Why Deep-Water Dissolved Oxygen Is Higher in G̱andaawuu.ngaay Xyangs (Juan Perez Sound), Haida Gwaii, Than Other British Columbia Fjords

Abstract

G̱andaawuu.ngaay Xyangs (Juan Perez Sound) is a fjord-like area and ecological hotpot on the east coast of Haida Gwaii, British Columbia, within Gwaii Haanas National Park Reserve, National Marine Conservation Area Reserve, and Haida Heritage Site. A collaboration among the Council of the Haida Nation, Parks Canada, and Fisheries and Oceans Canada has been ongoing since 2017 to advance understanding of the oceanography and marine ecology within and around Gwaii Haanas. Oceanographic data collected year-round by subsurface moorings and annually on research cruises revealed winter dissolved oxygen concentrations (DO) greater than 5 mLL⁻¹ (217 μmol kg⁻¹) as deep as 350 m in G̱andaawuu.ngaay Xyangs and no evidence of hypoxia throughout the water column. This observation differs from other British Columbia fjords, where maximum deep DO is generally observed in summer and values can be hypoxic or anoxic in winter. To explain this high DO, potential energy in the water column was calculated and compared with wind energy. Strong winds and weak stratification facilitated mixing of the water column each winter enabling ventilation. Oxygen loss from the winter high was caused by both frequent episodes of advection of dense, DO-poor water from shelf waters into G̱andaawuu.ngaay Xyangs, and by remineralization. In comparison, in Rivers Inlet, weak winds and strong stratification prevented full water column mixing and ventilation. Although climate-driven changes such as intensified upwelling, enhanced stratification, and region-wide deoxygenation could cause future hypoxia, protecting the integrated land-ocean ecosystem in G̱andaawuu.ngaay Xyangs is more important than ever before.