ALBERT

Description: The transports associated with the Subantarctic Front (SAF) and the Polar Front (PF) account for the majority of the volume transport of the Antarctic Circumpolar Current (ACC). After passing through Drake Passage, the SAF and the PF veer northward over the steep topography of the North Scotia Ridge. Interaction of the ACC with the North Scotia Ridge influences the sources of the Malvinas Current. This ridge is a major obstacle to the flow of deep water, with the majority of the deep water passing through the 3100 m deep gap in the ridge known as Shag Rocks Passage. Volume transports associated with these fronts were measured during the North Scotia Ridge Overflow Project, which included the first extensive hydrographic survey of the ridge, carried out in April and May 2003. The total net volume transport northward over the ridge was found to be 117 ± 10 Sv (1 Sv = 106m3s- 1). The total net transport associated with the SAF was approximately 52 ± 4 Sv, and the total transport associated with the PF was approximately 58 ± 5 Sv. Weddell Sea Deep Water was not detected passing through Shag Rocks Passage, contrary to some previous inferences.

Description: Published

Description: Harrat Rahat (,10 Ma) is one of the largest volcanic fields on western Arabia. In the north of the field, some of the youngest volcanic centres evolved through either point-like, complex or multiple aligned vents (i.e. along fissures), and have pyroclastic cones, lapilli fall deposits and/ or lava flows associated with them. The products reflect dominantly Hawaiian eruptions, and only one centre experienced phreatomagmatism. Results from new 3He surface-exposure dating provide constraints on stratigraphy of the youngest (,0.3 Ma) products. The rocks are compositionally alkali-basalt and hawaiite, with intra-plate basalt (prevalent mantle (PREMA)) affinity. Each eruption displays a distinct whole-rock composition in an overall linear trend. We suggest that the magma source for each centre is similar, and that composition of the products is different due to different degrees of fractionation. In a single eruption, the magma that reaches the surface first is the least evolved, with the most evolved magma erupting last. We also found that the most primitive magmas erupt less explosively. We think that the degree of magma evolution might correlate with ascent times, assuming that the more evolved magma spent more time en route.We suggest that magma ascent time is likely to be longer than that of other more primitive intra-plate basalts.

Description: Permafrost landscapes are changing around the Arctic in response to climate warming, with coastal erosion being one of the most prominent and hazardous features. Using drone platforms, satellite images, and historic aerial photographs, we observed the rapid retreat of a permafrost coastline on Qikiqtaruk – Herschel Island, Yukon Territory, in the Canadian Beaufort Sea. This coastline is adjacent to a gravel spit accommodating several culturally significant sites and is the logistical base for the Qikiqtaruk – Herschel Island Territorial Park operations. In this study we sought to (i) assess short-term coastal erosion dynamics over fine temporal resolution, (ii) evaluate short-term shoreline change in the context of long-term observations, and (iii) demonstrate the potential of low-cost lightweight unmanned aerial vehicles (“drones”) to inform coastline studies and management decisions. We resurveyed a 500 m permafrost coastal reach at high temporal frequency (seven surveys over 40 d in 2017). Intra-seasonal shoreline changes were related to meteorological and oceanographic variables to understand controls on intra-seasonal erosion patterns. To put our short-term observations into historical context, we combined our analysis of shoreline positions in 2016 and 2017 with historical observations from 1952, 1970, 2000, and 2011. In just the summer of 2017, we observed coastal retreat of 14.5 m, more than 6 times faster than the long-term average rate of 2.2±0.1 m a−1 (1952–2017). Coastline retreat rates exceeded 1.0±0.1 m d−1 over a single 4 d period. Over 40 d, we estimated removal of ca. 0.96 m3 m−1 d−1. These findings highlight the episodic nature of shoreline change and the important role of storm events, which are poorly understood along permafrost coastlines. We found drone surveys combined with image-based modelling yield fine spatial resolution and accurately geolocated observations that are highly suitable to observe intra-seasonal erosion dynamics in rapidly changing Arctic landscapes.

Description: Snow cover affects the variability of the physical properties of sea ice. The snow’s unique thermal and optical properties govern the mass and energy fluxes in the sea ice system. They are important for sea ice evolution, energy exchanges between the ocean and the atmosphere, and light availability for ecosystems below the sea ice. Furthermore, snow significantly impacts remote sensing retrievals, especially for sea ice thickness. Yet, data on the physical properties of snow and its effects on sea ice are extremely limited, especially in Antarctica. This leads to large uncertainties in the coupling of climate feedback and results in significant biases in model representations of the sea ice cover. During our field campaign from October-December 2022 in McMurdo Sound, we quantitatively investigated the physical properties of snow on Antarctic sea ice, following the same protocols used during the MOSAiC expedition. The season’s unique sea ice conditions provided the ideal laboratory to study a range of snow conditions and to differentiate between sea ice and snow drivers for the atmosphere-sea ice-ocean system. Our set of snow measurements on sea ice, unprecedented in Antarctica, includes ground snow/ice measurements, automatic weather and radiation stations, and drone-based measurements. These extensive measurements made it possible to capture the physical properties of snow and their spatial variability and simultaneously measure the different components of the energy balance at varying spatial scales. We will use this dataset to improve our understanding of snow's role in the Antarctic sea ice system.

Description: The increasing amount of fresh water entering the Southern Ocean due to mass loss from the Antarctic ice sheet and ice shelves loss has been proposed as a mechanism responsible for the lack of decline in Antarctic sea ice area, in contrast to the sea-ice loss seen in the Arctic. Though increased Antarctic ice-mass loss is expected to impact climate it is absent from almost all current coupled climate models, which typically enforce that the continent remain in perpetual mass balance. Further, previous model experiments suggest that the climate response to Antarctic mass loss depends on the model used, and that the reasons for this model dependence are not clear. We use the HadGEM3-GC3.1 model to contribute model experiments to the Southern Ocean Freshwater release model experiments Initiative (SOFIA), an international model intercomparison, in which freshwater is added to the ocean surrounding Antarctica to simulate the otherwise missing ice-sheet mass loss. This unique suite of models will allow us to evaluate HadGEM3-GC3.1, identify reasons for model discrepancies, and quantify the potential impact of the absence of increasing Antarctic ice-mass loss on Antarctic sea ice and climate. We will give an overview of the SOFIA project and present preliminary results from the “antwater” experiment outlined in the SOFIA protocol in which a constant freshwater input of 0.1 Sv is distributed evenly around Antarctica at the ocean surface under pre-industrial forcing. We will show the response of Antarctic sea ice and the local and global climate to this freshwater forcing.

Description: Potential future impacts on sea ice and other climate variables from changing freshwater outflow from the Antarctic ice sheets and ice shelves were examined in this study. Fully-coupled model experiments were run using ramped freshwater, including latent heat effects, under historical and RCP8.5 greenhouse gas forcings. Specifically, three climate model scenarios in CCSM4.0 for 1980-2100 (FWIncr, FWConst, FWOff) and one idealized experiment for 1850-1950 (FWIncrHist) were run and compared with a control. We chose to run from base years of 1850 for pre-industrial conditions and 1980 for a year we assumed the Antarctic ice sheet was in mass balance. We then increased freshwater fluxes to give the approximate equivalent of 3 m of sea level rise over a 150 year period. For FWIncrHist, sea ice area continued to increase over the 100 year period. For FWIncr, sea ice area increased for approximately 78 years, when it began to decrease. Two shorter branched runs (FWConst, and FWOff) were carried out to test the persistence of the effects, one where the additional fresh water and latent heat effects were switched off and the other where the freshwater was held constant at the point where sea ice area behaviour “turned around”. This was to separate out the effects of greenhouse gas forcing on the ramped freshwater and latent heat effects over long time periods. The persistence of the effects on sea ice area were relatively short, with a return to control conditions in less than a decade when freshwater was switched off.