Elsevier

Cretaceous Research

Volume 29, Issues 5–6, October–December 2008, Pages 725-753
Cretaceous Research

Evolving ideas about the Cretaceous climate and ocean circulation

https://doi.org/10.1016/j.cretres.2008.05.025Get rights and content

Abstract

The Cretaceous is a special episode in the history of the Earth named for a unique rock type, chalk. Chalk is similar to modern deep-sea calcareous ooze and its deposition in epicontinental seas occurred as these areas became an integral part of the ocean. The shelf-break fronts that today separate inshore from open-ocean waters cannot have existed during the Late Cretaceous probably because the higher sea level brought the base of the wind-mixed Ekman layer above the sea floor on the continental margins.

A second peculiarity of the Cretaceous is its warm equable climate. Tropical and polar temperatures were warmer than today. Meridional and ocean-continent temperature gradients were lower. The warmer climate was a reflection of higher atmospheric levels of greenhouse gasses, CO2 and possibly CH4, reinforced by higher water vapor content in response to the warmer temperatures. Most of the additional energy involved in the meridional heat transport system was transported as latent heat of vaporization of H20 by the atmosphere. Poleward heat transport may have been as much as 1 Petawatt (20%) greater than it is today. C3 plants provided for more efficient energy transport into the interior of the continents.

Circulation of the Cretaceous ocean may have been very different from that of today. It is impossible for large areas of the modern ocean to become anoxic, but episodes of local anoxia occurred during the earlier Cretaceous and became regional to global during the middle of the Cretaceous. The present ocean structure depends on constant wind systems, which in turn depend on stability of the atmospheric pressure systems forced by polar ice. During most of the Cretaceous the polar regions were ice free. Without polar ice there were seasonal reversals of the high-latitude atmospheric pressure systems, resulting in disruption of the mid- and high latitude wind systems. Without constant mid-latitude westerly winds, there would be no subtropical and polar fronts in the ocean, no well-developed ocean pycnocline, and no tropical subtropical gyres dominating ocean circulation. Instead the ocean circulation would be accomplished through mesoscale eddies which could carry warmth to the polar regions.

Greater knowledge and understanding of the Cretaceous is critical for learning how the climate system operates when one or both polar regions are ice free.

Introduction

The Cretaceous has long been recognized as a special episode in the history of the Earth and several of the most important ideas in geology derive from the study of Cretaceous rocks. Among the major stratigraphic units into which Earth history is divided, only the Cretaceous and the Carboniferous are named for unique sedimentary deposits. For the Cretaceous, the special type of rock is chalk (fr. craie for the rock, Crétacé for the time interval). Chalk was immortalized in Huxley's famous public lecture to the working men of Norwich, England and published in Macmillans Magazine (Huxley, 1868). When deep sea deposits were recovered from the North Atlantic in 1853 it became apparent that such deposits were not restricted to the late Mesozoic, but that somehow the oceanic plankton producing the modern Globigerina ooze had thrived in the seas covering the continents during the Late Cretaceous. The question as to how open-ocean plankton penetrated into shallow seas and even to the shore awaits a definitive answer.

A second peculiarity of the Cretaceous is evidence for warm conditions extending into the polar regions, at first conjectured from the presence of limestone (chalk) deposits in Denmark and Sweden (Lyell, 1837). During the latter part of the 19th century there was debate over whether the Earth had a meridional temperature gradient and climate zones prior to the Tertiary. After Lord Kelvin's calculations of the loss of heat by the Earth (Lord Kelvin, 1863, Lord Kelvin, 1864) it was thought that the internal heat flux from the cooling Earth exceeded the solar energy flux until the Cenozoic. Hence, most scientists believed that the climate of the entire planet had been initially hot, with gradual cooling during the Precambrian, Paleozoic and Mesozoic. The Cretaceous was the last epoch of geologic time during which the Earth was uniformly warmed by the heat flux from the interior of the Earth. With the beginning of the Cenozoic the radiation from the sun came to exceed the flux of energy from the interior of the Earth and permitted a meridional temperature gradient to develop. Today we know that the energy flux from the sun, measured in hundreds of watts per square meter, has dominated the heat flux from the interior of the Earth, measured in hundredths of a watt per square meter, since the early Archaean. However in the late 19th century cooling of the Earth was assumed to be not only responsible for pre-Tertiary climates, but to drive many geologic processes.

Neumayr (1883) countered the idea of homogenous climates prior to the Cenozoic by demonstrating that the biogeographic distribution of ammonites and other marine molluscs showed that meridional climate zones had existed at least since the beginning of the Jurassic. It was in this context that he applied the terms boreal, temperate, and equatorial to the latitudinally distinct fossil assemblages. He also recognized a number of distinct biogeographic regions and believed that the boundaries between the biogeographic provinces were determined by ocean currents. His ideas were challenged by Ortmann (1896) who argued that the distributions of fossils only reflected paleobiogeographic regions, not climatic differences, and that their boundaries had nothing to do with ocean circulation. However, Haug (1910), in his global account of stratigraphy, accepted Neumayr's ideas and recognized the importance of rudists as indicators of equatorial conditions. Haug used the terms “boréale, équatoriale, australe, and tempérée nord et sud” in describing climatic zones of the Mesozoic. Much work has been accomplished in using proxies to document Cretaceous temperatures and using numerical models to understand the climate of the Cretaceous, but uncertainties remain.

Shortly after the arguments for climate zones on a warm Earth had been developed, two revolutionary ideas were introduced into geology. Chamberlin (1899) proposed that changes in the amount of a greenhouse gas, CO2 might be responsible for the alternation of ice ages and interglacials and account for globally warm climates. Subsequently, he suggested that a reversal of the thermohaline circulation of the ocean might also be responsible (Chamberlin, 1906).

Another major idea arose as the concept of climate-related biogeographic provinces in the Jurassic and Cretaceous was developed further by Uhlig (1911). Although overthrusts in the Alps had been proposed earlier by Bertrand and others, Uhlig recognized that the apparent sharpness of the boundaries between the Alpine-Carpathian faunas and those of northern Europe were a result of large-scale horizontal movement of parts of the Earth's surface. His ideas of mobility of the Earth's surface anticipated the more general work of Alfred Wegener and modern plate tectonics. The most important tools in making plate tectonic reconstructions of the continents and oceans are seafloor magnetic lineations. Unfortunately, these are unambiguous only for the Atlantic. They are incomplete guides for reconstruction of the Indian and Pacific Oceans and their surrounding areas, and offer little if any information on the past locations of terranes. Because much of the Cretaceous seafloor has been subducted (57% of the latest Cretaceous, 80% of the mid-Cretaceous, and 95% of the earliest Cretaceous!), there are a variety of reconstructions differing particularly in treatment of the Caribbean, Tethys, Indian and Pacific Oceans (for further information see the detailed discussion in Hay et al., 1999).

Finally, rare cores of Cretaceous deep sea sediment were recovered in expeditions after WWII. Some of these contained black shales. On the first leg of the Deep Sea Drilling Project more extensive recovery of Cretaceous black shales was made in the deep western Atlantic off the Bahamas. This initiated an ongoing discussion about whether and how the ocean could become anoxic.

Because the Cretaceous was so different from the modern world, because its sediments are widespread and often visible in outcrops, and because it is the oldest period for which plate tectonic reconstructions can still be constrained by seafloor magnetic lineations, it will always be the best example of a radically different state of the Earth. Although studies of the Cretaceous climate are not often cited in works dealing with future climate change, background knowledge of the Cretaceous has shaped many of the arguments. The Cretaceous is a laboratory for testing ideas about causes and effects of global climate change.

Section snippets

The chalk problem

Early Cretaceous strata resemble those of most other geologic periods, but starting in the Cenomanian and lasting in many parts of the world until the end of the Maastrichtian, conditions became unique in Earth history. Chalk is a porous, earthy, limestone made up of the calcitic remains of calcareous nannofossils and planktonic foraminifera. As a deposit it is analogous to modern deep-sea Globigerina/nannoplankton ooze. However, it was deposited over broad areas of the continental platforms.

The problem of the warm, equable climate

As Neumayr (1883) and Uhlig (1911) had proposed, there was clearly a meridional climatic zonation, reflected in the modern use of the terms “Boreal” and “Tethyan” to describe the two major climate zones, even though the equator-pole temperature gradients were less than today. However, their “boreal realm” was in northern Europe, and on modern plate tectonic reconstructions it plots at a latitude of about 30° N (Voigt et al., 1999, Mutterlose et al., 2003). Hay (1995a) suggested that the Boreal

The anoxic ocean problem

Broecker (1969) published an informative abstract entitled “Why the deep sea remains aerobic,” observing that today the supply of oxygen to the deep ocean overwhelms any possible supply of organic carbon from the surface waters. At the same time, the Deep Sea Drilling project recovered black shales from the deep Atlantic off the Bahamas. This initiated a debate which has become the “anoxic ocean conundrum.” The problem has plagued many paleoceanographers: to achieve anoxia in the deeper waters

Summary and conclusions

The Cretaceous is a special episode in the history of the Earth. Its uniqueness was early recognized by giving the name of a unique rock type, chalk, to this interval of geologic time. Chalk turned out to be similar to modern deep-sea calcareous ooze, but the question remains; why was it deposited on the continental blocks only during the Cretaceous. In part, this may have been simply due to the evolution of the calcareous plankton. Planktonic foraminifera have their origins in the Jurassic and

Acknowledgments

This work was supported by grants from the Deutsche Forschungsgemeinschaft. The author is indebted to Sascha Flögel, Wolf-Christian Dullo, Silke Voigt, Elisabetta Erba, Erle Kauffman, Claudia Johnson, Enriqueta Barrera and many other colleagues for helpful discussions.

References (314)

  • J. Erez et al.

    Experimental paleotemperature equation for planktonic foraminifera

    Geochimica et Cosmochimica Acta

    (1983)
  • V.S. Abreu et al.

    Oxygen isotope synthesis; a Cretaceous ice-house?

    Mesozoic and Cenozoic Sequence Stratigraphy of European Basins

    Society for Sedimentary Geology Special Publication

    (1998)
  • A. Ahlberg et al.

    Enigmatic Late Cretaceous high paleo-latitude lonestones in Chukotka, northeasternmost Asia

    GFF

    (2002)
  • T.J. Algeo et al.

    Modern and ancient hypsometries

    Journal of the Geological Society London

    (1991)
  • N.F. Alley et al.

    First known Cretaceous glaciation: Livingston Tillite Member of the Cadne-owie Formation, South Australia

    Australian Journal of Earth Sciences

    (2003)
  • S. Arrhenius

    On the influence of carbonic acid in the air upon the temperature of the ground

    Philosophical Magazine

    (1896)
  • M.A. Arthur et al.

    Marine black shales: Depositional mechanisms and environments of ancient deposits

    Annual Reviews of Earth and Planetary Sciences

    (1994)
  • R.A. Askin

    Late Cretaceous-early Tertiary Antarctic outcrops: Evidence for past vegetation and climates

    The Antarctic Paleoenvironment: a Perspective on Global Change

    Antarctic Research Series

    (1992)
  • E. Barrera et al.

    Antarctic marine temperatures: late Campanian through early Eocene

    Paleoceanography

    (1987)
  • E. Barrera et al.

    Evidence for thermohaline-circulation reversals controlled by sea-level change in the latest Cretaceous

    Geology

    (1997)
  • E. Barrera et al.

    Evolution of late Campanian-Maastrichtian marine climates and oceans

    Evolution of the Cretaceous Ocean-Climate System

    Geological Society of America Special Paper

    (1999)
  • E.J. Barron

    The oceans and atmosphere during warm geologic periods

  • E.J. Barron

    Ancient climates: investigation with climate models

    Reports on Progress in Physics

    (1984)
  • E.J. Barron

    Climatic implications of the variable obliquity explanation of Cretaceous-Paleogene high-latitude floras

    Geology

    (1984)
  • E.J. Barron

    Numerical climate modelling, a frontier in petroleum source rock prediction: results based on Cretaceous simulations

    American Association of Petroleum Geologists Bulletin

    (1985)
  • E.J. Barron et al.

    A “simulation” of mid-Cretaceous climate

    Paleoceanography

    (1995)
  • E.J. Barron et al.

    Model simulations of Cretaceous climates: The role of geography and carbon dioxide

    Proceedings of the Royal Society of London Series B

    (1992)
  • E.J. Barron et al.

    Model simulations of Cretaceous climates: The role of geography and carbon dioxide

  • E.J. Barron et al.

    Paleogeography, 180 million years ago to the present

    Eclogae Geologicae Helvetiae

    (1981)
  • E.J. Barron et al.

    An ice-free Cretaceous? Results from climate model simulations

    Science

    (1981)
  • E.J. Barron et al.

    Climate Model Application in Paleoenvironmental Analysis

    SEPM (Society for Sedimentary Geology) Short Course

    (1994)
  • E.J. Barron et al.

    Model simulation of the Cretaceous ocean circulation

    Science

    (1989)
  • E.J. Barron et al.

    Mid Cretaceous ocean circulation: results from model sensitivity studies

    Paleoceanography

    (1990)
  • E.J. Barron et al.

    Past climate and the role of ocean heat transport: Model simulations for the Cretaceous

    Paleoceanography

    (1993)
  • E.J. Barron et al.

    Atmospheric circulation during warm geologic periods: is the equator-to-pole surface-temperature gradient the controlling factor

    Geology

    (1982)
  • E.J. Barron et al.

    The role of geographic variables in explaining paleoclimates: Results from Cretaceous climate model simulations

    Journal of Geophysical Research

    (1984)
  • E.J. Barron et al.

    Warm Cretaceous climates: High atmospheric CO2 as a plausible mechanism

    The Carbon Cycle and Atmospheric CO2: Natural Variations Archaean to Present

    American Geophysical Union Geophysical Monograph

    (1985)
  • A.W.H.

    Shell porosity of Recent planktonic foraminifera as a climatic index

    Science

    (1968)
  • A.W.H. et al.

    Orbulina universa d'Orbigny in the Indian Ocean

    Micropaleontology

    (1973)
  • R.C. Beardsley et al.

    The Nantucket Shoals Flux Experiment (NSFE79). Part I: a basic description of the current and temperature variability

    Journal of Physical Oceanography

    (1985)
  • R.C. Beardsley et al.

    The Nantucket Shoals Flux Experiment (NSFE79)

    Journal of Physical Oceanography

    (1992)
  • H.F. Belding et al.

    Bathymetric maps: Eastern Continental Margin, USA

    (1970)
  • B.E. Bemis et al.

    Reevaluation of the oxygen isotopic composition of planktonic foraminifera: Experimental results and revised paleotemperature equations

    Paleoceanography

    (1998)
  • M.R. Bennet et al.

    Global cooling inferred from dropstones in the Cretaceous: fact or wishful thinking?

    Terra Nova

    (1996)
  • M.R. Bennet et al.

    Dropstones, their origin and significance

    Palaeogeography, Palaeoclimatology, Palaeoecology

    (1996)
  • J.C. Bergengren et al.

    Modeling global climate-vegetation interactions in a doubled CO2 world

    Climatic Change

    (2001)
  • R.A. Berner

    A model for calcium, magnesium and sulfate in seawater over Phanerozoic time

    American Journal of Science

    (2004)
  • K.L. Bice et al.

    A multiple proxy and model study of Cretaceous upper ocean temperatures and atmospheric CO2 concentrations

    Paleoceanography

    (2006)
  • K.L. Bice et al.

    Possible atmospheric CO2 extremes of the warm mid-Cretaceous (late Albian-Turonian)

    Paleoceanography

    (2002)
  • G. Boccaletti et al.

    The thermal structure of the upper ocean

    Journal of Physical Oceanography

    (2004)
  • Cited by (293)

    View all citing articles on Scopus
    View full text