Boron isotope pH proxy

This Waterloo was unfortunate for the author considers the boron method to be basically sound and potentially extremely powerful. The answer to the benthic enigma may lie in species-to-species differences in the boron isotope vital effect for benthic foraminifera. The measurement method use by Sanyal et al. (1996) required a large number of benthic shells in order to get enough boron to analyze. This created a problem because, as benthics are rare among foraminifera shells, mixed benthics rather than a single species were analyzed. If the boron isotope pH proxy is to... 

Figure 14 Estimates of mixed-layer pH and atmospheric CO2 derived from boron isotope analyses of planktonic foraminifera recovered from drill cores taken in the western equatorial Pacific. Results are replotted from Pearson and Palmer (2000). Note that uncertainty associated with both pH and CO2 estimates amphfies in the Early Cenozoic. This reflects the intrinsic insensitivity of the boron isotope pH proxy at low pH (see Eigure 12). Atmospheric CO2 estimates require additional assumptions about the size of the DIC pool in surface waters.

Isotopes Illuminate Chemical Change Boron Isotope pH Proxy... 

Honisch, B. Hemming, N. G. Loose, B. Comment on "A critical evaluation of the boron isotope-pH proxy The accuracy of ancient ocean pH estimates" by M. Pagani, D. Lemarchand, A. Spivack and J. Gaillardet. 

Sanyal A., Bijma J., Spero H., and Lea D. W. (2001) Empirical relationship between pH and the boron isotopic composition of Globigerinoides sacculifer. implications for the boron isotope paleo-pH proxy. Paleoceanography 16, 515-519. 

Boron isotopes as a paleo-pH proxy and Mg/Ca as a paleo-temperamre proxy are also discussed, because information provided by these relatively new proxies has important implications for the better-established records mentioned in the preceding paragraph. The application of boron isotopes to reconstructing surface water pH provides a means of estimating past atmospheric CO2 levels. Much of the discussion of the marine strontium isotope record in the past has been linked to implicit assumptions about Cenozoic variations in atmospheric CO2 levels. New boron isotope results indicate that previous assumptions... 

Spivack A. J., You C.-F., and Smith H. J. (1993) For-aminiferal boron isotope ratios as a proxy for surface ocean pH over the past 21 Myr. Nature 363, 149-151. 

First, the 8 B of boron incorporated into the biogenic carbonates of all these coral and foraminiferal species increase with pH. This is the basis of the 8 B-pH proxy. Second, there are offsets between different groups and species. The corals appear to be isotopically heavier... 

Honisch B, Hemming NG (2004) Ground-truthing the boron isotope paleo-pH proxy in planktonic foraminifera shells Partial dissolution and shell size effects. Paleoceanography 19 PA4010. 

Continuing in this vein, Hemming (this volume) considers more recent feedbacks between life and atmospheric changes that affect climate. He rrses boron isotopes, which serve as a proxy for ancient ocean pH. Because of interactions between the atmosphere and surface ocean, these isotopic data reveal natural variations in atmospheric CO2 concentrations. Understanding such natural co-variabihty in atmospheric composition and climate is essential if we are to document and predict the role of anthropogenic influences on present and future climates. 

The apphcation of these basic chemical principles to geologic and errvirorunental problems will be discussed in reference to the boron isotope paleo-pH proxy. 

Testing theoretical geochemical relationships under controlled, but nearnatural conditions, can provide convincing evidence that a proxy is approximating the parameter of interest. A brief review of both abiotic and biotic CaCOs experiments that have added to oirr knowledge of the boron isotope paleo-pH proxy is presented. 

While more study is necessary to further refine this proxy, it is clear that the major control on the boron isotope composition of carbonates is the pH of the... 

Establishing the clear relationship between the boron isotope composition of marine carbonates and the pH of seawater set the stage for determining pH of ancient oceans. While a review of these applications has been presented previously (see (44)), a brief discussion here will present the final (and most important) step in the proxy development story. 

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