Shelfbreak Frontal and Exchange Processes and the

OOI Pioneer Array: An Overview

Glen GawarkiewiczWHOI

Pioneer Array Modeling WorkshopU. Massachusetts-Dartmouth

June 4, 2012

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

Regional Circulation

From P. Fratantoni

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

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150-80 40

Cross-shelf Distance (km)

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

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

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400120 280

Cross-shelf Distance (km)

Alongshelf Velocity

Cross-shelf Velocity

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

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

Patterns of Sea Surface Temperature(Bisagni et al., 2009)

Mean shelfbreak frontal position1973-1992 (Drinkwater et al., 1994)

Mountain, 2003

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)

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120

40 40.4

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

Extreme Events: Nutrientadvection to outer shelf: June 2005

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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

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

Shelfbreak Exchange Processes

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

OOI ObservatoriesRegional Cabled Observatory(Pacific Northwest)

Global Observatories(Station Papa NE PacificIrminger SeaArgentine BasinSouthern Ocean)

Coastal ObservatoriesEndurance Line- OregonPioneer Array- New England

Cyberinfrastructure Initiative

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

OOI Pioneer Array

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

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

Mooring Array (after Pioneer Science Workshop Feb. 2011)

Sensors

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

Modified Mooring Siting

Shifts in siting suggestedBy Industry representatives

Central and CentralOffshore moorings overknown shipwrecks

Upstream line now has3 moorings and not 2

Anomalous Warm Conditions- Autumn 2011

Bottom Temperature7 Deg C warming

Drifter and Sea Surface Temperature OOI Test Moorings

Gawarkiewicz et al2012

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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?

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

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

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

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

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

eMOLT – Environmental Monitors on Lobster Traps

A cooperative observing program including temperature, currents, and video

Interest in Collaboration

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 (jon.hare@noaa.gov)