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Shelfbreak Frontal and Exchange Processes and the
OOI Pioneer Array: An Overview
Glen GawarkiewiczWHOI
Pioneer Array Modeling WorkshopU. Massachusetts-Dartmouth
June 4, 2012
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OutlineRegional Circulation
Mean frontal and velocity structure
Secondary circulation and frontal upwelling
Synoptic observations: Some extreme examples
Summary of exchange processes
Pioneer Array Science and Configuration
Autumn, 2011- Gulf Stream interaction with the shelfbreak and outer shelf
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Regional Circulation
From P. Fratantoni
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A climatological view in summer
C. Linder
Mean position of thefoot of the front is 100 m isobath
Typical temperature differences4 Deg. C and typical salinity Differences 2 PSU across front
Westward jet is driven by bothcross-shelf density differences aswell as alongshelf pressuregradient (e.g. Hopkins, 1982;Lentz, 2010; Zhang et al., 2011)
Note bottle-nose dolphin sightings(Palka, pers. comm.) from 1998overlaid on front
Temperature
Salinity
0
150-80 40
Cross-shelf Distance (km)
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Seasonal climatological circulation (Zhang et al., 2011)
Uses new 3-D climatologyfrom Naomi Fleming andJohn Wilkin
Offshore flow near surfaceand bottom in all seasonsbalanced by onshore flowat mid-depth
Modeled mean fields aresimilar to long-termmooring measurementssummarized by Lentz(2010)
Consistent upwelling nearshelfbreak
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Long-term mean velocity structure (Flagg et al., 2006)
Data collected from M/V Oleandertransits from NJ to Bermuda
Mean jet velocity 13 cm/s, max35 cm/s, 30 km jet width
Vertical scale of jet is 50 m,Relative vorticity/f ~ 0.2
Data shows offshore flow nearbottom consistent with observationsOver the New England shelf
Jet core is over the 120 m isobathbut varies from 80 to 150 mIsobaths
Enormous variability characterizesthe shelfbreak region
20
400120 280
Cross-shelf Distance (km)
Alongshelf Velocity
Cross-shelf Velocity
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Bottom Boundary Layer Detachment and Frontal Upwelling
Estimated upwelling rates:
Houghton and Visbeck (1997)Houghton et al. (2006)Barth et al. (1998)Barth et al. (2004)Pickart (2000)
By differing methods (dye release, isopycnal float,advection/diffusion analysis ofheat balance along isopycnals)Vertical velocities estimatedfrom 5-20 m/day
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Synoptic Observations:Correlation Scales
Observations from July/August, 1996:Large amplitude frontal meander withwavelength of 40 km and cross-shelfamplitude of 30 km (Gawarkiewicz et al., 2004)
Correlation scales7-10 km near surfaceApproximately 1 day
July 26 July 29 July 31
Temperature at 50 m depth
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Patterns of Sea Surface Temperature(Bisagni et al., 2009)
Mean shelfbreak frontal position1973-1992 (Drinkwater et al., 1994)
Mountain, 2003
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Two Extreme Examples of Frontal Position: May 2007
Foot of front- 115 mJet at 40.07 Deg. NMax. cross-shelf gradientAt 40.10 (temp. at 40 m depth)
0
120
40 40.4
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Two Extreme Examples of Frontal Position- May, 2008
Foot of front shoreward of 40.67 Deg. N., less than 70 m depthMaximum cross-shelf temperature gradient at 40 m- 40.45 Deg. NCore of jet near 40.4 Deg. N
40 40.6
36
30
0
120
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Extreme Events: Nutrientadvection to outer shelf: June 2005
0
60040.5 40
Max Jet Velocity- 52 cm/s
Onshore flow max ~20 cm/s
Nitrate- Key is 10 mM/L
0
20040.5 40
Salinity
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Commercial FishingTrawlers- bottom- 30-250 fathoms- 60-80 vessels
Lobstering- 50-200 fathoms- 19 vessels
Red crab- 250-400 fathoms- 4 vessels
Longliners- bottom- 50-150 fathoms- 7 vessels
Longliners- pelagic- 150-1500 fathoms- 30 vessels
Gillnetters- 50-100 fathoms- 30-40 vessels
Rod and reel- 40-250 fathoms- 80-100 vessels
Total vessels- 334
Total crew- 1225
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Shelfbreak Exchange Processes
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Key PointsShelfbreak front and jet are highly variable on a
wide variety of time scales
Surface and bottom boundary layers play major role in cross-shelf transport and exchange
Correlation scales are order 10 km in horizontal and 1 day temporally
Upper shelf is subject to episodic injections of high nitrate waters- impact on ecosystem not known but appears to be injected into frontal upwelling circulation
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OOI ObservatoriesRegional Cabled Observatory(Pacific Northwest)
Global Observatories(Station Papa NE PacificIrminger SeaArgentine BasinSouthern Ocean)
Coastal ObservatoriesEndurance Line- OregonPioneer Array- New England
Cyberinfrastructure Initiative
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Coastal Observatories- Pioneer Array
Focus on shelfbreak processes and nutrient exchange between shelf and slope
Will move between regions every 5 years
Design was centered around AUV and glider surveys to resolve shelfbreak front and jet
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OOI Pioneer Array
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Multi-Scale Approach
Moorings- Tides, intrusions, surface mixed layerprocesses
AUVs- frontal structure andmeandering, cross-shelfexchange and nutrientdistributions
Gliders- slope features andvariability, warm core rings,offshore forcing of shelfbreakfront
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Pioneer Science ThemesOverriding theme- Exchange of heat, salt, nutrients,
carbon between the deep ocean and continental shelf
Nutrient and carbon cycling over the outer continental shelf and upper continental slope
Abundance, distribution, and bio-diversity of phytoplankton near the shelfbreak
Controls on the abundance and distribution of organisms at higher trophic levels
Impact of extreme events including winter storms and hurricanes
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Mooring Array (after Pioneer Science Workshop Feb. 2011)
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Sensors
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Negotiations with Fishing Industry
After Public Hearings in Fall 2010, further direct negotiations set up between Commercial Fishing Industry representatives and OOI Scientists
Commercial Fishermen’s Research Foundation moderated 4 half day meetings and has written a summary report
Science Representatives- Al Plueddemann, GG (WHOI), Oscar Schofield (Rutgers Univ.), Wendell Brown (U. Massachusetts-Dartmouth)
Topics covered- Safety issues, siting of moorings, liability, utility of Pioneer results for fisheries science
Process included representative from Senator Whitehouse’s (RI) office
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Modified Mooring Siting
Shifts in siting suggestedBy Industry representatives
Central and CentralOffshore moorings overknown shipwrecks
Upstream line now has3 moorings and not 2
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Anomalous Warm Conditions- Autumn 2011
Bottom Temperature7 Deg C warming
Drifter and Sea Surface Temperature OOI Test Moorings
Gawarkiewicz et al2012
12
20
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The ChallengeHow do we organize the community to maximize
scientific benefits of Pioneer Array?
How best do we use numerical modeling to improve observational strategy and generate better understanding of exchange processes and their implications for ecosystem dynamics?
How best do we communicate the value of science at the shelfbreak to the general public as well as the commercial fishing industry working at the shelfbreak?
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Oceanography BranchNOAA NMFS NEFSC
Branch Objectives
• To monitor the fishery-relevant components of the Northeast U.S. Shelf ecosystem
• To index the seasonal, annual and decadal changes in the conditions of the ecosystem
• To include information in stock, ecosystem, and climate assessments
background image from http://www.po.gso.uri.edu/~dave/htn_fronts.html
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Scientific Interests in Shelfbreak front
Processes of exchange across the shelfbreak front•nutrients – physical processes•plankton – bio-physical processes•adult fish/cephalopods/marine mammals/turtles/etc – biological processes
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Scientific Interests in Shelfbreak front
Importance of shelfbreak front exchange to populations and the ecosystem•nutrients – regional primary productivity•plankton – supply/loss of plankton to/from the shelf and importance to population dynamics (e.g. zooplankton, meroplankton)•adults – winter habitat off-shelf / summer habitat on-shelf; mechanisms and cues for movement / aggregation
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Oceanography Branch – NEFSC
Scientific Interests
Importance of shelf-slope exchange to populations and the ecosystem
•nutrients – regional primary productivity
•plankton – supply or loss of plankton to the shelf and importance to population dynamics (e.g. zooplankton, meroplankton)
•adults – winter habitat off-shelf / summer habitat on-shelf; mechanisms and cues for movement / aggregation
Interest in Collaboration
Four surveys per yearADCP, nutrients, OA, T, S, D, plankton, seabirds, whale, fish,
Two surveys per yearADCP, OA, T, S, D, plankton, fish
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Monthly XBT, TSG, and Plankton Sampling Surveys across MAB on a merchant vessel (partnering with URI [ADCP] and WHOI [auto XBT launcher])
Interest in Collaboration
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eMOLT – Environmental Monitors on Lobster Traps
A cooperative observing program including temperature, currents, and video
Interest in Collaboration
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Please accept my apologizes for not attending
We are very interested in collaborating on science and on observing
Perspective: processes important to the Northeast U.S. shelf ecosystem
Contact: Jon Hare ([email protected])