Climate of the Past Discussions
www.clim-past-discuss.net
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2010
10.5194/cpd-6-1391-2010
http://www.clim-past-discuss.net/6/1391/2010/
http://www.clim-past-discuss.net/6/1391/2010/cpd-6-1391-2010.html
http://www.clim-past-discuss.net/6/1391/2010/cpd-6-1391-2010.pdf
1391
1419
2010-07-21
A new interpretation of the two-step <i>δ</i><sup>18</sup>O signal at the Eocene-Oligocene boundary
M. Tigchelaar
mtigch@hawaii.edu
A. S. von der Heydt
H. A. Dijkstra
Institute of Marine and Atmospheric Research Utrecht, Utrecht University, Utrecht, The Netherlands
The most marked step in the global climate transition from
"Greenhouse" to "Icehouse" Earth occurred at the
Eocene-Oligocene (E–O) boundary, 33.7 Ma. Evidence for climatic
changes comes from many sources, including the marine benthic
<i>δ</i><sup>18</sup>O record, showing an increase by 1.2–1.5‰
at this time. This positive excursion is characterised by two steps,
separated by a plateau. The increase in <i>δ</i><sup>18</sup>O values
has been attributed to rapid glaciation of the Antarctic continent,
previously ice-free. Simultaneous changes in the <i>δ</i><sup>13</sup>C
record are indicative of a greenhouse gas control on climate.
Previous studies show that a decline in <i>p</i>CO<sub>2</sub> beyond a certain
threshold value may have initiated the growth of a Southern
Hemispheric ice sheet. These studies were not able to conclusively
explain the remarkable two-step profile in
<i>δ</i><sup>18</sup>O. Furthermore, they did not address the potential
role of changes in ocean circulation in the E–O transition. Here
a new interpretation of the <i>δ</i><sup>18</sup>O signal is presented,
based on model simulations using a simple coupled 8-box-ocean,
4-box-atmosphere model with an added land ice component. The model
was forced with a slowly decreasing atmospheric carbon dioxide
concentration. It is argued that the first step in the
<i>δ</i><sup>18</sup>O represents a shift in meridional overturning
circulation from a Southern Ocean to a bipolar source of deep-water
formation, which is associated with a cooling of the deep sea. This
shift can be initiated by a small density perturbation in the model,
although there is also a parameter regime for which the shift occurs
spontaneously. The second step in the <i>δ</i><sup>18</sup>O profile
occurs due to a rapid glaciation of the Antarctic continent. This new
interpretation is a robust outcome of our model and is in good
agreement with proxy data.
Bijl,~P K., Schouten,~S., Sluijs,~A., Reichart,~G.-J., Zachos,~J C., and Brinkhuis,~H.: Early Palaeogene temperature evolution of the Southwest Pacific Ocean, Nature, 461, 776–779, 2009.
Coxall,~H K. and Pearson,~P N.: The Eocene–Oligocene Transition, in: Deep-Time Perspectives on Climate Change: Marrying the Signal from Computer Models and Biological Proxies, edited by: Williams,~M., Haywood,~A M., Gregory,~F J., and Schmidt,~D N., 351–387, The Micropalaeontological Society Special Publication, 2007.
Coxall,~H K., Wilson,~P A., Pälike,~H., Lear,~C H., and Backman,~J.: Rapid stepwise onset of Artarctic glaciation and deeper calcite compensation in the Pacific Ocean, Nature, 433, 53–57, 2005.
DeConto,~R M. and Pollard,~D.: Rapid Cenozoic glaciation of Antarctica induced by declining atmospheric \chemCO_2, Nature, 421, 245–249, 2003a.
DeConto,~R M. and Pollard,~D.: A~coupled climate-ice sheet modeling approach to the Early Cenozoic history of the Antarctic ice sheet, Palaeogeogr. Palaeocl., 198, 39–52, 2003b.
Dockery,~D. and Lozouet,~P.: Biotic patterns in Eocene-Oligocene Molluscs of the Atlantic Coastal Plain, USA, in: From Greenhouse to Icehouse, edited by: Prothero,~D R., Ivany,~L., and Nesbitt,~E A., 303–340, Columbia University Press, 2003.
Erez,~J. and Luz,~B.: Experimental paleotemperature equation for planktonic foraminifera, Geochim. Cosmochim. Ac., 47, 1025–1031, 1983.
Gildor,~H. and Tziperman,~E.: Sea ice as the glacial cycles' climate switch: role of seasonal and orbital forcing, Paleoceanography, 15, 605–615, 2000.
Gildor,~H. and Tziperman,~E.: A~sea ice climate switch mechanism for the 100-kyr glacial cycles, J. Geophys. Res., 106, 9117–9133, 2001.
Gildor,~H., Tziperman,~E., and Toggweiler,~J.: Sea ice switch mechanism and glacial-interglacial \chemCO_2 variations, Global Biogeochem. Cy., 16, GB0203, doi:10.1029/2001GB001446, 2002.
Hay,~W W., Flögel,~S., and Söding,~E.: Is the initiation of glaciation on Antarctica related to a~change in the structure of the ocean?, Global Planet. Change, 45, 23–33, 2005.
Huber,~M. and Nof,~D.: The ocean circulation in the southern hemisphere and its climate impacts in the Eocene, Palaeogeogr. Palaeocl., 231, 9–28, 2006.
Huber,~M. and Sloan,~L C.: Heat transport, deep waters, and thermal gradients: coupled simulation of an Eocene greenhouse climate, Geophys. Res. Lett., 28, 3481–3484, 2001.
Lear,~C H., Elderfield,~H., and Wilson,~P A.: Cenozoic deep-sea temperatures and global ice volumes from Mg/Ca in benthic foraminiferal calcite, Science, 287, 269–272, 2000.
Lear,~C H., Rosenthal,~Y., Coxall,~H K., and Wilson,~P A.: Late Eocene to early Miocene ice-sheet dynamics and the global carbon cycle, Paleoceanography, 19, PA4015, doi:10.1029/2004PA001039, 2004.
Lear,~C H., Bailey,~T R., Pearson,~P N., Coxall,~H K., and Rosenthal,~Y.: Cooling and ice growth across the Eocene–Oligocene transition, Geology, 36, 251–254, 2008.
Liu,~Z., Pagani,~M., Zinniker,~D., DeConto,~R., Huber,~M., Brinkhuis,~H., Shah,~S R., Leckie,~R M., and Pearson,~A.: Global cooling during the Eocene-Oligocene climate transition, Science, 323, 1187–1190, 2009.
Livermore,~R., Nankivell,~A., Eagles,~G., and Morris,~P.: Paleogene opening of Drake passage, Earth Planet. Sc. Lett., 236, 459–470, 2005.
Markwick,~P J., Rowley,~D B., Ziegler,~A M., Hulver,~M L., Valdes,~P J., and Sellwood,~B W.: Late Cretaceous and Cenozoic global palaeogeographies: Mapping the transition from a \quthot-house to an \qutice-house world, GFF, 122, 103, 2000. %\blackboxDo you meand Geol. Foren. Stock. For.?: I believe that it was published as Geol. Foren. Stock. For. until 1994, but that it is since then called GFF. See http://www.informaworld.com/smpp/title~db=all~content=t902829199 GFF is part of the ISI Journal Title Abbreviation Index
Merico,~A., Tyrrell,~T., and Wilson,~P A.: Eocene/Oligocene ocean de-acidification linked to Antarctic glaciation by sea-level fall, Nature, 452, 979–982, 2008.
Oberhuber,~J M.: An atlas based on \squtCOADS data set, Tech. Rep 15, Max-Planck-Institut für Meteorologie, 1988.
Oerlemans,~J.: Correcting the \chem\delta^18O deep-sea temperature record for Antarctic ice volume, Palaeogeogr. Palaeocl., 208, 195–205, 2004.
Pagani,~M., Zachos,~J C., Freeman,~K H., Tipple,~B., and Bohaty,~S.: Marked decline in atmospheric carbon dioxide concentrations during the paleogene, Science, 309, 600–603, 2005.
Pearson,~P N., Foster,~G L., and Wade,~B S.: Atmospheric carbon dioxide through the Eocene–Oligocene climate transition, Nature, 461, 1110–1113, 2009.
Rea,~D K. and Lyle,~M W.: Paleogene calcite compensation depth in the eastern subtropical Pacific: answers and questions, Paleoceanography, 20, PA1012, doi:10.1029/2004PA001064, 2005.
Scher,~H D. and Martin,~E E.: Timing and climatic consequences of the opening of Drake passage, Science, 312, 428–430, 2006.
Stommel,~H.: Thermohaline convection with two stable regimes of flow, Tellus, 13, 224–230, 1961.
Thomas,~D J.: Evidence for deep-water production in the North Pacific Ocean during the early Cenozoic warm interval, Nature, 430, 65–68, 2004.
Thomas,~D J., Bralower,~T J., and Jones,~C E.: Neodymium isotopic reconstruction of late Paleocene–early Eocene thermohaline circulation, Earth Planet. Sc. Lett., 209, 309–322, 2003.
Thual,~O. and McWilliams,~J C.: The catastrophe structure of thermohaline convection in a~two-dimensional fluid model and a~comparison with low-order box models, Geophys. Astro. Fluid, 64, 67–95, 1992.
Via,~R K. and Thomas,~D J.: Evolution of Atlantic thermohaline circulation: Early Oligocene onset of deep-water production in the North Atlantic, Geology, 34, 441–444, 2006.
Welander,~P.: Thermohaline effects in the ocean circulation and related simple models, in: Large-Scale Transport Processes in Oceans and Atmosphere, edited by: Willebrand,~J. and Anderson,~D L T., 163–200, D. Reidel, 1986.
Williams,~Jr.,~R S. and Ferrigno,~J G.: Satellite Image Atlas of Glaciers of the World, USGS Fact Sheet 2005–3056, 2005.
Zachos,~J C. and Kump,~L R.: Carbon cycle feedbacks and the initiation of Antarctic glaciation in the earliest Oligocene, Global Planet. Change, 47, 51–66, 2005.
Zachos,~J C., Quinn,~T M., and Salamy,~K A.: High-resolution (10$^4$ years) deep-sea foraminiferal stable isotope records of the Eocene–Oligocene climate transition, Paleoceanography, 11, 251–266, 1996.