Title

An investigation of the sclerosponge Ceratoporella nicholsoni as a high-resolution paleoclimate proxy

Date of Award

2005

Availability

Article

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Marine Geology and Geophysics

First Committee Member

Peter K. Swart, Committee Chair

Abstract

The calcifying sclerosponge, Ceratoporella nicholsoni, was thoroughly investigated as an archive of isotopic and elemental paleoclimate proxies. Methods of developing age models using radiometric uranium-series dating were modified for the special case of a particulate filter feeder and the age models were verified and tuned using non-radiometric anthropogenic parameters. It is established that six sclerosponges from the Bahamas display depth-dependant growth rates averaging 170 mum·y-1. It was also established that previously used methods of high-resolution Sr/Ca cycle quantification to contribute to understanding of growth models are only applicable in environments with a high seasonal temperature range where annual temperature changes are discernible from instrumental variability. High-resolution methods of sampling the dense aragonite basal skeleton of these sclerosponges were used to test the reproducibility of isotope and elemental records at different resolutions. Resolution limitations for the sub-sampling of these skeletons were identified, with laser ablation being more capable of very high (<20 mum) sampling resolution than micro-milling (>50 mum). These subsampling resolution limits were applied in conjunction with improved age models to develop calibrations of delta18O and Sr/Ca to temperature. Finally, the calibrations developed in this project were used to apply a dual proxy approach in deconvolving the decadal scale salinity and temperature signals in delta18O records. In doing so, sclerosponge records of salinity, temperature, and density demonstrated the advantages of a proxy capable of recording subsurface and surface water masses to discern possible circulation changes of the N. Atlantic Ocean. Sclerosponges from the northeast and central Caribbean Sea all suggest significant increases in temperature and salinity of the subtropical underwater that are related to changes in forcing at the surface source regions where this water mass takes on its properties. This result differs from temporally-limited instrumental studies that suggest deepening of isopycnal surfaces as the cause of observed changes in salinity and temperature.

Keywords

Physical Oceanography; Biogeochemistry; Geochemistry

Link to Full Text

http://access.library.miami.edu/login?url=http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3185018