Insights into surface circulation and mixing in James Bay and Hudson Bay from dissolved organic matter optical properties

Abstract

Hudson Bay and James Bay are fed by numerous rivers, which also deliver large amounts of dissolved organic matter (DOM). The objective of this study is to assess Hudson Bay wide DOM spatial distribution using ultraviolet-visible light absorption and excitation-emission matrix fluorescence spectroscopies. Overall, a five-component PARAFAC model was validated using 1060 discrete samples collected over nine field campaigns between 2009 and 2018 and including the first samples from James Bay ( n = 112). Regional and seasonal variations were observed. Particularly striking was a 9-fold difference in concentration between coastal and marine zones of these bays, which implies limited mixing between those regions. Seasonal variations in absorption coefficient at 355 nm and terrestrial humic-like components were found only in east Hudson Bay, revealing a regional disparity in seasonal DOM behaviour. The summer intensities and relative abundances of DOM revealed that cyclonic circulation transports terrestrial DOM around James Bay following its eastern shores before being transported northward along the western coast of Belcher Islands. The vertical distribution of DOM indicated that fluorescent DOM is delivered to the deeper layer by winter convective mixing in northern Hudson Bay. • Limited mixing between the coastal and marine regions of the bay is observed. • The strong terrestrial signal of east James Bay is found in northern Belcher Island. • DOM is delivered to the deeper layer by winter convection in northern Hudson Bay.