Submitted to: Global and Planetary Change
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2000
Publication Date: N/A
Interpretive Summary: Sediment deposits found in fjords and along coastlines have the ability to preserve climate signals from the time they were deposited. By studying the lithology of the deposits and the isotopic signature of various chemical species contained within the microfossils buried in the deposits it is possible to infer the past climate of the region. We built and employed a series of numerical models to simulate the erosional and depositional processes involved in building these sedimentary sequences. By initializing the models with realistic boundary conditions (topography, bathymetry, etc) and forcing the models with what has been inferred to be the time climate since the last glacial maximum up to modern conditions we were able to create synthetic sedimentary deposits and compare these with observations. In order to simulate the sedimentary sequences correctly it is necessary to model each of the major depositional/erosional processes correctly and to allow for the natural complex interactions that occur among these processes. The processes include: river discharge, river sediment flux, changing sea level, storm events, subsidence, sedimentary plumes, turbidity currents, debris flows and compaction. The modeling effort allowed us the quantify the effect of each process on the deposits in differing areas of the depositional basin. Through this, we were able to determine optimal locations for the preservation of past climate change signals. The interplay between the various processes was key in determining the preservation potential of the climate signal.
Technical Abstract: To use basin stratigraphy for studying past climate change it is important to understand the influence of evolving boundary conditions (river discharge and sediment flux, initial bathymetry, sea level, subsidence) and the complex interplay of the redistribution processes (plumes, turbidity currents, debris flows). To provide understanding of this complexity, we have employed source to sink numerical models to evaluate which process dominates the observed variability in a sedimentary record of two coastal Pacific basin, Knight Inlet in British Columbia and the Eel Margin of northern California. During the last glacial period the Eel River supplied comparatively more sediment with a less variable flux to the ocean, while today the river is dominated by episodic events. Model results show this change in the variability of sediment flux to be as important to the deposit character as is the change in the volume of sediment supply. Due to the complex interaction of flooding events and ocean storm events, the more episodic flood deposits of recent times are less well preserved than the flood deposits associate with an ice-age climate. In Knight Inlet the evolving boundary conditions (rapidly prograding coastline, secondary transport by gravity flows from sediment failures) are a strong influence on the sedimentary record. The delta and gravity flow deposits punctuate the sedimentary record formed by hemipelagic sedimentation from river plumes. Missing time intervals due to sediment failures can take away the advantage of the otherwise amplified lithologic record of discharge events, given the enclosed nature of the fjord basin.