Late Oligocene decoupling of temperature and pCO2; insights from TEX86 paleothermometry

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Author(s): O'Brien, Charlotte Lucy; Pagani, Mark
Author Affiliation(s): Primary:
Yale University, Department of Geology and Geophysics, New Haven, CT, United States
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Current paleo-proxy reconstructions for the late Oligocene (∼28-23 Ma) indicate a decoupling of temperature and pCO2. Specifically, benthic oxygen isotope data suggest either stable conditions or warming/deglaciation, while alkenone-based pCO2 estimates indicate a decline from ∼700 to 400 ppm. Existing sea surface temperature (SST) proxy estimates for this interval are sparse and the appearance of decoupling could be fallacious. Using late Oligocene marine sediments from a range of oceanographic and latitudinal settings, in particular Atlantic Ocean sites ODP 929A (5°N), DSDP 608 (42°N) and DSDP 516F (30°S), we are applying the TEX86 paleothermometer to provide improved constraints on late Oligocene warmth. Thought to originate mainly from planktonic, ammonia-oxidizing Thaumarchaeota, the sedimentary TEX86 signal is complicated by potential influences from additional sources and non-thermal effects (e.g., water chemistry, nutrient dynamics, growth stage and ecology). Thus, we are simultaneously testing assumptions regarding the fidelity of the TEX86 paleo-SST proxy. Our new TEX86H-SST data from Atlantic site ODP 929A indicate stable SSTs in the tropics (often reflective of global conditions) during the late Oligocene, with no reduction in SST coincident with declining pCO2 during the period ∼28-24 Ma. Importantly, TEX86H-SST data show a lack of coherence with latitude exemplified by similar stable SSTs, ∼28°C, at tropical and southern mid-latitude Atlantic sites ODP 929 and DSDP 516F, respectively. This absence of a decrease in SST with increasing site latitude suggests that additional non-thermal factors may be influencing the TEX86 signal at certain locations and/or a need for regional-based TEX86-SST calibrations. Indeed, if our tropical TEX86-SST reconstructions (∼28°C) are valid then this would imply the late Oligocene tropical Atlantic was no warmer than the Pliocene, contradicting multiple lines of evidence that the world was warmer (e.g., higher pCO2, lighter benthic δ18O values and lower ice volume). We shall critically evaluate the implications of our TEX86 data with respect to both (1) late Oligocene climate dynamics and (2) the validity of the TEX86-SST proxy across multiple late Oligocene ocean sites.
Year of Publication: 2016
Research Program: DSDP Deep Sea Drilling Project
IPOD International Phase of Ocean Drilling
ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Carbon dioxide; Ceara Rise; Cenozoic; DSDP Site 516; DSDP Site 608; Deep Sea Drilling Project; Equatorial Atlantic; IPOD; Leg 154; Leg 72; Leg 94; North Atlantic; Northeast Atlantic; ODP Site 929; Ocean Drilling Program; Oligocene; Paleoclimatology; Paleogene; Paleotemperature; Rio Grande Rise; South Atlantic; Tertiary; Upper Oligocene
Coordinates: N055834 N055834 W0434423 W0434423
N425012 N425013 W0230515 W0230515
S301636 S301635 W0351706 W0351707
Record ID: 2017051614
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