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Shelfbreak Frontal and Exchange Processes and the OOI Pioneer Array: An Overview

Shelfbreak Frontal and Exchange Processes and the OOI Pioneer Array: An Overview. Glen Gawarkiewicz WHOI Pioneer Array Modeling Workshop U. Massachusetts-Dartmouth June 4, 2012. Outline. Regional Circulation Mean frontal and velocity structure Secondary circulation and frontal upwelling

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Shelfbreak Frontal and Exchange Processes and the OOI Pioneer Array: An Overview

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  1. Shelfbreak Frontal and Exchange Processes and the OOI Pioneer Array: An Overview Glen Gawarkiewicz WHOI Pioneer Array Modeling Workshop U. Massachusetts-Dartmouth June 4, 2012

  2. Outline • Regional 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

  3. Regional Circulation From P. Fratantoni

  4. A climatological view in summer Temperature Mean position of the foot of the front is 100 m isobath Typical temperature differences 4 Deg. C and typical salinity Differences 2 PSU across front Westward jet is driven by both cross-shelf density differences as well as alongshelf pressure gradient (e.g. Hopkins, 1982; Lentz, 2010; Zhang et al., 2011) Note bottle-nose dolphin sightings (Palka, pers. comm.) from 1998 overlaid on front 0 150 -80 40 Salinity Cross-shelf Distance (km) C. Linder

  5. Seasonal climatological circulation (Zhang et al., 2011) Uses new 3-D climatology from Naomi Fleming and John Wilkin Offshore flow near surface and bottom in all seasons balanced by onshore flow at mid-depth Modeled mean fields are similar to long-term mooring measurements summarized by Lentz (2010) Consistent upwelling near shelfbreak

  6. Long-term mean velocity structure (Flagg et al., 2006) Alongshelf Velocity Data collected from M/V Oleander transits from NJ to Bermuda Mean jet velocity 13 cm/s, max 35 cm/s, 30 km jet width Vertical scale of jet is 50 m, Relative vorticity/f ~ 0.2 Data shows offshore flow near bottom consistent with observations Over the New England shelf Jet core is over the 120 m isobath but varies from 80 to 150 m Isobaths Enormous variability characterizes the shelfbreak region 20 400 120 280 Cross-shelf Distance (km) Cross-shelf Velocity

  7. 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 of heat balance along isopycnals) Vertical velocities estimated from 5-20 m/day

  8. Synoptic Observations:Correlation Scales July 26 July 29 July 31 Temperature at 50 m depth Correlation scales 7-10 km near surface Approximately 1 day Observations from July/August, 1996: Large amplitude frontal meander with wavelength of 40 km and cross-shelf amplitude of 30 km (Gawarkiewicz et al., 2004)

  9. Patterns of Sea Surface Temperature(Bisagni et al., 2009) Mean shelfbreak frontal position 1973-1992 (Drinkwater et al., 1994) Mountain, 2003

  10. Two Extreme Examples of Frontal Position: May 2007 0 120 40 40.4 Foot of front- 115 m Jet at 40.07 Deg. N Max. cross-shelf gradient At 40.10 (temp. at 40 m depth)

  11. Two Extreme Examples of Frontal Position- May, 2008 36 0 120 30 40 40.6 Foot of front shoreward of 40.67 Deg. N., less than 70 m depth Maximum cross-shelf temperature gradient at 40 m- 40.45 Deg. N Core of jet near 40.4 Deg. N

  12. Extreme Events: Nutrientadvection to outer shelf: June 2005 Max Jet Velocity- 52 cm/s 0 0 200 40.5 40 600 Nitrate- Key is 10 mM/L 40.5 40 Salinity Onshore flow max ~20 cm/s

  13. Commercial Fishing Trawlers- 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

  14. Shelfbreak Exchange Processes

  15. Key Points • Shelfbreak 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

  16. OOI Observatories Regional Cabled Observatory (Pacific Northwest) Global Observatories (Station Papa NE Pacific Irminger Sea Argentine Basin Southern Ocean) Coastal Observatories Endurance Line- Oregon Pioneer Array- New England Cyberinfrastructure Initiative

  17. 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

  18. OOI Pioneer Array

  19. Multi-Scale Approach Moorings- Tides, intrusions, surface mixed layer processes AUVs- frontal structure and meandering, cross-shelf exchange and nutrient distributions Gliders- slope features and variability, warm core rings, offshore forcing of shelfbreak front

  20. Pioneer Science Themes • Overriding 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

  21. Mooring Array (after Pioneer Science Workshop Feb. 2011)

  22. Sensors

  23. 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

  24. Modified Mooring Siting Shifts in siting suggested By Industry representatives Central and Central Offshore moorings over known shipwrecks Upstream line now has 3 moorings and not 2

  25. Anomalous Warm Conditions- Autumn 2011 20 12 Bottom Temperature 7 Deg C warming Gawarkiewicz et al 2012 Drifter and Sea Surface Temperature OOI Test Moorings

  26. The Challenge • How 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?

  27. Oceanography Branch NOAA 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

  28. 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

  29. 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

  30. Oceanography Branch – NEFSC Scientific Interests Interest in Collaboration • 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 Four surveys per year ADCP, nutrients, OA, T, S, D, plankton, seabirds, whale, fish, Two surveys per year ADCP, OA, T, S, D, plankton, fish

  31. Interest in Collaboration Monthly XBT, TSG, and Plankton Sampling Surveys across MAB on a merchant vessel (partnering with URI [ADCP] and WHOI [auto XBT launcher])

  32. Interest in Collaboration eMOLT – Environmental Monitors on Lobster Traps A cooperative observing program including temperature, currents, and video

  33. 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)

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