Cool La Niña During the Warmth of the Pliocene?

The role of El Niño–Southern Oscillation (ENSO) in greenhouse warming and climate change remains controversial. During the warmth of the early-mid Pliocene, we find evidence for enhanced thermocline tilt and cold upwelling in the equatorial Pacific, consistent with the prevalence of a La Niña–like state, rather than the proposed persistent warm El Niño–like conditions. Our Pliocene paleothermometer supports the idea of a dynamic “ocean thermostat” in which heating of the tropical Pacific leads to a cooling of the east equatorial Pacific and a La Niña–like state, analogous to observations of a transient increasing east-west sea surface temperature gradient in the 20th-century tropical Pacific.

[1]  S. Philander,et al.  Interdecadal Climate Fluctuations That Depend on Exchanges Between the Tropics and Extratropics , 1997, Science.

[2]  M. Budyko,et al.  Anthropogenic Climate Change , 1991 .

[3]  G. P. Lohmann,et al.  Incorporation and preservation of Mg in Globigerinoides sacculifer: implications for reconstructing the temperature and 18O/16O of seawater , 2000 .

[4]  S. George Philander,et al.  Role of tropics in changing the response to Milankovich forcing some three million years ago , 2003 .

[5]  J. Picaut,et al.  Tropical pathways, equatorial undercurrent variability and the 1998 La Niña , 2002 .

[6]  H. Elderfield,et al.  Variations in Mg/Ca and Sr/Ca ratios of planktonic foraminifera caused by postdepositional dissolution: Evidence of shallow Mg‐dependent dissolution , 1996 .

[7]  Maureen E. Raymo,et al.  Mid-Pliocene warmth: stronger greenhouse and stronger conveyor , 1996 .

[8]  M. Huber,et al.  Eocene El Niño: Evidence for Robust Tropical Dynamics in the "Hothouse" , 2003, Science.

[9]  W. Cai,et al.  Evidence for a time‐varying pattern of Greenhouse warming in the Pacific Ocean , 2000 .

[10]  E. Maier‐Reimer,et al.  Ocean General Circulation Model Sensitivity Experiment with an open Central American Isthmus , 1990 .

[11]  D. Lea,et al.  Multispecies approach to reconstructing eastern equatorial Pacific thermocline hydrography during the past 360 kyr , 2003 .

[12]  A. Fedorov,et al.  Is El Nino changing? , 2000, Science.

[13]  K. Trenberth,et al.  Interannual variations in the atmospheric heat budget , 2002 .

[14]  Thomas J. Crowley.  Modeling pliocene warmth , 1991 .

[15]  W. Chaisson,et al.  Pliocene development of the east‐west hydrographic gradient in the equatorial Pacific , 2000 .

[16]  Henry Elderfield,et al.  Calibration of Mg/Ca thermometry in planktonic foraminifera from a sediment trap time series , 2003 .

[17]  R. Seager,et al.  Twentieth-Century Sea Surface Temperature Trends , 1997, Science.

[18]  A. Ravelo,et al.  PLIOCENE-PLEISTOCENE EVOLUTION OF EASTERN TROPICAL PACIFIC SURFACE WATER CIRCULATION AND THERMOCLINE DEPTH , 1997 .

[19]  D. Pollard,et al.  Modeling of middle Pliocene climate with the NCAR GENESIS general circulation model , 1996 .

[20]  G. Schmidt.  Error analysis of paleosalinity calculations , 1999 .

[21]  M. Cane,et al.  El Nino's tropical climate and teleconnections as a blueprint for pre-Ice Age climates , 2002 .

[22]  M. Latif,et al.  Sensitivity of equatorial Pacific and Indian Ocean watermasses to the position of the Indonesian Throughflow , 2000 .

[23]  M. Cane,et al.  Closing of the Indonesian seaway as a precursor to east African aridification around 3–4 million years ago , 2001, Nature.

[24]  D. Lea,et al.  Climate impact of late quaternary equatorial pacific sea surface temperature variations , 2000, Science.

[25]  K. Rodgers,et al.  Extratropical sources of Equatorial Pacific upwelling in an OGCM , 2003 .

[26]  J. Zachos,et al.  Early Pliocene deep water circulation in the western equatorial Atlantic: Implications for high‐latitude climate change , 1998 .