Cenozoic Paleoceanography 1986: an Introduction

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12-1987

Cenozoic paleoceanography 1986: An introduction

W. H. Berger University of California - Davis

Larry A. Mayer University of New Hampshire, [email protected]

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Recommended Citation Berger, W.H., and Mayer, L.A., 1987, Cenozoic paleoceanography 1986: An introduction, in Berger, W.H. and Mayer, L.A., eds. Paleoceanography, vol. 2, no. 6, pp. 613-623

This Article is brought to you for free and open access by the Center for Coastal and Ocean Mapping at University of New Hampshire Scholars' Repository. It has been accepted for inclusion in Affiliate Scholarship by an authorized administrator of University of New Hampshire Scholars' Repository. For more information, please contact [email protected]. PALEOCEANOGRAPHY,VOL. 2, NO. 6, PAGES 613-623, DECEMBER 1987

CENOZOIC PALEOCEANOGRAPHY 1986: AN INTRODUCTION

W. H. Berger

Scripps Institution of Oceanography University of California, San Diego La Jolla

L. A. Mayer

Department of Oceanography Dalhousie University Halifax, Nova Scotia, Canada

Absgracg. New developments in Cenozoic Toronto, 1980: Berger and Crowell [1982]; paleoceanography include the application Zfirich, 1983: Hs•i and Weissert [1985]), we of climate models and atmospheric general note several new developments. Of special circulation models to questions of climate interest are (1) the application of reconstruction, the refinement of climate modeling to questions bearing on conceptual models for interpretation of the ocean heat budget; (2) the the carbon isotope record in terms of (semi)quantitativeinterpretation of 613C carbon mass balance, paleocirculation, signals in calcareous sediments in terms paleoproductivity, and the regional of carbon mass balance, paleocirculation, mapping of paleoceanographic events by and paleoproductivity; (3) the geographic acoustic stratigraphy. Sea level change mapping of paleoceanographic events in emerges as a master variable to which cores and by seismic reflection profiling, changes in the ocean environment must be and (4) the increasing appreciation of the traced in many cases, and tests of the importance of sea level as a master onlap-offlap paradigm therefore are of control variable, and of the complexities crucial importance. associated with its reconstruction. Each one of these topics figured INTRODUCTION prominently in contributions to the Cenozoic Ocean Symposium 1986, both in Symposia are useful in gauging the rate talks and in poster sessions. Climate of advance in the particular branch of modeling was represented by Eric Barron science they aim to represent, in the (Eocene equator-to-pole surface ocean present case, Cenozoic Paleoceanography. temperatures).The 613C signal wasthe Comparing the scope of topics addressed at focus of studies by Michael Arthur and Woods Hole, in 1986, with those addressed associates (paleoproductivity in the by earlier conferences in the field (Kiel, earliest Tertiary), by Lloyd Keigwin 1974: Riedel and Saito [1979]; Harriman, (climatic change in the late Miocene), by New York, 1978: Talwani et al. [1979]; Nobuaki Niitsuma (carbon cycle changes in Houston, 1979: Warme et al. [1981]; the late Neogene), by Fay Woodruff (Miocene deep-sea benthic foraminifera) and by Kenneth Miller and associates Copyright 1987 (Paleogene benthic foraminifera). Event by the American Geophysical Union. stratigraphy was the subject of contributions by Gerta Keller and John Paper number 7PO882. Barron (Cenozoic deep-sea hiatuses), by 0883-8305/87/007P-0882510.00 Brian McGowran (Late Eocene events), by 614 Berger and Mayer' Cenozoic Paleoceanography

SOLAR

ATMOSPHERE TERRESTRIAL 002,H20,ETC. 1RAiIATIO i AEROSOLS VOLCANISM

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-• 'LATE TECTON IC,..S•.. Fig. 1. Major components of the climate system, controlling ocean dynamics, and depositional patterns on the seafloor. From Berger and Labeyrie [1987], modified.

Larry Mayer (seismic stratigraphy in the TEMPERATURE GRADIENT MODELING equatorial Pacific), by Gregory Mountain and associates (deepwater circulation in The quantitative reconstruction of the North Atlantic), by Daniel Muller paleoclimatic conditions and their (Messinian salinity crisis), and by Robert physical modeling was pioneered by the Thunnell and associates (Late Neogene CLIMAP project and associated Mediterranean connections). Sea level investigations [CLIMAP, 1976; Gates, 1976; changes, finally, were scrutinized by Manabe and Hahn, 1977]. This work not only Theodore Moore and associates (short-term had a profound effect on paleoceanography changes in sea level). but also on the development of modeling A selection of these contributions itself, in the new emphasis on the role of appears here in this volume, as well as the ocean and on geological processes in solicited papers from conference the climate machine (Figure 1). Not so participants. In what follows we offer a long ago the treatment of the ocean as a brief introduction to the particular four moisture source with fixed temperature topics listed. It is understood, of distributions ("swamp ocean") was standard course, that a host of other research in general circulation models. Also, the topics are being worked on vigorously (for appreciation of the complexity of geologic example, see Kennett [1985]), not the climatic feedback, via albedo and carbon least the traditional ones concerned with dioxide, was quite limited. documentation of Cenozoic ocean conditions The quantitative approach to and with ever increasing stratigraphic paleoclimate is now penetrating into pre- resolution. For the latter, the ground Pleistocene periods. In a recent study, rules are being changed rapidly, thanks to Barron and Washington [1985] used climate a new emphasis on high-frequency cyclicity modeling to explore the consequences of [Arthur and Garrison, 1986] o apparent equator-to-pole temperature Berger and Mayer' Cenozoic Paleoceanography gradients, as deduced from oxygen isotope more than a decade ago [Shackleton and measurements on calcareous fossils. They Kennett, 1975].' However, the concluded that the proposed warm interpretation of these signals in the temperatures at high latitudes in the Cenozoic could not build on a Pleistocene Cretaceous could not be explained with tradition, as for oxygen isotopes, and favorable geographical boundary conditions thus considerably lagged the availability alone (such as continental positions and of data. sea level). They postulated therefore a Fluctuations in the •13C of the oceanfs distinct effect from greenhouse gases. A carbon pool are now generally seen as similar conclusion was reached by changes in the input or output ratio of Schneider et al. [1985]. Presumably, given inorganic and organic carbon [Tappan, enough constraints on this greenhouse- 1968; Fischer and Arthur, 1977; Scholle dominated temperature residual, the actual and Arthur, 1980], while differences amount of CO2 in the air could be between oceans are explained in terms of estimated, with very interesting basin-to-basin fractionation [Vincent et implications for geochemistry. al., 1980; Shackleton et al., 1983b; For the Woods Hole Symposium, Barron Keigwin and Boyle, 1985; Miller and again tested the equator-to-pole Fairbanks,1985]. Differencesin the •13C temperature gradient against model of shallow and deep water are linked to predictions, this time for the Eocene. the nutrient concentration in the deep Essentially, he found that reported ocean, applying the arguments put forward temperatures and the model logic are by Broecker [1973]. A special case of the incompatible, suggesting that either change in input/output ratio is the geologic information has been buildup and decay of biosphere mass, i.e., misinterpreted, or that the model is forests, which was urged by Shackleton deficient, or both. [1977] as an explanation for transient It is possible that the problem in fact •13Cchanges in Pleistoceneoceans. lies with the current practice of Based on these ideas, the explanation neglecting the effects of evaporation- for major•13C excursions seen in the precipitation patterns on temperature Cenozoic record is straightforward: If the reconstruction from oxygen isotopes. If, benthic and the planktonic signals are on the whole, warm waters deliver parallel everywhere, the cause of moisture, and cold waters accept it (as is fluctuations is interaction with an the case today), then the use of the slope external reservoir. If changes are of 4.2 whichrelates changesin •180 to asymmetric between ocean basins, the cause changes in temperature in the Epstein is inter-ocean exchange (mainly variations equation [Epstein et al., 1953; Emiliani, in the production of North Atlantic Deep 1955] is incorrect. It is too small, and Water). If changes are different for the applied value should in fact lie benthics and planktonics, variations in somewhere between 4.5 and 5 (depending on productivity are involved. the minimum planetary temperature). The A prominent example for the first case, equator-to-pole temperature gradient, that is, ocean-wide•13C excursion,is then, would be correspondingly increased centered on the Early to Middle Miocene by 10-20%, presumably alleviating some of (Figure 2). The buildup of organic carbon the problems with modeling the gradient. within the Monterey Formation and In any case, Barronfs approach will lead equivalent marginal marine deposits all to the s•arpening of tools and arguments around the Pacific appears to correlate in both the data-gathering and the with the carbon isotope anomaly. Under the computational aspects of paleoceanographic assumptions of constant input of carbon, reconstruction. and of constant output of carbonate, the amount of excess organic carbon sequestered can be calculated: It.is about THE CARBON ISOTOPE SIGNAL one (present-day) ocean carbon mass, distributed over some 4 m.y. [Vincent and The major patterns of the carbon Berger, 1985]. If one accepts the idea isotope stratigraphy of the Cenozoic that a more vigorous extraction of organic ocean, that is, the range of fluctuations carbon should have led to a decrease in and the differences between planktonic and atmospheric C02, the possibility of a benthic foraminifera, were established chemoclimatic feedback loop emerges, together with the oxygen isotope patterns whereby CO2 drawdownproduces cooling and 616 Berger and Mayer: Cenozoic Paleoceanography

<•7.5 interglacial cycles had previously been 8 established by the ice core studies in Bern and Grenoble [Berner et al., 1980; 10 Delmas et al., 1980]. Broecker argued that

12 the atmospheric pC02, other things being equal, is a function of the efficiency o 14 <• 1•.8 with which carbon is removed from the 0 surface waters of the ocean, whose carbon ..-... '""•:.....;iiii!iiiiii!iiiiiiiiiiiiiCARBON' ,,,-,1• 5 URSION Y •' chemistry equilibrates with the atmosphere. The efficiency of extraction

18 in turn depends on the amount of nutrients brought up by the upwelling deep water. 70 Relatingthe recordof delta •13Cto the productivity pump has proved a useful exercise. Shackleton et al. [1983a] applied this concept to the Pleistocene 22i i i i I •:•20.4 record, and Shackleton [1985] also 24 3 2 1 0 -1 $mO(%o) $•sC(%0) rece•tl• •sed•t to grogose• constraint o• the •tmosgher•c gCO2, • •e•er•l, for •. 2. •el•t•oQsh•gbet•ee• Mo•tere• •13C the gre-?le•$toce•e.•$ •r•me•t excur$•oQ•Qd •180 $h•ft •t 15 m.•., b•$edoQ •dd•e$$e$the q•est•oQof ho• to estimate •sotogestr•t•r•gh• • the trog•c•l •d• tot•l CO2 • the ocean.•e•lect• m•or Oce• (DSD?$•te 21•; V•ce•t et •1. [1985]). corrections,•t m• be formulated•s follo•$: (1) the sh•11o•-to-deeg [From Berger, 1985]. differencein •13Cdivided by 20 (the per mil deviation of the •13C of marine hence further upwelling and extraction of organic matter) yields the percentage of carbon. total carbon extracted from the surface The peculiar position of the Monterey waters, relative to deep waters; (2) the carbon episode, with respect to the timing maximum extraction in surface waters is of bottom water cooling, is then explained given by the amount of organic carbon as climatic preconditioning through CO2 which can be remobilized through oxidation drawdown. The rapid increase of the at depth, which is limited by the amount temperature gradient between the tropics of oxygen available in the deep water; (3) and the region of bottom water formation, by multipying the maximum possible about 15 m.y. ago, suggests that a extraction of organic carbon from shallow threshold was reached on a more general waters, with the percentage it represents cooling trend. We propose that this (fromdelta •13C), oneobtains the maximum threshold corresponds to the immigration amount of total ocean carbon in the ocean. of polar air masses into the region of In turn, total ocean carbon yields the potential bottom water formation. No atmospheric carbon content under concomitant ice buildup is necessary. If reasonable assumptions regarding ocean this is so, the polar front, after temperature and chemical sta e. Following immigration, would have been delicately thislogic, and given the •i•c record, a situated just beyond the Antarctic coastal proposal of a pCO2 of 10 times present or zone. Thus relatively minor fluctuations more [Berner et al., 1983] becomes in its position would have had substantial unrealistic. Thus Shackleton's approach effects on deep-water formation. The data points the way toward direct calculation of Woodruff et al. [1981] on the isotopic of atmospheric CO2 from the deep-sea composition of deep-sea benthic record. foraminifera suggest that large excursions in deepwater properties did indeed occur EVENT STRATIGRAPHY: HIATUSES during the early mid-Miocene cooling episode. One result of fundamental importance Developmentof the thinkingon shallow- which emerged from deep-sea drilling is to-deep • C differences was greatly that ocean history is punctuated by stimulated by Broecker's [1982] model of distinct events which are reflected in productivity-controlled pC02 variations. rather sudden changes in the facies of The reality of changes in the atmospheric superposed sediments [Berggren and CO2 content parallel to glacial- Hollister, 1977; Berger et al., 1981]. Berger and Mayer: Cenozoic Paleoceanography

Commonly, these changes are accompanied by mechanical erosion in the Atlantic extinction and radiation, suggesting, simultaneously with increased carbonate perhaps not surprisingly, that evolution dissolution in the Pacific, where CO2-rich in the ocean is driven by physical changes waters collect "downstream". Also, a in the ocean-atmosphere system [e.g., sudden supply of soil carbon to the ocean, Benson, 1975; Wei and Kennett, 1986]. due to lowering of sea level and increased One especially interesting aspect of erosion, should result in a global ocean history punctuation is hiatus carbonate dissolution event. In addition, formation. The presence of hiatuses changes in coastal upwelling intensity and interrupting the deep-sea record (a record basin-shelf fractionation offer mechanisms initially probed with the expectation of for a change in depositional patterns finding maximum continuity) elicited which should produce hiatuses in some surprise and vexation and proved a most areas and accelerate accumulatio• in intriguing and difficult problem [van others. Such possible explanations can be Andel et al., 1975; Moore et al., 1978]. testedusing the •13Crecord, together In retrospect, surprise was perhaps not with mass balance considerations. called for. Geologic periods are counted present if their fossils are found. Over EVENT STRATIGRAPHY: SEISMIC PROFILING much of the present-day North Pacific no fossils are deposited because both Acoustic stratigraphy yields continuous carbonate and silica (such as is coverage of the sedimentary record of delivered) are dissolved on the seafloor. paleoceanographic events and is an ideal Furthermore, older deposits migrating down tool for interpolation between core sites. the flank of the Mid-Ocean Ridge and away The apparent synchroneity of globally from the equator are subject to chemical correlative oceanographic events has erosion, especially in areas where important implication for our residual materials are removed, for understanding of the driving mechanisms of example, by the interaction of these events, and this raises the critical bioturbation and gentle bottom currents. question of chronostratigraphic control. Hiatus formation, then, is widespread as a The correlations drawn between the steady-state process. seismically detected, physical, chemical, There is, however, evidence for and oceanographic events described in episodic hiatus formation as well, that Figure 3 are based on a "broad-brush" is, for sporadic removal of previously definition of synchroneity (equal to or deposited sediment, or contemporaneous less than 500,000 years difference) removal over limited periods of time. To determined by the worst case temporal obtain clues, in a given case, as to type resolution afforded by the collective of hiatus involved (steady-state, biostratigraphies [Mayer et al., 1986]. episodic) and processes responsible If we work with a single, intermally (mechanical or chemical erosion, consistent data set, however, and look in contemporaneous, or postdepositional), one detail at the relationships between these must discover the exact regional and parameters, we see that at a higher level bathymetric extent of such a surface. Two of resolution the seismic, physical, and methods have been used: the painstaking chemical events are not truly synchronous. mapping of hiatuses based on coring In the region of the middle/late Miocene results [Keller and Barron, 1983; Keller boundary at Deep Sea Drilling Site 575, et al., 1987], and continuous seismic for example (Figure 4), we clearly see a profiling [Mayer et al., 1986]. sequence of events: an isotopic excursion Core-for-core mapping of hiatuses is fromrelatively heavy•180 valuesto limited by core coverage, quality of core relatively light ones, followed by an material, and biostratigraphic control. extreme carbonate dissolution event and Nevertheless, broad patterns emerge and then a rapid return to relatively high give rise to interesting hypotheses carbonate. The seismic horizon associated regarding hiatus formation. Cooling with this sequence (1 M-P) is the result events, as seenin an increaseof •O18 and of the impedance contrast caused by the in the lowering of sea level, figure rapid change from high to low carbonate. prominently in recent attempts to explain Our best attempt to determine the position hiatuses. Cooling tends to turn up the of these events within Exxon•s "eustatic rate of formation of North Atlantic Deep curve" framework [Haq et al., 1987] places Water, which would produce increased the dissolution event within a phase of 618 Berger and Mayer' Cenozoic Paleoceanography

Impedanc.e (g cm'2 sec-1 x 102) Velocity(m sec -1) Density(g cm-3 ) Carbonate(%) 1800 2550 3300 4050 1500 1710 1920 2130 1.10 1.40 1.70 2.00 2.0 30.5 59.0 87.5

IM-M, IM-B, -M P-G - 0 •IM-P P-G 100 , •mM-R•--• -- •• mM-R

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P-G Gcncralchmanc dcgradanon Northernhcmispherc glac•auon Reorganizationof NADW andNorth Atlantic scismic evcnt Closingof Isthmusof Panama Vail event

IM-M Gcncralcoohng Final isolationof Mediterranean,formation of cvapontcs 0.1 IncrcasedSouth Atlannc glac•anon Vail event

IM-B Gcncralchmatic degradanon Shoalingof thc calcitecompcnsanon depth Incrcascdprovincialism in all microfossil 0.2 assemblages Vail event

IM-P Major coohng Incrcase•n provincialismin all species Change•n styleof carbonarcdeposition in Pacificfrom h•ghvalucs with low- amphtudcfluctuations to large- amphtudcoscdlanons Incrcasc•n sdicadcposmon m Pacific Major reorganizationof westcrnNorth Atlantic bottom-water circulation and North Atlantic seismic event Vad cvent

0.4 mM-R H•gh-lantudccooling Faunaichanges Icc buildupin fia•tarcnca Intcnslficanon of AABW Vail event

eM-L Cessationof Mloccncwarming 0.5 Closingof Tethys NorwegianSea ovcrflow •nto North Atlantic IntensifiedPacific upwelling Montereycarbon excursion Vad event

eM-Y Openingof DrakePassage 0.6 eM-O Establishment of c•rcum-Antarcnc current and steepnorth-south thermal gradients Faunalchanges Field record Synthetic Field record Vad event

Fig. 3. Seismic reflectors in central equatorial Pacific sediments and interpretation [after Mayer et al., 1986]. (1) reflectors and synthetic seismograms used to determine the depth of seismic events, (2) acoustic and physical properties of DSDP Site 574 and position of reflectors, and (3) correlative oceanographic events associated with reflectors. Berger and Mayer' Cenozoic Paleoceanography 619

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Fig. 4. Biostratigraphy, oxygen isotope, and carbonate stratigraphy of upper i00 m of DSDP Site 575 [after Vincent and Killingley, 1985], where 1M-P marks position of seismic horizon. rapid sea level rise, but the precise regimes, i.e., basin/ margin, high correlation of the carbonate event with latitude/ low latitude, Atlantic/ Pacific, the sea level curve is not possible at to well-documented sea level or climatic this time. records. At present the information needed A close look at the temporal to carry out such studies is not readily relationships between the isotope, available. While high-resolution seismic carbonate, and seismic records over this profiling provides the means to trace interval appears to support basin-margin "events" over large distances, we cannot fractionation as a mechanism for deep-sea as yet draw precise stratigraphic ties hiatus formation (a shift to isotopically from one area to the next. If event lighter &180followed closely by a mapping is to reach its potential as a dissolution event). This simple tool for addressing the fundamental relationship, however, is by no means problems of the oceans response to universal; even a quick perusal of forcing, a concerted effort is necessary corresponding carbonate and oxygen isotope to generate a generalized, high-resolution curves at this site reveals that the marine stratigraphy. ocean's response to sea level and climatic events is dominated by critical thresholds SEA LEVEL CHANGE and by changes in the rate of change, which are clearly nonlinear interactions. There is little doubt that sea level is Indeed, it is the sensitivity of the a master variable in Cenozoic seismic signal to the facies contrasts paleoceanography, occupying a central produced by these non-linear interactions position in the feedback system of that makes seismic profiling an appealing climate, circulation, productivity, and tool for paleoceanographic investigations. carbonate chemistry. A change in the One approach to unraveling the nature relative area of ocean and land directly of oceanic response to changes in affects the radiation balance through conditions is to examine the simultaneous albedo and water vapor and heat transport response of different depositional mechanisms. The changing wind field in 620 Berger and Mayer: Cenozoic Paleoceanography

300

200

lOO

_ 100 HARDENBOL 7979 200 ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' ' ' I ' ' • ' 60 50 40 Myr BP 30 20 ]0 0

E LATE E MIDDLE L E LATE EARLY M L EL i PALEOCENEEOCENE OLIGOCENE MIOCENE J J

Fig. 5. Sea level variation from geometry of sediment bodies within passive margins, according to Vail and Hardenbol [1979] (solid line), based on Vail et al. [1977], and Haq et al. [1987] (dotted line).

turn affects shallow circulation, and the determination of sea level variation is a changing relationship between thermocline most urgent task. Atoll stratigraphy and and shelf edge has consequences for the geochemical arguments, e.g., Sr-isotopes, dynamics of eddy formation and upwelling. are being employed for this purpose. Bottom water production, of course, is Results should prove interesting and tied to heat transport and evaporation should greatly stimulate quantification of patterns, which are sensitive to sea sea level effects in global ocean level. sedimentation models. Critical evaluation The productivity of the ocean depends of the sea level paradigm will play a on the concentration of nutrients, which crucial part in the further development of is, in part, a function of continental all of paleoceanographic research. exposure (a measure of sea level), and also of the intensity of recycling, which is influenced indirectly by sea level REFERENCES change. The carbonate chemistry, finally, is a product of a number of factors, of Arthur, M. A., and R. E. Garrison, which shelf-basin fractionation is the one Cyclicity in the Milankovitch band most directly dependent on sea level. through geologic time: an Thus arises the intense interest of introduction, Paleoceanography, 1, paleoceanographers in sea level 369-372, 1986. reconstructions, and the instant Barron, E. J., and W. M.Washington, Warm popularity of the "Exxon sea level curve" Cretaceous climates: high atmospheric [Vail et al., 1977] as a possible driver CO2 as a plausible mechanism, in The for the record of sedimentation rates, GarbonGycle and AtmosphericGO2: stable isotopes, fluctuations of the Natural Variations Archean to carbonate compensation depth, and hiatus Present, Geophys. Monogr. Ser., vol. abundances. The latest incarnation of this 32, edited by E. T. Sundquist and curve [Haq et al., 1987] deviates W. S. Broecker, pp. 546-553, AGU, appreciably from an earlier one [Vail and Washington D.C., 1985. Hardenbol, 1979] (see Figure 5). This Benson, R. H., The origin of the suggests that there is considerable psychrosphere as recorded in changes latitude in the range of possible of deep-sea ostracod assemblages, interpretations of the basic record, that tethaia, 8, 69-83, 1975. is, the geometry of sediment bodies in Berger, W. H., Carbon dioxide increase passive margins. Thus independent and climate prediction: clues from Berger and Mayer: Cenozoic Paleoceanography 6Pl

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W. H. Berger, Scripps Institution of (Received November 2, 1987; Oceanography, University of California, revised November 10, 1987: San Diego, La Jolla, CA 92093. accepted November 11, 1987.)