Characterization of iron diagenesis in marine sediments using refined iron speciation and quantized iron(Ⅲ)-oxide reactivity:a case study in the Jiaozhou Bay,China

As a case study, refined iron（Fe） speciation and quantitative characterization of the reductive reactivity of Fe（Ⅲ）oxides are combined to investigate Fe diagenetic processes in a core sediment from the eutrophic Jiaozhou Bay.The results show that a combination of the two methods can trace Fe transformation in more detail and offer nuanced information on Fe diagenesis from multiple perspectives. This methodology may be used to enhance our understanding of the complex biogeochemical cycling of Fe and sulfur in other studies. Microbial iron reduction（MIR） plays an important role in Fe（Ⅲ） reduction over the upper sediments, while a chemical reduction by reaction with dissolved sulfide is the main process at a deeper（〉 12 cm） layer. The most bioavailable amorphous Fe（Ⅲ） oxides [Fe（Ⅲ）am] are the main source of the MIR, followed by poorly crystalline Fe（Ⅲ） oxides [Fe（Ⅲ）pc）]and magnetite. Well crystalline Fe（Ⅲ） oxides [Fe（Ⅲ）wc] have barely participated in Fe diagenesis. The importance of the MIR over the upper layer may be a combined result of the high availability of highly reactive Fe oxides and low availability of labile organic matter, and the latter is also the ultimate factor limiting sulfate reduction and sulfide accumulation in the sediments. Microbially reducible Fe（Ⅲ） [MR-Fe（Ⅲ）], which is quantified by kinetics of Fe（II）-oxide reduction, mainly consists of the most reactive Fe（Ⅲ）am and less reactive Fe（Ⅲ）pc. The bulk reactivity of the MR-Fe（Ⅲ） pool is equivalent to aged ferrihydrite, and shows down-core decrease due to preferential reduction of highly reactive phases of Fe oxides.

Effect of high iron concentration enrichment on the phytoplankton in the Prydz Bay

Shipboard iron enrichment phytoplankton incubations were carried out in the Prydz Bay, Antarctic, in January through to March 2002. Waters for the three incubations (Exp 1, 2 and 3) were collected from 20 m depth in three stations (St. Ⅰ-1, Ⅶ-1 and Ⅶ-5), respectively. Although the nutrient concentrations in the surface waters of the three stations were consistently high, the Chl a concentrations varied considerably. Chl a concentrations in the 20 m depth of St. Ⅰ-1 and Ⅶ-1 were 0.13-0.17 μg·dm -3 and 0.20-0.26 μg·dm -3, respectively, while this figure was 2.35- 2.65 for St. Ⅶ-5. There were six levels of enriched iron concentrations (control 5, 10, 20, 40 and 80 nM) in Exp 1 (6-29th, January) while three enriched iron levels (control 10 and 40 nM) were arranged in Exp 2 and 3 (both were from 20th February to 4 th March). The iron enrichments stimulated the phytoplankton growth and nutrient drawdown in Exp 1 and Exp 2. In Exp 3, phytoplankton growth and nutrient drawdown were at nearly the same rate in the control and iron enriched bottles. In Exp 1, Chl a concentrations in the bottles with 20, 40 and 80 nM iron enrichments grew exponentially to 40- 43 μg·dm -3 on the 17th, 17th and 19th day, respectively, with a growth rate of 0.36- 0.38 d -1. Chl a concentration in the bottle enriched with 10 nM iron reached its peak ( 19.35 μg·dm -3) on the 23rd day (growth rate 0.27 d -1). Phytoplankton growth rates in the control bottle and the bottle enriched with 5 nM iron were 0.13 and 0.16 d -1, respectively. In Exp 2, the Chl a growth rates were 0.13, 0.32 and 0.40 d -1 in the control bottle and bottles with 10 and 40 nM iron enrichments, respectively. It seems that 10 nM iron enrichment was not enough to stimulate the phytoplankton to reach their maximum growth rate. The result that the phytoplankton <10 μm bloomed in Exp 1 and 2 was controversial to the “Ecumenical Iron Hypothesis” of Morel et al. (1991) that upon enrichment of iron, phytoplankton >10 μm would grow faster than phytoplankton <10 μm.

In vitro iron enrichment experiments in the Prydz Bay, the Southern Ocean: A test of the iron hypothesis

In "high nitrate, low chlorophyll" (HNLC) ocean regions, iron has been typically regarded as the limiting factor for phytoplankton production. This "iron hypothesis" needs to be tested in various oceanic environments to understand the role of iron in marine biological and biogeochemical processes. In this paper, three in vitro iron enrichment experiments were performed in Prydz Bay and at the Polar Front north of the Ross Sea, to study the role of iron on phytoplankton production. At the Polar Front of Ross Sea, iron addition significantly (P<0.05, Student's t-test) stimulated phytoplankton growth. In Prydz Bay, however, both the iron treatments and the controls showed rapid phytoplankton growth, and no significant effect (P>0.05, Student's t-test) as a consequence of iron addition was observed. These results confirmed the limiting role of iron in the Ross Sea and indicated that iron was not the primary factor limiting phytoplankton growth in Prydz Bay. Because the light environment for phytoplankton was enhanced in experimental bottles, light was assumed to be responsible for the rapid growth of phytoplankton in all treatments and to be the limiting factor controlling field phytoplankton growth in Prydz Bay. During the incubation experiments, nutrient consumption ratios also changed with the physiological status and the growth phases of phytoplankton cells. When phytoplankton growth was stimulated by iron addition, N was the first and Si was the last nutrient which absorption enhanced. The Si/N and Si/P consumption ratios of phytoplankton in the stationary and decay phases were significantly higher than those of rapidly growing phytoplankton. These findings were helpful for studies of the ma- rine ecosystem and biogeochemistry in Prydz Bay, and were also valuable for biogeochemical studies of carbon and nutrients in various marine environments.

Evidence for coupled iron and nitrate reduction in the surface waters of Jiaozhou Bay

Iron and nitrate(NO_(3)^(-))are dominant physiologically required nutrients for phytoplankton growth,and iron may also play a key role in the marine nitrogen cycle.In this study,we investigated the temporal and spatial distributions of dissolved iron(DFe)and Fe(Ⅱ)in the surface waters of Jiaozhou Bay(JZB)from April 2 to July 26,2017.High concentrations of DFe and Fe(Ⅱ)predominantly occurred in nearshore and estuarine stations and concentrations were generally higher in April and May.The highest DFe concentration was observed along the coast of Hongdao(51.55 nmol/L)in May,while the lowest concentration was observed in the western coastal region(2.88 nmol/L)in April.The highest and lowest Fe(Ⅱ)concentrations were observed in the Licun estuary(22.42 nmol/L)and outer bay(0.50 nmol/L)in May,respectively.We calculated the proportions of nitrate,nitrite,and ammonium in dissolved inorganic nitrogen(DIN)as well as the ratio of Fe(Ⅱ)to DFe in all four months.The mean Fe(Ⅱ)/DFe ratio was 0.48 in April,0.43 in May,0.69 in June,and 0.32 in July.The mean ratio of NO_(3)^(-)to DIN was 0.78 in April,0.54 in May,0.20 in June,and 0.62 in July.NO_(3)^(-)/DIN continuously decreased in the first three months,while Fe(Ⅱ)/DFe remained high,which suggests that the reduction of iron and nitrate occurred simultaneously in the surface waters of JZB.

博弈视角下我国铁矿石进口价格谈判的长短期均衡

目前,我国钢铁行业出现了产能过剩和较高的库存,铁矿石现货价格下跌,这一现象是经济发展周期的客观表象,还是三大矿商瓦解中钢协"统一战线"的一个营销策略。本文分别从短期和长期两个角度对这一问题做出分析,以博弈论为工具建立新的理论模型和研究框架,所得结论显示:在短期内我国钢铁行业集中度较低的情况下,钢企之间的博弈结果是"囚徒困境"均衡,这在一定程度上解释了我国铁矿石进口价格"逢谈必涨"的迷局,铁矿石进口价格短期下跌是矿商营销策略的可能性较大;而在长期内我国钢铁行业集中度较高的前提下,铁矿石价格下跌是钢铁行业发展周期的客观趋势。根据博弈结果,寻找我国钢企在短期内摆脱铁矿石价格谈判困境的方法和措施,以及如何在铁矿石价格谈判的长期博弈中抢占先机,做到未雨绸缪,提出一些前瞻性的观点和建议。