The Glaciation of Northern England

The Devensian Glaciation of Northern England
I felt I should bite the bullet, and translate some of my papers for the general public. And so, below is what is otherwise:

Davies, B.J., Roberts, D.H., O Cofaigh, C., Bridgland, D.R., Riding, J.B., Phillips, E.R., and Teasdale, D., 2009. Interlobate ice-sheet dynamics during the Last Glacial Maximum at Whitburn Bay, County Durham, England. Boreas 38, pp. 555-578

The paper is available to download from Swetswise (if you have a license / are a member of university). Please use the citation above. Whitburn is a town north of Newcastle, and there is a car park and tea shop next to the beach, making it an easy site to visit.

Introduction
This paper examined the glacial sediments in coastal exposures at Whitburn Bay, Co. Durham, and used heavy minerals and stone lithologies to determine the provenance (source) of the ice lobes that deposited them. These glacial sediments were deposited during the Last Glacial Maximum, that is, the most recent period of maximum extent of the British Ice Sheet. This occurred 29 - 21,000 years before present.

Map showing the location of Whitburn Bay, north-eastern England

The last British-Irish Ice Sheet was a highly dynamic ice sheet. It reacted rapidly to external forcings by the atmosphere and oceanic currents. Modelling by people at Aberystwyth University has suggested that the dynamic cycles of the ice sheet occurred in step with temperature variations recorded in ice cores from Greenland.

The Tyne Valley Glacier
The map above shows the Tyne Gap. Whitburn Bay has two tills; these are sediments deposited directly at the base of a glacier. During the LGM, a glacier flowed along the Tyne Gap and out into the North Sea. It deposited a well-consolidated till with Pennine stones - Carboniferous limestones and shales - indicating its western provenance. Upon recession of the Tyne Glacier, numerous fluvio-glacial landforms were deposited in the Tyne Gap.

A boulder pavement was deposited at the top of this first till. You can clearly see the boulders, at the same height, in the photograph below. The boulders are orientated in the same direction, faceted and striated, and have flat tops. Water-lain gravels are interbedded beside and between the boulders. These boulders melted out from the base of the Tyne Valley glacier as it quiesced, stagnated and melted. Finer material was washed away by abundant meltwater at the ice-bed interface.

Photographs of the lower till from the Tyne Valley glacier at Whitburn Bay.

The North Sea Lobe
After the recession of the Tyne Valley glacier, the North Sea Lobe surged forwards. This glacier had its headlands in northern Scotland, and contains lots of Scottish igneous and metamorphic pebbles and minerals. The North Sea Lobe trapped many proglacial lakes between it and the higher ground inland, including Glacial Lake Wear and Glacial Lake Humber. Dates on mosses at Skipsea, further south, indicate that the North Sea Lobe existed after 21 ka BP. Dates on Glacial Lake Humber in the Humber estuary indicate that it was still in existence at 16 ka BP.

The North Sea Lobe was a strong and dynamic part of the British-Irish ice sheet. The Tweed Valley ice stream was diverted southwards by the North Sea Lobe. Orientation data preserved in the glacial sediments along the northern English coastline show that it consistently flowed onshore.

Ice flow pathways during the Last Glacial Maximum

Ice Marginal Canals
Incised downwards into the upper North Sea Lobe till at Whitburn Bay are numerous bedded sands and gravels. They range from well-sorted, low energy sands and clays to high-energy sands and gravels. Some of them are tightly folded and deformed - see below.

These sands and clays represent a very late-stage ice marginal subglacial drainage system. As the amount of water at the ice bed exceeded the carrying capacity of the groundwater and porewater pressure of the tills, it was evacuated by drainage channels. In places, the groundwater carrying capacity was exceeded dramatically and explosively, with water bursting out as a hydrofracture.

This helps us understand the deglaciation of northern England. During the late stages of the Last Glacial Maximum, the ice sheet was warm based and well lubricated at its bed. Abundant meltwater was rapidly evacuated by subglacial channels. Ice marginal lakes were present to the west of the ice lobe, dammed by the ice to the east and the higher ground to the west. The ice probably melted and retreated rapidly in response to a warming climate.

Scandinavian Ice in the North Sea Basin
A large question is why the North Sea Lobe was flowing onshore during the LGM. Why did it divert the Tweed Ice Stream southwards? I think that the North Sea Lobe was constrained in the North Sea by the Scandinavian ice sheet. Contact in the North Sea did not the lobe to spread eastwards as would have been expected.

In addition, the sediments immediately to the coast of northern England are potentially more 'slippy', aiding faster ice flow in this direction. A forebulge in the North Sea from the Scandinavian ice sheet could have resulted in higher ground to the east of the North Sea Lobe, also directing it southwards.

In my opinion, these factors are only small. There must have been contact between these ice sheets at the Last Glacial Maximum. Dates from open-marine shell fauna in the northern North Sea indicate open-marine conditions at 22 ka BP. I think that the ice sheets were confluent at 29 ka BP, and this provided a mechanism to turn the ice sheet southwards. Upon recession of the Scandinavian ice sheet, the North Sea Lobe continued to flow southwards with minimal eastward relaxation, perhaps aided by slippier sediments and the forebulge. The reaction time of ice sheets is slow enough for the North Sea Lobe to not have had time for all the flow to resume a more natural, eastwards direction.

Antarctica's ice shelves and sea level rise

Ice Shelves of the Antarctic Peninsula
Antarctica is fringed with floating ice shelves. They are floating extensions of the Antarctic Peninsula ice sheet, and can be very large indeed. The Ross Ice Shelf is the size of France - see the map below. However, in recent years, the dramatic and rapid loss of ice shelves fringing the Antarctic Peninsula have hit the news.

The Antarctic Peninsula is the third ice sheet on Antarctica. The West Antarctic Ice Sheet (WAIS) and East Antarctic Ice Sheet are the other two. The Antarctic Peninsula Ice Sheet (APIS) is of great interest because it is the most temperate of the three ice sheets, and contains up to 0.6 m sea level rise (in addition to the +1.0 m sea level rise predicted by the IPCC over the next 100 years).

The Antarctic Peninsula. Credit: USGS

The disintegration of the Antarctic Ice Shelves
The first ice shelf to dramatically disintegrate was the Larsen B ice shelf. Read about it in a British Antarctic Survey press release here. The Larsen B Ice Shelf began to collapse in 1995, and disintegrated over a matter of weeks. An armada of icebergs was dispatched into the Weddell Sea. More recently it appears that the Wilson Ice Shelf has begun to disintegrate. This has been accelerated by a 3C warming over the last 50 years; the Antarctic Peninsula is one of the most rapidly warming places on Earth.

The Impact of the Loss of the Ice Shelves
As ice shelves float at their specific density, their melting has no direct impact on sea level rise. You can test this yourself. Find yourself two water glasses. Put two 'ice bergs' (ice cubes) in one and fill it with water so that the ice cubes float. Mark the water level on the glass and note what happens when the ice melts - it will stay at the same level. With the second glass, put in four or five ice cubes and fill the glass so that most of the ice cubes are covered but they are not floating. When the ice melts, the water level in the glass will rise.

This is an important point to note. Melting ice shelves, like the floating ice cubes, will not cause the water level to rise. However, ice shelves are an important part of the glacial system, and strongly effect the ice dynamics within the continental ice sheet. With their loss, internal continental, non-floating ice speeds up, and calves more ice bergs into the ocean, rising sea level.

This works in the following manner. Ice shelves are pinned and grounded at certain points; they form in large bays and are constrained at their edges. They hold back the onshore fast-flowing ice streams. Ice streams are corridors of faster-flowing ice that is melted at its base. Ice streams drain the majority of the ice from ice caps, and contribute to the majority of ice dynamics. The ice streams are the same as the ice cubes that were not floating, and by adding more ice to the glass, the water level will rise.

Ice streams of the WAIS

Since the collapse of some of the ice shelves fringing the Antarctic Peninsula, outlet glaciers and ice streams in the vicinity have increased in speeds of up to 5 times, releasing large amounts of meltwater and ice bergs into the ocean. This of course is directly relevant to sea level rise. The role of sea ice is important as sea ice protects ice shelves from waves and storms, which can destabilise the ice shelf and aid its collapse.

The collapse of the ice shelves is one of the most visible aspects of modern climate change. It is very important to act now to curb global warming, to protect these fragile systems. Their destruction could result in real and rapid sea level rise, threatening our coastal towns, cities and wildlife habitats. With a large majority of the world's population living near the sea, we cannot afford to ignore this problem.

Climate Change Sceptics

Proving Climate Change
I was going to write about sea level and climate change, but have decided that this massive and complicated topic has already been covered in much more detail and has been much better written. I couldn’t possibly compete. However, when reading the New Scientists’ focus on Climate Change, I was struck by the number of comments along the lines of, ‘This is theory, we won’t believe it until you prove it’. Two things came to my attention. Firstly, that climate change has been accorded almost myth or religious-like status, and has become something that you can either ‘believe’ or ‘disbelieve’. Secondly, that many people are profoundly naive about the way in which science works. And so I was motivated to write a brief piece about scientific research design. Stay with me now – I’ll make it as interesting as possible!

The process of refutation
Early scientists thought that the best way to come up with a ‘unifying scientific law’ was through empirical observation. This is inductive research. Scientists carefully made observations of natural occurrences, and then formulated a law about their form / genesis / process etc. However, in the 20th Century, Karl Popper argued that science could only move forwards through a process of refutation. The classical example is this: a scientist goes to a lake, and counts the number of swans. He notes their colour, characteristics, behaviour, etc. He goes to the lake every day for a year, and at the end, proposes the law that all swans are white. Popper points out this is flawed; for to state that all swans are white, you must see all swans, everywhere, that ever existed. You only need to see one black swan to disprove this theory. Scientists should instead propose hypotheses, and then seek to disprove them. Scientists must always be critical. This is deductive, critical approach is fundamental to modern science.

As science matured throughout the twentieth century, this approach was gradually seen as inadequate. Under Popperism, the scientist is forced to always reject the entire hypothesis, and this does not bring the theory any closer to the truth. Thomas Kuhn in the 1960s proposed the concept of a paradigm or research programme. A paradigm has a fundamental core of hypotheses that are regarded as scientists as the truth, or as close to the truth as possible. This core is surrounded by an outer ring of auxiliary hypotheses, that are constantly being tested, updated and revised. Over time, these auxiliary hypotheses may call into question or threaten the paradigm’s core hypotheses, and may lead to a paradigm shift, a revolution, where the paradigm is entirely rejected, and replaced with a new one. The core hypotheses form a series of assumptions that a scientist makes when designing a piece of research, and this allows him to reject only the part of the hypothesis that is flawed. By continually testing and revising the auxiliary hypotheses, science either moves ever closer to the truth, or the assumptions are revised or rejected.

Within the field of glacial geology, a paradigm shift occurred in the 1990s. Up until this point, it was thought that most ice movement within fast-flowing ice streams was due to internal deformation of the ice, with possibly some lubrication of water at the ice bed inducing basal sliding. However, geophysical surveys and boreholes drilled though the Siple Coast ice streams in Antarctica indicated highly saturated sediment at the base of the ice stream, where most of the forward momentum occurs through subglacial deformation. We now understand ice streams to achieve fast flow through sediment deformation and the base, possibly with some basal sliding. Subglacial deformation is now a 'hot topic' in Quaternary Geology.

Siple Coast Ice Streams.

Other classic examples of paradigm shifts include flat earth / round earth, and whether geological formations of Britain were deposited by a Great Flood (Catastrophism) or by ongoing geological actions (Uniformitarianism).

Designing experiments to test climate change
Of course, this all can work very nicely if we have a simple little system, can we can easily create hypotheses, test them, and make conclusions. An example of this could involve pendulums. You can assume, based on previous research, that a weight on the end of a string will swing in a consistent manner. You want to find out whether the period of the pendulum swing is based on the amplitude - how far the pendulum swings. You hypothesise that if you start the pendulum swinging from twice as far away, the pendulum swing will take twice as long. You can set up a series of experiments to test, observe and time pendulum swings, and then evaluate whether your hypothesis is refuted or upheld. The key point is that the hypothesis is testable.

Unfortunately, the atmosphere, the oceans, and the ice sheets form a huge, interconnected system with numerous complex feedbacks. We cannot perturb this system to observe what happens. It is therefore necessary to conduct a measure of critical inductive research. The term 'critical' means that we still create testable hypotheses. We must make observations of the past and present, analyse trends and identify anomalies. We must situate our hypotheses, research aims and objectives, and research questions critically within the research programme and we must be aware of the paradigm within which we operate. Only then can we conduct relevant and useful research whilst still respecting Popperian ideals.

Who’s the climate sceptic now?
The way in which scientists are fundamentally trained from the start of their careers induces a highly sceptical attitude. Scientists are always trying to disprove their own theories. And because a theory can never be proven, climate change will remain a theory. However, it is important to note that over the last few years, the paradigm of climate change has evolved. Most scientists now accept the ‘hard core’ hypotheses as close to the truth. These core hypotheses state that the climate is changing, that atmospheric CO2 emissions are rapidly rising, and are now above any atmospheric CO2 within the last 600,000 years. Most scientists will accept the retreat of Alpine glaciers, rising sea level and rising temperatures. Surrounding this core is a more flexible belt, with hypotheses regarding the proportion of human intervention in the climate. And around the edge, hypotheses regarding the rate of change, comparisons to past change, and likely future change and sea level rise are regularly tested and updated. Scientists are the ultimate climate sceptics, who seek only to provide the best data possible, and who are always critical of their own and other’s work.

Climate change isn’t something one should or could ‘believe’ in or blindly accept; it is something we should constantly challenge. But we must make informed decisions. It is very important not to just take sides without reading all the arguments.

Why is glacial research relevant to climate change?

Ice sheets as analogues
Current worries about climate change mean that investigations of past ice sheets have become increasingly important. Past glaciations can be compared to modern polar ice caps, and can put recent changes in polar ice sheet dynamics (e.g. ice shelf loss, and acceleration of polar ice flow rates) into a long-term context. By using past glaciations as analogues, we can increase our ability to predict future ice-ocean-atmosphere interactions. We can look at past ice shelf collapses, for example, to see what the recent collapse of the Larsen ice shelf is likely to mean for the glaciers on the Antarctic Peninsula.


Modelling ice sheets
By using models of past ice sheets (like Alun Hubbard, Aberystwyth), which can be tightly constrained by geological data (such as the BRITICE project, which aims to summarise all the geological data available on the last British ice sheet), we can increase our confidence in these mathematical models and apply them to the Greenland and Antarctic ice caps, better predicting future ice melt and resulting sea level rise.


Subglacial Processes
It is obviously very difficult to access the subglacial environment. Although some people are trying it (like Doug Benn), it is logistically diffcult, expensive, and dangerous. You can bury probes like Jane Hart, but again, you only get a very limited understanding of subglacial processes. However, by conducting detailed sedimentological investigations of glacial sediments left behind after an ice sheet has retreated, you can make numerous inferences about the subglacial environment. This generates data that can be used effectively to feed into glaciological models and that can be applied to modern ice caps, aiding our understanding of current rapid retreat and thinning of polar ice streams (like Jakobshavn, Greenland). I used detailed sedimentary analysis of sediments in Durham to understand what went on at the end of the Last Glacial Maximum in eastern England.



Sea Level Uncertainty
A large part of the uncertainty of future sea level (see the graph, taken from the IPCC) rise comes from uncertainty in ice dynamical processes. This was highlighted by the IPCC as a top research priority. Most of the predicted rise in sea level over the next 100 years comes from surface melting. However, marine-terminating ice streams in Greenland (that is, fast flowing sectors of the Greenland Ice Sheet that end in the ocean) have recently experienced rapid thinning and acceleration, losing mass to the North Atlantic. We have little understanding of the processes operating in these ice streams, so it is important to study past ice sheets, putting these short-term events into a longer term context and improving our understanding of dynamical ice sheet processes. Antarctica has had a long history of research.


Antarctic Research
The Antarctic Peninsula and West Antarctic ice sheets, in particular, are vulnerable to sea level rise, atmospheric and oceanic warming, and could result in catastrophic and rapid sea level rise over the next few hundred years. The recent loss of the Larsen Ice Shelf and resulting increase in velocity and draw down of rapid outlet glaciers in the region, suggests that this process could even be beginning now. The Pine Island and Thwaites glaciers, in West Antarctica, are currently thinning and experiencing very rapid flow. In light of this, a longer-term understanding of Antarctic ice sheet dynamics is ever more important.

See this image from the USGS to see where the Antarctic Peninsula is.

Why keep a Quaternary Science Blog?

I feel that science outreach is very important. Tax payers pay for all these expeditions to polar regions, and they have a right to know what we do with their money. It also strikes me that it is difficult for non-academics and students to access and understand the latest peer-reviewed publications regarding ice sheets, climate change, global warming and sea level rise. These subjects have been constantly in the news for the last few months, and I felt that it was important to communicate my science directly with the people.

My golden aim is to communicate science better to the masses. I'll start with a few issues that are particularly important, attempting to summarise sea level rise and a few other key problems. I might translate a few of my publications here for the general public. And thereafter I will talk about papers or conference presentations that are particularly interesting.

Another blog which is worth a look is Chris Vernon .

When on fieldwork in Antarctica I plan to keep a blog so people can see what Antarctic research really involves.

I also think that writing this blog encourages me to think deeply about important issues and to consolidate my thoughts.

I hope you enjoy these articles and look forward to responding to any comments!

Best wishes,

Bethan