The old boys: ahead of the curve!

In the past decade or so, interest in glacier microbiology and “bioalbedo” has intensified, but it is important to remember that these ideas are not new. In fact, the early polar explorers wrote on these topics over 150 years ago and even identified species of algae in cryoconite and the role of ice algae for accelerating melt.

A.E. Nordenskiold in Greenland
A.E. Nordenskiold in Greenland

Cryoconite represents the best studied and most biodiverse microbial habitat on ice surfaces. Although cryoconite studies have increased in frequency over the past twenty years, the concepts which underpin our current understanding were largely established in the nineteenth century. The term ‘cryoconite’ itself was coined by Adolf E. Nordenskiold to describe dust filled depressions on the Greenland ice sheet in records from the 1870s. Papers such as Gribbon et al (1979) and Wharton et al (1985) are commonly credited with providing the first explanation of cryoconite hole formation, but actually Nordenskiold proposed a mechanism of enhanced melt beneath dark layers of sediment way back in the late 1870s and pre-empted modern glacial microbiology by appreciating cryoconite holes as microbial habitats. Furthermore, Nordenskiold examined individual cryoconite granules, recognising them to be aggregates of mineral grains and organic matter and even identifying cyanobacteria as the dominant species within them (Leslie, 1879). Further detailed analysis of cryoconite grain composition was provided by Bayley (1891) who identified further mineralogical and biological matter. Cryoconite hole morphology was further studied by Drygalski (1897) and Hobbs (1910). Interestingly, Nordenskiold identified fine dusts on ice surfaces which he suggested were of cosmic origin; being well into the industrial era it is possible that his observations were related to early anthropogenic contamination (now becoming a prolific topic of study), although he considered Greenland to be too remote to be affected by distant industry.

Cryoconite holes, which Nordenskiold described as a major hazard on the Greenland ice sheet
Cryoconite holes, which Nordenskiold described as a major hazard on the Greenland ice sheet

Although modern glacial microbiology is facilitated by advanced techniques and methodologies, the conclusions drawn by studies over the past century have predominantly confirmed the intuition and basic empirical observations of the pre-1900 glaciologists.

In the 1880’s, Nansen observed thin veils of photosynthetic algae with extremely high spatial coverage on the Greenland ice sheet which he suggested to impact glacier melt rates. This predates Yallop et al’s (2012) study, which uses modern techniques to draw the same conclusions, by over a century. Similarly, Cook et al (2010) proposed a mechanism of lateral equilibration in cryoconite holes, but this was not an entirely new concept – Gerdel and Drouet (1960) alluded to widening of cryoconite holes in their paper over fifty years previously. Recent studies of cryoconite biodiversity using molecular techniques build on Steinbock’s (1936) and Charlesworth’s (1957) early-mid twentieth century optical microscope studies. Even large scale spatial variability in cryoconite microbiota was touched upon by Nansen in1891 who suggested that concentrations of biogenic glacier impurities decreased with distance from the ice margin on the Greenland ice sheet (reported in Nansen 1924), which was mirrored by recent studies by Hodson et al (2008), Yallop et al (2012), Stibal et al (2012) and Cook et al (2012). What modern glacial microbiology has done is put numbers on the old ideas – to turn what was qualitative into something quantitative, and to add detail. We have delicately coloured-in between the lines sketched out by the early explorers.

Nordenskiold's ship, SS Vega
Nordenskiold’s ship, SS Vega

What faces us now is to examine glacial microbiological responses to environmental changes and links with climate. This post simply emphasises the amazing diligence and foresight of the early polar explorers in pre-empting 150 years of future science.

REF:

Bayley, W.S. 1891. Mineralogy and Petrography. The American Naturalist, 25 (290): 138-146

Cook, J.M., Hodson, A.J., Anesio, A.M., Hanna, E., Yallop, M., Stibal, M., Telling, J., Huybrechts, P. 2012. An improved estimate of microbially mediated carbon fluxes from the Greenland Ice Sheet. Journal of Glaciology, 58 (212)

Cook, J.; Hodson, A.; Telling, J.; Anesio, A.; Irvine-Fynn, T.; Bellas, C. 2010. The mass-area relationship within cryoconite holes and its implications for primary production. Annals of Glaciology, 51 (56): 106-110.

Charlesworth, J.K. (1957): The Quaternary Era 1. Edward Arnold, London. 1700 pp.

Drygalski, E. von. 1897. Die Kryokonitlocher. Gronland-expedition der Gesellschaftfur Erdkunde zu Berlin 1891-1893, Bd 1: 93-103

Gerdel, R.W., Drouet,

Gribbon, P.W.F. 1979. Cryoconite holes on Sermikavsak, West Greenland. Journal of Glaciology, 22 (86): 177-181

Hobbs, H. 1910. Characteristics of inland-ice of the Arctic regions. Proceedings of the American Philosophical Society, 49 (194): 57-129

Hodson, A.J., Boggild, C., Hanna, E., Huybrechts, P., Langford, H., Cameron, K., Houldsworth, A. 2011. The cryoconite ecosystem on the Greenland ice sheet. Annals of Glaciology,51 (56):123 – 129

Leslie, A., (1879) The Arctic Voyages of Adolf Erik Nordenskiöld. MacMillan and Co., London, UK, 447 pp.

Nansen, F., 1924: Blant sel og Bjørn. Dybwads, Oslo, trans. B. Bigelow.

Nordenskjold, N.E. (1875): Cryoconite found 1870, July 19th-25th, on the inland ice, east of Auleitsivik Fjord, Disco Bay, Greenland; Geol. Mag., Decade 2, 2, 157-162.

Nordenskiöld, A. E., 1883: Nordenskiöld on the inland ice of Greenland. Science, 2, 732–739.

Steinbock, O. 1936. Uber ktyokonitlocher und ihre biologische Bedeutung, Zeitschrift fur Gletschergrund, 24: 1-21

Wharton, R. A., McKay, C. P., Simmons, G. M., and Parker, B. C., 1985: Cryoconite holes on glaciers. BioScience, 35: 449-503.

Yallop, M.L., Anesio, A.J., Perkins, R.G., Cook, J., Telling, J., Fagan, D., MacFarlane, J., Stibal, M., Barker, G., Bellas, C., Hodson, A., Tranter, M., Wadham, J., Roberts, N.W. 2012. Photophysiology and albedo-changing potential of the ice-algal community on the surface of the Greenland ice sheet. ISME Journal, 6: 2302 – 2313

Glacier carbon fluxes on Antarcticglaciers.org

I wrote an article about carbon on glacier ice for Antarcticglaciers.org which went online today. I’m really happy to have contributed to this great website! Check it out here.

Cryoconite Holes
A particularly extensive cryoconite field – a site of carbon fixation!

For any of my students who read this – explore the Antarcticglaciers website, it is a great resource for cryosphere information to supplement the lecture material!

Anthropogenic Impacts on Svalbard

A big well done to Sheffield PhD student Krystyna Koziol for co-authoring a recent paper in the journal ‘Trends in Analytical Chemistry’ detailing the impact of anthropogenic pollutants identified on the Svalbard Archipelago.

The Svalbard archipelago has a special significance for glaciologists – it is the site of the world’s most northerly human settlement (the research base at Ny Alesund) and represents one of the more accessible and well managed research bases in the High-Arctic, despite being one of the more remote. It is set in a wonderfully serene and pristine Arctic fjord where whales, seals, and occasionally polar bear migrate, where scientists can take a short boat ride to the magical 80 degree line of latitude, and glaciers spill down valleys and calve dramatically into the water.

The famous polar bear sign in Longyearbyen - the gateway to Svalbard
The famous polar bear sign in Longyearbyen – the gateway to Svalbard

However, this paper by Kozak et al (2013) in Analytical Chemistry underlines the sad fact that the Svalbard archipelago may not be as pristine as it seems. Not only are the Svalbard glaciers thinning and receding at an alarming rate, anthropogenically derived pollutants are impacting upon ecosystem balance.

The Arctic is not only uniquely beautiful, it also has a predictive role for global environmental changes and provides an early warning regarding the ecological impact of toxic chemicals. Pollutants from distant sources are having a tangible impact upon the Svalbard archipelago – even pollutants which were emitted decades ago and have been kept in long term atmospheric suspension are still being deposited and impacting the rare and fragile local flora and fauna. Studies of Arctic pollutants such as Kozak et al’s (2013) are essential components of global environmental monitoring, and more papers like this will help us to better understand our impacts and how best to manage them in the future.

Further North - exploring the glaciated areas around Ny Alesund
Further North – exploring the glaciated areas around Ny Alesund

REF:

Kozak, K., Polkowska, Z., Ruman, M., Kozioł, K., Namieśnik, J. 2013. Analytical studies on the environmental state of the Svalbard archipelago provide a critical source of information about anthropogenic global impact. Trends in Analytical Chemistry, 50: 107 – 126

Ice Core Review

The aim of this post is not just general interest, but specifically to provide an informal overview of ice cores for my Earth Surface Processes and Environments students (if you are one of them, the material here complements the lecture on Tuesday 15th October. Further notes and the lecture slides are available on Udo).

Ice coring is an extremely useful tool which allows us to reconstruct temperatures, atmospheric and oceanic conditions, volcanism and other events which occurred in the distant past. Without ice cores we would not have such a good grasp upon the timing of glacial and interglacial cycles, we would not have temperature records spanning the last 800,000 years, and the predictions we make about future climate change would be far less reliable.

A scientist removing a freshly drilled core from an antarctic field site (NSIDC)
A scientist removing a freshly drilled core from an antarctic field site (NSIDC)

But what exactly are they? Ice cores are cylinders of ice removed from a glacier or ice sheet by drilling downwards from the surface. This means they represent a vertical profile of the internal structure of the mass of ice. This is useful because the vertical profile of an ice mass contains a stratigraphy, much like a sedimentary record, since ice is deposited with an annual periodicity. Glacier ice forms when snow precipitates onto a glacier surface, is buried by further snowfall and compacted into ice. The thickness of ice layers can therefore tell us something about the rate of deposition in a given year.

Snow and ice are comprised of water molecules; however, not all water molecules are equal. Different isotopes of oxygen (molecules with the same number of protons and electrons, but different numbers of neutrons) exist in the ocean and atmosphere. The major isotopes are 18O and 16O. 18O has a greater atomic weight than 16O and more energy is therefore required to evaporate water molecules containing 18O from the hydrosphere into the atmosphere, and therefore the ratio of these molecules in the air provides a proxy for temperature. Atmospheric water molecules are precipitated to form glacier ice. The warmer the global temperature, the more ‘heavy’ 18O molecules are preserved when ice accumulates on glaciers and ice sheets. Thanks to careful calibration, we can measure the oxygen isotope ratios and provide a value for average temperatures for specific years in the distant past. Its also useful to know that isotopes of other elements can also be used in the same way – deuterium, for example is a ‘heavy’ form of hydrogen, measurements of which can also be used as a temperature proxy.

Temperature and CO2 reconstructions from ice core data
Temperature and CO2 reconstructions from ice core data

There are some complicating factors with isotope proxies, however, since it is not only temperature which influences their rate of deposition. For example, heavy isotopes are more readily precipitated and therefore travel less distance from their site of evaporation before they are deposited, meaning there is a negative gradient of heavy isotope concentration with distance inland from an ocean source. This is known as the continental effect. Secondly, altitude has a similar effect, since heavier isotopes will condense and precipitate at lower altitudes than lighter isotopes. Since ice can flow and therefore move location post-deposition, this can complicate palaeotemperature reconstructions. Furthermore, isotopes can diffuse out of layers of ice over long time scales, so records become somewhat less reliable with age. There is also a seasonal signal (due to temperature changes between summer and winter) in the ratio of preserved isotopes.

Along with snow, various impurities are also laid down via atmospheric deposition. These impurities can include particulate organic matter, atmospheric pollutants, and volcanic ash. Specific events, such as the volcanic eruption of Vesuvius in AD79 can be identified in ice cores due to the specific mineralogy and composition of sediment deposited in the aftermath of the event. This is useful for dating ice cores, as will be discussed shortly. Events such as nuclear bomb tests and the Chernobyl incident can also be identified in ice cores due to the radioactive minerals preserved in glacier ice.

Relative dating of ice is therefore relatively simple – we can often identify layers by counting up or down the ice core from a point which represents an event with a known date – for example we know that three layers of ice above the AD79 Pinatubo eruption represents ice deposited in AD84. However, this requires knowledge of the location within an ice core of specific events, which is not always the case or can be laborious and slow to find. Therefore other, pre-analysed ice cores are often used to help ‘map’ a new ice core, or identify the known events along its profile. However, this assumes common conditions of depositions for both the standard and the new ice cores. Furthermore, identifying annual accumulation layers can be difficult in very old ice due to ice being compressed by the vast weight of overlying ice, or deformed by shear and stress forces in the body of a glacier and ice sheet. Ice cores can also be compared to oceanic sediment cores, which record events in much the same way as glacier ice.

Absolute dating of ice cores requires elements with a known and measurable half life (usually carbon) to be extracted from specific layers and dated. C and Cl have radio-isotopes which are commonly used for absolute dating of ice cores. The problem with this is that a lot of ice has to be melted to attain large enough samples of the gases for accurate dating.

Ice cores in storage
Ice cores in storage

The longest ice cores successfully extracted to date are over 2km in length and were sourced from Antarctica. These cores have provided us with temperature records going back 800,000 years. This data revealed the remarkable synchronicity between variations in the earth’s orbit around the sun with changes in earth’s global average temperature and helped to uncover the crucial ice-albedo feedback mechanism for global climate regulation. Without these data, we would not know the timing or forcings of the great ice ages, glacial and interglacial periods, or shorter timescale climate changes. They illustrate the effects of changing solar activity, of oceanic circulation patterns, and are recording twentieth and twenty-first century anthropogenic climate change as we speak. Ice core data has been invaluable in attributing contemporary climatic change to human activity, in particular because it has elucidated precisely the effect of a range of natural forces, and shown them to be insufficient to explain recent global temperatures.

Ice cores, therefore, are an extremely important tool in climate science.