Four seasonal cruises were conducted on a 270-km-long transect normal to the coast of Nova Scotia. Most biological variables measured along this transect show maximum values in the outer 90 km. These maxima usually occur closely associated with an oceanic front which is a consistent feature of this region. Enhanced vertical transport of nutrients is postulated to occur along this front, although the mechanism is unknown. A model proposed several years ago to explain shelf enrichment off the northeastern United States was examined and found to be consistent with the Scotian Shelf data. Sporadic advection of nutrient-rich Slope Water onto the shelf at the average rate of 0.33 cm∙s−1 would, upon entering the euphotic zone, satisfy 20% of phytoplankton nutrient requirements during the spring and summer. Recycling would account for the remaining 80%. Key words: phytoplankton, zooplankton, enrichment, Scotian Shelf, excretion, fronts, nutrients, productivity, advection, recycling

Blooms of the toxic dinoflagellate Karenia brevis are common in the Gulf of Mexico, yet no in situ studies of zooplankton and K. brevis have been conducted there. Zooplankton abundance and taxonomic composition at non-bloom and K. brevis bloom stations within the Ecology of Harmful Algal Blooms (ECOHAB) study area were compared. At non-bloom stations, the most abundant species of zooplankton were Parvocalanus crassirostris, Oithona colcarva, and Paracalanus quasimodo at the 5-m isobath and P. quasimodo, O. colcarva, and Oikopleura dioica at the 25-m isobath. There was considerable overlap in dominance of zooplankton species between the 5 and 25-m isobaths, with nine species contributing to 90% of abundance at both isobaths. At stations within K. brevis blooms however, Acartia tonsa, Centropages velificatus, Temora turbinata, Evadne tergestina, O. colcarva, O. dioica, and P. crassirostris were dominant. Variations in abundance between non-bloom and bloom assemblages were evident, including the reduction in abundance of three key species within K. brevis blooms.

The Cariaco Basin, off the northeast coast of Venezuela, has long been the center of attention of scientists trying to explain paleoclimate. This peculiar anoxic basin records climate change over several dozen millennia within layers of sediment [ Black eta ., 1999]. A joint U.S.‐Venezuelan research effort launched in 1995—the Carbon Retention in a Colored Ocean (CARIACO) Program— provides a link between the sediment record and processes near the surface of the ocean for this basin. Sediment traps maintained by the program show that over 5% of the organic carbon contained in particles formed near the surface through primary production (photosynthesis) by phytoplankton reaches 275 m depth, and nearly 2% reaches 1,400 m.This flux is significant, because it represents a sink for carbon dioxide, which is a greenhouse gas, and because it helps explain the record of ancient climate stored at the bottom of the Cariaco Basin.

Earthquakes are commonly cited as one possible triggering mechanism for turbidity flows—dense sediment–water plumes that can transport large volumes of sediment great distances down slope—in both marine and lacustrine settings1,2,3,4,5,6. Heezen and Ewing1 were the first to make such a suggestion, attributing breaks in a sea-floor telephone cable in the North Atlantic Ocean to turbidity flows generated by the 1929 Grand Banks earthquake. Anumber of workers have consequently used sedimentary turbidite records to reconstruct the earthquake histories of various regions2,7,8. Here we present direct observations of a seismically induced turbidity flow. Measurements of light scattering and sediment fluxes in the Cariaco basin indicate that the earthquake that occurred along the coast of northern Venezuela on 9 July 1997 resulted in considerable downslope displacement of sediments—probably >105 tonnes into the deep part of the basin. In such a seismically active region, this mechanism of sediment transport may be responsible for a significant component of the long-term sediment accumulation in the basin. Furthermore, this process may result in the sequestration in deep sea sediments of large amounts of carbon initially deposited at shallow depths.

1.1. The effect of food availability on the respiratory quotient (RQ) of Daphnia magna was measured by simultaneous measurement of oxygen consumption and 14CO2 release.2.2. The RQ changes with the concentration of food. Starving animals show an RQ of 0.7. With increasing food availability, the RQ increases to reach a plateau at approx 1.1, above the “incipient limiting level concentration”.3.3. Thus, Daphnia magna metabolizes fat at low food concentrations and synthesizes lipids under favourable food conditions.

A method is described for measurement of the in situ feeding rate of planktonic herbivores. Freshly caught Zooplankton are washed with filtered sea water and frozen. The gut contents are later analysed using acetone extracts of the entire sample. Fluorescence peaks due to ingested chlorophyll are easy to quantify for sample sizes of 20–200 animals. This method obviates some of the problems, such as confinement and previous feeding history, associated with extrapolation from laboratory experiments to field conditions. The method is illustrated by an investigation of diel feeding patterns of marine copepods. Initial results indicate the complexity of these patterns, with either a single night peak or dawn and dusk peaks for adult copepods. Diel variations in feeding activity appear to occur in addition to, but closely interacting with, the diel vertical migrations of the animals.