Middle Wisconsinan and recent wet site mummified wood, humus, peat, and pollen, Santa Rosa Island, Florida

Abstract

Macrobotanical samples obtained from submerged, previously buried, tree stumps in growth position and peat and humus/humate layers from the surf zone of Santa Rosa Island were identified and dated by 14C analysis. Dates obtained clustered in two time spans, <2000 yr BP and 30 000–33 500 yr BP, with one outlier at >45 440 yr BP. These subfossil macrobotanicals are well preserved in spite of submergence. Conifers of the family Cupressaceae (cf. Juniperus virginiana) and Pinaceae and a dicotyledon of the family Lauraceae (cf. Persea) are the principal tree species identified. Presence of these species in the current surf zone in conjunction with modern vegetation distribution indicates sea level was lower during the Middle Wisconsin and Late Holocene. Microbial decay patterns in a Pleistocene wood sample suggest basidiomycete infestation by brown-rot fungi prior to burial and successional decay by actinomycete bacteria during its waterlogged state. Extensive destruction of S 2 microfibrils of the secondary cell wall that left a residual skeleton of lignin and presence of pyrite framboids in Pleistocene wood inform on its depositional history. Pollen/spore assemblages from Holocene humus/humate suggest a former maritime forest habitat with back-barrier freshwater basins. Macrobotanical identification, radiocarbon dates, and palynological indicators suggest Santa Rosa Island is an unstable barrier island at a critical point of degradation due to marine intrusion coincident with global sea-level rise, storm overwash burial of existing maritime plant communities, and accelerated erosion of former vegetational foci by sand aggradation. The 14C date and location of stump sub-samples SRI 1b and SRI 1f in conjunction with previously reported regional 14C dates indicate that SRI 1 occupied a topographic high during marine oxygen isotope chronozone (OIC) 3 rather than being near sea level. Holocene samples spanning the last two millennia verify the occurrence of maritime forest and high dune habitat taxa in the present surf zone.