Planktonic foraminifera dissolution

Adelseck C.G., Jr. and Berger W.H. (1975) On the dissolution of planktonic foraminifera and associated microfossils during settling and on the sea floor. In Dissolution of Deep-Sea Carbonates (eds. A. Be and W. Berger), pp. 70-81. Cushman Foundation for Foraminiferal Research, Special Publication 13, W. Sliter. 

Berger W.H. and Piper D.J.W. (1972) Planktonic foraminifera Differential settling, dissolution, and redeposition. Limnol. Oceanogr. 17, 275-287. 

Keir R.S. and Hurd D.C. (1983) The effect of encapsulated fine grained sediment and test morphology on the resistance of planktonic foraminifera to dissolution. Mar. Micropaleontol. 8, 183-214. 

Berger (12) has identified another sediment marker level in the sediments. This is the level at v hich the proportion of "resistant" planktonic foraminifera show the first significant increase. Berger s estimate of minimum dissolution loss at the Rq level is 10 percent. Adelseck s (11) experimentally determined amount of dissolution necessary to produce the Rq level is approximately 50 percent dissolution. 

Lxthmann G. P. (1995) A model for variation in the chemistry of planktonic foraminifera due to secondary calcification and selective dissolution. Paleoceanography... 

Brown S. and Elderfield H. (1996) Variations in Mg/Ca and Sr/ Ca ratios of planktonic foraminifera caused by postdeposi-tional dissolution—evidence of shallow Mg-dependent dissolution. Paleoceanography 11(5), 543-551. 

Caron D. A., Anderson O. R., Lindsey J. L., Faber J. W. W., and Lin Lim E. (1990) Effects of gametogenesis on test structure and dissolution of some spinose planktonic foraminifera and implications for test preservation. Mar. Micropaleontol. 16, 93-116. 

Wu G. and Berger W. H. (1989) Planktonic foraminifera differential dissolution and the Quaternary stable isotope record in the west equatorial Pacific. Paleoceanography 4(2), 181-198. 

Several studies support the idea that the chemical composition of biogenic carbonate is modified by partial dissolution under the infiuence of bottom waters or porewaters that are undersaturated with respect to calcium carbonate (e.g. Rosenthal et al. 2000). In a study of planktonic foraminifera conducted by Brown Elderfield (1996), artificial partial dissolution of G. tumida tests resulted in a decrease in both Mg/Ca and Sr/Ca, but there was no significant change for G. sacculifer. The cause of this reduction is thought to be preferential dissolution of high-Mg inner (chamber) calcite, which forms in warmer waters than the low-Mg calcite crust (keel). In theory, it should be possible to correct for such effects if the extent of dissolution can be quantified. A number of dissolution indicators, including foraminiferal test weights (e.g. Broecker Clark 2001) and calcite crystallinity (Bassinot et al. 2004), have been tested, but none have been widely applied to date. 

HONISCH, B. Hemming, N. G. 2004. Ground-tmthing the boron isotope paleo-/)H proxy in planktonic foraminifera shells partial dissolution and shell size effects. Paleoceanography, 19 PA4010, doi 10.1029/2004PA001026. 

Planktonic shell thickness. A third indicator of CaC03 dissolution within the water column comes from a more subtle examination of the shells of foraminifera, the thickness of their walls in fact. This technique was pioneered by Lohmann (1995) and further pursued by Broecker and Clark (2001). What they find is that the shell thickness of forams increases throughout the first kilometer of the water column, and decreases below 3 km, representative of dissolution within the water column. 

Event II was the main plankton extinction and productivity crisis coimected to the rapid collapse of the surface-to-deep water carbon isotope gradient and drops in barium and carbonate accumulation rates. Curiously, there was a hundredfold increase in the concentration of foraminifera relative to total carbonate. It could be due to intensified deep circulation with winnowing of the fine fraction. Or possibly to better the preservation of the dissolution-prone planktonic forms through deepening of the CCD and/or lowered rates of in situ dissolution caused by decreased decay of organic carbon in sediment pore waters. There is support for this idea from the fact that coccoHths tend to be more dissolution-resistant than foraminifera, also from calcite dissolution above the calcite saturation horizon is driven mainly by titration by metabolic carbon dioxide derived from organic carbon decay at or near the sediment-water interface. 

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