant pat-
tern of inheritance with virtually complete pene-
trance and are linked to mutations in the APP,
presenilin 1, and presenilin 2 genes (5). The APP
mutations close to the sites of b-org-secretase
www.sciencemag.org SCIENCE VOL 323 13 MARCH 2009 1473
REPORTS
on April 7, 2009 www.sciencemag.orgDownloaded from
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