Graduation Year

2010

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Geology

Major Professor

Gregory S. Herbert, Ph.D.

Co-Major Professor

Peter Harries, Ph.D.

Committee Member

Jonathan Wynn, Ph.D.

Committee Member

Eric Oches, Ph.D.

Committee Member

Terrence Quinn, Ph.D.

Keywords

Siderastrea, Pinecrest, Bermont, Phosphorus, Salinity

Abstract

Future climate change has been the subject of considerable speculation

with scientists called upon to predict timing, magnitude, and impact of these

changes.

The Pliocene Warm Period serves as the best-available, pre-modern

analog to predicted climate changes, and Pliocene climate anomalies are

examined as possible scenarios for future climate change. Comparing modern

conditions to the mean climate state of the Pliocene is essential for better

constrained predictions of future climate change, and seasonal

paleoenvironmental records provide a data set more analogous to instrumental

observations and thereby reducing the uncertainty in modeled climate changes.

This study first examines the potential of large gastropod shells as a

paleoclimate proxy. Specimens of Busycon sinistrum, active in winter, and

Fasciolaria tulipa , active in the summer, were collected alive from Tampa Bay

and St. Joseph Bay in the hope of establishing a multi-year record of seasonality.

The δ18O time series of each shell were compared with predicted δ18O, based on

local marine temperature variations, and both species cease shell growth during

the winter months, despite opposing seasons of feeding activity. As none of the

profiles provide information on winter environmental parameters, this

sclerochronological system was replaced by work on pristine specimens of the

scleractinian coral Siderastrea spp.



Seasonal δ18O and Sr/Ca time series from two Pliocene corals, collected

from the Lower Pinecrest Member of the Tamiami Formation in southwest

Florida, were used to calculate seawater δ18O variations. Inferred salinity in the

Pliocene has a reversed seasonal pattern from that of modern annual salinity

variations, and is interpreted to be a response to an increase in winter

precipitation, a teleconnection of the Pliocene “Super El Niño.” Concentrations of

variance in the typical ENSO frequency band are not apparent above the 95%

confidence interval, suggesting that the Pliocene was dominated by a perennial,

rather than an intermittent, El Niño-like state.



Further geochemical analyses from both Pliocene and Pleistocene

Siderastrea

spp. corals indicate a high nutrient nearshore marine environment in

south Florida. Marine phosphates, inferred from P/Ca analyses, were

significantly higher in the Pliocene Tamiami Fm. than in the Early Pleistocene

Caloosahatchee and Bermont Fms, and the decline in nutrients preceded local

extinction by > 0.5 Ma. Additionally, high-resolution P/Ca analyses of an

individual coral reveal no evidence of seasonality required by a previously

hypothesized upwelling-based nutrient delivery mechanism

The Pliocene nearshore marine environment in southwest Florida was

characterized by higher nutrients than in the Pleistocene and precipitation

patterns similar to modern El Niño teleconnections.

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