The yield of organic C or total organic matter from a standard carbonate-free marine sediment containing 23 .04% N-acetyl glucosamine (io% organic C) was determined using i) a CHN analyzer on untreated sediment, 2) CHN analysis of acidified and filtered sediment, 3) CHN analysis of acidified centrifuged sediment, 4) wet oxidation by the Walkley and Black method, and 5) loss on ignition at 475-500°C . ioo% of the organic C added was recovered by CHN analysis of untreated sediment, but after treatment with acid (necessary to remove carbonates from most sediments) only o.19% and 1 .32% of the C added could be recovered . Wet oxidation yielded only 76 .6% organic C . Loss on weight after combustion in a muffle furnace yielded ioo% of the total organic matter. It is very difficult to avoid carbonate interference if simple techniques of analysis are used . For most work by marine ecologists organic carbon and nitrogen may be measured by a combination of CHN analysis and loss of weight on ignition of sediments freed of organic matter by precombustion below 5oo°C .

Stations in a survey of benthic invertebrates on the Canadian continental shelf and slope of southeastern Baffin Island, in Ungava Bay, and on the northern Labrador Shelf, fell into definite groups as a result of an objective analysis of similarity in species composition. The groupings were shown to correspond to major water masses in the area. Groups corresponding to cold surface water masses, to the deep Irminger Atlantic water mass, and to mixtures of these with adjacent water masses were observed. The Irminger Atlantic group dominated on the Baffin Island continental shelf. Species diversity, also measured in the study, was high, with large numbers of species present in low abundance.

Benthic macroinvertebrate standing crop at 14 stations on the Canadian continental shelf, southeast of Baffin Island, ranged from 19.8 to 479.9 g/m2 and was about the same size for given depths, as reported for the Grand Banks of Newfoundland, and higher than reported in more southerly portions of the eastern North American continental shelf. Standing crop was correlated negatively with depth and sediment content of both fine and medium sand.

No abstract

Extremely dense, localized concentrations of Turton's wedge clam Mesodesma deauratum (Turton) were found in quantitative grab samples on poorly sorted, medium to fine, low organic content sands (total organic carbon < 0.05%) at depths of 44–51 m at a single location on eastern Southeast Shoal of the Grand Banks of Newfoundland. Mean densities ranged from 24 to 5890 individuals∙m−2 and wet weight standing crop from 0 to 21.4 kg∙m−2. A peak standing crop of 69.4 kg∙m−2 was observed in one grab. There was a strong bimodal size distribution (17–27 and 34–56 mm shell length) at the site, but the two size groups never occurred together. Based on external growth checks, the smaller individuals were 4–5 yr old and the larger ones 10 to more than 15 yr. This population is suggested to be a relict of shallow littoral populations which probably existed in the area in the late Wisconsinan glacial period.