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

  • 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 (this information is current as of April 7, 2009 ):
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can be found at: Supporting Online Material
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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
) 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
) 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
. 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
from 1980 to
2000. Those estimates may not have adequately
accounted for the 20 Tg year
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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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
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20. Intergovernmental Panel on Climate Change, Climate
Change 2007: The Physical Science Basis. Contribution of
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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).
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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
Supporting Online Material
Materials and Methods
Figs. S1 to S7
Table S1
22 October 2008; accepted 23 January 2009
Recent Changes in Phytoplankton
Communities Associated with Rapid
Regional Climate Change Along the
Western Antarctic Peninsula
Martin Montes-Hugo,
Scott C. Doney,
Hugh W. Ducklow,
William Fraser,
Douglas Martinson,
Sharon E. Stammerjohn,
Oscar Schofield
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.,
Coastal Ocean Observation Lab, Institute of Marine and
Coastal Sciences, School of Environmental and Biological
Sciences, Rutgers University, New Brunswick, NJ 08901, USA.
Department of Marine Chemistry and Geochemistry, Woods
Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
The Ecosystems Center, Marine Biological Laboratory, Woods
Hole, MA 02543, USA.
Polar Oceans Research Group, Post
Office Box 368, Sheridan, MT 59749, USA.
Ocean Sciences,
University of California, Santa Cruz, CA 95064, USA.
*To whom correspondence should be addressed. E-mail:
13 MARCH 2009 VOL 323 SCIENCE www.sciencemag.org1470
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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
) 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
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
over the entire study region (Table 1) that
resembles Chl
declines reported in northern
Monthly change of recent climatology (1998-2006)
with respect to the past (1978-1986)
Northern sub-region Southern sub-region
Sea ice
Sea ice
*** *
** **
** **
solid (Dec)
horizontal (Jan)
oblique (Feb)
Sea ice
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
chlorophyll a concentration data derived from satellites (1978 to 1986 and 1998 to 2006).
Decadal variations (present past) of mean Chl
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
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
is the monthly average of satellite-derived Chl a (mg m
) from 1978 to 1986;
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
% and dChl
in situ
% are relative changes in
monthly averaged Chl a [100 (Chl a
Chl a
)/Chl a
] 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
% 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 SCIENCE VOL 323 13 MARCH 2009 1471
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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
), 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
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
values (monthly
mean up to 6.58 mg m
) during 2005 and 2006.
These years were characterized by a substantial
decrease in sea ice extent (~17.4 × 10
~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
) 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
January) or in situ (up to 38 mg m
, 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
; ship, up to
25 mg m
, 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
Nbin /N
Nbin /N
Chlin situ
(mg m-3)(mg m
Large cells
Small cells
Fucoxanthin bin
70° W 65° W 60° W -10 -5 0 5 10
-30 -20 -10 0 10 20 30
dChls (mg m-3)
dChls (mg m-3)
Change on satellite-derived chlorophyll a
(dChls(present-past), mg m-3)
-6 6
Antarctic Peninsula
Fig. 2. Variation of phytoplankton biomass, composition,
and cell size distribution over the WAP region. (A)Averageof
pixel-by-pixel absolute difference (t
) in satellite-derived
chlorophyll a concentration [dChl
)] between the mean January observations for 1978 to
1986 (t
) and mean January observations for 1998 to 2006
). Positive (negative) dChl
corresponds to an increase
(decrease) of Chl
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
are evident in the satellite data. N
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.
on April 7, 2009 www.sciencemag.orgDownloaded from
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
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).
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30. This research is part of the Palmer Antarctica Long-Term
Ecological Research (LTER) project (
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
Supporting Online Material
Materials and Methods
SOM Text
Figs. S1 to S5
Tables S1 to S9
11 August 2008; accepted 12 January 2009
A Recessive Mutation in the APP
Gene with Dominant-Negative Effect
on Amyloidogenesis
Giuseppe Di Fede,
Marcella Catania,
Michela Morbin,
Giacomina Rossi,
Silvia Suardi,
Giulia Mazzoleni,
Marco Merlin,
Anna Rita Giovagnoli,
Sara Prioni,
Alessandra Erbetta,
Chiara Falcone,
Marco Gobbi,
Laura Colombo,
Antonio Bastone,
Marten Beeg,
Claudia Manzoni,
Bruna Francescucci,
Alberto Spagnoli,
Laura Cantù,
Elena Del Favero,
Efrat Levy,
Mario Salmona,
Fabrizio Tagliavini
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 SCIENCE VOL 323 13 MARCH 2009 1473
on April 7, 2009 www.sciencemag.orgDownloaded from
... The link between climate change and DMS production is complex and involves a great number of oceanic and atmospheric processes: in polar regions, the maximum DMS concentrations in the water occurs in early summer and is primarily associated with sea-ice break-up (Stefels et al., 2018). Although the retreat in sea ice will directly impact on the release of DMSP and DMSP-producing algae, changes in the physical environment can also indirectly impact on phytoplankton productivity and composition through changes in light and nutrient availability (Ducklow et al., 2007;Montes-Hugo et al., 2009). ...
... Previous studies found that DMS concentrations in sea water are related to phytoplanktonic biomass (expressed by Chla concentration) or to primary productivity that are, in turn, controlling the biogenic aerosol (Minikin et al., 1998;Preunkert et al., 2007). ...
... The slope of the regression line is higher for the class with nssSO 2− 4 > 3 nMol m −3 . The two different slopes can be associated with different situations: for nssSO 2− 4concentrations below 3 nMol m −3 , the MSA-nssSO 2− 4 relationship is expected to be produced by aged biogenic aerosol with possible additional nssSO 2− 4 contributions coming from the oxidation of SO 2 emitted by the near volcano Erebus (Boichu et al., 2010) (Fig. 1) or from long-range transport from northern latitudes (Minikin et al., 1998). ...
Full-text available
This paper presents the results of simultaneous high time-resolution measurements of biogenic aerosol (methane sulfonic acid (MSA), non-sea salt sulfate nssSO42-) with its gaseous precursor dimethylsulfide (DMS), performed at the Italian coastal base Mario Zucchelli Station (MZS) in Terra Nova Bay (MZS) during two summer campaigns (2018–2019 and 2019–2020). Data on atmospheric DMS concentration are scarce, especially in Antarctica. The DMS maximum at MZS occurs in December, one month earlier than at other Antarctic stations. The maximum of DMS concentration is connected with the phytoplanktonic senescent phase following the bloom of Phaeocystis antarctica that occurs in the polynya when sea ice opens up. The second plankton bloom occurs in January and, despite the high dimethylsufoniopropionate (DMSP) concentration in seawater, atmospheric DMS remains low, probably due to its fast biological turnover in seawater in this period. The intensity and timing of the DMS evolution during the two years suggest that only the portion of the polynya close to the sampling site produces a discernible effect on the measured DMS. The closeness to the DMS source area and the occurrence of air masses containing DMS and freshly formed oxidation products allow us to study the kinetic of biogenic aerosol formation and the reliable derivation of the branch ratio between MSA and nssSO42- from DMS oxidation that is estimated to be 0.84±0.06. Conversely, for aged air masses with low DMS content, an enrichment of nssSO42- with respect to MSA, is observed. We estimate that the mean contribution of freshly formed biogenic aerosol to PM10 is 17 % with a maximum of 56 %. The high contribution of biogenic aerosol to the total PM10 mass in summer in this area highlights the dominant role of the polynya on biogenic aerosol formation. Finally, due to the regional and year-to-year variability of DMS and related biogenic aerosol formation, we stress the need for long-term measurements of seawater and atmospheric DMS and biogenic aerosol along the Antarctic coast and in the Southern Ocean.
... Chlorophyll-a concentrations demonstrate a long-term increase along the western Antarctic Peninsula (figure 6c; Brown et al. 2019). This increase was also observed in remote ocean color imagery comparing the periods 1978-1986-2006(Montes-Hugo et al. 2009) and covering the mid-to southern part of the peninsula coterminous with the Palmer sampling region. Montes-Hugo and colleagues (2009) also inferred from discrete diatom pigment (fucoxanthin) measurements that diatoms were increasing in the same region. ...
The marine coastal region makes up just 10% of the total area of the global ocean but contributes nearly 20% of its total primary production and over 80% of fisheries landings. Unicellular phytoplankton dominate primary production. Climate variability has had impacts on various marine ecosystems, but most sites are just approaching the age at which ecological responses to longer term, unidirectional climate trends might be distinguished. All five marine pelagic sites in the US Long Term Ecological Research (LTER) network are experiencing warming trends in surface air temperature. The marine physical system is responding at all sites with increasing mixed layer temperatures and decreasing depth and with declining sea ice cover at the two polar sites. Their ecological responses are more varied. Some sites show multiple population or ecosystem changes, whereas, at others, changes have not been detected, either because more time is needed or because they are not being measured.
... The climate in Antarctica is rapidly changing, especially in the Western Antarctic Peninsula (WAP) region (Vaughan et al., 2003;Turner et al., 2014), where surface waters have increased by ∼1 • C during the past 50 years, and subsurface waters are projected to increase 0.4-0.6 • C during the next century with an increase of as much as 1 • C by the year 2200 (Meredith and King, 2005;Yin et al., 2011). The sirens of warming are apparent in the collapse of ice shelves, sharp declines in Adélie penguin populations, shifts in phytoplankton distribution and a reduction in krill habitat and abundance (Clarke et al., 2007;Stammerjohn et al., 2008;Montes-Hugo et al., 2009;Atkinson et al., 2019). Much less is known about the impact of warming on the Antarctic fish fauna because of the inherent difficulties in monitoring fish populations in this remote, expansive and iceladen region. ...
Full-text available
The Southern Ocean surrounding the Western Antarctic Peninsula region is rapidly warming. Survival of members of the dominant suborder of Antarctic fishes, the Notothenioidei, will likely require thermal plasticity and adaptive capacity in key traits delimiting thermal tolerance. Herein, we have assessed the thermal plasticity of several cellular and biochemical pathways, many of which are known to be associated with thermal tolerance in notothenioids, including mitochondrial function, activities of aerobic and anaerobic enzymes, antioxidant defences, protein ubiquitination and degradation in cardiac, oxidative skeletal muscles and gill of Notothenia coriiceps warm acclimated to 4°C for 22 days or 5°C for 42 days. Levels of triacylglycerol (TAG) were measured in liver and oxidative and glycolytic skeletal muscles, and glycogen in liver and glycolytic muscle to assess changes in energy stores. Metabolic pathways displayed minimal thermal plasticity, yet antioxidant defences were lower in heart and oxidative skeletal muscles of warm-acclimated animals compared with animals held at ambient temperature. Despite higher metabolic rates at elevated temperature, energy storage depots of TAG and glycogen increase in liver and remain unchanged in muscle with warm acclimation. Overall, our studies reveal that N. coriiceps displays thermal plasticity in some key traits that may contribute to their survival as the Southern Ocean continues to warm.
... This is because NO 3 --fueled new production at steady state is equivalent to the organic C that can be exported from total production in the euphotic layer (Eppley and Peterson, 1979). In this regard, phytoplankton species shifts toward smaller values could substantially lower C export efficiency as well as primary production (Montes-Hugo et al., 2008;Montes-Hugo et al., 2009;Lee et al., 2015, Mendes et al., 2012Rozema et al., 2017;Schofield et al., 2017). The undergoing reductions in diatom silica production in response to ocean acidification and shifts toward smaller cells could reduce the vertical fluxes of diatoms and diminish C export efficiency before the end of this century (Petrou et al., 2019). ...
Full-text available
Quantifying the temporal variability in phytoplankton productivity is essential for improving our understanding of carbon (C) and nitrogen (N) dynamics and energy flows in natural aquatic ecosystems. Samples were collected at three-day intervals from December 2018 to January 2019 from fixed station in Marian Cove, Antarctica to determine the C and N (NO3 - and NH4 +) uptake by phytoplankton. Considerable fluctuations in the total C and N productivities were observed, which led to dynamic changes in the phytoplankton communities and a stronger coupling between the phytoplankton biomass. The increased rate of NO3 - uptake coincided with an enhanced C uptake mainly by microphytoplankton (>20 µm), followed by an increase in NH4 + uptake towards the end of sampling period. However, the <2 µm fraction (picophytoplankton) showed little variation in C and NO3 - uptake, and the proportions of assimilated NH4 + contributed to more than half of the total assimilated inorganic N. The increased NH4 + did not increase the total phytoplankton biomass and C production. Interestingly, after January 9 (maximum chlorophyll a, C, and N uptake) there was a shift to a predominantly easterly wind (>6 m s-1), which rapidly decreased the total chl-a, C and N uptake rate to ~4% of the highest values (0.6 mg m-3, 1.0 mg C m-3 h-1, 0.1 mg N m-3 h-1, respectively) on January 12. The phytoplankton community was also replaced by neritic and ice-related species. These findings suggest that strong temporal shifts in phytoplankton C and N assimilation are strongly influenced by external forces (wind stress).
... Given the high interannual variability of the blooms and the patchiness observed during individual years, however, the importance of different processes in controlling the timing and intensity of the bloom, as well as long-term trends, remain unknown. The long-term trends in chlorophyll based on satellite ocean color observations were estimated to be negative in the northern part of the grid and positive in the southern part (Montes-Hugo et al., 2009), related to sea ice decrease, winds, and changes in mixed layer depth (MLD). With less sea ice in the northern part of the WAP, where more light is available throughout the year, the region is more exposed to wind mixing, which deepens the MLD and lowers photosynthetically available radiation (PAR). ...
The ocean coastal-shelf-slope ecosystem west of the Antarctic Peninsula (WAP) is a biologically productive region that could potentially act as a large sink of atmospheric carbon dioxide. The duration of the sea-ice season in the WAP shows large interannual variability. However, quantifying the mechanisms by which sea ice impacts biological productivity and surface dissolved inorganic carbon (DIC) remains a challenge due to the lack of data early in the phytoplankton growth season. In this study, we implemented a circulation, sea-ice, and biogeochemistry model (MITgcm-REcoM2) to study the effect of sea ice on phytoplankton blooms and surface DIC. Results were compared with satellite seaice and ocean color, and research ship surveys from the Palmer Long-Term Ecological Research (LTER) program. The simulations suggest that the annual sea-ice cycle has an important role in the seasonal DIC drawdown. In years of early sea-ice retreat, there is a longer growth season leading to larger seasonally integrated net primary production (NPP). Part of the biological uptake of DIC by phytoplankton, however, is counteracted by increased oceanic uptake of atmospheric CO2. Despite lower seasonal NPP, years of late sea-ice retreat show larger DIC drawdown, attributed to lower air-sea CO2 fluxes and increased dilution by sea-ice melt. The role of dissolved iron and iron limitation on WAP phytoplankton also remains a challenge due to the lack of data. The model results suggest sediments and glacial meltwater are the main sources in the coastal and shelf regions, with sediments being more influential in the northern coast.
... (Beaugrand et al., 2010;Benedetti et al., 2021;Zhang et al., 2021). Previous studies have confirmed that warming would have the most dramatic effects on ecosystems in high-latitude marine areas, particularly in the polar regions (Kahru et al., 2011;Montes-Hugo et al., 2009). However, recent evidence from both models and field observations has suggested that the effects of warming on marine ecosystem function and food webs will not only be limited to high latitudes but also be significant in temperate waters (McGinty et al., 2021;O'Gorman et al., 2019;Schmidt et al., 2020). ...
Full-text available
The northern Pacific Ocean is one of the most sensitive areas globally to climate change. Copepods typically account for between 60% and 90% of mesozooplankton in the open ocean. Because copepods are a key link in marine food webs, their response to environmental changes is an important topic in marine biodiversity and ecosystem functioning relationships. The relationship between copepod assemblages and the marine environment in the northern Pacific Ocean from a traits-based perspective has been largely unknown until now. In this study, we used the functional traits and geographic distribution of 177 copepod species along a latitudinal gradient, ranging from 4°S to 46°N in the northern Pacific Ocean, to evaluate the latitudinal variation of functional diversity and assembly rules of copepod assemblages. Based on a cluster analysis of four key functional traits, seven functional groups were identified. Redundancy analysis revealed environmental preferences for different functional groups. Large carnivores showed a stronger preference for higher temperatures than small carnivores, Omnivores and herbivores showed a stronger preference for higher chlorophyll a concentrations. The distribution of detritivores was nearly independent of temperature and chlorophyll a concentration. Most functional diversity indices showed non-linear decreasing trends along the latitudinal gradient. These trends remained stable in the tropic and subtropic regions (WARM and NPSG), but decreased sharply in the Kuroshio extension and Pacific subarctic gyres regions (KURO and PSAG). A null model revealed the assembly rules of copepod assemblage significantly varied with latitude: environmental filtering was dominant in the KURO and PSAG, whereas both environmental filtering and limited similarity played important roles in the WARM and NPSG, in addition to the neutral process. Our results suggested that with ocean warming, a northward shift in the distribution range of specific functional groups (such as large carnivores) might significantly alter the biodiversity and ecosystem function of zooplankton communities in the Kuroshio extension region. This study highlights the importance of a traits-based approach in the study of biodiversity and ecosystem function in pelagic ecosystems at large scales.
... In the Western Antarctic Peninsula (WAP) and Northern Antarctic Peninsula (NAP), the sea ice sea-son has decreased by 85 d (Stammerjohn et al. 2008), and air temperatures have increased at one of the fastest rates on the planet (0.5°C decade −1 from 1951 to 2011) (Turner et al. 2014). Increased ocean warming events have been changing the phytoplankton community structure around the Antarctic Peninsula (AP) in recent decades (Montes-Hugo et al. 2009. A decrease in large-cell diatoms, increases in cryptophytes that are less suitable for grazing by Antarctic krill Euphausia superba (hereafter 'krill') (Haberman et al. 2003) and the concurrent decrease in the sea ice extent negatively affect krill abundance (Massom & Stammerjohn 2010). ...
The Atlantic sector of the Southern Ocean has been rapidly changing over the last century. Many of those changes are driven by climate anomalies such as the El Niño Southern Oscillation and the Southern Annular Mode, which affect biological processes that scale up the food web. In this paper, we use δ13C and δ15N time-series of dentine growth layer groups (as a proxy of individual foraging history from multiple years, n = 41 teeth) to assess temporal shifts in foraging habits of subadult/adult male Antarctic fur seals Arctocephalus gazella in 2 areas of high concentration of Antarctic krill Euphausia superba: the South Shetland Islands and the South Orkney Islands. Our analyses, which represent the first long-term isotopic assessment of male AFS sampled in Antarctic waters, revealed a significant decrease of δ13C (0.04 ‰yr-1) from 1974 to 2015. Nitrogen isotope values also increased after the late 1990s. The observed changes are likely driven by shifts in latitudinal and longitudinal distribution of krill and increased incorporation of 15N-enriched sources (higher trophic level prey and/or feeding in different areas) in the most recent period for reasons that are not yet clear. We were able to trace ecosystem changes through isotopic bio-archives of Antarctic fur seals, highlighting the role of this species as an ecosystem indicator of the trophic cascade effects caused by climate change in the Southern Ocean.
The cycling of dissolved organic matter in the productive west Antarctic Peninsula (WAP) region is not well understood. For this study, dissolved organic carbon (DOC) and nitrogen (DON) concentrations and other biogeochemical measurements were collected along the WAP shelf during austral summer 2017. Concentrations of both DOC and DON in the upper ocean were lower than in lower latitudes (38.13–48.00 μmol C L⁻¹, 2.90–10.52 μmol N L⁻¹). DOC is produced along with particulate organic carbon during primary production, and is subsequently consumed by bacteria. DON shows high variability and is more likely the product of bacterial activity only in the surface waters. The N-isotopic composition of nitrate and particulate nitrogen showed intense nitrification, especially along the coast, and supports the findings of intense upper ocean cycling of organic matter of both particulate and dissolved forms. Export of DOM from the productive surface layer was negligible in the shelf waters of the WAP. Samples from glacial melt areas showed increased DON concentrations (7.88–10.52 μmol N L⁻¹) so we conclude that increasing warming and continuing melting of Antarctic glaciers may lead to higher concentrations of dissolved organic matter but also higher bacterial activity with more intense upper-ocean carbon and nitrogen cycling.
In January 2022, during scientific cruise 87 on the RV Aсademiс Mstislav Keldysh in the Atlantic sector of the Southern Ocean, three hydrobiophysical cross-sections were performed in the Bransfield Strait. Bioluminescent signal was measured in a layer of 0-200 m at each of the 24 stations located at three sites. For the first time, a new hydro-biological system "Salpa MA +" was used, which made it possible to obtain novel data in the photic layer of the studied water area. Bioluminescence studies were accompanied by simultaneous measurements of background indicators: temperature, electrical conductivity, photo-synthetically active radiation, as well as they were compared with the data of plankton samples processing. Bioluminescent potential was registered at almost all the stations. The maximum level of bioluminescence was registered in the area of the archipelago of the South Shetland Islands, where the maximum accumulation of Salpa thompsoni, Foxton 1861 was noted. The purpose of this work is to identify the main factors and patterns affecting the intensity of the bioluminescence field in the region under study.
Technical Report
Full-text available
The Southern Ocean plays a central role in the Earth System by connecting the Earth’s ocean basins, and it is a crucial link between the deep ocean, surface ocean and atmosphere. Hence, the ongoing changes in the Southern Ocean impact global climate, rates of sea level rise, biogeochemical cycles and ecological systems. Yet, understanding of the causes and consequences of these changes is limited by the short and incomplete nature of observations. To address this issue, sustained, integrated and multidisciplinary observations are needed. Due to the size of the Southern Ocean, this requires international agreement on the priority observations to be collected, and also internationally coordinated data management and delivery. The Southern Ocean Observing System (SOOS) was initiated in 2011 to support these efforts. In the last decade, SOOS has enhanced regional coordination and observing system capabilities through network development, data curation and publication, development of data discovery and coordination tools, and providing strong advocacy mechanisms for the Southern Ocean community. Significant data gaps remain in observations of the ice-affected ocean, sea ice habitats, the ocean at depths >2000 m, the air-ocean-ice interface, biogeochemical and biological variables, and for seasons other than summer. This Science and Implementation Plan articulates the scientific priorities for SOOS through the identification of these key gaps in the observational network and by identifying the priorities in addressing these gaps. This Plan covers the five year period 2021-2025, with emphasis on the capabilities required to support data collection and delivery, and the objectives and actions that SOOS will implement. Five Science Themes have been identified, each encompassing a number of Key Science Challenges. These Themes and Challenges incorporate many scientific drivers that are cross-disciplinary, reflecting the highly-interconnected nature of the Southern Ocean, and Theme 5 is cross-cutting and highlights a number of linkages amongst Themes 1-4. The Themes provide a framework for enhancing the coordination of international data collection and delivery efforts that will contribute to understanding and quantifying the state and variability of: Theme 1: Southern Ocean cryosphere Theme 2: Southern Ocean circulation Theme 3: Southern Ocean carbon and biogeochemical cycles Theme 4: Southern Ocean ecosystems and biodiversity Theme 5: Southern Ocean-sea ice-atmosphere fluxes Addressing the data gaps across these inherently interconnected Themes sustainably and systematically requires parallel advances in coordination networks, cyberinfrastructure and data management tools, observational platform and sensor technology, and development of internationally agreed sampling and analytical standards and data requirements of key variables. In recognition of this, SOOS has also identified a number of Foundational Capabilities that will need to be developed or expanded.
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A 480 year record of the oxygen-isotope ratios, dust content, chemical species and net accumulation from ice cores drilled in 1989 90 on Dyer Plateau in the Antarctic Peninsula is presented. The continuous analyses of small (sub-annual) samples reveal well-preserved annual variations in both sulfate content and δ18O, thus allowing an excellent time-scale to be established. This history reveals a recent pronounced warming in which the last two decades have been among the warmest in the last five centuries. Furthermore, unlike in East Antarctica, on Dyer Plateau conditions appear to have been fairly normal from AD 1500 to 1850 with cooler conditions from 1850 to 1930 and a warming trend dominating since 1930. Reconstructed annual layer thicknesses suggest an increase in net accumulation beginning early in the 19th century and continuing to the present. This intuitive conflict between increasing net accumulation and depleted δ18O (cooler climate) in the 19th century appears widespread in the peninsula region and challenges our understanding of the physical relationships among moisture sources, air temperatures and snow accumulation. The complex meteorological regime in the Antarctic Peninsula region complicates meaningful interpretation of proxy indicators and results in a strong imprint of local high-frequency processes upon the larger-scale climate picture.
Full-text available
We diagnose the contribution of four main phytoplankton functional groups to the production and export of particulate organic carbon (POC), CaCO3, and opal by combining in a restoring approach global oceanic observations of nitrate, silicic acid, and alkalinity with a simple size-dependent ecological/biogeochemical model. In order to determine the robustness of our results, we employ three different variants of the ocean general circulation model (OGCM) required to transport and mix the nutrients and alkalinity into the upper ocean. In our standard model, the global export of CaCO3 is diagnosed as 1.1 PgC yr-1 (range of sensitivity cases 0.8 to 1.2 PgC yr-1) and that of opal as 180 Tmol Si yr-1 (range 160 to 180 Tmol Si yr-1). CaCO3 export is found to have three maxima at approximately 40°S, the equator, and around 40°N. In contrast, the opal export is dominated by the Southern Ocean with a single maximum at around 60°S. The molar export ratio of inorganic to organic carbon is diagnosed in our standard model to be about 0.09 (range 0.07 to 0.10) and found to be remarkably uniform spatially. The molar export ratio of opal to organic nitrogen varies substantially from values around 2 to 3 in the Southern Ocean south of 45°S to values below 0.5 throughout most of the rest of the ocean, except for the North Pacific. Irrespective of which OGCM is used, large phytoplankton dominate the export of POC, with diatoms alone accounting for 40% of this export, while the contribution of coccolithophorids is only about 10%. Small phytoplankton dominate net primary production (NPP) with a fraction of ~70%. Diatoms and coccolithophorids account for about 15% and less than 2% of NPP, respectively. These diagnosed contributions of the main phytoplankton functional groups to NPP are also robust across all OGCMs investigated. Correlation and regression analyses reveal that the variations in the relative contributions of diatoms and coccolithophorids to NPP can be predicted reasonably well on the basis of a few key parameters.
Full-text available
Over the last half century, the Antarctic Peninsula (AP) has been among the most rapidly warming regions on Earth. This has led to increased summer snowmelt, loss of ice shelves, and retreat of 87% of marine and tidewater glacier fronts. Tidewater-glacier flow is sensitive to changes in basal water supply and to thinning of the terminus, and faster flow leads directly to sea level rise. The flow rates of most AP tidewater glaciers have never been measured, however, and hence their dynamic response to the recent changes is unknown. We present repeated flow rate measurements from over 300 glaciers on the AP west coast through nine summers from 1992 to 2005. We show that the flow rate increased by ~12% on average and that this trend is greater than the seasonal variability in flow rate. We attribute this widespread acceleration trend not to meltwater-enhanced lubrication or increased snowfall but to a dynamic response to frontal thinning. We estimate that as a result, the annual sea level contribution from this region has increased by 0.047 +/- 0.011 mm between 1993 and 2003. This contribution, together with previous studies that assessed increased runoff from the area and acceleration of glaciers resulting from the removal of ice shelves, implies a combined AP contribution of 0.16 +/- 0.06 mm yr-1. This is comparable to the contribution from Alaskan glaciers, and combined with estimated mass loss from West Antarctica, is probably large enough to outweigh mass gains in East Antarctica and to make the total Antarctic sea level contribution positive.
Full-text available
The mechanisms by which variability in sea ice cover and its effects on the demography of the Antarctic krill Euphausia superba cascade to other ecosystem components such as apex predators remain poorly understood at all spatial and temporal scales, yet these interactions are essential for understanding causal links between climate change, ecosystem response and resource monitoring and management in the Southern Ocean. To address some of these issues, we examined the long-term foraging responses of Adelie penguins Pygoscelis adeliae near Palmer Station, western Antarctic Peninsula, in relation to ice-induced changes in krill recruitment and availability. Our results suggest that (1) there is a direct, causal relationship between variability in ice cover, krill recruitment, prey availability and predator foraging ecology, (2) regional patterns and trends detected in this study are consistent with similar observations in areas as far north as South Georgia, and (3) large-scale forcing associated with the Antarctic Circumpolar Wave may be governing ecological interactions between ice, krill and their predators in the western Antarctic Peninsula and Scotia Sea regions. Another implication of our analyses is that during the last 2 decades in particular, krill populations have been sustained by strong age classes that emerge episodically every 4 to 5 yr. This raises the possibility that cohort senescence has become an additional ecosystem stressor in an environment where ice conditions conducive to good krill recruitment are deteriorating due to climate warming. In exploring these interactions, our results suggest that at least 1 'senescence event' has already occurred in the western Antarctic Peninsula region, and it accounts for significant coherent decreases in krill abundance, predator populations and predator foraging and breeding performance. We propose that krill longevity should be incorporated into models that seek to identify and understand causal links between climate change, physical forcing and ecosystem response in the western Antarctic Peninsula region.
Full-text available
This paper describes spatial distribution patterns of the phytoplankton community (composition, cell abundance and biomass concentration) in relation to local environmental conditions in the Southern Ocean. Sampling was performed during summer 1997 off the coast of the western Antarctic Peninsula between Anvers Island and Marguerite Bay. Phytoplankton was characterized by relatively low biomass throughout most of the study area and was dominated by nanoalgae (<20 mum). Phytoplankton varied along an on-offshore gradient, with decreasing total cell abundance, chlorophyll a (chl a) concentration and carbon biomass toward the open ocean. Chl a concentration showed surface or subsurface maxima in coastal and middle-shelf waters, and deep maxima between similar to40 and 100 m in oceanic waters. Across-shelf variability in phytoplankton correlated with vertical stability in the water column, which appears to be the major parameter affecting phytoplankton community structure in the area. We hypothesize that the deep chl a maximum offshore may be associated with iron limitation in near-surf ace waters and higher iron concentration in 'winter waters' (subsurface remnant of Antarctic Surface Waters). On a smaller spatial scale, a cluster analysis showed great regional variability in phytoplankton assemblages. The area was divided into 4 main regions based on differences in the phytoplankton composition and concentration. Three peaks in phytoplankton abundance were found on a north-to-south gradient in near-shore waters: a Cryptomonas spp. bloom near Anvers Island, a small unidentified phytoflagellate bloom in Grandidier Channel, and a diatom bloom in Marguerite Bay. These assemblages resemble different stages of the phytoplankton seasonal succession, and may be related to the progressive sea-ice retreat, which might have regulated the timing of the onset of the phytoplankton seasonal succession in a north-south gradient. Biological environmental factors, such as seeding of the water column by epontic algae and selective zooplankton herbivory, are hypothesized to affect community composition in coastal regions. We conclude that large-scale variability in phytoplankton community structure is related to water column physical conditions and possibly iron availability, while mesoscale variability, as seen in coastal waters, is more likely due to seasonal succession of different algae groups.
Full-text available
The Antarctic Peninsula region is undergoing rapid change: a warming in winter of almost 6°C since 1950, the loss of six ice shelves, the retreat of 87% of the marine glaciers, and decreases in winter sea-ice duration. Concurrently, there is evidence of ecosystem change along the western Antarctic Peninsula (wAP). Since the life histories of most polar marine species are synchronized with the seasonal cycle of sea ice, we assess how the seasonal sea-ice cycle is changing in the wAP region. Four new metrics of seasonal sea-ice variability were extracted from spatial maps of satellite derived daily sea-ice concentration: (a) day of advance, (b) day of retreat, (c) the total number of sea-ice days (between day of advance and retreat), and (d) the percent time sea-ice was present (or sea-ice persistence). The spatio-temporal variability describes distinct on-to-offshore and alongshore differences in ice–ocean marine habitats, characterized overall by a longer sea-ice season in coastal regions (6.8–7.9 months) versus a shorter sea-ice season over the shelf (4.1–5.3 months), with on-to-offshore differences increasing south-to-north. Large perturbations in the seasonality of the marine habitat occur in association with ENSO and Southern Annular Mode (SAM) variability. The local atmospheric response to these climate modes is largely a strengthening of the meridional winds during spring-to-autumn, which in turn affect the timing of the sea-ice retreat and subsequent advance. These perturbations are embedded in overall trends towards a later sea-ice advance, earlier retreat and consequently shorter sea-ice season, the impacts of which are expected to affect ecosystem functionality in the wAP region. A suite of ocean–atmosphere–ice interactions are described that are consistent with the amplified warming in late autumn, early winter.
Preface 1. The Southern Ocean 2. Phytoplankton and primary production 3. Sea ice microbial communities 4. Zooplankton 5. Krill 6. Nekton 7. Fish 8. Seals 9. Whales 10. Birds 11. Benthic communities 12. The fast ice and the ice shelves 13. Ice edge processes 14. Decomposition and the roles of bacteria and protozoa 15. Ecosystem dynamics 16. Resource exploitation 17. Ecosystem changes resulting from resource exploitation 18. Management of the living resources Epilogue Appendix.
Compared to the rest of the world's oceans, high-resolution late Holocene paleoclimatic data from the Southern Ocean are still rare. We present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the Antarctic Peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr. Analyses completed include measurement of magnetic susceptibility and granulometry, bed thickness, particle size, percent organic carbon, bulk density, and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances. Downcore variability of these parameters demonstrates the significance of both short-term cycles, which recur approximately every 200 yr, and longer term events (≈2500 yr cycles) that are most likely related to global climatic fluctuations. In the upper 600 cm of the core, lower values of magnetic susceptibility (MS) are correlated with lower bulk density, the presence of thinly laminated units, specific diatom assemblages, and generally higher total organic carbon content. Below 600 cm, magnetic susceptibility is uniformly low, though variability in other parameters continues. The magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material. This signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows (high total organic carbon). The role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data. In particular, magnetic susceptibility lows are characterized by higher than normal abundances of Chaetoceros resting spores. Corethron criophilum and/or Rhizosolenia spp. also are found, as is a higher ratio of the most common species of Fragilariopsis versus species of Thalassiosira. These assemblages are indicative of periods of high primary productivity driven by the presence of a melt-water stabilized water column. The 200 yr cyclicity noted in other paleoclimatic records around the world suggests a global forcing mechanism, possibly solar variability. In addition to the cyclic changes in productivity, overall elevated productivity is noted below 600 cm, or prior to ca. 2500 yr B.P. This increased productivity may represent the tail end of a Holocene climatic optimum, which is widely recognized in other parts of the world, but as yet is poorly documented in Antarctica.
We measured time series of the vertical particle flux at three locations in the Ross Sea, Antarctica, between January 1990 and February 1992 as part of an interdisciplinary project focusing on the accumulation and recycling of organic C and biogenic Si on a polar shelf. We estimate area-wide annual average fluxes through the deep water column of 5 g organic C m-2 yr-l and 30 g biogenic Si m-2 yr-1, values similar to the highest annual average fluxes to the subsurface reported for other areas of the Antarctic continental shelf. Total particle and biogenic Si fluxes are highest during January and February in the southwestern Ross Sea, beneath a seasonally recurrent bloom of the diatom Fragilariopsis curta. Organic C fluxes are highest in the central Ross Sea, consistent with a surface water algal assemblage dominated by the prymnesiophyte Phaeocystis. While organic C flux decreases with depth at all three sites, the result of remineralization within the water column, biogenic opal fluxes are higher in near-bottom traps than at 230 m at the two western Ross Sea sites. Some biogenic opal must be supplied to these deep traps via horizontal advection and possibly resuspension. Fecal pellets and large aggregates contributed between 4 and 70% of the vertical flux and settled at rates of 60 to >400 m d-1. Maximum particle fluxes occur 2 to 10 weeks after surface waters become ice free. We discuss three hypotheses to explain lags between production and settling: (1) advection from surface waters with different ice cover characteristics, (2) lags in the development of a grazing Zooplankton community, and (3) early season windinduced inhibition of primary production. Interannual variability in surface wind stress is empirically linked to variability in biogenic fluxes. Windiness and relative phasing of the annual cycles of ice cover and air temperature may be responsible for the development of different algal communities in the central versus western Ross Sea.
The global ocean chlorophyll archive produced by the CZCS was revised using compatible algorithms with SeaWiFS. Both archives were then blended with in situ data to reduce residual errors. This methodology permitted a quantitative comparison of decadal changes in global ocean chlorophyll from the CZCS (1979-1986) and SeaWiFS (1997-2000) records. Global spatial distributions and seasonal variability of ocean chlorophyll were similar, but global means decreased over the two observational segments. Major changes were observed regionally: chlorophyll concentrations decreased in the northern high latitudes while chlorophyll in the low latitudes increased. Mid-ocean gyres exhibited limited changes. The overall spatial and seasonal similarity of the two data records suggests that the changes are due to natural variability. These results provide evidence of how the Earth's climate may be changing and how ocean biota respond.