| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | July 9, 2014 |
| Latest Amendment Date: | January 8, 2015 |
| Award Number: | 1436079 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Candace Major
OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | September 1, 2014 |
| End Date: | August 31, 2017 (Estimated) |
| Total Intended Award Amount: | $696,199.00 |
| Total Awarded Amount to Date: | $696,199.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
615 W 131ST ST NEW YORK NY US 10027-7922 (212)854-6851 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
61 Rt 9W palisades NY US 10964-8000 |
| Primary Place of
Performance Congressional District: |
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| Unique Entity Identifier (UEI): |
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| Parent UEI: |
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| NSF Program(s): | Marine Geology and Geophysics |
| Primary Program Source: |
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| Program Reference Code(s): |
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| Program Element Code(s): |
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| Award Agency Code: | 4900 |
| Fund Agency Code: | 4900 |
| Assistance Listing Number(s): | 47.050 |
ABSTRACT
The "Mid-Pleistocene Transition" (MPT) was the biggest reorganization of the global climate system in the recent geological past. It refers to the interval, occurring roughly a million years ago, when the lengths of ice age cycles shifted from ~40,000 to 100,000 years and ice ages became more extreme. During the MPT, atmospheric carbon dioxide (CO2) shifted significantly towards lower values, which would enhance climate cooling. Since the missing CO2 would have been stored in the ocean, it has been inferred that the decrease is a response to changes in the deep-ocean's circulation (also known as "thermohaline circulation"). This shift in the mode of climate variability occurred without significant change in the system's energy inputs (i.e., astronomical forcing), thus implying that non-linear responses of the climate system and/or internal changes within the ocean-atmosphere-cryosphere were ultimately responsible. This research will help quantify the interaction between deep-ocean circulation, the carbon cycle, and global climate change during this critical climatic period. Because the pre-MPT reflects a climate state characterized by elevated glacial atmospheric CO2 and smaller ice sheets, improving understanding of this transition will help scientists and policy makers to better predict and prepare for predicted high atmospheric CO2 levels in the future.
Specifically, this research explores geological archives of past deep-ocean circulation and carbonate chemistry to help elucidate the history of ocean circulation and CO2 over the MPT. The work applies novel geochemical proxies (Nd isotopes, B isotopes and B/Ca ratios) to (1) reconstruct and quantify thermohaline circulation and CO2 changes in the deep-ocean and (2) apply these indicators to establish the nature and timing of this major climatic transition. Using sediment cores from different water depths in the northern, tropical, and south Atlantic will allow the research team to track lateral and vertical changes in the thermohaline circulation before, during and after the MPT. The Nd isotope data will complement the published benthic carbon stable isotope data, which also reflect thermohaline circulation but are also affected by biology (productivity), air-sea equilibration and changes in the global carbon budget. The project will also investigate deep-ocean CO2 storage by estimating seawater-pH and carbonate saturation from boron isotopes and B/Ca ratios in benthic foraminifers. Paired analysis of these proxies provides the opportunity to address the hypothesis that deep-ocean circulation facilitated the coeval drawdown of atmospheric pCO2 during glacial periods, which in turn enhanced high-latitude ice sheet growth, and established the boundary conditions for the development of 100-kyr cycles. Funding supports graduate and undergraduate research, and public outreach via the Lamont-Doherty Earth Observatory Annual Open House.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
Intellectual Merit: The Mid-Pleistocene Transition (MPT), which occurred around one million years ago, marks a fundamental change that occurred in global climate. Before the MPT, ice age cycles were ~41,000 years long, afterward they were ~100,000 years long and the ice ages have been more extreme. Ice ages are driven by the amount of heat received by the Earth from the sun, and relate to shifts in the Earth’s orbit. Since this did not change, there had to be a change within the Earth’s atmosphere-ocean system.
This project delineated the strength of the deep ocean circulation system and deep ocean carbon dioxide storage before, during, and after the MPT. It addressed the role of changes in the global deep ocean circulation, and its relationships to deep ocean carbon dioxide storage and in turn the amount of carbon dioxide in the atmosphere, on the climate changes associated with the MPT. We showed that at ~950,000 years ago there was a major slowdown of the global deep ocean circulation, which is a key means of moving heat around the earth, and especially to the Arctic region around the Atlantic, where continental ice sheets grow during ice ages and melt during interglacials. This allowed for more carbon dioxide to be stored in the oceans, which caused a major decrease in the amount of atmospheric carbon dioxide. As a greenhouse gas that keeps heat in the atmosphere, lower amounts of atmospheric carbon dioxide allow for more heat to escape to space, and making the Arctic colder, so that not all the winter snow melts, and ice sheets accumulate. This “ocean circulation crash” at 950,000 years lasted for 100,000 years. The ice age in which the crash occurred was followed by a “weak interglacial”, because the configuration of the earth’s orbit during this interglacial did not allow for the usual amount of heat to reach the high latitudes. During that weak interglacial the deep ocean circulation remained weak, less heat was transferred to the far north, also carbon dioxide remained low, and the continental ice survived into the next ice age and beyond. This was the first 100,000 year cycle. We conclude that the MPT “ocean circulation crash” had a major impact on the climate system, generating the conditions for 100,000 year cycles ever since.
Broader Impacts: Understanding the role of deep ocean circulation and carbon storage will be particularly important for our understanding of how the climate system works, and how the carbon dioxide that humans are adding to the atmosphere might be mitigated. Carbon dioxide and temperatures are rising, and knowing what happened in the past and why is a key to knowing what to do in the future. Incorporating our findings into projections of future climate change may form essential components for designing policies that deal with life on a changing planet. This project trained three Ph.D. students, a postdoctoral scientist, two lab assistants/technicians who will begin doctoral programs in 2018, and three undergraduates.
Last Modified: 12/06/2017
Modified by: Steven L Goldstein
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