Upstream Propagation of Sea‐Level Signals in Fluvio‐Deltaic Environments: Time‐Lags and the Dynamics of the Fluvial Surface

• Published in: Geophysical research letters Vol. 49; no. 8
• Main Authors: Kollegger, M., Lorenzo‐Trueba, J., Fernandes, A. M., Singh, A., Abeyta, A.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 28.04.2022
• Subjects: Climate change; Concavity; Delayed response; Deltaic deposits; Deltas; Deposition; fluvial delta; Fluvial deposits; Fluvial sediments; fluvial surface concavity; fluvial surface dynamics; Global climate; Oscillations; Propagation; Rivers; Sea level; Sea level changes; sea‐level cycles; shoreline; Stratigraphy; Upstream
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL097956

Stratigraphic interpretation generally relies upon the assumption that the fluvio‐deltaic surface responds uniformly to sea‐level changes; however, recent theoretical work suggests that changes in its relief and concavity can influence the propagation of sea‐level information upstream and result in geologically long‐lived lags in the system response. We test this theoretical result using measurements from a experimental delta subject to high and low magnitude sea‐level oscillations. In both cases, changes in relief and curvature of the fluvio‐deltaic profile result in the proximal portion of the profile being out of phase with respect to sea‐level cycles, whereas the nearshore regions remain in phase. These results underscore the importance of delayed response to sea‐level variations in the upstream portion of river deltas, often resulting in net erosion during sea‐level rise and potentially complicating the reconstruction of paleo sea‐level from deltaic deposits. Plain Language Summary Throughout Earth's history, minor or significant changes in sea level have occurred in tandem with changes in global climate. River deltas, which form when sediment‐laden rivers meet the ocean, can be sensitive to changes in sea level. Therefore, the deposits of ancient deltas can be used to piece together information about past changes in sea level. However, recovery of such information can be complicated by the different ways in which deltas adjust to sea‐level change. For example, a simplified model suggests that the delta part above sea level will experience erosion when sea‐level falls and deposition when sea‐level rises. In this work, we show that different delta parts can undergo erosion and deposition simultaneously while sea‐level is falling or rising. We used an experimental delta to study how different delta parts respond to changes in “sea level”. A key finding is that erosion commonly occurs in upstream parts of the delta during sea‐level rise, contradicting traditional models. We therefore recommend caution in reconstructions of sea‐level change that rely on erosion in the upstream parts of deltas as an indication of sea‐level fall. Key Points The landward portion of the experimental deltaic profile response to sea‐level oscillations is delayed by up to half a period Such a delay in the response is associated with subtle changes in the curvature and relief of the deltaic profile Shifts in curvature and relief can lead to river incision and river terrace formation during sea‐level rise