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首页> 外文期刊>Carbonates And Evaporites >Carbon isotope values as paleoclimatic indicators. Study on stalagmite from Nerja Cave, South Spain
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Carbon isotope values as paleoclimatic indicators. Study on stalagmite from Nerja Cave, South Spain

机译：碳同位素值作为古气候指标。西班牙南部内尔哈洞石笋的研究

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In theory, it should be possible to use C-isotope variations in speleothems as a monitor of past climate change in a manner analogous to O-isotopes. C isotope values are related to the terrestrial C cycle and provide information about soil and vegetation. Variations in the carbon isotopic composition (δ~(13)C) values of speleothems reflect changes of the vegetation type in the vicinity of a cave and arise because of the differences in the photosynthetic pathways between C3 and C4 type vegetation. Carbon isotopes in speleothems may serve as indicators of vegetative change, climatic conditions, and karst processes. Carbon isotope variations in speleothems arise from a variety of causes from both surface environment (local climate, bioproductivity, vegetation type, etc.) and subsurface environment in which rain water passes through the soil zone and then the epikarst into cave voids. Even within the cave, environmental local processes such as evaporation, drip rates, and changes in cave air pCO_2 controlled by seasonal ventilation can influence the final δ~(13)C values found in the speleothem record. Interpretation of δ~(13)C records may require several consecutive processes. In the present study, the δ~(13)C record of a stalagmite from Nerja Cave was examined to evaluate the roles of environmental processes and local cave conditions on speleothem δ~(13)C values. Stalagmite consisted of aragonite crystals with mineralogical composition uniform. There was no observed evidence to indicate recrystallization of aragonite to calcite or the presence of alternating mineral laminae. The influence of vegetation on speleothem δ~(13)C primarily reflects changes in the density of vegetative cover and biomass. Greater vegetative cover contributes to lower δ~(13)C values as more biogenic CO_2 is dissolved into the seepage water. When vegetative cover is reduced by changes in climate, or from deforestation, the vegetative contribution of biogenic CO_2 diminishes and speleothem δ~(13)C values increase. Ventilation of Nerja Cave may also induce changes in cave air pCO_2 that contributed to the δ~(13)C record. During cold periods, enhanced air exchange may have occurred between the cold, dense air outside and the internal cave atmosphere. Increased air exchange could have lowered pCO_2 of the cave air, increased degassing, and enriched the precipitating aragonite in ~(13)C.
机译：从理论上讲，应该有可能以类似O同位素的方式，在脾科中使用C同位素变化来监测过去的气候变化。 C同位素值与地球C循环有关，并提供有关土壤和植被的信息。炭疽菌的碳同位素组成（δ〜（13）C）值的变化反映了洞穴附近植被类型的变化，并且由于C3和C4型植被之间光合作用途径的差异而产生。鞘脂中的碳同位素可以作为营养变化，气候条件和岩溶过程的指标。地衣碳同位素的变化是由表层环境（局部气候，生物生产力，植被类型等）和地下环境引起的各种原因引起的，雨水先经过土壤区域，然后上岩溶进入洞穴空隙。即使在洞穴内，环境局部过程（如蒸发，滴水速率和受季节性通风控制的洞穴空气pCO_2的变化）也可能影响在闪血虫记录中发现的最终δ〜（13）C值。解释δ〜（13）C记录可能需要几个连续的过程。在本研究中，对内尔哈洞石笋的δ〜（13）C记录进行了研究，以评估环境过程和局部洞穴条件对蛇纹石δ〜（13）C值的作用。石笋由文石组成均匀的文石晶体组成。没有观察到证据表明文石重结晶为方解石或存在交替的矿物薄片。植被对斑竹δ〜（13）C的影响主要反映了植被覆盖度和生物量的变化。随着更多的生物源CO_2溶解在渗流水中，更大的植物覆盖率有助于降低δ〜（13）C值。当由于气候变化或森林砍伐而减少植被覆盖时，生物CO_2的营养作用就会减少，而鞘翅目δ〜（13）C值会增加。内尔哈洞的通风还可能引起洞内空气pCO_2的变化，从而导致δ〜（13）C记录。在寒冷时期，外部寒冷的密集空气与内部洞穴大气之间可能发生了增强的空气交换。增加的空气交换可能降低了洞穴空气的pCO_2，增加了脱气，并使〜（13）C中的沉淀文石富集。

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