Nd isotopic structure of the Pacific Ocean 70-30 Ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world

Nd isotopic structure of the Pacific Ocean 70-30 Ma and numerical evidence for vigorous ocean circulation and ocean heat transport in a greenhouse world

The oceanic meridional overturning circulation (MOC) is a crucial component of the climate system, impacting heat and nutrient transport, and global carbon cycling. Past greenhouse climate intervals present a paradox because their weak equator‐to‐pole temperature gradients imply a weaker MOC, yet in...

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Bibliographic Details
Published in:Paleoceanography Vol. 29; no. 5; pp. 454 - 469
Main Authors: Thomas, Deborah J., Korty, Robert, Huber, Matthew, Schubert, Jessica A., Haines, Brian
Format: Journal Article
Language:English
Published: Washington Blackwell Publishing Ltd 01-05-2014
Subjects:
Carbon cycle
Cenozoic
Climate change
Climate models
Climate system
Deep sea drilling
Deep water
Greenhouses
Heat
Heat transport
Internal waves
Isotopes
Marine
meridional overturning circulation
Nd isotopes
numerical modeling
Nutrient transport
Ocean circulation
Ocean Drilling
Ocean temperature
Paleoclimate science
Plateaus
Submarine plateaus
Temperature gradients
Water circulation
IS, South Pacific
IN, North Pacific
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Summary:The oceanic meridional overturning circulation (MOC) is a crucial component of the climate system, impacting heat and nutrient transport, and global carbon cycling. Past greenhouse climate intervals present a paradox because their weak equator‐to‐pole temperature gradients imply a weaker MOC, yet increased poleward oceanic heat transport appears to be required to maintain these weak gradients. To investigate the mode of MOC that operated during the early Cenozoic, we compare new Nd isotope data with Nd tracer‐enabled numerical ocean circulation and coupled climate model simulations. Assimilation of new Nd isotope data from South Pacific Deep Sea Drilling Project and Ocean Drilling Program Sites 323, 463, 596, 865, and 869 with previously published data confirm the hypothesized MOC characterized by vigorous sinking in the South and North Pacific ~70 to 30 Ma. Compilation of all Pacific Nd isotope data indicates vigorous, distinct, and separate overturning circulations in each basin until ~40 Ma. Simulations consistently reproduce South Pacific and North Pacific deep convection over a broad range of conditions, but cases using strong deep ocean vertical mixing produced the best data‐model match. Strong mixing, potentially resulting from enhanced abyssal tidal dissipation, greater interaction of wind‐driven internal wave activity with submarine plateaus, or higher than modern values of the geothermal heat flux enable models to achieve enhanced MOC circulation rates with resulting Nd isotope distributions consistent with the proxy data. The consequent poleward heat transport may resolve the paradox of warmer worlds with reduced temperature gradients. Key Points Results show deep water sinking in North and South Pacific during greenhouse Vigorous and separate overturning circulation in Atlantic and Pacific Strong vertical mixing may have enhanced ocean heat transport
Bibliography:ArticleID:PALO20108
NSF S-STEM - No. 0806926
istex:AAF5D103612F1AC4DE54E917C50A8379E21FAC2A
NSF-ATM - No. 0927946
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ReadmeTables S1-S4
ObjectType-Article-1
SourceType-Scholarly Journals-1
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ISSN:0883-8305
2572-4517
1944-9186
2572-4525
DOI:10.1002/2013PA002535