Increasing Multiyear Sea Ice Loss in the Beaufort Sea: A New Export Pathway for the Diminishing Multiyear Ice Cover of the Arctic Ocean

Historically, multiyear sea ice (MYI) covered a majority of the Arctic and circulated through the Beaufort Gyre for years. However, increased ice melt in the Beaufort Sea during the early 2000s was proposed to have severed this circulation. Constructing a regional MYI budget from 1997 to 2021 reveals that MYI import into the Beaufort Sea has increased year-round, yet less MYI now survives through summer and is transported onwards in the Gyre. Annual average MYI loss quadrupled over the study period and increased from ∼7% to ∼33% of annual Fram Strait MYI export, while the peak in 2018 (385,000 km2) was similar in magnitude to Fram Strait MYI export. The ice-albedo feedback coupled with the transition toward younger thinner MYI is responsible for the increased MYI loss. MYI transport through the Beaufort Gyre has not been severed, but it has been reduced so severely to prevent it from being redistributed throughout the Arctic Ocean

Arctic Ocean outflow and glacier-ocean interactions modify water over the Wandel Sea shelf (northeastern Greenland)

Abstract. The first-ever conductivity–temperature–depth (CTD) observations on the Wandel Sea shelf in northeastern Greenland were collected in April–May 2015. They were complemented by CTDs taken along the continental slope during the Norwegian FRAM 2014–2015 drift. The CTD profiles are used to reveal the origin of water masses and interactions with ambient water from the continental slope and the tidewater glacier outlet. The subsurface water is associated with the Pacific water outflow from the Arctic Ocean. The underlying halocline separates the Pacific water from a deeper layer of polar water that has interacted with the warm Atlantic water outflow through the Fram Strait, recorded below 140 m. Over the outer shelf, the halocline shows numerous cold density-compensated intrusions indicating lateral interaction with an ambient polar water mass across the continental slope. At the front of the tidewater glacier outlet, colder and turbid water intrusions were observed at the base of the halocline. On the temperature–salinity plots these stations indicate a mixing line that is different from the ambient water and seems to be conditioned by the ocean–glacier interaction. Our observations of Pacific water are set within the context of upstream observations in the Beaufort Sea and downstream observations from the Northeast Water Polynya, and clearly show the modification of Pacific water during its advection across the Arctic Ocean. Moreover, ambient water over the Wandel Sea slope shows different thermohaline structures indicating the different origin and pathways of the on-shore and off-shore branches of the Arctic Ocean outflow through the western Fram Strait. </jats:p

Micrometeorological and Thermal Control of Frost Flower Growth and Decay on Young Sea Ice

Frost flowers are transient crystal structures that form on new and young sea ice surfaces. They have been implicated in a variety of biological, chemical, and physical processes and interactions with the atmosphere at the sea ice surface. We describe the atmospheric and radiative conditions and the physical and thermal properties of the sea ice and atmosphere that form, decay, and destroy frost flowers on young sea ice. Frost flower formation occurred during a high-pressure system that caused air temperatures to drop to −30˚C, with relative humidity of 70% (an undersaturated atmosphere), and very calm wind conditions. The sea ice surface temperature at the time of frost flower initiation was 10˚–13˚C warmer than the air temperature. Frost flowers grew on nodules raised above the mean surface height by 5 mm, which were 4˚–6˚C colder than the bare, brine-wetted, highly saline sea ice surface that provided the necessary moisture. The cold nodules created potential water vapour supersaturation zones above them with respect to air over the brine skim. Frost flowers formed and grew overnight in the absence of shortwave radiation, while the net longwave radiation was negative and dominated the net all-wave radiation balance at the surface. The observed crystal habits of the frost flowers were long needles, betraying their origin from the vapour phase at temperatures between −20˚C and −30˚C. After a night of growth, frost flowers decayed in association with increased solar radiation, a net surface radiation balance of 0 W m-2, increased air and surface temperatures, increased wind speed, and decreased relative humidity. We hypothesize that these conditions increased vertical mixing, which eroded near-surface water vapour saturation and initiated sublimation. The frost flowers finally were rapidly destroyed by snowfall.Les fleurs de glace sont des structures cristallines transitoires qui se forment sur des surfaces de glace de mer nouvelles et jeunes. Elles découlent de divers processus et interactions biologiques, chimiques et physiques avec l’atmosphère, à la surface de la glace de mer. Nous décrivons les conditions atmosphériques et radiatives de même que les propriétés physiques et thermiques de la glace de mer qui forment, détériorent et détruisent les fleurs de glace sur la jeune glace de mer. La formation de fleurs de glace s’est produite lorsqu’un système de haute pression a fait baisser les températures de l’air à −30 ˚C, avec une humidité relative de 70 % (atmosphère sous-saturée) et un régime des vents très calme. À l’amorçage des fleurs de glace, la température à la surface de la glace de mer était de 10˚ à 13 ˚C plus chaude que la température de l’air. Les fleurs de glace se sont formées sur des nodules élevés au-dessus de la hauteur moyenne de la surface dans une mesure de 5 mm, ce qui était entre 4˚ et 6 ˚C plus froid que la surface de glace de mer brute, saumurée et fortement saline qui a fourni l’humidité nécessaire. En ce qui a trait à l’air au-dessus de l’écume de saumure, les nodules de froid ont créé des zones potentielles de sursaturation de vapeur d’eau au-dessus. Des fleurs de glace se sont formées et ont grossi pendant la nuit, en l’absence de rayonnement de courtes longueurs d’onde, tandis que le rayonnement net de grandes longueurs d’onde était négatif et dominait l’équilibre du rayonnement net de toutes ondes à la surface. L’habitus cristallin observé dans les fleurs de glace prenait la forme de longues aiguilles, trahissant son origine de la phase vapeur à des températures variant de −20 ˚C à −30 ˚C. Après une nuit de croissance, les fleurs de glace se sont détériorées en présence du rayonnement solaire accru, du bilan radiatif de la surface de 0 W m-2, des températures accrues de l’air et de la surface, de la plus grande vitesse du vent et de l’humidité relative réduite. Nous formulons l’hypothèse que ces conditions ont eu pour effet d’augmenter le mélange vertical, ce qui a érodé la saturation de vapeur d’eau près de la surface et déclenché la sublimation. Par la suite, les fleurs de glace ont été rapidement détruites par la chute de neige

Atypical chemokine receptor 4 shapes activated B cell fate

Activated B cells can initially differentiate into three functionally distinct fates-early plasmablasts (PBs), germinal center (GC) B cells, or early memory B cells-by mechanisms that remain poorly understood. Here, we identify atypical chemokine receptor 4 (ACKR4), a decoy receptor that binds and degrades CCR7 ligands CCL19/CCL21, as a regulator of early activated B cell differentiation. By restricting initial access to splenic interfollicular zones (IFZs), ACKR4 limits the early proliferation of activated B cells, reducing the numbers available for subsequent differentiation. Consequently, ACKR4 deficiency enhanced early PB and GC B cell responses in a CCL19/CCL21-dependent and B cell-intrinsic manner. Conversely, aberrant localization of ACKR4-deficient activated B cells to the IFZ was associated with their preferential commitment to the early PB linage. Our results reveal a regulatory mechanism of B cell trafficking via an atypical chemokine receptor that shapes activated B cell fate

Measurement of the t t-bar production cross section in the dilepton channel in pp collisions at sqrt(s) = 7 TeV

The t t-bar production cross section (sigma[t t-bar]) is measured in proton-proton collisions at sqrt(s) = 7 TeV in data collected by the CMS experiment, corresponding to an integrated luminosity of 2.3 inverse femtobarns. The measurement is performed in events with two leptons (electrons or muons) in the final state, at least two jets identified as jets originating from b quarks, and the presence of an imbalance in transverse momentum. The measured value of sigma[t t-bar] for a top-quark mass of 172.5 GeV is 161.9 +/- 2.5 (stat.) +5.1/-5.0 (syst.) +/- 3.6(lumi.) pb, consistent with the prediction of the standard model.Comment: Replaced with published version. Included journal reference and DO

Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV

A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7 TeV is presented. The data were collected at the LHC, with the CMS detector, and correspond to an integrated luminosity of 4.6 inverse femtobarns. No significant excess is observed above the background expectation, and upper limits are set on the Higgs boson production cross section. The presence of the standard model Higgs boson with a mass in the 270-440 GeV range is excluded at 95% confidence level.Comment: Submitted to JHE