MARACOOS Ocean Gliders: Mapping the Mid Atlantic Cold Pool Wendell Brown, Richard Arena and Kathryn Tremblay Department of Estuarine and Ocean Sciences / School for Marine Science and Technology ABSTRACT The Cold Pool is a distinctive along-shelf band of remnant winter water that is bottom-trapped in the Mid-Atlantic Bight (MAB) between Cape Cod and Cape Hatteras each summer. Cold Pool waters, which evolve significantly in space between March and November, strongly influence the MAB ecosystem (including fisheries). Thus our goal is to forecast the disposition of the Cold Pool, which cannot be “seen” by satellites. Over the past few years, Mid-Atlantic Regional Association Coastal Ocean Observing System (MARACOOS) researchers are learning how to use autonomous Slocum ocean gliders, which vertically saw-tooth their way forward through the ocean, to map the Cold Pool waters. These ocean gliders typically measure temperature, salinity, oxygen, chlorophyll, and optical backscatter. Because Cold Pool waters (CPWs) have distinctive temperature and salinity signatures, they can be distinguished by individual MARACOOS gliders as they zig-zag back and forth across the shelf during their 25-day missions between Massachusetts and New Jersey. During 2007 a series of individual glider missions enabled us to show that: (1) in late May, the MAB water column stratifies vertically, thus bottom-trapping CPWs; (2) during summer CPWs warm by about 1oC per month; and (3) during autumn CPWs lose their distinctive identity; as successive storms homogenize the MAB ocean. Last autumn during the MARACOOS-led “GliderPalooza”, a trio of gliders measured different parts of the Cold Pool simultaneously; thus enabling us to better define an important coastal ocean habitat. In the future, glider measurements will be assimilated into numerical ocean models that will be able to forecast Cold Pool disposition. Mid Atlantic Regional Association Coastal Ocean Observing System WHAT IS THE COLD POOL? The Cold Pool is a swath of bottom-trapped remnant winter water that is observed between Cape Cod and Cape Hatteras from late spring (when the surface water warms ) through early autumn (when storms homogenize the water column ). The May 2013 bottom temperature map produced by the ESPRESSO numerical model (to the right) defines the spatial variability of the Cold Pool Water . Because CPW strongly affects the Mid Atlantic Bight ecosystem, including fisheries , we seek to forecast its time-space variability. Launching a Slocum ocean glider COLD POOL Model Simulation May 2013 OCEAN GLIDER COLD POOL MEASUREMENTS : 2007 These autonomous gliders are able to very slowly (about 1/2 mph!) saw-tooth their way along a user-determined horizontal trajectory (E.g., to the right). During 2007, we conducted multiple glider missions (typically lasting for 3-4 weeks) which measured 6 cross-shelf “slices” of the Cold Pool during its Massachusetts to New Jersey transit. [SEE Leg -1 - south of Massachusetts EXAMPLES BELOW] What is in an autonomous underwater glider? Surfacings - every few hours - oC GLIDER PALOOZA: 2013 During September & October 2013 MARACOOS coordinated more than eight ocean glider missions between Nova Scotia and Georgia. Half of those gliders measured the disintegration of the Mid Atlantic Bight Cold Pool. These data were assimilated into one or more research operational numerical ocean models that were able to produce near real-time maps and forecasts of the Cold Pool. Northern Zig-Zag Glider Trajectory : May 2007 (Leg-1 highlighted) Late Spring 2007 Leg-1 glider “slice” through the “new” Cold Pool (deep blue) ….temperature (oC) minimum located. UMass Dartmouth 2013 Glider Palooza “Triangle” ~120m |-------------- 1 kilometer --------------| HOW DO OCEAN GLIDERS WORK? Ocean gliders sink and “glide” downward from the sea surface – when its computer triggers a piston that draws in some seawater and therefore extra weight. Near the bottom, a reverse action causes the glider to rise and “glide” upward towards the surface. As the glider saw-tooths its way through the ocean it measures ocean properties (e.g., temperature) . Every few hours, the glider pauses at the surface and transmits its data via satellite back to the laboratory – thus providing us with a near real-time picture of the internal structure of the ocean. Northern Zig-Zag Glider Trajectory : Early Fall 2007 (Leg-1 highlighted) Early Fall 2007 Leg-1 glider slice through the “aging” Cold Pool ….note 3oC CP warming Acknowledgements: These glider operations are supported in part by NOAA’s Integrated Ocean Observing System Pgm. and Office of Naval Research