A possible connection between hydrography and the distribution of Calanus finmarchicus on the Norwegian midshelf in 1997

• Published in: ICES Journal of Marine Science
• Main Authors: Pedersen, O-P., Tande, K. S., Timonin, A., Semenova, T.
• Format: Text
• Language: English
• Published: Oxford University Press 2000
• Subjects: Articles; Helgeland; Calanus finmarchicus; Vestfjorden
• Online Access: http://icesjms.oxfordjournals.org/cgi/content/short/57/6/1645; https://doi.org/10.1006/jmsc.2000.0980

Three cruises were conducted in April, May/June, and July 1997 in order to describe the demography of Calanus finmarchicus on the Norwegian midshelf. The Norwegian Atlantic Current and the Norwegian Coastal Current dominate the study region. The differences in the physical conditions of the water masses are most evident along an east–west axis, showing cold, less saline water masses closer to the coast, whereas Atlantic water masses dominate at the shelf break and the open ocean. Seasonal lateral movement mixes coastal and Atlantic Water, and the clearly defined gradients present in spring are gradually eroded. The overall seawater temperature in 1997 appears to have been higher than the mean of the past decades. The observed vertical shift in the chlorophyll a from surface bloom in spring to a deepwater chlorophyll a maximum around 50 m in July is a consistent feature, but during the period of investigation there was extensive patchiness with respect to the distribution of chlorophyll. The start of recruitment from G 0 of C. finmarchicus differs in time over the Norwegian midshelf, with two regions (off Møre and in Vestfjorden/Helgeland) clearly ahead of the other areas. The formation of G 1 C. finmarchicus seems to be dictated by the stabilization of water masses on the shelf and by a longitudinal/latitudinal offset of the ascent of CV to the surface, which was particularly prominent in the open ocean. The broad mesoscale pattern of the temporal propagation of Calanus shows that G 1 starts at the shelf, propagates towards the open ocean covering all three regions, and finally returns as G 2 to the shelf with a pulse of CI–II during July and most likely August.