SEMINAR: GEOTOPICS Next Monday updated: Dr. Kaufman (2/28, 3:15 pm)

[Qiong Zhang <qzhang@rsmas.miami.edu>]

 

##### G  E  O  T  O  P  I  C  S  #####

    P  r  e  s  e  n  t  s

3:15 PM, Monday,  February 28th, 2011

   SLAB Seminar Room, S/A 103

Refreshments 3:00 PM

Alan Jay Kaufman
Professor, University of Maryland


“AN EMPIRICAL RE-EVALUATION OF THE BORON ISOTOPE/pH PROXY IN MARINE CARBONATES”

The unique set of geochemical characteristics of the boron isotope system in seawater and marine biological carbonates makes it appealing for paleo-pH reconstructions. First, pH dependant equilibration of boric acid B(OH)₃^o and borate anion B(OH)₄^- in seawater is accompanied by a large isotope fractionation, i.e. 27.2‰. Second, d¹¹B in marine carbonates suggests the predominant uptake of borate anion. However, the recent discovery of both BO3- and BO4-coordinated structures in almost equal abundances in calcite and aragonite points to subtleties in biologically mediated boron uptake, which have yet to be clearly resolved.  Recently we designed a series of pH-controlled precipitation experiments of inorganic calcite and aragonite in order to isolate purely abiological effects on the boron isotope co-precipitation with carbonates The preliminary results from aragonite precipitates at pH~8.7 are in excellent agreement with the d¹¹B of aqueous borate predicted by 27.2‰ fractionation.

Cheers
Qiong Zhang

Marine Geology and Geophysics
Rosenstiel School of Marine and Atmospheric Science
University of Miami
4600 Rickenbacker Causeway
Miami Fl 33149