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 Synoptic observations: Some extreme examples Summary of exchange processes Pioneer Array Science and Configuration Autumn, Gulf Stream interaction with the shelfbreak and outer shelf

Regional Circulation From P. Fratantoni

A climatological view in summer C. Linder 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 Temperature Salinity Cross-shelf Distance (km)

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

Long-term mean velocity structure (Flagg et al., 2006) 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 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 of heat balance along isopycnals) Vertical velocities estimated from 5-20 m/day

Synoptic Observations: Correlation Scales 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) Correlation scales 7-10 km near surface Approximately 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 position (Drinkwater et al., 1994) Mountain, 2003

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

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

Extreme Events: Nutrient advection to outer shelf: June Max Jet Velocity- 52 cm/s Onshore flow max ~20 cm/s Nitrate- Key is 10 mM/L Salinity

Commercial Fishing Trawlers- bottom fathoms vessels Lobstering fathoms- 19 vessels Red crab fathoms- 4 vessels Longliners- bottom fathoms- 7 vessels Longliners- pelagic fathoms- 30 vessels Gillnetters fathoms vessels Rod and reel fathoms vessels Total vessels- 334 Total crew- 1225

Shelfbreak Exchange Processes

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

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

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 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

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

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 suggested By Industry representatives Central and Central Offshore moorings over known shipwrecks Upstream line now has 3 moorings and not 2

Anomalous Warm Conditions- Autumn 2011 Bottom Temperature 7 Deg C warming Drifter and Sea Surface TemperatureOOI Test Moorings Gawarkiewicz et al

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?

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

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 year ADCP, nutrients, OA, T, S, D, plankton, seabirds, whale, fish, Two surveys per year ADCP, 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