Speakers

Jim Rose (Royal Holloway, University of London, London)
Phil Gibbard (University of Cambridge, Cambridge)

Why are terrestrial records important?

The term ‘terrestrial records’ encompasses a range of environmental archives on land. These include: lake and river sediments; ice core records; peat deposits; and exposed coastal cliff sections. Together, these settings contain valuable depositional archives of environmental change, which allow us to reconstruct earth surface processes. These are important for our understanding of long-term change, and projecting how surface processes might respond to future environmental scenarios. This is one of the oldest and most established forms of Quaternary environmental research, going back to the pioneering work of Charles Lyell and Louis Agassiz, among many others.

It is important to remember that the terrestrial record is as much about the deposits that are available, as those that are missing. The terrestrial environment is one of erosion – by river action, glaciation, wind, and more recently, human activities. There is never a full sequence of environmental changes recorded on the land, but the gaps in the record can also be valuable indicators of past environmental change, as sediments are perpetually deposited, reworked, and eventually transported offshore. As Ager once said, in some instances, there are more gaps than record!

 

Terrestrial records are inherently localised in their scope, but by combining a range of sites and depositional settings, we can begin to develop a regional network of environmental change. This is termed ‘stratigraphy’ and allows us to explore regional patterns in the response of earth surface processes to environmental change.

What have been the major developments in the use of terrestrial records?

Traditionally, in the 19th Century, Quaternary terrestrial records were used to reconstruct glacial advances and river system change, through the use of sedimentary sequences and geomorphological features.

Since then, some of the major developments have used terrestrial geomorphological and sedimentary records to:

  • Assess recent tectonic activity.
  • Understand processes operating at the glacier-bed interface.
  • Understand periglacial processes.
  • Explore how rapidly terrestrial environments have responded to climate change in the past.
  • Establish the timing of terrestrial environmental change through the development of dating techniques such as 14C and optically stimulated luminescence (OSL).
  • Using ‘marker horizons’ to tie together the fragmentary terrestrial record. For example, we can identify the same tephra (volcanic ash) layer at multiple sites – these would have all been deposited at the same time, when the source volcano erupted.
  • Develop a ‘multiproxy’ approach to the study of terrestrial environments. This includes the combined analysis of records such as: microfossils (such as pollen); macrofossils (such as shells and bones); and isotopes.
  • Develop a detailed mammalian biostratigraphy – where animal bones are used to reconstruct the sequence of past environmental change based on their ideal environmental tolerances.
  • Develop a detailed record of palaeotlithic archaeology.

 

As part of these developments, the key advances in our approach to the study of terrestrial environments have been:

  • To look at the earth as an integrated system. The work of D. Q. Bowen transformed our outlook on earth surface processes, and encouraged terrestrial scientists to consider the interactions between different parts of the system.
  • To link the reconstructions of Quaternary environments to the processes causing these environmental shifts. This is important for the application of Quaternary studies for our understanding of present and future environmental change. The work of John Birks (using pollen to demonstrate ecological processes); Geoff Boulton (using sediments to demonstrate glacial processes); and Colin Ballantyne (using sediments and landforms to indicate periglacial processes) have been particularly key here.

 

 

What are the major challenges?
  • Future developments will rely on the continued integration of terrestrial records (as well marine archives) to understand long-term earth surface processes. We can then apply this understanding to projections of future change.
  • Terrestrial records play a valuable role in our understanding of environmental forcing mechanisms and the impacts of these on different parts of the earth system.
  • We also need to consider the role of antecedent (previous) conditions in shaping earth surface processes at a variety of timescales: sub-annual through to glacial-interglacial cycles. For example, glacial activity may condition earth surface processes long after the glacier has retreated.
  • As we develop more detailed stratigraphical frameworks, using multiple terrestrial records for example, we must take into account the limits of correlations.
  • When comparing and correlating different sites, there may be offsets in the timing of earth surface process response to a particular climate shift. One site may respond more rapidly than another. Similarly, when correlating marine and terrestrial archives, there are likely to be different leads and lags.
  • The identification of marker horizons (such as tephra layers) are becoming increasingly important to correlate between multiple sites.