Chap. 9. Paleoceanography Chap. 9. Paleoceanography

– the Deep-Sea Record– the Deep-Sea Record Pleistocene Oceanography Pleistocene Oceanography The Ice Age Ocean The Ice Age Ocean The Pleistocene Cycles The Pleistocene Cycles Dynamic of change Dynamic of change Tertiary Oxygen Isotope Record Tertiary Oxygen Isotope Record Fluctuations of the Carbonate Line Fluctuations of the Carbonate Line Fluctuations in Oxygenation of the Deep Fluctuations in Oxygenation of the Deep

Ocean Ocean

Fig.9.1 Recovering the Pleistocene record by piston coring. The corer is a wide-diameter model; note the white sediment in the core nose. Note also that the core barrel was bent during the operation (on the upper end), Other equipment on deck: deep-sea camera frame (with protective grid), hydrophone for seismic profiling (wrapped on spool), box corer (aft). [SIO Eurydice Expedition 1975]

9.1 Background 9.1 Background Beginning in 1968, an enormous amBeginning in 1968, an enormous am

ount of effort in this subject, especiount of effort in this subject, especially through the work of the CLIMally through the work of the CLIMAP group in Pleistocene oceanograpAP group in Pleistocene oceanography, and through the extensive drillinhy, and through the extensive drilling in the deep sea by g in the deep sea by Glomar ChalleGlomar Challengernger. .

About 1 million years to the past 10About 1 million years to the past 100 million years 0 million years

9.2 The Ice Age Ocean 9.2 The Ice Age Ocean 9.2.1 Why an Ice Age9.2.1 Why an Ice Age

Several glaciations were discovered, with warm intervals separatinSeveral glaciations were discovered, with warm intervals separating them. g them.

How many such advances and retreats of continental ice were therHow many such advances and retreats of continental ice were there? e?

What is the time-scale of these cycles? What is the time-scale of these cycles? How do the cycles relate to astronomical factors, that is, the rotatiHow do the cycles relate to astronomical factors, that is, the rotati

on of the Earth and its paths around the Sun? on of the Earth and its paths around the Sun? These questions were difficult to even attempt to answer from the These questions were difficult to even attempt to answer from the

land record: each succeeding glaciation erased many of the traces land record: each succeeding glaciation erased many of the traces of the previous one. of the previous one.

The The study of long cores from the deep sea floorstudy of long cores from the deep sea floor opened new possi opened new possibilities. bilities.

Why is there an ice age at all? Why is there an ice age at all? We do not know for sure. We do not know for sure. It is colder during an ice age than before aIt is colder during an ice age than before a

nd after, so that the Earth heat budget is innd after, so that the Earth heat budget is involved. volved.

The budget is largely controlled by The budget is largely controlled by albedoalbedo and by and by the greenhouse effectthe greenhouse effect. .

Albedo was increased and greenhouse gasAlbedo was increased and greenhouse gases were decreased. es were decreased.

9.2.2 Conditions in a Cold Ocean9.2.2 Conditions in a Cold Ocean

How did the ice age ocean differ from the present How did the ice age ocean differ from the present one? one?

Surface currents were stronger. Surface currents were stronger. The ocean surface was cooler than today. The ocean surface was cooler than today. Some ocean regions cooled more than others, Some ocean regions cooled more than others,

and the regional degree of change depends and the regional degree of change depends closely on the movement of boundaries of closely on the movement of boundaries of climatic zones. climatic zones.

Surface currents were stronger.Surface currents were stronger. Surface currents are driven by Surface currents are driven by windswinds, and winds depend on , and winds depend on

horizontal temperature gradientshorizontal temperature gradients. . With the ice rim and the polar front much closer to the Equator, With the ice rim and the polar front much closer to the Equator,

the temperature difference between ice (0°C or less)and the the temperature difference between ice (0°C or less)and the tropics (≈25°C) was compressed into a much shorter distance tropics (≈25°C) was compressed into a much shorter distance than now. than now.

Hence the temperature gradient was greater, winds were Hence the temperature gradient was greater, winds were stronger, and so were ocean currents. stronger, and so were ocean currents.

Equatorial Equatorial upwellingupwelling was was intensifiedintensified as a consequence, and also as a consequence, and also coastal upwelling. coastal upwelling.

Thus, at the same time that fertility decreased in high latitudes, Thus, at the same time that fertility decreased in high latitudes, due to ice cover, it increased in mid-latitudes (because of due to ice cover, it increased in mid-latitudes (because of intensified mixing) and in the subtropics (due to upwelling). intensified mixing) and in the subtropics (due to upwelling).

The ocean surface was cooler than today.The ocean surface was cooler than today.

With a substantial part of northern continents and seas under With a substantial part of northern continents and seas under iceice, t, the Earth reflected the Sun's radiation more readily (had a he Earth reflected the Sun's radiation more readily (had a higher ahigher albedolbedo) than today, hence, it absorbed less of the radiation and its a) than today, hence, it absorbed less of the radiation and its atmosphere was cooler. tmosphere was cooler.

A cold atmosphere holds less water than a warm one and large areA cold atmosphere holds less water than a warm one and large areas on land therefore were as on land therefore were drierdrier than today: Dry areas (such as gras than today: Dry areas (such as grasslands and deserts) reflect more sunlight than wet ones (such as foslands and deserts) reflect more sunlight than wet ones (such as forests). rests).

A more fertile ocean would be slightly more reflective than a cleaA more fertile ocean would be slightly more reflective than a clear dark blue one with less algal growth. r dark blue one with less algal growth.

All these factors favored reflection of the Sun's radiation back intAll these factors favored reflection of the Sun's radiation back into space, and hence favored cooling. o space, and hence favored cooling.

Table 9.1 albedo values of ocean and land surface

Some ocean regions cooled more than others, and Some ocean regions cooled more than others, and the regional degree of change depends closely on the regional degree of change depends closely on the movement of boundaries of climatic zones.the movement of boundaries of climatic zones.

If, for example, an area is near the boundary of If, for example, an area is near the boundary of subtropics and temperate belt, it will then subtropics and temperate belt, it will then belong alternately to one or the other zone. belong alternately to one or the other zone.

Thus, here the changes are substantial. Thus, here the changes are substantial. Conversely, changes can be minimal in the Conversely, changes can be minimal in the

center of tropical or subtropical climatic center of tropical or subtropical climatic regions. regions.

For example, Korea!For example, Korea!

Fig.9.2 Approximate distribution of sea surface temperatures for northern hemisphere summer, during the last ice age maximum (about 18000 years ago;"18K map"). Note the extent and thickness of ice.[CLIMAP Project Members, 1976, Science 191:1131, simplified]

9.2.3 The 18K Map 9.2.3 The 18K Map

From the information shown in 18K map, the ice age ocean 18,0From the information shown in 18K map, the ice age ocean 18,000 years ago was characterized by: 00 years ago was characterized by:

Increased thermal gradients along polar fronts, especially in tIncreased thermal gradients along polar fronts, especially in the North Atlantic and Antarctic. he North Atlantic and Antarctic.

Equatorward displacement of polar frontal systems Equatorward displacement of polar frontal systems

General cooling of most surface waters, General cooling of most surface waters, by by about 2.3°C, on the averageabout 2.3°C, on the average. .

Increased upwelling along the Equator iIncreased upwelling along the Equator in Pacific and Atlantic. n Pacific and Atlantic.

Increased coastal upwelling and strentheIncreased coastal upwelling and strenthening of eastern boundary currents ning of eastern boundary currents

Nearly stable positions and temperatures Nearly stable positions and temperatures of the central gyres in the major ocean bof the central gyres in the major ocean basins. asins.

Fig.9.3 Rate and timing of glacial meltwater discharge compared with subarctic summer insolation. Discharge calculated from a depth-versus-age curve for Barbados corals (A. palmata). Heavy line time scale based on radiocarbon dating; thin line time and colleagues, Nature 1990, 345: 405;dashed line summer insolation at 60°N, based on calculations by A. Berger.

9.2.4 Pulsed Deglaciation 9.2.4 Pulsed Deglaciation It took between 7000 and 8000 It took between 7000 and 8000

years, approximately, to reducyears, approximately, to reduce the ice masses to something le the ice masses to something like today. ike today.

The sea level rose some The sea level rose some 120 120 mm. .

Recent detailed work on corals Recent detailed work on corals in Barbados confirmed earlier iin Barbados confirmed earlier indications that ndications that deglaciation ocdeglaciation occurred in pulses or stepscurred in pulses or steps. .

Step 1; 13.5~12.5 ka (Termination Ia) Step 1; 13.5~12.5 ka (Termination Ia) Step 2; 11~9.5 kyrs (Termination Ib) Step 2; 11~9.5 kyrs (Termination Ib) Agrees exactly with two major warming stAgrees exactly with two major warming st

eps known from northern Europe eps known from northern Europe

Two major pulsesTwo major pulses

Comparison with the sComparison with the summer insolation curvummer insolation curve at high northern latite at high northern latitudes suggests that udes suggests that unuunusually warm summers sually warm summers are responsibleare responsible for initi for initiating melting. ating melting.

Younger DryasYounger Dryas The retreat of the polar front in the North Atlantic also tool place in the dThe retreat of the polar front in the North Atlantic also tool place in the d

iscontinuous manner. iscontinuous manner. A substantial re-advance of this front occurred during the Younger DryaA substantial re-advance of this front occurred during the Younger Drya

s, between 11,000 and 10,000 radiocarbon years. s, between 11,000 and 10,000 radiocarbon years. According to ice core measurements, some 12,800 and 11,700 calendar yeAccording to ice core measurements, some 12,800 and 11,700 calendar ye

ars. ars. The origin is entirely unknown …. The origin is entirely unknown …. Meteorites?Meteorites?

Fig9.4 a-c. The Pleistocene record in deep sea sediments. a Carbonate cycles of the eastern Pacific, magnetically dated b G. Menardii pulses (left) and transfer temperature cycle (right) compared with oxygen isotope stratigraphy, Caribbean Sea c Dissolution cycles compared with oxygen isotope stratigraphy, western Pacific

9.3 The Pleistocene Cycles 9.3 The Pleistocene Cycles 9.3.1 The Evidence 9.3.1 The Evidence

The Pleistocene record shows The Pleistocene record shows a long series of a long series of alternating clialternating climatic statesmatic states. .

The cycles express themselves The cycles express themselves as fluctuations in faunal and flas fluctuations in faunal and floral composition, in the abundoral composition, in the abundance of carbonate, and in the cance of carbonate, and in the content of δontent of δ1818O of foraminiferal O of foraminiferal shells and in other properties. shells and in other properties.

9.3.2 The Carbonate Cycles of the 9.3.2 The Carbonate Cycles of the equatorial Pacific equatorial Pacific

Dissolution cyclesDissolution cycles high dissolution in interglacialshigh dissolution in interglacials (low CaCO (low CaCO

33 val val

ues) ues) low dissolution in glaciallow dissolution in glacial (high CaCO (high CaCO

33 values). values).

Productivity variations play a secondary role in Productivity variations play a secondary role in producing the cycles. producing the cycles.

Fluctuation of the sea level must Fluctuation of the sea level must be important. be important.

During low sea level, shelves are exposed. During low sea level, shelves are exposed. There is no place for carbonate to go except ontThere is no place for carbonate to go except ont

o the deep sea floor. o the deep sea floor. Conversely, during interglacials the high sea leConversely, during interglacials the high sea le

vel allows shallow water carbonates to build uvel allows shallow water carbonates to build up. p.

This carbonate is extracted from the ocean, and This carbonate is extracted from the ocean, and is no longer available for deposition on the deeis no longer available for deposition on the deep sea floor. p sea floor.

The Atlantic carbonate cycles are largely The Atlantic carbonate cycles are largely dilution cycles. dilution cycles.

During glacials the supply of terrigenous materials from the contineDuring glacials the supply of terrigenous materials from the continents surrounding the Atlantic is greatly increased. nts surrounding the Atlantic is greatly increased.

In high latitudes the activity of the ice grinds up enormous masses of In high latitudes the activity of the ice grinds up enormous masses of rock. rock.

The plant cover, which protects soil from erosion, is less dense. The plant cover, which protects soil from erosion, is less dense. In the subtropics deserts are wide-spread, delivering dust. In the subtropics deserts are wide-spread, delivering dust. Flash floods in semi-arid regions are efficient conveyors of huge amFlash floods in semi-arid regions are efficient conveyors of huge am

ounts of material. ounts of material. The tropical rain forest is much reduced, and semi-arid regions are eThe tropical rain forest is much reduced, and semi-arid regions are e

xpanded. xpanded. The shelves are exposed, and subject to erosion. The shelves are exposed, and subject to erosion. All these factors contribute to the All these factors contribute to the glacial increase of terrigenous depglacial increase of terrigenous dep

osition ratesosition rates. . As the supply of terrigenous material increases, of course, the As the supply of terrigenous material increases, of course, the proporpropor

tion of carbonate in pelagic sediments decreasedtion of carbonate in pelagic sediments decreased accordingly. accordingly.

9.3.3 The Faunal (and Floral) Cycles 9.3.3 The Faunal (and Floral) Cycles

Warm-cold cyclesWarm-cold cycles; abundance of warm-water and col; abundance of warm-water and cold-water planktonic foraminifera. d-water planktonic foraminifera.

They are well defined in their amplitudes. They are well defined in their amplitudes. They tend to avoid intermediate values, suggesting thThey tend to avoid intermediate values, suggesting th

at there are two prefered states: warm, and cold, but at there are two prefered states: warm, and cold, but nnot in betweenot in between. .

The present time rather unusual in being so warm: foThe present time rather unusual in being so warm: for the last one half million years or so the climate was r the last one half million years or so the climate was mostly much more severe. mostly much more severe.

9.3.4 Oxygen Isotope Cycles 9.3.4 Oxygen Isotope Cycles C. Emiliani (1955) from several long core taken in the Caribbean aC. Emiliani (1955) from several long core taken in the Caribbean a

nd North Atlantic nd North Atlantic Species with the lowest δSpecies with the lowest δ1818O, reasoning that these species must livO, reasoning that these species must liv

e in shallow water and therefore reflect surface water temperature. e in shallow water and therefore reflect surface water temperature. The composition of seawater controls The composition of seawater controls 1818O/O/1616O ratios. O ratios. During build-up of the ice, During build-up of the ice, 1818O stays preferentially in the ocean, inO stays preferentially in the ocean, in

creasing the creasing the 1818O/O/1616O ratio. O ratio.

Loess Record in China: Drought-Wet CyclesLoess Record in China: Drought-Wet Cycles

Glacial intervals are characterized by eolian dust Glacial intervals are characterized by eolian dust deposits and interglacials by soil development. deposits and interglacials by soil development.

Maximum wind supply occurred both during onsMaximum wind supply occurred both during onset of glacials and during their maximum. et of glacials and during their maximum.

Such supply of dust by wind has implications for Such supply of dust by wind has implications for deep-sea sedimentation - perhaps (as dust brings deep-sea sedimentation - perhaps (as dust brings phosphate and iron) even for productivity in the ophosphate and iron) even for productivity in the ocean. cean.

Loess in ChinaLoess in China

Fig.9.5 a-d. Correlation of loess profiles from Xifeng (China, see inset) with marine δ18O record during the last 500000 years. a Loess profile, L loess; S soil b Same profile with refined ages of loess sedimentation based on correlation to eolian flux record in (C); c Eolian flux record of the North Pacific, Core V 21-146 (mg/cm2/kyr) from 3968 m water depth and with a distance of more than 300 km from the loess source area; δ18O-Stratigraphy (‰, PDB) of this core, used for dating.[S. a. Hovan et al. 1989, Nature, 340:296]

Loess Record in China: Drought-Wet Cycles Loess Record in China: Drought-Wet Cycles

9.3.5 Milankovitch Cycles and Dating 9.3.5 Milankovitch Cycles and Dating The isotopic variations clearly indicate some sort of reThe isotopic variations clearly indicate some sort of re

gular cycling such as could be produced by the Milankgular cycling such as could be produced by the Milankovitch mechanism which invokes regular variations in ovitch mechanism which invokes regular variations in the Earth's orbital parameters as a cause for the successthe Earth's orbital parameters as a cause for the succession of ice ages separated by warm periods. ion of ice ages separated by warm periods.

The hypothesis of Milutin Milankovitch (1879-1958) sThe hypothesis of Milutin Milankovitch (1879-1958) states that long-term fluctuations in the radiocarbon rectates that long-term fluctuations in the radiocarbon received from the Sun, during summer seasons, in the higeived from the Sun, during summer seasons, in the high latitudes of the northern hemisphere, have controlled h latitudes of the northern hemisphere, have controlled the occurrence of ice ages over the last 600,000 years. the occurrence of ice ages over the last 600,000 years.

A time-scale for the isotopic A time-scale for the isotopic variations was needed. variations was needed.

C-14 dating of the uppermost C-14 dating of the uppermost portion of the record, and portion of the record, and extrapolation downward is not very extrapolation downward is not very reliable. reliable.

Uranium dating of corals Uranium dating of corals Magnetic reversals Magnetic reversals

Precession Precession The axis is not stationary The axis is not stationary

in space, and does not in space, and does not always point to the always point to the North Star as at the North Star as at the present. present.

Instead, it describes a Instead, it describes a circle, of which the circle, of which the North Star is one point. North Star is one point.

The circle is completed The circle is completed once in about 21,000 once in about 21,000 years. years.

Obliquity The inclination of the Earth's axis to the plane of its orbit changed through time. It is 66 1/2° at present, but varies between about 65° and 68° once in 41000 years. High obliquity obviously means warm summers and cold winters.

Eccentricity The earth's orbit about the sun is not a circle but an ellipse. The ratio between the long and the short axis varies through time. One cycle takes about 100000 years.

Lower panel curves showing the orbital periodicities contained in the oxygen isotope record in a subantarctic deep sea core. The solid line in the middle represents the original isotope record; superimposed (dotted line) is the eccentricity variation. Top curve 23000- year component extracted from the isotope record by band pass filter (a statistical method); bottom curve obliquity component extracted in a similar fashion. Inset right illustrates obliquity.[J. D. Hays et al., 1976, Science 194: 1121] M. Milankovithch's classical paper was published in 1920; Theorie mathematique des phenomenes thermiques produits par la radiation solaire, Gauthier-Villars, Paris, 339 pp.

Fig.9.6 The Croll-Milankovith Theory of the ice ages, and its test. upper 3 panels. Curves showing orbital parameters as calculated by A. L. Berger[ in M. A. Kominz et al., 1979, Earth Planet Sci. Lett. 45:392]. 1m=100000yrs. The eccentricity is the deviation of the orbit from a perfect circle, for which e-0. The eccentricity varies with a period near 100000 years. The precession parameter is a function of both the position of perihelion (point of Earth's orbit which is closest to the Sun) with respect to the equinoxes (day = night positions) and the eccentricity of the orbit (which makes the difference of equinox and perihelion significant in terms of seasonal irradiation). The periodicity of the precession parameter is near 21000years. Note the small variations during times of low eccentricity. The obliquity is the  angle of the Earth's axis, with respect to the vertical on the orbital plane (inset, lower right). It varies with a period of 41000 years.

Fig.9.7 Oxygen isotope record of G. sacculifer, ODP Site 806, western equatorial Pacific. Age scale based on counting obliquity cycles extracted from the record (and set at 42000 years; see Fig.9.6). 5, 9,15, etc Isotope stages; o15, o30, 045 position of crests of obliquity-related cycles; MPR, eccentricity-dominated-B/M, Brunhes-Matuyama boundry. at 790kyrs. A. B. C. major cyclostratigraphic subdivisions, each with 15 obliquity cycles, where o15 = 625000 yrs; "Milankovitch Epoch" o15-o30 "Croll Epoch"; o30-o45 "Laplace Epoch".

9.3.6 A Change in Tune 9.3.6 A Change in Tune The stabilization of the maximum amplitude and the "saw-tooth" shape of The stabilization of the maximum amplitude and the "saw-tooth" shape of

the curve. the curve. Neither of these properties is at all understood, because the dynamics of Neither of these properties is at all understood, because the dynamics of

atmosphere-ocean interaction cannot yet be modeled on the time scale atmosphere-ocean interaction cannot yet be modeled on the time scale which is appropriate here. which is appropriate here.

It is interesting how much the 100,000-year It is interesting how much the 100,000-year eccentricityeccentricity cycle dominates the scene throughout the last 900,000 ycycle dominates the scene throughout the last 900,000 years. ears.

The lower half of the Quarternary essentially has no 10The lower half of the Quarternary essentially has no 100,000 years cycles at all. 0,000 years cycles at all.

The δThe δ1818O fluctuations are entirely dominated by the O fluctuations are entirely dominated by the obliobliquityquity cycle. cycle.

9.4 The Carbon Connection 9.4 The Carbon Connection 9.4.1 A Major Discovery 9.4.1 A Major Discovery

The reconstruction of the composition of the The reconstruction of the composition of the Pleistocene Pleistocene atmosphere from ice coresatmosphere from ice cores

Glacial COGlacial CO22 concentrations in air were concentrations in air were lowerlower than interglacial than interglacial ones by a factor of 1.5. ones by a factor of 1.5.

Fig.9.8 Carbon dioxide concentrations in the Vostok ice core from Antarctica(J. M. Bamola et al., 1987, Nature 329:408), compared with a productivity-related δ13C signal from the eastern tropical Pacific (N. J. Shackleton et al.,  1983 Nature 306:319). The signal plotted is the difference in δ13C of a planktonic and a benthic species, which constitutes a proxy for the nutrient content in deep water. The time scale of the CO2 record was adjusted using the deuterium record in the ice and the δ13C record in the sediments.

Methane gas also was measured; the fluctuations are Methane gas also was measured; the fluctuations are similar to those of carbon dioxide. similar to those of carbon dioxide.

The observed amplitude of COThe observed amplitude of CO22 variation correspond to variation correspond to a greenhouse effect of between 1 and 2 ˚C. a greenhouse effect of between 1 and 2 ˚C.

Fig.9.9 Sketch of a mechanism linking productivity to the carbon dioxide content of the atmosphere. According to W. S. Broecker (ocean chemistry during glacial time. Geochim Cosmochim Acta, 46, 1689-1705, 1982) when phosphate is added to the ocean a new equilibrium is established, with surface waters being more CO2-depleted than before. This then reduces atmospheric CO2. An increased in nutrient supply, through bio-pumping, also increases δ13C of the dissolved inorganic the carbon in surface water (by preferential removal of 12C into organic matter which sinks). Thus, the biopump mechanism provides a simple conceptual model linking pCO2 and the difference in δ13C of planktonic and benthic foraminifers (as shown in Fig.9.8)

9.4.2 Paleoproductivity 9.4.2 Paleoproductivity • phosphate is added to the ocean (increased nutrient supply)• CO2-depleted surface waters • reduced atmospheric CO2

• Increase in δ13C of DIC• linking pCO2 and the difference in δ13C of planktonic and benthic foraminifers

Biological PumpingBiological Pumping

The corresponding difference in δThe corresponding difference in δ1313C, which is C, which is picked up in shells of planktonic and benthic fpicked up in shells of planktonic and benthic foraminifers, is a measure of the intensity of the oraminifers, is a measure of the intensity of the fractionation resulting from the biological pumfractionation resulting from the biological pumping. ping.

This intensity depends entirely on the nutrient This intensity depends entirely on the nutrient content of deep ocean waters. content of deep ocean waters.

The bio-pump model for changing COThe bio-pump model for changing CO22 conten content of the atmosphere implies higher productivity t of the atmosphere implies higher productivity of the ocean during glacial time. of the ocean during glacial time.

Good independent evidence that Good independent evidence that productivity productivity was higher during glacialswas higher during glacials. .

Off NW Africa, the rate of burial of organic caOff NW Africa, the rate of burial of organic carbon was higher during glacials. rbon was higher during glacials.

The cause is increased eastern boundary upwelThe cause is increased eastern boundary upwelling due to an increase in trade winds and monling due to an increase in trade winds and monsoonal winds. soonal winds.

Fig.9.10 a, b. Paleoproductivity reconstructions for the late Pleistocene, off NW Africa.

a Oxygen isotopes, sedimentation rates, and organic matter content in Meteor core 12392. Right resulting paleoproductivity estimates. Isotope stages as in Figs.9.7. and 9.4 c. (1 Holocene; 2-4 last glaciation; 5a-e last inetglacial; 6 earlier glaciation).

b Importance of wind in producing changes in upwelling, as seen in correlation with dust supply (from which the strength of the wind is calculated

The general increase in productivity may have The general increase in productivity may have resulted in the burial of sufficient additional resulted in the burial of sufficient additional carbon to pull down the COcarbon to pull down the CO22 content content significantly. significantly.

During times of low sea level, carbonate During times of low sea level, carbonate deposition would have been greatly decreased deposition would have been greatly decreased on the shelves. on the shelves.

This would have increased the carbonate ion This would have increased the carbonate ion content of the ocean and hence the "alkalinity" content of the ocean and hence the "alkalinity" of the ocean. of the ocean.

This allows the ocean to retain a large share of This allows the ocean to retain a large share of the total COthe total CO22 in the system. in the system.

9.4.3 The Long-Range View 9.4.3 The Long-Range View Not just the ocean's exchange with the atmosphere, but also the Not just the ocean's exchange with the atmosphere, but also the

weathering of silicates on land, and the input of COweathering of silicates on land, and the input of CO22 from from volcanism volcanism

The weathering process can be summarily described by the The weathering process can be summarily described by the formula formula

COCO22 + CaSiO + CaSiO33 → CaCO → CaCO33 + SiO2 + SiO2 which shows long-term uptake of COwhich shows long-term uptake of CO22 from the atmosphere. from the atmosphere. Long-term decrease in COLong-term decrease in CO22 through mountain building and deep through mountain building and deep

erosion. erosion. Mountain-building and sea level drop proceeded all through the Mountain-building and sea level drop proceeded all through the

late Tertiary. late Tertiary. Changing ratio of strontium isotopes within marine sediments Changing ratio of strontium isotopes within marine sediments One possible cause for the onset of the ice ages: a drop in One possible cause for the onset of the ice ages: a drop in

atmospheric COatmospheric CO22 as a long-term trend within the late Tertiary as a long-term trend within the late Tertiary

9.5 Tertiary Oxygen Isotope Record 9.5 Tertiary Oxygen Isotope Record 9.5.1 Trends and Events: Oxygen Isotopes 9.5.1 Trends and Events: Oxygen Isotopes

An overall cooling trend since the Cretaceous, from the An overall cooling trend since the Cretaceous, from the increase of oxygen-18 in benthic foraminifera. increase of oxygen-18 in benthic foraminifera.

Tertiary Oceans : the Cooling Planet

Fig.9.11 a, b. Schematic diagram of the planetary cooling trend in the Cenozoic.

a Generalized sea level curve, showing overall regression (J. Thiede et al., 1992, Polarforschung 61[1]; 1; based on a compilation by L. A. Frakes).

b oxygen isotopic composition of planktonic and benthic foraminifera in deep-sea sediments. Vertical lines marked MM and EO show approximate position of major cooling steps, which involve high latitudes and deep ocean water masses

The oxygen isotopic composition of planktonic and of beThe oxygen isotopic composition of planktonic and of benthic foraminifera shows separate trends for low latitudenthic foraminifera shows separate trends for low latitudes, but similar trends for high latitudes. s, but similar trends for high latitudes.

Thus, the Tertiary cooling trend is Thus, the Tertiary cooling trend is indeed largely a high lindeed largely a high latitude (and deep water) phenomenonatitude (and deep water) phenomenon. .

In general, then, temperature gradients must have increasIn general, then, temperature gradients must have increased throughout the Tertiary, especially since the end of the ed throughout the Tertiary, especially since the end of the Oligocene some 20 to 25 million years ago. Oligocene some 20 to 25 million years ago.

Wind speed depends strongly on temperature gradients. Wind speed depends strongly on temperature gradients. If so, winds and their offspring, the surface currents, greaIf so, winds and their offspring, the surface currents, grea

tly increased since the Oligocene, as did coastal and mid-tly increased since the Oligocene, as did coastal and mid-ocean upwelling. ocean upwelling.

Direct evidence is found in the increasing diatom supply, Direct evidence is found in the increasing diatom supply, both in the northern North Pacific and around the Antarctboth in the northern North Pacific and around the Antarctic, during the Late Tertiary. ic, during the Late Tertiary.

9.5.2 The Great Partitioning 9.5.2 The Great Partitioning

All through the Tertiary, changes in geography All through the Tertiary, changes in geography due to due to plate motionsplate motions affect the configuration of affect the configuration of exchange between ocean basins. exchange between ocean basins.

The gateways control access to the Arctic OceThe gateways control access to the Arctic Ocean (east and west of Greenland), connnect the an (east and west of Greenland), connnect the global ocean along the Equator ("Tethys Oceaglobal ocean along the Equator ("Tethys Ocean" between Africa and Eurasia, Panama Straitn" between Africa and Eurasia, Panama Straits, Indonesian Seaway between Borneo and Nes, Indonesian Seaway between Borneo and New Guinea), and control the evolution of the Cirw Guinea), and control the evolution of the Circumpolar Current (Tasmanian Passage, Drake cumpolar Current (Tasmanian Passage, Drake Passage). Passage).

The Great PartitioningThe Great Partitioning

Fig.9.12 Geography of the middle Eocene (ca 45 Ma) and major critical valve points for ocean circulation. Tropical valves are closing (filled rectangles), high latitude valves and opening up (open rectangles) throughout the Cenozoic.[Base map from B. U. Haq, Oceanologica Acta, 4 Suppl.:71]

The Great PartitioningThe Great Partitioning

The difference from the present ocean to the Eocene oThe difference from the present ocean to the Eocene ocean 45 million years ago consists mainly in the tropicean 45 million years ago consists mainly in the tropical gateways and the opening of the poleward ones. cal gateways and the opening of the poleward ones.

One of the most fascinating is the One of the most fascinating is the drying out of the Mdrying out of the Mediterraneanediterranean between about 6 to 5 million years ago. between about 6 to 5 million years ago.

Huge amount of salt were deposited at that time, so mHuge amount of salt were deposited at that time, so much that the salinity of the global ocean may have beeuch that the salinity of the global ocean may have been reduced by 6 %.n reduced by 6 %.

Messinian CrisisMessinian Crisis

9.5.3 The Grand Asymmetries 9.5.3 The Grand Asymmetries What are the consequences for ocean circulation of the laWhat are the consequences for ocean circulation of the la

rge-scale valve switch executed by continents moving awrge-scale valve switch executed by continents moving away from Antarctica? ay from Antarctica?

Restricted Southern Ocean; cold box Restricted Southern Ocean; cold box The average ocean has to be cold. The average ocean has to be cold. Deep-sea and cold-water faunas become global, while troDeep-sea and cold-water faunas become global, while tro

pical ones become more provincialpical ones become more provincial. . Tertiary ocean history; the increased displacement of the Tertiary ocean history; the increased displacement of the

intertropical convergence zone (ITCZ, the heat equator) tintertropical convergence zone (ITCZ, the heat equator) to the north of Equator. o the north of Equator.

Several causes Several causes The whitening of the Antarctic continent; the effect of pThe whitening of the Antarctic continent; the effect of p

ushing climatic zones northward ushing climatic zones northward The northward movement of large continental masses The northward movement of large continental masses

which sets up monsoonal regimes favorable for northwwhich sets up monsoonal regimes favorable for northward heat transfer ard heat transfer

The uplift of Tibet and the Himalayas; The uplift of Tibet and the Himalayas; strengthening of strengthening of monsoons and an increase in weatheringmonsoons and an increase in weathering

The peculiar geographic configuration in both major ocThe peculiar geographic configuration in both major oceans, Atlantic and Pacific, which provides for deflectioeans, Atlantic and Pacific, which provides for deflection of westward-flowing equatorial currents, sending then of westward-flowing equatorial currents, sending them northward to m northward to strenghen the Gulf Stream and the Kurostrenghen the Gulf Stream and the Kuroshioshio. .

The Grand AsymmetriesThe Grand Asymmetries

The end result is that the southern The end result is that the southern hemisphere is robbed of heat by the hemisphere is robbed of heat by the northern hemisphere. northern hemisphere.

Glaciers in southern New Zealand are in Glaciers in southern New Zealand are in walking distance from the seashore, at a walking distance from the seashore, at a latitude which corresponds to that of the latitude which corresponds to that of the vineyards of Bordeaux! vineyards of Bordeaux!

9.5.4. The Onset 9.5.4. The Onset of the (Northern) Ice Age of the (Northern) Ice Age

The ice age could proceed in Antarctica, The ice age could proceed in Antarctica, while being kept out of northern latitudes. while being kept out of northern latitudes.

Eventually, the overall cooling caught up Eventually, the overall cooling caught up with the north as well, between with the north as well, between 3.5 and 3.5 and 2.5 million years ago2.5 million years ago. .

Fig.9.13 a, b. Onset of the ice age. a Sudden increase in the abundance of detrital mineral grains at DSDP Site 116, NW Atlantic, indicating glacial activity on the adjacent continent.

b change from a low variability climate (L) to a high variability ocean climate (H), as indicated in the oxygen isotope stratigraphy of a piston core from the central equatorial Pacific. The isotopes refer to the benthic foraminifer Globocassidulina subhlobosa, whose present composition is near +3.54‰ at this site. Magnetic stratigraphy controls the time scale. PP

Panama Seaway closes gradually within the Gauss Epoch.

Northern glaciation set in, and the planetary climate moved into the glacial cycles.

Fig.9.14 The middle Miocene "silica switch" from the North Atlantic to the North Pacilic, suggesting the turning on of the Nordic heat pump about 15 million year ago. Silica-rich sequences marked black. [F. Woodruff and S. M. Savin. 1989, Paleoceanog. 4:87, based on a compilation by G. Keller and J. A. Barron, 1983m Geol Soc Am Bull 94:590]

9.5.5 The Mid-Miocene Cooling Step 9.5.5 The Mid-Miocene Cooling Step

Silica Switch: the large-scale transfer of dissolved silicate from the Atlantic to the Pacific between 15 and 10 million years ago.

Diatomite in the Pohang Basin?

This increase reflects This increase reflects both both growth of ice on growth of ice on Antarctica and a world Antarctica and a world wide cooling of abyssal wide cooling of abyssal waterswaters. .

A substantial carbon A substantial carbon isotope excursion toward isotope excursion toward heavy values heavy values

Synchronous with the Synchronous with the onset of abundant onset of abundant sedimentation of organic-sedimentation of organic-rich sediments in the rich sediments in the margins of the Pacific. margins of the Pacific.

A drastic A drastic increase in oxygen isotope valuesincrease in oxygen isotope values in in benthic foraminifera between benthic foraminifera between 15 and 13 million 15 and 13 million years ago. years ago.

9.5.6 The End-of-Eocene Cooling 9.5.6 The End-of-Eocene Cooling Eocene Eocene There was less of a There was less of a

temperature gradient temperature gradient driving the machine. driving the machine.

That is, the winds were That is, the winds were weak, and hence the weak, and hence the upwelling that upwelling that concentrates organic-concentrates organic-rich sediments, silica, rich sediments, silica, and phosphate in in the and phosphate in in the margins. margins.

Eocene-Oligocene Step Eocene-Oligocene Step The polar regions cooled at the end of the early Tertiary, pThe polar regions cooled at the end of the early Tertiary, p

resumably due to thermal isolation of the Arctic and Antarresumably due to thermal isolation of the Arctic and Antarctic and due to positive feedback from snow cover and chactic and due to positive feedback from snow cover and changing vegetation. nging vegetation.

The polar front migrated Equator-ward, pushing a late EoThe polar front migrated Equator-ward, pushing a late Eocene rainbelt away from Antarctic shores. cene rainbelt away from Antarctic shores.

We see the effect on the oxygen isotope values in high latituWe see the effect on the oxygen isotope values in high latitudes: they quickly move to high values during the late Eocedes: they quickly move to high values during the late Eocene, with an especially dramatic change at the Eocene-Oligone, with an especially dramatic change at the Eocene-Oligocene boundary. cene boundary.

This is the point at which the water on high latitude shelves This is the point at which the water on high latitude shelves is cold enough, and saline enough, to sink and fill the deep is cold enough, and saline enough, to sink and fill the deep ocean basinsocean basins. .

Fig.9.15 Fundamental and rapid change in nannofossil content of deep-sea sediments from latest Cretaceous to earliest Tertiary ("K/T-Boundary"). A highly diversified tropical assemblage is replaced by a less diversified assemblage of opportunistic species, including dinoflagellate cysts (large sphere with hole_ and the stress- tolerant form Braarudosphaera (pentagon). Sample spacing at the left side

9.6 The Cretaceous-Tertiary Boundary 9.6 The Cretaceous-Tertiary Boundary 9.6.1 The Evidence for Sudden Extinction 9.6.1 The Evidence for Sudden Extinction

A major biostratigraA major biostratigraphic break phic break

The catastrophe hapThe catastrophe happened in a geologicapened in a geologically short time, less thlly short time, less than 100,000 years. an 100,000 years.

9.6.2 The Cause of Extinction 9.6.2 The Cause of Extinction There is little reason to suspect fundamental differences in There is little reason to suspect fundamental differences in

circulation or heat budget between the latest Cretaceous acirculation or heat budget between the latest Cretaceous and the early Paleogene. nd the early Paleogene.

Many hyotheses Many hyotheses Impact scenario; collision with a large mass of rock cominImpact scenario; collision with a large mass of rock comin

g in from outer space (e.g., a body ca. 10 km in diameter) g in from outer space (e.g., a body ca. 10 km in diameter) The evidence rests on the observation that The evidence rests on the observation that iridiumiridium is greatl is greatl

y enriched in the K/T boundary layer, and that y enriched in the K/T boundary layer, and that shocked qushocked quartzartz is present. is present.

Even a candidate for an impact crater has been found, on tEven a candidate for an impact crater has been found, on the Yacatan peninsula in Mexico, the 200-km-diamter he Yacatan peninsula in Mexico, the 200-km-diamter ChicChicxulub structurexulub structure. .

Alternative scenarios are being Alternative scenarios are being debated as well, mainly those debated as well, mainly those centered on volcanism. centered on volcanism.

Still a matter of lively discussion Still a matter of lively discussion A prolonged darkening of the sun A prolonged darkening of the sun Acid rain Acid rain Drastic change in temperature Drastic change in temperature

9.7 Plate Stratigraphy and CCD Fluctuations 9.7 Plate Stratigraphy and CCD Fluctuations 9.7.1 Backtracking and CCD Reconstruction 9.7.1 Backtracking and CCD Reconstruction

Paleodepth Reconstruction Paleodepth Reconstruction The position of the CCD varies through time. The position of the CCD varies through time. How exactly does the CCD fluctuate? How exactly does the CCD fluctuate? What can this tell us about the changing chemistry anWhat can this tell us about the changing chemistry an

d fertility of the ocean?d fertility of the ocean? Before we can reconstruct the CCD fluctuations, we hBefore we can reconstruct the CCD fluctuations, we h

ave to account for the subsidence of the sea floor, doave to account for the subsidence of the sea floor, down the flanks of the Mid-Ocean Ridge. wn the flanks of the Mid-Ocean Ridge.

Fig.9.16 Determination of paleodepth of the CCD by backtracking of drill sites. Subsidence track and sediment sequence of Site 137 Central Atlantic, Lithologic symbols (from left to right at case); broken lines clays; dots calcareous ooze; random dashes (below 400m depth) basalt. CCD is reached near 3.6 km depth, 90 million years ago.

BacktrackingBacktracking First, we identify the point wFirst, we identify the point w

hich corresponds to the basehich corresponds to the basement age of a given deep sea rment age of a given deep sea record, on the subsidence curvecord, on the subsidence curve. e.

Then we walk back up the cuThen we walk back up the curve, the distance correspondirve, the distance corresponding to the age of the sediment fng to the age of the sediment for which we wish determine tor which we wish determine the depth of deposition. he depth of deposition.

We get a paleodepth estimate, We get a paleodepth estimate, as a difference to present watas a difference to present water depth, for the time of depoer depth, for the time of deposition. sition.

To refine this estimate, we suTo refine this estimate, we subtract on half of the thickness btract on half of the thickness of the sediment deposited sincof the sediment deposited since, to account for both the buile, to account for both the buildup of the sea floor and for isdup of the sea floor and for isostatic subsidence. ostatic subsidence.

Fig.9.18 Reconstructions of CCD fluctuations for various oceanic regions. Solid and dashed lines. Reconstructions of Tj. H. van Andel et al., 1977, J Geol 85:651. Dotted line Reconstructions of W. H. Berger, P. H., 1975, Rev Geophys Space Phys 13:561. The reconstructions agree in the general patterns of the fluctuations, which appear correlated with sealevel changes on the whole.

9.7.2 Atlantic and Pacific 9.7.2 Atlantic and Pacific CCD Fluctuations CCD Fluctuations

The CCD stood high in The CCD stood high in the late Eocene, dropped the late Eocene, dropped in the earliest Oligocene, in the earliest Oligocene, rose in the Miocene rose in the Miocene when it reached a peak when it reached a peak between 10 and 15 years between 10 and 15 years ago, and then fell to its ago, and then fell to its present depth near 4.3 present depth near 4.3 km. km.

CCD FluctuationCCD Fluctuation An overall similarity in the CCD fluctuations of Pacific aAn overall similarity in the CCD fluctuations of Pacific a

nd Atlantic: a sign that the chemical climate of the ocean ind Atlantic: a sign that the chemical climate of the ocean is changing on a global scale. s changing on a global scale.

Eocene and Miocene have a shallower CCD than OligoceEocene and Miocene have a shallower CCD than Oligocene and Plio-Pleistocenene and Plio-Pleistocene. .

A certain parallelism of this pattern with oxygen isotope vA certain parallelism of this pattern with oxygen isotope variations and with sea-level variations. ariations and with sea-level variations.

Periods of high sea level are characterized by shallow CCPeriods of high sea level are characterized by shallow CCDD and warm high latitudes; periods of low sea level have and warm high latitudes; periods of low sea level have a deep CCD and cold high latitudes (and deep waters). a deep CCD and cold high latitudes (and deep waters).

9.7.3 Possible Causes 9.7.3 Possible Causes of CCD Fluctuations of CCD Fluctuations

The relationship between paleotemperature and sea leThe relationship between paleotemperature and sea level: transgression equals low albedo, hence warming; vel: transgression equals low albedo, hence warming; regression equals high albedo, hence cooling. regression equals high albedo, hence cooling.

The The concept of basin-shelf fractionationconcept of basin-shelf fractionation. . Internal cycling of carbonate within the deep ocean bInternal cycling of carbonate within the deep ocean b

asins. asins.

The concept The concept of basin-shelf fractionation. of basin-shelf fractionation.

The shelf, being shallow, is favored place for carbonate to The shelf, being shallow, is favored place for carbonate to accumulate, because of the correlation between solubility accumulate, because of the correlation between solubility and pressure. and pressure.

Flooded shelves are carbonate traps, and remove CaCOFlooded shelves are carbonate traps, and remove CaCO33 from the ocean so that the deep sea floor starves. from the ocean so that the deep sea floor starves.

Conversely, bared shelves supply carbonate to the deep Conversely, bared shelves supply carbonate to the deep sea.  A deep CCD should mean more carbonate in the sea.  A deep CCD should mean more carbonate in the deep ocean. deep ocean.

Unfortunately, sedimentation rates were actually at an all-Unfortunately, sedimentation rates were actually at an all-time low in the Oligocene when the CCD was depressed. time low in the Oligocene when the CCD was depressed.

Mass balance alone cannot control the CCD fluctuations. Mass balance alone cannot control the CCD fluctuations.

Internal cycling of carbonate within Internal cycling of carbonate within the deep ocean basins the deep ocean basins

The biological productivity of the ocean is responsiblThe biological productivity of the ocean is responsible for precipitating carbonate. e for precipitating carbonate.

Removal of solids from a solution lowers saturation. Removal of solids from a solution lowers saturation. High productivity results in an undersaturated ocean High productivity results in an undersaturated ocean

with a shallow CCDwith a shallow CCD. . Fertility high in the Eocene and Miocene, low in the Fertility high in the Eocene and Miocene, low in the

Oligocene. Oligocene.

Fig.9.19 Cretaceous organic-rich sediments in the continental margin off the US East Coast. The diagram is highly schematic and is based on both drilling and seismic profiler records. 1 Basalt; 2 greenish-gray limestone; 3 red clayey limestone; 4 white and gray limestone ;5 calcareous ooze and chalk; 6 black clay; 7 multicolored clay; 8 hemipelagic mud; 9 terrigenous sand and clay. Age; JUR Jurassic; CRET Creataceous; TERT Tertiary: QUA Quaternary.

9.8 Cretqceous Oceans: a Question of Oxygenation 9.8 Cretqceous Oceans: a Question of Oxygenation 9.8.1 A "Stagnant" Ocean? 9.8.1 A "Stagnant" Ocean?

When the DSDP first recovered mid-Cretaceous sediments in the Atlantic When the DSDP first recovered mid-Cretaceous sediments in the Atlantic Ocean, it was found that some of these were very rich in organic matter, Ocean, it was found that some of these were very rich in organic matter, indicating either high organic supply to the sea floor, or reduced losses of indicating either high organic supply to the sea floor, or reduced losses of organics due to low oxygen content in deep water at the time, or both. organics due to low oxygen content in deep water at the time, or both.

Anoxic Events Anoxic Events

9.8.2 Modern Analogs9.8.2 Modern Analogs

the partially restricted basin with estuarine circulation; Blthe partially restricted basin with estuarine circulation; Black Sea, Baltic Sea ack Sea, Baltic Sea

the open ocean continental slope, where it is intersected by the open ocean continental slope, where it is intersected by a strong oxygen minimum; Gulf of California, Indian consta strong oxygen minimum; Gulf of California, Indian constinental slope of the Arabian Sea inental slope of the Arabian Sea

A high supply of organic matter relative to the oxygen supA high supply of organic matter relative to the oxygen supply from the deep water into which the organic matter fallply from the deep water into which the organic matter falls. s.

To obtain "black" deposits, we can increase productivity wTo obtain "black" deposits, we can increase productivity while keeping the oxygen supply constant, or decrease the oxhile keeping the oxygen supply constant, or decrease the oxygen supply, keeping productivity constant. ygen supply, keeping productivity constant.

Fig.9.20 Modern analogs of black shale deposition. a Black Sea, with strong salinity stratification preventing vertical overturn and hence blocking supply of oxygen to the deep layers. b Intersection of an oxygen minimum layer with a continental margin, in the northern Indian Ocean. The minimum layer is a worldwide phenomenon; it is reinforced in areas of high production.

Modern analogs of deposition under low oxygen Modern analogs of deposition under low oxygen conditions. conditions.

Mid-Cretaceous Mid-Cretaceous

No evidence for high productivity No evidence for high productivity It has to be a low supply of oxygen It has to be a low supply of oxygen

which is crucial factor. which is crucial factor.

9.8.3 Oxygen in a Warm Ocean 9.8.3 Oxygen in a Warm Ocean

At present, the ocean has a temperature of At present, the ocean has a temperature of between 0° and 5°C. between 0° and 5°C.

Saturation values for oxygen are near 7.5 ml/l. Saturation values for oxygen are near 7.5 ml/l. Typical actual values in the deep ocean are Typical actual values in the deep ocean are

between 3 and 5 ml/l, that is, about 3.5 ml/l between 3 and 5 ml/l, that is, about 3.5 ml/l lower, because of oxygen consumption lower, because of oxygen consumption through decay. through decay.

Oxygen in a Warm OceanOxygen in a Warm Ocean For the Cretaceous ocean, deep water temperatures close tFor the Cretaceous ocean, deep water temperatures close t

o 15°C. o 15°C. Oxygen saturation is near 5.5 ml/l, which is 2 ml/l less than Oxygen saturation is near 5.5 ml/l, which is 2 ml/l less than

for the present cold deep water. for the present cold deep water. A typical value near 2ml/l for the deep Cretaceous ocean, aA typical value near 2ml/l for the deep Cretaceous ocean, a

fter subtracting a loss to account for decay. fter subtracting a loss to account for decay. Under these conditions, any above-average loss of oxygen iUnder these conditions, any above-average loss of oxygen i

n an ocean basin with estuarine-type circulation would man an ocean basin with estuarine-type circulation would make the basin susceptible for developing regional oxygen defke the basin susceptible for developing regional oxygen deficiency. iciency.

Unusually high supply of terrigenous organic matter to sucUnusually high supply of terrigenous organic matter to such a basin could further reduce the oxygen supply. h a basin could further reduce the oxygen supply.

9.8.4 Milankovitch in the Cretaceous? 9.8.4 Milankovitch in the Cretaceous?

Many pelagic sediments of Cretaceous age show distiMany pelagic sediments of Cretaceous age show distinct cyclic deposition. nct cyclic deposition.

Alternations of organic-rich and carbonate-rich facies Alternations of organic-rich and carbonate-rich facies are typical. are typical.

The detailed mathematical analyses indicates that orbiThe detailed mathematical analyses indicates that orbital cycles were important. tal cycles were important.

What might be the mechanism translating orbital infoWhat might be the mechanism translating orbital information into sediment cycles, during ice-free times? - rmation into sediment cycles, during ice-free times? - We do not know! We do not know!

Fig.9.21 "Oceanic Anowic Events" of Schlanger and Jenkyns, and δ13C record of pelagic marine limestones, showing coincidence of the "events" with positive δ13C excursions (generated through the lock-up of 12C-rich carbon).  Width of blank band reflects uncertainty in the value of δ13C . Lower part; Cretaceous stages from Berrassian (right) to Maastrichtian (left). OAEs are centered in the Aptian, Cenomanian/Turonian and Santonian/Campanian

9.8.5 "Anoxic Events" and Volcanism 9.8.5 "Anoxic Events" and Volcanism The widespread occurrence of Cretaceous organic-rich The widespread occurrence of Cretaceous organic-rich

sediments sediments Distinct positive excursions in the δDistinct positive excursions in the δ1313C record C record

Fig.9.22 correlation of the rate of production of ocean crust with sea level and temperature changes, black shale and oil formation, and the abundance of magnetic reversals; basis of the superplume hypothesis of black shale formation.

There is evidence for enormouThere is evidence for enormous outpouring of basaltic lava in s outpouring of basaltic lava in the South Pacific around 120 the South Pacific around 120 million years ago in the Aptiamillion years ago in the Aptian. n.

Enhance volcanic activity; the Enhance volcanic activity; the Ontong Java Plateau east of NOntong Java Plateau east of New Guinea, which is some 40 ew Guinea, which is some 40 km thick and has the size of Tekm thick and has the size of Texas xas

The release of carbon dioxide tThe release of carbon dioxide to the atmosphere may be untio the atmosphere may be untimately responsible for anaerobmately responsible for anaerobism in the deep sea ism in the deep sea

The coincidence of major volcThe coincidence of major volcanism, anaerobism (and petrolanism, anaerobism (and petroleum formation), and sea level eum formation), and sea level rise, certainly is striking. rise, certainly is striking.