Spatial Distribution of Arctic Bacterioplankton Abundance Is Linked to Distinct Water Masses and Summertime Phytoplankton Bloom Dynamics (Fram Strait, 79°N)

Abstract

The Arctic is impacted by climate warming faster than any other oceanic region on Earth. Assessing the baseline of microbial communities in this rapidly changing ecosystem is vital for understanding the implications of ocean warming and sea ice retreat on ecosystem functioning. Using CARD-FISH and semi-automated counting, we quantified 14 ecologically relevant taxonomic groups of bacterioplankton (Bacteria and Archaea) from surface (0–30 m) down to deep waters (2,500 m) in summer ice-covered and ice-free regions of the Fram Strait, the main gateway for Atlantic inflow into the Arctic Ocean. Cell abundances of the bacterioplankton communities in surface waters varied from 105 cells mL–1 in ice-covered regions to 106 cells mL–1 in the ice-free regions. Observations suggest that these were overall driven by variations in phytoplankton bloom conditions across the Strait. The bacterial groups Bacteroidetes and Gammaproteobacteria showed several-fold higher cell abundances under late phytoplankton bloom conditions of the ice-free regions. Other taxonomic groups, such as the Rhodobacteraceae, revealed a distinct association of cell abundances with the surface Atlantic waters. With increasing depth (>500 m), the total cell abundances of the bacterioplankton communities decreased by up to two orders of magnitude, while largely unknown taxonomic groups (e.g., SAR324 and SAR202 clades) maintained constant cell abundances throughout the entire water column (ca. 103 cells mL–1). This suggests that these enigmatic groups may occupy a specific ecological niche in the entire water column. Our results provide the first quantitative spatial variations assessment of bacterioplankton in the summer ice-covered and ice-free Arctic water column, and suggest that further shift toward ice-free Arctic summers with longer phytoplankton blooms can lead to major changes in the associated standing stock of the bacterioplankton communities.

Marine Plankton during the Polar Night: Environmental Predictors of Spatial Variability

“…The autumn season is the period when nutrient concentrations tend to increase [ 26 , 29 , 30 ]. Our study revealed the enhanced contents of nutrients in seawater relative to the summer and autumn observations [ 29 , 51 , 89 , 90 , 91 , 92 ]. This pattern can be explained by low phytoplankton biomasses recorded in both regions, and the effective regeneration of the nutrients in the water column.…”

Diversity and Selection of Surface Marine Microbiomes in the Atlantic-Influenced Arctic

“…Multiple studies have addressed the present and future impact of Atlantification on microbiomes in the North Atlantic, the Barents Sea, and to the west and north of Svalbard. Many of these recent observations and future predictions have focused on shifts in phytoplankton biogeography (poleward expansion), the blooming dynamics, and/or the relative abundances of phytoplankton rather than the distinction of specific taxa or notably the invasion of new taxa (Barton et al, 2016 ; Carter-Gates et al, 2020 ; Orkney et al, 2020 ; Oziel et al, 2020 ; Cardozo-Mino et al, 2021 ). These changes were mainly connected to changing bottom-up controls and intensified surface current velocities instead rather than being directly linked to increasing temperature.…”

The polar night shift: seasonal dynamics and drivers of Arctic Ocean microbiomes revealed by autonomous sampling

“…The recent deployment of autonomous devices within the FRAM infrastructure program affords the unique opportunity for continuous year-round records. These considerably expand summertime observations of microbial diversity and activity in the WSC and EGC [ 27 – 32 ], shaped by a combination of sea ice cover, nitrate availability, and mixed layer depth [ 33 , 34 ]. Annual records also help to understand the biological responses to the northward expansion of subarctic habitats, termed Atlantification, which propagates through the entire food web [ 35 ].…”