Tidal Effects on Seabird-Bathymetry Associations and Physical Oceanography in the San Juan Channel

Abstract

In the southern San Juan Channel, flood tides bring an influx of cold, saline oceanic water, while warmer, fresher water flows out of the channel on ebb tides. Variation in tidal conditions thus has important effects on the physical properties of the water in the channel. The objective of this study was to measure these effects on both slack-flood and spring-neap scales of tidal variation. To accomplish this, measurements of physical water properties were taken repeatedly in the same location over the course of a flood tide on four consecutive days. Water density was found to increase as the flood tide progressed within each day, and also as tidal condition changed from neap to spring over the course of the four days. Data taken under similar tidal and seasonal conditions in 2012 did not show the same strong relationship, but given unusually cold water temperatures present in the channel in 2012, this is not inconsistent with the previously stated model of how tidal input affects physical water properties.