ArticlePDF AvailableLiterature Review

The Geological Record of Ocean Acidification

March 2012
Science 335(6072):1058-63

DOI:10.1126/science.1208277

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PubMed

Authors:

Bärbel Hönisch

Columbia University

Andy Ridgwell

University of California, Riverside

Daniela N Schmidt

University of Bristol

Ellen Thomas

Yale University

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Ocean acidification may have severe consequences for marine ecosystems; however, assessing its future impact is difficult because laboratory experiments and field observations are limited by their reduced ecologic complexity and sample period, respectively. In contrast, the geological record contains long-term evidence for a variety of global environmental perturbations, including ocean acidification plus their associated biotic responses. We review events exhibiting evidence for elevated atmospheric CO2, global warming, and ocean acidification over the past ~300 million years of Earth’s history, some with contemporaneous extinction or evolutionary turnover among marine calcifiers. Although similarities exist, no past event perfectly parallels future projections in terms of disrupting the balance of ocean carbonate chemistry—a consequence of the unprecedented rapidity of CO2 release currently taking place.

When CO 2 dissolves in seawater, it reacts with water to form carbonic acid, which then dissociates to bicarbonate, carbonate, and hydrogen ions. The higher concentration of hydrogen ions makes seawater acidic, but this process is buffered on long time scales by the interplay of seawater, seafloor carbonate sediments, and weathering on land. Shown are the major pathways of reduced carbon (black) and of alkalinity (yellow). Processes leading to ocean acidification and/or reduction of CaCO 3 saturation are indicated in red, and processes leading to ocean alkalinization and/or CaCO 3 saturation increases are indicated in blue. Anthropogenic perturbations are marked in italics. Approximate fluxes are printed in parentheses (PgC year −1 ), whereas reservoir inventory values are shown in brackets [PgC]. Natural carbon cycle fluxes are from (70); anthropogenic fluxes for 2008 are from (57), which for the land sink is significantly above its 1990-2000 average of 2.6 PgC year −1 due to the 2008 La Niña state (8).

…

Compilation of data-based [(B) and (C)] and model-reconstructed [(C) and (D)] indicators of global carbon cycle evolution over the past 300 My together with candidate ocean acidification events (A). (A) Summarization of the degree to which events (table S1) have some similarity to modern ocean acidification. The similarity index (table S1) is color-coded, where red indicates 3/most similar, orange indicates 2/partly similar, and yellow indicates 1/unlike. (B) Proxy-reconstructed atmospheric PCO 2 (2) grouped by proxy: yellow circles indicate paleosol d 13 C, light blue squares indicate marine phytoplankton d 13 C, red triangles indicate stomatal indices/ ratios, dark blue inverted triangles indicate planktic foraminiferal d 11 B, green five-pointed stars indicate liverwort d 13 C, purple six-pointed stars indicate sodium carbonates, with 10-My averages shown by gray bars. For plotting convenience, estimates exceeding 3000 matm are not shown [primarily paleosol d 13 C from the uppermost Triassic/lowermost Jurassic (2)]. (C) Ocean Mg/Ca ratios (red triangles, left axis), reconstructed from fluid inclusions (2) and echinoderm fossil carbonate [red squares (71)] together with the Phanerozoic seawater model of (72) (red line). Also shown (blue circles, right axis) is [Ca 2+ ] from fluid inclusions (2) and models [blue line (72)]. (D) Model-reconstructed changes in mean ocean surface pH at 20-My intervals [black line (73)].

…

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DOI: 10.1126/science.1208277

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The Geological Record of Ocean Acidification

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The Geological Record of

Ocean Acidification

Bärbel Hönisch,

*Andy Ridgwell,

Daniela N. Schmidt,

Ellen Thomas,

4,5

Samantha J. Gibbs,

Appy Sluijs,

Richard Zeebe,

Lee Kump,

Rowan C. Martindale,

Sarah E. Greene,

2,10

Wolfgang Kiessling,

Justin Ries,

James C. Zachos,

Dana L. Royer,

Stephen Barker,

Thomas M. Marchitto Jr.,

Ryan Moyer,

Carles Pelejero,

Patrizia Ziveri,

18,19

Gavin L. Foster,

Branwen Williams

Ocean acidification may have severe consequences for marine ecosystems; however, assessing

its future impact is difficult because laboratory experiments and field observations are limited by

their reduced ecologic complexity and sample period, respectively. In contrast, the geological

record contains long-term evidence for a variety of global environmental perturbations, including

ocean acidification plus their associated biotic responses. We review events exhibiting evidence

for elevated atmospheric CO

, global warming, and ocean acidification over the past ~300 million

years of Earth’s history, some with contemporaneous extinction or evolutionary turnover among

marine calcifiers. Although similarities exist, no past event perfectly parallels future projections

in terms of disrupting the balance of ocean carbonate chemistry—a consequence of the

unprecedented rapidity of CO

release currently taking place.

The geological record is imprinted with nu-

merous examples of biotic responses to

natural perturbations in global carbon cy-

cling and climate change (Fig. 1), some of which

could have been caused by large-scale ocean

acidification. By reconstructing past changes in

marine environmental conditions, we can test hy-

potheses for the causes and effects of future-

relevant stressors such as ocean acidification on

ecosystems (1). However, for the fossil record to

be of direct utility in assessing future ecosystem

impacts, the occurrence and extent of past ocean

acidification must be unambiguously identified.

In recent years, a variety of trace-element and

isotopic tools have become available that can be

applied to infer past seawater carbonate chemis-

try. For instance, the boron isotopic composition

B) of marine carbonates reflects changes in

seawater pH, the trace element (such as B, U, and

Zn)–to-calcium ratio of benthic and planktic for-

aminifer shells records ambient [CO

−

], and the

stable carbon isotopic composition (d

C) of or-

ganic molecules (alkenones) can be used to es-

timate surface ocean aqueous [CO

](2).

Because direct ocean geochemical proxy

observations are still relatively scarce, past ocean

acidification is often inferred from a decrease in

the accumulation and preservation of CaCO

marine sediments, potentially indicated by an in-

creased degree of fragmentation of foraminiferal

shells (3). However, it is difficult to distinguish

between the original calcification responses to

chemical changes in the surface ocean and post-

mortem conditions at the sea floor. For instance,

planktic calcifiers may secrete heavier or lighter

shells (4), but that signal may be modified at the

sea floor through dissolution or overgrowth after

deposition (5,6). This duality can introduce con-

troversy over the identification of causes and

effects, the drivers of biological change, and

REVIEW

Lamont-Doherty Earth Observatory of Columbia University,

Palisades, NY 10964, USA.

School of Geographical Sciences,

University of Bristol, Bristol BS8 1SS, UK.

School of Earth

Sciences,UniversityofBristol,Bristol,BS81RJ,UK.

Depart-

ment of Geology and Geophysics, Yale University, New Haven,

CT 06520, USA.

Department of Earth and Environmental

Sciences, Wesleyan University, Middletown, CT 06459, USA.

Ocean and Earth Science, National Oceanography Centre

Southampton, University of Southampton, Southampton SO14

3ZH, UK.

Department of Earth Sciences, Utrecht University,

3584 CD Utrecht, Netherlands.

School of Ocean and Earth

Science and Technology, Department of Oceanography, Uni-

versity of Hawaii at Manoa, Honolulu, HI 96822, USA.

Depart-

ment of Geosciences, Pennsylvania State University, University

Park, PA 16802, USA.

Department of Earth Sciences, Uni-

versity of Southern California (USC), Los Angeles, CA 90089,

USA.

Museum für Naturkunde at Humboldt University, 10115

Berlin, Germany.

Department of Marine Sciences, University

of North Carolina–Chapel Hill, NC 27599, USA.

Earth and

Planetary Sciences Department, University of California Santa

Cruz, CA 95064, USA.

School of Earth and Ocean Sciences,

Cardiff University, Cardiff CF10 3AT, UK.

Department of Geo-

logical Sciences and Institute of Arctic and Alpine Research,

University of Colorado, Boulder, CO 80309, USA.

University of

South Florida St. Petersburg, Department of Environmental

Science, Policy, and Geography, St. Petersburg, FL 33701, USA.

Institució Catalana de Recerca i Estudis Avançats and Depart-

ment of Marine Biology and Oceanography, Consejo Superior

de Investigaciones Científicas, 08003 Barcelona, Catalonia, Spain.

Institute of Environmental Science and Technology, Universitat

Autònoma de Barcelona, 01893 Barcelona, Spain.

Depart-

ment of Earth Sciences, Vrije Universiteit, 1081HV Amsterdam,

Netherlands.

W. M. Keck Science Department of Claremont

McKenna College, Pitzer College, and Scripps College, Claremont,

CA 91711, USA.

*To whom correspondence should be addressed. E-mail:

hoenisch@ldeo.columbia.edu

Organic-

walled

dinocysts

Deglaciation PETM Toarcian

OAE

Cretaceous

asteroid impact

End-Triassic

mass extinction

End-Permian

mass extinction

Calcareous

nannofossils

0 100 Time (My) 200 300

Planktic

foraminifers

Benthic

foraminifers

Shallow reef

builders

Fig. 1. Idealized diversity trajectories of the calcareous and organic fossil lineages discussed in the text.

Extinction and radiation suggest events of major environmental change throughout the past 300 My.

Calcareous plankton is shown in black, calcareous benthos in blue, and organic fossils in green, and the

line thickness indicates relative and smoothed species richness. Highlighted events (vertical red lines)

have been associated with potential ocean acidification events (Fig. 4). Calcareous organisms were not

uniformly affected at all times, suggesting the importance of synergistic environmental factors to ex-

tinction, adaptation, and evolution as well as different sensitivity due to physiological factors. Iden-

tification of a paleo-ocean acidification event therefore requires independent geochemical evidence

for ocean chemistry changes. Images of organisms are exemplary. References and further information

on the displayed organisms are available in the supporting online material.

2 MARCH 2012 VOL 335 SCIENCE www.sciencemag.org

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whether past intervals of ocean acidification

are characterized by environmental conditions

relevant for the near future. Coeval changes in

ocean circulation will also introduce regional

biases in proxy records and hence affect global

interpretations.

Here, we review the factors controlling ocean

acidification, describe evidence for the occurrence

of ocean acidification events in the past, and dis-

cuss the potential as well as weaknesses of the

geological record in helping us predict future eco-

system changes.

Is Ocean Acidification Primarily a

pH-Decline Phenomenon?

The current rate of anthropogenic CO

release

leads to a surface ocean environment charac-

terized not only by elevated dissolved CO

and

decreased pH (7) but, critically, decreased satura-

tion with respect to calcium carbonate (CaCO

a compound widely used by marine organisms

for the construction of their shells and skeletons

(8). In contrast, slower rates of CO

release lead

to a different balance of carbonate chemistry

changes and a smaller seawater CaCO

saturation

response, which may induce differential biotic

response or even no response at all, invalidating a

direct analog. The reason for a smaller saturation

response to slow CO

release is that the alkalinity

released by rock weathering on land must ulti-

mately be balanced by the preservation and burial

of CaCO

in marine sediments (Fig. 2), which

itself is controlled by the calcium carbonate sat-

uration state of the ocean (9). Hence, CaCO

saturation is ultimately regulated primarily by

weathering on long time scales, not atmospheric

partial pressure of CO

(PCO

). While weathering

itself is related to atmospheric PCO

(10), it is

related much more weakly than ocean pH, which

allows pH and CaCO

saturation to be almost

completely decoupled for slowly increasing at-

mospheric PCO

Using a global carbon cycle model (2), we

show the progressive coupling between CaCO

saturation and pH as the rate of CO

emissions

increases and sources (weathering) and sinks

(CaCO

burial) of alkalinity are no longer ba-

lanced. For rapid century-scale and thus future-

relevant increases in atmospheric PCO

, both

surface ocean pH and saturation state decline in

tandem (Fig. 3). The projected decrease in ocean

surface saturation state—here, with respect to

aragonite (W

aragonite

)—is an order of magnitude

larger for a rapid CO

increase than for a slow

[100 thousand years (ky)] CO

increase. Ulti-

mately, saturation recovers while the pH remains

suppressed, reflecting how changes in the oce-

anic concentrations of dissolved inorganic carbon

(DIC) and alkalinity make it possible to have

simultaneously both high CO

and high carbon-

ate ion concentration saturation ([CO

−

], which

controls saturation), but with the relatively greater

increase in [CO

] causing lower pH. The key to

unlocking the geological record of ocean acid-

ification is hence to distinguish between long-

term steady states and transient changes. We use

the term “ocean acidification event”for time in-

tervals in Earth’s history that involve both a re-

duction in ocean pH and a substantial lowering

of CaCO

saturation, implying a time scale on

the order of 10,000 years and shorter (Fig. 3).

Indications of Paleo-Ocean Acidification

With these criteria in mind, we review (in reverse

chronological order) the intervals in Earth’shistory

for which ocean acidification has been hypothe-

sized, along with the evidence for independent

geochemical and biotic changes. We confine this

review to the past ~300 million years (My) be-

cause the earlier Phanerozoic (and beyond) lacks

the pelagic calcifiers that not only provide key

proxy information but also create the strong deep-

sea carbonate (and hence atmospheric PCO

) buf-

fer that characterizes the modern Earth system

(9). Our criteria for identifying potentially future-

relevant past ocean acidification are (i) massive

release, (ii) pH decline, and (iii) saturation

decline. We also discuss evidence for the time

scale of CO

release, as well as for global warming.

Events are given a similarity index that is based

on available geochemical data (table S1) and are

indicated in Fig. 4A.

Late Pleistocene deglacial transitions. The

last deglaciation is the best documented past event

associated with a substantive (30%) CO

rise:

189 to 265 matm between 17.8 to 11.6 ky before

pCO2(g)

CO2(aq)

+ H2OH

++ HCO3

-2H++CO

Atmosphere [850]

Ocean [38000]

Terrestrial

biosphere [2000]

Fossil fuel CO2 emissions (8.5)

Emissions from land use change (1.0)

CO2 uptake (2.0)

Net CO2 dissolution (2.3)

Net CO2 fixation (10)

CaCO3 dissolution (0.6)

water column

CaCO3 dissolution (0.4)

sea floor

Shallow water

Corg burial (0.1)

Shallow water

CaC O3 burial (0.1)

Low temperature basaltic alteration

Carbonate (0.1)

Kerogen (0.1)

weathering

Silicate

weathering

(0.1)

Metamorphism

Volcanism

(0.1)

Calcification (1.1)

Deep sea

CaCO3 burial (0.1)

Corg oxidation (9.9)

Corg oxidation (0.1)

Reservoir inventory

values [PgC]

Processes leading to

ocean acidification

and/or reduction of

CaCO3 saturation and

their approximate

fluxes (PgC yr-1)

Processes leading to

ocean alkalinization

and/or CaCO3

saturation-increases

and their approximate

fluxes (PgC yr-1)

Volcanism

Surface sediments

Fossil fuels . . . . . .

Shales . . . . . . . . . . . . .

Mantle . . . . . . . . . . . . .

Carbonate rocks . . . .

[0.003

106]

[0.005

106]

[12

106]

[32

106]

[65

106]

Fig. 2. When CO

dissolves in seawater, it reacts with water to form carbonic

acid, which then dissociates to bicarbonate, carbonate, and hydrogen ions. The

higher concentration of hydrogen ions makes seawater acidic, but this process

is buffered on long time scales by the interplay of seawater, seafloor carbonate

sediments, and weathering on land. Shown are the major pathways of reduced

carbon (black) and of alkalinity (yellow). Processes leading to ocean acid-

ification and/or reduction of CaCO

saturation are indicated in red, and pro-

cesses leading to ocean alkalinization and/or CaCO

saturation increases are

indicated in blue. Anthropogenic perturbations are marked in italics. Ap-

proximate fluxes are printed in parentheses (PgC year

−1

), whereas reservoir

inventory values are shown in brackets [PgC]. Natural carbon cycle fluxes are

from (70); anthropogenic fluxes for 2008 are from (57), which for the land

sink is significantly above its 1990–2000 average of 2.6 PgC year

−1

due to the

2008 La Niña state (8).

www.sciencemag.org SCIENCE VOL 335 2 MARCH 2012 1059

REVIEW

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the present (B.P.) (11). Boron isotope estimates

from planktic foraminifers show a 0.15 T0.05

unit decrease in sea surface pH (12) across the

deglacial transition—an average rate of decline

of ~0.002 units per 100 years compared with the

current rate of more than 0.1 units per 100 years

(table S1). Planktic foraminiferal shell weights

decreased by 40 to 50% (4), and coccolith mass

decreased by ~25% (13). In the deep ocean,

changes in carbonate preserva-

tion (14), pH [from foraminiferal

B(15)] and [CO

−

][from

foraminiferal B/Ca and Zn/Ca

(16,17)] differed between ocean

basins, reflecting covarying

changes in deep-water circula-

tion and an internal carbon shift

within the ocean. The regional

nature of these variations high-

lights the general need for careful

evaluation of regional versus glob-

al effects in paleo-studies.

Oligocene–Pliocene. The cli-

mate of the Oligocene to Plio-

cene [34 to 2.6 million years ago

(Ma)] contains intervals of ele-

vated temperature and modest

deviations of atmospheric PCO

from modern values (Fig. 4). Of

particular interest has been the

Pliocene warm period [3.29 to

2.97 Ma (18,19)], which is char-

acterized by global surface tem-

peratures estimated to be ~2.5°C

higher than today (19), atmospher-

ic PCO

between 330 to 400 matm

(Fig. 4C) (18,20), and sea surface

(T)

~0.06 to 0.11 units lower

(18) than the preindustrial. Eco-

logical responses to the warming

include migration of tropical for-

aminifer species toward the poles

(21), but there are no documented

calcification responses or increased

nannoplankton extinction rates

(22). The early to middle Miocene

(23 to 11 Ma) and Oligocene (34

to 23 Ma) were also character-

ized periods of elevated temper-

atures and slightly higher PCO

compared with preindustrial val-

ues (Fig. 4C) but, because of their

long duration, were not associ-

ated with changes in CaCO

sat-

uration (Fig. 3C).

Paleocene–Eocene. Evidence

for rapid carbon injection asso-

ciated with the Paleocene–Eocene

Thermal Maximum (PETM, 56

Ma) as well as a number of smaller

transient global warming events

(hyperthermals) during the late

Paleocene and early Eocene (58

to 51 Ma) comes primarily from

observations of large [up to –4

per mil (‰)] negative d

Cexcursions(23)

associated with pronounced decreases in calci-

um carbonate preservation (24). Depending on

the assumed source, rate, and magnitude of CO

release (25),a0.25to0.45unitdeclineinsurface

seawater pH is possible, with a reduction in mean

surface ocean aragonite saturation from W=3

downto1.5to2(1). The calcite compensation

depth (CCD) (8)roseby~2kmtoshallowerthan

1.5 km in places (24) (compared with >4 km

today). Although a pH decrease or PCO

increase

remains to be confirmed by geochemical proxies

for any of the hyperthermal events, the amount

of carbon injected can be modeled on the basis

of consistent carbonate d

C and CCD changes,

yielding between ~2000 and 6000 PgC for the

onset of the PETM (26,27). However, as with the

last glacial transition, deep sea geochemistry ap-

pears strongly modulated by regional ocean cir-

culation changes (28), which adds an additional

layer of complexity to global extrapolation and

highlights the importance of adequate spatial cov-

erage of the data.

PETM sediments record the largest extinction

among deep-sea benthic foraminifers of the past

75 My (29), and a major change in trace fossils

indicates a disruption of the macrobenthic com-

munity (30). However, the covariation of ocean

acidification, warming, and corresponding oxygen

depletion (fig. S2) (23) precludes the attribution of

this extinction to a single cause (1,29). In shallow

water environments, a gradual shift from calcar-

eous red algae and corals to larger benthic foramin-

ifers as dominant calcifiers started in the Paleocene

and was completed at the PETM with the collapse

of coralgal reefs and larger benthic foraminiferal

turnover (31). This event is recognized as one of

the four major metazoan reef crises of the past

300My(Fig.1)(32). In marginal marine settings,

coccolithophore (33) and dinoflagellate cyst (34)

assemblages display changes in species compo-

sition, but these are interpreted to reflect sensitiv-

ity to temperature, salinity stratification, and/or

nutrient availability (34,35), not necessarily acid-

ification (fig. S2). In the open ocean, the occur-

rence of deformities in some species of calcareous

nannoplankton has been described (36), but de-

spite a strong change in assemblages, there is no

bias in extinction or diversification in favor of

or against less or more calcified planktic spe-

cies (37).

Cretaceous and Cretaceous-Paleogene. The

well-known mass extinction at 65 Ma is gener-

ally accepted to have been triggered by a large

asteroid impact (38). In addition to potential ter-

restrial biomass or fossil carbon burning, the im-

pact may have caused the emission of SO

from

vaporized gypsum deposits at the impact site

and/or nitric acid aerosols produced by shock

heating of the atmosphere, which could have led

to acid rain and hence potentially to rapid acid-

ification of the surface ocean (38). Although

planktic calcifiers exhibited elevated rates of ex-

tinction and reduced production (22,39), reef

corals did not experience a major extinction (32),

and benthic foraminifers were not affected in ei-

ther shallow or deep waters (29). Because mul-

tiple environmental changes covaried and proxy

data for marine carbonate chemistry are not yet

available, unambiguous attribution of the planktic

extinctions to any one driver such as ocean acid-

ification is currently not possible.

The earlier Cretaceous (K) (Fig. 4A) is gen-

erally a time of massive chalk deposition (mainly

Time (years)

Atmospheric

(␮atm)

300

400

500

600

1 10 100 1,000 10,000 100,000

Mean ocean

surface ⍀

aragonite

Mean ocean

surface ⍀

aragonite

2.0

Mean ocean

surface pH

SWS

7.9

8.0

8.1

8.2

Mean surface pHSWS

Time to a doubling of P

(years)

101

102

103

104

105

3.0

4.0

8.1 8.0 7.9

2.0

3.0

4.0

stabilization

Rising CO

Fig. 3. The trajectories of mean ocean surface pH and aragonite

saturation (W

aragonite

)becomeprogressivelydecoupled as the rate of

atmospheric PCO

change increases. The four panels show the results

of a series of experiments in an Earth system model (2). (A) Prescribed

linear increases of atmospheric PCO

(on a log

scale) from ×1 to ×2

preindustrial CO

, with the different model experiments spanning

a range of time scales (but experiencing the same ultimate CO

change). (B) Evolution of mean surface pH in response to rising CO

aragonite

.(D) A cross-plot illustrating

how W

aragonite

is progressively decoupled from pH as the rate of PCO

increase slows, with future-relevant rate of PCO

increase showing a

diagonal trajectory from top left to bottom right, whereas slow PCO

increases result in an almost horizontal trajectory toward lower pH

with very little saturation change. All plots are color-coded from red

(“fast”)toblue(“slow”). These model results include both climate

and long-term (silicate) weathering feedback. See (2)andfig.S1for

the role of these and other feedbacks.

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in the form of nannofossil calcite),

as well as one of elevated PCO

(Fig. 4B) and lower pH (Fig. 4D).

This association can be miscon-

ceived as evidence that marine

calcification will not be impaired

under conditions of low pH in the

future. However, this reasoning is

invalid because extended periods

of high PCO

(Fig. 4B) do not nec-

essarily result in a suppressed sea-

water calcite saturation state (Fig. 3)

(1,40), which exerts an impor-

tant control on organisms’calcifi-

cation (41).

Cretaceous and Jurassic oce-

anic anoxic events. The Mesozoic

oceanic anoxic events (OAEs) (in

particular, OAE 2 ~93 Ma, OAE1a

~120 Ma, and Toarcian OAE ~183

Ma) were intervals during which

the ocean’s oxygen minimum and

deep anoxic zones expanded mark-

edly (42). The onsets of these OAEs

have been linked to the emplace-

ment of large igneous provinces,

degassing large amounts of CO

and associated environmental con-

sequences of warming, lower oxy-

gen solubility, and possibly ocean

acidification (42). Some of the

Cretaceous OAEs were associated

with turnover in plankton commu-

nities (43). Deformities and some

minor size reduction in coccoliths,

as well as a massive increase in

the abundance of heavily calcified

nannoconids, have been observed

(44,45). However, similar to more

recent events, there is difficulty in

unequivocally attributing observa-

tions to surface water acidification

given the covariation of environ-

mental changes (46).

Because most old sea floor

(~180 Ma or older) is subducted,

the sedimentary record of the

Toarcian OAE is now restricted to former con-

tinentalmargins. Sedimentary organic and inor-

ganic carbon deposits display initially negative,

followed by positive d

C excursions, which is

consistent with an influx of CO

into the at-

mosphere followed by organic carbon burial

(42). The negative isotopic transition occurs in

distinct negative d

C shifts, each estimated to

occur in less than 20 ky (47) and possibly in as

little as 650 years (48). The Toarcian OAE is

associated with a reef crisis that was particularly

selective against corals and hypercalcifying

sponges (animals with a large skeletal-to–

organic biomass ratio) (Fig. 4B) (32) and with a

decrease in nannoplankton flux (49). Again,

these observations could have been a response

to any one or combination of a number of dif-

ferent contemporaneous environmental changes.

Triassic–Jurassic. The Triassic–Jurassic (T/J)

mass extinction is linked to the coeval emplace-

ment of the Central Atlantic Magmatic Province

(50). Proxy records across the T/J boundary

(~200 Ma) suggest a doubling of atmospheric

PCO

over as little as 20 ky (51,52), although

the absolute PCO

estimates differ greatly between

proxies, with leaf stomata suggesting an increase

from 700 to 2000 matm, whereas pedogenic car-

bonates indicate an increase from 2000 to 4400

matm (Fig. 4C) (2). Decreased carbonate satura-

tion is inferred from reduced pelagic carbonate

accumulation in shelf sediments (53), although

shallow water carbonate deposition can vary in

response to many parameters, not only acidifica-

tion. A calcification crisis amongst hypercalcify-

ing taxa is inferred for this period (Fig. 4B), with

reefs and scleractinian corals experiencing a near-

total collapse (32). However, the observation that

tropical species were more affected than extra-

tropical species suggests that global warming may

have been an important contributor or even dom-

inant cause of this extinction (32).

Permian–Triassic. The Permo–Triassic (P/T)

mass extinction (252.3 Ma) was the most severe

of the Phanerozoic Era and coincided, at least in

part, with one of the largest known continental

eruptions, the Siberian trap basalts. Recent es-

timates for the total CO

release put it at ~13,000

to 43,000 PgC in 20 to 400 ky (54–56)—an an-

nual carbon release of ~0.1 to 1 PgC [compared

with 9.9 PgC in 2008 (57)]. There is some obser-

vational evidence for carbonate dissolution in

shelf settings (54), but its interpretation is again

debated (58). There is abundant evidence for

ocean anoxia, photic zone euxinia (enrichment in

Fig. 4. Compilation of data-based

[(B) and (C)] and model-reconstructed

[(C) and (D)] indicators of global

carbon cycle evolution over the

past 300 My together with candi-

date ocean acidification events (A).

(A) Summarization of the degree to

which events (table S1) have some

similarity to modern ocean acidifica-

tion. The similarity index (table S1)

is color-coded, where red indicates

3/most similar, orange indicates

2/partly similar, and yellow indicates

1/unlike. (B)Proxy-reconstructed

atmospheric PCO

(2) grouped by

proxy: yellow circles indicate paleo-

sol d

C, light blue squares indicate

marine phytoplankton d

C, red

triangles indicate stomatal indices/

ratios, dark blue inverted triangles

indicate planktic foraminiferal d

green five-pointed stars indicate

liverwort d

C, purple six-pointed

stars indicate sodium carbonates,

with 10-My averages shown by gray

bars. For plotting convenience, es-

timates exceeding 3000 matm are not

shown [primarily paleosol d

Cfrom

the uppermost Triassic/lowermost

Jurassic (2)]. (C) Ocean Mg/Ca ratios

(red triangles, left axis), reconstructed

from fluid inclusions (2) and echino-

derm fossil carbonate [red squares

(71)] together with the Phanerozoic

seawater model of (72) (red line).

Also shown (blue circles, right axis)

is [Ca

] from fluid inclusions (2)

and models [blue line (72)]. (D)

Model-reconstructed changes in

mean ocean surface pH at 20-My

intervals [black line (73)].

2500

2000

1000

Time (millions of years before present)

1000 200 300

Carbon/climate

perturbation events

100

0200 300

Mg/Ca (mol mol

-1

)

[Ca

] (mol mol

-1

)

K J Tr P

PgN

oarcian OAE

End Cretaceous

Triassic/

Jurassic

OAE 2

OAE 1a

Deglacial transitions

Cenozoic Mesozoic Paleozoic

Phanerozoic

1500

500

Modern (pre-industrial)

Paleocene/

Eocene

Permian/

Triassic

3000

Band estimates

up to ~5000 µatm

at 201 Ma

Atmospheric

(␮atm)

0.0

7.4

7.6

7.8

8.0

8.2

1.0

2.0

4.0

5.0

6.0

7.0

Mean ocean

surface pH

SWS

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hydrogen sulfide) (59), and strong warming (54),

but no direct proxy evidence for pH or carbonate

ion changes. Knoll et al.(59) inferred the prefer-

ential survival of taxa with anatomical and phys-

iological features that should confer resilience

to reduced carbonate saturation state and hyper-

capnia (high CO

in blood) and preferential ex-

tinction of taxa that lacked these traits, such as

reef builders (32).

Is There a Geologic Analog for the Future?

A number of past ocean carbon-cycle perturbation

events share many of the characteristics of an-

thropogenic ocean acidification (Fig. 4 and table

S1), with the notable exception of the estimated

rates of CO

release. In the general absence of

direct proxy evidence for lower pH and reduced

saturation before the Pliocene, global carbon cycle

models can be used to infer the magnitude of

carbon release by fitting observed changes in the

C of calcium carbonates and organic remnants

(60). However, as well as needing information on

the source and isotopic composition of the added

carbon, the time scale of d

C change is critically

important to the estimation of CO

fluxes (25).

Because of the lack of open-ocean sediments and

increasingly poor temporal and spatial resolution

of the geological record further back in time, it is

difficult to place adequate constraints on the

duration and rate of CO

release. Radiometric

dating techniques are not accurate enough to

identify Mesozoic intervals of 10-ky duration,

although orbital spectral analysis of highly

resolved isotope and/or sedimentological records

can help to partly overcome this—for example,

if a d

C excursion is shorter or longer than one

precession cycle [21 ky (51)]. Even for the well-

studied PETM, the duration of the main phase

of this carbon injection is still debated (35,61),

and model-inferred peak rates of ≤1PgCper

year (26,61) could potentially be an underestimate.

Additional complications arise because car-

bon may not have been released at a uniform rate

and, in the extreme, may have occurred in the

form of rapid pulses. In such cases, the assump-

tion of an average emissions rate throughout

the entire duration of the pulsed release will fail

to capture the potential for episodes of intense

acidification. For instance, although the total

duration of the CO

release from the T/J–age

Central Atlantic Magmatic Province was esti-

mated to be ~600 ky, pulses as short as ~20 ky

have been suggested (51,62). Similarly, the main

phase of OAE1a (excluding the recovery inter-

val) was ~150 ky (45) and hence too slow for

carbonate saturation to be significantly affected

(Fig. 3), but major volcanic eruptions and thus

rapid CO

release could potentially have produced

future-relevant perturbations in the carbon cycle.

Substantially improved chronologies and higher-

resolution records are needed to refine estimates

of rate.

Given current knowledge of the past 300 My

of Earth’s history (Fig. 4 and table S1), the PETM

and associated hyperthermal events, the T/J, and

potentially the P/T all stand out as having excel-

lent potential as analog events, although the T/J

and P/T are much more poorly constrained be-

cause of the absence of deep-sea carbonate de-

posits. OAEs may also be relevant but were

associated with less severe volcanism (CO

re-

lease) than were the older events (P/T and T/J).

The last deglacial transition, although charac-

terized by temperature and CO

-increase, is two

orders of magnitude slower than current anthro-

pogenic change. It is also thought to largely rep-

resent a redistribution of carbon within the ocean

and to the atmosphere and terrestrial biosphere

and hence did not have as potent and globally

uniform an acidification effect as an input from

geological reserves. Because of the decoupling

between pH and saturation on long time scales

(Fig. 3), extended intervals of elevated PCO

such

as the middle Miocene, Oligocene, and Cretaceous

can be firmly ruled out as future-relevant analogs.

What Are the Perspectives for Using the Geological

Record to Project Global Change?

Only rapid or pulsed CO

release events can

provide direct future-relevant information. As-

sessment of such events critically depends on

independent geochemical quantification of the

associated changes in the carbonate system, spe-

cifically seawater-pH and CaCO

saturation. Geo-

chemical proxy estimates are not yet available

for the Cretaceous and beyond and need to be

obtained to verify whether ocean acidification

did indeed happen. This is challenging, because

in addition to the potential for increasing post-

depositional alteration and reduced stratigraphic

exposure, uncertainty over the chemical and iso-

topic composition of seawater increases and lim-

its our interpretation of these proxies (63,64).

Future studies will have to improve and expand

geochemical estimates and their uncertainties of

surface and deep-ocean carbonate chemistry as-

sociated with carbonate dissolution and ecolog-

ical changes. This includes finding new archives

to study the secular evolution of seawater chem-

istry but also the laboratory study of living proxy

carriers under conditions mimicking past seawater

chemistry. An unfortunate aspect of the geolog-

ical record, however, is the lack of deep-sea car-

bonates in the Early Jurassic and beyond, which

further reduces our ability to reconstruct the car-

bonate chemistry of those older events.

The sensitivity of ocean chemistry to CO

re-

lease, and the relationship between induced pH

and PCO

changes, vary through time and further

complicate the picture. For instance, seawater

calcium and magnesium ion concentrations were

different in the past (Fig. 4C). This alters the ocean’s

carbonate ion buffering capacity and hence sen-

sitivity of the Earth system to carbon perturbation

(65) because all other things being equal, higher

ambient Ca

concentrations means that a lower

carbonate ion concentration is required to achieve

the same saturation and hence balance weathering.

Varying seawater Mg/Ca ratios may potentially

also affect the mineralogy of marine calcifiers,

where the more soluble high-Mg calcite predom-

inated Neogene reefs and reefs during the Per-

mian through Early Jurassic, and more resistant

low-Mg calcite predominated during the Late

Jurassic through Paleogene (66). Thus, on this

mineralogical basis the response of marine cal-

cifiers to ocean acidification and seawater geo-

chemistry during the P/T and T/J would arguably

be closer to the modern than, for example, dur-

ing the PETM (67). Improved estimates of past

seawater–Mg/Ca composition are necessary to

better evaluate all of this.

Although we have concentrated on the pros-

pects for extracting information from the geo-

logical record concerning the impact of ocean

acidification, we must question whether it really

is necessary to isolate its effect on marine orga-

nisms from other covarying factors (68). In par-

ticular, consequences of increasing atmospheric

will also be associated with warming in the

surface ocean and a decrease in dissolved oxy-

gen concentration (69). Massive carbon release,

whether future or past, will hence share the same

combination and sign of environmental changes.

The strength of the geological record therefore

lies in revealing past coupled warming and ocean

acidification (and deoxygenation) events as an

“integrated”analog, with future and past events

sharing the same combination and sign of en-

vironmental changes. However, in additionally

driving a strong decline in calcium carbonate sat-

uration alongside pH, the current rate of (mainly

fossil fuel) CO

release stands out as capable of

driving a combination and magnitude of ocean

geochemical changes potentially unparalleled

in at least the last ~300 My of Earth history,

raising the possibility that we are entering an

unknown territory of marine ecosystem change.

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Acknowledgments: Funding for the “Workshop on Paleocean

Acidification and Carbon Cycle Perturbation Events”was

provided by NSF OCE 10-32374 and Past Global Changes

(PAGES). We thank the workshop participants for stimulating

discussions and contributions to this manuscript, and the USC

Wrigley Institute on Catalina Island for hosting the workshop.

Particular thanks are owed to Thorsten Kiefer of PAGES, who

initiated the workshop and supported it at all stages. This

work is a contribution to the “European Project on Ocean

Acidification”(EPOCA). Data presented in Fig. 4 are

presented in tables S2 and S3 (2).

Supporting Online Material

www.sciencemag.org/cgi/content/full/335/6072/1058/DC1

SOM Text

Figs. S1 to S3

Tables S1 to S3

References (74–217)

10.1126/science.1208277

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CORRECTIONS & CLarifiCations

www.sciencemag.org sCiEnCE ERRATUM POST DATE 16 MARCH 2012

Erratum

Review: “The geological record of ocean acidification” by B. Hönisch et al. (2 March,

p. 1058). The affiliation for author Carles Pelejero was incomplete. The complete affiliation

is: “Institució Catalana de Recerca i Estudis Avançats and Department of Marine Biology and

Oceanography, Institut de Ciències del Mar, Consejo Superior de Investigaciones Científicas,

08003 Barcelona, Catalonia, Spain.”

CORRECTIONS & CLarifiCations

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Full-text available

Feb 2025

Boron isotopes have been used to reconstruct marine pH but less frequently in marginal marine environments (lagoons, coastal shelves), where paleo‐archives are abundant. The dynamic nature of these systems complicates environmental reconstruction, requiring a multi‐proxy approach to constrain changes in conditions. Celestun Lagoon (Yucatan, Mexico), influenced by mixing groundwater and seawater, offers a unique setting to explore such systems. We analyzed salinity (⁸⁷Sr/⁸⁶Sr, δ¹⁸O), temperature (δ¹⁸O, Mg/Ca), and respiration (δ¹³C, weight% organic C) proxies alongside δ¹¹B and B/Ca in calcite of infaunal foraminifera Ammonia parkinsoniana. Results revealed spatial variability in δ¹¹Bcalcite along the lagoon salinity gradient, ranging from 8.06 to 18.53‰, with higher δ¹¹B variability near groundwater discharge and seagrass beds. This suggests low‐pH, high‐DIC groundwater and primary production influence the δ¹¹B signature. Low concentrations of dissolved [B], [Mg], and [Ca] in groundwater shift the dissociation constant pKB* and possibly the fractionation factor αB. Notably, some δ¹¹Bcalcite values (8.06‰) were lower than expected (11.0‰), suggesting complex influences from source δ¹¹Bwater, pKB*, or dietary carbon with distinct boron signatures. Despite variability, foraminifera δ¹¹Bcalcite (mean ± SD = 13.22 ± 3.41‰, n = 21) aligned with calculated mean δ¹¹Bborate (13.64 ± 1.55‰, n = 19), supporting potential use of δ¹¹B for paleo‐pH reconstructions in marginal marine settings. However, a large sample size may be required to capture average conditions. These findings emphasize the need for more studies to constrain boron isotopes in marginal marine environments which are critical for interpreting paleo‐archives in continental shelves and shallow seas.

中国海及邻近区域碳库与通量综合分析

Article

Sep 2018

Kunshan Gao

The impact of ocean acidification on gastropod shell dissolution and microstructure

Article

Mar 2025

O możliwości zastosowania dwutlenku węgla jako nośnika energii do transportu z dna morskiego.

Article

Mar 2025

Osiągnięcie założonej przez Unię Europejską redukcji emisji CO2 o 50% do 2050 roku niemożliwe jest bez opracowania technologii wychwytywania dwutlenku węgla i jego bezpiecznego składowania. Ponieważ na nasze życie codzienne coraz większy wpływ mają debaty publiczne, naukowe i polityczne na temat globalnego ocieplenia (od ekstremalnych zjawisk pogodowych do topnienia lodowców), których skutkiem często są regulacje prawne, należy opracować odpowiednie technologie eliminujące przyczyny tych zjawisk. W związku z tym ograniczenie antropogenicznej emisji dwutlenku węgla mającej znaczący wpływ na występowanie efektu cieplarnianego jest jednym z najważniejszych problemów do rozwiązania w dziedzinie szeroko pojętej ochrony środowiska (Mazurkiewicz i inni, 2005). Kluczową rolę w absorpcji antropogenicznych emisji CO2 do atmosfery odgrywają morza i oceany pokrywające około 70% powierzchni globu. Od kilku lat autorzy prowadzą badania związane z transportem urobku z dużych głębokości oraz przedstawili kilka jego koncepcji (Filipek W., Broda K.: 2016, 2017, 2018, 2019, 2023). W niniejszym artykule autorzy podążając za ogólnoświatowym trendem dotyczącym zagospodarowania CO2 pochodzenia antropogenicznego zajęli się próbą jego wykorzystania jako medium roboczego do transportu z dna morskiego. W rozważaniach autorzy skupili się głównie na możliwej do wykorzystania energii zgromadzonej w analizowanym medium roboczym. Autorzy zdają sobie sprawę z negatywnych skutków oddziaływania dwutlenku węgla na środowisko morskie. Niemniej jednak uznaliśmy, biorąc pod uwagę przyszłe badania nad wykorzystaniem tego medium roboczego, za konieczne rozważenie w pierwszej kolejności tak zwanego układu otwartego, czyli swobodnej wymiany CO2 pomiędzy modułem transportowym a otoczeniem. Z naszego punktu widzenia jest to bowiem ważna informacja będąca punktem odniesienia do przyszłych rozważanych koncepcji wykorzystania tego medium w tzw. obiegu zamkniętym, czyli przyjęcia, że nie występuje transmisja

Paleoclimatic variation during the Cambrian Stage 4 on the southern North China Block: insights from lithological and geochemical indicators

Article

Mar 2025
INT J EARTH SCI

The early Cambrian is the first greenhouse climate period of the Phanerozoic, often accompanied by the distribution of coeval evaporite and calcrete deposits, strong chemical weathering, and enhanced dolomitization. Abundant lithological climate indicators are widely developed in the mixed siliciclastic carbonates of tidal flats to limestones of carbonate platforms in the study area. It is generally believed that evaporite is a typical product of the greenhouse climate background, while the fenestral fabric, dolomite breccia, and ruiniform horizon in the carbonate rock in the study area represent the formation of sediments in the long-term exposure environment, and whether they represent the arid and hot paleoclimate is not clear. This paper attempts to reveal their relevance with paleoclimatic variation during Cambrian Stage 4 on the southern North China Block. The results reveal that lithological indicators, such as fenestral fabric, dolomite breccia, ruiniform horizon, and gypsum, halite pseudomorphs, are characteristic of the lower part of Stage 4, suggesting an exposed, hot, and arid climate. In contrast, lithological indicators reflecting a warm and humid climate, including oolitic limestone and oncoid bearing oolitic limestone are more prevalent in the upper part. Geochemical data (Sr, Ba, and Mg, etc.) further support this climatic transition, with a marked accumulation of dry-associated elements in the lower part of Stage 4 and a significant increase in moisture-associated elements in the upper part. The paleoclimatic transformation during Cambrian Stage 4 is characterized by the extensive development of various types of dolomites and abundant lithological indicators reflecting hot and arid paleoclimatic conditions in the lower part of Stage 4 and the disappearance of dolomites and relevant lithological climatic indicators in the upper part. It exhibits a transition from a hot and arid environment to a warm and humid environment, analogous to the modern sabkha dolomite model (supratidal-intertidal evaporation pump dolomitization). This similarity provides critical insights into the greenhouse climate of the early Cambrian period.

Eccentricity pacing of the Paleocene-Eocene Thermal Maximum: Multi-section astrochronology and statistical insights in China

Article

Mar 2025
GLOBAL PLANET CHANGE

Calcareous plankton and shallow-water benthic biocalcifiers: Resilience and extinction across the Cenomanian-Turonian Oceanic Anoxic Event 2

Article

Mar 2025
PALAEOGEOGR PALAEOCL

A simple model for the CaCO3 saturation state of the ocean: The “Strangelove,” the “Neritan,” and the “Cretan” Ocean

Article

Full-text available

Dec 2003
GEOCHEM GEOPHY GEOSY

[1] A simple model of the CaCO3 saturation state of the ocean is presented. It can be solved analytically and is intended to identify the fundamental controls on ocean carbonate ion concentration. It should also attract researchers unfamiliar with complex biogeochemical models. Despite its limitations, the model-calculated CaCO3 saturation state of today's ocean agrees well with observations. In general, the model reveals three distinctly different modes of operation: The “Strangelove Ocean” of high supersaturation which is dominated by inorganic CaCO3 precipitation, (2) the “Neritan Ocean” of indefinite saturation dominated by biogenic shallow-water CaCO3 precipitation, and (3) the “Cretan Ocean” of low saturation dominated by biogenic pelagic CaCO3 precipitation. In the latter mode, the deep ocean [CO32−] is remarkably stable, provided that the biogenic production of CaCO3 exceeds the riverine flux of Ca2+ and CO32−. This explains the overall constancy of the saturation state of the ocean documented over the last 100 Ma. The model is then used to address diverse questions. One important result is that the recovery of the oceanic carbonate chemistry from fossil fuel neutralization in the future will be accelerated due to expected reduced biogenic calcification.

CO2-Forced Climate and Vegetation Instability During Late Paleozoic Deglaciation

Article

Full-text available

Jan 2007
SCIENCE

The late Paleozoic deglaciation is the vegetated Earth’s only recorded icehouse-to-greenhouse transition, yet the climate dynamics remain enigmatic. By using the stable isotopic compositions of soil-formed minerals, fossil-plant matter, and shallow-water brachiopods, we estimated atmospheric partial pressure of carbon dioxide (pCO2) and tropical marine surface temperatures during this climate transition. Comparison to southern Gondwanan glacial records documents covariance between inferred shifts in pCO2, temperature, and ice volume consistent with greenhouse gas forcing of climate. Major restructuring of paleotropical flora in western Euramerica occurred in step with climate and pCO2 shifts, illustrating the biotic impact associated with past CO2-forced turnover to a permanent ice-free world.

Regulation of atmospheric CO2 by deep-sea sediments in an Earth system model

Article

Full-text available

Jun 2007

We have extended the GENIE-1 Earth system model to include a representation of sedimentary stratigraphy and the preservation of biogenic carbonates delivered to the ocean floor. This has enabled us to take a novel approach in diagnosing modern marine carbon cycling: assimilating observation of the calcium carbonate (CaCO3) content of deep-sea sediments with an ensemble Kalman filter. The resulting calibrated model predicts a mean surface sediment content (32.5 wt%) close to the observed value (34.8 wt%), and a global burial rate of CaCO3 in deep sea sediments of 0.121 PgC yr-1, in line with recent budget estimates of 0.10-0.14 PgC yr-1. We employ the GENIE-1 model in quantifying the multimillennial-scale fate of fossil fuel CO2 emitted to the atmosphere. In the absence of any interaction between ocean and sediments, an equilibrium partitioning of CO2 is reached within ˜1000 years of emissions ceasing, with 34% (645 ppm) remaining in the atmosphere out of a total fossil fuel burn of 4173 PgC. An additional 12% of CO2 emissions (223 ppm) are sequestered as bicarbonate ions (HCO3-) by reaction with deep-sea carbonates ("seafloor CaCO3 neutralization") on a timescale of ˜1.7 ka. Excess of carbonate weathering on land over deep-sea burial results in a further net transformation of 14% of CO2 emissions (261 ppm) into HCO3- ("terrestrial CaCO3 neutralization") on a timescale of ˜8.3 ka. We have also assessed the importance of a changing climate in modulating the stabilization of atmospheric CO2 through ocean-sediment interaction. Increased ocean stratification suppresses particulate organic carbon export, which in turn enhances seafloor CaCO3 preservation. The resulting reduction in the sequestration of fossil fuel CO2 represents a new positive feedback on millennial-scale climate change.

Causes and consequences of globally warm climates in the early Paleogene

Book

Jan 2003

Synchrony between the Central Atlantic magmatic province and the Triassic–Jurassic mass-extinction event?

Article

Feb 2007
PALAEOGEOGR PALAEOCL

Past changes of ocean carbonate chemistry

Article

Jan 2011

Isotopic Imprint of Climate and Hydrogeochemistry on Terrestrial Strata of the Triassic-Jurassic Hartford and Fundy Rift Basins

Article

Jan 1988

In the Hartford basin, caliche calcites in fluvial mudstones and stones have isotopic compositions (δ 13C = -7.3 to -3.8‰ PDB; δ 18O = -8.0 to -5.6‰ PDB) that reflect paleosol processes during climatic conditions that varied from warm and dry in Late Triassic time to relatively cooler and probably wetter in the Early Jurassic. Isotopic compositions of caliche calcites in redbeds in the Fundy basin indicate a parallel climate change from Late Triassic to Early Jurassic time, but also that the climate was relatively hotter and probably drier over the entire interval, as compared to the Hartford basin. -Authors

F OSSIL P LANTS AS I NDICATORS OF THE P HANEROZOIC G LOBAL C ARBON C YCLE

Article

May 2002

▪ Abstract Developments in plant physiology since the 1980s have led to the realization that fossil plants archive both the isotopic composition of atmospheric CO2 and its concentration, both critical integrators of carbon cycle processes through geologic time. These two carbon cycle signals can be read by analyzing the stable carbon isotope composition (δ13C) of fossilized terrestrial organic matter and by determining the stomatal characters of well-preserved fossil leaves, respectively. We critically evaluate the use of fossil plants in this way at abrupt climatic boundaries associated with mass extinctions and during times of extreme global warmth. Particular emphasis is placed on evaluating the potential to extract a quantitative estimate of the δ13C of atmospheric CO2 because of the key role it plays in understanding the carbon cycle. We critically discuss the use of stomatal index and stomatal ratios for reconstructing atmospheric CO2 levels, especially the need for adequate replication, and present...

The search for the origin of planktic Formaninifera

Article

May 2003

Planktic Foraminifera are an extremely abundant, important and successful group of marine protists. They are particularly useful in reconstructing past environments and for biostratigraphic dating. Despite their importance, the origin of the group is uncertain. Previous work has suggested that they evolved from a benthic ancestor during the Triassic or, perhaps, the Mid-Jurassic (?Bajocian), but a reason for their origination has remained unclear. Here, we present evidence from the Toarcian (early Jurassic) of NW Europe that the origin of the planktic Foraminifera may have been one of the results of the early Toarcian oceanic anoxic event. This event appears to have been associated with a massive dissociation of gas hydrates and other, perhaps related, water chemistry changes.

Causes and consequences of extreme Permo-Triassic warming to globally equable climate and relation to the Permo-Triassic extinction and recovery

Article

Feb 2004
PALAEOGEOGR PALAEOCL

Permian waning of the low-latitude Alleghenian/Variscan/Hercynian orogenesis led to a long collisional orogeny gap that cut down the availability of chemically weatherable fresh silicate rock resulting in a high-CO2 atmosphere and global warming. The correspondingly reduced delivery of nutrients to the biosphere caused further increases in CO2 and warming. Melting of polar ice curtailed sinking of O2- and nutrient-rich cold brines while pole-to-equator thermal gradients weakened. Wind shear and associated wind-driven upwelling lessened, further diminishing productivity and carbon burial. As the Earth warmed, dry climates expanded to mid-latitudes, causing latitudinal expansion of the Ferrel circulation cell at the expense of the polar cell. Increased coastal evaporation generated O2- and nutrient-deficient warm saline bottom water (WSBW) and delivered it to a weakly circulating deep ocean. Warm, deep currents delivered ever more heat to high latitudes until polar sinking of cold water was replaced by upwelling WSBW. With the loss of polar sinking, the ocean was rapidly filled with WSBW that became increasingly anoxic and finally euxinic by the end of the Permian. Rapid incursion of WSBW could have produced ∼20 m of thermal expansion of the oceans, generating the well-documented marine transgression that flooded embayments in dry, hot Pangaean mid-latitudes. The flooding further increased WSBW production and anoxia, and brought that anoxic water onto the shelves. Release of CO2 from the Siberian traps and methane from clathrates below the warming ocean bottom sharply enhanced the already strong greenhouse. Increasingly frequent and powerful cyclonic storms mined upwelling high-latitude heat and released it to the atmosphere. That heat, trapped by overlying clouds of its own making, suggests complete breakdown of the dry polar cell. Resulting rapid and intense polar warming caused or contributed to extinction of the remaining latest Permian coal forests that could not migrate any farther poleward because of light limitations. Loss of water stored by the forests led to aquifer drainage, adding another ∼5 m to the transgression. Non-peat-forming vegetation survived at the newly moist poles. Climate feedback from the coal-forest extinction further intensified warmth, contributing to delayed biotic recovery that generally did not begin until mid-Triassic, but appears to have resumed first at high latitudes late in the Early Triassic. Current quantitative models fail to generate high-latitude warmth and so do not produce the chain of events we outline in this paper. Future quantitative modeling addressing factors such as polar cloudiness, increased poleward heat transport by deep water and its upwelling by cyclonic storms, and sustainable mid-latitude sinking of warm brines to promote anoxia, warming, and thermal expansion of deep water may more closely simulate conditions indicated by geological and paleontological data.