Search

We present the design and preliminary results from ocean deployments of Zooglider, a new autonomous zooplankton-sensing glider. Zooglider is a modified Spray glider that includes a low-power camera (Zoocam) with telecentric lens and a custom dual frequency Zonar (200 and 1000 kHz). The Zoocam quantifies zooplankton and marine snow as they flow through a defined volume inside a sampling tunnel. Images are acquired on average every 5 cm from a maximum operating depth of ~ 400 m to the sea surface. Biofouling is mitigated using a dual approach: an ultraviolet light-emitting diode and a mechanical wiper. The Zonar permits differentiation of large and small acoustic backscatterers in larger volumes than can be sampled optically. Other sensors include a pumped conductivity, temperature, and depth unit and chlorophyll a fluorometer. Zooglider enables fully autonomous in situ measurements of mesozooplankton distributions, together with the three-dimensional orientation of organisms and marine snow in relation to other biotic and physical properties of the ocean water column. It is well suited to resolve thin layers and microscale ocean patchiness. Battery capacity supports 50 d of operations. Zooglider includes two-way communications via Iridium, permitting near-real–time transmission of data from each dive profile, as well as interactive instrument control from remote locations for adaptive sampling.

Since 2005, Spray underwater gliders have been used to sample sections across the southern California Current System (CCS). Properties measured are depth-averaged velocity and profiles of temperature, salinity, Acoustic Doppler Profiler shear, chlorophyll a fluorescence, and 750-kHz acoustic backscatter. Although slow and carrying a relatively small sensor suite, gliders observed multiple 350-700-km sections that reveal details of known elements of the CCS circulation like the California Current and Undercurrent as well as a previously undescribed undercurrent 100-200 km offshore. The long time series with high spatial resolution disclose the close link between fronts in physical and biological variables, both the main pycnocline front and secondary weaker but sharp fronts farther offshore. These fronts appear to organize chlorophyll and acoustic backscatter fields, particularly during spring. Much of the patchiness of chlorophyll is associated with vertical displacements of fields that are much smoother within potential density surfaces. The horizontal structure of both chlorophyll and spice (the dynamically passive variable formed from temperature and salinity) appear to be formed by mesoscale stirring. © 2008, by the American Society of Limnology and Oceanography, Inc.

The multi-year mean, mid-depth circulation of the subpolar North Atlantic Ocean from direct velocity measurements obtained over a 7.5-year period by 211 neutrally-buoyant, profiling, subsurface floats is estimated. A statistical analysis of these velocity data is presented and features of the circulation from 400-1500m dept as measured by the floats is described.

The analysis of interdecadal physical and biological variability is made challenging by the relative shortness of available time series. It is showed that a composite analysis of climatic records recently used to identify regime shifts which is likely to find them in Gaussian, red noise with stationary statistics.

Estimates of time-averaged velocity in the North Atlantic Ocean are presented using wind, hydrographic, and bottom-topography data. Hyperbolic dynamics are reviewed with emphasis on determining a numerical model. Results are compared with those obtained using other methods. Values for time-averaged velocity are affected by errors in density and variations in the free mode.

A composite analysis is examined of time series that proposed to identify regime shifts and using time series with stationery statistics and plausible frequency content, it demonstrated that the composite analysis had an uncomfortably high rate of false positives. It did not conclude whether or not true regimes exist, or physical and biological process is coupled.