Prograded coastal barriers provide paleoenvironmental records of storms and sea level during late Quaternary highstands
Records of past shoreline evolution, storm impacts, and variations in sea level are essential to accurately assess the vulnerability of beaches to future climate change. Prograded sandy barriers provide the opportunity to utilize our understanding of coastal dynamics documented over decades to determine storm impacts over centuries and sea‐level change over millennia. Composite coastal barriers that have prograded throughout the Pleistocene and Holocene maintain, within their stratigraphy, a record of shoreline evolution extending back to when sea level was known to be higher than today (Marine Isotope Stage or MIS 5e), including high‐energy events during these late Quaternary highstands. This study utilizes ground‐penetrating radar to image the facies architecture of a composite barrier system in Bream Bay, New Zealand. The resulting stratigraphic record mapped paleo‐beachfaces with decimeter resolution spanning ∼5 kilometers from the active shoreline, bridging timescales of coastal evolution over orders of magnitude. Charting the elevation of the beachfaces provides evidence of overall sea‐level falls from +5 to +2 m above present in the Pleistocene and from a ∼2‐m mid‐Holocene highstand. Sixty paleo‐beachfaces with distinct storm‐related signatures are identified within the Pleistocene morphostratigraphy. In the past ∼6,000 years 25 major storm events were recorded, giving an average period between events of ∼230 years. These unprecedented data provide insight, as well as input to forecasting models, needed to mitigate and manage future impacts of global warming.