| NSF Org: |
OPP Office of Polar Programs (OPP) |
| Recipient: |
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| Initial Amendment Date: | July 14, 2017 |
| Latest Amendment Date: | July 14, 2017 |
| Award Number: | 1708427 |
| Award Instrument: | Standard Grant |
| Program Manager: |
Colene Haffke
OPP Office of Polar Programs (OPP) GEO Directorate for Geosciences |
| Start Date: | September 1, 2017 |
| End Date: | February 28, 2021 (Estimated) |
| Total Intended Award Amount: | $397,974.00 |
| Total Awarded Amount to Date: | $397,974.00 |
| Funds Obligated to Date: |
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| History of Investigator: |
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| Recipient Sponsored Research Office: |
2145 N TANANA LOOP FAIRBANKS AK US 99775-0001 (907)474-7301 |
| Sponsor Congressional District: |
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| Primary Place of Performance: |
PO Box 757880 Fairbanks AK US 99775-7880 |
| 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): | ANS-Arctic Natural Sciences |
| 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
The Arctic Ocean is undergoing rapid change. Implications are significant for strategic and tactical military planning; regional, and perhaps global, climate; northern ecosystems and cultures; and economic interests. Climate models qualitatively agree that these changes will persist. Projections of when specific benchmarks, such as an ice-free summer Arctic Ocean, will be reached vary by several decades. Reducing uncertainty in Arctic change projections is an important task. This project identifies tides and near-inertial (NI) waves, with periods of approximately 12 hours, as the major components of Arctic ocean velocity fields, mixing rates and ice dynamics that are not presently represented in global coupled climate models. The project will provide the Arctic community with a database of time-dependent tidal and NI energy in select current meter records. Also, it will provide a carefully-validated, high-resolution, fully-forced Arctic coupled ocean/sea-ice model (OIM) for quantifying the effects of high-frequency (HF) processes on seasonal and longer-term variability of the Arctic Ocean and its ice pack. The project will contribute to STEM workforce development through support for the training of a post-doctoral associate and a graduate student, and through support for two early-career scientists. K-12 outreach will be enabled through in-person and webinar programs at schools in AK, TX, WA and OR. A public-friendly video with visualization of model results will be prepared and distributed to schools and other communities including coastal Alaskan villages, and highlighted on the project website.
Motivated by observations of strong HF ocean currents and ice drift velocities that are very sensitive to
changes in sea-ice state, sparse measurements of HF time series of ocean mixing and ice deformation,
and coarse-grid models with parameterized tide forcing, this project tests the following hypothesis: "Energetic, HF processes, including tides and wind-generated NI waves, are critical contributors to the seasonal cycle and longer-term trends of the Arctic's 3-D hydrography and circulation, sea-ice characteristics, and exchanges of heat, freshwater and momentum between the atmosphere, ocean and sea-ice." The program's specific goals are to map the time-dependent distribution of HF energy in the ocean and ice throughout the Arctic; assess the role of HF processes in the Arctic ice and upper ocean; develop understanding of the HF processes coupling the sea ice, ocean, and atmosphere; and quantify the effect of HF processes on seasonal cycles and longer-term trends. Taking advantage of rapidly growing databases for ocean and sea-ice velocities, and improvements in resolution and physical realism of OIMs, it integrates analyses of tidal and NI signals in select Arctic ocean moorings and sea-ice drift data, validation of a high resolution (~2 km x 106 vertical levels) pan-Arctic OIM with full atmospheric and tidal forcing, and comparison of a suite of model simulations with different forcing to identify dominant HF processes. Simulations with simplified forcing (e.g., removing tides and low-pass filtering the winds to reduce NI forcing) will identify key factors involved in HF influence on ocean and sea-ice state on seasonal and longer time scales. Focus areas include the effect of HF processes on ice formation and dispersion of river freshwater and heat fluxes in shelf seas, on mixing of Atlantic- and Pacific-sourced waters along the Arctic continental slopes, on feedbacks between ocean and sea-ice HF processes, and on the seasonal cycle of atmospheric heat exchange with the ocean and sea ice.
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.
Project Outcomes
Collaborative Research: Three-dimensional structure of Arctic tides and near-inertial oscillations, and their role in changing the Arctic Ocean and ice pack
Award 1708427
PI: Igor Polyakov, co-PIs: Andrey Pnyushkov, Seth Danielson
Introduction
The Arctic Ocean is undergoing rapid change, with significant implications for regional and perhaps global climate, northern ecosystems and cultures, and economic interests. Climate models qualitatively agree that these changes will persist; however, projections of when specific benchmarks (e.g., ?summer ice free?) will be reached vary by several decades. Reducing uncertainty in Arctic change projections is an urgent task. The program identifies tides and near-inertial (NI) waves as the major components of Arctic ocean velocity fields, mixing rates and ice dynamics that are not presently represented in global coupled climate models. However, there are still numerous gaps in our understanding of the role of high-frequency motions in shaping dynamics of the new Arctic. With that in mind, this element of the program had a goal of quantifying time dependence of the vertical structure of tidal and NI currents in all available Arctic ocean moorings.
Major accomplishments
Atlas of Arctic Ocean tides
The program provides the Arctic community with a database of time-dependent tidal and NI energy in all available current meter records suitable for quantifying the effects of high-frequency processes on seasonal and longer-term variability of the Arctic Ocean and its ice pack. For that, the Arctic Tidal Atlas was developed, which includes long-term (one year and longer) ocean current observations from several hundred instruments, and archived at the NSF Arctic Data Center and is published by Nature Scientific Data journal. We consider this activity as our major accomplishment.
Baumann, T. M., I. V. Polyakov, L. Padman, S. Danielson, I. Fer, M. Janout, W. Williams, A. V. Pnyushkov, Arctic tidal current atlas. Nature Scientific Data, 7, 275, doi: https://doi.org/10.1038/s41597-020-00578-z.
The Atlas is a compilation of 429 moored current timeseries from the last two decades throughout the Arctic (Fig. 1). It contains different tidal current products designed for the analysis of tidal parameters from monthly to inter-annual time scales: 10-30 h band-pass filtered currents, which include all semidiurnal and diurnal tidal constituents, and wind-driven inertial currents for the analysis of high-frequency variability. This compilation allows for a wide range of possible uses, including local case studies, assessment of long-term trends, and validation of ocean circulation models. This Atlas may be a valuable tool for resource management and industrial applications such as fisheries, navigation and offshore construction.
This analysis provides daily time series of tidal constituents including length of major and minor axes, phase and other standard tidal analysis parameters. Examples include vertical profiles of tidal current amplitudes for data spatially averaged within several clusters (Fig. 2, left) and statistical parameters (Fig. 2, right). A peer?reviewed paper will describe the processing and provide a first analysis of Arctic?wide spatiotemporal variability of tidal currents.
Increasing of tidal-band currents in the eastern Arctic Ocean
Another key activity of the project was analysis of tidal and NI currents in the Arctic Ocean. A 15-year (2004-2018) record of mooring observations from the upper 50m ocean in the eastern Eurasian Basin reveals increased current speeds and shear (Fig. 3), associated with increasing coupling between wind, ice, and oceanic currents and their vertical shear over 2004-2018, particularly in summer. Substantial increases in both current speeds and shears in the upper 50 m are dominated by amplification of semidiurnal currents. For the first time the strengthened upper ocean currents and shear are observed to coincide with weakening stratification. This coupling links the Atlantic Water heat to the sea ice, a consequence of which would be reducing regional sea ice volume. Our published results point to a new positive feedback mechanism in which reduced sea ice extent facilitates more energetic ventilation of the Atlantic water (Polyakov et al. 2020).
Last Modified: 05/10/2021
Modified by: Igor V Polyakov
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