An Evaluation of the Consequences of Persistent Small-Scale Biological Structure on Upper Ocean Trophic Processes

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Observations with recently developed microstructure instrumentation indicate that what had previously been described as small scale biological patchiness may not be due to stochastic fluctuations in biological structure, but may be undersampled observations of persistent, small scale structure. Persistent, sub 1-meter structure in the upper ocean poses serious problems for the interpretation of data from finescale and mesoscale observational programs. It is likely that such sampling programs are underestimating the in situ rate processes associated with sub 1-meter structure, as well as the abundance and distributional patterns of biological and chemical properties. The common occurrence of thin layers and the temporal/spatial coherence of these layers compel us to evaluate their role in upper ocean processes. Therefore, the overall objectives of this project are to evaluate the contribution of these sub-1-meter features to upper ocean trophic dynamics through direct measurements of nutrient concentration, particulate matter, autotrophic production, and heterotrophic processes, and to undertake a detailed study of the occurrence, persistence, and composition of thin biological layers in the ocean. In addition, our unique high resolution biological and physical sampling system will permit us to investigate the mechanisms of layer formation, persistence and erasure. We will determine the distribution and temporal coherence of thin layers of plankton biomass within the euphoric zone over extended time periods and characterize the composition of biological thin layers using bio optical and bio acoustical sensors as well as via discrete sampling of individual thin layers. We will also assess autotrophic and heterotrophic rate processes inside and outside of persistent small scale features and map the areal extent of coherent thin layers. We will also quantify the association of thin layers with local physical processes, specifically stratification, small scale shear, and turbulent mixing, as well as the large scale velocity field and the frequency and amplitude of internal waves. Finally, we will investigate the association of thin layers with local surface forcing conditions and evaluate the contribution of biological rates occurring within layers to total water column processes. This data set will provide a unique opportunity to evaluate, quantitatively, the role of persistent small scale structure in oceanic planktonic food webs. Without a clear evaluation of these processes, estimates of biological rates obtained with conventional sampling approaches will be biased. +n ±i ╝n ¼f S u m m a r y I n f o r m a t i o n ( ++++++++++++ 8 Û ++++++++++++ ++++++++++++ ++++++++++++ + _ Ûª▓ ÑOh ª' +'ª▒0 Ý + Õ $ H l + ¢ ╗ D h + R:\WWUSER\TEMPLATE\NORMAL.DOT =l James William Ammerman Joanne MCcreary @ =-vÞ ▀ @ -+Y+ª) @ dP¹ ▀ } } @ ¶+ª Microsoft Word 6.0 10 Õªe =- e P ┐ P f f f f f f p f ÷ 1 z z z z z z z z ( = = f T s ; ÷ z z z z z ÷ z z z z z z z z z P X z z + z