Inorganic carbon cycling and biogeochemical processes in an Arctic inland sea (Hudson Bay)

Abstract

Abstract. The distributions of carbonate system parameters in Hudson Bay, which not only receives nearly one-third of Canada's river discharge but is also subject to annual cycles of sea-ice formation and melt, indicate that the timing and magnitude of freshwater inputs play an important role in carbon biogeochemistry and acidification in this unique Arctic ecosystem. This study uses basin-wide measurements of dissolved inorganic carbon (DIC) and total alkalinity (TA), as well as stable isotope tracers (δ 18 O and δ 13 C DIC ), to provide a detailed assessment of carbon cycling processes within the bay. Surface distributions of carbonate parameters reveal the particular importance of freshwater inputs in the southern portion of the bay. Based on TA, we surmise that the deep waters in the Hudson Bay are largely of Pacific origin. Riverine TA end-members vary significantly both regionally and with small changes in near-surface depths, highlighting the importance of careful surface water sampling in highly stratified waters. In an along-shore transect, large increases in subsurface DIC are accompanied by equivalent decreases in δ 13 C DIC with no discernable change in TA, indicating a respiratory DIC production on the order of 100 µmol kg −1 DIC during deep water circulation around the bay.

Using <sup>226</sup>Ra and <sup>228</sup>Ra isotopes to distinguish water mass distribution in the Canadian Arctic Archipelago

“…1, 6). Lower 228 Ra activities were found at higher salinities and depths, comparable to values reported byBurt et al (2016b) in the North Sea, where elevated 228 Ra activities were present within the shallow, Ra-SP) was obtained (slope= -2.467x), whereas for the deeper samples a less negative slope was found (slope= -0.4854x). The more negative slope, associated with the surface samples collected throughout the CAA, indicates that the system is heavily influenced by the influx of 228 Ra from the CAA shelf sediments.(Fig.…”

“…Additionally, both long-lived Ra isotopes are formed from the decay of different Thorium (Th) isotopes in sediments and are distributed to the ocean through porewater advection and diffusion across the sediment-water interface, primarily along coastlines or the bottom boundary layer (Charette et al, 2015). Since 228 Ra is more rapidly regenerated within sediments and its half-life is shorter than 226 Ra, it is closely associated with coastal and continental shelf regions where its abundance decreases rapidly away from its source towards the open waters, thus tracking the sediment-ocean or shelf-ocean transition (van Beek et al, 2007;Burt et al, 2016b;Kadko and Muench, 2005; Kawakami and Kusakabe, 2008;Moore et al, 1980Moore et al, , 2008Rutgers van der Loeff et al, 1995).…”

“…12). Furthermore, when considering δ 18 O, conservative mixing from a riverine source can be excluded (see also Burt et al, 2016b;Kipp et al, 2018;Moore, 2000Moore, , 2007. On the other hand, the δ 18 O values of -3 --4 ‰ imply that the 228 Ra source is under riverine influence, as the δ 18 O signature of the sea-ice end-member 21 485 490 495 500 is generally thought to be approximately -2‰ (e.g., Eicken et al, 2002;Thomas et al, 2011;Yamamoto-Kawai et al, 2009, and references therein, see also Thomas et al, 2011 Fig.…”

Resistance of Arctic phytoplankton to ocean acidification and enhanced irradiance

“…The environmental conditions prevailing in the Arctic could promote high physiological plasticity towards varying pCO 2 levels. The Arctic marine carbonate system is indeed characterized by naturally high pCO 2 variability, caused by the higher CO 2 solubility under low seawater temperatures, the lower buffering capacity due to the low alkalinity, and the effects of intense seasonal primary production in some regions (Wassmann and Reigstad 2011;Shadwick et al 2013;Thoisen et al 2015;Burt et al 2016). Phytoplankton species occurring in such environments thus need to be able to acclimate to a wide range of pCO 2 levels.…”

Impact of tidal dynamics on diel vertical migration of zooplankton in Hudson Bay

“…Typically, salinity gradients and freshwater discharge play an important role in determining species diversity (Witman et al, 2008). Seasonality in food availability is another significant challenging factor for zooplankton in high latitudes (Bandara et al, 2016;Carmack and Wassmann, 2006;Varpe, 2012).…”