Physical and biogeochemical variability from hours to years at the BermudaTestbed Mooring site: June 1994-March 1998

The Bermuda Testbed Mooring (BTM), initiated in 1994, provides important in formation concerning periodic and episodic processes. The BTM enables colle ction of virtually continuous data during periods of inclement weather when traditional sampling is not possible, and provides otherwise inaccessible data in the important spectral range of minutes to a month. New methodologi es and analyses are evolving for interdisciplinary mooring measurements. Fo r example, BTM and shipboard temperature and spectral downwelling irradianc e data sets have been compared and are in good agreement. Several meteorolo gical parameters determined using operational analyses and climatological e stimates also compare favorably with BTM calculations. Kinetic energy (by frequency domain), de-correlation time scales, and spect ra were computed using the BTM data sets. The ratio of kinetic energy attri buted to periods less than 2 days to that in periods greater than 2 days is generally greater at 45 m than at 71 m (the winter season being the except ion). The upper layer has more kinetic energy due to inertial motions, whil e the lower layer is more influenced by mesoscale eddies. It is inferred th at important interactions occur between these layers. It is hypothesized th at the specific timing of the onset of spring stratification and fall break down of stratification, as well as accompanying phytoplankton blooms, are c ontrolled by the specific synoptic wind forcing and mesoscale eddy conditio ns. An example of this scenario is described using unique BTM observations of a fall bloom event. Specifically, (1) a mode eddy with a shallow (roughl y 80 m) nutricline passed the site, (2) deepening of the mixed layer (from about 50-175 m) caused entrainment of nutrients into the euphotic layer, an d (3) a three-fold increase in depth-integrated chlorophyll was observed. F inally, de-correlation time scales were found to lie between 5 and 15 days for the key physical and biological variables. These de-correlation scales set upper limits on sampling intervals necessary to resolve the important p hysical and biogeochemical processes. (C) 2001 Elsevier Science Ltd. All ri ghts reserved.