The respective role of atmospheric carbon dioxide and orbital parameters on ice sheet evolution at the Eocene-Oligocene transition

Denton and Hughes (1983, Quaternary Research 20, 125–144) postulated that sea level linked a global ice-sheet system with both terrestrial and grounded marine components during late Quaternary ice ages. Summer temperature changes near Northern Hemisphere melting margins initiated sea-level fluctuations that controlled marine components in both polar hemispheres. It was further proposed that variations of this ice-sheet system amplified and transmitted Milankovitch summer half-year insolation changes between 45 and 75°N into global climatic changes. New tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the Antarctic Ice Sheet, thus fitting the concept of a globally interlocked ice-sheet system. But recent atmospheric modeling results (Manabe and Broccoli, 1985, Journal of Geophysical Research 90, 2167–2190) suggest that factors other than areal changes of the grounded Antarctic Ice Sheet strongly influenced Southern Hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres. Atmospheric carbon dioxide linked to high-latitude oceans is the most likely candidate (Shackleton and Pisias, 1985, Atmospheric carbon dioxide, orbital forcing, and climate. In “The Carbon Cycle and Atmospheric CO2: Natural Variations Archean to Present” (E. T. Sundquest and W. S. Broecker, Eds.), pp. 303–318. Geophysical Monograph 32, American Geophysical Union, Washington, D.C.), but another potential influence was high-frequency climatic oscillations (2500 yr). It is postulated that variations in atmospheric carbon dioxide acted through an Antarctic ice shelf linked to the grounded ice sheet to produce and terminate Southern Hemisphere ice-age climate. It is further postulated that Milankovitch summer insolation combined with a warm high-frequency oscillation caused marked recession of Northern Hemisphere ice-sheet melting margins and the North Atlantic polar front about 14,000 14C yr B.P. This permitted renewed formation of North Atlantic Deep Water, which could well have controlled atmospheric carbon dioxide (W. S. Broecker, D. M. Peteet, and D. Rind, 1985, Nature (London) 315, 21–26). Combined melting and consequent sea-level rise from the three warming factors initiated irreversible collapse of the interlocked global ice-sheet system, which was at its largest but most vulnerable configuration.

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On the sensitivity of the Devonian climate to continental configuration, vegetation cover and insolation

10.5194/cp-2018-36 ◽

2018 ◽

Cited By ~ 1

Author(s):

Julia Brugger ◽

Matthias Hofmann ◽

Stefan Petri ◽

Georg Feulner

Keyword(s):

Carbon Dioxide ◽

Vegetation Cover ◽

Atmospheric Carbon Dioxide ◽

Climate Model ◽

Climate System ◽

The Arctic ◽

Late Devonian ◽

Orbital Parameters ◽

Atmospheric Carbon ◽

The Impact

Abstract. During the Devonian period (419 to 359 million years ago), life on Earth witnessed decisive evolutionary break-throughs, most prominently the colonisation of land by vascular plants and vertebrates. At the same time, it is also a period of major marine extinction events coinciding with marked changes in climate. There is limited knowledge about the causes of these changes and their interactions. It is therefore instructive to explore systematically how the Devonian climate system responds to changes in critical boundary conditions. Here we use coupled climate-model simulations to investigate separately the influence of changes in orbital parameters, continental configuration and vegetation cover on the Devonian climate. Variations of Earth's orbital parameters affect the Devonian climate system, with the warmest climate states at high obliquity and high eccentricity, but the amplitude of global temperature differences is smaller than suggested by an earlier study based on an uncoupled atmosphere model. The prevailing mode of climate variability on decadal to centennial timescales relates to surface air temperature fluctuations in high northern latitudes which are mediated by coupled oscillations involving sea-ice cover, ocean convection and a regional overturning circulation in the Arctic. Furthermore, we find only a small biogeophysical effect of changes in vegetation cover on global climate during the Devonian, and the impact of changes in continental configuration is small as well. Assuming decreasing atmospheric carbon dioxide concentrations throughout the Devonian, we then set up model runs representing the Early, Middle and Late Devonian. Comparing the simulations for these timeslices, the temperature evolution is dominated by the strong decrease in atmospheric carbon dioxide. In particular, the albedo change due to the in- crease in land vegetation alone cannot explain the temperature rise found in Late Devonian proxy data which remains difficult to reconcile with reconstructed falling carbon-dioxide levels. Simulated temperatures are significantly lower than estimates based on oxygen-isotope ratios, suggesting a lower δ18O ratio of Devonian seawater.

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Atmospheric carbon dioxide: a driver of photosynthetic eukaryote evolution for over a billion years?

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.2011.0276 ◽

2012 ◽

Vol 367 (1588) ◽

pp. 477-482 ◽

Cited By ~ 5

Author(s):

David J. Beerling

Keyword(s):

Carbon Dioxide ◽

Evolutionary Biology ◽

Atmospheric Carbon Dioxide ◽

Photosynthetic Eukaryote ◽

Ecosystem Responses ◽

Photosynthetic Eukaryotes ◽

Evolutionary Changes ◽

Eukaryote Evolution ◽

Atmospheric Carbon

Exciting evidence from diverse fields, including physiology, evolutionary biology, palaeontology, geosciences and molecular genetics, is providing an increasingly secure basis for robustly formulating and evaluating hypotheses concerning the role of atmospheric carbon dioxide (CO 2 ) in the evolution of photosynthetic eukaryotes. Such studies span over a billion years of evolutionary change, from the origins of eukaryotic algae through to the evolution of our present-day terrestrial floras, and have relevance for plant and ecosystem responses to future global CO 2 increases. The papers in this issue reflect the breadth and depth of approaches being adopted to address this issue. They reveal new discoveries pointing to deep evidence for the role of CO 2 in shaping evolutionary changes in plants and ecosystems, and establish an exciting cross-disciplinary research agenda for uncovering new insights into feedbacks between biology and the Earth system.

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