Evidence for the southward migration of mud banks in Florida Bay

The latticework of shallow polygonal mud banks encircling deeper ponds is a key morphological characteristic of Florida Bay. Composed of lime mud produced largely by calcareous algae and epibionts, these banks limit water exchange between the interior Bay and ocean waters from both the Gulf of Mexico and the Atlantic. They also influence salinity and benthic habitat distribution. It has been proposed that the position of mud banks may be dynamic, migrating southwards with time, but no long-term study has examined the spatial arrangement of banks within Florida Bay over sufficiently long timescales to ascertain movement. Using time-separated bathymetry surveys and aerial photography datasets spanning a period of many decades, this study establishes that indeed the bank positions are temporally dynamic. The work was conducted using geographic information systems (GIS), with all data referenced to the position of relatively stable islands. The analysis reveals a southward migration trend (headings ranging from 280° to 240°) with rates averaging 1.27 m/year. For the first time in Florida Bay, the migration and vector of movement for mud banks have been documented. Despite the southward movement, mud bank morphology remained consistent. It is speculated that strong winter winds out of the north/northeast provide the mechanism for such migration. uthward migration of fine-grained, biogenic mud banks in Florida Bay demonstrates how change-detection remote sensing can be used to audit a geological process operating at time-scales of centuries. Though the available data may be unusually rich for Florida Bay, the study shows how the dynamics of other coastal systems may be accessed using a comparable work-flow. Similarly, the results here have implications for the geologic record and reevaluating paleo-landscapes where mudrock shoals have been identified.