Research Document - 1999/057

Development of a Sea Surface Temperature Index for the Canadian East Coast; Nutrient and Dissolved Oxygen Variability on the Scotian Shelf: a Preliminary Report from the Zonal Monitoring Program

By Brian Petrie, Philip Yeats and Peter Strain

Abstract

We calculate a single ocean climate index from a 17 year time series of satellite-derived, sea surface temperatures for the Canadian east coast from Hamilton Bank to Georges Bank. This index accounts for 59% (49%) of the annual (seasonal) temperature variability. The index is in phase throughout the region, i.e., shows widespread warming or cooling episodes. Comparison with in situ data indicates that the index captures the broad-scale variations of the regional ocean climate, particularly for the Newfoundland Shelf. The annual cycle of nitrate variability for the central Scotian Shelf shows a typical cycle: high nitrate levels at shallow depths during winter, followed by a rapid depletion in spring, low levels throughout the summer and a gradual increase in the late fall. Estimates of the primary production, derived by converting nitrate to carbon, compare favourably with in situ measurements but are substantially smaller than satellite calculations. The nitrate and dissolved oxygen pool on the Scotian Shelf has varied substantially over the past 30 years. Recently, the invasion of the Scotian Shelf by Labrador Slope Water has lead to decreasing nitrate and increasing dissolved oxygen levels, much like what transpired during the mid-60s when a similar event occurred.

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