Decadal Variability in Subsurface Nutrient Availability on the Scotian Shelf Reflects Changes in the Northwest Atlantic Ocean
N. Lehmann,
D. C. Reed,
C. Buchwald
et al.
Abstract:Subsurface nutrients on the Scotian Shelf, an ocean region at the convergence of the subpolar and subtropical western boundary currents (i.e., Labrador Current (LC) and Gulf Stream (GS)), are chiefly modulated by upstream shelf and slope waters. Yet little is known about long‐term fluctuations in the advective transport of nutrients to the shelf. Here, we synthesized nutrient and hydrographic data from 1975 to 2020 to characterize decadal changes in upper (60–150 m) and lower (150–200 m) subsurface nutrient av… Show more
“…Here, we demonstrate that psB12 quota in 8102 significantly decreased in low N:P, despite no change in growth rate or significant change in demand (MetH abundance) (Fig 2A,C). This result is of potential importance for the Scotian Shelf region, as a decrease in dissolved nitrogen relative to phosphorus has been observed since 2010 and is expected to continue in the future (Lehmann et al, 2023). On average, the N:P ratio in environmental samples was (3.5 ± 4.5 N:P) (Table S2) however no correlation between N:P and psB12 (pM) was observed.…”
Section: Variability In Psb12 Quotas and Protein Inventories In Synec...mentioning
Cobalamin influences marine microbial communities because an exogenous source is required by most eukaryotic phytoplankton, and demand can exceed supply. Pseudocobalamin, psB12, is a cobalamin analog that is produced and used by most cyanobacteria but is not directly available to eukaryotic phytoplankton. A subset of microbes can remodel pseudocobalamin into cobalamin, but a scarcity of pseudocobalamin measurements impedes our ability to evaluate its importance for marine cobalamin production. Here, we perform simultaneous measurements of pseudocobalamin and methionine synthase (MetH), the key protein that uses it as a co-factor, inSynechococcuscultures and natural communities. InSynechococcussp. WH 8102, pseudocobalamin quota decreases in low temperature (17 °C) and low N:P, while MetH did not. Pseudocobalamin and MetH quotas were influenced by culture methods (batch vs semi-continuous) and growth phase (exponential vs stationary). Despite the variability present in cultures, we found a comparably consistent quota of 296 ± 101 pseudocobalamin molecules per cyanobacterial cell in the Northwest Atlantic Ocean, suggesting that cyanobacterial cell counts may be sufficient to estimate pseudocobalamin inventories in this region. This work offers insights into cellular pseudocobalamin metabolism and the environmental and physiological conditions that may influence it and provides environmental measurements to further our understanding of when and how pseudocobalamin can influence marine microbial communities.
“…Here, we demonstrate that psB12 quota in 8102 significantly decreased in low N:P, despite no change in growth rate or significant change in demand (MetH abundance) (Fig 2A,C). This result is of potential importance for the Scotian Shelf region, as a decrease in dissolved nitrogen relative to phosphorus has been observed since 2010 and is expected to continue in the future (Lehmann et al, 2023). On average, the N:P ratio in environmental samples was (3.5 ± 4.5 N:P) (Table S2) however no correlation between N:P and psB12 (pM) was observed.…”
Section: Variability In Psb12 Quotas and Protein Inventories In Synec...mentioning
Cobalamin influences marine microbial communities because an exogenous source is required by most eukaryotic phytoplankton, and demand can exceed supply. Pseudocobalamin, psB12, is a cobalamin analog that is produced and used by most cyanobacteria but is not directly available to eukaryotic phytoplankton. A subset of microbes can remodel pseudocobalamin into cobalamin, but a scarcity of pseudocobalamin measurements impedes our ability to evaluate its importance for marine cobalamin production. Here, we perform simultaneous measurements of pseudocobalamin and methionine synthase (MetH), the key protein that uses it as a co-factor, inSynechococcuscultures and natural communities. InSynechococcussp. WH 8102, pseudocobalamin quota decreases in low temperature (17 °C) and low N:P, while MetH did not. Pseudocobalamin and MetH quotas were influenced by culture methods (batch vs semi-continuous) and growth phase (exponential vs stationary). Despite the variability present in cultures, we found a comparably consistent quota of 296 ± 101 pseudocobalamin molecules per cyanobacterial cell in the Northwest Atlantic Ocean, suggesting that cyanobacterial cell counts may be sufficient to estimate pseudocobalamin inventories in this region. This work offers insights into cellular pseudocobalamin metabolism and the environmental and physiological conditions that may influence it and provides environmental measurements to further our understanding of when and how pseudocobalamin can influence marine microbial communities.
The Gulf of St. Lawrence (GSL), along with the St. Lawrence Estuary, is the largest estuarine system in North America. It is a biologically productive sea and an important fishing ground in Canada. The objectives of this study are to determine how climate changes will affect primary production in the GSL and on the eastern Scotian Shelf, and to determine the drivers of the changes. We use a regional ocean model forced with downscaled output of the Max-Planck Institute Earth System Model to study the changes in net primary production under the climate change scenario of Representative Concentration Pathway 8.5 (RCP8.5). Results reveal a projected 13.4% decrease in annual primary production across the GSL system over the next 70 years. This decline primarily stems from reduced nutrient concentrations in the upper layer, despite the increase in nutrients supplied by rivers. Enhanced freshwater influx and ocean surface warming contribute to heightened stratification, that in turn reduce the vertical nutrient fluxes from deeper layers. This mechanism affects the upwelling of nutrient-rich water at the head of the Laurentian Channel in the Lower St. Lawrence Estuary, leading to a 22% reduction in the vertical nitrate flux in the future. Additionally, nutrient concentrations in the water masses entering the GSL at the Strait of Belle Isle and at Cabot Strait are also reduced. Due to declining sea-ice concentration, the phytoplankton bloom is expected to occur between 9 and 23 days earlier under a warmer climate, and last for up to 24 days longer, depending on the GSL subregions, compared to the historical period (2001-2020). Biological productivity at higher trophic levels, and thus fisheries productivity, could be negatively impacted under the RCP8.5 climate change scenario.
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