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Review article: Weddell Sea polynya Formation, Cessation and Climatic Impacts
No full textOpen-ocean polynyas, openings in the sea ice, reappeared extensively in 2016 and 2017 over the Maud Rise in the Weddell Sea after a 40-year hiatus, raising a series of unresolved questions about the atmosphere-ice-ocean interactions in the Antarctic region. These major polynyas significantly influence moisture and heat exchange between the atmosphere and ocean, impacting both regional and global climate dynamics, as well as ecosystem functioning and biogeochemical processes. Notably, they could play a crucial role in contributing to the formation of Antarctic Bottom Water and influencing global ocean circulation. In this Review, we synthesize current knowledge on the drivers and impacts of Weddell Sea polynyas. Recent occurrences have been linked to factors such as a strengthening Weddell Gyre, a negative Southern Annular Mode, extreme local atmospheric conditions (atmosphere river and cyclones), and subsurface ocean heat buildup which acts as a preconditioning factor. The associated deep ocean convection from these polynyas can enhance air-sea gas exchange and trigger earlier phytoplankton blooms due to the influx of iron and nutrients from the deep ocean. While advancements in observation and modeling techniques have significantly improved our understanding of polynyas, substantial uncertainties remain regarding their interaction with recent Antarctic sea ice loss, their sensitivity to ocean mixing schemes and their excessive size or frequency in climate simulations, and future projections. Therefore, future research should focus on developing comprehensive four-dimensional regional observatories and targeted, assimilated coupled models that accurately capture atmosphere-ice-ocean interactions across various timescales
Understanding Sub‐Lithospheric Small‐Scale Convection by Linking Models of Grain Size Evolution, Mantle Convection, and Seismic Tomography
No full textThe interaction between aging oceanic plates and their underlying mantle is a crucial component of the plate tectonic cycle. Sub‐lithospheric small‐scale convection (SSC) explains why plates appear not to thicken after a certain age. Here, we link grain‐scale processes, dynamic models of asthenospheric flow, and seismic observations to gain new insights into the mechanisms of SSC. We present high‐resolution 3D geodynamic models of oceanic plate evolution with an Earth‐like rheology including coupled diffusion/dislocation creep and their interplay with evolving olivine grain size. Our models quantify how rheology affects the morphology and temporal stability of SSC, and we directly relate these quantities to geophysical observations from the Pacific OBS Research into Convecting Asthenosphere (ORCA) experiment. We convert variations in temperature, pressure, grain size, water content and stable melt fraction to seismic velocity and attenuation, seeking to match the wavelength and pattern of observed longitudinal convective rolls, the young SSC onset age, the large seismic velocity heterogeneity, low absolute seismic velocities, and high seismic attenuation. This requires low ( Pa s) asthenospheric viscosity, the contribution of both diffusion and dislocation creep to deformation, and the presence of volatiles and melt. Although SSC occurs at plate ages 60 Ma in our best‐fit model, the plate thermal structure approximately matches global observations of heat flux and bathymetry, indicating an important role of vigorous SSC in Earth's plate dynamics. However, reconciling all seismological observations is challenging, and additional mechanisms are required to explain the strong velocity heterogeneities suggested by body wave tomography.
Plain Language Summary
As oceanic tectonic plates age, they get colder and thicker. At some point, portions of the base of the plates may drip off into the hot mantle underneath them, a process known as “small‐scale convection” (SSC). This might explain diverse geophysical observations, including seismic imaging of cold blobs beneath the plates and the finding that plates seem to stop cooling with increasing age after they turn 70 million years old. We conducted computer simulations of aging oceanic plates that include novel components, such as more complex treatment of viscosity and its interplay with the size of crystal grains in rocks. Grain size turns out to be a key parameter in determining both how cold drips evolve and how seismic waves propagate through those rocks, which is how we identify structures beneath the surface. We link together the computer simulations with seismological studies by using simulated structure to predict synthetic earthquake data, for comparison with observations. In particular, we seek to match various attributes of apparent SSC seen recently beneath the central Pacific ocean plate. We find that small‐scale convection is indeed reproduced by our simulations, and determine that it manifests in a way that is consistent with several real‐Earth observations.
Key Points
3D models with complex rheology and evolving grain size require low asthenospheric viscosity to match observed SSC in the central Pacific
In our models, the seafloor depth–age curve flattens at a plate age (60 Ma) matching global observations, despite young SSC onset (35 Ma)
A small amount of melt and volatiles is required to match the observed asthenospheric low seismic velocities and high attenuatio
Short Cruise Report RV ALKOR AL641
No full textKiel (Germany) - Kiel (Germany)
29th September - 10th October 202
First Analysis of Climate Forcing and Response to Updated Historical Anthropogenic Aerosol With the New CMIP7 Model ICON XPP
No full textThe simple plumes (SP) parameterization for anthropogenic aerosol effects on radiation and clouds has been used in the Coupled Model Intercomparison Project phase six (CMIP6) and beyond. This study documents the new SP forcing data in preparation for use in CMIP phase seven (CMIP7) and its first application in the newly developed coupled atmosphere-ocean-river model ICON XPP. We assess historical trends and spatio-temporal differences for the aerosol optical depth of SP and find moderate differences compared to the CMIP6 data variant of SP. Radiative effects of anthropogenic aerosols from SP are estimated with atmosphere-only experiments of ICON XPP. The global all-sky effective radiative forcing (ERF all) is −0.33 WM-2 for the 2014 anthropogenic aerosols against the pre-industrial level. Using either the CMIP6 version of SP or the different climate state of present-day compared to pre-industrial yield a similar 'ERF all' of anthropogenic aerosol in ICON XPP, with global mean differences of 0.05 Wm-2 . Climate responses to the anthropogenic aerosols are computed with three-member ensembles of fully-coupled historical experiments with ICON XPP. ICON XPP shows no apparent differences in global mean responses for outgoing shortwave radiation, temperature, and precipitation when the updated SP data are prescribed in comparison to experiments that use the CMIP6 variant of SP. Such small present-day differences suggest that future extensions of historical data for SP, not an update of the entire historical period, might be sufficient for climate studies, unless larger revisions of past emissions will be made
Using Genetic Algorithms for Research Software Structure Optimization
No full textOur goal is to generate restructuring recommendations for research software systems based on software architecture descriptions that were obtained via reverse engineering. We reconstructed these software architectures via static and dynamic analysis methods in the reverse engineering process. To do this, we combined static and dynamic analysis for call relationships and dataflow into a hierarchy of six analysis methods. For generating optimal restructuring recommendations, we use genetic algorithms, which optimize the module structure. For optimizing the modularization, we use coupling and cohesion metrics as fitness functions. We applied these methods to Earth System Models to test their efficacy. In general, our results confirm the applicability of genetic algorithms for optimizing the module structure of research software. Our experiments show that the analysis methods have a significant impact on the optimization results. A specific observation from our experiments is that the pure dynamic analysis produces significantly better modularizations than the optimizations based on the other analysis methods that we used for reverse engineering. Furthermore, a guided, interactive optimization with a domain expert’s feedback improves the modularization recommendations considerably. For instance, cohesion is improved by 57% with guided optimization
The Storfjorden earthquake sequence: role of inherited crustal heterogeneity
No full textA strong earthquake sequence in Storfjorden, south of Svalbard, was initiated by an Mw 6.1 event on 2008 February 21. Earthquake distribution and fault plane solutions indicate that seismic activity is controlled by unmapped NE-SW striking oblique-normal faults, contrasting with the major N-S oriented faults mapped onshore Svalbard. We present a geophysical model derived from an ocean bottom seismometer profile crossing the seismogenic zone to identify structures in the crust and uppermost mantle that potentially control the earthquake source mechanism. Traveltime forward modelling using ray tracing, combined with traveltime tomography and gravity-magnetic modelling, reveal distinct crustal domains across the earthquake region. Crystalline crustal P-wave velocities range from 6.1 to 6.7 km s−1 at the Moho depth in the eastern section. The western profile section exhibits a higher Vp velocity lower crust (6.6–7.0 km s−1) with Vp/Vs ratios of 1.75–1.8 and high density (∼3100 kg m−3). Basement depth reaches 8 km in the west, forming a sedimentary basin, and shallows eastward. The Moho remains relatively flat at 29–32 km depth throughout the profile. The N–S oriented Caledonian suture, identified from deep seismic and potential field data, traverses the Storfjorden earthquake zone. The lithological contacts within the suture zone, inferred from the new OBS data, may facilitate seismic failure oblique to the N–S oriented structure, following the regional stress field
The chromosomal genome sequence of the elephant ear sponge, Spongia lamella (Schulze, 1879), and its associated microbial metagenome sequences
No full textWe present a genome assembly from a specimen of Spongia lamella (Elephant ear; Porifera; Demospongiae; Dictyoceratida; Spongiidae). The genome sequence has a total length of 130.43 megabases. Most of the assembly (98.43%) is scaffolded into 10 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 16.67 kilobases in length. Metagenome-assembled genomes (MAGs) representing different lineages within the Poribacteria, Rhodothermota, Chloroflexota, Acidobacteriota and Actinomycetota phyla were identified, along with one single lineage of ammonia-oxidising archaea affiliated with the genus Nitrosopumilus (phylum Thermoproteota)
The chromosomal genome sequence of the stone sponge Petrosia ficiformis (Poiret, 1789) and its associated microbial metagenome sequences
No full textWe present a genome assembly from an individual Petrosia ficiformis (stone sponge; Porifera; Demospongiae; Haplosclerida; Petrosiidae). The genome sequence is 191.3 megabases in span. Most of the assembly is scaffolded into 18 chromosomal pseudomolecules. The mitochondrial genome has also been assembled and is 18.89 kilobases in length. Gene annotation of the host organism assembly identified 18,339 protein coding genes. The metagenome of the specimen was also assembled, and 112 binned bacterial genomes were identified, including 57 high-quality MAGs. Besides MAGs characteristic of HMA sponge symbionts (i.e., Chloroflexota, Acidobacteriota), the P. ficiformis specific symbiont Candidatus Synechococcus feldmanni (formerly Aphanocapsa feldmanni (Cyanobacteriota) was recovered, as well as notably MAGs of several candidate phyla (Candidatus Latescibacteria, Poribacteria, Tectomicrobia, Dadabacteria, Kapabacteria and Binatia)
