| NSF Org: |
OPP Office of Polar Programs (OPP) |
| Recipient: |
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| Initial Amendment Date: | August 10, 2015 |
| Latest Amendment Date: | July 29, 2019 |
| Award Number: | 1504404 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Gregory Anderson
greander@nsf.gov (703)292-4693 OPP Office of Polar Programs (OPP) GEO Directorate for Geosciences |
| Start Date: | August 15, 2015 |
| End Date: | July 31, 2020 (Estimated) |
| Total Intended Award Amount: | $437,500.00 |
| Total Awarded Amount to Date: | $437,500.00 |
| 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 Route 9W - PO Box 1000 Palisades NY US 10964-1000 |
| 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): | ARCSS-Arctic System Science |
| 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): | 47.078 |
ABSTRACT
Non-technical
The salinity of water in the Arctic Ocean determines much of its buoyancy and thus how stable the various layers of water are. This is important because stability of the stratification of the ocean determines its circulation, heat transport and formation of deep water, which in turn affect the local and regional climate system, as well as ocean/atmosphere/climate interaction in lower latitudes. Thus understanding the basic processes of the circulation, buildup, and release of lower salinity water (called 'freshwater') is of fundamental importance for understanding future states of the Arctic Ocean. This project will study the dynamics and variability of the freshwater components and the overall freshwater inventories, in the region of the ocean north of Greenland, where water and sea ice ultimately take one of two pathways south. The main goal of the study is to understand how buoyancy is redistributed within the Arctic Ocean and how freshwater accumulates and is released. The project is especially interested in the role distinct freshwater components play in this process. For this purpose data collected as part of the Arctic Observing Network will be compared to model simulations and vice versa to test hypotheses concerning the circulation, accumulation and release of freshwater and its components in the Arctic Ocean and to test the performance of an Arctic Ocean model. This project will create data products for researchers and educators interested in the Arctic and its response to climate change. Circulation patterns of the individual freshwater components and other synthesized outputs, along with information and documentation needed to assist educators, will be made publicly available through an online site that is expected to have significant traffic from educators in academia and secondary school levels. This project will provide the core of a PhD dissertation for a graduate student.
Technical
Understanding the basic processes of the circulation, buildup, and release of freshwater is of fundamental importance for examining possible future scenarios of the freshwater lens covering the Arctic Ocean, the role of freshwater in internal circulation within the Arctic, and the role of freshwater in deep water formation in the convective regions of the Nordic seas and the North Atlantic. This project will study the dynamics and variability of the freshwater components and the overall freshwater inventories, in the Switchyard (SY) region in the context of an Arctic Ocean-wide analysis of freshwater component sources and pathways. The main goal of the study is to understand how buoyancy is redistributed within the Arctic Ocean and how freshwater accumulates and is released. There will be special emphasis on the role distinct freshwater components play in this process.
Recent long-term observations conducted in the Switchyard (SY) region as part of the Arctic Observing Network (AON) program, have revealed detailed information on both the total freshwater balance, and the components contributing to it: Pacific Water (PW), Meteoric Water (MW: River Runoff and P-E), and Sea Ice Meltwater (SIMW). The SY observations along a section between Alert and the North Pole show rapid changes in the contributions of individual freshwater components to the total inventory along with gradual changes in the total freshwater content. From backtracking the surface circulation in time based on sea ice drift patterns, the group infers that the rapid changes in the freshwater components are probably due to shifts in the sea ice and surface water source regions and pathways on time scales as short as one year, the frequency of their observations.
This project will combine the SY freshwater component data with those from previous (icebreaker) expeditions to characterize the main features of their distributions. In a second step, the team will extend the sea ice tracking method developed by Maslanik and Fowler to include Ekman transport in the surface ocean and will download GCM runs that simulate individual FW components. They will track the observed freshwater components back to their source regions, and forward to their exit points from the Arctic, and will identify mechanisms impacting the freshwater component circulation, especially in the SY region where they have an 8-year time series. The principal intellectual contributions will come from integrating observed freshwater component inventories and pathways with those obtained from model simulations, inferring the dynamics governing the freshwater component distributions and their adjustment as functions of source terms and atmospheric forcing.
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.
In the Arctic Ocean, the distribution of relatively salty and fresh waters is critical to many phenomena, including sea ice formation and melting, the large-scale ocean currents, and the formation of deep waters that sink and spread out across the abyssal world ocean. Most of the water in the Arctic flows in from the Atlantic, which is very salty. It is transformed in the Arctic by the addition of river runoff, sea-ice melt and relatively fresh inflow from the Pacific Ocean. We and other researchers have developed techniques to separate Arctic water samples into these constituents, based on small amounts of dissolved chemicals, known as ‘tracers’. That is: by measuring the ratio of heavy and light isotopes of water, concentrations of nutrients (nitrate, phosphate and silica), dissolved oxygen levels, and the salinity of water, we can estimate what fractions of that water was recently in the Pacific, or the Atlantic, or locked up in sea ice, or has flowed in from a river or fallen as rain and snow over the ocean. These components combine to determine the salinity of the water, which in the Arctic determines its density, which is important in many of the physical properties of the Arctic.
We discovered in a time series of measurements between Greenland and the North Pole that the contribution of these ‘water-mass’ components can change very quickly in the Arctic, but that the overall salinity of the water changes much more slowly. Prompted by that observation, we set out to document the distribution of water types in the Arctic, and combine that with data on the Arctic currents, and how those might change over time, to see what drives the changes we had seen. In the end, we weren’t able to answer our original question. But along the way, our team was able to uncover some fascinating new knowledge about how the Arctic system works.
We were able to quantify the extent to which heavy isotopes of water are preferentially incorporated into sea ice.
We established a new way to estimate the amount of sea-ice formed from a sample of water, using dissolved noble gases (neon and helium) instead of water isotope ratios. Comparing estimates from these two different methods, we were able to use the difference to quantify the amount of gas exchanged between the air and the ocean over several years. The trick with that is that in the Arctic, the water is perennially under sea ice, and this is the first time that we’ve been able to estimate how quickly gas permeates the sea ice cover.
We participated with another team from Mississippi in establishing a new way to identify the Pacific inflow influence on a water sample, using dissolved gallium instead of nutrients. This method is a bit more expensive, but it seems to be more stable because it is not subject to biological processes as nutrients are. Using this new method, we showed that earlier estimates of vertical mixing of freshwater downward in the Arctic were probably too low.
We participated with teams from Boulder CO and Montreal in enhancing a “Sea Ice Tracking Utility” to project sea-ice drift and transport of material into the future using output from a climate model. This enhanced utility is now being used to inform studies of how Arctic communities adapt to changing climatic conditions along the coastlines.
We compared two different methods to determine the transit time along Arctic currents, one using tritium and helium measurements; the other using sulfur-hexaflouride measurements. Our comparison showed that overall the two methods were in excellent agreement, but that for young waters (less than about 5 years since leaving the surface) there were important differences.
We used these transient tracers to estimate the transit time along currents that run along or over the continental slopes and ridges of the Arctic Ocean seafloor. And we showed how those currents vary as one goes deeper into the Arctic water column.
Much of the work on this project was part of two PhD students’ dissertations, one focused on water mass decomposition and motions; the other on how sea-ice formation impacts chemical signals in the Arctic. In addition, we incorporated undergraduate science majors and high school students into our project by linking processes in a local wetland to processes in the Arctic Ocean.
Overall, while we didn’t get to the conclusions we sought at the beginning of the project, the work turned out to be extremely productive.
Last Modified: 11/17/2020
Modified by: Robert Newton
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