HR: 14:25h
AN: OS53B-04 INVITED     [Abstracts]
TI: The Formation and Maintenance of Finescale Planktonic Structure in the Upper Ocean: Evaluating the Balance Between Vertical and Horizontal Processes
AU: * Cowles, T J
EM: tjc@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg, Corvallis, OR 97331-5503 United States
AU: Dale, A
EM: acd@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg, Corvallis, OR 97331-5503 United States
AU: Wijesekera, H
EM: hemantha@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg, Corvallis, OR 97331-5503 United States
AU: Boyd, T
EM: tboyd@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg, Corvallis, OR 97331-5503 United States
AU: Pegau, S
EM: pegau@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg, Corvallis, OR 97331-5503 United States
AU: Kosro, P M
EM: kosro@coas.oregonstate.edu
AF: Oregon State University, College of Oceanic and Atmospheric Sciences, 104 COAS Admin Bldg, Corvallis, OR 97331-5503 United States
AB: Numerous finescale (1 m to 3 m) and microscale (0.01 m to 1 m) observations of the vertical structure of plankton have revealed local maxima of phytoplankton and zooplankton within narrow layers (0.5 to 2 m thick). These layers have been observed to persist over ecologically relevant time intervals (hrs to days), while extending many kilometers in the horizontal dimension. What are the limits on the physical and biological processes that permit planktonic layers to persist on these temporal and spatial scales? This presentation will examine the formation and maintenance of planktonic layers through an evaluation of the interplay between intermittent small-scale vertical mixing and vertical gradients in horizontal advection. The analysis will focus on observations made over the Oregon continental shelf, where planktonic thin layers have been documented with four different systems: 1) a free-fall profiling system that provided centimeter-scale resolution of hydrographic properties, bio-optical properties, and vertical shear; 2) a undulating towed system (MiniBat) that provided 0.25m resolution of hydrographic and bio-optical properties; 3) a Bluefin AUV that provided vertical shear, hydrographic and bio-optical properties along a 15-20km track while undulating across a thin planktonic layer; 4) vertical shear and acoustic backscatter from a moored 500 KHz ADP. Data from all systems suggest that steep concentration gradients at the boundaries of planktonic layers correspond to local maxima in vertical shear within vertical intervals of local stratification. Although intermittent vertical mixing processes may erase steep vertical gradients in planktonic structure, it appears that the formation and maintenance of vertical structure of phytoplanktonic distributions, and their horizontal extent, are strongly influenced by advection and velocity shear.
DE: 4815 Ecosystems, structure and dynamics
DE: 4855 Plankton
DE: 4524 Fine structure and microstructure
DE: 4568 Turbulence, diffusion, and mixing processes
SC: Ocean Sciences [OS]
MN: 2004 AGU Fall Meeting