Turbidites sporadically deliver large amounts of sediment from shelf areas to deep marine depocenters. These submarine mass movements are well recognized in marine sediment cores, yet their formation, triggers and controls are less well constrained. In a now published paper in Earth and Planetary Science Letters, we have analyzed seven marine sediment cores in three study sites along the Chile convergent margin. The sites span a pronounced on-shore climatic gradient from arid in the North to humid in the South.
Sediments in the three sites provide a detailed record of turbidite deposition over the last glacial-deglacial cycle from ~20 ka to present. All sites reveal a steep decline of turbidite frequency and thickness during deglaciation, a temporal pattern that has commonly attributed to sea-level rise and inundation of shelf areas. Our data suggest, however, that sea-level rise is not the most dominant control. Rather, turbidite deposition ceases simultaneously with pronounced climatic change on-shore predating significant changes in sea-level. Warming and changes in precipitation have likely altered terrestrial erosion and sediment transport systems. Analysis of the on-shore geomorphological situation suggests that sediment connectivity played an important role although its control differs regionally. While highly connected systems along the steep gradients in the northern part of our study site have rapidly conveyed the erosional signal of aridification, retreating piedmont glaciers in the southern part left numerous proglacial lakes that act as sediment traps. These sediment traps shut down coarse sediment transfer to the marine realm.
Our analysis shows that turbidites can be reliable recorders of onshore climatic change. The exact role of the effects of the sediment transport system, however, may strongly differ while producing similar depositional patterns offshore, and it is challenging to invert these from the sedimentary record alone. Understanding the terrestrial sediment transport system on millennial time scales is thus of vital importance for the interpretation of sediment records of climate variability.
Bernhardt A, Schwanghart W, Hebbeln D, Stuut J-BW, Strecker MR. 2017. Immediate propagation of deglacial environmental change to deep-marine turbidite systems along the Chile convergent margin. Earth and Planetary Science Letters 473 : 190–204. [DOI: 10.1016/j.epsl.2017.05.017]. **** Free pdf download link active until August 16, 2017 ****