Surface ocean losing resilience to thermal stress
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Active ice sheet conservation cannot stop the retreat of Sermeq Kujalleq glacier, Greenland
Active conservation of an ice sheet seeks to reduce ice sheet mass loss and sea level rise. Here we explore the response of Sermeq Kujalleq in Greenland to limiting warm water inflow to the fjord it terminates by raising the sill by an artificial barrier at its mouth. We asynchronously couple an ice sheet model with a fjord model, and simulate glacier evolution with varying climate scenarios from the year 2020 to 2100. The tallest barrier cools the fjord water and reduces melt at the ice front. But this has minor impacts on glacier retreat under SSP5-8.5 and SSP2-4.5. Cooling the atmospheric forcing to 1990s levels reduces glacier retreat, but even reducing water temperatures with a barrier cannot stabilize the glacier. The glacier seems to be in an unstoppable phase of marine ice sheet instability on a rapidly deepening retrograde sloping bed and in water much deeper than in 2000s.
Protein signatures predict coral resilience and survival to thermal bleaching events
Coral bleaching events from thermal stress are increasing globally in duration, frequency, and intensity. While bleaching can cause mortality, some corals survive, reacquire symbionts, and recover. We experimentally bleached Montipora capitata to examine molecular and physiological differences between corals that recover (resilient) and those that die (susceptible). Corals were collected and monitored for eight months post-bleaching to identify genets with long-term resilience. Using an integrated systems-biology approach that included quantitative proteomics, 16S rRNA sequencing to characterize the coral microbiome, total coral lipids, symbiont community composition and density, we explored molecular-level mechanisms of tolerance in corals pre- and post-bleaching. Prior to thermal stress, resilient corals have a more diverse microbiome and abundant proteins essential for carbon acquisition, symbiont retention, and pathogen resistance. Protein signatures of susceptible corals showed early symbiont rejection and utilized urea for carbon and nitrogen. Our results reveal molecular factors for surviving bleaching events and identify diagnostic protein biomarkers for reef management and restoration.
Mixed-layer lipidomes suggest offshore transport of energy-rich and essential lipids by cyclonic eddies
Mesoscale eddies are ubiquitous features in the ocean affecting the cycles of nutrients and carbon. Cyclonic eddies formed in Eastern Boundary Upwelling Systems can substantially modulate primary production by phytoplankton and the vertical and lateral export of organic carbon. However, the impact of eddy activity on the biochemical composition of eukaryotic phytoplankton, bacteria and archaea and associated consequences for carbon and energy flows are largely unknown. Here, we investigated the microbial lipidome in the surface ocean in and around a cyclonic eddy formed in the coastal upwelling system off Mauritania. We show that the eddy contained almost three times the amount of lipids compared to the surrounding open-ocean and coastal waters. The eddy lipid signature with energy-rich triacylglycerols and essential fatty acid-containing membrane lipids of eukaryotic phytoplankton origin was further significantly different from the ambient waters. Strong variability in lipid distributions within the eddy was related to differences in microbial community composition. Estimates indicate that in the Mauritanian upwelling area, as much as 9.7 ± 2.0 gigagrams of lipid carbon per year is delivered to the open ocean by coastal cyclonic eddies potentially fueling higher trophic levels and contributing to the maintenance of secondary productivity and carbon export offshore.
Onshore intensification of subtropical western boundary currents in a warming climate
Subtropical western boundary currents (WBCs) refer to swift narrow oceanic currents that flow along the western edges of global subtropical ocean basins. Earlier studies indicated that the WBCs are extending poleward under a warming climate. However, owing to limited observations and coarse resolution of climate models, how greenhouse warming may affect the zonal structure of the WBCs remains unknown. Here, using seven high-resolution climate models, we find an onshore intensification of the WBCs in a warming climate. The multimodel ensemble mean of onshore acceleration ranges from 0.10 ± 0.08 to 0.51 ± 0.24 cm s−1 per decade over 1950–2050. Enhanced oceanic stratification associated with fast surface warming induces an uplift of the WBCs, leading to the projected change. The onshore intensification could induce anomalous warming that exacerbates coastal marine heatwaves, reduces ability of the coastal oceans to absorb anthropogenic carbon dioxide and destabilizes methane hydrate stored below the sea floor of shelf regions.
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