The relationship between Pacific thermohaline circulation and the evolution of early Paleogene climate

Author(s): Thomas, Deborah J.
Author Affiliation(s): Primary:
Texas A&M University, Department of Oceanography, College Station, TX, United States
Volume Title: Geological Society of America, South-Central Section, 38th annual meeting
Source: Abstracts with Programs - Geological Society of America, 36(1), p.7; Geological Society of America, South-Central Section, 38th annual meeting, College Station, TX, March 15-16, 2004. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: The evolution of early Paleogene climate began with a long-term warming trend culminating in peak Cenozoic warmth, followed by intense cooling that ultimately led to the onset of the icehouse. While various mechanisms have been proposed, this long-term climatic evolution remains largely unexplained. Changes in the magnitude of poleward heat transport via thermohaline circulation may have played a role in the long-term evolution of Cenozoic climate. For example, one mechanism proposed to explain warm polar temperatures during the greenhouse interval invokes increased equator-pole heat transport through more vigorous deep-sea convection. However, intensified oceanic circulation is difficult to reconcile with diminished meridional thermal gradients. Neodymium isotope records from Ocean Drilling Program Leg 198 (Shatsky Rise, northwest Pacific Ocean) shed light on the relationship between thermohaline circulation and global climate evolution. The 143Nd/144Nd ratio is a tracer of deep-water mass circulation because of Nd's short residence time relative to oceanic mixing, and fossil fish debris record the deep-water Nd isotopic composition at a given location. Three fish-debris Nd isotopic records generated from a depth-transect of sites at Shatsky Rise (ODP Sites 1208, 1209, and 1211) indicate that a single deep-water mass encompassed the depth range of at least ∼2400 to 3300m. The Nd isotopic composition (expressed in epsilon units) of this water mass varied considerably over the time interval investigated. The primary trend begins with an increase in εNd values from ∼-4.5 to ∼-2.5 from ∼70 to ∼58 Ma. From ∼58 to ∼45 Ma, εNd values fluctuate somewhat but remain relatively high (∼-3). Subsequently, εNd values decrease to ∼-4.5 by ∼35 Ma. The major transitions in water mass composition at Shatsky Rise correspond to the major shifts in global climate as deduced from the δ18O compilation of Zachos et al. (2001). One explanation for the relationship between deep-water mass composition and climate is that the intensity of thermohaline circulation was diminished during periods of extreme global warmth and then intensified during the late Eocene as cooling progressed. This suggests that thermohaline circulation responded to, rather than forced, long-term global climate change.
Year of Publication: 2004
Research Program: ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Cenozoic; Chordata; Isotope ratios; Isotopes; Leg 198; Lower Paleogene; Metals; Nd-144/Nd-143; Neodymium; North Pacific; Northwest Pacific; O-18/O-16; ODP Site 1208; ODP Site 1209; ODP Site 1211; Ocean Drilling Program; Oxygen; Pacific Ocean; Paleo-oceanography; Paleoclimatology; Paleogene; Pisces; Rare earths; Shatsky Rise; Stable isotopes; Tertiary; Thermohaline circulation; Vertebrata; West Pacific
Coordinates: N360800 N360800 E1581200 E1581200
N323900 N324000 E1583100 E1583000
N320000 N320000 E1575100 E1575100
Record ID: 2004063825
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