Award Abstract # 2202760
Collaborative Proposal: Tectonic degassing as a possible solution to the Miocene climate enigma

NSF Org: OCE
Division Of Ocean Sciences
Recipient: BROWN UNIVERSITY
Initial Amendment Date: June 23, 2022
Latest Amendment Date: June 23, 2022
Award Number: 2202760
Award Instrument: Standard Grant
Program Manager: Alan Wanamaker
awanamak@nsf.gov
 (703)292-7516
OCE
 Division Of Ocean Sciences
GEO
 Directorate for Geosciences
Start Date: July 1, 2022
End Date: June 30, 2025 (Estimated)
Total Intended Award Amount: $543,482.00
Total Awarded Amount to Date: $543,482.00
Funds Obligated to Date: FY 2022 = $543,482.00
History of Investigator:
  • Weimin Si (Principal Investigator)
    weimin_si@brown.edu
  • Timothy Herbert (Co-Principal Investigator)
Recipient Sponsored Research Office: Brown University
1 PROSPECT ST
PROVIDENCE
RI  US  02912-9100
(401)863-2777
Sponsor Congressional District: 01
Primary Place of Performance: Brown University
RI  US  02912-9019
Primary Place of Performance
Congressional District:
01
Unique Entity Identifier (UEI): E3FDXZ6TBHW3
Parent UEI: E3FDXZ6TBHW3
NSF Program(s): GLOBAL CHANGE,
Marine Geology and Geophysics
Primary Program Source: 01002223DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s): 1304, 1389, 1620, 4444, 5720, 8070, 9150
Program Element Code(s): 157700, 162000
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

About 20 million years ago, the Earth was much warmer than today and the Antarctic was nearly ice-free. However, a mysterious climatic transition happened around 14 million years ago and the Earth went through a series of cooling events since then. The persistent cooling over millions of years ultimately led to the emergence of the bi-polar icehouse climate of today. Scientists have long been puzzled about what processes could have caused the cooling. One idea is that the rise of the Himalayas mountains may have sped up erosion and increased the rate of chemical weathering, a process that draws down atmospheric carbon dioxide. Other scientists suggest that the cooling may have been caused by a slowdown in the supply of carbon dioxide from deep inside the earth. The idea is that the formation rate of oceanic crustal rocks decelerated about 14 million years ago. That would have caused a decrease in the release of carbon dioxide from the Earth's interior into the atmosphere. The decrease in the supply of that greenhouse gas then led to the decrease in global temperatures. This study will help address this cooling mystery by providing improved estimates of past global temperatures. Those estimates will come from analyses of organic molecules preserved in deep-sea sediments and from climate model simulations. The new global temperature reconstruction will help determine the relative contributions of mountain building and carbon dioxide release from the Earth's interior to changes in the carbon cycle. The study will provide a better picture of how tectonic processes on Earth, both on land and at the sea floor, influence long-term global climate. The project broader impacts include support for a postdoctoral researcher at both institutions, support for a graduate student and undergraduate researchers at Brown University, and support for K-12 focused outreach activity through an existing program at Brown University.

Beginning in the Middle Miocene (~14 Ma), the Earth experienced sustained cooling of 10-12 degrees C that ended the generally warm climate that had prevailed since the Mesozoic. A major enigma about this Miocene climate transition is whether it is driven by reduced carbon dioxide degassing (source) or enhanced weathering removal (sink). Assuming a relatively constant seafloor spreading rate over time, previous studies suggest that the carbon dioxide drawdown (and the global cooling) was caused by enhanced chemical weathering. That could have been due to either the uplift of the Himalayas or the emergence of the tropical maritime continent, which exposed easily weathered volcanic material in one of the warmest, wettest areas of the world. Recent sea surface temperature reconstructions, however, reveal that the Middle Miocene was much warmer than previously thought, raising the puzzle of whether reduced weathering alone is sufficient to sustain the large warming; an enhanced carbon dioxide flux is probably required to balance the expected weathering sink of carbon dioxide under warm Middle Miocene conditions. This study is motivated by a challenge to the weathering hypothesis based on recent evidence of a ~30% reduction in global crustal production rate since 15 Ma. This project will generate new biomarker sea surface temperature estimates with global coverage for the Miocene, filling temporal and spatial gaps of current datasets. Along with proxy analysis, the study will also develop new Miocene climate simulations sampling a wide range of model physics and boundary conditions to reproduce the Miocene large-scale temperature and hydrological cycle. The model simulations will be used to probe source/sink configurations compatible with Miocene temperatures and mass balance in the carbon cycle. By synthesizing the model-data information, the project will develop an improved reconstruction of the Miocene climate which will ultimately allow for estimation of the relative contribution of different source-sink terms (i.e., the Himalayas, the maritime continent, and the carbon dioxide degassing associated with seafloor spreading) in driving the Miocene temperature and atmospheric carbon dioxide evolution.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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Robinson, Marci M. and Dowsett, Harry J. and Herbert, Timothy D. "Very high Middle Miocene surface productivity on the U.S. mid-Atlantic shelf amid glacioeustatic sea level variability" Palaeogeography, Palaeoclimatology, Palaeoecology , v.606 , 2022 https://doi.org/10.1016/j.palaeo.2022.111249 Citation Details
Si, Weimin and Novak, Joseph B. and Richter, Nora and Polissar, Pratigya and Ma, Ruigang and Santos, Ewerton and Nirenberg, Jared and Herbert, Timothy D. and Aubry, Marie-Pierre "Alkenone-derived estimates of Cretaceous <i>p</i> CO2" Geology , 2024 https://doi.org/10.1130/G51939.1 Citation Details

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