Potential and limitations of Sr/Ca ratios in coccolith carbonate: new perspectives from cultures and monospecific samples from sediments
Potential and limitations of Sr/Ca ratios in coccolith carbonate: new perspectives from cultures and monospecific samples from sediments
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DOI：
10.1098/rsta.2001.0966
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发表时间：
2002-04-15
期刊：
影响因子：
5
通讯作者：
Young, JR
中科院分区：
文献类型：
--
作者：
Stoll, HM;Ziveri, P;Young, JR
球粒岩的Sr/Ca比值最近被提出作为球粒岩藻（一种海洋藻类）过去生长速率的潜在指标，球粒岩藻在全球碳酸盐和碳循环中起着关键作用。我们通过实验室培养研究和分析来自地表沉积物的单特异性球砾石组合来综合校准这一代理。球石线虫Helicosphaera carteri， Syracosphaera pulchra和Algirospira robusta的培养证实了Sr/Ca每度增加1-2%，这是之前在Emiliania huxleyi和Gephyrocapsa oceanica中发现的。这种影响不仅仅是由于生长速率随温度升高而增加，在古海洋学研究中必须加以考虑。在恒温条件下，在赫胥黎、细鳞钙藻和大洋钙藻的限光培养中，在给定物种的可能生长和钙化率范围内，球石Sr/Ca比值变化10%。在相同的培养条件下，不同品种间Sr/Ca比值相差30%。尽管在钙化和有机碳固定速率最高的细胞中，比例最高，但在较低的速率下，存在很大的分散，这表明不同的机制控制着种间和种内的球粒Sr/Ca变化。在赤道太平洋和索马里沿海地区的实地研究中，岩屑Sr/Ca与上升流强度和生产力有关。与G. oceanica或Florisphaera profunda的小粒粒岩（Sr/Ca变化6-15%）相比，像C. leptoporus这样的大粒粒岩（Sr/Ca变化23-55%）的响应更动态。这一反应表明，尽管温度的影响，球粒石Sr/Ca仍有潜力作为球粒石菌产量的指标。如果不同物种的Sr/Ca变化响应准确地反映了它们对上升流的变化生产力响应（而不是Sr/Ca随生产力变化的不同斜率），那么球岩石Sr/Ca可以为球岩石生态的过去变化提供有用的数据。球粒石Sr/Ca变化的机制尚不清楚，但可能与碳获取过程中的生化循环密切相关，而不是与锶在方解石球粒石晶体中掺入的化学动力学效应有关。
The Sr/Ca ratio of coccoliths was recently proposed as a potential indicator of past growth rates of coccolithophorids, marine algae, which play key roles in both the global carbonate and carbon cycles. We synthesize calibrations of this proxy through laboratory culture studies and analysis of monospecific coccolith assemblages from surface sediments. Cultures of coccolithophorids Helicosphaera carteri, Syracosphaera pulchra and Algirospira robusta confirm a 1-2% increase in Sr/Ca per degreesC previously identified in Emiliania huxleyi and Gephyrocapsa oceanica. This effect is not due merely to increases in growth rate with temperature and must be considered in palaeoceanographic studies. In light-limited cultures of E. huxleyi, Calcidiscus leptoporus and G. oceanica at constant temperature, coccolith Sr/Ca ratios vary by 10% across the range of possible growth and calcification rates for a given species. Among different species under similar culture conditions, Sr/Ca ratios vary by 30%. Although the highest ratios are in the cells with highest calcification and organic carbon fixation rates, at lower rates there is much scatter, indicating that different mechanisms control interspecific and intraspecific coccolith Sr/Ca variations. In field studies in the Equatorial Pacific and Somalia coastal region, coccolith Sr/Ca correlates with upwelling intensity and productivity. A more dynamic response is observed in larger coccoliths like C. leptoporus (23-55% variation in Sr/Ca) than in smaller coccoliths of G. oceanica or Florisphaera profunda (6-15% variation in Sr/Ca). This response suggests that, despite temperature effects, coccolith Sr/Ca has potential as an indicator of coccolithophorid productivity. If the variable Sr/Ca response of different species accurately reflects their variable productivity response to upwelling (and not different slopes of Sr/Ca with productivity), coccolith Sr/Ca could provide useful data on past changes in coccolith ecology. The mechanism of coccolith Sr/Ca variations remains poorly understood but is probably more closely tied to biochemical cycles during carbon acquisition than to chemical kinetic effects on Sr incorporation in the calcite coccolith crystals.