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Award Detail

Awardee:FLORIDA STATE UNIVERSITY
Doing Business As Name:Florida State University
PD/PI:
  • Kevin Speer
  • (850) 645-5625
  • kspeer@fsu.edu
Co-PD(s)/co-PI(s):
  • Louis C St Laurent
  • Peter Lazarevich
Award Date:07/09/2007
Estimated Total Award Amount: $ 2,631,343
Funds Obligated to Date: $ 2,641,753
  • FY 2008=$890,036
  • FY 2007=$768,889
  • FY 2009=$412,095
  • FY 2010=$281,011
  • FY 2011=$289,722
Start Date:07/01/2007
End Date:06/30/2013
Transaction Type:Grant
Agency:NSF
Awarding Agency Code:4900
Funding Agency Code:4900
CFDA Number:47.050
Primary Program Source:040100 NSF RESEARCH & RELATED ACTIVIT
Award Title or Description:Collaborative Research: DIMES, Diapycnal and Isopycnal Mixing in the Southern Ocean
Federal Award ID Number:0622670
DUNS ID:790877419
Parent DUNS ID:159621697
Program:PHYSICAL OCEANOGRAPHY

Awardee Location

Street:874 Traditions Way, 3rd Floor
City:TALLAHASSEE
State:FL
ZIP:32306-4166
County:Tallahassee
Country:US
Awardee Cong. District:02

Primary Place of Performance

Organization Name:Florida State University
Street:874 Traditions Way, 3rd Floor
City:TALLAHASSEE
State:FL
ZIP:32306-4166
County:Tallahassee
Country:US
Cong. District:02

Abstract at Time of Award

The overturning circulation of the ocean plays a governing role in the earth's climate because of the enormous capacity of the ocean to hold heat and carbon dioxide. The Southern Ocean, which surrounds Antarctica, plays a disproportionate role in this overturning circulation because this is one of the main areas where deep waters rise to the surface to exchange heat and carbon dioxide with the atmosphere. Although the Antarctic Circumpolar Current (ACC) system brings deep water to the surface, dynamical constraints inhibit meridional exchanges. Ocean eddies are believed to play a dominant role in transporting water south across the ACC above deep ridges, feeding water driven northward by the intense winds. The extent to which this Isopycnal circulation is "short-circuited" by mixing across density layers is important to climate models but is unknown. Intellectual Merit: Conceptual models of global meridional overturning and numerical predictions for future climate are strongly sensitive to the methods used to represent mixingalong and across the Antarctic Circumpolar Current (ACC), where isopycnals are steeply tilted. Neither diapycnal nor isopycnal mixing has been measured in the Southern Ocean in a systematic way. The goals of the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) are to measure eddy mixing along density surfaces in the subsurface ocean (isopycnal mixing), and across those density layers (diapycnal mixing), and to determine how those processes depend on the larger scale dynamics of the ocean, so that they can be properly represented in numerical models of ocean circulation and of climate. To reveal these processes at work in the ACC, a chemical tracer and 75 floats that follow the water along isopycnal surfaces will be released in the ACC near 1300 m depth, 60 S, and 110 W, early in 2008. Floats that measure fine-structure T, S, and velocity within and above the tracer cloud will be released at the same time. The floats and tracer will be carried by the ACC over the relatively smooth bottom of the SE Pacific, spreading both across and along the current as they travel. After a year, the leading edge of the tracer will just start to pass over the ridges of Drake Passage into the Scotia Sea. Another 75 isopycnal floats will be released near the center of the tracer patch at this time. Trajectories of the floats, measured acoustically with an array of sound sources, will be used to study and to measure isopycnal dispersion. Spreading of the tracer will give integrated measures of both isopycnal and diapycnal dispersion. The eddy field, and its vertical structure, will be studied with sea surface height measured by satellite altimeters, and with hydrographic profiles taken from research vessels and from autonomous instruments drifting with the tracer. Turbulent dissipation, from which diapycnal mixing can be estimated, will be measured with ship-based free-falling profilers to study the spatial and temporal scales of the mixing and to examine suspected hot spots of mixing. Shear driving this mixing will be measured with the free-falling profilers and with special floats drifting with the tracer and floats that profile between the surface and the tracer layer. Broader Impact: DIMES will deploy a variety of instruments including microstructure and finestructure profilers and and isopycnal-following autonomous floats, some for the first time in Southern Ocean. The mixing results will be made available to aid in improving representations of mixing in climate models. In addition, profiling DIMES floats will augment the Argo database for the Southern Ocean. The project will involve a postdoctoral investigator, graduate students at Florida State University and Scripps Institution of Oceanography and will offer research opportunities to one to two undergraduates per year. This project is a contribution to the U.S. CLIVAR (CLImate VARiability and predictability) program.

Publications Produced as a Result of this Research

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Sallee, Jean-Baptiste; Speer, Kevin; Rintoul, Steve; Wijffels, S. "Southern Ocean Thermocline Ventilation" JOURNAL OF PHYSICAL OCEANOGRAPHY, v.40, 2010, p.509-529.

Ren, Li; Speer, Kevin; Chassignet, Eric P. "The mixed layer salinity budget and sea ice in the Southern Ocean" JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS, v.116, 2011, p.1-40.

Sallee, J. B.; Speer, K.; Rintoul, S. R. "Mean-flow and topographic control on surface eddy-mixing in the Southern Ocean" JOURNAL OF MARINE RESEARCH, v.69, 2011, p.753-777.

Ren, L., K. Speer, and E. P. Chassignet "The mixed layer salinity budget and sea ice in the Southern Ocean" J. Geophys. Res., v.116, 2011, p.. doi:doi:10.1029/2010JC006634. 

Marshall, J, K. Speer "Closing the meridional overturning circulation through Southern Ocean upwelling," Nature Geoscience, v.5, 2012, p.171. doi:doi:10.1038/ngeo1391. 

Marshall, John; Speer, Kevin "Closure of the meridional overturning circulation through Southern Ocean upwelling" NATURE GEOSCIENCE, v.5, 2012, p.171-180.

Sall�©e, J.-B., K. Speer, S. Rintoul, and S. Wijffels "Southern Ocean Thermocline Ventilation," Journal of Physical Oceanography, v.40, 2010, p.509.

Sallee, J.B., K. Speer, R. Morrow, and R. Lumpkin "An estimate of Lagragian eddy statistics and diffusion in the mixed layer of the Southern Ocean" journal of marine research, v.66, 2008, p.441.

Lu, J., and K. Speer "Topography, Jets, and Eddy Mixing in the Southern Ocean" Journal of Marine Research, v.68, 2010, p.479.

Lu, Jianhua; Speer, Kevin "Topography, jets, and eddy mixing in the Southern Ocean" JOURNAL OF MARINE RESEARCH, v.68, 2010, p.479-502.

Sallée, J.B., K. G. Speer and S. R. Rintoul "Zonally asymmetric response of the Southern Ocean mixed-layer depth to the Southern Annular Mode" Nature Geoscience, v.3, 2010, p.273. doi:DOI: 10.1038/NGEO812 

Sallee, J. B.; Speer, K. G.; Rintoul, S. R. "Zonally asymmetric response of the Southern Ocean mixed-layer depth to the Southern Annular Mode" NATURE GEOSCIENCE, v.3, 2010, p.273-279.

Sallee, J.-B., K. Speer, and S. Rintoul "Mean-flow and topographic control on surface eddy-mixing in the Southern Ocean" Journal of Marine Research, v.69, 2011, p.1.


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.

DIMES, which stands for "Diapycnal and Isopycnal Mixing in the Southern Ocean" is a field program aimed at measuring diapycnal and isopycnal mixing in the Southern Ocean, along the tilting isopycnals of the Antarctic Circumpolar Current.

Diapycnal mixing makes the ocean more vertically uniform, while isopycnal mixing stirs ocean proerties like heat and carbon dioxide horizontally - or more precisely "laterally", along surfaces of constant density.

 

The Meridional Overturning Circulation (MOC) of the ocean is a critical regulator of the Earth's climate processes. Climate models are highly sensitive to the representation of mixing processes in the southern limb of the MOC, within the Southern Ocean, although the lack of extensive in situ observations of Southern Ocean mixing processes has made evaluation of mixing somewhat difficult. Theories and models of the Southern Ocean circulation have been built on the premise of adiabatic flow in the ocean interior, with diabatic processes confined to the upper-ocean mixed layer. Interior diapycnal mixing has often been assumed to be small, but a few recent studies have suggested that diapycnal mixing might be large in some locations, particularly over rough bathymetry. Depending on its extent, this interior diapycnal mixing could significantly affect the overall energetics and property balances for the Southern Ocean and in turn for the global ocean. The goals of DIMES are to obtain measurements that will help us quantify both along-isopycnal eddy-driven mixing and cross-isopycnal interior mixing.


Last Modified: 07/05/2013
Modified by: Kevin Speer

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