Responding to Change: Propagation of Environmental Signals During Landscape Transience

Terrestrially derived sediments in sedimentary archives are regularly used to reconstruct past climatic or tectonic conditions. Sediments are generally produced in mountainous areas and transported via sediment routing systems (SRSs) to a zone of final deposition. Environmental reconstructions are based on the assumption that changes in climatic or tectonic conditions generate signals within the transported sediment. However, experimental and numerical studies have shown that not all signals are faithfully transmitted, but can be modified, buffered or even lost during transport along SRSs. Previous studies suggest that signals in the form of sediment flux pulses can only be faithfully transmitted to the deposition zone, if the time required by a SRS to return to steady state conditions (the ‘response time’) is shorter than the period of changes in boundary conditions. As response times increase with the length of the system, short-period climate cycles should not be detectable within sedimentary archives fed by large river systems. However, although the response times of the Mississippi, the Indus or the Ganges are estimated on the order of 10⁵ to 10⁶ years, several sedimentary proxies in offshore archives seem to record shorter-period climate changes.

Following a change in boundary conditions, rivers immediately begin to adjust their geometry. This adjustment phase until new steady state conditions are reached is regarded as transience. An individual signal in response to a change in boundary conditions might be generated early during this transient phase. Hence, the signal can be transported through and stored within the SRS as a measurable change of a sedimentary parameter (or ‘proxy’) even before the SRS has returned to steady state conditions, i.e. before the characteristic response time has passed. Hence, it is important to gain quantitative insight into the time scales required for a portion of sediment, which carries a signal, to travel to the sedimentary archive. This signal transfer time is different from the SRS response time, but may be more important to the interpretation of past environmental change. 

We suggest that signal transfer times depend on:

• The hydraulic characteristics of the sediment fraction on which a certain parameter (proxy) is measured, as they determine how frequently the fraction is in motion, and

• The probability of transient storage while the fraction travels through the SRS.

This Research Topic seeks to bring together new concepts and results on signal generation during environmental changes, as well as signal transport and archiving during the transient state of the SRS. We welcome articles (Original Research, Review or Mini Review, Method, and Data Reports) addressing, but not limited to, the following themes:

• Numerical modeling and analog experiments of proxy generation, transport and deposition along sediment routing systems;

• Field studies of proxy generation, transport and deposition along sediment routing systems;

• Comparison of proxy propagation measured on different grain-size ranges;

• Tracing of environmental signals through a system;

• Novel proxy methodologies ; and

• The connectivity of sediment routing systems and signal transport.