Sea ice dynamics drive benthic microbial communities in McMurdo Sound, Antarctica

Globally, Earth’s warming climate is evidently driving sea ice variability in high latitude regions. In the Arctic, older and thicker multi-year sea ice is declining and transitioning into younger and more ephemeral first-year sea ice. Whereas in Antarctica, sea ice extent is increasing around the continent, masking strong regional reductions around the Western Antarctic Peninsula. Models predict that sea ice will continue to decline into the 21ˢᵗ Century globally. Reduced sea ice cover is expected to impact marine ecosystem functioning through increased primary productivity at the sea surface and increased flux of organic matter to the seafloor. Seafloor sediments are a critical component of the marine ecosystem as sites of organic matter remineralisation and nutrient regeneration, processes which are driven by microorganisms. Despite their importance, our understanding of sediment biogeochemical processes, their connectivity to the water column and to primary productivity at the surface is limited, particularly in polar regions. This impedes our ability to predict the impacts of climate change on marine ecosystem functioning. This study sampled marine sediments from two strategically chosen sites ~60 km apart in McMurdo Sound, Antarctica, where organic matter concentrations were high due to firstyear ice conditions and productive open ocean source waters (Cape Evans), and low due to multi-year ice and oligotrophic source waters (New Harbour). Using high-throughput 16S rRNA gene amplicon sequencing and sediment geochemistry data (chlorophyll-α, phaeophytin, TOC, TN, δ13C, δ15N) this study compared the structure and composition of the sediment microbial communities at these two contrasting sites. The bacterial richness and evenness (alpha diversity) was comparatively greater in the low organic matter sediments underneath the multi-year ice cover than in the high organic matter sediments underneath first-year ice. Significant site-based compositional differences between the two study sites were found. Compositional differences in the high organic matter sediments were driven by known heterotrophic algal biopolymer degrading taxa Flavobacteriales, Cytophagales, and Verrucomicrobiales, and sulfate-reducing bacteria Desulfobulbales, potentially reflecting a sediment legacy of high algal-derived organic matter flux. Whereas the low organic matter sediment communities were driven by chemoautotrophic taxa Nitrosopumilaeles, Nitrospirales, and Steroidobacterales which are known to be involved in carbon fixation and nitrogen cycling, reflecting the legacy of oligotrophic conditions in these sediments. The marine sediments at New Harbour and Cape Evans were not influenced by wind-blown terrestrial surface sediments from the neighbouring Taylor Valley. Additionally, this study supported the hypothesis that subsurface brine channels from the Taylor Valley could be discharging into McMurdo Sound at New Harbour by detecting low abundances of taxa associated with high saline environments (e.g. Thiohalorhabdales). Overall, the findings from this study suggest that climate driven sea ice reductions and increased organic matter flux may shift sediment communities from autotrophy towards heterotrophy, thus impacting sediment biogeochemistry. This study contributes towards our understanding of marine sediment processes and marine ecosystem functioning. Additionally, this study provides a baseline of understanding of sediment microbial communities in McMurdo Sound which will support future research further examining community functional capabilities. Finally, this study contributes a first report of the direct impacts of climate driven sea ice change on sediment microbial communities in Antarctica

Sea ice dynamics drive benthic microbial communities in McMurdo Sound, Antarctica

Climate change is driving dramatic variability in sea ice dynamics, a key driver in polar marine ecosystems. Projected changes in Antarctica suggest that regional warming will force dramatic shifts in sea ice thickness and persistence, altering sea ice-associated primary production and deposition to the seafloor. To improve our understanding of the impacts of sea ice change on benthic ecosystems, we directly compared the benthic microbial communities underlying first-year sea ice (FYI) and multi-year sea ice (MYI). Using two tractable coastal habitats in McMurdo Sound, Antarctica, where FYI (Cape Evans) and MYI (New Harbour) prevail, we show that the structure and composition of the benthic microbial communities reflect the legacy of sea ice dynamics. At Cape Evans, an enrichment of known heterotrophic algal polysaccharide degrading taxa (e.g., Flavobacteriaceae, unclassified Gammaproteobacteria, and Rubritaleaceae) and sulfate-reducing bacteria (e.g., Desulfocapsaceae) correlated with comparatively higher chlorophyll a (14.2±0.8μgg−1) and total organic carbon content (0.33%±0.04), reflecting increased productivity and seafloor deposition beneath FYI. Conversely, at New Harbour, an enrichment of known archaeal (e.g., Nitrosopumilaceae) and bacterial (e.g., Woeseiaceae and Nitrospiraceae) chemoautotrophs was common in sediments with considerably lower chlorophyll a (1.0±0.24μgg−1) and total organic carbon content (0.17%±0.01), reflecting restricted productivity beneath MYI. We also report evidence of a submarine discharge of sub-permafrost brine from Taylor Valley into New Harbour. By comparing our two study sites, we show that under current climate-warming scenarios, changes to sea ice productivity and seafloor deposition are likely to initiate major shifts in benthic microbial communities, with heterotrophic organic matter degradation processes becoming increasingly important. This study provides the first assessment of how legacy sea ice conditions influence benthic microbial communities in Antarctica, contributing insight into sea ice–benthic coupling and ecosystem functioning in a polar environment

Impact of opioid-free analgesia on pain severity and patient satisfaction after discharge from surgery: multispecialty, prospective cohort study in 25 countries

Background: Balancing opioid stewardship and the need for adequate analgesia following discharge after surgery is challenging. This study aimed to compare the outcomes for patients discharged with opioid versus opioid-free analgesia after common surgical procedures.Methods: This international, multicentre, prospective cohort study collected data from patients undergoing common acute and elective general surgical, urological, gynaecological, and orthopaedic procedures. The primary outcomes were patient-reported time in severe pain measured on a numerical analogue scale from 0 to 100% and patient-reported satisfaction with pain relief during the first week following discharge. Data were collected by in-hospital chart review and patient telephone interview 1 week after discharge.Results: The study recruited 4273 patients from 144 centres in 25 countries; 1311 patients (30.7%) were prescribed opioid analgesia at discharge. Patients reported being in severe pain for 10 (i.q.r. 1-30)% of the first week after discharge and rated satisfaction with analgesia as 90 (i.q.r. 80-100) of 100. After adjustment for confounders, opioid analgesia on discharge was independently associated with increased pain severity (risk ratio 1.52, 95% c.i. 1.31 to 1.76; P < 0.001) and re-presentation to healthcare providers owing to side-effects of medication (OR 2.38, 95% c.i. 1.36 to 4.17; P = 0.004), but not with satisfaction with analgesia (beta coefficient 0.92, 95% c.i. -1.52 to 3.36; P = 0.468) compared with opioid-free analgesia. Although opioid prescribing varied greatly between high-income and low- and middle-income countries, patient-reported outcomes did not.Conclusion: Opioid analgesia prescription on surgical discharge is associated with a higher risk of re-presentation owing to side-effects of medication and increased patient-reported pain, but not with changes in patient-reported satisfaction. Opioid-free discharge analgesia should be adopted routinely