Flank margin caves are karst features that develop in the freshwater/saline mixing zone within the carbonate islands of the Bahamas. The flank margin caves that are currently exposed developed during the last interglacial sea level highstand (+6 m; ~125 ka). Initially small ovid chambers, the caves increase in size to about 100 m2, then interconnect with adjacent chambers to form medium-sized caves. At about 1000 m2, these medium-size caves interlink forming large caves that are laterally extensive, vertically restricted, do not penetrate the fresh-water lens a significant amount, and run parallel to the axis of the ridge in which they formed. Small caves have a much smaller area to perimeter ratio than do large caves. As cave chambers grow and interconnect, perimeters become much more complex, and the number of bedrock columns in the cave increases. These results have implications for water resource management, and porosity modeling.

Caves on carbonate islands are useful indicators of past sea level because cave formation is dependent on sea-level controlled freshwater lens position (flank margin caves), or form in direct contact with coastal processes (sea caves). Sea-level curves present a useful proxy for glacioeustatic and paleoclimate studies, so caves offer useful data. Once a flank margin cave is breached, it may be modified and eroded by waves. This overprinting leads to morphology similar to that of sea caves. While both indicate past sea level, they reveal differing information about the amount of denudation that has occurred to expose them (a paleoclimate indicator), so differentiation of these cave types is important. This study presents some of the first sea cave data from carbonate islands, and makes morphological comparisons between flank margin caves and sea caves from the Bahamas, California, and Maine. Using morphometric techniques, these caves can be distinctly identified.

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