Impacts of orbital forcing and atmospheric carbon dioxide on Miocene ice-sheet expansion

The processes causing the middle Miocene global cooling, which marked the Earth's final transition into an ‘icehouse’ climate about 13.9 million years ago (Myr ago), remain enigmatic. Tectonically driven circulation changes and variations in atmospheric carbon dioxide levels have been suggested as driving mechanisms, but the lack of adequately preserved sedimentary successions has made rigorous testing of these hypotheses difficult. Here we present high-resolution climate proxy records, covering the period from 14.7 to 12.7 million years ago, from two complete sediment cores from the northwest and southeast subtropical Pacific Ocean. Using new chronologies through the correlation to the latest orbital model, we find relatively constant, low summer insolation over Antarctica coincident with declining atmospheric carbon dioxide levels at the time of Antarctic ice-sheet expansion and global cooling, suggesting a causal link. We surmise that the thermal isolation of Antarctica played a role in providing sustained long-term climatic boundary conditions propitious for ice-sheet formation. Our data document that Antarctic glaciation was rapid, taking place within two obliquity cycles, and coincided with a striking transition from obliquity to eccentricity as the drivers of climatic change.

[1]  N. Shackleton,et al.  Intensified deep Pacific inflow and ventilation in Pleistocene glacial times , 2001, Nature.

[2]  L. Sloan,et al.  Trends, Rhythms, and Aberrations in Global Climate 65 Ma to Present , 2001, Science.

[3]  Michael A. Arthur,et al.  Miocene evolution of atmospheric carbon dioxide , 1999 .

[4]  B. Flower,et al.  Middle Miocene deepwater paleoceanography in the southwest Pacific: Relations with East Antarctic Ice Sheet development , 1995 .

[5]  André Berger,et al.  On the Structure and Origin of Major Glaciation Cycles .2. the 100,000-year Cycle , 1993 .

[6]  Jacques Laskar,et al.  A long-term numerical solution for the insolation quantities of the Earth , 2004 .

[7]  N. Shackleton,et al.  The 100,000-year ice-Age cycle identified and found to lag temperature, carbon dioxide, and orbital eccentricity , 2000, Science.

[8]  P. Müller,et al.  Productivity, sedimentation rate, and sedimentary organic matter in the oceans—I. Organic carbon preservation , 1979 .

[9]  M. Raymo,et al.  The 41 kyr world: Milankovitch's other unsolved mystery , 2003 .

[10]  H. Elderfield,et al.  Cenozoic deep-Sea temperatures and global ice volumes from Mg/Ca in benthic foraminiferal calcite , 2000, Science.

[11]  Michael A. Arthur,et al.  Interpreting carbon-isotope excursions: carbonates and organic matter , 1999 .

[12]  D. Sugden,et al.  Cenozoic landscape evolution of the Convoy Range to Mackay Glacier area, Transantarctic Mountains: Onshore to offshore synthesis , 2004 .

[13]  J. Kennett.  Cenozoic evolution of Antarctic glaciation the Circum-Antarctic Ocean and their impact on global paleoceanography , 1977 .

[14]  R. Jahnke,et al.  The global ocean flux of particulate organic carbon: Areal distribution and magnitude , 1996 .

[15]  P. Pearson,et al.  Atmospheric carbon dioxide concentrations over the past 60 million years , 2000, Nature.

[16]  S. Savin,et al.  Mid‐Miocene isotope stratigraphy in the deep sea: High‐resolution correlations, paleoclimatic cycles, and sediment preservation , 1991 .

[17]  James D. Wright,et al.  Unlocking the Ice House: Oligocene‐Miocene oxygen isotopes, eustasy, and margin erosion , 1991 .

[18]  Jian Xu,et al.  Carbon reservoir changes preceded major ice-sheet expansion at the mid-Brunhes event , 2003 .

[19]  Jean Jouzel,et al.  A 420,000 year deuterium excess record from East Antarctica: Information on past changes in the origin of precipitation at Vostok , 2001 .

[20]  Caroline H. Lear,et al.  Rapid stepwise onset of Antarctic glaciation and deeper calcite compensation in the Pacific Ocean , 2005, Nature.

[21]  Ola M. Johannessen,et al.  The Polar Oceans and Their Role in Shaping the Global Environment: Johannessen/The Polar Oceans and Their Role in Shaping the Global Environment , 1994 .

[22]  R. Zahn,et al.  Paleocurrent reconstruction of the deep Pacific inflow during the middle Miocene: Reflections of East Antarctic Ice Sheet growth , 2003 .

[23]  B. Flower,et al.  Middle Miocene ocean-climate transition: High resolution oxygen and carbon isotopic records from Dee , 1993 .

[24]  Fridtjof Nansen,et al.  The polar oceans and their role in shaping the global environment : the Nansen centennial volume , 1994 .

[25]  Wallace S. Broecker,et al.  The Carbon cycle and atmospheric CO[2] : natural variations Archean to present , 1985 .

[26]  M. Loutre,et al.  Does mean annual insolation have the potential to change the climate Earth and Planetary Science Let , 2004 .

[27]  S. Ferraz-Mello.  Estimation of Periods from Unequally Spaced Observations , 1981 .

[28]  M. Raymo,et al.  Tectonic forcing of late Cenozoic climate , 1992, Nature.

[29]  Michael Schulz,et al.  The Mid-Pleistocene climate transition: onset of 100 ka cycle lags ice volume build-up by 280 ka , 1997 .

[30]  D. Lea,et al.  Middle Miocene Southern Ocean Cooling and Antarctic Cryosphere Expansion , 2004, Science.

[31]  J. Zachos,et al.  Climate Response to Orbital Forcing Across the Oligocene-Miocene Boundary , 2001, Science.