Enigmatic carbonate isotope values in shark teeth: Evidence for environmental and dietary controls
Enigmatic carbonate isotope values in shark teeth: Evidence for environmental and dietary controls
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DOI：
10.1016/j.palaeo.2023.111943
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发表时间：
2023-12-14
影响因子：
3
通讯作者：
Kim，Sora L.
中科院分区：
文献类型：
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作者：
Karnes，Molly E.;Chan，Rachel L.;Kim，Sora L.
鲨鱼牙齿的化石记录非常丰富，并在其化学中整合了生理信息，生态相互作用和古海洋学条件。化石鲨鱼牙齿非常适合进行稳定同位素分析，因为它们的釉质具有很高的化学稳定性，因此不易受成岩作用的影响。鲨鱼釉质的碳酸盐碳同位素组成（δ 13CCO3）虽然常用于哺乳动物的古生态学研究，但一直是个谜。在这里，我们调查了现代鲨鱼牙齿中的多个稳定同位素系统（δ 13 Corg，δ 13 CCO3，δ 18 OCO3，δ 18 OPO4），以确定不同系统之间的关系，并为现代鲨鱼和化石鲨鱼的未来研究建立一个解释框架。现代鲨鱼牙齿中δ 18OPO4和δ 18OCO3值之间的相关性比预期的要弱（r2 = 0.44），这与迄今为止对哺乳动物的研究形成对比，表明该指标不是鲨鱼牙齿化石中成岩蚀变的适当测试。现代牙用胶原的有机碳同位素组成（δ 13 Corg）介于− 16.0 ‰至− 10.8 ‰之间。鲨鱼牙釉质的δ 13CCO3值远高于胶原蛋白，在-6.0 ‰~10.3 ‰之间，两者之间无直接关系。相反，我们发现δ 13Corg和δ 13CCO3值之间的分馏（ε）与δ 18OCO3值相对应，而不是δ 18OPO4值。这可能是由于鲨鱼釉质中的碳源在膳食碳和溶解无机碳（DIC）之间分配，或者牙齿形成过程中的生理差异改变了碳酸盐同位素的分馏。我们将现代牙齿的分馏因子应用于化石鲨鱼牙齿的碳酸盐同位素组成，以预测δ 13 Corg值。尽管鲨鱼牙釉质碳酸盐的碳源还需要进一步研究，但我们的研究结果表明，鲨鱼牙齿化石可以为古代海洋生态系统的碳循环提供见解。
Shark teeth are abundant in the fossil record and integrate physiological information, ecological interactions, and paleo-oceanographic conditions in their chemistry. Fossil shark teeth are well suited for stable isotope analysis because their enameloid is resistant to diagenetic alteration due to its high chemical stability. Although often used in paleoecological studies of mammals, carbonate carbon isotope compositions (δ13CCO3) in shark enameloid have remained enigmatic. Here, we investigate multiple stable isotope systems (δ13Corg, δ13CCO3, δ18OCO3, δ18OPO4) within modern shark teeth to determine relationships between the different systems and build an interpretative framework for future studies of both modern and fossil sharks. There is a weaker than expected correlation between δ18OPO4and δ18OCO3values in modern shark teeth (r2= 0.44), which contrasts with mammalian studies to date and suggests this metric is not an appropriate test for diagenetic alteration in fossil shark teeth. Organic carbon isotope composition (δ13Corg) measured from modern dental collagen ranges from −16.0‰ to −10.8‰. The enameloid δ13CCO3values we measured are much higher than collagen, ranging from −6.0‰ to 10.3‰, and there is no direct relationship between δ13Corgand δ13CCO3values in shark teeth. Instead, we found the fractionation (ε) between δ13Corgand δ13CCO3values to correspond with δ18OCO3values but not δ18OPO4values. This could be due to the carbon source in shark enameloid being partitioned between dietary carbon and dissolved inorganic carbon (DIC) or physiological differences in the tooth formation process changing the fractionation of carbonate isotopes. We applied the fractionation factor from modern teeth to carbonate isotope compositions of fossil shark teeth to predict δ13Corgvalues. Although the carbon sources to shark enameloid carbonate needs further investigation, our results suggest that fossil shark teeth could provide insights into carbon cycling of ancient marine ecosystems.