The physical model with temperature and pressure controlled for measuring acoustic velocity of marine sediments

Abstract

The superficial marine sediment is an important boundary of ocean acoustic propagation. So, the acoustic property of seafloor surface is always research hotspot. The acoustic property of sediment is affected by temperature and pressure which is not considered by conventional lab acoustic measurement. A new type of system, called “Small-scale Geo-acoustic Physical Model Pilot System” (SGPMP) has been developed. The system measures geo-acoustic property of sediment under specific temperature, pressure and frequency conditions which can be controlled conveniently and accurately. The components, structure, measurement principle, error analysis and application example of this system are introduced in this article. As a laboratory platform, the system makes it convenient for us to study the relationship between the temperature, pressure, frequency and acoustic properties of marine sediment.     

Oxygen isotopes of phosphatic compounds—Application for marine particulate matter, sediments and soils

The phosphate oxygen isotopic composition in naturally occurring particulate phosphatic compounds (δ¹⁸O_p) can be used as a tracer for phosphate sources and to evaluate the cycling of phosphorus (P) in the environment. However, phosphatic compounds must be converted to silver phosphate prior to isotopic analysis, a process that involves digestion of particulate matter in acid. This digestion will hydrolyze some of the phosphatic compounds such that oxygen from the acid solution will be incorporated into the sample as these phosphatic compounds are converted to orthophosphate (PO₄³⁻). To determine the extent of incorporation of reagent oxygen into the sample, we digested various phosphatic compounds in both acid amended with H₂¹⁸O (spiked) and unspiked acid and then converted the samples to silver phosphate for δ¹⁸O_p analysis. Our results indicate that there is no isotopic fractionation associated with acid digestion at 50 °C. Furthermore, we found that reagent oxygen incorporation is a function of the oxygen to phosphorus ratio (O:P) of the digested compound whereby the percentage of reagent oxygen incorporated into the sample is the same as that which is required to convert all of the P-compounds into orthophosphate. Based on these results, we developed a correction for reagent oxygen incorporation using simple mass balance, a procedure that allows for the determination of the δ¹⁸O_p of samples containing a mixture of phosphatic compounds. We analyzed a variety of environmental samples for δ¹⁸O_p to demonstrate the utility of this approach for understanding sources and cycling of P.     

Black carbon in marine particulate organic carbon: Inputs and cycling of highly recalcitrant organic carbon in the Gulf of Maine

To increase our understanding of the roles of black carbon (BC), a highly sorptive and recalcitrant material, we measured BC concentrations and fluxes in marine particulate organic carbon (POC) out of the water column in the Gulf of Maine (GoM), a representative coastal area downwind of important BC sources of the Northeastern United States. Concentrations ranged from < 0.1 to 16 μg/L in the spring and late summer, typically contributing between 1 and 20% of the POC. Water-column export fluxes were near 10 g_BC/m²∙yr. These observations suggest that (a) up to 50% of the “molecularly uncharacterized” POC in this region's seawater is combustion-derived BC, and (b) the “bioavailabilities” of hydrophobic pollutants like polycyclic aromatic hydrocarbons (PAHs) would be influenced substantially by sorption to BC. The observed BC spatial distributions imply that a large part of the BC was carried offshore by wind and that much of it is accumulated in the coastal sediments. On a global scale, these results suggest the GoM and other coastal areas with similar BC loadings accumulate significant amounts of highly recalcitrant organic carbon that remineralizes on geological time scales in the world's oceans.     

Relocation effects of dredged marine sediments on mercury geochemistry: Venice lagoon,Italy

Understanding the biogeochemical process of Hg is critical in the overall evaluation of the ecological impacts resulting from the reuse of Hg-contaminated dredged sediment. Sediment banks (V1 and V2) were constructed with freshly dredged sediments from a navigational channel in Venice Lagoon, Italy, with the goal of clarifying potential differences in the biogeochemistry of Hg between the reused dredged sediments and those from surrounding sites (SS1 and S2). Toward this purpose, Hg and monomethylmercury (MMHg) concentrations, and Hg methylation rates (MMRs) in the surface 2.5 cm sediments were monitored, along with ammonium, iron, sulfate and sulfide concentrations in the pore waters of banks and surrounding sites from November 2005 to February 2007. Pore water analyses indicate that the bank sediments are characterized by lower levels of sulfate and iron, and by higher levels of ammonium and sulfide compared to the surrounding sediments. With respect to Hg speciation, the fractions of MMHg in total Hg (%MMHg/Hg) and the MMRs were significantly lower in the bank V1 compared to those in the reference site SS1, whereas the %MMHg/Hg and the MMRs were similar between V2 and S2. A negative correlation is found between the logarithm of the particle-water partition coefficient of Hg and the MMR, indicating that the reduced MMRs in V1 are caused by the limited concentrations of dissolved Hg. Organic matter appears to play a key role in the control of MMR via the control of Hg solubility.     

海洋沉积物含水率对部分碱金属及碱土金属元素含量的影响及意义

利用电感耦合等离子体光谱仪(ICP-AES)对海洋表层沉积物及上覆海水、海洋沉积物国家标准物质、陆地的水系沉积物及土壤国家标准物质进行检测以对比海洋沉积物含水率对部分碱金属及碱土金属元素分析结果所造成的影响。结果显示海洋沉积物含水率对钠离子影响最大,往往有超过50%的钠离子来自其中所含海水的贡献,而海洋沉积物含水率对钾、钙、镁的影响则较为微弱。因此,研究海洋沉积物化学组分时有必要考虑其所含海水对钠含量的贡献,以期达到不同海洋沉积物化学组分的可比性。     

盐酸、温度、时间及粒径对海洋沉积物碳酸盐去除的影响

通过南海北部表层沉积物相同体积不同盐酸浓度(0.1和1.0 mol.L-1)、不同温度(23和60℃)、不同时间(6、12和24h)和不同颗粒粒径样品(<160μm和<32μm)的交叉条件实验,利用各条件实验后样品的总碳含量及稳定碳同位素组成分析结果,研究了盐酸、温度、时间及颗粒粒径对碳酸盐去除的影响。结果表明,从提高沉积物碳酸盐盐酸酸解反应速率和效率及获取稳定可靠的TOC、δ13C有机质等参数的角度出发:(1)盐酸用量及浓度是最重要的影响因素;(2)升高反应温度是不必要的,升高反应温度既会抑制反应的进行,又会导致盐酸浓度下降并加速有机质分解,从而对沉积物总有机碳含量及其δ13C等的准确分析产生不利影响;(3)在1.0 mol.L-1盐酸过量的条件下,碳酸盐的大量分解在6h之前已基本完成;(4)颗粒粒径愈小,愈有利于样品的均匀混合及反应的进行,相应的分析结果离散度亦愈小。     

应用木质素示踪楚科奇海表层沉积物中有机碳的来源和降解程度

埋藏在海洋沉积物中的有机碳是大气二氧化碳的净汇,而埋藏过程主要发生在陆架区。北冰洋拥有全球最大的陆架,接收大量来自河流和沿岸侵蚀输运的陆源有机碳,楚科奇海作为北冰洋的边缘海,是有机碳埋藏的重要海区之一。本研究选用楚科奇海和海台的表层沉积物（陆架区33~82.69 m,陆坡区164.63~3 763 m）,通过木质素,结合粒度、比表面积、有机碳百分含量（OC%）、有机碳稳定同位素（δ13C）等指标来示踪楚科奇海沉积物有机碳的来源和降解程度。结果表明,有机碳载荷从陆架到陆坡有明显的降低趋势;δ13C的范围指示有机碳可能来自苔藓、草本裸子植被、浮游植物和冰藻等;木质素丁香基酚（S）与香草基酚（V）的比值（S/V）和肉桂基酚（C）与香草基酚（V）的比值（C/V）表明裸子植物的草本组织贡献了更多的陆源有机碳;此外,较高含量的C9DA二酸（干酪根氧化产物）表明干酪根也可能是楚科奇海表层沉积物中有机质来源的重要组成。指示降解的参数[（Ad/Al） s、（Ad/Al） v、（Ad/Al） p、3,5-Bd/V]在陆架和陆坡沉积物中的差异表明陆坡沉积物中有机质的降解过程受到水动力分选以及原位降解等因素的影响更为明显。     

南极罗斯海柱样沉积物中有机碳和氮元素地球化学特征及其来源

南极周边海域沉积物中的有机碳和氮元素地球化学特征对于深入研究全球碳循环和海洋生态环境演变具有重要意义。本文对取自南极罗斯海的RBA08C柱状样沉积物进行了有机碳和氮元素地球化学特征分析。结果表明：RBA08C柱样中TOC含量在顶部0~12cm呈现随柱深增加而降低的趋势, 自12cm以深含量总体相对稳定; TN总体具有与TOC相同的变化趋势, 两者含量变化呈现较强正相关性, 说明可能具有相同来源; 沉积物TOC/TN比值和δ13C值揭示RBA08C柱样有机质主要为海洋生源沉积, 其含量变化应主要受控于上层水体生产力、沉积速率和氧化还原环境等因素的共同作用; RBA08C柱样的TOC埋藏率约为50%, 与位于普里兹湾埃默里冰架边缘的IS-4站柱样相同, 加之较为相近的TOC和TN含量及变化趋势, 表明两者可能具有相近的沉积速率, 其所在的海区是南极海域较重要的碳循环和碳储区。     

Correction for effects of temperature and pressure on sound speed in shallow seafloor sediments

Abstract

Three types of sediments were selected to measure their sound speed under changing temperature and pressure conditions in laboratory. The effects of temperature and pressure on sound speed in sediments and their trends were analyzed. The results showed that, with increasing temperature and pressure, the sound speed exhibits an increasing trend in all selected sediments. For each sample, the ratio of the sound speed in sediments to that in seawater almost remained unchanged at different pressures and temperatures, with a maximum fluctuation of 1.09% for temperature dependence and 0.68% pressure dependence. Combining the analysis of experimental results and sound speed correction procedure given by Hamilton, specific correction formulas of sound speed for temperature and pressure were presented. The laboratory-measured sound speed in the experiment and the sound speed obtained in the South Yellow Sea were corrected to reduce the effects of temperature and pressure using the correction formulas. The results show that the correction formulas with constant sound speed ratio are effective for correcting the sound speed measurement errors caused by changes in temperature and pressure. As a further consideration, the effects of the fluctuation of sound speed ratio on sound speed correction were analyzed.     

Remineralization and accumulation of organic carbon and nitrogen in marine sediments of eutrophic bays: the case of the Bay of Concepcion, Chile

The Bay of Concepcion (36°40′S; 73°02′W) is a semi-enclosed and shallow embayment in which biogeochemical processes are seasonally coupled to coastal upwelling during the austral spring and summer. The nutrient cycle in the bay is complex due to the combined effects of a pronounced O₂ minimum layer and high nutrient concentrations both originating from subsurface equatorial water during coastal upwelling and a rapid rate of sediment nutrient recycling. The sediments are characterized by a high content of organic matter mainly due to the extremely high rates of phytoplankton production and deposition. During the upwelling period, a black flocculent layer frequently covers the sediment–water interface in the inner part of the bay where an extensive mat of Beggiatoa spp. develops. Three approaches are used to analyse the extent to which the benthic system recycles or retains nutrients at two stations, located at the centre (station C, St. C) and mouth (station B, St. B) of the bay for a 1-year period (March 1996–1997): (1) estimation of C and N remineralization rates based on SO₄²⁻ reduction measurements, (2) calculation of C and N turnover rates using a diagenetic model applied to total organic carbon and total nitrogen vertical distributions and, (3) construction of C and N budgets from direct measurements of sedimentation (from a sediment trap) and estimates of the C and N burial rates. Depth-integrated SO₄²⁻ reduction rates varied between 3.4 (winter) and 25.5 (summer) mmol m⁻² d⁻¹. Estimated C and N oxidation rates ranged between 7.9 and 87.8 mol C m⁻² yr⁻¹ and between 0.9 and 6.9 mol N m⁻² yr⁻¹, respectively. Each approach yielded minor differences in the C and N remineralization rates (and also minor differences between both studied stations), except when the kinetic model was applied to C and N distribution without including the presence of the flocculent layer. The rates of carbon oxidation and sulphate reduction were considerably higher than in other coastal sediments with similar depositional regime. The C and N burial rates were 2.23 and 0.21 (St. C) and 1.30 and 0.09 (St. B) mol m⁻² yr⁻¹, respectively. The C/N ratio of the buried fraction was ca. 10.6 at St. C and 14.4 at St. B. Because the observed differences in burial rates could not be ascribed to distinctive depositional (both stations have similar sediment accumulation rates) and oceanographic (similar O₂ concentration and hydrography) conditions, differences may be due to in part spatial heterogeneity in the supply of organic matter. The degree of preservation of organic matter as plankton detritus and nitrogen accumulating bacterial biomass associated with Beggiatoa spp. at St. C may also be involved.     

温度、盐度对海湾扇贝(Argopecten irradians)南北亚种回交幼虫生长和存活的影响

开展了海湾扇贝南北亚种杂交子代同海湾扇贝北方亚种间回交、杂交子二代及北方亚种对照组等群体的基因型和温度、盐度等环境因素之间的互作研究。研究结果表明,杂种F2和回交组别相对纯种组别存在生长优势。温度和盐度均对不同基因型群体的生产和存活产生显著的影响,其中在逆境温度下杂种F2和回交组能够更加适应并表现出更高的生长优势,而在盐度中结果却并非如此,这表明基因型和环境之间的互作机制比较复杂。研究结果为继续在不同海区环境下开展海湾扇贝回交育种提供了积极的理论依据和实践参考。     

环境因子对塔玛亚历山大藻生长的综合影响

利用多因子实验设计,研究了主要环境因子温度、盐度和光照强度对麻痹性贝毒产毒藻——塔玛亚历山大藻(Alexandrium tamarense)生长的影响.经三维ANOVA统计分析(Tukey test)结果表明,在实验条件范围内(温度12,19,25,32℃;盐度10,18,25,30,35和光照强度0.02×1016,0.08×1016,0.3×1016,1.6×1016s-1/cm2),温度、光照强度和盐度对藻生长率有显著的影响(P<0.001).光照强度和温度、盐度和温度、光照强度和盐度以及这3个因子之间存在显著的相互作用(P<0.001),在本实验中该藻生长的最适条件是19℃,1.6×1016s-1/cm2,盐度30.根据塔玛亚历山大藻的生长特性,我们探讨了这些环境因子在塔玛亚历山大藻赤潮形成机制中的作用.     

温、盐度对海湾扇贝稚贝迁移行为、生长和存活影响的实验

本文在实验室条件下,研究了温、盐度与海湾扇贝稚贝迁移、生长及存活的关系。其适合生长的温、盐度范围分别为16～28℃和19～34,最适温度和盐度分别为22℃,31.2;适合存活的盐度范围为19～39,盐度低于11或高于43,稚贝死亡严重;适合存活的温度为10～28℃。本文同时对温、盐度与稚贝附着后的迁移行为的关系进行了探讨。     

On the relevance of iron adsorption to container materials in small-volume experiments on iron marine chemistry: Fe-aided assessment of capacity, affinity and kinetics

Iron chemistry in seawater has been extensively studied in the laboratory, mostly in small-volume sample bottles. However, little has been reported about iron wall sorption in these bottles. In this paper, radio-iron ⁵⁵Fe was used to assess iron wall adsorption, both in terms of capacity, affinity and kinetics. Various bottle materials were tested. Iron sorption increased from polyethylene/polycarbonate to polymethylmetacrylate (PMMA)/high-density polyethylene/polytetrafluoroethylene to glass/quartz, reaching equilibrium in a 25–70 h period. PMMA was studied in more detail: ferric iron (Fe(III)) adsorbed on the walls of the bottles, whereas ferrous iron (Fe(II)) did not. Considering that in seawater the inorganic iron pool mostly consists of ferric iron, the wall will be a factor that needs to be considered in bottle experiments.The present data indicate that for PMMA with specific surface (S)-to-volume (V) ratio S/V, both iron capacity (42 ± 16 × 10^− 9 mol/m² or 1.7 × 10^− 9 mol/L recalculated for the S/V-specific PMMA bottles used) and affinity (log K_Fe'W = 11.0 ± 0.3 m²/mol or 12.4 ± 0.3 L/mol, recalculated for the S/V-specific PMMA bottles used) are of similar magnitude as the iron capacity and -affinity of the natural ligands in the presently used seawater and thus cannot be ignored.Calculation of rate constants for association and dissociation of both Fe'L (iron bound to natural occurring organic ligands) and Fe'W (iron adsorbed on the wall of vessels) suggests that the two iron complexes are also of rather similar kinetics, with rate constants for dissociation in the order of 10 ⁻⁴–10^− 5 L/s and rate constants for association in the order of 10⁸ L/(mol s). This makes that iron wall sorption should be seriously considered in small-volume experiments, both in assessments of shorter-term dynamics and in end-point observations in equilibrium conditions. Therefore, the present data strongly advocate making use of iron mass balances throughout in experiments in smaller volume set-ups on marine iron (bio) chemistry.     

Multiple controls on the paleoenvironment of the Early Cambrian marine black shales in the Sichuan Basin,SW China: Geochemical and organic carbon isotopic evidence

In order to understand the paleoenvironment of the Early Cambrian black shale deposition in the western part of the Yangtze Block, geochemical and organic carbon isotopic studies have been performed on two wells that have drilled through the Qiongzhusi Formation in the central and southeastern parts of Sichuan Basin. It shows that the lowest part of the Qiongzhusi Formation has high TOC abundance, while the middle and upper parts display relative low TOC content. Redox-sensitive element (Mo) and trace elemental redox indices (e.g., Ni/Co, V/Cr, U/Th and V/(V + Ni)) suggest that the high-TOC layers were deposited under anoxic conditions, whereas the low-TOC layers under relatively dysoxic/oxic conditions. The relationship of the enrichment factors of Mo and U further shows a transition from suboxic low-TOC layers to euxinic high-TOC layers. On the basis of the Mo-TOC relationship, the Qiongzhusi Formation black shales were deposited in a basin under moderately restricted conditions. Organic carbon isotopes display temporal variations in the Qiongzhusi Formation, with a positive excursion of δ¹³C_org values in the lower part and a continuous positive shift in the middle and upper parts. All these geochemical and isotopic criteria indicate a paleoenvironmental change from bottom anoxic to middle and upper dysoxic/oxic conditions for the Qiongzhusi Formation black shales. The correlation of organic carbon isotopic data for the Lower Cambrian black shales in different regions of the Yangtze Block shows consistent positive excursion of δ¹³C_org values in the lower part for each section. This excursion can be ascribed to the widespread Early Cambrian transgression in the Yangtze Block, under which black shales were deposited.     

Modelling the effects and economics of managed realignment on the cycling and storage of nutrients, carbon and sediments in the Blackwater estuary UK

A hydrodynamic model is developed for the Blackwater estuary (UK) and used to estimate nitrate removal by denitrification. Using the model, sediment analysis and estimates of sedimentation rates, we estimate changes in estuarine denitrification and intertidal carbon and nutrient storage and associated value of habitat created under a scenario of extensive managed realignment. We then use this information, together with engineering and land costs, to conduct a cost benefit analysis of the managed realignment. This demonstrates that over a 50–100 year timescale the value of the habitat created and carbon buried is sufficient to make the large scale managed realignment cost effective. The analysis reveals that carbon and nutrient storage plus habitat creation represent major and quantifiable benefits of realignment. The methodology described here can be readily transferred to other coastal systems.     

Sources and preservation of organic matter in Plum Island salt marsh sediments (MA, USA): long-chain n-alkanes and stable carbon isotope compositions

Elemental (TOC, TN, C/N) and stable carbon isotopic (δ¹³C) compositions and n-alkane (nC_16–38) concentrations were measured for Spartina alterniflora, a C₄ marsh grass, Typha latifolia, a C₃ marsh grass, and three sediment cores collected from middle and upper estuarine sites from the Plum Island salt marshes. Our results indicated that the organic matter preserved in the sediments was highly affected by the marsh plants that dominated the sampling sites. δ¹³C values of organic matter preserved in the upper fresh water site sediment were more negative (−23.0±0.3‰) as affected by the C₃ plants than the values of organic matter preserved in the sediments of middle (−18.9±0.8‰) and mud flat sites (−19.4±0.1‰) as influenced mainly by the C₄ marsh plants. The distribution of n-alkanes measured in all sediments showed similar patterns as those determined in the marsh grasses S. alterniflora and T. latifolia, and nC₂₁ to nC₃₃ long-chain n-alkanes were the major compounds determined in all sediment samples. The strong odd-to-even carbon numbered n-alkane predominance was found in all three sediments and nC₂₉ was the most abundant homologue in all samples measured. Both δ¹³C compositions of organic matter and n-alkane distributions in these sediments indicate that the marsh plants could contribute significant amount of organic matter preserved in Plum Island salt marsh sediments. This suggests that salt marshes play an important role in the cycling of nutrients and organic carbon in the estuary and adjacent coastal waters.     

Iron and phosphorus effects on the growth of Cryptomonas sp. (Cryptophyceae) and their availability in sediments from the Pearl River Estuary, China

Based on lab-culture experiments analyzing limitation and combination of iron and phosphorus on the growth of Cryptomonas sp. (Cryptophyceae), and the study of accumulation and release of Fe-bound P in sediment cores collected from the marine region of the Pearl River Estuary, China, reasons for the high frequency of phytoplankton bloom therein are discussed. Results show that the combined effect of Fe and P can obviously accelerate algal development, and the optimum culture conditions maintaining maximum growth rate are 0.05 μM Fe and 50 μM P. Cellular contents of Fe and P is consistent and the P:Fe molar ratio is 159:1. The optimum range of the P:Fe molar ratio in culture experiments for cell incubation is 500–1400. The vertical trends of total Fe and total P variations in sediments are parallel. Fe-bound P is the main species of inorganic sedimentary P. Through continuous leaching with agitation, 34–80% of exchangeable P and 4–23% of exchangeable Fe are concurrently released from the surficial sediments. This is a possible way by which nutrients are made available to phytoplankton. These factors might be responsible for a high frequency of harmful algal blooms in the Pearl River Estuary.