Evidence for Upwelling of Corrosive " Acidified" Water onto the Continental Shelf

Abstract

The absorption of atmospheric carbon dioxide (CO2) into the ocean lowers the pH of the waters. This so-called ocean acidification could have important consequences for marine
ecosystems. To better understand the extent of this ocean acidification in coastal waters, we conducted hydrographic surveys
along the continental shelf of western North America from central Canada to northern Mexico. We observed seawater that is
undersaturated with respect to aragonite upwelling onto large portions of the continental shelf, reaching depths of ∼40 to
120 meters along most transect lines and all the way to the surface on one transect off northern California. Although seasonal
upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this region, the ocean uptake of anthropogenic
CO2 has increased the areal extent of the affected area.

Full text

DOI: 10.1126/science.1155676
, 1490 (2008); 320Science
et al.Richard A. Feely,
Water onto the Continental Shelf
Evidence for Upwelling of Corrosive "Acidified"
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Evidence for Upwelling of Corrosive
“Acidified” Water onto the
Continental Shelf
Richard A. Feely,
1
*
Christopher L. Sabine,
1
J. Martin Hernandez-Ayon,
2
Debby Ianson,
3
Burke Hales
4
The absorption of atmospheric carbon dioxide (CO
2
) into the ocean lowers the pH of the waters.
This so-called ocean acidification could have important consequences for marine ecosystems. To
better understand the extent of this ocean acidification in coastal waters, we conducted
hydrographic surveys along the continental shelf of western North America from central Canada
to northern Mexico. We observed seawater that is undersaturated with respect to aragonite
upwelling onto large portions of the continental shelf, reaching depths of ~40 to 120 meters along
most transect lines and all the way to the surface on one transect off northern California. Although
seasonal upwelling of the undersaturated waters onto the shelf is a natural phenomenon in this
region, the ocean uptake of anthropogenic CO
2
has increased the areal extent of the affected area.
O
ver the past 250 years, the release of
carbon d ioxide ( CO
2
) from industrial and
agricultural activities has resulted in atmo-
spheric CO
2
concentrations that have increased by
about 100 parts per million (ppm). The atmo-
spheric concentration of CO
2
is now higher than
it has been for at least the past 650,000 years, and
is expected to continue to rise at an increasing
rate, leading to pronounced changes in our cli-
mate by the end of this century (1). Since the
beg in ni ng of the in du st ri a l era, the oceans have
absorbed ~127 ± 18 billion metric tons of carbon
as CO
2
from the atmosphere, or about one-third
of the anthropogenic carbon emissions released
(2). This process of absorption of anthropogenic
CO
2
has benefited humankind by substantially
reducing the greenhouse gas concentrations in
the atmosphere and minimizing some of the im-
pacts of global warming. However , the ocean’s
daily uptake of 22 million metric tons of CO
2
has
a sizable impact on its chem i s t r y and bio l o gy.
Recent hydrogra phic surveys and modeling studies
have confirmed that the uptake of anthropogenic
CO
2
by the oceans has resulted in a lowering of
seawater pH by about 0.1 since the beginning of
the industrial revolution (3–7). In the coming
decades, this phenomenon, called “ocean acidi-
fication,” could affect some of the most funda-
mental biological and geochemical processes of
the sea and seriously alter the fundamental struc-
ture of pelagic and benthic ecosystems (8).
Estimates of future atmospheric and oceanic
CO
2
concentrations, based on the Intergovernmental
Panel on Climate Change (IPCC) CO
2
emission
scenarios and general circulation models, indicate
that atmospheric CO
2
concentration s could exceed
500 ppm by the middle of this century , and 800
ppm near the end of the century . This increase would
result in a decrease in surface-wate r pH of ~ 0.4 by
the end of the century , and a corresponding 50%
decrease in carbonate ion concentration (5, 9). Such
rapid changes are likely to negatively affect marine
ecosystems, seriously jeopardizing the multifaceted
economies that currently depend on them (10).
The reaction of CO
2
with seawater reduces
the availability of carbonate ions that are neces-
sary for calcium carbonate (CaCO
3
)skeletonand
shell formation for marine organisms such as
corals, marine plankton, and shellfish. The extent
to which the organisms are affected depends
largelyontheCaCO
3
saturation state (W), which
is the product of the concentrations of Ca
2+
and
CO
3
2−
divided b y the apparent stoichiometric
solubility product for either aragonite or calcite:
W
arag
=[Ca
2+
][CO
3
2−
]/K′
sp
arag
(1)
W
cal
= [Ca
2+
][CO
3
2−
]/K′
sp
cal
(2)
where the calcium concentration is estimated
from the salinity, and the carbonate ion con-
1
Pacific Marine Environmental Laboratory/National Oceanic and
Atmospheric Administration, 7600 Sand Point Way NE, Seattle,
WA 98115–6349, USA.
2
Instituto de Investigaciones Oceano-
logicas, Universidad Autonoma de Baja California, Km. 103 Carr.
Tijuana-Ensenada, Ensenada, Baja California, Mexico.
3
Fisheries
and Oceans Canada, Institute of Ocean Science, Post Office Box
6000, Sidney, BC V8L 4B2, Canada.
4
College of Oceanic and
Atmospheric Sciences, Oregon State University, 104 Ocean
Administration Building, Corvallis, OR 97331–5503, USA.
*To whom correspondence should be addressed. E-mail:
richard.a.feely@noaa.gov
134°W 130°W 126°W 122°W 118°W 114°W
Lon
g
itude
52°N
50°N
48°N
46°N
44°N
42°N
40°N
38°N
36°N
34°N
32°N
30°N
28°N
26°N
1
2
3
4
5
6
7
8
9
10
11
12
13
20
40
60
80
100
120
140
160
180
200
220
240
260
Depth (m)
Latitude
Fig. 1. Distribution of the depths of the undersaturated water (aragonite saturation < 1.0; pH < 7.75) on
the continental shelf of western North America from Queen Charlotte Sound, Canada, to San Gregorio
Baja California Sur, Mexico. On transect line 5, the corrosive water reaches all the way to the surface in the
inshore waters near the coast. The black dots represent station locations.
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centration is calculated from the dissolved in-
organic carbon (DIC) and total alkalinity (TA)
measurements (11). In regions where W
arag
or
W
cal
is > 1.0, the formation of shells and skeletons
is favored. Below a value of 1.0, the water is
corrosive and dissolution of pure aragonite and
unprotected aragonite shells will begin to occur
(12). Recent studies have shown that in many
regions of the ocean, the aragonite saturation ho-
rizon shoaled as much as 40 to 200 m as a direct
consequence of the uptake of anthropogenic CO
2
(3, 5, 6). It is shallowest in the northeastern
Pacific Ocean, only 100 to 300 m from the ocean
surface, allowing for the transport of under-
saturated waters onto the continental shelf during
periods of upwelling.
In May and June 2007, we conducted the
North American Carbon Program (NACP) West
Coast Cruise on the Research Ship Wecoma along
the continental shelf of western North America,
completing a series of 13 cross-shelf transects
from Queen Charlotte Sound, Canada, to San
Gregorio Baja California Sur, Mexico (Fig. 1).
Full water column conductivity-temperature-depth
rosette stations were occupied at specified locations
along each transect (Fig. 1). Water samples were
collected in modified Niskin-type bottles and an-
alyzed for DIC, TA, oxygen, nutrients, and dis-
solved and particulate organic carbon. Aragonite
and calcite saturation, seawater pH (pH
SW
), and
partial pressure of CO
2
(pCO
2
) were calculated
from the DIC and TA data (11).
The central and southern coastal region off
western North America is strongly influenced by
seasonal upwelling, which typically begins in early
spring when the Aleutian low-pressure system
moves to the northwest and the Pacific High moves
northward, resulting in a strengthening of the
northwesterly winds (13, 14). These winds drive
net surface-water Ekman transport offshore, which
induces the upwelling of CO
2
-rich, intermediate-
depth (100 to 200 m) offshore waters onto the
continental shelf. The upwelling lasts until late
summer or fall, when winter storms return.
During the cruise, various stages and strengths
of upwelling were observed from line 2 off central
Vancouver Island to line 11 off Baja California,
Mexico. We observed recent upwelling on lines
5 and 6 near the Oregon-California border. Co-
incident with the upwelled waters, we found evi-
dence for undersaturated, low-pH seawater in the
bottom waters as depicted by W
arag
values < 1.0
and pH values < 7.75. The corrosive waters
reached mid-shelf depths of ~40 to 120 m along
lines 2 to 4 and lines 7 to 13 (Fig. 1). In the region
of the strongest upwelling (line 5), the isolines of
W
arag
= 1.0, DIC = 2190, and pH = 7.75 closely
followed the 26.2 potential density surface (Fig.
2). This density surface shoaled from a depth of
~150 m in the offshore waters and breached the
surface over the shelf near the 100-m bottom
contour , ~ 40 km from the coast. This shoaling of
the density surfaces and CO
2
-rich waters as one
approaches land is typical of strong coastal up-
welling conditions (15–18). The surface-water
pCO
2
on the 26.2 potential density surface was
about 850 matm near the shelfbreak and higher
inshore (Fig. 2), possibly enhanced by respiration
processes on the shelf (17). These results indicate
that the upwelling process caused the entire water
column shoreward of the 50-m bottom contour to
become undersaturated with respect to aragonite,
a condition that was not predicted to occur in open-
ocean surface waters until 2050 (5). On line 6, the
next transect south, the undersaturated water was
close to the surface at ~22 km from the coast. The
lowest W
arag
values (<0.60) observed in the near-
bottom waters of the continental shelf corre-
sponded with pH values close to 7.6. Because the
calcite saturation horizon is located between 225
and 400 m in this part of the northeastern Pacific
(19), it is still too deep to shoal onto the continental
shelf. Nevertheless, the calcite saturations values
drop in the core of the upwelled water (W
cal
<1.3).
As noted, the North Pacific aragonite satura-
tion horizons are among the shallowest in the
global ocean (3). The uptake of anthropogenic
CO
2
has caused these horizons to shoal by 50 to
100 m since preindustrial times so that they are
within the density layers that are currently being
upwelled along the west coast of North America.
200
100
200
100
200
100
200
100
126°W 125.5°W 125°W 124.5°W
200
100
0
0
0
0
0
15
14
13
12
11
10
9
8
7
6
5
4
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
8.5
8.3
8.1
7.9
7.7
7.5
7.3
2350
2250
2150
2050
1950
1850
1450
1300
1150
1000
850
700
550
400
250
Colors:
Temp (°C)
Contours:
Potential
Density
Aragonite
Saturation
State
pH
Dissolved
Inorganic
Carbon
(µmol kg
-1
)
pCO
2
(µatm)
Depth (m)Depth (m)Depth (m)Depth (m)Depth (m)
A
B
C
D
E
Fig. 2. Vertical sections of (A) temperature, (B) aragonite saturation, (C)pH,(D)DIC,and(E) pCO
2
on
transect line 5 off Pt. St. George, California. The potential density surfaces are superimposed on the
temperature section. The 26.2 potential density surface delineates the location of the first instance in
which the undersaturated water is upwelled from depths of 150 to 200 m onto the shelf and outcropping
at the surface near the coast. The red dots represent sample locations.
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Although much of the corrosive character of these
waters is the natural result of respiration processes at
intermediate depths below the euphotic zone, this
region continues to accumulate more anthropogenic
CO
2
and, therefore, the upwelling processes will
expose coastal organisms living in the water column
or at the sea floor to less saturated waters, exacerbat-
ing the biological impacts of ocean acidification.
On the basis of our observed O
2
values and es-
timated O
2
consumption rates on the same density
surfaces (18–20), the upwelled water off northern
California (line 5) was last at the surface about
50 years ago, when atmospheric CO
2
was about
65 ppm lower than it is today . The open-ocean an-
thropogenic CO
2
distributions in the Pacific have
been estimated previously (4, 19, 21). By determin-
ing the density dependence of anthropogenic CO
2
distributions in the eastern-most North Pacific sta-
tions of the Sabine et al.(21)dataset,weestimate
that these upwelled waters contain ~31 ± 4 mmol kg
−1
anthropogenic CO
2
(fig. S2). Removing this signal
from the DIC increases the aragonite saturation
state of the waters by about 0.2 units. Thus, without
the anthropogenic signal, the equilibrium aragonite
saturation level (W
arag
= 1) would be deeper by
about 50 m across the shelf, and no undersaturated
waters would reach the surface. W ater already in
transit to upwelling centers carries increasing an-
thropogenic CO
2
and more corrosive conditions to
the coastal oceans of the future. Thus, the under-
saturated waters, which were mostly a problem for
benthic communities in the deeper waters near the
shelf break in the preindustrial era, have shoaled
closer to the surface and near the coast because of
the additional inputs of anthropogenic CO
2
.
These observations clearly show that seasonal
upwelling processes enhance the advancement of
the corrosive deep water into broad regions of the
North American western continental shelf. Because
the region experiences seasonal periods of enhanced
aragonite undersaturation, it is important to under-
stand how the indigenous organisms deal with this
exposure and whether future increases in the range
and intensity of the corrosiveness will affect their
survivorship. Presently, little is known about how
this intermittent exposure to corrosive water might
affect the development of larval, juvenile, and adult
stages of aragonitic calcifying organisms or finfish
that populate the neritic and benthic environments in
this region and fuel a thriving economy . Laboratory
and mesocosm experiments show that these changes
in saturation state may cause substantial changes in
overall calcification rates for many species of marine
calcifiers including corals, coccolithophores, foram-
inifera, and pteropods, which are a major food
source for local juvenile salmon (8, 22–30). Similar
decreases in calcification rates would be expected
for edible mussels, clams, and oysters (22, 31). Other
research indicates that many species of juvenile fish
andshellfishofeconomicimportancetocoastalre-
gions are highly sensitive to higher-than-normal
CO
2
concentrations such that high rates of mortality
are directly correlated with the higher CO
2
con-
centrations (31, 32). Although comprehensiv e field
studies of organisms and their response to sporadic
increases in CO
2
along the western North American
coast are lacking, current studies suggest that further
research under field condition s is warranted. Our
results show that a large section of the North Amer-
ican continental shelf is affected by ocean acidifi-
cation. Other continental sh el f regio ns may also
be affected where anthropogenic CO
2
-enriched
water is being upwelled onto the shelf.
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Biology and Biogeochemistry Program.
Supporting Online Material
www.sciencemag.org/cgi/content/full/1155676/DC1
Materials and Methods
Figs. S1 and S2
References
25 January 2008; accepted 13 May 2008
Published online 22 May 2008;
10.1126/science.1155676
Include this information when citing this paper.
Regulation of Hepatic Lipogenesis
by the Transcription Factor XBP1
Ann-Hwee Lee,
1
* Erez F. Scapa,
2,3
David E. Cohen,
2,3
Laurie H. Glimcher
1,2
*
Dietary carbohydrates regulate hepatic lipogenesis by controlling the expression of critical enzymes
in glycolytic and lipogenic pathways. We found that the transcription factor XBP1, a key regulator of
the unfolded protein response, is required for the unrelated function of normal fatty acid synthesis
in the liver. XBP1 protein expression in mice was elevated after feeding carbohydrates and
corresponded with the induction of critical genes involved in fatty acid synthesis. Inducible, selective
deletion of XBP1 in the liver resulted in marked hypocholesterolemia and hypotriglyceridemia,
secondary to a decreased production of lipids from the liver. This phenotype was not accompanied by
hepatic steatosis or compromise in protein secretory function. The identification of XBP1 as a regulator
of lipogenesis has important implications for human dyslipidemias.
H
epatic lipid synthesis increases upon in-
gestion of excess carbohydrates, which
are converted into triglyceride (TG) in
the liver and transported to adipose tissue for
energy storage. Dysregulation of hepatic lipid
metabolism is closely related to the development
of metabolic syndrome, a condition characterized
by central obesity, dyslipidemia, elevated blood
glucose, and hypertension (1). In mammals, he-
patic lipid metabolism is controlled by transcrip-
tion factors, such as liver X receptor (LXR), sterol
regulatory element–binding proteins (SREBPs),
and carbohydrate response element–binding pro-
tein (ChREBP), that regulate the expression of
1
Department of Immunology and Infectious Diseases,
Harvard School of Public Health, Boston, MA 02115,
USA.
2
Department of Medicine, Harvard Medical School,
Boston, MA 02115, USA.
3
Division of Gastroenterology, Brigham
and Women’s Hospital, Boston, MA 02115, USA.
*To whom correspo ndence should be addressed. E-mail:
lglimche@hsph.harvard.edu (L.H.G.); ahlee@hsph.harvard.
edu (A.-H.L.)
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