Ikaite Abundance Controlled by Porewater Phosphorus Level: Potential Links to Dust and Productivity
Ikaite Abundance Controlled by Porewater Phosphorus Level: Potential Links to Dust and Productivity
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DOI：
10.1086/681918
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发表时间：
2015-05
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影响因子：
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通讯作者：
Xiaoli Zhou;Zunli Lu;R. Rickaby;E. Domack;J. Wellner;H. Kennedy
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文献类型：
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作者：
Xiaoli Zhou;Zunli Lu;R. Rickaby;E. Domack;J. Wellner;H. Kennedy
硅钙石是矿物伊卡石 (CaCO3·6H2O) 在失去水合水后的假晶，以独特的自形晶体形式出现，有时聚集成直径达数十厘米的玫瑰花结。虽然人们普遍认为富含有机物的环境、甲烷渗漏和高磷酸盐水平对于伊卡石的形成很重要，但人们普遍认为古代沉积序列中的镁橄榄石矿产反映了接近冰点的温度，即使在温室气候时期的高纬度地区也是如此。为了充分了解硅藻土的古环境意义，有必要对现代伊伊特环境进行全面检查。温度是对伊卡石的存在进行定量限制的最重要参数。底水温度低虽然是矿物形成的必要条件，但不足以满足其生长；需要其他控制来解释许多寒冷环境中没有 ikaite。在这项研究中，我们讨论了碳酸盐化学对伊卡石形成的控制。我们对保存完好的伊卡石沉积物岩心的地球化学数据进行了汇编，为磷酸盐的重要性提供了进一步的证据。浅层冷孔隙水中的磷酸盐浓度高于~400 μM，可能是广泛的伊卡石沉淀的必要参数。因此，古代序列中丰富的硅藻土标志着过去孔隙水磷浓度升高的时期和地区，这也可能与高表面生产力和/或铁施肥有关。
Glendonites are pseudomorphs of the mineral ikaite (CaCO3·6H2O) after loss of hydration water and occur in distinctive euhedral crystalline forms, sometimes clustered as rosettes of up to tens of centimeters in diameter. While it is generally accepted that organic-rich environments, methane seeps, and high phosphate levels are important for ikaite formation, glendonite occurrences in ancient sedimentary sequences are widely considered to reflect near-freezing temperatures, even at high latitudes during periods of greenhouse climates. To fully understand the paleoenvironmental significance of glendonites, a comprehensive examination of the modern ikaite setting is necessary. Temperature is the most important parameter that has been quantitatively constrained for the presence of ikaite. Low bottom-water temperature, while a required condition for formation of the mineral, is not adequate for its growth; other controls are necessary to explain the absence of ikaite in many cold environments. In this study, we discuss the control of carbonate chemistry on ikaite formation. Our compilation of geochemical data from sediment cores with well-preserved ikaite provide further evidence for the importance of phosphate. A phosphate concentration above ∼400 μM in shallow and cold porewater may be the requisite parameter for extensive ikaite precipitation. Thus, abundant glendonites in ancient successions mark past periods and regions of elevated porewater phosphorus concentrations, which may also be related to high surface productivity and/or iron fertilization.