Why are fossils important when studying glaciers?

Asked by Edward

Hello Edward! Great question.

Fossils can be very useful in understanding past environmental change; this can be linked to past glacier fluctuations so that we can understand what the environment or climate was like when glaciers in the past grew larger or smaller.

For example, fossil pollen from plants can be found in cores from lake sediments or peat bogs. This can tell us about past vegetation, which is linked to regional climate. Chironomids, which are a kind of non-biting midge, can tell us about past temperatures. In the ocean, tiny animals like foraminifera can tell us about past ocean conditions.

When glaciers are in equilibrium with climate and are therefore maintaining their position, they can make landforms like moraines (a pile of rocky and muddy debris) at their terminus. Sometimes, organic material like plant material or shells may be picked up by the glacier and deposited in the moraine. We can can then use techniques like radiocarbon dating to understand the date when the moraine was formed.

How pure is the oldest ice water?

Submitted by Phyllis

Hello Scientists:

I am wondering about the purity of the oldest water that makes up the oldest glaciers. That is, if a very old (pre-Homo-sapiens) sample of ice is taken from a glacier in Antarctica, what is found in there? It’s not salty, I would guess, but is it extremely pure? Does it hold small life forms? How does it compare to a similar UNFROZEN water sample today, i.e., a sample from a relatively pure source like a remote lake?

Thank you!!

-Phyl

Hi Phyl,

Thanks for a fascinating question! To answer this, we’ll take a look at some ice cores. Ice cores are long, continuous samples of ice obtained by drilling down deep into an ice sheet. The oldest ice recovered from a continuous ice core is around 800,000 years old, from Dome C of the East Antarctic Ice Sheet1, drilled by the European Project for Ice Coring in Antarctica. This ice is more than old enough to be before any significant human influence!

Ice sheets accumulate through the evaporation of sea water, which falls as snow on the ice sheet, and builds up. The evaporation process cleans most of the impurities from the snow, so ice-sheet ice is nearly pure, but still contains trace amounts of sea salts, and other things like dust and ash from volcanoes and forest fires. Once humans came, more pollutants were added, such as the spike in Caesium-137 concentrations due to nuclear weapons testing in the 1950s2.

No life has been recorded living within ice sheets, as it’s an extreme place to live. However, bacteria have been found living in snow in polar regions3 and dead microbes are found within ice at the bottom of the Antarctic Ice Sheet4. Even subglacial lakes have been found to contain life in the form of bacteria5.

Even the remotest of lakes, by comparison, are far less pure. Although lake water is generally fresh water, it arrives in the lake as runoff from the land, via streams, or from glacial meltwater. The salinity of lakes is relatively low, except endorheic lakes – lakes that have no outlet, which can become salty through evaporation and concentration of salts. Lakes are also open to atmospheric pollution, and human pollutants, as well as dust and ash from natural sources, can become dissolved or trapped within the lake waters.

Hope that answers your questions!

Andy

  1. Augustin, L. et al. Eight glacial cycles from an Antarctic ice core. Nature 429, 623–628 (2004).
  2. Pourchet, M., Magand, O., Frezzotti, M., Ekaykin, A. & Winther, J. G. Radionuclides deposition over Antarctica. J. Environ. Radioact. 68, 137–158 (2003).
  3. Redeker, K. R., Chong, J. P. J., Aguion, A., Hodson, A. & Pearce, D. A. Microbial metabolism directly affects trace gases in (sub) polar snowpacks. J. R. Soc. Interface 14, (2017).
  4. Priscu, J. C. et al. Geomicrobiology of subglacial ice above Lake Vostok, Antarctica. Science (80-. ). 286, 2141–2144 (1999).
  5. Christner, B. C. et al. A microbial ecosystem beneath the West Antarctic ice sheet. Nature 512, 310–313 (2014).

 

What temperatures are ice cores stored at?

Question: how cold do we need to keep ice cores to save the data? Submitted by Kettaashano Hi Kettaashano, Thank you for a very interesting question! The world’s major ice core storage facilities, such as the National Science Foundation Ice Core Facility, store ice cores in large freezers at a temperature of around -36°C. Often, such facilities also house a slightly warmer (around -25°C) ‘examination room’ where scientists analyse the ice cores. Interestingly, there is now a push amongst ice core scientists to develop even colder storage facilities (Dalton, 2009), after evidence showing that the oxygen trapped within tiny bubbles in the ice (which is used to reconstruct Earth’s past temperatures) can be lost to the outside air by diffusion when stored at temperatures of between -20°C and -30°C (Bender et al., 1995). This is important as the loss of oxygen may lead scientists to make incorrect conclusions about the working of Earth’s climate system. It has been shown that storage temperatures of -50°C can limit this oxygen loss (Ikeda-Fukazawa et al., 2005), so ice core researchers are now keen to rebuild storage facilities that can achieve these temperatures. I hope this helps! Jacob References Bender, M., Sowers, T. and Lipenkov, J., 1995. On the concentrations of O2, N2, and Ar in trapped gases from ice cores. Journal of Geophysical Research, 100, 18651-18660. Dalton, R. 2009. Ice core researchers hope to chill out. Nature, 460, 786-787. Ikeda-Fukazawa, T., Fukumizu, K., Kawamura, K., Aoki, S., Nakazawa, T. and Hondoh, T., 2005. Effects of molecular diffusion on trapped gas composition in polar ice cores. Earth and Planetary Science Letters229, 183-192.

Does the Antarctic Ice Sheet transport glacial erratics?

Dear Malcolm,

Thank you for your question on glacial erratics. Below is a summary of the main debris transport pathways in glacial systems.

Debris can be supplied to a glacier system from supraglacial or subglacial sources. Supraglacial sources include rock or snow avalanches from valley sides or mountain peaks that rise above an ice sheet/cap surface (these are known as nunataks). Debris of a smaller grain-size (e.g. volcanic ash, dust) can also be added to glacier surfaces from windfall. Subglacial debris can either be derived from erosion at the glacier bed, or where supraglacial debris is lowered through a glacier (e.g. via crevasses or moulins).

Whether debris is supplied at the glacier surface (supraglacial) or at the bed (subglacial) goes some way in determining its transport pathway. Debris transported on a glacier surface is referred to as high-level debris transport. This material is also commonly termed passively transported debris because there is little modification of rock debris transported on the glacier surface. However, debris that falls on the glacier surface does not always remain there. It may descend to an englacial or subglacial position due to burial within primary ice stratification in the accumulation zone, or it may descend through crevasses or moulins.

By contrast, debris transported at the glacier bed is known as low-level debris transport. This type of debris is often termed actively transported because it is modified (e.g. rock edges are rounded off) during the process of transport. At the bed, debris can be transported via traction, within subglacial meltwater streams, or within the basal ice itself. Once entrained in basal ice debris may be transferred to different levels in a glacier. The folding and thrusting of ice as it deforms (e.g. where squeezed between narrow valley walls) can be enough to elevate basal debris into englacial, or even supraglacial, positions. Similarly, basal debris often emerges at the glacier surface close to the snout, due to compressive ice flow (put simply, slower flowing ice at the margin may be overridden by faster flowing ice immediately up-glacier, bringing with it basal debris).

To return to your question about Antarctic erratics, like all glaciers, debris is transported at the surface, within, and at the bed of the Antarctic Ice Sheet. An interesting point to note is that there is very little terrain above the ice sheet surface in Antarctica, which almost completely submerges the underlying topography (including mountain chains). This provides a natural limit on the amount of debris supplied to the ice sheet surface. However, surface debris does occur, and erratic rocks have been identified from past advances of the Antarctic Ice Sheet, such as those on James Ross Island, and they provide a valuable means of reconstructing ice sheet history through cosmogenic isotope dating techniques.

I hope this answer has been useful in outlining the main transport pathways in Antarctic glaciers, and glacial systems more generally. Do not hesitate to get in touch with more questions!

Jacob

How much of the Antarctic Ice Sheet is below sea level?

Hi Luke, thanks for your question!

An answer to your question can be found in the recent BEDMAP2 (an ice bed, surface, and thickness dataset for the Antarctic Ice Sheet) paper.

In terms of area:

5.50 x 10^6 km^2 (or 5,500,000 km^2) of ice is grounded below sea level.

The total area of the ice sheet is 12.295 x 10^6 km^2 (or 12,295,000 km^2).

Therefore, ~45% of the ice sheet is grounded below sea level.

What is the source of Larsen C Ice Shelf?

Looking at maps of Larsen C, the area of the shelf is many time larger than the area of the glaciers that I assume would accumulate snow and feed it.  This made me wonder about the source of the Larsen Ice Shelf. Is most of Larsen C’s ice mass originally from the glaciers or was it accumulated in place as snow falls on the shelf itself?

Asked by Todd

Hi Todd,

Great question! The ice shelf receives mass from the glaciers on land that flow into it, and from snowfall directly on to the ice shelf, and from sea water freezing on to its base. It loses mass by submarine melting, sublimation and calving icebergs.

Is the breakaway of the Larsen C Iceberg normal?

Question:
my question:
Fact: A massive iceberg weighing more than one trillion tons has broken away from western Antarctica
Speculation: Global Warming

My Question: In 1911 – the Titanic sank due to icebergs in the shipping lanes – was this Global Warming? Probably not?
Speculation: It seems icebergs break away are normal

 

Asked by Greg,

 

Hi Greg,

You are completely right that iceberg calving is a completely normal process in Antarctica. Antarctica loses about 1089 Gt of ice per year through calving icebergs – exceeded only by basal melt.

This iceberg is unusually large, but we cannot attribute its calving event directly to climate change. We could only do this if we saw a sustained increase or change in calving behaviour over a long period of time, and were able to exclude dynamic factors that can cause changes in calving behaviour.

We are concerned that the calving of the iceberg might destablise Larsen C Ice Shelf and make it more vulnerable however – more information here.

How do we know how old the Antarctic Ice Sheet is?

The oldest penetrated Antarctic ice is about 800,000 years old. However, I have read that the Antarctic Ice Sheet has been present for several millions of years. Is there any direct evidence for older ice, or is it simply an inference from dC18 values from somewhere, or something like that? Do global sea-level curves support the older ice story?

-Asked by Joe

Hi Joe,

That is a great question. In fact, there are several ways in which we know when ice first began to accumulate on the Antarctic continent. Firstly, offshore seismic surveys and drilling campaigns of sediments on the continental slope and shelf. These sediments are dated using biostratigraphical methods (such as dinoflagellate cysts), strontium isotopes analysis on pristine shells, and by isotopic analysis of volcanic rocks (see Davies et al., 2012). Some of this evidence comes from the Antarctic Peninsula, summarised here.

This is supported by the deep-sea record of del18O, which is a proxy for global ice volume, and global eustatic sea level change. Together, these indices suggest that glaciation began on Antarctica around 35 million years ago.

 

Davies, B.J., Hambrey, M.J., Smellie, J.L., Carrivick, J.L., Glasser, N.F., 2012. Antarctic Peninsula Ice Sheet evolution during the Cenozoic Era. Quaternary Science Reviews 31, 30-66.

What do I need to study to become a glaciologist?

Asked by Johnny

Hi Johnny,

Thanks for your question! Glaciology encompasses a number of disciplines, from maths, physics and chemistry, geology and geography. A science background is necessary but there is a huge range of specialities within glaciology, ranging from numerical modelling (needs maths and physics and computer science) to geomorphological mapping (needs Geography or Geology). A degree in a science subject, followed by a Masters and most likely a PhD is the route into becoming a professional glaciologist.

Do glaciers recede during summer and advance during winter?

Is there a significant cyclic variation in the position of the glacier terminus along the year?

-Asked by Felix

Hi Felix.

This is a great question. In some areas with glaciers with especially fast response times, this may indeed be the case. Some glaciers in places like Scandinavia and Iceland have small annual moraines, which form each year, as the glacier recedes in the summer and the terminus position stabilises in the winter. However, this is not the case for most glaciers, as the response time of the glacier is typically longer than a single year.