| NSF Org: |
OCE Division Of Ocean Sciences |
| Recipient: |
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| Initial Amendment Date: | February 20, 2018 |
| Latest Amendment Date: | January 6, 2023 |
| Award Number: | 1756363 |
| Award Instrument: | Continuing Grant |
| Program Manager: |
Baris Uz
bmuz@nsf.gov (703)292-4557 OCE Division Of Ocean Sciences GEO Directorate for Geosciences |
| Start Date: | March 1, 2018 |
| End Date: | February 29, 2024 (Estimated) |
| Total Intended Award Amount: | $1,400,231.00 |
| Total Awarded Amount to Date: | $1,400,231.00 |
| Funds Obligated to Date: |
FY 2019 = $116,810.00 FY 2020 = $632,549.00 |
| History of Investigator: |
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| Recipient Sponsored Research Office: |
266 WOODS HOLE RD WOODS HOLE MA US 02543-1535 (508)289-3542 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
266 Woods Hole Road, MS 21 Woods Hole MA US 02543-1535 |
| 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): | PHYSICAL OCEANOGRAPHY |
| Primary Program Source: |
01001920DB NSF RESEARCH & RELATED ACTIVIT 01002021DB NSF RESEARCH & RELATED ACTIVIT |
| 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
Variability in the transport of heat, freshwater and mass in the North Atlantic has been linked to a number of societally relevant factors including sea level change, the melting of sea and glacial ice, and anthropogenic carbon storage in the deep ocean. However, the current understanding of the drivers of such changes is limited, making an investigation of overturning in the Sub-polar region a key ocean research priority. This field program explicitly addresses this gap. Furthermore, by engaging the larger international community studying the North Atlantic, Overturning in the Sub-polar North Atlantic Program (OSNAP) is playing a key role in catalyzing scientific progress by promoting international collaborations, synthesis, and the sharing of resources and by training future generations. Key to the latter is a network of early career scientists whose professional growth will continue to be facilitated through targeted activities that have been tested and improved during OSNAP's initial phase. Graduate students and post-docs will be trained in seagoing operations and in the processing and analysis of observational data.
The overall goal of this field project, in conjunction with other measurements in the North Atlantic, is to establish determination of the linkage between intermediate and deep water formation and the overturning circulation--a connection that is present in climate models, but has yet to be observed. This project will also provide the first comprehensive view of spreading pathways for the deep waters in the Sub-polar basin. Starting in 2014, the US-led international project, Overturning in the Sub-polar North Atlantic Program (OSNAP), provides a continuous record of the full-water column, trans-basin fluxes of heat, mass and freshwater in the Sub-polar North Atlantic, in partnership with the UK, Netherlands, Canada, Germany and China. Data from the first 21 months of the full OSNAP observing system has been used to produce an initial time series of the meridional overturning, heat and freshwater fluxes for the Sub-polar basin. These preliminary results reveal a highly variable overturning in the basin, interior pathways for overflow waters, surprisingly energetic boundary current systems on timescales from days to months, and a strong overflow plume in the Iceland Basin. The additional two years of OSNAP observations will cover a time frame sufficient to make comparisons with other overturning time series and optimize the OSNAP measurement system--all necessary tasks prior to a request for longer term measurements. This component of OSNAP (OSNAP East) is for the eastern array between Greenland and Scotland in coordination with the UK and the Netherlands. The US contribution includes the East Greenland inshore and offshore arrays, the Iceland Basin array, and the integration of all OSNAP measurements. The sub-goal for OSNAP East is to quantify the structure and transport of the boundary currents off the east coast of Greenland and within the Iceland Basin, as well as determine their variability and forcing mechanisms.
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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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.
The global meridional overturning circulation is a system of inter-connected currents that circle the globe, some near the sea surface transporting warm water from equator to poles and others returning the cooled water from poles toward the equator well below the sea surface. This current system is an integral component of Earth’s climate and it also sequesters heat and carbon dioxide in the deep ocean. It has sometimes been referred to as the Great Ocean Conveyor, but this analogy belies the enormous complexity of this system of currents, which has many branches that can strengthen and weaken, and shift in location, over months to years. The currents below the sea surface are particularly mysterious as they are much harder to measure than surface currents. Mathematical models predict that this system of currents may slow down as a result of global warming, which would have major impacts on human lives and livelihoods, as well as on other life on Earth. These currents need to be measured over long time periods to better understand if and how they are changing, and what drives those changes.
the vastness of the deep ocean means that individual or small groups of scientists can only look at one piece at a time. But if those efforts are coordinated, then we can get an integrated view. That is the case for the Overturning in the Subpolar North Atlantic Program, where multiple investigators from a half-dozen countries are combining their efforts to measure all the heat-carrying currents across a single line in the northern North Atlantic.
In this project, the strength of deep boundary currents at two locations—east of Greenland and in a deep fracture zone crossing the mid-Atlantic ridge—have been monitored using moored sensors to measure velocity, temperature and salinity since 2014.
The measurements have been shared with the larger OSNAP team to generate an integrated view of all the currents crossing the OSNAP line, with the result that since 2014, there hasn’t yet been a significant change in the strength of the overturning circulation. This could change at any time.
New discoveries were made at the two locations covered by this project: a 25% reduction in the amount of water transported by the deep boundary current east of Greenland was observed from 2017-2020 due in part to a noticeable freshening of the current at the same time. This has not yet translated into a change in the integrated transport across the whole North Atlantic. The same freshening was observed at the second location, in the Bight Fracture Zone, and a sizeable seasonal cycle was observed for the first time. This 2-year record (2015-2017) is not long enough to say whether there is a long-term change in the transport of the deep currents there.
This project has contributed to both an integrated and regional understanding of the deep currents in the North Atlantic, which will lead to better predictions of how ocean currents and climate may change in the future.
Last Modified: 06/25/2024
Modified by: Amy S Bower
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