Quantitative precipitation estimation over antarctica using different ze-sr relationships based on snowfall classification combining ground observations

Snow plays a crucial role in the hydrological cycle and energy budget of the Earth, and remote sensing instruments with the necessary spatial coverage, resolution, and temporal sampling are essential for snowfall monitoring. Among such instruments, ground-radars have scanning capability and a resolution that make it possible to obtain a 3D structure of precipitating systems or vertical profiles when used in profiling mode. Radars from space have a lower spatial resolution, but they provide a global view. However, radar-based quantitative estimates of solid precipitation are still a challenge due to the variability of the microphysical, geometrical, and electrical features of snow particles. Estimations of snowfall rate are usually accomplished using empirical, long-term relationships between the equivalent radar reflectivity factor (Ze) and the liquid-equivalent snowfall rate (SR). Nevertheless, very few relationships take advantage of the direct estimation of the microphysical characteristics of snowflakes. In this work, we used a K-band vertically pointing radar collocated with a laser disdrometer to develop Ze-SR relationships as a function of snow classification. The two instruments were located at the Italian Antarctic Station Mario Zucchelli. The K-band radar probes the low-level atmospheric layers, recording power spectra at 32 vertical range gates. It was set at a high vertical resolution (35 m), with the first trusted range gate at a height of only 100 m. The disdrometer was able to provide information on the particle size distribution just below the trusted radar gate. Snow particles were classified into six categories (aggregate, dendrite aggregate, plate aggregate, pristine, dendrite pristine, plate pristine). The method was applied to the snowfall events of the Antarctic summer seasons of 2018–2019 and 2019–2020, with a total of 23,566 min of precipitation, 15.3% of which was recognized as showing aggregate features, 33.3% dendrite aggregate, 7.3% plates aggregate, 12.5% pristine, 24% dendrite pristine, and 7.6% plate pristine. Applying the appropriate Ze-SR relationship in each snow category, we calculated a total of 87 mm water equivalent, differing from the total found by applying a unique Ze-SR. Our estimates were also benchmarked against a colocated Alter-shielded weighing gauge, resulting in a difference of 3% in the analyzed periods

Dust Transport to the Taylor Glacier, Antarctica, During the Last Interglacial

Changes in the composition of dust trapped in ice provide evidence of past atmospheric circulation and earth surface conditions. Investigations of dust provenance in Antarctic ice during glacial and interglacial periods indicate that South America is the primary dust source during both climate regimes. Here, we present results from a new ice core dust archive extracted from the Taylor Glacier in coastal East Antarctica during the deglacial transition from Marine Isotope Stage 6 to 5e. Radiogenic strontium and neodymium isotopes indicate that last interglacial dust is young and volcanic, in contrast to the observed preindustrial and Holocene (Marine Isotope Stage 1) dust composition. The dust composition differences from the last interglacial and current interglacial period at the site require a profound difference in atmospheric transport and environmental conditions. We consider several potential causes for enhanced transport of volcanic material to the site, including increased availability of volcanic material and large‐scale atmospheric circulation changes.Plain Language SummaryFluctuations in the isotopic composition of dust particles transported atmospherically and trapped in East Antarctic ice during glacial and interglacial periods provide glimpses into past earth surface conditions and atmospheric dynamics through time. Here we present new ice core records of dust from the Taylor Glacier (Antarctica), extending back to the transition into the last interglacial period (~130,000 years ago). Dust deposited at this site during the last interglacial period has a significantly more volcanic dust composition compared to the current interglacial dust, caused by a pronounced wind direction change and/or increased subaerial exposure of volcanic material. The distinct dust compositions during two separate interglacial periods suggest significant differences in conditions at the dust source areas and atmospheric dynamics to this peripheral Antarctic site.Key PointsLast interglacial dust composition in Taylor Glacier ice is distinct from MIS 1 recordSr and Nd isotope signatures indicate a young volcanic sourceGeochemical data suggest a change in provenance and atmospheric circulation between MIS 5e and MIS 1Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/148354/1/grl58638_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/148354/2/grl58638.pd

Metal Ion-dependent Heavy Chain Transfer Activity of TSG-6 Mediates Assembly of the Cumulus-Oocyte Matrix

The matrix polysaccharide hyaluronan (HA) has a critical role in the expansion of the cumulus cell-oocyte complex (COC), a process that is necessary for ovulation and fertilization in most mammals. Hyaluronan is organized into a cross-linked network by the cooperative action of three proteins, inter-α-inhibitor (IαI), pentraxin-3, and TNF-stimulated gene-6 (TSG-6), driving the expansion of the COC and providing the cumulus matrix with its required viscoelastic properties. Although it is known that matrix stabilization involves the TSG-6-mediated transfer of IαI heavy chains (HCs) onto hyaluronan (to form covalent HC·HA complexes that are cross-linked by pentraxin-3) and that this occurs via the formation of covalent HC·TSG-6 intermediates, the underlying molecular mechanisms are not well understood. Here, we have determined the tertiary structure of the CUB module from human TSG-6, identifying a calcium ion-binding site and chelating glutamic acid residue that mediate the formation of HC·TSG-6. This occurs via an initial metal ion-dependent, non-covalent, interaction between TSG-6 and HCs that also requires the presence of an HC-associated magnesium ion. In addition, we have found that the well characterized hyaluronan-binding site in the TSG-6 Link module is not used for recognition during transfer of HCs onto HA. Analysis of TSG-6 mutants (with impaired transferase and/or hyaluronan-binding functions) revealed that although the TSG-6-mediated formation of HC·HA complexes is essential for the expansion of mouse COCs in vitro, the hyaluronan-binding function of TSG-6 does not play a major role in the stabilization of the murine cumulus matrix

ClimAntartide. Il sito Web

Il rapporto tecnico presenta la nuova versione del sito internet dell'Osservatorio Meteo-Climatologico Antartico (http://www.climantartide.it). Antartico (http://www.climantartide.it). Il sito, creato nella sua prima versione nel 2003, ha sempre avuto il compito di promuovere le attività dell'Osservatorio e di rendere accessibili alla comunità scientifica i dati meteo-climatici acquisiti durante le campagne antartiche. La nuova versione pubblicata nel 2017 è caratterizzata da una nuova struttura, alleggerita e conforme ai nuovi standard e alle nuove tecniche di visualizzazione. La lettura è divenuta più immediata, la catalogazione dei dati è ora affidata ad algoritmi specifici mentre procedure automatiche gestiscono le richieste dati da parte degli utenti. Il sito è così divenuto, nel corso del tempo, una complessa applicazione web-db.This technical report presents the new version of the Antarctic Meteo-Climatological Observatory website (http://www.climantartide.it). The first website version was published in the 2003 with the task of promoting the activities of the Observatory and of providing to the scientific community meteoclimatological data acquired during the Antarctic campaigns. The 2017 release is characterized by a new structure conforming to new standards and visualization techniques. Now the web surfing is more immediate, specific algorithms manage the database while automated procedures handle data requests from users. In this way the website has become, over time, a complex web-db application

Bromine, Iodine and Mercury on the East Antarctic plateau: preliminary results from sampling along a traverse.

Sunlit snow is photochemically active and plays a key role in the exchange of gas phase species between the cryosphere and the atmosphere. Bromine (Br), Iodine (I) and Mercury (Hg) can be photoactivated by the UV radiation and released from the snowpack into the atmosphere. Mercury is a heavy toxic metal very labile in the snowpack where it can be photoreduced back to elemental Hg (Hg(0)) and exchanged with the atmosphere. Similarly, iodine can undergo photochemical activation in surface snow and be remitted in the atmosphere where it has a role in new particle formation. Bromine is involved in the polar mercury cycle (Atmospheric mercury depletion events) as well as contributing to the polar tropospheric ozone cycle causing the so-called Ozone depletion events. However, it seems to be more stable after deposition into the snowpack. Here we present measurements of bromine, iodine and mercury performed by ICP-MS, on bulk and surface snow samples taken over a 600 km traverse in East Antarctica (East Antarctic International Ice Sheet Traverse, EAIIST 2019). The samples give us deposition records of the last season and the last few years for the surface and bulk samples, respectively. The analyses show a decrease of concentrations toward the inland except for the sites characterised by a strong snow metamorphosis caused mainly by the wind friction. Future studies will investigate the possible link between the concentration profile and the variation of the solar radiation reaching the Antarctic Plateau during spring caused by the ozone hole formation

Sea salt sodium record from Talos Dome (East Antarctica) as a potential proxy of the Antarctic past sea ice extent

Antarctic sea ice has shown an increasing trend in recent decades, but with strong regional differences from one sector to another of the Southern Ocean. The Ross Sea and the Indian sectors have seen an increase in sea ice during the satellite era (1979 onwards). Here we present a record of ssNa+ flux in the Talos Dome region during a 25-year period spanning from 1979 to 2003, showing that this marker could be used as a potential proxy for reconstructing the sea ice extent in the Ross Sea and Western Pacific Ocean at least for recent decades. After finding a positive relationship between the maxima in sea ice extent for a 25-year period, we used this relationship in the TALDICE record in order to reconstruct the sea ice conditions over the 20th century. Our tentative reconstruction highlighted a decline in the sea ice extent (SIE) starting in the 1950s and pointed out a higher variability of SIE starting from the 1960s and that the largest sea ice extents of the last century occurred during the 1990s

Bromine, Iodine and Mercury Spatial Variability and Seasonal Accumulation Along the EAIIST Traverse

This research investigates the possible influence of the ozone hole on the geochemical cycles, between the cryosphere and the atmosphere, of iodine (I), bromine (Br), and mercury (Hg) in East Antarctica. Both Br and I promotes the destruction of the tropospheric ozone layer and while iodine is a photoreactive element, bromine is expected to have no significant post-depositional mechanisms in the snowpack. Hg is a toxic heavy metal present in the environment in several different chemical forms and as iodine, once in the snowpack, it can be photoactivated by the ultraviolet (UV) radiation (280-320 nm mainly) and released from the snowpack into the atmosphere. They have a well-known diurnal cycle of exchange between surface snow and the atmosphere, and here we try to identify the connection between the ozone hole cycle and the Hg and I spatial distribution and seasonal cycle. The increased amounts of UV radiation reaching the snow surface due to ozone layer depletion, could promote the photo-reactivity of mercury and iodine in the photic zone of the snow leading to their higher re-emission from the snow surface. In surface and bulk snow samples and in shallow core from the East Antarctic International Ice Sheet Traverse project (EAIIST), concentration measurements are performed by ICP-MS and experimental data are compared to data from atmospheric chemical models such as CAM-CHEM. Concentration results in surface snow show a decreasing trend for mercury and iodine moving inland along the EAIIST route, toward the centre of the ozone hole. Bromine has no significant post-depositional mechanisms and probably the inland surface snow concentration is influenced by spring coastal bromine explosions. Comparing the bulk and surface samples we can hypothesize that iodine undergoes spring summer snow recycling and accumulates in the snow during the winter months when photochemistry ceases. Mercury instead, seems controlled by an interplay of the oxidative capacity of the atmosphere and surface snow photochemistry emissions. On going shallow cores analysis are expected to improve our knowledge about the seasonal accumulation of the analytes and what influences them. Moreover, we expect to find a tipping point, a change into the iodine concentration, and possibly the mercury concentration, corresponding with the ozone hole formation. These results would define iodine and/or mercury as proxy for the stratospheric ozone layer

Human Pentraxin 3 Binds to the Complement Regulator C4b-Binding Protein

The long pentraxin 3 (PTX3) is a soluble recognition molecule with multiple functions including innate immune defense against certain microbes and the clearance of apoptotic cells. PTX3 interacts with recognition molecules of the classical and lectin complement pathways and thus initiates complement activation. In addition, binding of PTX3 to the alternative complement pathway regulator factor H was shown. Here, we show that PTX3 binds to the classical and lectin pathway regulator C4b-binding protein (C4BP). A PTX3-binding site was identified within short consensus repeats 1–3 of the C4BP α-chain. PTX3 did not interfere with the cofactor activity of C4BP in the fluid phase and C4BP maintained its complement regulatory activity when bound to PTX3 on surfaces. While C4BP and factor H did not compete for PTX3 binding, the interaction of C4BP with PTX3 was inhibited by C1q and by L-ficolin. PTX3 bound to human fibroblast- and endothelial cell-derived extracellular matrices and recruited functionally active C4BP to these surfaces. Whereas PTX3 enhanced the activation of the classical/lectin pathway and caused enhanced C3 deposition on extracellular matrix, deposition of terminal pathway components and the generation of the inflammatory mediator C5a were not increased. Furthermore, PTX3 enhanced the binding of C4BP to late apoptotic cells, which resulted in an increased rate of inactivation of cell surface bound C4b and a reduction in the deposition of C5b-9. Thus, in addition to complement activators, PTX3 interacts with complement inhibitors including C4BP. This balanced interaction on extracellular matrix and on apoptotic cells may prevent excessive local complement activation that would otherwise lead to inflammation and host tissue damage