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Cryospheric Sciences

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Ice Cores “For Dummies”

Ice Cores “For Dummies”

Ice cores are important tools for investigating past climate as they are effectively a continuous record of snowfall, which preserves historical information about climate conditions and atmospheric gas composition. In this new “For Dummies” post, we discuss the history and importance of ice-core science, and look at the way we can use ice core chemistry to reconstruct past climate.


Ice sheets, archives of our past

When snow falls on the surface of an ice sheet it begins to compact the snow beneath it – eventually it will be compacted enough to be transformed into ice. Simultaneously, atmospheric air held between the snowflakes is slowly trapped in the ice – forming small air bubbles. In areas where mean annual temperatures at the ice surface remain below 0C, such as Greenland and Antarctica, there is little surface melting, so this snow builds up to form thick ice sheets – up to 3000 metres in some part of East Antarctica! Low surface melt means that the snow that is compressed into ice each year forms a continuous record of the annual snowfall and atmospheric gas concentrations at the time of deposition, but how do we access this record..?

Snow that is compressed into ice each year forms a continuous record of the annual snowfall and atmospheric gas concentrations at the time of deposition

…We drill ice cores – of course!

An ice core is a cylinder of ice that is retrieved from the ice sheet by drilling vertically downwards. The core is drilled in sections from the surface, deep into the ice sheet (Fig. 1) using a rotating drill. Each section of the core is processed at the drill site and often cut further into shorter sections of ~55 cm for more practical transport and analysis in labs. A great deal of equipment is needed to achieve this and drilling is a slow and careful process often taking several field seasons to drill a deep core. An example of a drilling camp is shown in Fig. 2, housing scientists and engineers involved in drilling an ice core on the Fletcher Promontory, West Antarctica.

Figure 1: a) Ice core drill being lowered into the ice on Pine Island Glacier [Credit: Alex P. Taylor] b) Dr Rob Mulvaney processing the Berkner Island ice core, Weddell Sea, Antarctica [Credit: R. Mulvaney]

Figure 2: The layout of the Fletcher Promontory ice-drilling project, Weddell Sea, Antarctica. In the background the large Weatherhaven tent houses the drill rig, the central Weatherhaven tent is used for storage and equipment and a simple shower, the nearest Polarhaven tent is the mess tent, and the Polarhaven tent to the left houses the main generator. The pyramid tents in the foreground are the sleeping tents, and the two to the right are used for toilet facilities [Credit: Mulvaney et al., 2014]

Where to drill an ice core for the best record?

To get a good record of climate we want to find an area of ice that has many annual layers (good temporal resolution) that has not been disturbed by high ice flow velocities, usually these conditions can be found at an ice dome or divide. An ice sheet is a large plateau with a relatively stable rate of annual snowfall; the dome (or ice divide) is the point in the ice sheet where there is only vertical flow (compression) of ice (Fig. 3). Horizontal flow of ice is greater with the greater distance from the dome. Therefore, domes are the ideal site on the ice sheet or ice cap to drill for an ice core to ensure no interference with the snowfall history at the site. It is reasonable to assume that the ice-core record taken from a site with high annual snowfall will not extend the furthest back in time; similarly, a low annual snowfall and a large ice-sheet thickness will offer a record spanning much further back in time.

Figure 3: Ice flow within the ice sheet showing the zero flow at the ice divide – the ideal site for an ice core [Credit: Snowball Earth]

For Antarctica, the amount of snowfall across the ice sheet depends on the distance from the coast and sources of moisture; the highest mean annual snowfall is found at West Antarctic ice sheet sites whilst the lowest values are inland on the East Antarctic ice sheet, one of the driest deserts on Earth. In addition to the West and East Antarctic ice sheets, the Antarctic Peninsula is the third and final sector of the continent with high mean annual snowfall comparable to West Antarctica. In comparison to Antarctica, the Greenland ice sheet has a relatively high present-day mean annual snowfall, varying across the ice sheet between 10 and 30 cm per year. Therefore, if your aim is to find the oldest ice on Earth, East Antarctica is a good place to start looking, see our post on the quest to drill an ice core that contains ice which is over a million years old. Additionally, for the longest records it is paramount to find a drilling location with no (or at least very low) annual melting at the bedrock.

If your aim is to find the oldest ice on Earth, East Antarctica is a good place to start looking

What does an ice core actually record?

Once an ice core has been drilled and cut into sections, some of the sections are analysed and others are preserved. This is particularly important as some of the analysis is destructive (e.g. melting of the ice to extract water and gas). Therefore an archive of the ice core itself is needed. So, what information can we obtain from analysing the core and how is it done?

Annual layers, past snowfall and past temperatures!

Reconstructing the past surface temperature and snowfall is incredibly useful for understanding climate processes and changes through time in order to assess any present-day local and regional changes in climate. We can do this by:

          • Measuring the thickness of the annual layers: This is done by counting layers in the core, either by visual identification of the peaks in deposition or use of a computer algorithm. The thickness of a specific year depends on how much snow fell at the site and on how much the snowfalls of the following years compacted this specific layer. We can estimate the strain caused by compaction which allows us to extract historical annual snowfall.
          • Past air temperatures (Stable Water Isotope Record): An additional method to reconstruct past snowfall is from the ratios of the stable water isotopes from the water that forms snow and precipitation. The ratio of stable water isotopes has a linear relationship with surface temperature (see box below). Mathematical reconstructions of accumulation using the temperature reconstructions from stable water isotopes are employed in ice core profiles where the compaction of annual snowfall results in an annual layer thickness beyond standard laboratory resolution, such as Antarctic sites. Following the accumulation reconstruction, the rate of compaction of the annual snowfall to ice and subsequent ‘thinning’ of the deposited snowfall layer must be estimated by glaciological modelling.
          • Trace-element analysis: For the upper depths of a deep ice core, or an ice core with an easily-resolvable annual layer thickness, the continuous analysis of an ice core for stable water isotopes offers a sub-annual view of the climate record.

            Figure 4: Seasonal deposition of four chemical species in the WAIS Divide ice core. Pink: electrical conductivity measurements; Black: Black Carbon; Red: non-sea salt Sulphur; Blue: Sodium. Each panel, shows the averaged annual record for 2 different periods: the Antarctic Cold Reversal (ACR, 13-14,000 years ago – bold line) and the Holocene, (10-11,000 years ago – thin line) the [Credit: Fig. 2, Sigl et al., 2016 ]

            The deposition of a number of chemical elements increases during the summer season and decreases during the winter.When these elements are measured in the ice core they can be depicted as an almost-sinusoidal record, indicating the historical seasons. High-resolution ice-core profiles can be dated by counting these annual layers, and have been done so across Greenland and at the West Antarctic Ice Sheet (WAIS) Divide ice core site. Fig. 4 shows two annual signals over 24 months for four different chemicals that are deposited in ice cores (Sigl et al., 2016). The peak in seasonal deposition is shown twice for each chemical, at different times in history, but the seasonality of these species remains strong throughout time.
Reconstructing Past Temperatures
We commonly think of water as H2O - a molecule containing two hydrogen atoms and one oxygen atom. However, atoms (i.e. Hydrogen and Oxygen) come in several forms, known as isotopes - atoms with the same number of protons, but differing numbers of neutrons. Those isotopes that don't decay over time and are preserved in the ice core are know as stable water isotopes. It is possible to measure the amount of each different stable water isotope present in an ice core by melting the ice core and using a mass spectrometer to analyse the water produced.

The snow that eventually forms ice cores starts its life as ocean water which is evaporated and transported to the polar regions. Water isotopes with more neutrons are heavier and therefore require more energy to evaporate and transport. The amount of energy available to do this is related to temperature. Therefore heavier isotopes are found in ice cores in higher amounts at warmer periods in the planet's history! Find out more  here!

Atmospheric gas

Ice-core measurements of atmospheric gases correlate well with direct measurements taken from the atmosphere dating back to 1950. As a result of this, ice-core scientists can assume that the atmospheric gas concentrations measured in ice cores reflects the atmospheric conditions at the time the gas was entrapped in the ice core. Hence, ice cores tell us that carbon dioxide concentrations have been relatively stable for the last millennia until around 1800 AD but since then a rise of almost 40% has been measured in both ice cores and direct atmospheric measurements (Fig. 5).

Figure 5: 1000 years of atmospheric CO2 concentrations from various Antarctic ice cores (DML, South Pole, Law Dome and Siple Dome) and the direct measurements in Mauna Loa Observatory [Credit: Ashleigh Massam, compiled from open access data sources]

Carbon dioxide concentrations have been relatively stable for the last millennia until around 1800 AD but since then a rise of almost 40% has been measured

In addition to comparison with present-day measurements, the trapped gases offer a record of direct atmospheric and greenhouse gas concentrations, including methane, carbon dioxide and nitrous oxide (Fig. 6) on a longer timescale – up to 800,000 years (Loulergue et al., 2008). Records show the connection between fluctuations in the atmosphere and long-term global climate variations (e.g. temperature) on a millennial timescale (Kawamura et al., 2007). The long-term trends show a pattern in the gas concentrations that compare well with glacial-interglacial climate. The phasing and timing of the eight glacial cycles covered by this record are dominated by the orbital cycle of the Earth on a 96,000-year periodicity, with a warm, interglacial period between each cold period. However, as we will see later in this blog post, this may not be the case when we look further back in time!

Figure 6: Variations of temperature (from present day mean temperature, black), atmospheric carbon dioxide (in part per million by volume — blue) and methane (in part per billion per volume red) over the past 800,000 years, from the EPICA Dome C ice core in Antarctica. Modern value (of 2009) of carbon dioxide and methane are indicated by arrows. [Credit : Centre for Ice and Climate , University of Copenhagen. Re-used with permission ]

Other climate proxies

Chemistry preserved in the ice also offers a proxy (=a means) to reconstruct other seasonally-deposited tracers:

                        • Information on past sea-ice extent can be obtained from chemicals found in ice cores which are also present in sea salt such as sodium, chlorine and methanesulphonic acid (MSA) (Sommer et al., 2000; Curran et al., 2003; Rothlisberger et al., 2003).
                        • The seasonal deposition of elements such as iron, magnesium and calcium, which are linked to dust from far-afield and the short-term climate variability such as atmospheric circulation (Fuhrer et al., 1999).
                        • Finally, volcanic layers in the ice core such as tephra and sulphate deposit provides a unique timestamp to a specific depth. These layers were deposited at the same time, all over the world and can be pinpointed to a specific volcanic eruption. Deposits of the same layer outside of a glaciated landscape, (e.g. within rock layers ) can often be dated using radiocarbon (Carbon-14) or another radiogenic dating methods. Additional age horizons can be interpreted by events assumed to occur in the world at the same time, such as rapid climate events. Age constraints are beneficial to interpreting deep ice-core records that are not analysed at a sub-annual resolution by offering pinpoint age horizons to an ice-core record.

Current knowledge from ice-core records

As we have seen, ice core are important because they put the current climate variations into the context of a long-term climate history. Additionally, polar ice cores can allow us to looks at variations between the northern and southern hemisphere. Ice cores also extend back much, much further in time than terrestrial weather stations or satellite records:

Figure 7: Deep ice core locations in Greenland and Antarctica [Credit and more details: NSIDC ]

The current past climate record tells us about glacial and inter-glacial periods (Fig. 6) but also allows us to look at finer detail – i.e. the variability within these periods, which were previously assumed stable.  For example, ice cores have led to the discovery of Dansgaard-Oeschger events; which are are rapid climate fluctuation events, characterised by rapid warming followed by gradual cooling to return to glacial conditions, 25 of these events have happened during the last glacial period.

Records from the Northern and Southern hemisphere also allow us to link these small and large scale changes in climate in the two hemispheres. For example, ice cores analysed from both poles show a ‘call and response’ signal between Dansgaard-Oeschger events in the Northern Hemisphere and events in the Antarctic climate record. The southern hemisphere cooled during the warm phases of Dansgaard-Oeschger events in the northern hemisphere (Buizert et al., 2015), and vice versa during northern hemispheric cooling (see our previous blog post on the subject).

There are already over a dozen ice cores taken from Greenland and Antarctica (Fig. 7), offering a clear and detailed history of the climate during the Late Quaternary period (Fig. 6), going back up to 800,000 years (Quaternary = last 2.6 million years). As we mentioned earlier the timing of glacial and inter-galcial cycles in this 800,000 year old record is dominated by the orbital cycle of the Earth (96,000-year periodicity). However, marine records show that frequency of glacial-interglacial cycles was different before this time (Lisiecki and Raymo, 2005). It is in order to better understand these changes that the quest for the oldest was formed – beginning last month the mission aims to drill an ice core of ice older than 800,000 years to gain detailed information about the climate even further back in time.

Detailed records from high-resolution ice cores improves our understanding of the response of the planet to deglaciation events

The continuous and high-resolution of ice-core records, together with marine and terrestrial records, offers a global view of coupled processes from ice sheet calving events, changes to ocean circulation and heat transport and the subsequent cooling events across the Earth. Detailed records from high-resolution ice cores improves our understanding of the response of the planet to deglaciation events from the large ice sheets that once covered much of the northern hemisphere. Melting ice sheets pose a significant threat to the planet from rising sea levels and the freshwater input leading to inevitable changes in climate.

Edited by Emma Smith and Sophie Berger


Ashleigh Massam is a final-year PhD student based in the Ice Dynamics and Palaeoclimate group at the British Antarctic Survey and with the Department of Geography at Durham University. Her project is developing the age-depth profiles of three ice cores drilled at James Ross Island, Fletcher Promontory and Berkner Island, West Antarctica, by a combination of high-resolution trace-element analytical techniques and modelling ice-sheet processes.

Ice-Hot News : The “Oldest Ice” quest has begun

Ice-Hot News : The “Oldest Ice” quest has begun

This is it! The new European horizon 2020 project on Oldest Ice has been launched and the teams are already heading out to the field, but what does “Old Ice” really mean? Where can we find it and why should we even care? This is what we (Marie, Olivier and Brice) will try to explain somewhat.


Why do we care about old ice, ice cores and past climate?

Figure 1: Drilling an ice core [Credit: Brice Van Liefferinge]

Figure 1: Drilling an ice core [Credit: Brice Van Liefferinge]

Unravelling past climate and how it responded to changes in environmental conditions (e.g. radiative forcing) is crucial for our understanding of the current climate and for predicting how climate will likely change in the future.

Ice cores contain unique and quantitative information on the past climate (e.g. atmospheric gas concentration). The caveat is that at the moment, we can “only” go back up to 800,000 years at EPICA Dome C ice core (Parrenin et al, 2007).

Nonetheless, marine records tell us that during the Mid-Pleistocene there was a major climate transition (0.8-1.2 million years ago): a change in the frequency of glacial-interglacial cycles in the Northern Hemisphere. Instead of an ice age every 40,000 year, the climate changed to what is termed a “100,000 year world”. Unfortunately, the time resolution of marine records are too coarse to provide details on the mechanisms behind such climate changes. We must therefore rely on ice cores to obtain a high enough temporal resolution. Furthermore, the ice traps air bubbles and can therefore provide a record of the atmospheric composition that can be used to directly measure the paleo atmosphere through the transition.

The new European project ‘Oldest ice’ was set up for this very objective: crack the Mid-Pleistocene Transition climate. It brings together engineers, experimentalists and modellers from 14 Universities around the world.

In this post, we will focus on the first mission of the project: locating areas with million year old ice in Antarctica. The next steps will be to:

  • develop the drilling technology,

  • improve our geophysical knowledge of the identified site,

  • and finally, reach the “holy grail”: recover ice from the very base of the ice sheet with a target age of 1.5 Million years.

The whole project is anticipated to last 10 years!

The new European project ‘Oldest ice’ was set up for this very objective: crack the Mid-Pleistocene Transition climate

The first mission: “Where to find million year old ice?”

Oldest Ice (ice more than 1 mio. years old) can only be recovered in Antarctica, but where exactly? This question has to be answered in a two-step approach:

  1. On a large scale, we must first narrow down places in Antarctica where Oldest Ice might be found. To do that, we rely on models.

  2. Then, we can focus our analysis on those regions by gathering field data in the form of airborne radar surveys. Further ground-based work is currently taking place.

On a larger scale, Oldest Ice in Antarctica requires:

  1. Thick ice and cold bed. We need thick ice to reconstruct past climate variations with sufficient temporal resolution (e.g. is there enough ice to measure air bubbles or other climate markers). However, the thicker the ice, the higher the basal temperature. If the bottom of the ice is too warm, the ice at the base will start to melt, potentially destroying the Oldest Ice of the ice sheet.
    Finding a suitable drill site hence requires a good trade-off between thickness and cold-bed conditions.

  2. Slow-moving ice. This is found mainly at the centre of the ice sheet. Imagine this: if ice were to flow at as little as 1 m per year over a period of 1.5 Million years, it would have travelled 1,500 km over that time interval! However, there is a catch: slow-moving areas are also low-accumulation areas, and low accumulation means warmer ice. This is because the ice is cooled by the addition of cold snow at the surface that then gets transformed to ice and then travels downwards. Indeed, the greater the accumulation, the deeper the “cold snow” can penetrate into the ice sheet!

  3. Undisturbed ice. In order to obtain an interpretable climate record, the ice recovered from the drill needs to be stratigraphically ordered, i.e. no mixing of the ice can have occurred so that we can assume that time increases with depth when we measure ice composition down the core. Variations in the height of the bedrock can induce such ice mixing.

(more information can be found in Van Liefferinge and Pattyn (2013))

Figure 2. Potential locations of cold bed (basal temperatures 2000 m), slow motion (horizontal flow speeds <2m/yr) The colour bar represents the basal temperature. The two insets focus on Dome C and Dome F, two areas highly likely to store million year old ice. [Credit: Brice Van Lieffering, updated from Van Liefferinge, B. and Pattyn, 2013]

Figure 2. Potential locations of cold bed (basal temperatures 2000 m), slow motion (horizontal flow speeds <2m/yr) The colour bar represents the basal temperature. The two insets focus on Dome C and Dome F, two areas highly likely to store million year old ice. [Credit: Brice Van Lieffering, updated from Van Liefferinge, B. and Pattyn, 2013]

While boundary conditions such as ice thickness and accumulation rates are relatively well constrained, the major uncertainty remains in determining thermal conditions at the ice base. The thermal conditions depend on the geothermal heat flow (the flux of “energy” provided by the Earth which conducts heat into the crust) underneath the ice sheet. But to measure the geothermal heat flow, you need to reach the bed.

We need to find the ideal drilling location which would satisfy all these conditions – a bit of a “Goldilocks’ choice”: thick ice but not too much, low accumulation but not too low, low geothermal heat flow but high enough to not get folded basal ice. To do this we use several models: a simple one which calculates the minimum geothermal heat flow needed to reach the pressure melting point that we can then compare to data sets, and a more complex one resolving in three dimensions the temperature field with thermomechanical coupling (i.e. linking the ice-flow component to the heat-flow component). The combination of modelling approaches shows that the most likely oldest ice sites are situated near the ice divide areas (close to existing deep drilling sites, but in areas of smaller ice thickness) (see Figure 2).

Give it a go: Try to find million year old ice yourself using this Matlab© tool: http://homepages.ulb.ac.be/~bvlieffe/old-ice.html

The combination of modelling approaches shows that the most likely oldest ice sites are situated near the ice divide areas

On finer scales: we need deep radiostratigraphy and age modelling

Radar profiles

Figure 3. Radargram from the new OIA radar survey (Young et al., in review) with isochrones interpreted in red [Credit: Marie Cavitte]

Figure 3. Radargram from the new Oldest Ice A radar survey (Young et al., in review) with isochrones interpreted in red [Credit: Marie Cavitte]

Radargrams (see figure 3) are powerful tools to observe the internal structure of the ice: variations in density, acidity and ice fabric all can create conductivity contrasts, which result in radar visual stratigraphy. Below the firn column (the compacting snow, up to 100 m thick), most returns are related to acidity variations, corresponding to successive depositional events (i.e. snowfall). Radar stratigraphy in this case can be considered isochronal, i.e. every visible line (see figure 3) were formed at the same moment, (Siegert et al., 1999). Such radar isochrones can then be traced for kilometres throughout the ice sheet where radar data has been acquired. When radar lines intersect an ice core site, the radar stratigraphy can then be dated by matching the isochrone-depths to the ice core depths at the site and then transferring the age-depth timescale.

This allows to date entire sub-regions. However, the very bottom of the ice column is often difficult to interpret: radar isochrones cannot always be continuously followed from the ice core.

Radargrams are powerful tools to observe the internal structure of the ice

The newly acquired Oldest Ice A radar survey (Young et al., in review) over the Dome C region (see figure 2 for location) gives very rich stratigraphic information and the proximity of the EPICA Dome C ice core has allowed the dating of the isochrones. The ice sheet in this area could only be dated to ~360,000 years (Cavitte et al., 2016) and not further back in time because deeper isochrones are tricky to tie to the ice core, and other times, there is no clear signal (deep scattering ice, visible near the bedrock, at the bottom of Figure 3). As such, we need an age model to try to describe the age-depth relation below the deepest dated isochrones.

Modelling the ice

Figure 4. More precise analysis of the Dome C Oldest Ice target, with the lines representing the Oldest Ice A airborne survey collected in winter 2015/16 (Young et al., in review). The colours represent the modelled age of the ice 60 meters above the bedrock, in thousands of years. We can see that this whole region has a lot of potential for recovering million year old ice. [Credit: Olivier Passalacqua]

Figure 4. More precise analysis of the Dome C Oldest Ice target, with the lines representing the Oldest Ice A airborne survey collected in winter 2015/16 (Young et al., in review). The colours represent the modelled age of the ice 60 meters above the bedrock, in thousands of years. We can see that this whole region has a lot of potential for recovering million year old ice. [Credit: Olivier Passalacqua]

The age of the ice primarily depends on its vertical velocity, so we can use a simple 1D model to describe the motion of the ice in the vertical direction. We run the model for an ensemble of vertical velocity profiles and basal melt rates, and consider the distribution of the basal ages (i.e. model ages) given by the profiles that reproduce the observations the best (i.e. isochrones ages).

We need an age model to try to describe the age-depth relation below the deepest dated isochrones

After running the model, it appears that many areas of the Oldest Ice A survey region host very old ice (see red and yellow dots on figure 4 which represent ages > 1 million years). A high enough bottom age gradient, provided by the dated isochrones, is required to ensure sufficiently old ice as a drilling target. Following initial calculations, it will probably be a better choice to drill on the flank of the bedrock relief than on its top.

So in the end, where do we find the oldest ice?

We have to find areas which provide a good compromise between thick ice (for the a good temporal resolution in the ice core) but not too thick (to avoid basal melting). The best sites will be the ones close to the surface ridge (to ensure limited displacement of the ice), standing above the surrounding subglacial lakes, and for which a lot of undated isochrones below the last dated isochrone are visible.

To find out more about Beyond EPICA and keep track of progress visit the project  website and follow @OldestIce on twitter!

Edited by Sophie Berger


Brice Van Liefferinge is a PhD student and a teaching assistant at the Laboratoire de Glaciology, Université libre de Bruxelles, Belgium. His research focuses on the basal conditions of the Antarctic ice sheet. He tweets as @bvlieffe.

Marie Cavitte is a PhD student at the Institute for Geophysics at the University of Texas at Austin, Texas. Her research focuses on understanding radar internal stratigraphy and using it as a means to constrain the temporal stability of the East Antarctic Ice Sheet interior.

Olivier Passalacqua is a PhD student at the Laboratoire de Glaciologie et Géophysique de l’Environnement, Grenoble, France.

Members of the consortium

  • Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI, Germany), Coordination
  • Institut Polaire Français Paul Émile Victor (IPEV, France)
  • Agenzia nazionale per le nuove tecnologie, l’energia e lo sviluppo economico sostenibile (ENEA, Italy
  • Centre National de la Recherche Scientifique (CNRS, France)
  • Natural Environment Research Council – British Antarctic Survey (NERC-BAS, Great Britain)
  • Universiteit Utrecht – Institute for Marine and Atmospheric Research (UU-IMAU, Netherlands)
  • Norwegian Polar Institute (NPI, Norway)
  • Stockholms Universitet (SU, Sweden)
  • Universität Bern (UBERN, Switzerland)
  • Università di Bologna (UNIBO, Italy)
  • University of Cambridge (UCAM, Great Britain)
  • Kobenhavns Universitet (UCPH, Denmark)
  • Université Libre de Bruxelles (ULB, Belgium)
  • Lunds Universitet (ULUND, Sweden)

Non-Europan partners

  • Institute for Geophysics, University of Texas at Austin (UTIG, US)
  • Australian Antarctic Division (AAD, Australia)

Image of the Week – Inside a Patagonian Glacier

Image of the Week – Inside a Patagonian Glacier

Chilean Patagonia hosts many of the most inhospitable glaciers on the planet – in areas of extreme rainfall and strong winds. These glaciers are also home to some of the most spectacular glacier caves on Earth, with dazzlingly blue ice and huge vertical shafts (moulins). These caves give us access to the heart of the glaciers and provide an opportunity to study the microbiology and water drainage in these areas; in particular how this is changing in relation to climate variations. Our image of this week shows the entrance to one of these caves on Grey Glacier in the Torres del Paine National Park.


“Glacier karstification”

Glaciers in Patagonia are “temperate”, which means that the ice temperature is close to the melting point. As glacial melt-water runs over the surface of this “warm” ice it can easily carve features into ice, which are similar to those formed by limestone dissolution in karstic landscapes. Hence, this phenomenon is called Glacier karstification. It is this process that forms many of the caves and sinkholes that are typically found on temperate glaciers.

From the morphological (structural) point of view, glaciers actually behave like karstic areas, which is rather interesting for a speleologist (scientific cave explorer). Besides caves and sinkholes one often finds other shapes similar to karstic landscapes. For example, small depressions on the ice surface formed by water gathering in puddles, whose appearance resembles small kartisic basins (depressions). Of all the features formed by glacier karstification glacier caves are the most important from a glaciological perspective.

Glacier caves can be divided in two main categories:

  • Contact caves – formed between the glacier and bed underneath; or at the contact between extremely cold and temperate ice by sublimation processes (Fig. 2a)
  • Englacial caves – form inside the glacier – as shown in our image of the week today. Most of these caves are formed by runoff, where water enters the glacier through a moulin (vertical shaft) and are the most interesting for exploration and research (Fig. 2b)
Figure 2: Two different types of caves explored on the Grey Glacier. A- Contact formed between the glacier bed and overlying ice [Credit: Tommaso Santagata]. B- Entrance to an englacial cave [Credit: Alessio Romeo/La Venta].

Figure 2: Two different types of caves explored on the Grey Glacier. A- Contact formed between the glacier bed and overlying ice [Credit: Tommaso Santagata]. B- Entrance to an englacial cave [Credit: Alessio Romeo/La Venta].

Exploring the moulins of a Patagonian glacier

Located in the Torres del Paine National Park area (see Fig. 3), the Grey glacier was first explored in 2004 by the association La Venta Esplorazioni Geografiche. In April of this year, a team of speleologists went back to the glacier to survey the evolution of the glacier.

Figure 3: Map of Grey Glacier with survey site of 2004 and 2016 indicated by red dot [Adapted from: Instituto Geografico Militar de Chile ]

Figure 3: Map of Grey Glacier with survey site of 2004 and 2016 indicated by red dot [Adapted from: Instituto Geografico Militar de Chile ]

Grey glacier begins in the Andes and flows down to it’s terminus in Grey Lake, where it has three “tongues” which float out into the water (Fig, 3). As with many other glaciers, Grey Glacier is retreating, though mass loss is less catastrophic than some of Patagonia’s other glaciers (such as the Upsala – which is glaciologically very similar to the Grey Glacier). Grey Glacier has retreated by about 6 km over the last 20 years and has thinned by an average of 40 m since 1970.

In 2004 research was concentrated on the tongue at the east of this Grey Glacier (Fig. 3 – red dot), which is characterised by a surface drainage network with small-size surface channels that run into wide moulin shafts, burying into the glacier. In this latest expedition, the same area was re-examined to see how it had changed in the last 12 years.

Several moulins were explored during the 2016 expedition, including a shaft of more than 90 m deep and some horizontal contact caves (Fig 2). The glacier has clearly retreated and the surface has lowered a lot from the 2004 expedition. The extent of the thinning in recent years can be easily measured on the wall of the mountains around the glacier. Interestingly the entrance to the caves which were explored in 2004 and in 2016 was in the same position as 12 years ago, although the reasons for this are not yet clear.

The entrance of two of the main moulins which were explored were also mapped in 3D using photogrammetry techniques (see video below). The 3D models produced help us to better understand the shape and size of these caves and to study their evolution by repeating this mapping in the future. For more information about the outcome of this expedition, please follow the Inside the Glaciers Blog.

 

 

Further Reading:

Books on the subject:

  • Caves of the Sky: A Journey in the Heart of Glaciers, 2004, Badino G., De Vivo A., Piccini L.
  • Encyclopaedia of Caves and Karst Science, 2004, Editor: Gunn J.

Edited by Emma Smith and Sophie Berger


tom_picTommaso Santagata is a survey technician and geology student at the University of Modena and Reggio Emilia. As speleologist and member of the Italian association La Venta Esplorazioni Geografiche, he carries out research projects on glaciers using UAV’s, terrestrial laser scanning and 3D photogrammetry techniques to study the ice caves of Patagonia, the in-cave glacier of the Cenote Abyss (Dolomiti Mountains, Italy), the moulins of Gorner Glacier (Switzerland) and other underground environments as the lava tunnels of Mount Etna. He tweets as @tommysgeo

Black Carbon: the dark side of warming in the Arctic

Black Carbon: the dark side of warming in the Arctic

When it comes to global warming, greenhouse gases – and more specifically CO2 – are the most often pointed out. Fewer people know however that tiny atmospheric particles called ‘black carbon’ also contribute to the current warming. This post presents a paper my colleague and I recently published in nature communications. Our study sheds more light into the chemical make-up of black carbon, passing through the Arctic.


Black Carbon warms the climate

 Figure 1: Global radiative forcing of CO2 (green) compared to black carbon (blue). The colored bars show the mean change in radiative forcing due to the concentration of CO2 and BC in the atmosphere. The estimated range for the expected radiative forcing is everything between the white lines, which show the 90% confidence interval. (Data according to Boucher et al. 2013 (IPCC 5th AR) and Bond et al. 2013). [Credit: Patrik Winiger]

Figure 1: Global radiative forcing of CO2 (green) compared to black carbon (blue). The colored bars show the mean change in radiative forcing due to the concentration of CO2 and BC in the atmosphere. The estimated range for the expected radiative forcing is everything between the white lines, which show the 90% confidence interval. (Data according to Boucher et al. 2013 (IPCC 5th AR) and Bond et al. 2013). [Credit: Patrik Winiger]

Black Carbon (BC) originates from incomplete combustion caused by either natural (e.g., wild fires) or human (e.g., diesel car emissions) activities. As the name suggests, BC is a dark particle which absorbs sunlight very efficiently. In scientific terms we call this a strong positive radiative forcing, which means that the presence of BC in the atmosphere is helping to heat the planet. Some estimates put its radiative forcing in second place, only after CO2 (Figure 1). The significant thing about BC is that it has a short atmospheric lifetime (days to weeks), meaning we could quickly avoid some climate warming by getting rid of its emissions. Currently global emissions are increasing year by year and on snow and ice, the dark particles have a longer lasting effect due to the freeze and thaw cycle, where BC can re-surface, before it is washed away. It is important however to note, that our main focus on emission reduction should target (fossil-fuel) CO2 emissions, because they will affect the climate long after (several centuries) they have been emitted.

Arctic amplification: strongest warming in the North Pole

The Arctic is warming faster than the rest of our planet. Back in 1896, the Swede Arrhenius, (better known for his works: in chemistry), calculated, that a change in atmospheric CO2 – which at that time was a good 100 ppm lower than today – would change the temperature at higher latitudes (towards the poles) more than at lower latitudes.

Figure 2: Observation based global surface temperature anomalies for Jan-Mar (2016) in °C with respect to a 1961-1990 base year. Credit: GISTEMP Team, 2016: GISS Surface Temperature Analysis (GISTEMP). NASA Goddard Institute for Space Studies. Dataset accessed 2016-10-15 at http://data.giss.nasa.gov/gistemp/ [Hansen et al., 2010].

Figure 2: Surface temperature anomalies (in °C) for Jan-Mar (2016) with respect to a 1961-1990 baseline. [ Credit: NASA — GISTEMP (accessed 2016-10-15) and Hansen et al., 2010].

The problem with his calculations – as accurate and impressive they might have been – was, that he ignored the earth’s geography and seemed unaware of the big heat capacity of the oceans. On the southern half of our planet there is a lot more water, which can take up more heat, as compared to the northern half with more land surface. Thus, in reality the latitudes on the southern hemisphere have not heated as much as their northern counterparts and this effect came to be known as Arctic amplification.

Dark particles on bright snow and ice

Figure 3: Welcome to the Greenland Ice Sheet everybody. Probably an extreme case of ice covered in cryoconite, captured in August 2014 [Credit: Jason Box, (LINK: http://darksnow.org/)].

Figure 3: Ice covered in cryoconite, Greenland Ice Sheet, in August 2014 [Credit: Jason Box — Dark Snow project].

Greenhouse gases and BC are not the only reasons for the increase in temperature change and earlier onset of the melting season in the Arctic. Besides BC, there are other ‘light absorbing impurities’ such as dust, microorganisms, or a mixture of all of the above, better known as cryoconite. They all absorb solar radiation and thus decrease the albedo – the amount of solar energy reflected back to space – of the underlying white surface. This starts a vicious cycle by which these impurities melt the snow or ice and eventually uncover the usually much darker surface (e.g., rock or open sea water), leading to more solar absorption and the cycle continues. The effect and composition of these impurities are currently intensively studied on the Greenland ice sheet (check out the Black and Bloom, as well as the Dark Snow projects).

 Black Carbon effect on climate is highly uncertain

One of the reasons for the high uncertainty of BC’s climate effects is the big range in effects it has (see white line on Figure 1), when it interacts with snow and ice (or clouds and the atmosphere).

Another source of uncertainty is probably the big estimated range in the global, and especially in the regional emissions of BC in the Arctic. For example, the emission inventory we work with (ECLIPSE), is based on international and national statistics that indicate how much of a certain fuel (diesel, coal, gas, wood, etc.) is used, and in which way it is used (vehicle sizes, machine type and age, operating conditions, etc.). These numbers can vary a lot. If we, for example, line up different emission inventories of man-made emissions (Figure 4), by comparing the two different fractions of BC (fossil fuels vs. biomass burning) at different latitudes, then we see that the closer we get to the North pole, the more these emission inventories disagree. And this is still ignoring atmospheric transport or emissions of natural sources, such as wildfires.

Computer models, necessary to calculate global climate change, are partly based on input from these emission inventories. Models used for the calculation of the transport of these tiny particles have vastly improved in recent years, but still struggle at accurately mimicking the seasonality or extent of the observed BC concentrations. To some extent this is also due to the range of parametrization in the model, mainly the lifetime of BC, including its removal from the atmosphere by wet scavenging (e.g., rain). So to better understand black carbon effects on climate, more model calculations are necessary, for which the emission inventory estimates need to be verified by observations.

Figure 4: Fraction biomass burning of BC (fbb) at different latitudes North, estimated by three different emission inventories. The green line shows the GAINS emission inventory, which was the precursor to the ECLIPSE inventory (Klimont et al. 2016) [Credit: Patrik Winiger]

Figure 4: Fraction biomass burning of BC (fbb) at different latitudes North, from three different emission inventories. The green line shows the GAINS emission inventory, which was the precursor to the ECLIPSE inventory (Klimont et al. 2016) [Credit: Patrik Winiger]

How do we trace the origin of black carbon?

This is where the science of my colleagues and me comes in. By looking at BC’s isotopic ratio of stable-carbon (12C/13C) and its radiocarbon (14C) content we were able to deduce information about the combustion sources (Figure 5).

Plants (trees) take up contemporary radiocarbon, naturally present in the atmosphere, by photosynthesis of atmospheric CO2. All living organisms have thus more or less the same relative amount of radiocarbon atoms, we talk of a similar isotopic fingerprint. BC from biomass (wood) burning thereby has a contemporary radiocarbon fingerprint.

When they die, organisms stop incorporating contemporary carbon and the radiocarbon atoms are left to decay. Radiocarbon atoms have a relative short (at least on geological time-scales) half-life of 5730 years, which means that fossils and consequentially BC from fossil fuels are completely depleted of radiocarbon. This is how the measured radiocarbon content of a BC sample gives us information on the relative contributions of fossil fuels vs. biomass burning.

The stable carbon isotopic ratio gives information on the type of combustion sources (liquid fossil fuels, coal, gas flaring or biomass burning). Depending on how a certain material is formed (e.g., geological formation of coal), it has a specific isotopic ratio (of 12C/13C), like a fingerprint. Sometimes isotopic fingerprints can be altered during transport (because of chemical reactions or physical processes like condensation and evaporation). However, BC particles are very resistant to reactions and change only very little. Hence, we expect to see the same fingerprints at the observation site and at the source, only that the isotopic signal at the observation site will be a mixture of different source fingerprints.

Figure 5/ Carbon isotopic signatures of different BC sources, summarized by E.N. Kirillova (2013).

Figure 5: Carbon isotopic signatures of different BC sources, summarized by E.N. Kirillova (2013). To give information about the isotopic fingerprint, the delta-notation is used (small delta for 12C/13C, and big delta for 12C/14C). The isotopic values show how much a certain sample is different, on a per mil scale, from an international agreed isotopic standard value (or ratio) for carbon isotopes. [Credit: fig 1 from  Kirillova (2013)]

Where does the black carbon in European Arctic come from?

In our study (Winiger et al, 2016), we observed the concentrations and isotopic sources of tiny particles in airborne BC for over a year, in the European Arctic (Abisko, Sweden), and eventually compared these observations to model results, using the freely available atmospheric transport model FLEXPART and emission inventories for natural and man-made BC emissions.

Seeing our results we were first of all surprised at how well the model agreed with our observations. We saw a clear seasonality of the BC concentrations, like it has been reported in the literature before, and the model was able to reproduce this. Elevated concentrations were found in the winter, which is sometimes referred to as Arctic haze. The combustion sources showed a strong seasonality as well. The radiocarbon data showed, that fossil fuel combustion dominated in the winter and (wood) biomass burning during the low BC-burden periods in the summer. With a combination of the stable isotope fingerprints and Bayesian statistics we further concluded, that the major fossil fuel emissions came from liquid fossil fuels (most likely diesel). The model predicted a vast majority of all these BC emissions to be of European origin. Hence, we concluded, that the European emissions in the model had to be well constrained and the model parametrization of BC lifetime and wet-scavenging had to be fairly accurate for the observed region and period. Our hope is now that our work will be implemented in future models of BC effects and taken into account for future BC mitigation scenarios.

Figure 6: This is an example from the model calculations, showing where the (man-made) BC came from in January 2012. Abisko's position is marked as a blue star. The darker (red) spots show sources of higher BC contribution. This winter example was among the three highest observed (in terms of BC concentration) and the sources were ~50% wood burning, ~20% liquid fossil fuels (diesel) and ~30% coal. Some of the darkest spots can clearly be attributed to European cities.

Figure 6: Example from the model calculations, showing where the (man-made) BC came from in January 2012. Abisko’s position is marked as a blue star. The darker (red) spots show sources of higher BC contribution. This winter example was among the three highest observed (in terms of BC concentration) and the sources were ~50% wood burning, ~20% liquid fossil fuels (diesel) and ~30% coal. Some of the darkest spots can clearly be attributed to European cities. [Credit: fig4b from Winiger et al (2016)]

References

  • Anderson, T. R., E. Hawkins, and P. D. Jones (2016), CO2, the greenhouse effect and global warming: from the pioneering work of Arrhenius and Callendar to today’s Earth System Models, Endeavour, in press, doi:10.1016/j.endeavour.2016.07.002.
  • Arrhenius, S. (1896), On the influence of carbonic acid in the air upon the temperature of the ground., Philos. Mag. J. Sci., 41(August), 239–276, doi:10.1080/14786449608620846.
  • Hansen, J., R. Ruedy, M. Sato, and K. Lo (2010), Global surface temperature change, Rev. Geophys., 48(4), RG4004, doi:10.1029/2010RG000345.
  • Klimont, Z., Kupiainen, K., Heyes, C., Purohit, P., Cofala, J., Rafaj, P., Borken-Kleefeld, J., and Schöpp, W.: Global anthropogenic emissions of particulate matter including black carbon, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-880, in review, 2016.
  • Kirillova, Elena N. “Dual isotope (13C-14C) Studies of Water-Soluble Organic Carbon (WSOC) Aerosols in South and East Asia.” (2013). ISBN 978-91-7447-696-5 pp. 1-37
  • Winiger, P., Andersson, A., Eckhardt, S., Stohl, A., & Gustafsson, Ö. (2016). The sources of atmospheric black carbon at a European gateway to the Arctic. Nature Communications, 7.

Edited by Sophie Berger, Dasaraden Mauree and  Emma Smith
This is joint post with the Atmospheric Division , given the interdisciplinarity of the topic featured.


portraitPatrik Winiger is a PhD student at the Department of Environmental Science and Analytical Chemistry and the Bolin Centre for Climate Research, at Stockholm University. His research interest focuses on impact and mitigation of Short Lived Climate Pollutants and anthropogenic CO2 emissions. Currently he investigates the sources of black carbon aerosols in the Arctic. He tweets as @PatrikWiniger

 

Image of The Week – Plumes of water melting Greenland’s tidewater glaciers

fig1figoftheweek

Figure 1: Simulation of a plume at a tidewater glacier in a general circulation model (MITgcm). Left – water temperature and right – time-averaged submarine melt rate in metres per day. Shown are face-on views of a tidewater glacier, as if you were under the water in front of the glacier, looking towards the calving front. 250 m3/s of fresh water emerges into the ocean from a channel at the bottom of the glacier, forming a plume. As the plume rises towards the fjord surface it mixes turbulently with warm ocean water, causing the plume to warm with height. Further details of this simulation can be found here: Slater et al. 2015.

Loss of ice from The Greenland Ice Sheet currently contributes approximately 1 mm/year to global sea level (Enderlin et al., 2014). The most rapidly changing and fastest flowing parts of the ice sheet are tidewater glaciers, which transport ice from the interior of the ice sheet directly into the ocean. In order to better predict how Greenland will contribute to future sea level we need to know more about what happens in these regions.


Tidewater glaciers meet the ocean at the calving front (Fig. 2), where ice undergoes melting by the ocean (“submarine melting”) and icebergs calve off into the sea. In recent decades, tidewater glaciers around Greenland have retreated (due to increased loss of ice at the calving front) and started flowing faster. This in turn causes more ice to be released into the ocean, contributing to sea level. Understanding the cause of these changes at tidewater glaciers is an ongoing topic of research.

Figure 2: Kangiata Nunata Sermia, a large tidewater glacier in south-west Greenland. The expression of a plume originating at the base of the calving front is visible on the fjord surface as turbid sediment-rich water. [Credit: Peter Nienow]

Figure 2: Kangiata Nunata Sermia, a large tidewater glacier in south-west Greenland. The expression of a plume originating at the base of the calving front is visible on the fjord surface as turbid sediment-rich water. [Credit: Peter Nienow]

One possible cause of change is an observed warming of the ocean around Greenland (Straneo and Heimbach, 2013). A warming of the ocean is likely to lead to increased submarine melt rates, which may in turn influence iceberg calving if, for example, melting results in instability of the ice at the calving front. Submarine melt rates are thought to be increased further by upwelling of warm water at the calving front (Fig. 1 and Fig. 2).

This upwelling water, called a plume, may be initiated by submarine melting of the ice, or by fresh glacial meltwater from the ice sheet surface. This fresh glacial meltwater penetrates to the base of the glacier and flows into the ocean from beneath the glacier, which may be hundreds of metres underwater. Once in the ocean, the meltwater rises buoyantly because of a density difference between the meltwater and ocean water, forming a plume. In order to better understand the effect of plumes on submarine melting, we can model plumes using a numerical model (e.g. MITgcm). Our image of the week (Fig. 1) shows such a model, which we can use to estimate submarine melt rates. In combination with simpler analytical approaches (Jenkins et al., 2011; Slater et al., 2016), we can estimate how submarine melt rates may change over time and from glacier to glacier (Carroll et al., 2016), and begin to assess the effect of submarine melting on tidewater glaciers and ultimately on future sea level rise.

Edited by Teresa Kyrke-Smith and Emma Smith


donalds_face

Donald Slater is a PhD student in the Glaciology and Cryosphere Research Group at the University of Edinburgh. His research focusses on understanding the effect of the ocean on the Greenland Ice Sheet. For more information look up his website or follow him on twitter @donald_glacier.

Sea Level “For Dummies”

Sea Level “For Dummies”

Looking out over the sea on a quiet day with no wind, the word “flat” would certainly pop up in your mind to describe the sea surface. However, this serene view of a flat sea surface is far from accurate at the global scale.

The apparent simplicity behind the concept of sea level hides more complex science that we hope to explain in a simple manner in today’s “For Dummies” post, which will give you the keys to understand the important aspects of past sea change, and an ability to look into and understand how sea level is a key factor in the future.

Everyone will be familiar with news stories about current sea level rise, but it can be very confusing to understand what this means in real terms; how fast it is happening and why we should care about it anyway. So to begin with, let’s have a look at what we mean by sea level?


Sea Level – It’s all about gravity!

[Read More]

Image of the Week – Satellite Measurements of Arctic Sea Ice

Image of the Week – Satellite Measurements of Arctic Sea Ice

Sea ice is an important part of the Earth’s climate system. When sea ice forms, it releases heat and salt. When sea ice melts, it takes up heat and adds freshwater to the salty ocean water. It is also important for the exchange of energy between the atmosphere and the ocean surface, and for the ocean currents that transport warm and cold water from the equator to the poles and back.

The main route of sea ice moving south from the Arctic Ocean is through Fram Strait. This is the passage between  Greenland and Svalbard around 75-80°N latitude (see map). Today’s “Image of the Week” shows the amount of sea ice that flows  through this pathway each day (known as the mean observed volume flux) for October-November 2006.


What is sea ice volume flux and how is it computed?

Sea ice volume flux sounds a bit wordy – so what is it and why do we use it? Let’s start with the sea ice volume  – this simply tells us how much sea ice there is. In order to calculate the volume, you need to know not only the concentration of sea ice (i.e. the fraction of ocean covered by ice) but also its thickness. The flux parts comes in when we want to talk about the amount of sea ice moving through an area (e.g. Fram Strait). In order to calculate sea ice volume flux, you need to know both sea ice volume and drift. The latter is the displacement of sea ice over a certain period of time, typically measured in kilometres per day. So the volume flux is basically a measure of the volume of ice that moves through a certain area over a given time! Simple!?

An aerial view of the helicopter taking data of the sea ice below.

An aerial view of the helicopter taking data of the sea ice below. Photo credit: Alice O’Connor.

What does the “Image of the Week” show?

The  map was constructed by Spreen et al. (2009) from satellite data and provided one of the first estimates of  sea ice volume flux through Fram Strait exclusively using satellites.  However, it is  challenging to accurately measure sea ice thickness in the summer using satellites because of the  melt ponds (pools of open water forming on sea ice when temperatures are higher, i.e. summer) that interfere with the satellite signals. A few measurements of sea ice thickness have been collected in the summer from British and US submarines in the 1980s and 1990s but only in the region near the pole.  A recent study presents a way to compute sea ice volume fluxes through Fram Strait in the summer using a new dataset of ground-based and airborne electromagnetic ice thickness measurements (Krumpen et al., 2016).

In this new study, the concentration of sea ice is found from satellite measurements (passive microwave sensors to be specific). The sea ice drift can be found by using both satellite data and observations from buoys. Finally, the thickness of the sea ice comes from surveys using radar instruments on the ground or from an aircraft. This data was collected during 5 summers, by combining the three of these measurements, Krumpen et al., (2016) calculated the sea ice volume flux during the summer!

In the figure below, the red lines show the sea ice area flux using the concentration and drift only through Fram Strait in July and August from 1980 to 2012. Positive values mean that sea ice moves out of the Arctic Basin, while negative values represent sea ice that goes into the Arctic Basin. The figure shows that there are large variations in sea ice area flux from year to year.

The black dots are the volume fluxes (area flux times thickness) for the 5 summer seasons where the ice thickness was measured. The dots show that in some summers sea ice volume flux is negative, meaning that sea ice moves into the Arctic Basin. In other summers, for example in 2010, sea ice moves out of the Arctic Basin.

July (black, gray shading for uncertainty) and August (red, light red shading for uncertainty) sea ice area fluxes through Fram Strait (left axis). Black dots show sea ice volume flux for the 5 campaigns during which ice thickness is computed using electromagnetic measurements (right axis). Positive values mean that sea ice is moving out out of the Arctic Ocean while negative values mean that sea ice is flowing into the Arctic Ocean. [Figure 8 of Krumpen et al. (2016)]

July (black, gray shading for uncertainty) and August (red, light red shading for uncertainty) sea ice area fluxes through Fram Strait (left axis). Black dots show sea ice volume flux for the 5 campaigns during which ice thickness is computed using electromagnetic measurements (right axis). Positive values mean that sea ice is moving out out of the Arctic Ocean while negative values mean that sea ice is flowing into the Arctic Ocean. [Figure 8 of Krumpen et al. (2016)]

What comes next…

If field campaigns in the future continue to measure sea ice thickness in the summer, the calculations can be continued and we will learn more about the volume of sea ice that is transported through Fram Strait in the summer. This is important if we are to measure the balance of sea ice in the Arctic Ocean.

Edited by Nanna B. Karlsson


DavidDavid Docquier is a post-doctoral researcher at the Earth and Life Institute of Université catholique de Louvain (UCL) in Belgium. He works on the development of processed-based sea-ice metrics in order to improve the evaluation of global climate models (GCMs). His study is embedded within the EU Horizon 2020 PRIMAVERA project, which aims at developing a new generation of high-resolution GCMs to better represent the climate.

Image of the Week – Hidden Beauty on a Himalayan Glacier

Image of the Week –  Hidden Beauty on a Himalayan Glacier

Today’s image of the week comes from stunning setting of Chhota Shigri Glacier in the Pir Panjal Range of northern India. The range is part of the Hindu-Kush Karakorum Himalaya region which is a notoriously challenging place to work as it is very remote and completely inaccessible during the winter months. However, when have these challenges ever stopped a hardy glaciologist?! 

Our image this week was taken during a field expedition as part of an ongoing long term monitoring program in the area and today we are going to tell you why the region is so important (other than being the source of some rather good photos!)


Why is monitoring glaciers in the Himalaya so important?

Location of Chhota Shigri Glacier taken from Wagon et al., 2007

The Hindu-Kush Karakorum Himalaya region is made up of the biggest mountain ranges on Earth which contain the largest ice mass outside of the polar regions. This region provides water to 50-60% of the world’s population (Wagon et al., 2007), some of which comes from glacial melt water, therefore it is critical to understand how the glaciers in this region may respond to ongoing climate change and predict the impact this may have for the future. As glaciers are very sensitive to changing climate they are also used to understand climate variations at annual and decadal timescales in the region.

Chhota Shigri Glacier is representative of many glaciers in this region and was chosen as the site for a long-term monitoring program in 2002. It was chosen for a number of reasons including previous field studies on the glacier in the 1980s,  glacier geometry, accessibility and its dynamic environment; with areas of partial debris cover and supraglacial lakes (as seen in the image above). The data record on this glacier now continuously spans 13 years and the program has become a benchmark for studying Himalayan glaciers.

What do we see on the picture

The beautiful shot shows a supraglacial lake, a pond of liquid water, on the top of the Chhota Shigri Glacier. This supraglacial lake is an ephemeral lake, forming immediately after winter season. Supraglacial lakes form due to the melting of snow/ice and their presence helps to determine surface melt rates. When the lake water drains it also allows the distribution of subsurface hydrological conduits to be investigated. If the lake does not drain and exists long term there may be glacial lake outburst floods. These are a natural hazard and must be monitored and better understood. This is just one of the aspects of Chhota Shigri Glacier that is being investigated by the long term monitoring program.

Chhota Shigri Glacier has the longest monitoring record

The long term monitoring program, initiated on Chhota Shigri Glacier in 2002, has recorded the evolution of mass balance, ice velocity, ice thickness, stream runoff and melt water quality. The program is a joint collaboration between India and France under the frame work of DST/CEFIPRA programme at School of Environmental Science, Jawaharlal Nehru University, New Delhi. Presently, the annual and seasonal mass balance series (13 years) of Chhota Shigri glacier since 2002 is the longest continuous record in the entire Hindu-Kush Karakorum Himalaya region and represents a benchmark for climate change studies in this region. To measure the annual and seasonal mass balance, we survey the glacier at the end of winter season (May/June) for winter balance measurements and end of summer (September end/October) for annual measurements. We monitor a network of ablation stakes distributed throughout the entire ablation zone (including debris-covered area) to estimate the glacier-wide ablation. To estimate the accumulation we drill snow cores or dig snow pits at representative locations within the accumulation zone (>5150 m) of Chhota Shigri Glacier. For more detailed information and the results of this monitoring see Azam et al. (2016) and Ramanathan (2012).

Long term monitoring on Chhota Shigri Glacier (a) accumulation zone at the end of summer (area is largely covered in dust with clearly visible medial moraine . (b) accumulation zone at the end of winter (fresh snow cover), (c) ablation stake (bamboo) installation in a partly debris covered region during the summer and, (d) drilling of snow core at top of the glacier during winter (Credit: Arindan Mandal/JNU).

Long term monitoring on Chhota Shigri Glacier (a) accumulation zone at the end of summer (area is largely covered in dust with clearly visible medial moraine . (b) accumulation zone at the end of winter (fresh snow cover). (c) ablation stake (bamboo) installation in a partly debris covered region during the summe. (d) drilling of snow core at top of the glacier during winter (Credit: Arindan Mandal).

 

Acknowledgements

Thanks to Department of Science and Technology, Govt. of India, SAC-ISRO, CEFIPRA, INDICE, GLACINDIA and CHARIS for funding our research. Special thanks to Emma and Sophie for help in putting together this post.

Edited by Emma Smith and Sophie Berger


Arindan_PhotoArindan Mandal is a PhD student at the School of Environmental Science, Jawaharlal Nehru university, New Delhi, India under the supervision of Prof. AL. Ramanathan. His current work is focused on Chhota Shigri Glacier where he is working to analyse the past and present state of mass balance in the changing climate scenario and also to understand the complex local scale meteorological processes that drive the mass balance of the glacier. He is working to develop a coupled distributed surface energy-balance model combined with various glaciological and hydrological aspect using in-situ dataset to understand the processes that govern and runoff at Chhota Shigri glacier pro-glacial stream and its sensitivity to the future climate. He tweets as @141Arindan.
Contact Email: arindan.141@gmail.com,

Image of the Week — Looking for ice inside a volcano !

Image of the Week —  Looking for ice inside a volcano !

Who would think that one of the world’s most active volcano shelters the southernmost persistent ice mass in Europe!?

Yes, you can find ice inside Mount Etna!

Located at an altitude of about 2,040 m above sea level, the Ice Cave  (Grotta del Gelo) is well known among Mt Etna’s volcanic caves due to the presence of columns of ice on its walls and floor which occupy about the 30% of the cave’s volume and persist all year round.

How did the ice get there and why does it remain?

  • This cave a small lava tube of less than 100 metres long was formed during Etna’s longest eruption that occurred on its northern flank from 1614 to 1624 A.D. (Marino, 1999)
  • Once formed, the cave was subsequently filled with ice.
  • The shape of the cave enables the ice to persist because there is only one single entrance to the ice cave that insulate the air from the outside. This enables the temperature to stay below 0°C in some parts of the cave all year round. This is not the case with other lava tubes around Etna that have several entrances, which allows the air to circulate within the caves, causing warming

Exploring the Ice Cave

By studying ice inside caves, researchers can obtain very useful biological and paleo-climatological information. Although we don’t know much about the conditions of the ice mass and its evolution over the last few centuries, speleologists (Centre Speleogico Etneo) and scientists (Italian National Institutites of Geophysics and Volcanology) have studied the cave for the past 20 years.

The use of new technologies such as UAV’s (see THIS or THIS previous blog posts about other applications of UAVs in glaciology) or terrestrial laser scanners on glaciers and ice caves can give the possibility to monitor surface variations of hidden underground areas that have never been affected by human activities.

This year, researchers and speleologists from the Inside The Glaciers Project, organised a first expedition to the cave, to acquire precise measurements of the ice mass surface, with a terrestrial laser scanner.

After a long walk of about 4 hours through beautiful volcanic landscapes, the Inside The Glacier team arrived at the entrance of the cave. There they surveyed the Ice Cave for 5 hours, performing 17 scans to detect the ice mass with very high accuracy.

With these measurements it was possible to draw detailed topographic plant and sections of the cave and derive 3D models of its surfaces, obtaining first data that will be compared in future with other laser scanner surveys to help scientists to study the evolution of the ice mass inside the cave.

Topographic plant and profile of the Ice Cave derived from laser scanning data. Ice deposits are represented in cyan color.[Credit: Tommaso Santagata]

Topographic plant and profile of the Ice Cave derived from laser scanning data. Ice deposits are represented in cyan color.[Credit: Tommaso Santagata]

Acknowledgements

This expedition was organized within the “Inside The Glaciers” Project in collaboration with the Association La Venta Esplorazioni Geografiche, Etna Natural Park, Italian National Insitute of Geophysics and Volcanology (I.N.G.V.), Centro Speleologico Etneo, Federazione Speleologica Regionale Siciliana, Gruppo Servizi Topografici s.n.c.

(Edited by Sophie Berger and Emma Smith)


tom_picTommaso Santagata is a survey technician and geology student at the University of Modena and Reggio Emilia. As speleologist and member of the Italian association La Venta Esplorazioni Geografiche, he carries out research projects on glaciers using UAV’s, terrestrial laser scanning and 3D photogrammetry techniques to study the ice caves of Patagonia, the in-cave glacier of the Cenote Abyss (Dolomiti Mountains, Italy), the moulins of Gorner Glacier (Switzerland) and other underground environments as the lava tunnels of Mount Etna.
He tweets as @tommysgeo

Image of the Week – How ocean tides affect ice flow

Image of the Week – How ocean tides affect ice flow

Ice streams discharge approximately 90% of the Antarctic ice onto ice shelves , and ultimately into the sea into the sea (Bamber et al., 2000; Rignot et al., 2011). Whilst flow-speed changes on annual timescales are frequently discussed, we consider here what happens on much shorter timescales!

Previous studies have shown that ice streams can respond to ocean tides at distances up to 100km inland (e.g. Gudmundsson, 2006 ; Murray et al., 2007; Rosier et al, 2014); new high-resolution remotely sensed data provide a synpoptic-scale view of the response of ice flow in Rutford Ice Stream (West Antarctica), to ocean tidal motion.

These are the first results to capture the flow of an entire ice stream and its proximal ice shelf in all three spatial dimensions and in time.

The ocean controls the Antarctic ice sheet

The ice-ocean interface is very important as nearly all ice-mass loss occurs directly into the ocean in Antarctica (Shepherd et al., 2012). Many areas terminate on ice shelves (the floating ice that connects with the land ice), which are fed by the flow of ice from the ice sheet. Any changes to the floating ice shelf alter the forces acting on the grounded ice upstream, therefore directly affecting the ice sheet evolution (e.g. Gudmundsson, 2013; Scambos et al, 2004).

Because ocean tides are well-understood, we can use the response of grounded ice streams to ocean tidal uplift over the ice shelf to better understand how ice sheets respond to ocean-induced changes.

An ice stream and ice shelf respond to forcing by ocean tides

Floating ice shelves are directly affected by tides, as their vertical displacement will be altered. These tidal variations are on short timescales (hourly to daily) compared to the timescales generally associated with ice flow (yearly). The question therefore is, how much can the tides affect horizontal flow speeds, and how far inland of the ice shelf are these effects felt?

The movie below, by Brent Minchew et al, shows the significant response of Rutford Ice Stream and its ice shelf to forcing by the tides. Using high-resolution synthetic aperture radar data they are able to infer the significant spatio-temporal response of Rutford Ice Stream in West Antarctica to ocean tidal forcing. The flow is modulated by the ocean tides to nearly 100km inland of the grounding line. These flow variations propagate inland at a mean rate of approximately 30 km/day and are sensitive to local ice thickness and the mechanical properties of the ice-bed interface. Variations in horizontal ice flow originate over the ice shelf, indicating a change in (restraining force) over tidal timescales, which is largely attributable to the ice shelf lifting off of shallow bathymetry near the margins. Upstream propagation of ice flow variations provides insights into the sensitivity of grounded ice streams to variations in ice shelf buttressing.

Horizontal ice flow on Rutford Ice Stream inferred from 9 months of continuous synthetic aperture radar observations. (a) Total horizontal flow. Colormap indicates horizontal speed and arrows give flow direction. (b) Detrended horizontal flow variability over a 14.77-day period. Colormap indicates the along-flow component (negative values oppose flow) while arrows indicate magnitude and direction of tidal variability. Contour lines give secular horizontal speed in 20 cm/day increments. (c) Modelled vertical tidal displacement over the ice shelf. (Credit : Brent Minchew)

Reference

B. M. Minchew, M. Simons, B. V. Riel, and P. Milillo. Tidally induced variations in vertical and horizontal motion on Rutford Ice Stream, West Antarctica, inferred from remotely sensed observations. submitted to JGR, 2016

(Edited by Sophie Berger and Emma Smith)


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Teresa Kyrke-Smith is a postdoctoral researcher at the British Antarctic Survey, on the iSTAR grant. She works on using inversion methods to learn about the nature of basal control on the flow of Pine Island Glacier in West Antarctica. She completed her PhD two years ago in Oxford; her thesis focused on the feedbacks between ice streams and subglacial hydrology.

Brent Minchew is an National Science Foundation Postdoctoral Fellow also now based at the British Antarctic Survey.


 

 

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