Deep-Water Renewal Events; Insights into Deep Water Sediment Transport Mechanisms

K Ayranci,S E Dashtgard

doi:10.1038/s41598-020-63123-3

Abstract

Deep-water renewal (DWR) events are characterized in the Strait of Georgia, Canada using 11 years of real-time physical and chemical oceanographic data and seafloor videos. At least 6 DWRs occur per year at 300 m water depth and each event continues for over 3 days. They initiate during neap tides and are associated with increased turbidity. In the spring, DWRs introduce cold, oxygenated and nutrient-poor waters, and in the fall they introduce warm, oxygen-depleted, nutrient-rich and saline waters. Although the timing and magnitude of DWRs differ from year to year, we demonstrate that they are not restricted to two seasons, but continue throughout the year. High-resolution videos of DWRs show that these events comprise a plume of high suspended sediment concentration that flows parallel to the basin axis and deposits approximately 1.5 cm per event.

Highlights

Deep-water currents are efficient sediment transport mechanisms in modern and ancient systems[1,2,3,4,5,6], yet there is little known about their physical and chemical oceanographic properties, and even less about the physical manifestations of these currents
The Strait of Georgia (SoG) is situated between Vancouver Island and the mainland of British Columbia, Canada (Fig. 1)
Chemical characteristics of Deep-water renewal (DWR) vary throughout the year, all events started during neap tidal cycles and last for at least 3 days

Summary

Introduction

Deep-water currents are efficient sediment transport mechanisms in modern and ancient systems[1,2,3,4,5,6], yet there is little known about their physical and chemical oceanographic properties (see exceptions2,7,8), and even less about the physical manifestations of these currents. In the Strait of Georgia (SoG), Canada, deep-water renewal (DWR) events are documented as deep inflow currents[7,9] that cause fluctuations in chemical oceanographic properties such as salinity, dissolved oxygen, temperature and nutrient content[7,10,11,12]. Regardless of the driving mechanisms, DWRs are associated with intrusion of dense Pacific Ocean waters into the SoG through the narrow Juan de Fuca Strait (Fig. 1). The trapped dense waters flow fortnightly into the SoG during neap tides when there is minimum tidal mixing at the sills causing strong water stratification[7,9,10,14]. We analyze all available real-time physical and chemical oceanographic data (2009–2019) recorded at 300 m water depth off the Fraser River Delta and in the SoG (Fig. 1). We present still images extracted from video footage of a DWR in the SoG and discuss the physical manifestations of its passage

Methods

Results

Conclusion