David W. Menzel

A method for the determination of phytoplankton chlorophyll and phaeophytin by fluorescence

Abstract The concentration of chlorophyll, principally chlorophyll a , and after acidification phaeophytin, is measured in 85% acetone extracts using a sensitive fluorometer. The method is very sensitive in the 10 fluorescence units are equal to 0·001 O.D. 665 mμ 10 cm . The maximum variation is 15%. The method is highly suitable for routine analysis at sea or in the laboratory.

The annual cycle of primary production in the Sargasso Sea off Bermuda

Abstract Gross and net primary production have been measured at bi-weekly intervals for 18 months in the North-western Sargasso Sea 15 miles SE. of Bermuda in 1500 fm of water. Ancillary data include temperature, salinity, phosphate, nitrite, nitrate, disolved oxygen, plant pigments, light penetration and incident radiation. A seasonal cycle of production was observed with high levels in the winter and early spring, low levels in the later spring, summer and early fall. Gross production ranged from 0·13 to 2·00, averaging 0·44 g carbon assimilated/m2/day or 160 g C/m2/year. Net production ranged from 0·05 to 0·83 and averaged 0·20 g C/m2/day or 72 g C/m2/year. Production was closely dependent upon vertical mixing, high levels occuring when the water was isothermal and mixed to or near the depth of the permanent thermocline (400 m), low levels being associated with the presence of a seasonal thermocline in the upper 100 m. Nutrient concentrations were extremely low (maxima of 1·8 μgAN/L and 0·16 μg AP/L as inorganic compounds in the upper 100 m) and showed little seasonal variability. Mixing and enrichment from the permanent thermocline is negligible, production being largely dependent upon the rapid re-cycling of nutrients within the upper 400 m. The environmental factors controlling production which make this region differ from temperate or boreal waters, and which permit high production throughout the winter are: (1) low nutrient concentrations, (2) clear water, (3) relatively high incident radiation in winter, (4) a shallow winter mixed layer and (5) a rapid re-cycling of nutrients, possibly due to higher temperatures.

Sea surface chemistry and Langmuir circulation

Abstract When air was bubbled through filtered sea water organic particles were found in the spray droplets from bursting bubbles as well as in the bubbling chamber. These particles aggregated if left undisturbed. A suspension of particles had a high phosphorus content. Addition of these particles to filtered sea water decreased the apparent inorganic phosphate content of the sea water. The particle suspension exhibited a high degree of surface activity. We believe that wave-induced bubbles and surface circulation may constitute important mechanisms for production of organic particles in the ocean.

Marine Phytoplankton Vary in Their Response to Chlorinated Hydrocarbons

Photosynthesis and growth in cultures of four marine phytoplankton species, isolated from different oceanic environments, were affected by three chlorinated hydrocarbons (DDT, dieldrin, and endrin) to varying extents. This ranged from complete insensitivity in Dunaliella to toxicity at concentrations of 0.1 to 1.0 part per billion of the pesticides in Cyclotella. Other forms were intermediate in their response.

Organic carbon and the oxygen minimum in the South Atlantic Ocean

Abstract The relationship between organic matter and the oxygen minimum layer was studied in the southwest Atlantic. Data presented support the premise that the oxygen content of the Antartic Intermediate Water between, 36°S and 10°S, is independent of in situ decomposition of dissolved organic and particulate carbon. Oxygen concentrations were predicted by consideration of changes in salinity alone. It is concluded that the concentration of oxygen and organic carbon is controlled by the mixing of opposing water masses, at depths in excess of several hundred meters.

Particulate organic carbon in the deep sea

Abstract Data showing the distribution of particulate and dissolved organic carbon in the tropical Pacific and Atlantic Oceans are given and support the following conclusions : (1) surface standing crop has no measurable influence on the concentration of organic particles occurring at depth; (2) below a given distance of the surface, the distribution of these particles is homogeneous in time, space, and depth; (3) there is no consistent decrease in dissolved organic carbon with depth. Alternate theories to explain the observed pattern of particle distribution in the deep-sea are discussed.

The effects of enriching Sargasso sea water on the production and species composition of the phytoplankton

Abstract The technique of artificial enrichment of sea water has been used in an attempt to define nutrients critically limiting the growth of phytoplankton in the Sargasso Sea. It is shown that final population growth achieved with different enrichment is a function of time. In 3-day experiments, iron appeared essential while in 7-day experiments nitrogen and phosphorus alone produced large populations. It is postulated that the influence of iron may be catalytic since enrichment with aluminium produced identical growth curves. In addition the final population resulting from enrichment in terms of species composition was shown to be a function of the addition of specific nutrients.

The distribution of dissolved organic carbon in the Western Indian Ocean

Abstract The concentration of dissolved organic carbon between 0 and 2000 m depth was measured along a section from 20°S to 20°N in the Western Indian Ocean. No apparent correlation existed between primary production and the level of dissolved carbon in the euphotic zone. Deep water masses were characterized by temperature-salinity relationships and by the concentration of carbon. Calculations for the mixing of these water masses of differing origin on the basis of salinity, corresponded with similar calculations based on carbon. Assuming 90% conversion of total particulate organic matter to carbon dioxide by grazing organisms a minimum of 260 years is required to produce the amount of organic carbon present in the Arabian Sea. The conclusion is reached that carbon in solution and in particulate form in the ocean is extremely stable and subject to limited change by biological action.

The role of in situ decomposition of organic matter on the concentration of non-conservative properties in the sea

Abstract The concentration of organic matter in the ocean is examined in relation to the effect of its decomposition on the distribution of associated non-conservative properties of oxygen, nitrate, and phosphate. Current evidence illustrates the seemingly random distribution of dissolved carbon on an ocean wide scale within the relatively narrow limits of ± 0·2 mg C/1. below a depth of 400 m. Plots of associated indices of organic decomposition (oxygen, phosphate, and nitrate) against salinity suggest that these parameters, within unknown time scales, are quasiconservative. If modified by the activity of living organisms, their distribution can only be explained by unvarying metabolic activity at depth.

The nutrient chemistry of the sea surface

Abstract The concentrations of dissolved organic carbon, phosphate, ammonia, and nitrite are statistically higher at the sea surface than at 1 m. Silicate shows no significant difference at the 0·05 probability level in these two water strata. The possible mechanisms causing the accumulation of these nutrients at the sea surface are discussed.