Atmospheric Rivers (ARs) are structures that transport large amounts of moisture in the atmosphere. They were equated to land rivers, such as the Amazon River, which is the most powerful in the world, hence the origin of the name. According to the meteorological glossary of the American Meteorological Society (AMS), ARs are long, narrow, and transitory corridors of intense horizontal transport of water vapor, normally found in the lower troposphere, associated with the cold fronts of extratropical cyclones. In the mid-1970s, phenomena with similar characteristics were already being talked about, but it was only in 1990 that they were named “Atmospheric Rivers”.

Prolonged droughts and floods are clear evidence of climate change that can be closely linked to ARs. The ARs are responsible for transporting large amounts of moisture from tropical and extratropical regions to higher latitudes and polar regions, representing about 90% of the northward transport of moisture. They are found in both the Northern and Southern Hemispheres, where they intensify precipitation and cause flooding and landslides; and as an important component of the hydrological cycle, represent a strong contribution to the replenishment and redistribution of water in terrestrial rivers and groundwater, in the moisture content of the soils and even in the thickness of the snow layers in mountainous or polar regions. In the polar regions, ARs are also responsible for the formation of large polynyas, which are areas where one would expect to find sea ice, but that are thawed due to the transport of moisture from the tropics and extratropics.

The Arctic Amplification refers to the Arctic warming about two or three times faster than the rest of the globe, resulting in a decrease in the extent of the Arctic ice. Arctic ice loss can influence climate in mid-latitudes. The climate of the northern hemisphere has undergone several evident changes, with reductions in the amount of annual precipitation, prolonged droughts in some regions, increase in extreme precipitation phenomena, and an increase in the frequency of tropical and extratropical cyclones, among others.

How do ARs respond to Artic sea ice loss?

To better understand this aspect, which is still poorly supported in the literature, a study was carried out at the University of California, in the United States of America. In this study, the researchers used AR detection algorithms, which estimates the amount of water vapor transported in the atmosphere, forced by atmospheric climate models that consider the loss of Arctic sea ice. The researchers modelled the Northern Hemisphere in winter, corresponding with the passage of many tropical and extratropical cyclones, thus being associated with a greater number of ARs. The frequency response of ARs to Arctic sea ice loss corresponds to a global warming of 2°C, according to this study. In terms of region variation, this research concludes that over the North Pacific the ARs extend to the northeast and occur closer to the west coast of North America. Over the North Atlantic, the ARs move to the equator. The response of ARs at midlatitudes is mainly governed by changes in wind. Above 60°N latitude, weak winds tends to reduce the frequency of ARs while increasing atmospheric moisture (due to loss of sea ice) tends to increase their frequency, resulting in relatively small changes in the ARs.

However, other phenomena associated with climate change may contribute to changes in ARs, such as changes in ocean surface temperature. The Arctic amplification has motivated an increase in the frequency of extreme events and ARs, which has modified the climate of mid-latitudes, including extreme precipitation events, more rigorous winters, prolonged droughts and desertification.

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Source: Ma, W., Chen G., Peings Y., Alviz, N., Atmospheric River Response to Arctic Sea Ice Loss in the Polar Amplification Model Intercomparison Project, Geophysical Research Letters 48:20, e2021GL094883 (2021). DOI: 10.1029/2021GL094883.

Author: Cátia Lavinia Gonçalves

The global warming is unequal according to different regions, and the Arctic warms at a rate two times faster than the global average. This phenomenon, known as Arctic Amplification (AA), is associated mostly with the retreat of sea-ice in summer, but also with an increase of the snow cover in northern Europe and Asia between October and January.

Recently, the AA has been associated to more vigorous winters in mid-latitudes, which might be one of the causes of the cold waves registered in January and February 2021 over Asia, Europe, and the United States. For example, in the state of Texas this might have been one of the costliest natural phenomena ever as the lack of preparation of the energy sector to such cold conditions led to the interruption of electrical energy supply.

But how is AA related with extreme events in mid-latitudes during winter? One of the hypotheses is related with the polar vortex in the stratosphere (layer above the troposphere, between 15 and 50 km height). This vortex is known as a band with strong winds in the stratosphere that encircles the North Pole. When the vortex is strong and stable, the cold air stays confined in the Arctic and in the mid-latitudes the air is warmer than normal. However, when the polar vortex weakens, for example due to a sudden stratospheric warming, it can move to southern latitudes or split into two. In the Earth’s surface, the weakening of the vortex impacts the movement of colder air towards the mid-latitudes and warmer air towards the Arctic.

A recent study in the United States was based on a machine learning technique, which consists in applying algorithms that enable the automatic recognition of patterns, to understand the relationship between changes in the Arctic vortex with extreme winters in mid-latitudes. Thus, reanalyses (global data that contain historical information about the atmosphere, land surface and ocean) between 1980 and the beginning of 2021 were used, to identify different variability patterns of the polar vortex from October to December. Several patterns were identified in three different classes: normal polar vortex; polar vortex stronger than normal (strong low-pressure system), representing around 39% of the days; and polar vortex weaker than normal (weaker low-pressure system), representing around 38% of the days.

During the last 40 years, a higher frequency of weaker than normal patterns has been noticed, concurrently with a lower frequency of stronger patterns. This means that there is a higher number of events where the polar vortex is weaker, during autumn and winter, which promotes the propagation of colder air towards the mid-latitudes. As a result, AA might be related with more extreme cold events in the mid-latitudes during winter. If the patterns of weakened polar vortex continue to be observed, it is possible that in the future there is a higher frequency of extreme cold events during winter in more southern regions, where the population and infrastructures are not prepared for this type of phenomenon.

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Source: Cohen J., Agel L., Barlow M., Garfinkel C. I. & White I. Linking Arctic variability and change with extreme winter weather in the United States. Science 373, 1116–1121 (2021). DOI: 10.1126/science.abi9167.

Author: Carolina Viceto

In this study, the objective was to improve knowledge on the distribution of supraglacial lakes since the available information on this topic is scarce in East Antarctica. The authors used around 5 million km2 of high resolution satellite images to identify more than 65.000 lakes (> 1.300 km2) formed in the peak of thawing season (January 2017).

The lakes occur in marginal areas, where normally they develop at low elevation (< 100 m) and low superficial slopes (< 1 °), but can exist 500 km inland and altitudes of more than 1500 m. Further, these lakes are generally grouped a few kilometers of under the ice, below the line where the glaciers start floating. Around 60 % of the supraglacial lakes develop on the ice sheets (> 80 % per area), including some that are potentially vulnerable to collapse from hydro-fracture induced by the lake. In sum, this study suggests that parts of the ice sheets can be quite sensitive to climate warming.

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Source: Stokes, C.R., Sanderson, J.E., Miles, B.W.J. et al. Widespread distribution of supraglacial lakes around the margin of the East Antarctic Ice Sheet. Sci Rep 9, 13823 (2019) DOI: 10.1038/s41598-019-50343-5

Author: Cármen Sousa

To understand these mechanisms, it requires methods to observe surface and subsurface melting. For example, the collapse of the Larsen B Ice Shelf in 2002 was preceded by a well-developed surface expression of meltwater, but the collapse of the Wilkins Ice Shelf in 2008 was preceded by water below the surface that enabled hydrofracture.

The objective of these methods was to determine if the ice-shelf flexure/fracture response was associated with surface water ponding and drainage, and to discover what seismic signals are associated with the water ponding and movement. To do that, scientists took seismograms over a 3-year period from 2015 to 2017, and conducted a ground-based study of surface meltwater features on the ablating portion of the McMurdo Ice Shelf (McMIS), Antarctica.

The scientists discovered a diurnal cycle of seismicity, consisting of hundreds of thousands of small ice quakes in an area where there is substantial subsurface melting. This cycle can be explained by thermally induced bending and fracture of a frozen surface supported by solar radiation, penetration and absorption.

These results suggest by studying seismic waves may be useful in monitoring subsurface melting in a manner that complements other ground-based methods, as well as remote sensing. As a cycle of seismicity occurs, the scientists can test it, idealizing a thermal model of the ice shelf and simulating the development of subsurface partial melt layers and thus predict the ice’s future.

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Source: MacAyeal, D. R., Banwell, A. F., Okal, E. A., Lin, J., Willis, I. C., Goodsell, B., & MacDonald, G. J. (2018). Diurnal seismicity cycle linked to subsurface melting on an ice shelf. Annals of Glaciology, 1-21. doi: 10.1017/aog.2018.29

Author: Hugo Guímaro

3km in depth.

The ice cores contain information about various aspects of the past, such as greenhouse gases concentration (CO2 and CH4) and the presence of isotopes [1] which allow us to infer conclusions about the past temperature and investigate climate changes over time.

When the ice forms, small air bubbles become trapped in it. This give to us samples of the atmosphere of the that time. From the analysis of these bubbles it is possible to directly measure the concentration  of carbon dioxide – CO2,  and methane – CH4 in the atmosphere of that time.

Through comparison between Antarctica ice cores (ie. Law Dome and South Pole) and taking into account the necessary precautions to ensure the results were not affected by other impurities, it was found that the concentration of carbon dioxide (CO2) has been stable over the last millennium until the early nineteenth century. It then started to rise and currently it’s concentration is nearly 40% higher than it was before the industrial revolution. The concentration of Methane (CH4) over the last two centuries also shows an unprecedented rise. Its concentration is now more than double its pre-industrial level.

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Source: Steffensen, J. P., Andersen, K. K., Bigler, M., Clausen, H. B., Dahl-Jensen, D., Fischer, H., … & Masson-Delmotte, V. (2008). High-resolution Greenland ice core data show abrupt climate change happens in few years. Science, 321(5889), 680-684. doi: 10.1126/science.1157707

Author: Patrícia Azinhaga

Microplastics concentrations in Arctic Ice are higher than those found in North Atlantic (North of Scotia) or in the subtropical waters from South Pacific. Polymers [1] identified are used in a range of domestic and industrial activities. However isn’t yet possible to be sure of the microplastics’ origin in the Arctic Ice due to the fact it has contact with different rivers and oceans.

In the last years the Arctic Ocean fusion have raised to minimum historic levels on sea ice extension, as happened at September of 2012. If this tendency remains it is estimated that in the next decade can be released to the ocean more than 1 trillion of microplastics. Ambient consequences aren’t yet completely known but is clearly that these particles are ingested by a huge range of marine organisms including commercial species.

[1] a complex plastic constituted by simple molecules from different chemical reactions. Polymers are present in every person life for having a huge utility (domestic and industrial). Some variations are applied in plastic production (e.g. PVC, Teflon); synthetic fibres production (Nylon, Polyester. Dacron); Tires restoration; electric isolators (rubbers) and thermoplastics (CD’s, PET bottles, toys, cars,…)

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Source: Obbard, R. W., Sadri, S., Wong, Y. Q., Khitun, A. A., Baker, I., & Thompson, R. C. (2014). Global warming releases microplastic legacy frozen in Arctic Sea ice. Earth’s Future, 2(6), 315-320. doi: 10.1002/2014EF000240

Author: Patrícia Azinhaga

Snow has an important role in the soil, as it protects the ground surface from atmospheric processes (such as erosion caused by wind and rain, and energy exchange), and therefore influences the spatial distribution of permafrost. During the austral summer (hot season in the southern hemisphere), when the snow melts, nivation (areas of late snow accumulation), reduce in size. It is also during this time of the year that the Antarctic vegetation, comprised by small plants, have the opportunity to develop.

From all botanic groups (vascular  plants, algae, lichens, mosses and fungi), the lichens group is likely the best adapted to this polar environment due to its high tolerance to cold and dryness. One of the most abundant subgroups of lichens in the Antarctic Peninsula are the fruticose lichens (from the genus Usnea) that resemble small bushes and aggregate creating formations that occupy extensive areas.

One team from the University of Lisbon that focuses on the study of permafrost and climate change in the Antarctic Peninsula (one of the regions on the planet that shows the highest increase in the average air temperatures in the past decades), has been analyzing the relationship between the geographic distribution of these botanic communities and the snow characteristics using cartography and satellite imagery.

The main result in a study conducted in King George Island (South Shetland Arquipelago), shows that the communities of Usnea spp are located frequently on convex surfaces (higher topography), exposed to the wind where conditions are less prone to snow accumulation.

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Source: Vieira G., Mora C., Pina P., Schaefer C.. A proxy for snow cover and winter ground surface cooling: Mapping Usnea sp. communities using high resolution remote sensing imagery (Maritime Antarctica)”. Geomorphology 225 (15-11-2014) : 69–75. doi: 10.1016/j.geomorph.2014.03.049

Author: Ana Salomé

The study of 16 ice cores [3] showed that the lead contamination in Antarctica started in the beginning of the 20th century and still persists to this day. Unlike the Arctic where lead pollution peaked in the 1970s, lead pollution in Antarctica was as high in 1889 as it is now, beating polar explorers by more than 22 years.

Between 1650 and 1885, lead concentrations gradually increased from ~0.6 pg/g to ~1.8 pg/g [4]. Concentrations remained high until the late 1920s, with a temporary low during the Great Depression and again at the end of World War 2. From here on, lead concentrations increased rapidly to 5.7 pg/g by 1975 and remained elevated until the mid-1990s. Concentrations during the early 21st century were lower than the peak 20th century concentrations but well above background levels before the start of the Industrial Revolution. Snowfall in Antarctica has been increasing which in turn can influence the amount of lead deposited there. Nevertheless, this fact does not explain, by itself, the increase in the lead concentrations found in the Antarctic continent.

[1] Paleoclimate – Climate from an old geologic period

[2] Lead has 4 natural stable isotopes. In its natural state are: Pb-204 (1.4%), Pb-206 (24.1%), Pb-207 (22.1%) e Pb-208 (52.4%)

[3] Ice/rock/soil sample, extracted usually using a hollow pipe that allows the sample to remain intact

[4] Unit of measure: pg or picogram = 10-12 grams

Source:

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McConnell, J.R., Maselli, O.J., Sigl, M., Vallelonga, P., Neumann, T., Anschütz, H., 

Bales, R.C., Curran, M. a. J., Das, S.B., Edwards, R., Kipfstuhl, S., Layman, L., Thomas, E.R., 

2014. Antarctic-wide array of high-resolution ice core records reveals pervasive lead pollution 

began in 1889 and persists today. Sci. Rep. 4. doi: 10.1038/srep05848

Author: Eduardo Amaro