Environmental drivers of spring primary production in Hudson Bay

Abstract

Pertinent environmental factors influencing the microalgal bloom during sea-ice breakup in Hudson Bay were investigated in June 2018, producing the first observations of late spring primary production in the offshore waters of this vast inland sea. Phytoplankton production was found to commence at the onset of ice melt, with surface nutrient depletion leading to the formation of a subsurface chlorophyll maximum in the open waters of western Hudson Bay. Concurrently, the melting mobile ice cover in central Hudson Bay created favorable conditions for a diatom-dominated under-ice bloom, with photosynthetic characteristics and relatively high production confirming that phytoplankton cells were able to acclimate to increasing light levels. Lower mean values of phytoplankton production and total chlorophyll a (TChl a) concentration observed under the sea ice (414 mg C m–2 d–1 and 33.7 mg TChl a m–2) than those observed in open waters during the late bloom stage in the western region (460 mg C m–2 d–1 and 53.5 mg TChl a m–2) were attributed to reduced under-ice light levels and low surface concentrations of dissolved inorganic nitrogen (<2 μmol L–1) in central Hudson Bay. However, the highly abundant subice diatom, Melosira arctica, was estimated to contribute an additional 378 mg C m–2 d–1 to under-ice production in this region. Therefore, this subice algal bloom appears to play a similar role in the seasonally ice-covered sub-Arctic as in the central Arctic Ocean where it contributes significantly to local production. By updating historical total production estimates of Hudson Bay ranging between 21.5 and 39 g C m–2 yr–1 with our late spring observations including the novel observation of M. arctica, annual production was recalculated to be 72 g C m–2 yr–1, which equates to mean values for interior Arctic shelves.

Always ready? Primary production of Arctic phytoplankton at the end of the polar night

“…Exponential fitting indicated a Chl a-based specific growth rate constant of 0.46 d À1 (R 2 = 0.98), corresponding to a doubling of Chl a roughly every 36 h. As measured POC:Chl a ratios showed no clear trend (Table 1) Chl a may be used as a proxy for phytoplankton biomass for the short time span of this study. Such high POC:Chl a ratios, indicative a high nonphototrophic component of the particulate organic carbon pool, are commonly observed in high Arctic environments outside of bloom situations (Riedel et al 2008;Campbell et al 2016;Leu et al 2020;Matthes et al 2021). In combination with the observed increase in volume-based NPP, in situ as well as under reference conditions (Fig.…”

Sea Ice and Substratum Shape Extensive Kelp Forests in the Canadian Arctic

“…Annual productivity rates measured for S. latissima and L. solidungula at sites around Southampton Island in 2019 ranged from 23.1 to 67.8 g C m −2 y −1 (Filbee-Dexter, unpublished data) and for L. solidungula from Igloolik (Foxe Basin) in 1977 were 19.6 (±12.1 SD) g C m −2 y −1 (Chapman and Lindley, 1980). These measures of NPP are comparable to NPP for phytoplankton in Hudson Bay, Baffin Bay, and Labrador Sea (44-58 g C m −2 y −1 ) (Frey et al, 2020), 3.5× lower than estimates of combined ice algae and phytoplankton productivity for Hudson Bay (72 C m −2 y −1 ) (Matthes et al, 2021) and an order of magnitude lower than the productivity of most kelp forests (global average 516 ± 30 SE g C m −2 y −1 ; Pessarrodona et al, 2021b), yet the extensive area of kelp in the Eastern Canadian Arctic suggests these habitats are still cycling large quantities of carbon in the coastal zone, ranging from 2.2 to 6.4 Tg C y −1 and 10.4 to 30.6 Tg C y −1 , based on a lower depth limit of 10 and 40 m, respectively (Supplementary Table 4).…”

Content in fatty acids and carotenoids in phytoplankton blooms during the seasonal sea ice retreat in Hudson Bay complex, Canada

“…The post-bloom scenario observed in NWHB was characterized by strong nutrient depletion throughout the water column, suggesting that the bloom-deepening scenario had already occurred. A further sign of stressful growth conditions at surface was the highest PPC: PSC ratio observed (Figure 6; Matthes et al, 2021). The postbloom scenario showed low carotenoid and LC-PUFA water contents that were explained in our RDA model by high seawater dissolved silicate and a strong contribution of choanoflagellates to the protist community (Figure 7).…”

“…Due to the dominant northwesterly wind direction, sea ice breakup generally starts in the northwestern and eastern parts of Hudson Bay between May and June, and progresses toward the southern region where the last ice typically remains until late July (Andrews et al, 2018;Kirillov et al, 2020). Variability in spring ice conditions generates largely different spatial patterns in primary production between the different HBC sub-regions (Matthes et al, 2021).…”

“…Samples were stored at -80 C until analysis at the home laboratory. At the home laboratory pigments were extracted following Ras et al (2008) and Matthes et al (2021). Pigments and derivates were identified based on retention time and the spectral properties of external pigment standards.…”