Showing papers by "Lars Stemmann published in 2007"

Vertical distribution of aggregates (>110 µm) and mesoscale activity in the northeastern Atlantic: Effects on the deep vertical export of surface carbon

Abstract: Spatial and temporal variability in the distribution of marine aggregates (>110 mm) was studied using underwater video profilers in an area off the Iberian Peninsula and Azores Islands dominated by mesoscale and submesocale hydrodynamics in winter, spring, and summer 2001. In the 0-200-m layer, aggregates were most abundant in spring (100-120 mg dry weight [dry wt] m-3) and lowest during summer and winter (1-10 mg dry wt mm-3). In the deeper layers (down to 1,000 m), the seasonal pattern was different, with concentrations highest in spring and summer, and lowest in winter (e.g., at 800 m, 5-10 mg dry wt mm-3 in spring and summer; 1-5 mg dry wt mm-3 in winter). The seasonal change in the abundance of aggregates in the upper 1,000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps and with seasonal changes in the surface phytoplankton community. In an area dominated by eddies, surface accumulation of aggregates and export down to 1,000 m occur at mesoscale distances (<100 km). The occurrence of a rich aggregate layer may be related to mesoscale activity in water flow that drives nutrient inputs, phytoplankton production, and the formation of large aggregates. Such spatially constrained zones of massive export may be typical of frontal open-sea systems, and may have been missed by conventional sediment trap moorings, which cannot resolve export at this mesoscale level.

Vertical distribution (0–1000 m) of gelatinous zooplankton and particulate matter (60ìm<<5mm) along the Mid Atlantic ridge in the North Atlantic. Potential impact of appendicularians on particle aggregation

Abstract: The vertical distribution (0-1000 m depth) of macrozooplankton along the northern portion of the Mid-Atlantic Ridge (59°58N, 25°53W to 41°29N, 28°19W) was investigated during the MARECO program (June and July 2004) using the Underwater Video Profiler (UVP). Twelve relatively large (> 1 cm) groups were selected from the recorded images: sarcodines (with two sub-groups), crustaceans (excluding copepods), chaetognaths, ctenophores (with two sub-groups cydippids and lobates), siphonophores, medusae (with three subgroups Aeginura grimaldii, Aglantha spp. and all other medusae), appendicularians, and thaliaceans. The numerically dominant groups over the whole area were crustaceans (26%), medusae (20%) and appendicularians (17%). The gelatinous fauna were consistently most numerous between 400-900 m. Appendicularians, ctenophores and A. grimaldii occurred mostly below 300 m (maximum concentrations of 75, 58, and 30 individuals 100m-3, respectively). The macrozooplankton community below 200 m varied with the spatial distribution of the four regions defined by the temperature and salinity profiles. The results suggest that the Sub-Polar Front restricts the mixing of macrozooplankton communities down to 1000 m depth. The observed relationship between appendicularians and biovolume and size of particles is investigated in the four oceanic regions. Keywords: Gelatinous zooplankton, mesopelagic zooplankton, Sub Polar Front, North Atlantic, Underwater Video Profiler, MARECO .