Atlantic Fisheries Research Document 1996/002
Summary of biological oceanographic variables in the Newfoundland Region
By Pepin, P., Paranjape, M.A.
Abstract
This study provides a preliminary description of the temporal and spatial pattern in the variation of nutrients, phytoplankton and zooplankton in the Newfoundland region based on data from directed and ship-of-opportunity collections (1993-94) as well as using information from the CPR series (1959-1978, 1991, 1992) and from the Mobil Oil survey of the Grand Banks (1980-81). the principle objective was to describe and contrast the depth-dependent seasonal cycle in nutrient and phytoplankton abundance from a single site (station 27) with observations taken in the northern region of the Grand Banks (NAFO area 3L). All nutrients as well as chlorophyll concentrations exhibit strong seasonal cycles. Overall nitrate and phytoplankton concentrations are higher along the shelf edge, in correspondence with the offshore arm of the Labrador current. Phytoplankton concentration appears to show a peak in late April-early May but the precise timing of the spring bloom is uncertain because of the unavailability of data for the period preceding April. Maximum phytoplankton concentrations occur a t depths of 30-50m. It is apparent that there is a strong seasonal cycle at all depths with the greatest overall variability occurring at intermediate depths (10 and 50m). The seasonal cycle in integrated (0-100m) fluorescence levels from all CTD observations in NAFO area 3L shows a pattern which is similar to that of temperature residuals but is shifted further south along the shelf, possibly indicating advection of tracers. The seasonal cycle in the abundance of Calanus finmarchicus at station 27 is not marked as that of Calanus glacialis or Calanus hyperboreus. The abundance of Pseudoclanus sp. and Temora longicornis show higher levels during mid-fall. The seasonal cycles for these five species are similar to those observed from the CPR surveys conducted in NAFO areas 3K and 3L but differ substantially from those fro NAFO area 3NO. Differences in the seasonal cycle at Station 27 with other parts of NAFO area 3L may be due to local features or precesses (e.g. mixing, mixed layer depth, nutrient sources, advection). However, it is also possible that the variability in the level of some elements on the time scale of less than 30 days limits the degree of comparison possible form ship-of-opportunity collections. There are important questions pertaining to the sampling frequency and spatial resolution that would be essential in order to detect the "climactic" variability. However the nature of the sampling program required to supply "adequate monitoring" requires extensive evaluation and discussion because ship-of-opportunity based collections require substantial assumptions in the interpretation of data analysis. The current sampling resolution of biological oceanographic variables severely limits the comparison of available observations because of the possible influence of short-term and small-scale variability on the description of the seasonal cycle and in the measurement and understanding of interannual fluctuations about that mean cycle.
Accessibility Notice
This document is available in PDF format. If the document is not accessible to you, please contact the Secretariat to obtain another appropriate format, such as regular print, large print, Braille or audio version.
- Date modified: