5.1 Impacts on land systems - the cryosphere (video)
Presented by Dr. Damien Mansell.
There was a lot of material in this video, on a subject matter I was unfamiliar with, so there was a lot to take in. This is the first video I have had to re-watch, and pause to make notes in, some key points:
- The cryosphere is that part of the Earth's surface that is under ice.
- 99% of the Earth's glacier ice is over Greenland and Antarctica - this has potential (not forecast) to contribute to 65m of sea-level rise (Exeter cathedral in the video is 44m high).
- The last two decades have seen the glacial ice reduce in three ways over Greenland - thinning, less extent (frontal retreat) and increase in glacial flow speeds.
- For Greenland - half of the loss is from surface melt, the other half from blocks breaking off at the edges (calving).
- More snow will cause the glaciers to grow, but if the melt-rate increases to more than the rate added by snow, the net change will be less ice.
- If the glaciers spread more - you will have more ice at the edge - more melting and more "calving".
- On an average summer half of the surface will melt - in 2012 it was 97% and for two months longer than average.
- Surface water at high elevations mostly refreezes in place. At the edges, melt water either flows into the ocean (adding to sea level rise) or stays in place by forming lakes.
- These lakes can be up to 9km^2 in area, are darker and absorb more heat.
- Meltwater reaching the bed of the glacier and acting as a lubricant to make it flow faster is called Basel lubrication.
- So sudden releases of melt water contribute to more rapid spreading of the ice, and transport heat into the ice - which may soften it or cause it to spread more rapidly.
- Floating ice-shelves acts as a "flying buttress" and holds back the edge of the glaciers, slowing down their flow. If the over-sea-ice melts, it doesn't contribute to sea-level rise (it's mass has already been displaced), but it no longer holds back the ice over the land, which then flows out at a faster rate, which does contribute to sea-level rise.
- Something I realised later: sea-ice is ice formed at sea, whereas an ice-shelf is glacial in origin.
This is an interesting website showing daily reports on the extent of the Greenland ice-sheets, with reports on where the surface is melting, and the glacier front positions, and a total mass of the ice sheet, showing how it varies through the year, and has seen consistent loss in recent decades. 2012 was an extreme year with the rate of ice loss being outside two standard deviations of the mean.
There is a link to a second article on the marine ice sheet instability hypothesis which is a low probability / high impact scenario where a large part of the Western Antarctic ice could melt and contribute up to 3.3m in sea-level rise. This also links to an easy to read Discovery piece.
5.3 Glacial Retreat - article
Key bit on the GlacierWorks website is this video of the worlds highest photo exhibition, where we are talked through the "then" and "now" photos, where there are modern photos taken to reproduce the views of photos taken by some of the earliest expeditions to the Himalayas. The difference in the extent of the glaciers is truly shocking.
There is also a rather funky tool for comparing one photo with another with a slider to move and reveal one photo against another.
5.4 Calving Events - video
A time-lapse from Swansea Glaciology showing a large calving event at the Helheim Glacier in Greenland in 2010. Apparently this is the biggest calving event caught on camera, and was so large it was picked up by seismologists.
We are also asked to discuss how factors such as air temperature, water temperature, glacier speed and the fjord topography can control calving. Also to identify what are the key controlling processes?
So from what I've learnt above:
Rising air and water temperatures would lead to the melting of sea ice. This acts as a buttress to glaciers, so when this is removed the rate of flow of ice out of the glaciers increases. Warming of the ocean melts ice shelves (part of the glacier over water) from below, making them thinner and more prone to collapse or calving events.
Rising air temperatures also means more surface melting, some of which will flow out, some of which will be trapped in surface lakes. These lakes will also absorb more solar radiation/heat, warming the surrounding ice, making it weaker, and causing it to spread further. If the meltwater reaches the glacier bed it can act as a Basel lubricant increasing the rate of flow of the ice - this leads to more loss through calving as the ice sheet spreads out further.
The direction of the gradient and whether or not the bed below the glacier is above or below sea-level are also important. Ice melt from above sea-level leads to a rise in sea level. The grounding line is the boundary between the floating ice shelf and the grounded ice feeding it. This line can retreat if warmer ocean water melts the underside of the shelf or there is a major calving event.
This page ice-shelves is good at explaining ice shelf collapse.
5.5 Ocean Acidification - video
Presented by Dr. Ceri Lewis.
Another fact filled video, on a subject I know next to nothing about, so key points for me are:
- 70% of the planets surface is ocean, this is actually 99% of the living space for animals, as they are so deep.
- 1/3 of our oxygen comes from phytoplankton living in the oceans
- marine inverterbrates make up 76% of the 250,000 known species in the oceans, they are important to us because they are at the bottom of the food chain
- CO2 is really soluble in water, and 1/3 of atmospheric CO2 is absorbed
- CO2 + H20 = H2CO3 (carbonic acid), which dissociates into H+ and HCO3- ions, the concentration of H+ ions means the pH of seawater is about 8.1
- other carbonate ions enter the sea through natural weathering of rocks, or come from the shells of dead marine animals, this creates the "carbonate buffer", which soaks up excess H+ ions keeping the oceans pH stable for millions of years
- we're now adding more CO2 into the atmosphere, and this is getting absorbed by the oceans at a faster rate than the carbonate buffer can cope with, leading to ocean acidification
- pH of ocean has fallen 0.1 (30% increase in H+ ions on logarithmic scale) since the start of the industrial revolution, expected to drop by 0.3 to 0.4 pH units (120% increase in concentration of H+ ions) by the end of the century if we continue to emit CO2 at same rate
- calcium carbonate makes the shells and skeletons of many sea animals, calcification is the precipitation of calcium carbonate into the solid shell form, this is sensitive to dissolution (dissolving) again if the sea becomes under saturated with carbonate ions
- in colder Arctic and Antarctic waters, where CO2 dissolves more readily we're already seeing under saturation of carbonate ions and some small creatures showing signs of dissolution processes
- larger active animals (such as crabs) produce more CO2 so have better mechanisms for dealing with variations in CO2 levels, but smaller less active animals (such as limpets) can't cope as well and so are more sensitive to CO2 changes
- lots of marine animals reproduce with eggs and sperm released directly into seawater, then form small larvae which in turn develop calcium carbonate skeletons when growing
- this is very sensitive to acidification and exposing sea urchin larvae to acid levels expected at the end of the century show that the larvae don't develop as well, significantly fewer make it to adulthood
- this raises important questions about how can animals adapt sufficiently quickly, and what other stresses will be interacted with in polluted oceans
Links to two more documents
- FAQs about Ocean Acidification - includes an Ocean acidification chemistry 101 and a neat little PDF 20 Facts about Ocean Acidification.
- Acid test: the global challenge of ocean acidification - a documentary with Sigourney Weaver (not watched)
- An article on the NASA website, it explains in plain English about ocean acidification, and gives a couple of examples of the impacts.
- It highlights that coral reefs in particular, which are some of the most biologically diverse places on Earth will suffer on account of the reduction in availability of carbonate ions needed to build them, but acidification could contribute to the dissolving of the reefs.
- Pteropods are small marine snails which support small fishes, and in turn, larger fishes, penguins and whales and seabirds. Ocean acidification strips seawater of carbonate ions needed to build their new shells, and damages their existing ones.
- Ocean acidification will continue even if we stop putting more CO2 into the atmosphere, and the pH could potentially reduce to a level not seen in 20 million years. The rate is happening so fast, it is unclear how marine life and systems will react and how well they can cope with this rapid change.
- NASA has some satellite instrumentation that uses the colour of the ocean to provide information about ocean biology and chemistry.
- There is also a really big question about whether the oceans will become saturated with carbon dioxide and eventually cease to be a sink.
Two questions to answer:
Q. Will marine organisms be able to adapt to ocean acidification given the time scale for the predicted changes?
A. Well this is an unknown, as the oceans have not been this acidic for maybe 20 million years or more. The discussion groups highlight that major changes to the carbon and sulphur cycles in the past have coincided with mass species extinction events. Ceri Lewis' video explained that creatures higher up the food chain were likely to be more able to cope with these changes, but they are ultimately dependent upon creatures lower down the food chain which are more susceptible. From my limited understanding of natural selection is that evolution can effectively make leaps when situations change, so the question should really be, are there sufficient species able to adapt and maintain sufficient bio-diversity.
Q. Increased carbon dioxide in the atmosphere is likely to lead to sea level rise. Are rising sea levels more of a threat to humanity than ocean acidification?
This is a tricky one. I think we can see the direct impact of rising sea-levels and quantify these in a reasonably straight-forward way by identifying which parts of the globe will become less habitable and more prone to coastal weather events, and in turn determine the potential social and economic impacts. The impact from ocean acidification acts in two ways, one on the food-chain, of which it is difficult to make an assessment - and what proportion of the worlds population depends upon fish from the sea? The second is how this in turn affects the carbon cycle itself. It "feels like" rising sea-levels are more of a threat, but we don't really know what the full effects of ocean acidification could be, so it's difficult to quantify these.
Wow! 15 out of 15 this week, a first!
5.9 Reflect
- Lots of things learnt this week, I knew next to nothing about glaciers or ocean acidification, and now feel I have had a good introduction to both.
- I think this is the first time I've used my A'Level Chemistry knowledge in a long time - all those chemical reactions and equilibriums taking place with ions in the ocean has made me think about things long-dormant.
- I found the glacier video very fact heavy and had to re-watch it - a lot of material appeared to be crammed in to 8 minutes, but the following articles helped to reinforce some of the content. I think a few good diagrams would have conveyed the main points to me in a fairly concise way. That may be my learning style.
- The thing I struggled with the most was the concept of the grounding line and whether or not it's moving to and fro was a bad thing in itself - so maybe more time spent on the Antarctic Glaciers website is in order. I'm not sure that was a key point, but I spent a lot of time mulling it over.
This weeks feedback video is on YouTube.
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