Variations in the physico-chemical properties of San Juan Channel during fall season

Abstract

Variations in the physical and chemical properties of seawater greatly impact the diversity of organisms that live in the world’s ocean and marine ecosystems. Physical and chemical oceanographic properties such as temperature, salinity, dissolved oxygen (DO), and nutrients also serve as indicators of ocean and ecological health. In the San Juan Channel (SJC), previous research has provided the variation and effects of these factors individually e.g. temperature and salinity alone, or with either oxygen or nutrients, but not all together. The goal of this research then was to fill this knowledge gap, in addition to continuing the 20-year-long data of understanding the spatiotemporal variations of these parameters and to fit this year’s data with confirmed seasonal and interannual trends. Temperature and salinity data were collected using CTD while dissolved oxygen and nutrient samples were collected using Niskin bottles. Data from 2004-2024 were analyzed using multiple correlation and principal component analysis (PCA). Using PCA, this study confirmed that the water mass from the upper 50 m of North station is coming from the mixing of Strait of Juan de Fuca and Strait of Georgia, which has low nitrogen and phosphate and high DO and silicate. Meanwhile, the bottom depths of South station have its water mass attributed to the surface Pacific or mid Pacific waters, which has high nutrients and low DO. The dynamic mixing activities present in the bottom depths of North station and upper 50 m of South station show that the water masses are coming from the mixing of Strait of Juan de Fuca, Strait of Georgia, and surface Pacific waters, which indicate that the physical and chemical characteristics can also vary spatially and temporally. These findings suggest that PCA is a powerful analysis tool that can be used to identify water masses in the San Juan Archipelago using the relationship of the conservative and non-conservative tracers. Additionally, this study highlights the importance of continuous monitoring in this region as it provides an extensive idea of what is happening in the channel. Understanding how these properties can determine the dynamics of this unique system is crucial to oversee and predict future conditions such as warming, hypoxia, and eutrophication, and to manage the ecosystem and resources of this region.