Abundance, distribution, and isotopic composition of particulate black carbon in the northern Gulf of Mexico

There exists increasing evidence supporting the important role of black carbon in global carbon cycles. Particulate black carbon (PBC) is allochthonous and has distinct reactivities compared to the bulk particulate organic carbon (tot-POC) in marine environments. However, the abundance, geochemical behavior of PBC and its importance in oceanic carbon budget remain poorly understood. Here we report the abundance, distribution, and stable isotopic signatures of BC derived from the chemo-thermal oxidation (CTO-375) method (BCCTO) in the Gulf of Mexico. Our results show that BCCTO abundance decreased from shelf to basin, and more than a half of riverine BCCTO could be removed over the shelf. Moreover, BCCTO is much more refractory compared to the tot-POC and has δ13C values lower than those of BC-excluded POC. These results highlight the significance of PBC in marine carbon cycles and potentially suggest the need for a new end-member term in quantifying POC sources in the ocean. Key Points BC could result in an overestimate of autochthonous POC in the ocean13C abundance of soot BC is up to 12‰ lower than BC-excluded POC>50% of the riverine soot BC is removed on the shel

Depositional fluxes and residence time of atmospheric radioiodine (131I) from the Fukushima accident

Activities of radioiodine (131I) along with 210Pb and 210Po in time series precipitation samples were measured to determine the depositional fluxes of 131I in the Southern United States and its removal rate and residence time in the atmosphere during the Fukushima nuclear accident. Radioiodine released from the Fukushima accident reached the Southern United States within 11 days, giving rise to a concurrent 131I peak and anomalous 210Po/210Pb ratios in the precipitation samples. The cumulative 131I depositional flux was 4.6 卤 0.2 Bq m-2 during the maximum fallout. The removal rate of 131I out of the atmosphere, derived from a definite 131I integral model, ranged from 0.03 to 0.14 d-1 with an average of 0.08 卤 0.02 d-1, which corresponds to a residence time of 131I in the atmosphere of 12 卤 3 days, consistent with the resident timescale constrained by the 210Po/210Pb disequilibrium technique. These results support our hypothesis that radioiodine was removed from the atmosphere by precipitation within two weeks. It seemed that regions reachable by 131I transport within two weeks from Fukushima Japan would receive much more fallout, whereas places outside that distance would be relatively less polluted with radionuclides. 漏 2012 Elsevier Ltd

Phase partitioning and solubility of iron in natural seawater controlled by dissolved organic matter

The phase partitioning and solubility of Fe as well as its relationship with marine dissolved organic matter (DOM) in different natural seawater and phytoplankton cultures were examined using radiotracer and ultrafiltration techniques to better understand Fe biogeochemical cycling and its biological availability in the ocean. Fe solubility in seawaters was related to the filter's cutoff, with the Fe solubility in the <3 x 10(3) amu fraction being about one third of that in the <10 x 10(3) amu filtrate. The Fe solubility decreased from estuarine to coastal to oceanic seawater and then to DOM-free seawater. There was a significant linear relationship between Fe solubility or [FeL] concentration and the dissolved organic carbon concentration for the seawater of different origins tested, suggesting that Fe solubility was largely controlled by the amount of dissolved organic matter. In addition, Fe solubility was significantly enhanced by the presence of fresh phytoplankton exudates, indicating that the nature of organic ligands also plays an important role in controlling the Fe solubility in seawater. Most of the Fe-bound organic ligands were in the size fraction <10 x 10(3) amu and decreased from the estuarine to the coastal and then to the oceanic seawater. Among the standard macromolecular organic compounds examined, siderophores ( deferoxamine mesylate and ferrichrome) showed the highest binding capacity for Fe, and carrageenan (a high molecular weight sulfated acid polysaccharide) also slightly increased Fe solubility. Complexation of organic ligands with Fe appeared to be Fe-specific or Fe preferential. Our results highlight quantitatively the importance of DOM in controlling Fe solubility in seawater. Further studies are needed to elucidate the interrelationship between the biogeochemical cycles of Fe and the chemistry of DOM in the ocean

Adsorption and fractionation of thorium and protactinium on nanoparticles in seawater

NSF (OCE) [0850957]; Chinese Natural Science Foundation [41125020]; State Oceanic Administration of China [2010050012-3]Laboratory adsorption experiments were conducted to examine the role of particle composition in the scavenging and fractionation of Th-234 and Pa-233 on nanoparticles in seawater. Nanoparticles with known chemical composition and size were used, including SiO2, CaCO3, Fe2O3, Al2O3 and TiO2, representing biogenic opal, carbonate, metal oxides, and lithogenic particles, respectively. The results indicated that nanoparticles with the same size but different chemical compositions had different affinities for Th-234 and Pa-233, giving rise to different partition coefficient (K-d) values. Compared to Th-234, log IQ values of Pa-233 had a higher variability on different nanopartides, ranging from 3.10 to 5.39. In general, the log K-d values for Th-234 on CaCO3, Fe2O3, and Al2O3 were higher than those for Pa-233, while the opposite was true on SiO2 and TiO2 nanoparticles, resulting in a significant fractionation between Th-234 and Pa-233 during their adsorption on nanoparticle surfaces. Among the selected nanoparticles, Fe2O3 had the highest fractionation factor between Th-234 and Pa-233 (F-Th/Pa) while SiO2 had the lowest, following the order of Fe2O3 > CaCO3 > Al2O3 > TiO2 > SiO2. In addition to the effect of chemical composition, the concentration of nanoparticles or micro-particles also significantly affected the partitioning of Th-234 or Pa-233 between dissolved and particulate phases, showing a strong particle concentration effect with a general decrease in log K-d values with increasing particle concentration. Interestingly, results from adsorption experiments with binary nanoparticles, containing both SiO2 and CaCO3, clearly demonstrated an increase in log K-d values of Pa-233 with increasing SiO2/CaCO3 ratios of the adsorbent, but a decrease in the fractionation factor between Th-234 and Pa-233. However, the enhanced adsorption of Pa-233 on SiO2 nanoparticles or the increased log K-d value of Pa-233 occurred only when the abundance of SiO2 reached 60% (in wt.) or higher. Thorium, on the other hand, was less sensitive to particle composition during its adsorption on nanoparticles in seawater. Thus, it seems that the Th/Pa ratios of oceanic particles could be largely controlled by the relative abundance of biogenic silica. Further studies are needed to examine the role of natural organic matter, which affects surface properties and chemical speciation of trace elements, in regulating the adsorption of radionuclides on nanoparticles. (C) 2014 Elsevier B.V. All rights reserved

Speciation and transformation of phosphorus and its mixing behavior in the Bay of St. Louis estuary in the northern Gulf of Mexico

Water samples were collected for measurements of dissolved, colloidal, and particulate inorganic and organic phosphorus (P) from the Bay of St. Louis estuary in the northern Gulf of Mexico during August 2008 and October 2009. Laboratory mixing experiments were also carried out using end-member river water and seawater to examine key processes and mechanisms controlling the behavior of P during estuarine mixing. Dissolved organic P (DOP) was the dominant species in the total dissolved P (TDP) pool in both lower (S 25) regions, while dissolved inorganic P (DIP) predominated in mid-salinity regions (S of 10 similar to 20) comprising up to 75% of the TDP. Both DIP and DOP behaved non-conservatively during estuarine mixing showing dramatic changes and transformation between different P species. The total particulate phosphorus (TPP) accounted for up to 85% of total phosphorus (TP = TDP + TPP) in the low-salinity areas but fell to about 38% in higher salinity regions. The quasi-negative correlation between TDP and TPP and the similarity in mixing behavior between field observations and laboratory experiments supported our hypothesis that physicochemical processes, such as dynamic repartitioning between water and particles or adsorption/desorption, are the predominant mechanisms controlling the biogeochemical cycling of P species in the Bay of St. Louis. River export fluxes of DIP could be significantly underestimated without the quantification of particulate P species, especially in more pristine river basins. The value of the distribution coefficient (in terms of logK(d)) ranged from 4.4 to 5.6 and decreased with increasing suspended particulate matter concentration and salinity, indicating that P is highly particle reactive and the presence of colloidal P may play an important role in the cycling of P in estuarine environments. Colloidal inorganic P (CIP) and colloidal organic P (COP), as quantified by an ultrafiltration permeation model, comprised 0-62% of the DIP and 34-93% of the DOP with the highest values in the river mouth area, suggesting a river source for colloidal P. The % CIP dropped to below the detection limit as salinity increased, whereas % COP first decreased but increased again with increasing salinity, reflecting different sources for CIP and COP in the lower estuary. The DOC/DOP ratio decreased rapidly with increasing salinity indicating a diagenetically older dissolved organic matter pool from the river and a dynamic change in sources and chemical speciation of P in the estuary. (C) 2012 Elsevier Ltd. All rights reserved.NGI/NOAA [09-NGI-13, 09-NGI-04]; National Science Foundation (NSF-OCE) [0850957]; Xiamen University; China Ministry of Education; University of Southern Mississipp

Distribution and source of transparent exopolymer particles in the northern Bering Sea

透明胞外聚合颗粒物(TEP)是海水中大量存在的黏性颗粒物质,它对于海洋颗粒物的聚集、有机碳的埋藏、食物网物质的传递、痕量金属的清除与迁出等均起着重要作用。本研究开展了夏季北白令海陆架、陆坡和海盆区透明胞外聚合颗粒物含量和分布的研究。结果表明,北白令海TEP含量介于34~628Mg/M3(XEQ)之间,其中陆架、陆坡和海盆区TEP的平均含量分别为240,145和83Mg/M3(XEQ),整体呈现由陆架向外海降低的趋势。在陆坡和海盆区,TEP含量随着深度的增加而降低,但在陆架近底层水中,观察到TEP高含量的特征,与近底层水高的TSM,POC相对应。TEP与荧光强度、TSM、POC等的关系分析显示,研究海域TEP存在两个来源,其一为海洋上层水体的浮游生物,其主要贡献于陆架上层、陆坡和海盆水体;其二为陆架沉积物的底栖生物,其通过沉积物再悬浮贡献于陆架近底层水。Transparent exopolymer particles(TEP) are large,sticky particles in marine environments,and play a significant role in particle dynamics,carbon export,food web energy transfer and scavenging of trace metals.Samples were collected from the northern Bering Sea during summer 2010 for measurements of TEP and other hydrographic parameters to examine the abundance,distributions and sources of TEP.Our results showed that TEP concentrations ranged from 34 to 628 mg/m3(Xeq).The averaged TEP concentrations in the shelf,slope and basin were 240,145 and 83 mg/m3(Xeq),respectively,showing a general decrease from the shelf to the basin.In the slope and basin areas,TEP concentrations decreased with the increasing depth.However,high concentrations of TEP were observed in the shelf bottom waters,coincided with the high values of TSM and POC.The correlations between TEP and fluorescence,TSM and POC suggested two sources of TEP in the northern Bering Sea:(1) in situ production from planktons in the upper water column,and(2) benthic biological processes in the sediments.High TEP concentrations in the shelf bottom waters was predominantly derived from sediment resuspension,which may have a potential effect on carbon biogeochemical cycle and scavenging of trace elements in shelf regions.中国第四次北极科学考察项目;海洋公益性行业科研专项(201105022-4);福建省自然科学基金项目(2009J06026

The distribution and chemical speciation of dissolved and particulate phosphorus in the Bering Sea and the Chukchi-Beaufort Seas

Water samples were collected from the Bering Sea and the Chukchi-Beaufort Seas during the 4th Chinese Arctic Research Expedition in summer 2010 to examine the abundance, spatial distribution and phase partitioning of phosphorus (P) between dissolved and particulate, inorganic and organic phases. Measurements of P species included dissolved inorganic P (DIP), dissolved organic P (DOP) and five particulate P species operationally defined by sequential extraction techniques. Inorganic P was generally the predominant form of both dissolved and particulate P, comprising on average up to 91卤13% of the dissolved phase and 72卤23% of the particulate phase in the study area. Concentrations of DIP in the water column of the Chukchi Sea and Bering Sea were considerably higher than those in the Beaufort Sea (>3渭M vs. ~1渭M), showing a strong influence of North Pacific inflow waters. The percentage of DOP in the dissolved P pool was generally higher in surface waters than deeper waters, and higher in the Chukchi Sea than in the Bering Sea, consistent with their difference in primary productivity and reflecting sources of DOP from the surface waters. Within the particulate P pool, the labile P and ferric bound P were the two predominant species, especially in the upper water column (3 bound P and detrital P were the two least abundant particulate P species. A positive correlation between labile particulate P and particulate organic carbon (POC) or particulate nitrogen (PN) was observed, where labile P concentrations decreased with increasing DIP concentrations and decreasing biological activity in the upper water column, indicating the contribution of labile particulate P from biological production. Labile P was an active component in regeneration of particulate P in the water column. The authigenic P was relatively abundant in deeper waters, especially in the Bering Sea, suggesting an active transformation between labile-P and authigenic P and a possible sink for P as authigenic particulate P in the deeper water column. In contrast to labile P, authigenic P, and organic P, the distributions of ferric-bound P and detrital P were mostly regulated by physicochemical processes, such as lateral transport and sediment resuspension. Therefore, different particulate P species could play a distinct role in biogeochemical cycling of P in the water column and understanding the detailed chemical and phase speciation of P should provide a better understanding of the dynamic cycling of P in the marine environment. 漏 2012 Elsevier Ltd

Application of the cross-flow ultrafiltration technique to the study of colloidal uranium, thorium, radium isotopes and organic carbon in seawater

建立了由预过滤装置、蠕动泵、中空纤维超滤膜（Ａｍｉｃｏｎ Ｈ１０Ｐ１０－２０，标 称截留分子量 １０ ＫＤａ）和连接管组成的错流超滤系统，利用荧光标记的 ４０ ＫＤａ葡聚 糖和已知放射性活度的２３４Ｔｈ示踪剂评估了超滤膜的截留和吸附性质，探讨了２３４Ｔｈ 在超滤过程中的渗透行为，考查了该系统用于实际海水样品时铀、钍、镭同位素和有 机碳的质量平衡状况，结果表明，１０ ＫＤａ中空纤维超滤膜对４０ ＫＤａ葡聚糖具有良 好的截留效率（８５％），而吸附损失率为 １８％．铀、钍、镭同位素和有机碳在超滤过程 中均达到极佳的质量平衡，回收率 Ｒ＝ ９５％～ ９８％，优于大多数文献报道的值． ２３４Ｔｈ在超滤过程中的渗透行为可以很好地用渗透模型加以描述．研究组分胶体态含量占“溶解”态含量的份额大小顺序如下：钍同位素、有机碳、镭同位素约等于铀同 位素，这与社为强颗粒活性元素、铀和镭为水溶性元素的地球化学性质相吻合． 【英文摘要】 A cross-flow ultrafiltration system, including a prefilter (0. 22 μm), a Masterflex pump and a polysulfone hollow fiber 10 KDa ultrafiltration membrane (Amicon H10P10-20), is evaluated for its feasibility in sampling colloidal uranium, thorium, radium isotopes and organic carbon (OC) in seawater. The retention characteristics and sorptive potential of the ic KDa ultrafilter are examined through laboratory experiments using a 4o KDa fluoresceintagged dextran and standard 234Th as tracers. The mass balance ...国家自然科学基金!（编号：49706069）;; 国家自然科学基金!（98－美014

Distribution, partitioning and mixing behavior of phosphorus species in the Jiulong River estuary

Chinese Natural Science Foundation [40906040, 41125020]; State Oceanic Administration of China [2010050012-3]; U.S. NSF [0850957]; Natural Science Foundation of Fujian Province [2011J01277]; Fundamental Research Funds for the Central Universities of ChinaSurface and bottom water samples were collected along a salinity gradient from the Jiulong River estuary during May 2010 to examine the distribution and mixing behavior of dissolved and particulate phosphorus (P) species. Particulate P was further fractionated into five operationally defined phases through a sequential extraction method. In addition to field studies, laboratory experiments were carried out to examine key processes regulating the distribution and partitioning of P during estuarine mixing. Dissolved inorganic P (DIP) was the main species in the total dissolved P (TDP) pool, comprising up to 83 +/- 3% at river end-member station and 32 +/- 21% at coastal stations. While the concentration of dissolved organic P (DOP) changed little with salinity, DIP concentrations varied dramatically between stations, especially in the low-salinity (S < 3) and high-salinity regions, indicating intensive removal/addition and transformation between P species in the water column. The predominance of DIP and low abundance of DOP reflected a profound influence of anthropogenic inputs from the Jiulong River. The total particulate P (TPP) contributed up to 70 +/- 10% of the total phosphorus (TP = TDP + TPP) in the low-salinity area, showing a quasi-negative correlation with DIP during early estuarine mixing (S < 3), but the TPP decreased sharply with salinity, comprising 39 +/- 19% of the TP pool in middle and higher salinity regions. River inputs, biological production (mostly for biogenic apatite and organic P), and repartitioning of P between dissolved and particulate (labile P) phases were major factors responsible for the dynamic variations in P species in the estuary. Deviation in results of laboratory mixing experiments from those of the field investigation indicated that, in addition to physicochemical and biological processes, additional end-member waters and sediment resuspension also play a role in controlling the mixing behavior and biogeochemical cycling of P in the Jiulong River estuary. Values of the distribution coefficient of P (in terms of logK(d)) were consistently high, but they were similar among stations with different salinities and had a poor correlation with suspended particulate matter concentration, likely due to the relatively long flushing time, elevated DIP, and lower colloidal effect in the Jiulong River estuary. Compared with results from early studies, elevated DIP from anthropogenic sources seemed to have altered the mixing behavior of P species in the estuarine environment. (C) 2013 Elsevier B.V. All rights reserved

北冰洋：生物生产力的“沙漠”？

利用14C吸收法、3H吸收法、234Th/238U不平衡法和210Pbex测年法分别测定了北冰洋的初级生产力、细菌生产力、颗粒有机碳输出通量及沉积物有机碳埋藏速率.结果表明,北冰洋水柱积分生产力介于3.8～197.1mmolC/m2·d,高于早期的报道值,其中楚克奇陆架区初级生产力水平高于深海盆地.积分细菌生产力与初级生产力的比值大于0.5,表明在北冰洋寒冷的水体中细菌活动并未受到明显限制.由234Th/238U不平衡获得的234Th亏损程度、溶解态与颗粒态234Th停留时间、颗粒有机碳的输出通量均证实,北冰洋深海盆地仍存在一定的颗粒清除、迁出作用.夏季期间楚克奇陆架沉积物有机碳埋藏速率为25～35 mmol C/m2·d,占水柱初级生产力的 59％～82％,表明有机碳的输送与埋藏是非常高效的.上述证据均表明,至少在夏季期间,北冰洋并非生物生产力极其贫瘠的海洋“沙漠”,它存在相对活跃的海洋碳循环过程,重新评估北冰洋在全球碳循环中的作用显得更为重要。本工作受中国首次北极科学考察基金;国家自然科学基金（批准号:40076024）资助