High Latitude Dust — State of the Mountains

by James King

Daniel Bellamy, a PhD candidate, checking a meteorological station deployed next to the dried up river bed near the Kaskawulsh glacier terminus in May 2023. Photo: James King

Dust consists of fine atmospheric particulates (particles in the atmosphere) that come from various sources including soil disturbed by wind, volcanic eruptions, and pollution. This airborne dust is considered an aerosol, and once in the atmosphere, it can change the scattering and absorption of incoming solar radiation and affect local meteorology by altering cloud properties.

The majority of mineral aerosol (dust) emissions are found within the subtropical high atmospheric pressure regions of the globe, in both the northern and southern hemispheres. These particulate emissions are estimated to be between 1.700 and 4.9 billion tonnes per year[1]. However, high-latitude dust emission sources (defined as north of 55°N and south of 45°S) are generally not included in these global estimates because there is still a lack of knowledge surrounding their location, variability, and propensity to emit dust, and various other factors. However, recent research has estimated their current global contribution equivalent to the total annual emissions from Australia, or two-to-five per cent[2].

The dust emissions at these high latitudes are significant for three principal reasons: (1) the opportunities for sediment (and the nutrients that they contain) to be transported by water in these environments is greatly restricted due to frozen, or snow- and ice-covered, surfaces for the majority of the year; (2) the transport and deposition of dust can greatly alter local radiative budgets by absorbing or scattering relatively acutely angled sunlight[3], acting as ice or cloud condensing nuclei[4], further altering radiation budgets[5], and augmenting insolation on snow, ice, or frozen soils[6]; and (3) anthropogenic climate change impacts are being disproportionately witnessed at high-latitude regions in the form of higher than global average temperature and severe changes in precipitation patterns and type, impacting the delicate balance that limits dust emissions historically occurring in these regions[7].

A panorama of the *A’ą̈y Chù Valley* and Lhù’ààn Mân during a calm day taken from the top of Thechàl Dhâl in June 2021. This over one-kilometre deep and only four-five kilometre-wide pro-glacial valley is an example of why the current dust emissions from these regions are underestimated from most global estimates. Photo: Felicity Hik

Dust source regions hydrologically linked with glaciers are also known as paraglacial landscapes[8], and as such they respond with various lags and intensities to glacier activity. In most cases, the glaciers are the source of sediments that are acted upon by the wind. These sediments accumulate over time and provide a reservoir of fine sediments taken from the toe of the glaciated region by pro-glacial river systems and deposited downstream as a function of river discharge, topography, and sediment yield. The glacier erosion process is extremely efficient for producing fine material (known as glacial flour) as long as the glacier is active near a region that can produce a variety of depositional environments[9]. Early research on the propensity of these depositional surfaces to produce dust through deflation were truncated by infrequent observations, which concluded that most surfaces would be armoured by coarser particles by almost fifty per cent within one year and almost completely within four years[10]. However, observations were limited to an isolated surface that is not experiencing active pro-glacial deposition every year (e.g., pro-glacial valleys), whereas more recent research demonstrates that there are repeated annual dust emissions from the same or similar emission source regions, albeit with some variability[11].

Early morning dust emissions starting up in the Kaskawulsh Valley with undergraduate student Ulrike Richter looking on. Photo: Daniel Bellamy

Dust and deglaciation

Dust emissions from cold climates are not new nor understudied[12]. During previous cycles of deglaciation, including the most recent deglaciation impacting northern regions starting around 20,000 years before present, large amounts of sediment were transported by seasonal rivers away from the glacier terminus, where wind would act on the finer mode of the deposited material mostly near the margins of the river terraces[13]. Today, we see these accumulations of wind-sorted fine material, mostly preserved in regions where large geomorphic processes have yet to reoccur, but also in currently glaciated regions, known as loess deposits[14]. The loess is the leftover silt-sized material (~sixty micrometers) that has been left behind after the finer dust (<thirty micrometers) was transported by the wind hundreds of kilometres away. Loess deposits can be upwards of tens of meters, and are a reminder on the landscape of the disparate size of the previous icesheets compared to today. However, the reliance on dating techniques of loess with variable precision to recount the frequency of dust emission processes results in an incomplete understanding of the characteristics of cold climate dust emission dynamics[15].

“The glacier erosion process is extremely efficient for producing fine material (known as glacial flour) as long as the glacier is active near a region that can produce a variety of depositional environments.”

Examples of Recent Studies

Recent studies have been based in the Yukon, Alaska, Iceland, and Greenland, representing the better characterized high-latitude sources of dust in the northern hemisphere. These studies demonstrate that the potential for dust emissions from pro-glacial sources are at two key periods of the year, restricted by surface conditions: (1) a period of time after winter, when the surface snow begins to melt and exposes the fine valley sediment before being submerged by pro-glacial rivers; and (2) a period of time just before winter begins, when the pro-glacial rivers subside (from the reduction in solar radiation and the subsequent reduced meltwater production) to expose newly deposited glacial sediments[16]. This bi-annual emission conceptual model inadvertently relies on the presence of the wind during these opportunistic surface conditions to produce dust emissions, and although the analysis of local winds has been included as part of these previous studies to determine emission potential (e.g., dust day forward trajectories), they have been mostly constrained to times when there have been observed dust emissions from either satellite or weather station observations[17]. With dramatic changes in climate recently witnessed at high latitudes (e.g., increased average temperatures, changes in precipitation patterns), and specifically within the northern hemisphere due to anthropogenic climate change, the duration of the year that the above conditions (i.e., snow-covered soil or river flow) are present are also changing quickly[18]. These changes translate to the increased duration of the two periods of the year for surface conditions amenable to wind erosion, as the amount of snowfall in many regions is decreasing, and as the air temperature rises the amount of ice that can melt every summer season is eventually decreased[19].

Attendants of the Kluane First Nation 2023 Research Summit look over the *A’ą̈y Chù Valley* as part of a tour given by Gùdia Johnson during a dust storm on May 26, 2023. Photo: James King

An example of this climate-change induced end point is the Yukon’s Kaskawulsh Glacier in Kluane National Park, which terminates at a continental divide. Due to anthropogenic climate change, rapid glacier melt has concurrently extended the pro-glacial delta at unprecedented rates and carved a new channel within the terminal moraine to result in the abandoning of its discharge from one basin to the adjacent basin in 2016[20]. Since this switch, dust emissions from this valley are unabated as the surface waters are only provided by smaller side valleys in the spring or rainfall in the summer, leading to intense dust emission periods from April to October[21].

The wind regimes that are capable of eroding and transporting dust-sized particles in these and other high latitude regions are characterized by the presence of anomalous synoptic low-pressure ridges, diurnal katabatic flows, and topographically induced (and insolation reinforced) local heat lows under stable conditions[22]. The stability of high-pressure systems over a continent with ice-and-snow covered surfaces provides the potential for an air mass to remain in place for extensive periods of time, but that can also provide a strong pressure gradient between it and anomalous low-pressure ridges that arrive from coastal regions. This interaction between the two contrasting air masses can generate powerful winds draining from the higher elevation regions towards the coast[23]. These types of wind patterns have been responsible for dust events in Iceland and Greenland in the northern hemisphere, and are also a main driver of wind erosion events in Patagonia[24].

Cars navigate a dust storm crossing the Alaska Highway in late June 2016. Photo: Lance Goodwin

Katabatic winds

“Katabatic winds (from the Greek katabasis, meaning descend) are mainly generated by cooling air by ice-covered elevated surfaces.”

Katabatic winds (from the Greek katabasis, meaning descend) are mainly generated by cooling air by ice-covered elevated surfaces (e.g., glaciers, icefields, ice sheets) during radiative stable periods through the upwards emission of infrared radiation by the ice and subsequently the air above it, creating a cool and dense air mass, which then flows downslope from the differential pressure gradient force of it and the regions at lower altitudes[25]. This intense down-valley air flow is generated in the afternoon to evening when the radiative processes have generated enough cold air to produce a strong gradient[26]. Depending on the strength of the radiative cooling, the low-level jet that is produced can create surface winds easily beyond the threshold for sand or snow movement (five to ten metres per second), but normally has a peak wind strength twenty to 100 metres above the surface[27]. Return or up-valley flow, if any, takes a pathway much higher in the atmosphere (above 500 metres) creating an atmospheric condition that can result in the sustained katabatic flows beyond four-to-six hours synchronous with the end of the day[28]. As these winds are characterised by descending air, they warm adiabatically and can generate a surface drying mechanism for barren soils (e.g., during low river flow conditions in pro-glacial valleys in the spring and autumn enhancing the potential for wind erosion). In strong and sudden katabatic flows, it has been theorized that a hydraulic jump can occur where the down valley flow meets the stable boundary layer in the valley, which for the case of wind eroded sediment in suspension, could create a mechanism to inject the dust higher into the atmosphere[29]. Studies on katabatic flows at mid-latitudes have generated theories around the change in insolation provided by the sun rising or setting providing the energy gradient necessary to reinforce the wind flows from high to low elevations and vice versa[30]. However, in contrast, at high latitudes, the sunrise and sunset periods are more variable, with latitudes greater than 60°N not experiencing a sunset or sunrise between the end of April and end of August, potentially altering this dynamic. Katabatic wind models have yet to be applied for this condition (no sunrise or sunset) in driving erosive winds and presents a strong avenue for future research to better merge ground-based observations with larger-scale atmospheric modeling. Furthermore, the persistence of these thermally driven flows has yet to be fully applied to estimate the relative propensity of high-latitude sources to emit dust under a changing climate.

A photo of dust researcher Professor Richard Washington returning back from servicing a dust monitoring station during a dust storm in the *A’ą̈y Chù Valley*, May 2019. Photo: James King

Including Local and Indigenous Knowledge

To conclude, I wanted to highlight that although a large amount of the science referenced above focuses on place-based research in high-latitude regions, very few of those studies acknowledge the help that was received directly or indirectly by local communities nor any explicit mention of the Indigenous Nations on whose lands the research was conducted. As a science that studies how past processes may shape the landscape of the future in high-latitudes and the impact it will have on the climate, it is of great importance to include Indigenous methodologies and voices in this research. Recent works have highlighted the importance of these approaches, including providing, for example, ten calls to action for how western science can be done differently to collectively share the responsibility of reconciling the power imbalance of who and what questions science tries to answer[31]. Although this responsibility needs to be shared by researchers, it is also the burden of the funding organizations to support research programs that geniunely strive for inclusion within research design, or even better, to change the funding structure to allow for local nations to guide the research conducted on their lands[32]. The benefits are numerous, but ultimately, they include developing more appropriate science questions to directly inform local policy and climate adaptation at the same time as addressing colonial legacies.

James King is a geomorphologist and associate professor at Université de Montréal in the Département de Géographie. He explores the processes that influence the linkages of nutrient cycles and atmospheric dynamics that govern mineral aerosol emissions and deposition. He has worked in the mountains of northwestern Canada, as well as the USA, Mongolia and southern Africa.

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