Bay-head deltas across the northern Gulf of Mexico back step in response to the 8.2 ka cooling event

Estuaries along the northern Gulf of Mexico show rapid landward shifts in estuarine environments (back-stepping) around 8200 cal yr BP. Paleogeographic maps of the estuaries based on seismic data and cores, and constrained chronologically by radiocarbon dates, depict bay-head delta retreat in excess of 25 m/yr. During these events the sub-aerial delta plain flooded to create sub-tidal upper- and middle-bay environments. Abrupt sea-level rise associated with the 8200 cal yr BP climate-change event caused these estuaries and others around the world to reorganize abruptly. In the northern Gulf of Mexico, the sea-level rise associated with the event was only ∼0.1 m over a sub-decadal time period. This rise was superimposed on a background decelerating rate of sea-level rise of ∼1.0–0.5 m/century. The widespread bay-head delta back-stepping, documented here, may be an appropriate analog for possible abrupt future climate change in response to global warming. It also shows that estuaries fringed by low-gradient shorelines are highly sensitive to low-amplitude and sudden sea-level rise.