Freezing as a method of sample preservation for the analysis of dissolved inorganic nutrients in seawater

It is often desirable or necessary to store collected seawater samples prior to analysis for dissolved inorganic nutrients. It is therefore important to establish preservation and storage techniques that will ensure sample integrity and will not alter the precision or accuracy of analysis. We have performed a series of experiments on the storage of nutrient samples collected at the oligotrophic North Pacific benchmark Station ALOHA, using both standard autoanalyses and low-level techniques. Our results reveal that for oligotrophic oceanic waters, the immediate freezing of an unfiltered water sample in a clean polyethylene bottle is a suitable preservation method. This procedure is simple, it avoids potentially contaminating sample manipulations and chemical additions, and it adequately preserves the concentrations of nitrate + nitrite, soluble reactive phosphate, and soluble reactive silicate within a single water sample.     

Numerical comparisons of the damping of internal gravity waves in stratified fluids

Summary Comparisons are made of the attenuation of progressive internal waves in stratified fluids consisting of (a) a representation of a single thermocline, (b) a weak exponential density distribution and (c) a two-layer system. Effects of the earth's rotation are neglected, as also are heat and salt diffusion. Significant differences are found in the decay characteristics of the three density structures. Internal waves are most strongly damped in the layered system (c) whilst the calculated attenuation rates are least for the thermoclinic structure (a). All the internal modes investigated are, however, shown to be more strongly damped than the associated surface wave.     

The viscous damping of internal waves on the rotating earth

Summary A formula is derived for the spatial attenuation of the two possible modes of oscilation of a two-layer, rotating system. If the long-wave approximation is made, it is found with reference to the internal mode that this formula disagrees with an earlier result obtained byRattray [8]²).     

Damping characteristics of gravity waves obliquely incident on a monomolecular film: Part I

Viscous damping characteristics of long-crested gravity waves, propagating obliquely through a long monomolecular film of finite width, are considered for physical situations in which the wind is absent. The methods employed in the investigation are based on boundary-layer techniques, and formulae are derived for the local spatially-dependent decay coefficient and amplitude-function due to propagation of deep-water waves across extensible films. In II, such formulae are illustrated graphically to demonstrate the influence of angle of incidence, film edges, and surfactant properties, and some reference is made in relation to practically realisable values of the surface elasticity .     

Book reviews

Pure and Applied Geophysics -     

On progressive internal waves in non-uniform depths

Summary An expansion technique is used to investigate effects of finite amplitude on three-dimensional progressive internal waves in continuously stratified fluid of variable depth. The results are illustrated for the case of uniform density gradients. Reflection is neglected in the perturbation scheme. In two dimensions, damping of long progressive waves is considered through energy dissipation in the bottom boundary layer.     

Evolution of boundary‐layer aerosol particles due to in‐cloud chemical reactions during the 2nd Lagrangian experiment of ACE‐2

The second Aerosol Characterisation Experiment (ACE‐2) was aimed at investigating the physical, chemical and radiative properties of aerosol and their evolution in the North Atlantic region. In the 2nd "Lagrangian" experiment, an air mass was tracked over a 30‐h period during conditions of extensive stratocumulus cover. Boundary‐layer measurements of the aerosol size distribution obtained with a passive cavity aerosol spectrometer probe (PCASP) during the experiment show a gradual growth in size of particles in the 0.1–0.2 μm diameter mode. Simultaneously, SO₂ concentrations were found to decrease sharply from 800 to 20 ppt. The fraction of sulphate in aerosol ionic mass increased from 0.68±0.07 to 0.82±0.09 for small particles (diameter below 1.7 μm) and from 0.21±0.04 to 0.34±0.03 for large particles (diameter above 1.7 μm). The measurements were compared with a multicyclic parcel model of gas phase diffusion into cloud droplets and aqueous phase chemical reactions. The model was able to broadly reproduce the observed transformation in the aerosol spectra and the timescale for the transformation of SO₂ to sulphate aerosol. The modelled SO₂ concentration in the boundary layer fell to below half its initial value over a 6.5‐h time period due to a combination of the entrainment of cleaner tropospheric air and cloud chemical reactions. NH₃ and HCl gas were also found to play an important rôle in cloud processing in the model.