Diel variation of TCO2 in the upper layer of oceanic waters reflects microbial composition,variation and possibly methane cycling

Six diel TCO₂ cycles determined by infrared (IR) photometry from five drift stations occupied between 24 February and 16 March 1979 in the mixed layer of the northwestern Caribbean Sea are examined. Comparison of TCO₂ variation with coincident salinity and O₂ variation demonstrated that TCO₂ often co-varied with these independently measured variables. During five diel cycles TCO₂ variation was characterized by nocturnal production and diurnal consumption. The inverse, diurnal production of CO₂, occurred downstream from Misteriosa Bank, whose corals apparently contributed to a water mass having a twofold increase of POC and a sixfold larger population of heterotrophic nanoplankters. For the five diel studies carried out in waters with balanced or nearly blanced heterotrophic and phototrophic components of the nanoplankton, CO₂ consumption at constant salinity always occurred between 06.00 and 09.00 hrs. Net uptake often continued through 15.00 hrs, but not always in the absence of significant salinity changes. At constant salinity net O₂ evolution never exceeded 0.5 mol l^-1 h^-1 while net CO₂ uptake consistently averaged 3 mol l^-1 h^-1 for an apparent net production of 36 mg C m^-3 h^-1, which greatly exceeds the O₂ changes and open ocean ¹⁴C estimates from the literature. Diurnal consumption was apparently balanced by nocturnal production of CO₂ so that no significant net daily change in TCO₂ was observed. Departures from theoretical PQ and RQ and the possibility of nocturnal variations in formaldehyde and carbonate alkalinity imply that chemotrophs, both methane producers and methane oxidizers, play a significant role in CO₂ cycling. This could be through the metabolism of the nonconservative gases CH₄, CO, and H₂, and a link between chemotrophy and phototrophy through these gases is hypothesized. These open system measurements were subject to diffusion and documentable patchiness, but temporal TCO₂ changes appear to indicate the net direction of microbiological activity and join a growing body of literature showing dynamic variation in CO₂ and O₂ that exceeds estimates by ¹⁴C bottle assays of carbon fixation.     

Vertical distribution and feeding patterns of midwater fish in the central equatorial Atlantic II. Sternoptychidae

The vertical distribution of seven sternoptychid species was examined from RMT 1+8 samples collected aboard R. V. Meteor in March-April 1979 and from Royal Research Ship R.R.S. Discovery in July 1974 in the central equatorial Atlantic. During daytime sternoptychids occupied depths between 200 and 1250 m, with Sternoptyx pseudobscura living deepest, centering between 800 and 900 m, and Argyropelecus sladeni most shallow, aggregating predominantly at 300 and 400 m. They are all considered limited or partial migrants, ascending only some 100 and 200 m towards the surface at night. Only A. sladeni was observed to enter the epipelagic zone (0 and 200 m).-Feeding patterns were investigated from stomach content analyses of Sternoptyx diaphana, S. pseudobscura, Argyropelecus sladeni and A. affinis. Additional stomach contents were analysed from samples of S. diaphana, A. hemigymnus and A. olfersi collected in June 1985 from F.R.V. Walther Herwig in the temperate NE Atlantic at 46°N, 17°W by means of the Engel Trawl. The food spectrum of the six species is generally described, and additional dietary evidence regarding calanoid copepod prey is provided for four of these taxa. All sternoptychid species investigated were planktivorous, feeding predominantly on copepods and ostracods, except for the largest size class, which preyed heavily on euphausiids and amphipods. The relationship of predator size towards prey type and prey size is analysed for both Sternoptyx species. Of these, S. pseudobscura in particular exhibits taxonomic selectivity towards polychaete prey. The diet of both species of Sternoptyx included a number of epipelagic or even neustonic calanoid copepod species which contributed more than 50% of the total copepod population by numbers. So far it is not known how the predators find access to prey organisms of the upper 200 m, as netfeeding is considered unlikely. Cyclopoid copepods of the genus Sapphirina were observed as dietary component particular of S. diaphana.     

Determining the carbon-to-chlorophyll ratio of natural phytoplankton

For field samples, regression analyses of plots of chemically determined particulate organic carbon on chlorophyll are often employed to estimate the algal carbon-to-chlorophyll ratio (F) in the presence of appreciable amounts of nonalgal particulate organic carbon. Spurious results will be obtained, however, if the temporal rate of change of the algae or the nonplant matter reverses its sign during the sampling interval and the samples cannot be ordered correctly in time or space. Previously recognized sources of bias inherent in the chemical approach are also discussed. The great uncertainty of our present knowledge of F is pointed out. It is shown that the concentration of microscopically visible, nonliving particles in the sea isnot known. Renewed studies are suggested as a means of improving on the chemical approach to determining F. The general argument holds for the ratios of nitrogen (particle volume, etc.)-to-chlorophyll, carbon (nitrogen, particle volume, etc.)-to-ATP, and similar conversion factors.Contribution No. 932 from the Department of Oceanography, University of Washington, Seattle, Washington 98195, USA. The article is a revised and expanded version of a paper contributed at the Joint Oceanographic Assembly, September 1976, at Edinburgh, Scotland, UK.     

A ten-year study of chlorinated hydrocarbon insecticide residues in bovine milk in Illinois, 1972 - 1981

Milk supplies in Illinois were monitored for chlorinated hydrocarbon insecticide residues from 1972 through 1981. The percentage of milk samples that were contaminated with aldrin/dieldrin, DDT and its analogs, and BHC/lindane decreased during the 10-year sampling period. The percentage of samples contaminated with aldrin/dieldrin decreased from 98.7% in 1978 to 5.9% in 1981. The amount of aldrin/dieldrin residues found in contaminated samples also decreased from an average of 0.077 ppm (1972-79) to 0.001 ppm in 1980-81. The levels of chlordane and heptachlor/heptachlor epoxide residues in milk did not decrease, but residues of BHC and DDT decreased gradually over the 10-year period. The percentage of samples that had less than 0.1 ppm of all chlorinated hydrocarbon residues combined ranged from 10.6% to 25.7% during 1972 through 1978 and increased to 36.2% in 1979, 71.1% in 1980, and 61.4% in 1981.