Null broadening with snapshot-deficient covariance matrices in passive sonar

Adaptive-array beamforming achieves high resolution and sidelobe suppression by producing sharp s in the adaptive beampattern. Large-aperture sonar arrays with many elements have small resolution cells; interferers may move through many resolution cells in the time required for accumulating a full-rank sample covariance matrix. This leads to "snapshot-deficient" processing. In this paper, the -broadening technique originally developed for an ideal stationary problem is extended to the snapshot-deficient problem combined with white-noise constraint (WNC) adaptive processing. Null broadening allows the strong interferers to move through resolution cells and increases the number of degrees of freedom, thereby improving the detection of weak stationary signals.     

Inter-annual variability in larval supply to populations of three invertebrate taxa in the northern California Current

We investigated sources of inter-annual variability in larval supply to crab and sea urchin populations at Bodega Head and Point Reyes in northern California. During the spring and summer upwelling seasons of the years 1992 through 1997 we monitored the weekly settlement rates of nine species of crabs and two species of sea urchins. As observed in previous studies, daily values of alongshore windstress, temperature and salinity provided evidence for the poleward flow of relatively warm, low salinity water from south of Point Reyes, an apparent retention zone, during upwelling relaxation events. In years dominated by these events (1992, 1993, 1995 and 1996) we observed that alongshore windstress, temperature and salinity were coherent and temperature was significantly correlated with cancrid crab settlement. During these years the magnitude of cancrid crab settlement and the fraction of cancrid crabs relative to other crab species settling were high. Over four years of concurrent sampling there was consistently greater cancrid crab settlement at the Point Reyes site, within the retention zone, than at Bodega Head. Settlement of non-cancrid crabs (porcellanids, grapsids, pagurids and majids) was not as closely linked to intra-annual patterns of upwelling and relaxation, possibly due to the shorter seasonal availability of larvae allowing for the influence of fewer relaxation events. Settlement of this group among years was positively correlated with environmental indicators of strong seasonal upwelling; high salinity, Bakun upwelling index and low temperature. Sea urchin settlement events were observed in June and July of 1992, 1994 and 1997 during warming periods when salinity and temperature were increasing and alongshore windstress was low. Across the six years of the study, we found that cancrid crab larvae had a more even seasonal availability than larvae of non-cancrid species, which settled in greatest numbers during the early portion of the upwelling season. Sea urchins settled in greatest numbers during the later part of the upwelling season. Together these patterns demonstrate the taxon-specific way that inter-annual variability in larval supply is forced by the coincidence of larval availability with favorable physical transport mechanisms.     

An ecosystem model with iron limitation of primary production in the equatorial Pacific at 140°W

We construct a one-dimensional ecosystem model (nitrate, ammonium, phytoplankton, zooplnakton and detritus) with simple physics and biology in order to focus on the structural relations and intrinsic properties of the food web that characterizes the biological regime in the central equatorial Pacific at 140°W. When possible, data collected during the EgPac and other cruises were used to calibrate model parameters for two simulations that differ in the limiting nutrient, i.e. nitrogen or iron. Both simulations show annual results in good agreement with the data, but phytoplankton biomass and primary production show a more pronounced annual variability when iron is used as the limiting nutrient. This more realistically reproduces the variability of biological production and illustrates the greater coupling between vertical physical processes and biological production when the limiting nutrient is iron rather than nitrogen. The iron simulation also illustrates how iron supply controls primary production variability, how grazingbalances primary production and controls phytoplankton biomass, and how both iron supply and grazingcontrol primary production. These results suggest that it is not possible to capture primary production variability in the central equatorial Pacific with biological models using nitrogen as the limiting nutrient. Other indirect results of this modeling study were: (1) partitioning of export production between dissolved and particulate matter is almost equal, suggesting that the importance of DOC export may have been previously overestimated; (2) lateral export of live biomass has to be taken into account in order to balance the nitrogen budget on the equator at 140°W; and (3) preferential uptake of ammonium (i.e. nitrate uptake inhibition by ammonium) associated with high regeneration of nitrogen (low f ratio as a consequence of the food web structure imposed by iron limitation) largely accounts for the surface build-up of upwelled nitrate.     

Cd, Pb, Cu, Ni and Co distribution in the German Bight

Cd, Pb and Cu concentrations, dissolved and total, have been determined in the German Bight. In 1975, 1977, 1978, 1980 and 1983 water samples were collected at 215 sampling stations. In the 1983 mission samples were also analysed for Ni and Co. The samples were filtered and acidified immediately after collection. Analysis was performed by voltammetry.The analytical data indicate that a net portion of the Cd, the Weser being a distinct source for it, will cross the estuarine zone. Open sea Cd levels in the German Bight are about a factor 10 higher than North Atlantic values. Pb, being transported mainly with the suspended particulate phase (up to 99.5%), is better eliminated by sedimentation in the estuaries. Ni and Cu occur mainly in the dissolved phase. Pollution by Co is distinct in the Elbe, but the output is rapidly diluted to background contents below 10 ng kg⁻¹. An interpretation of the results from the different years yields a rather steady state situation in the German Bight.     

Chemical oceanography, vol. 8: Edited by J.P. Riley and R. Chester. Academic Press, London, 1983, xvi + 398 pp., £45.00/US $75.00 (hardcover)

Representative profiles of inorganic nitrogenous species dissolved in interstitial waters of coral reef sands are presented. Ammonium is the dominant nitrogenous species in these pore waters with concentrations of up to 40 μm. Nitrate is present but in lower concentrations. Nitrite is found only occasionally in trace amounts. Computations of diffusive fluxes and inferences concerning microbial activity are derived from the profile structures. Computed flux rates of nitrogenous species from the sediment to the water column range between 0.75 and 1.37 μM m^?1 h^?1. These inputs may represent a significant source of recycled nitrogen to the primary producers of the coral reef ecosystem.     

A community-wide intercomparison exercise for the determination of dissolved iron in seawater

The first large-scale international intercomparison of analytical methods for the determination of dissolved iron in seawater was carried out between October 2000 and December 2002. The exercise was conducted as a rigorously “blind” comparison of 7 analytical techniques by 24 international laboratories. The comparison was based on a large volume (700 L), filtered surface seawater sample collected from the South Atlantic Ocean (the “IRONAGES” sample), which was acidified, mixed and bottled at sea. Two 1-L sample bottles were sent to each participant. Integrity and blindness were achieved by having the experiment designed and carried out by a small team, and overseen by an independent data manager. Storage, homogeneity and time-series stability experiments conducted over 2.5 years showed that inter-bottle variability of the IRONAGES sample was good (< 7%), although there was a decrease in iron concentration in the bottles over time (0.8–0.5 nM) before a stable value was observed. This raises questions over the suitability of sample acidification and storage.