TY - JOUR
T1 - CaCO3 precipitation kinetics in waters from the Great Bahama Bank
T2 - Implications for the relationship between Bank hydrochemistry and whitings
AU - Morse, John W.
AU - Gledhill, Dwight K.
AU - Millero, Frank J.
N1 - Funding Information:
This research was primarily supported by funds from the Louis and Elizabeth Scherck Chair in Oceanography, Texas A&M University and the U.S. Department of Energy Grant DE-FG03-00ER-15033. Additional support was received from the National Science Foundation Chemical Oceanography Program. Over many years, and particularly in preparing this paper, we have gained an appreciation for the remarkably high quality of work and tremendously innovative nature of the study of Broecker and Takahashi (1966) . It set a high standard for subsequent research not only on whitings, but marine carbonate geochemistry in general. This paper has benefited significantly from the many insightful comments received from Drs. Wallace Broecker, Jeffrey Hanor, Alfonso Mucci, Eugene Schinn and Taro Takahashi, for which we are deeply grateful.
Copyright:
Copyright 2017 Elsevier B.V., All rights reserved.
PY - 2003/8/1
Y1 - 2003/8/1
N2 - The source of whitings on the Great Bahama Bank and their relationship to major changes in the chemistry of Bank waters have been among the longest and most hotly debated topics in carbonate geochemistry. In this paper, we demonstrate that the reaction kinetics of calcite with Bank waters for a given saturation state are similar to, but somewhat slower (2 to 3 times) than with Gulf Stream water. The interpretation of the reaction kinetics of suspended Bank sediment with Bank water requires that the precipitating phase be about twice as soluble as aragonite. Good agreement at equivalent saturation states was found between experimental precipitation rates and those calculated for the rate of change of Bank water chemistry in the region of whitings. These results indicate that the dominant mode of carbonate removal is via precipitation on resuspended sediments rather than the rapid pseudo-homogeneous precipitation of calcium carbonate in the water column resulting in the formation of a whiting. Estimates indicate that single aragonite needles may be resuspended many times over a period of decades during which they experience repeated overgrowth. A major portion (>98%) of suspended calcium carbonate is outside the visually dramatic whitings. Thus, as visually spectacular as they are, whitings do not represent a short-term locally massive precipitation of carbonate on the Great Bahama Bank, nor are they even likely to be the dominant sites of carbonate removal in this region. Although future refinements are needed that include seafloor processes, we have at this point arrived at a mechanistic kinetic model that provides a reasonably quantitative explanation for the hydrochemistry of the carbonate system on the northern Great Bahama Bank.
AB - The source of whitings on the Great Bahama Bank and their relationship to major changes in the chemistry of Bank waters have been among the longest and most hotly debated topics in carbonate geochemistry. In this paper, we demonstrate that the reaction kinetics of calcite with Bank waters for a given saturation state are similar to, but somewhat slower (2 to 3 times) than with Gulf Stream water. The interpretation of the reaction kinetics of suspended Bank sediment with Bank water requires that the precipitating phase be about twice as soluble as aragonite. Good agreement at equivalent saturation states was found between experimental precipitation rates and those calculated for the rate of change of Bank water chemistry in the region of whitings. These results indicate that the dominant mode of carbonate removal is via precipitation on resuspended sediments rather than the rapid pseudo-homogeneous precipitation of calcium carbonate in the water column resulting in the formation of a whiting. Estimates indicate that single aragonite needles may be resuspended many times over a period of decades during which they experience repeated overgrowth. A major portion (>98%) of suspended calcium carbonate is outside the visually dramatic whitings. Thus, as visually spectacular as they are, whitings do not represent a short-term locally massive precipitation of carbonate on the Great Bahama Bank, nor are they even likely to be the dominant sites of carbonate removal in this region. Although future refinements are needed that include seafloor processes, we have at this point arrived at a mechanistic kinetic model that provides a reasonably quantitative explanation for the hydrochemistry of the carbonate system on the northern Great Bahama Bank.
UR - http://www.scopus.com/inward/record.url?scp=0012498192&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0012498192&partnerID=8YFLogxK
U2 - 10.1016/S0016-7037(03)00103-0
DO - 10.1016/S0016-7037(03)00103-0
M3 - Article
AN - SCOPUS:0012498192
VL - 67
SP - 2819
EP - 2826
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
SN - 0016-7037
IS - 15
ER -