δ34S values in recent sea sediments and their significance using several sediment profiles from the western Baltic Sea
δ34S values in recent sea sediments and their significance using several sediment profiles from the western Baltic Sea
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DOI：
10.1080/10256016.2012.660528
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发表时间：
2012-01-01
影响因子：
1.3
通讯作者：
Nielsen, Heimo
中科院分区：
文献类型：
--
作者：
Hartmann, Martin;Nielsen, Heimo
各种硫组分（沉积物中的总硫含量，硫酸盐和H2S的孔隙水）的同位素比值进行了测量，在一些核心，从最近的海洋沉积物从Kieler Bucht（基尔湾）地区在波罗的海西部。此外，还测定了沉积物和孔隙水溶液中的总硫、硫酸盐、硫化物、氯化物、有机碳、铁和水的含量。沉积物中所含的硫（类似于干样品的0.3-2%）大部分是在沉积之后才引入的。这证实了Kaplan等人的讨论[The Distribution and Isotopic Abbreviation of Sulfur in Recent Marine Sediments off Southern加州，Geochim.宇宙化学。Acta 27，297（1963）]。有机物对沉积物中硫含量的贡献很小（在我们的样品中，约占总硫的5-10%）。孔隙水中的硫酸盐已被确定为沉积物中硫的来源。在正常的沉积过程中，硫酸盐通过扩散进行交换，对硫含量的变化有重要意义，这种交换一直深入到4-6厘米的沉积深度。在此过程中，因还原和形成硫化物或黄铁矿而消耗的硫酸盐大部分被取代。因此，最上面的沉积层代表了一个部分开放的系统的总硫。硫的成岩作用是他化作用，在4- 6cm深度以下，我们处理的是一个封闭系统。硫的进一步成岩作用是等化学作用.沉积物硫的同位素值主要受硫的影响，硫通过扩散进入沉积物，并通过随后的细菌还原作用结合为硫化物或黄铁矿。由于S-32的普遍减少和硫酸盐向公海的反向扩散，S-32富集发生在沉积物的最上层。沉积物中的S-34值一般在千分之-15至-35之间，而海水硫酸盐为千分之+20，沉积学或化学变化与同位素比值之间没有关系。在岩心中，连续的桑迪和粘土层的δ S-34值没有变化。然而，沉积速率似乎影响S-34值。在一个沉积速率相对较低的岩心中，S-34的δ值在千分之-29至-33之间，而沉积速率较高的岩心的δ值在千分之-17至-24之间。随着沉积物深度的增加，孔隙水硫酸盐浓度如预期的那样降低（在30-40 cm的深度，我们发现海水值的20 - 70%），以及增加的S-34值（有一次达到千分之60以上）。然而，孔隙水中硫化物的浓度随着沉积物深度的增加而增加（在不同程度上，在一种情况下达到每升80毫克S）。所有岩心中孔隙水硫化物的δ S-34值与硫酸盐硫的δ S-34值平行增加，δ差值几乎恒定在50-60%，这似乎证实了两种组分之间的成因关系。
The isotope ratios of various sulphur components (total sulphur content in the sediment, sulphate and H2S in the pore-water) were measured in a number of cores from recent marine sediments taken from the Kieler Bucht (Kiel Bay) region in the western Baltic Sea. Additionally, the quantitative contents of total sulphur, sulphate, sulphide, chloride, organic carbon, iron and water in the sediment and in the pore-water solutions, respectively, were determined.These investigations provided the following results:1. The sulphur contained in the sediment (similar to 0.3-2% of the dry sample) was for the most part introduced only after sedimentation. This confirms the deliberations of Kaplan et al. [The Distribution and Isotopic Abundance of Sulfur in Recent Marine Sediments off Southern California, Geochim. Cosmochim. Acta 27, 297 (1963)]. The organic substance contributes to the sulphur content of the sediment only to an insignificant degree (in our samples with similar to 5-10% of the total sulphur).2. The sulphate in the pore-waters has been identified as a source for sulphur in the sediment. During normal sedimentation, the exchange of sulphate by diffusion significant for changes in the sulphur content goes down to a sediment depth of 4-6 cm. In this process, the sulphate consumed by reduction and formation of sulphide or pyrite is mostly replaced. The uppermost sediment layer thus represents a partially open system for the total sulphur. The diagenesis of the sulphur is allochemical.At depths below 4-6 cm, we are dealing with a closed system. The further diagenesis of sulphur here is isochemical.3. The isotope values of the sediment sulphur are influenced primarily by sulphur which comes into the sediment by diffusion and which is bound by subsequent bacteriological reduction as either sulphide or pyrite. As a consequence of the prevailing reduction of S-32 and reverse-diffusion of sulphate into the open sea water, a S-32 enrichment takes place in the uppermost layer of the sediment. The delta S-34 values in the sediment range in general between -15 and -35 parts per thousand, while seawater sulphate is +20 parts per thousand.No relationship could be established between sedimentological or chemical changes and isotope ratios. In the cores, successive sandy and clayish layers showed no change in the delta S-34 values. However, the sedimentation rate seems to influence delta S-34 values. In one core with relatively low sedimentation rates, the delta S-34 values varied between -29 and -33 parts per thousand, while cores with higher sedimentation rates showed values between -17 and -24 parts per thousand.4. As sediment depth increases, the pore-water sulphate shows, as expected, decreasing concentrations (in a depth of 30-40 cm, we found between 20 and 70% of the seawater values), and increasing delta S-34 values (in one case reaching more than +60 parts per thousand).The concentration of sulphide in the pore-water increases, however, with sediment depth (to various extents, reaching 80 mg S per litre in one case). The delta S-34 values of the pore-water sulphide in all cores show increases paralleling the sulphate sulphur, with a nearly constant delta difference of 50-60% in all cores.This seems to confirm the genetic relationship between the two components.