Comparing Rhizon samplers and centrifugation for pore‐water separation in studies of the marine carbonate system in sediments
Comparing Rhizon samplers and centrifugation for pore‐water separation in studies of the marine carbonate system in sediments
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在沉积物中的海洋碳酸盐系统研究中比较 Rhizon 采样器和离心分离孔隙水
DOI：
10.1002/lom3.10286
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发表时间：
2018
期刊：
影响因子：
--
通讯作者：
A. Turchyn
中科院分区：
文献类型：
--
作者：
Z. Steiner;B. Lazar;J. Erez;A. Turchyn
孔隙沃茨中碳酸盐体系的准确描述在研究沉积有机质的降解、碳酸钙矿物的重结晶、矿物饱和状态的计算以及受pH影响的离子循环等方面具有重要价值。在此，我们分析了红海亚喀巴湾半远洋沉积物中使用离心和Rhizon采样器提取的孔隙水的水化学，和英格兰诺福克的一片浅盐沼。在这两个研究区域中，每种孔隙水分离技术的数据内部一致，但两种技术之间溶解无机碳（δ 13 C [DIC]）的测量同位素组成不同。我们进行了实验室实验，表明根茎和离心都容易使富含12 C的CO2脱气。我们建议，在用根茎采样期间，空气填充提取的孔隙水留下的空隙;结合膜的设计以排除空气，一些含水CO2扩散到这些气泡中，而不是采样器中。当根茎浸泡在去离子水中，然后在取样前立即用样品冲洗时，根茎产生可靠的钙、锶、锰和钡浓度数据。然而，用根茎进行孔隙水提取对于pH值和δ 13 C [DIC]的分析不太可靠。当试管完全填充且没有顶部空间并紧密密封时，离心可产生可靠的碳酸盐化学和主要元素数据。在低/无CO2气氛中工作（例如，N2手套箱）增加了在两种取样技术中从样品中损失CO2的机会，这是由于岩心与其周围环境之间的CO2负梯度增加。
An accurate description of the carbonate system in pore waters is valuable in studies involving the degradation of sedimentary organic matter, recrystallization of calcium carbonate minerals, calculations of mineral saturation state, and cycling of ions affected by pH. Here, we analyze water chemistry of pore water extracted using centrifugation and Rhizon samplers from hemipelagic sediments in the Gulf of Aqaba, Red Sea, and a shallow salt marsh from Norfolk, England. In both study areas, the data are internally consistent for each pore‐water separation technique, but the measured isotopic composition of the dissolved inorganic carbon (δ13C[DIC]) differs between the two techniques. We performed laboratory experiments that show that both Rhizons and centrifugation are prone to degassing of CO2 enriched with 12C. We suggest that during sampling with Rhizons, air fills the voids left by extracted pore water; combined with the membrane's design to exclude air, some of the aqueous CO2 diffuses into these air bubbles instead of the sampler. Rhizons produce reliable calcium, strontium, manganese, and barium concentration data when soaked in deionized water and then flushed with the sample immediately prior to sampling. However, pore‐water extractions with Rhizons are less reliable for analyses of pH and δ13C[DIC]. Centrifugation produces reliable carbonate chemistry and major element data when tubes are fully filled without headspace and sealed tightly. Working in CO2 low/free atmosphere (e.g., N2 glovebox) enhances the chance of losing CO2 from the sample in both sampling techniques due to increased negative gradient of CO2 between the core and its surrounding.