The ice arches that usually develop at the northern and southern ends of Nares Strait play an important role in modulating the export of Arctic Ocean multi-year sea ice. The Arctic Ocean is evolving ...towards an ice pack that is younger, thinner, and more mobile and the fate of its multi-year ice is becoming of increasing interest. Here, we use sea ice motion retrievals from Sentinel-1 imagery to report on the recent behavior of these ice arches and the associated ice fluxes. We show that the duration of arch formation has decreased over the past 20 years, while the ice area and volume fluxes along Nares Strait have both increased. These results suggest that a transition is underway towards a state where the formation of these arches will become atypical with a concomitant increase in the export of multi-year ice accelerating the transition towards a younger and thinner Arctic ice pack.
The North Atlantic Oscillation (NAO) is one of the most important modes of variability in the global climate system and is characterized by a meridional dipole in the sea level pressure field, with ...centers of action near Iceland and the Azores. It has a profound influence on the weather, climate, ecosystems, and economies of Europe, Greenland, eastern North America, and North Africa. It has been proposed that around 1980, there was an eastward secular shift in the NAO’s northern center of action that impacted sea ice export through Fram Strait. Independently, it has also been suggested that the location of its southern center of action is tied to the phase of the NAO. Both of these attributes of the NAO have been linked to anthropogenic climate change. Here the authors use both the one-point correlation map technique as well as empirical orthogonal function (EOF) analysis to show that the meridional dipole that is often seen in the sea level pressure field over the North Atlantic is not purely the result of the NAO (as traditionally defined) but rather arises through an interplay among the NAO and two other leading modes of variability in the North Atlantic region: the East Atlantic (EA) and the Scandinavian (SCA) patterns. This interplay has resulted in multidecadal mobility in the two centers of action of the meridional dipole since the late nineteenth century. In particular, an eastward movement of the dipole has occurred during the 1930s to 1950s as well as more recently. This mobility is not seen in the leading EOF of the sea level pressure field in the region.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Nares Strait is a major pathway along which multi-year sea ice leaves the Arctic, an ice class that has seen a recent dramatic reduction in extent. The winds that blow along the strait play ...an important role in modulating this ice export as well as in establishing the Arctic’s largest and most productive polynya, the North Water, that forms at its southern terminus. However, its remote location has limited our knowledge of the winds along the strait. Here we use automatic weather station data from Hans Island, in the middle of the strait, to assess the ability of a set of atmospheric renalyses and analyses with a common lineage but with varying horizontal resolution to represent the variability in the wind field. We find that the flow is highly bidirectional, consistent with topographic channeling, with the highest wind speeds from the north and that a model resolution of ~ 9 km is required to capture the observed variability. The wind field at Hans Island is also found to be representative of variability in the flow along much of Nares Strait.
Water mass transformation in the Nordic and Barents Seas, triggered by air-sea heat fluxes, is an integral component of the Atlantic Meridional Overturning Circulation (AMOC). These regions are ...undergoing rapid warming, associated with a retreat in ice cover. Here we present an analysis covering 1950-2020 of the spatiotemporal variability of the air-sea heat fluxes along the region's boundary currents, where water mass transformation impacts are large. We find there is an increase in the air-sea heat fluxes along these currents that is a function of the currents' orientation relative to the axis of sea-ice change suggesting enhanced water mass transformation is occurring. Previous work has shown a reduction in heat fluxes in the interior of the Nordic Seas. As a result, a reorganization seems to be underway in where water mass transformation occurs, that needs to be considered when ascertaining how the AMOC will respond to a warming climate.
Remyelination is limited in the majority of multiple sclerosis (MS) lesions despite the presence of oligodendrocyte precursor cells (OPCs) in most lesions. This observation has led to the view that a ...failure of OPCs to fully differentiate underlies remyelination failure. OPC differentiation requires intricate transcriptional regulation, which may be disrupted in chronic MS lesions. The expression of few transcription factors has been differentially compared between remyelinating lesions and lesions refractory to remyelination. In particular, the oligodendrocyte transcription factor myelin regulatory factor (MYRF) is essential for myelination during development, but its role during remyelination and expression in MS lesions is unknown. To understand the role of MYRF during remyelination, we genetically fate mapped OPCs following lysolecithin-induced demyelination of the corpus callosum in mice and determined that MYRF is expressed in new oligodendrocytes. OPC-specific
Myrf
deletion did not alter recruitment or proliferation of these cells after demyelination, but decreased the density of new glutathione
S
-transferase π positive oligodendrocytes. Subsequent remyelination in both the spinal cord and corpus callosum is highly impaired following
Myrf
deletion from OPCs. Individual OPC-derived oligodendrocytes, produced in response to demyelination, showed little capacity to express myelin proteins following
Myrf
deletion. Collectively, these data demonstrate a crucial role of MYRF in the transition of oligodendrocytes from a premyelinating to a myelinating phenotype during remyelination. In the human brain, we find that MYRF is expressed in NogoA and CNP-positive oligodendrocytes. In MS, there was both a lower density and proportion of oligodendrocyte lineage cells and NogoA+ oligodendrocytes expressing MYRF in chronically demyelinated lesions compared to remyelinated shadow plaques. The relative scarcity of oligodendrocyte lineage cells expressing MYRF in demyelinated MS lesions demonstrates, for the first time, that chronic lesions lack oligodendrocytes that express this necessary transcription factor for remyelination and supports the notion that a failure to fully differentiate underlies remyelination failure.
Over the past ten years, scientific and technological advances have established biocatalysis as a practical and environmentally friendly alternative to traditional metallo- and organocatalysis in ...chemical synthesis, both in the laboratory and on an industrial scale. Key advances in DNA sequencing and gene synthesis are at the base of tremendous progress in tailoring biocatalysts by protein engineering and design, and the ability to reorganize enzymes into new biosynthetic pathways. To highlight these achievements, here we discuss applications of protein-engineered biocatalysts ranging from commodity chemicals to advanced pharmaceutical intermediates that use enzyme catalysis as a key step.
The Beaufort Sea High (BSH), an anti‐cyclone over the Beaufort Sea, is an important feature of the summer atmospheric circulation over the Arctic Ocean. For example, years characterized by low Arctic ...sea ice extent are typically associated with the presence of a stronger BSH; with the opposite occurring during years with high sea ice extent. In this paper, we show that there exists variability on the decadal time scale in the intensity and location of the summer BSH. We also show that there has been a trend towards a stronger summer BSH that began in the late 1990s. This trend is shown to be coincident with a tendency towards a reduction in cyclogenesis during the summer over the Beaufort Sea. We argue that that these trends are the result of a warming of the troposphere in the western Arctic and the concomitant reduction in baroclincity.
Key Points
There is a recent trend towards a more intense summer Beaufort Sea High
This trend is coincident with a reduction in cyclogenesis over the Beaufort Sea
Both trends are the result of a reduction in baroclinicity over the Arctic Ocean
Deep convection in the subpolar North Atlantic ventilates the ocean for atmospheric gases through the formation of deep water masses. Variability in the intensity of deep convection is believed to ...have caused large variations in North Atlantic anthropogenic carbon storage over the past decades, but observations of the properties during active convection are missing. Here we document the origin, extent and chemical properties of the deepest winter mixed layers directly observed in the Irminger Sea. As a result of the deep convection in winter 2014-2015, driven by large oceanic heat loss, mid-depth oxygen concentrations were replenished and anthropogenic carbon storage rates almost tripled compared with Irminger Sea hydrographic section data in 1997 and 2003. Our observations provide unequivocal evidence that ocean ventilation and anthropogenic carbon uptake take place in the Irminger Sea and that their efficiency can be directly linked to atmospheric forcing.
Phytoplankton blooms over Arctic Ocean continental shelves are thought to be restricted to waters free of sea ice. Here, we document a massive phytoplankton bloom beneath fully consolidated pack ice ...far from the ice edge in the Chukchi Sea, where light transmission has increased in recent decades because of thinning ice cover and proliferation of melt ponds. The bloom was characterized by high diatom biomass and rates of growth and primary production. Evidence suggests that under-ice phytoplankton blooms may be more widespread over nutrient-rich Arctic continental shelves and that satellite-based estimates of annual primary production in these waters may be underestimated by up to 10-fold.
Offshore Antarctic polynyas-large openings in the winter sea ice cover-are thought to be maintained by a rapid ventilation of deep-ocean heat through convective mixing. These rare phenomena may alter ...abyssal properties and circulation, yet their formation mechanisms are not well understood. Here we demonstrate that concurrent upper-ocean preconditioning and meteorological perturbations are responsible for the appearance of polynyas in the Weddell Sea region of the Southern Ocean. Autonomous profiling float observations-collected in 2016 and 2017 during the largest polynyas to form near the Maud Rise seamount since 1976-reveal that the polynyas were initiated and modulated by the passage of severe storms, and that intense heat loss drove deep overturning within them. Wind-driven upwelling of record strength weakened haline stratification in the upper ocean, thus favouring destabilization in 2016 and 2017. We show that previous Weddell polynyas probably developed under similarly anomalous conditions, which are associated with a mode of Southern Hemisphere climate variability that is predicted to strengthen as a result of anthropogenic climate change.
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