The Antarctic Marginal Ice Zone (MIZ) accounts for 15% of the Southern Ocean's primary production (PP), but limited data has hindered understanding of its variability and connection to carbon export. ...Using a combination of gliders, biogeochemical Argo floats and satellite observations in the northeast Weddell Sea, we show that years with more sea‐ice formation over winter are followed by more intense phytoplankton blooms (∼15% greater daily PP) and export to 100 m (∼50% higher daily carbon export) the following summer. However, the carbon export beyond the deepest winter mixed layer did not vary in proportion to PP, suggesting different drivers of carbon export at depth compared to surface waters. Furthermore, across the entire MIZ, the response of blooms to sea‐ice volume was spatially variable, indicating the need to consider spatial heterogeneity in the response of the biological carbon pump to future sea‐ice changes.
Plain Language Summary
Algae in the ocean surface take up carbon dioxide from the atmosphere through photosynthesis and transfer it to the deep ocean when they die and sink. This process is key to maintaining a habitable planet and is known as the biological carbon pump (BCP). The seasonally ice‐covered ocean around Antarctica is one of the most active areas for algal growth, but also a region of rapid climate change. Because of the difficulty in taking measurements in this remote region, the physical and biological processes that control the growth and sinking of algae and its response to changing sea‐ice remain uncertain. In this study, we use a combination of satellites and autonomous robots to elucidate the role of sea‐ice variability on the BCP. We find that sea‐ice impacts algal growth by its influence on both the light and nutrient conditions needed for photosynthesis. Predicting the amount of algae that subsequently sinks to depth as carbon flux, although influenced by sea‐ice conditions, is more complex and linked to the greater marine ecosystem. Evidence suggests that the species of algae, zooplankton grazing, and the rate at which dead algae breaks down and sinks are important and should be a focus point for further research.
Key Points
High‐resolution in‐situ observations are used to characterize multi‐year phytoplankton bloom phenology and amplitude in the Antarctic Marginal Ice Zone
Years with greater sea‐ice volume drive deeper mixing that tend to support higher magnitude blooms in the northeast Weddell Sea
Carbon export efficiency is affected by bloom magnitude, community composition and water column stratification
In the sea‐ice‐impacted Southern Ocean, the spring sea‐ice melt and its impact on physical processes set the rate of surface water mass modification. These modified waters will eventually subduct ...near the polar front and enter the global overturning circulation. Submesoscale processes modulate the stratification of the mixed layer (ML) and ML properties. Sparse observations in polar regions mean that the role of submesoscale motions in the exchange of properties across the base of the ML is not well understood. The goal of this study is to determine the interplay between sea‐ice melt, surface boundary layer forcing, and submesoscale flows in setting properties of the surface ML in the Antarctic marginal ice zone. High‐resolution observations suggest that fine‐scale lateral fronts arise from either/both mesoscale and submesoscale stirring of sea‐ice meltwater anomalies. The strong salinity‐driven stratification at the base of the ML confines these fronts to the upper ocean, limiting submesoscale vertical fluxes across the ML base. This strong stratification prevents the local subduction of modified waters by submesoscale flows, suggesting that the subduction site that links to the global overturning circulation does not correspond with the location of sea‐ice melt. However, surface‐enhanced fronts increase the potential for Ekman‐driven cross‐frontal flow to modulate the stability of the ML and ML properties. The parameterization of submesoscale processes in coupled‐climate models, particularly those contributing to the Ekman buoyancy flux, may improve the representation of ML heat and freshwater transport in the ice‐impacted Southern Ocean during summer.
Plain Language Summary
Sea‐ice melt around Antarctica is an annual event in which the state of the surface ocean is transformed, during which over 15 trillion liters of freshwater enter the upper ocean. This fresh layer separates the upper ocean from the deep ocean and suppresses the exchange of heat and gases—like carbon dioxide—between the deep ocean and the atmosphere, with important implications for the climate system. Using state‐of‐the‐art autonomous underwater gliders, we observed key physical properties of the surface ocean following the melt of sea‐ice. The presence of fine‐scale fronts (sharp changes in density), of less than 10 km at horizontal scales, revealed that sea‐ice melt not only stabilizes the upper ocean, but also provides additional energy for small eddies and filaments to form. While the eddies are unable to extend deeper than the fresher surface layer, they enhance the ocean response to winds. These findings may contribute to the improvement of global climate models and our understanding of how the ocean will react to changes in sea‐ice under a warmer climate.
Key Points
Sea‐ice meltwater controls the buoyancy of the mixed layer during early summer
Mixed layer eddies grow from mesoscale meltwater lateral gradients but are confined to the surface boundary layer
Observations suggest that mixed layer variability at submesoscales is dominated by wind‐front interactions
Statistical analyses and model-data inter-comparisons are performed to evaluate the model's ability to reproduce the dynamics in the upper layers (<2000m) of the South Atlantic ocean. Outputs of an ...eddy-resolving Ocean General Circulation Model (OGCM) are analyzed and compared with observed data. The model, a 1/12-degree, 22-layer implementation of the Hybrid Coordinate Ocean Model (HYCOM) to the South Atlantic, was forced with monthly-mean products from the NCEP Reanalysis for the period 1960 to 2010. The numerical experiment was capable to reproduce the large scale and the mesoscale dynamic in the South Atlantic and in the Agulhas region. The vertical structure is in agreement with in situ data, the model has lower skill when compared with PIRATA lower temperatures, and is able to capture the seasonal and annual variability in the tropical Atlantic. Furthermore, sensitive change until 2007 is clear in the vertical structure, at 4°N–38°W; 0°–35°W and 10°S–10°W, suggesting an important change in the stratification. The primary results concern a significant change in the decadal anomalies of the temperatures and salinity, which exhibit a warmer and saltier water in the southeastern Atlantic. Furthermore, linear trends found in the transport time-series in the North Brazil Current, and the South Equatorial Current were seen to correspond with increasing trends of the warmer water from the Agulhas Current into South Atlantic. The integrated transport during the period 1960–2010, shows an increase in westward changes in the large-scale circulation south of Africa are show in the negative trends indicate a widening of the “Agulhas gap” and increase in westward volume transport since 1980. It is therefore suggested that variability in the Agulhas System on the last two decades is affecting the dynamic in the South Atlantic, namely the temperature and the volume transport, reach the tropical region of the Atlantic.
•Simulated the South Atlantic (SA) with a high resolution numerical implementation•Increasing trend in the SA and the SSH in the Agulhas retroflection region•Widening of the Agulhas gap and an increase in the transport by the Agulhas Current
Water mass transformation in the Southern Ocean is vital for driving the large‐scale overturning circulation, which transports heat from the surface to the ocean interior. Using profiling gliders, ...this study investigates the role of summertime buoyancy forcing and wind‐driven processes on the intraseasonal (1–10 days) mixed layer thermohaline variability in three Southern Ocean regions southwest of Africa important for water mass transformation—the Subantarctic Zone (SAZ), Polar Frontal Zone (PFZ), and Marginal Ice Zone (MIZ). At intraseasonal time scales, heat flux was shown as the main driver of buoyancy gain in all regions. In the SAZ and MIZ, shallow mixed layers and strong stratification enhanced mixed layer buoyancy gain by trapping incoming heat, while buoyancy loss resulted primarily from the entrainment of cold, salty water from below. In the PFZ, rapid mixing linked to Southern Ocean storms set persistently deep mixed layers and suppressed mixed layer intraseasonal thermohaline variability. In the polar regions, lateral stirring of meltwater from seasonal sea‐ice melt dominated daily mixed layer salinity variability. We propose that these meltwater fronts are advected to the PFZ during late summer, indicating the potential for seasonal sea‐ice freshwater to impact a region where the upwelling limb of overturning circulation reaches the surface. This study reveals a regional dependence of how the mixed layer thermohaline properties respond to small spatiotemporal processes, emphasizing the importance of surface forcing occurring between 1 and 10 days on the mixed layer water mass transformation in the Southern Ocean.
Plain Language Summary
The Southern Ocean extends from the cold and fresh polar waters near Antarctica to the warm and salty subtropics and is capped by a region called the mixed layer, where winds keep properties well mixed. Mixed layer waters play a key role in the Earth's climate by taking up heat from the atmosphere before being transported into the ocean interior, where they remain for centuries. The process by which heat leaves the mixed layer is poorly understood, but recent observations suggest that oceanic currents that vary on the scale of a few kilometers, that are not represented well in climate models, may dominate this exchange. Using autonomous ocean gliders at three locations from the northern to the southern Southern Ocean, we show that in the Subantarctic and sea‐ice‐impacted sea, shallow mixed layers lead to increased warming by trapping incoming heat from the atmosphere, while winds simultaneously mix up colder, saltier water from below. North of the sea‐ice‐impacted ocean, mixing by strong winds throughout the summer reduces mixed layer warming. Our findings show how mixed layer conditions within the Southern Ocean respond to daily weather variability, improving our understanding of how the ocean responds to the atmosphere above.
Key Points
Regional glider missions reveal 1–10 day mixed layer variability in the Subantarctic, Polar, and sea‐ice impacted Southern Ocean
Surface heating drives buoyancy gain in all regions, while entrainment leads to buoyancy loss in the Subantarctic and Marginal Ice Zone
In the Polar Frontal Zone, deep mixing by storms suppresses intraseasonal thermohaline variability
PARAMETRIC MANDIBLE RECONSTRUCTION PLATE Giddy, Brett; van der Merwe, Johan
South African journal of industrial engineering,
11/2020, Letnik:
31, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Hierdie studie ondersoek die vatbaarheid van 'n parametriese mandibel rekonstruksieplaat om die sjirurgiese aanvoortyd te verminder, die passing te verbeter en om die resspannings te verminder. Die ...parametriese plate is genereer aan die hand van gesimuleerde kefalometriese afmetings. 'n Eindige element analise en rekonstruksie plaat-mandibel passing toets is uitgevoer op verskeie kombinasies om te bepaal of die parametriese plaat 'n gepaste alternatief tot konvensionele rekonstruksie plate bied in terme van passing en strukturele vertoning. Die resultate toon dat die parametriese plaat struktureel beter is as 'n konvensionele plaat. Die toets het ook aangedui dat die plaat 'n redelike skatting van mandibel geometrie verskaf.
Abstract
The seasonal warming of Antarctic Winter Water (WW) is a key process that occurs along the path of deep water transformation to intermediate waters. These intermediate waters then enter the ...upper branch of the circumpolar overturning circulation. Despite its importance, the driving mechanisms that mediate the warming of Antarctic WW remain unknown, and their quantitative evaluation is lacking. Using 38 days of glider measurements of microstructure shear, we characterize the rate of turbulent dissipation and its drivers over a summer season in the northern Weddell Sea. Observed dissipation rates in the surface layer are mainly forced by winds and explained by the stress scaling (
r
2
= 0.84). However, mixing to the base of the mixed layer during strong wind events is suppressed by vertical stratification from sea ice melt. Between the WW layer and the warm and saline circumpolar deep water, a subsurface layer of enhanced dissipation is maintained by double-diffusive convection (DDC). We develop a WW layer temperature budget and show that a warming trend (0.2°C over 28 days) is driven by a convergence of heat flux through mechanically driven mixing at the base of the mixed layer and DDC at the base of the WW layer. Notably, excluding the contribution from DDC results in an underestimation of WW warming by 23%, highlighting the importance of adequately representing DDC in ocean models. These results further suggest that an increase in storm intensity and frequency during summer could increase the rate of warming of WW with implications for rates of upper-ocean water mass transformation.
Significance Statement
Around Antarctica, the summer warming of the subsurface cold Antarctic Winter Water feeds the upper layer of the overturning circulation. This study aims to quantify the mechanisms that mediate the warming of Antarctic Winter Water. Our results reveal that the observed warming of this layer can be explained by both surface wind-driven mixing processes as well as double-diffusive convection occurring beneath the Winter Water layer. Understanding the role of these mechanisms is important for understanding the regions upper-ocean heat distribution, the rates of water mass transformation and how they might respond to changes in sea ice, stratification, and the overlying large-scale winds.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
L'articolo si occupa di aspetti normativi e competitivi della penetrazione reciproca da parte delle banche canadesi e statunitensi nei rispettivi mercati nazionali . Gli autori valutano il grado in ...cui i fattori economici sono gli unici responsabili per la differenza nei tassi di crescita tra le banche nazionali ed estere in Nord America. Essi sostengono che il regolamento non ha inciso sullala crescita delle banche estere in Nord America affrontando la questione della reciprocità in regolamenti bancari , prima di esaminare le banche estere negli Stati Uniti e il modo in cui sono state regolamentate .The paper is concerned with regulatory and competitive aspects of the mutual penetration by Canadian and U.S. banks of each other’s domestic markets. The authors assess the degree to which economic factors alone are responsible for the difference in growth rates between domestic and foreign banks in North America. They argue that regulation has not affected the growth of foreign banks in North America by addressing the question of reciprocity in banking regulations, before examining foreign banks in the U.S. and the manner in which they have been regulated. U.S. banks operating in Canada are then dealt with. Finally, the results of an empirical test of the proposition that the growth of cross-border banking is attributable to factors other than differential regulation is presented. JEL: G21
The work identifies current and future changes in the international banking system, and considers the effect of these changes on regulation and on banking stability. In order to provide the proper ...context for the discussion, the authors begin with a review of certain salient events and changes of the 1970s, analysing the processes that have been set in motion and lessons to be learned. Several hypotheses about the future of international banking with regards to general trends and new directions are then offered. Four possible events of the 1980s and their ramifications for the banking system are then considered. Finally, the authors propose four actions for bank regulators in order to prepare for the coming landscape in which technology and banking sophistication will allow many new entrants into the field of wholesale banking. JEL: G21, G28
The paper is concerned with regulatory and competitive aspects of the mutual penetration by Canadian and U.S. banks of each other’s domestic markets. The authors assess the degree to which economic ...factors alone are responsible for the difference in growth rates between domestic and foreign banks in North America. They argue that regulation has not affected the growth of foreign banks in North America by addressing the question of reciprocity in banking regulations, before examining foreign banks in the U.S. and the manner in which they have been regulated. U.S. banks operating in Canada are then dealt with. Finally, the results of an empirical test of the proposition that the growth of cross-border banking is attributable to factors other than differential regulation is presented. JEL: G21
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