Open AccessModeling the Miocene climatic optimum: Ocean circulation
Author(s) -
Herold N.,
Huber M.,
Müller R. D.,
Seton M.
Publication year - 2012
Publication title -
paleoceanography
Language(s) - English
Resource type - Journals
eISSN - 1944-9186
pISSN - 0883-8305
DOI - 10.1029/2010pa002041
Subject(s) - geology , late miocene , oceanography , ocean gyre , climatology , north atlantic deep water , arctic dipole anomaly , shutdown of thermohaline circulation , northern hemisphere , ocean current , thermohaline circulation , arctic , arctic ice pack , paleontology , structural basin , antarctic sea ice , subtropics , fishery , biology
Ocean circulation is investigated using the Community Climate System Model 3 (CCSM3) forced with early to middle Miocene (∼20–14 Ma) topography, bathymetry, vegetation and modern CO 2 . Significant bottom water formation is modeled in the Weddell Sea along with intermediate North Component Water formation in the North Atlantic. This is attributed primarily to stronger‐ and weaker‐than‐modern convective preconditioning in the Weddell and Labrador Seas, respectively. Global meridional overturning and gyre circulation is weaker in the Miocene due to weaker midlatitude westerlies in the southern hemisphere, caused by lowering of the meridional surface temperature gradient, in addition to regional influences on convection. Subsurface temperatures in the Miocene are significantly higher in the far North Atlantic, Greenland‐Norwegian Seas and Arctic basin compared to the present. Ocean heat transport is symmetrical about the equator and resembles that simulated for late Cretaceous and early Cenozoic climates, suggesting the northern hemisphere dominated ocean heat transport active today developed after the middle Miocene. Simulated deep water warming in the Miocene is more than an order of magnitude lower than indicated by proxies. This discrepancy is not reconciled by higher CO 2 due to the persistence of sea‐ice at sites of deep water formation. This suggests that either the CCSM3 is insufficiently sensitive to Miocene boundary conditions, greater greenhouse forcing existed than is currently reconstructed, or that proxy records of warming are exaggerated. Given the diversity of global Miocene proxy records and their near‐unanimous estimate of a significantly warmer Earth, the first two options are more likely.