Coccolith morphological and assemblage responses to dissolution in the recent sediments of the East China Sea

Highlights

• Gephyrocapsa coccoliths (>3 μm) got thinner and lighter in response to dissolution in the sediments of East China Sea.

• The acidification experiments showed selective dissolution of the four dominant coccolith species/genera.

• Coccolith morphological parameters can be used as indices to evaluate coccolith dissolution in sediments.

Abstract

Evaluating carbonate dissolution in deep sea sediments is of key importance in understanding the variation of the carbonate compensation depth and the ocean carbon cycle in the geological past. Since coccoliths are one of the main contributors to oceanic CaCO3, their dissolution and preservation degrees in sediments can be a useful indicator for deep sea carbonate chemistry. Varying coccolith preservation conditions have been found due to dissolution caused by organic matter degradation in the recent surface sediments of the East China Sea, which provides a good basis for the study of coccolith morphological and assemblage responses to dissolution. We measured the coccolith weight, thickness, and length of Gephyrocapsa spp. (>3 μm) using a circularly polarized light microscope. It has been found that Gephyrocapsa spp. (>3 μm) coccoliths become thinner and lighter in response to dissolution, and coccolith assemblages are also altered in poorly preserved sediments. This phenomenon was confirmed by an acidification experiment on a sediment sample, which also showed that coccoliths became thinner and lighter under increasingly acidified conditions. There is selective dissolution, i.e., Emiliania huxleyi coccoliths are most dissolution-prone, followed by Gephyrocapsa spp. (3 μm), and Helicosphaera spp.. Coccolith morphological parameters can be used to quantitatively evaluate coccolith preservation and dissolution in sediment samples. We suggest that using size-normalized weight, a mean coccolith weight loss of ~30–50% can be assigned to moderate-poor preservation for coccoliths, as reflected by the measured coccolith morphological changes in the surface sediments and in the acidification experiment.

Jin X., Liu C. & Zhang H., 2019. Coccolith morphological and assemblage responses to dissolution in the recent sediments of the East China Sea. Marine Micropaleontology 152: 101709. doi: 10.1016/j.marmicro.2018.09.001. Article (subscription required).

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