Late Holocene sea-level rise in Tampa Bay: Integrated reconstruction using biomarkers, pollen, organic-walled dinoflagellate cysts, and diatoms

Abstract

a b s t r a c tA suite of organic geochemical, micropaleontological and palynological proxies was applied to sediments from Southwest Florida, to study the Holocene environmental changes associated with sea-level rise. Sediments were recovered from Hillsborough Bay, part of Tampa Bay, and studied using biomarkers, pollen, organic-walled dinoflagellate cysts and diatoms. Analyses show that the site flooded around 7.5 ka as a consequence of Holocene transgression, progressively turning a fresh/brackish marl-marsh into a shallow, restricted marine environment. Immediately after the marine transgression started, limited water circulation and high amounts of runoff caused stratification of the water column. A shift in dinocysts and diatom assemblages to more marine species, increasing concentrations of marine biomarkers and a shift in the Diol Index indicate increasing salinity between 7.5 ka and the present, which is likely a consequence of progressing sea-level rise. Reconstructed sea surface temperatures for the past 4 kyrs are between 25 and 26 C, and indicate stable temperatures during the Late Holocene. A sharp increase in sedimentation rate in the top w50 cm of the core is attributed to human impact. The results are in agreement with parallel studies from the area, but this study further refines the environmental reconstructions having the advantage of simultaneously investigating changes in the terrestrial and marine environment.

Unusual C35 to C38 alkenones in mid-Holocene sediments from a restricted estuary (Charlotte Harbor, Florida)

“…We have also detected unusual C 36 alkenones in sediments of two Florida estuaries: Tampa Bay (van Soelen et al, 2010) and Charlotte Harbor (van Soelen et al, 2012). As in Black Sea mid-Holocene sediments, C 36:2 EK is the predominant alkenone in the midHolocene sediments in these estuaries, while late Holocene sediments are dominated by the more common C 37 and C 38 alkenones.…”

“…The presence of C 36 alkenones in these sediments was established in earlier studies (van Soelen et al, 2010(van Soelen et al, , 2012; however until now double bond positions had not been determined. We now confirm that these alkenones are identical to the C 36:2 EK reported earlier in mid-Holocene sediments of the Black Sea by Xu et al (2001).…”

Paleoenvironmental Records Influenced by Sea Level Variations During the Holocene in the Vitória Bay Region, Espírito Santo State, Brazil

“…This increase of organic matter content marks the evolution of the environment for the establishment of the mangrove vegetation. Van Soelen et al (2010) observed the highest TOC values in a sample collected from Tampa Bay, Florida, and correlated with the stratification of the environment. The data obtained from the carbonized particulates associated with the increase in TOC at a time of sea level rises may also reflect the stratification of the environment.…”

“…This, associated with the greater occurrence of the species in flooded environments (Scott 1992), tends to corroborate the interpretation that the environment changed from a condition of greater salinity from the base of zone II to the base of zone III to a transitional environment (Figure 4). The evolution of Tampa Bay in Florida during the Holocene was the focus of a study by van Soelen et al (2010) from the proxies analyzed and correlated to the MT. From the sedimentary and vegetational dynamics of the surroundings of the bay, it was possible to observe a period of greater fluvial influence, passing through a period of transition and stabilization of the environment, culminating in the present stage, which is characterized as an estuarine environment.…”

Changes in Modern Pollen Assemblages and Soil Geochemistry along Coastal Environmental Gradients in the Everglades of South Florida

“…Superimposed on these environmental gradients are biotic gradients, as defined by a land-to-sea array of vegetation communities. Pollen analysis and X-ray fluorescence (XRF) analysis have been used in paleoecological studies to reconstruct the Holocene history of vegetation changes in the coastal wetlands of the southeastern U.S. (Willard et al, 2001;Donders et al, 2005;van Soelen et al, 2010van Soelen et al, , 2012Yao et al, 2015;Yao and Liu, 2017). However, with few exceptions (e.g., Willard et al, 2001), these reconstructions are not supported by surface samples documenting the changes in modern pollen assemblages and soil chemistry along various environmental gradients in these coastal wetland sites, particularly along the secondary environmental gradient in estuarine wetlands.…”