Benthic Oxygen Consumption and Organic Matter Turnover in Organic-poor, Permeable Shelf Sands

The high permeability of sediments and strong near-bottom currents cause seawater to infiltrate the surface layers of Middle Atlantic Bight shelf deposits. In this study, sandy sediment cores from 11 to 12 m water depth were percolated with filtered seawater on shipboard. Sedimentary oxygen consumption (SOC) increased non-linearly with pore water flow, approaching maximum rates of 120 mmol m⁻² d⁻¹ (May 2001) or 75 mmol m⁻² d⁻¹(July 2001). The addition of acetate to the inflowing water promptly enhanced the release of dissolved inorganic carbon (DIC) from the cores. DIC production rates were a linear function of acetate concentration, ranging from 100 to 300 mmol m⁻² d⁻¹ without substrate addition to 572 mmol m⁻² d⁻¹ with 100 mM acetate. The sediments also hydrolyzed a glucose pseudopolymer, and the liberated glucose prompted an increase of SOC. Our results suggest that decomposition rates of organic matter in permeable sands can exceed those of fine-grained, organic-rich deposits, when water currents cause advective interstitial flow, supplying the subsurface microbial community with degradable material and electron acceptors. We conclude that the highly permeable sand beds of the Middle Atlantic Bight are responsive within minutes to hours and efficiently operate as biocatalytical filters.     

塔克拉玛干沙漠腹地LAS和EC观测感热通量对比分析

利用2009年6月20日至7月3日塔克拉玛干沙漠腹地塔中地区地-气相互作用观测试验中的大孔径闪烁仪(LAS)和涡动相关仪(EC)观测资料,对LAS和EC在流动沙漠地区观测的感热通量差异进行了对比分析.结果表明:LAS和EC测得的感热通量变化趋势一致,两者有很好的相关性.总体来看,LAS的感热通量测量值大于EC测得的感热通量值.如果LAS和EC测量的允许差异|△H|≤50 W/m2时,LAS和EC测量结果无显著差异的频率达79%左右.因此,LAS完全适用于流动沙漠地区大尺度的感热通量的观测研究.     

涡动相关仪观测蒸散量的插补方法比较

涡动相关仪在长时间连续观测中,观测数据会有不同程度的缺失.应用6种不同的插补方法(平均昼夜变化法MDV,非线性回归方法NLR,动态线性回归方法DLR,查表法LUT,FAO-PM方法,HANTS方法)对北京密云站2007年涡动相关仪观测蒸散量数据进行了插补.结果表明:LUT方法在不同数据缺失时均得到较好结果(均方差小于8 W/m2);MDV和NLR方法更适合于短时间数据缺失的插补:DLR和FAO-PM方法在观测数据出现连续波动时插补结果较差.由LUT、DLR、NLR、HANTS、FAO-PM方法得到的年蒸散量分别为395.8 mm、409.9 mm、393.5 mm、390.7 mm、399.4 mm,差异在2.3～19.2 mm之间变化.对比分析了LUT方法得到的年蒸散量(潜热通量)与净辐射、降水量以及LAS观测潜热通量间的变化规律,表明插补结果合理.     

大孔径闪烁仪和涡动相关仪观测显热通量之间的尺度关系

利用北京昌平小汤山2002年、2004年涡动相关仪和大孔径闪烁仪的观测数据,借助解析足迹模型计算的源区,分析均匀、非均匀下垫面上涡动相关仪和大孔径闪烁仪观测显热通量之间的差异和关系.结果表明:地表的均匀与非均匀性质,直接影响涡动相关仪和大孔径闪烁仪观测的显热通量的差异大小.在分析均匀、非均匀地表上2种仪器源区重叠面积及重叠区域内足迹值大小与观测通量值之间的关系后,构建一个非均匀地表上2台涡动相关仪与1台闪烁仪观测通量之间的尺度关系式.     

Oxygen Consumption in Permeable and Cohesive Sediments of the Gulf of Aqaba

Oxygen profiles were measured in the sediments of the Gulf of Aqaba (Red Sea), an oligotrophic marine system affected by episodic seasonal flash floods and intense aeolian dry deposition. Sediment cores were retrieved from shallow (15–45 m), intermediate (250–561 m) and deep (700 m) water sites of south–north and east–west transects. Dissolved oxygen concentrations were measured simultaneously by using microelectrodes and microoptodes immediately after sampling and after transportation. Oxygen penetration depths were found to increase from 2 to 5 mm at the shallow water sites with sandy permeable sediments to 10–21 mm at the deeper sites with cohesive muddy sediments. This increase corresponds to decrease in oxygen diffusive fluxes at the sediment–water interface and oxygen consumption rates with depth. Oxygen consumption rates exhibit local maxima at the oxic–anoxic sediment boundary, which may be attributed to oxygen reduction coupled to oxidation of dissolved Fe(II) and Mn(II) at deep and intermediate water sites and of hydrogen sulfide at shallow water sites. Microelectrodes and microoptodes measurements of cohesive sediments from deep and intermediate water sites yielded similar results. By comparison, the microoptodes displayed more robust measurements than microelectrodes in sandy near-shore sediments. This was attributed to their flexible fiber structure that is less likely to break or to abruptly displace sand particles. After transportation of sediment cores from Eilat to Beer Sheva followed by ≤?24-h storage, no changes in oxygen fluxes and consumption rates were detected.     

Seasonal Composition of Benthic Macroinfauna Exposed to Hypoxia in the Northern Gulf of Mexico

Bottom-water hypoxia in the northern Gulf of Mexico has increased in severity (duration, frequency, and intensity) since the 1970s and has impacted the less-mobile benthos ever since. From September 2003 to October 2004, the macrobenthic density, species richness, community composition, and vertical distribution were studied at a frequently hypoxic station, C6B (28°52.10′ N and 90°28.00′ W). The polychaete-dominated community was approximately three times less dense and diverse in post-hypoxic months compared to pre-hypoxic months. The lowest oxygen concentrations in July 2004 did not significantly affect the infaunal community as predicted; rather, the response was observed 1 month later after a longer, low-oxygen exposure. The opportunistic, hypoxia-tolerant polychaete, Paraprionospio pinnata, population increased in July 2004 when other common species decreased, thereby maintaining pre-hypoxic densities. Determining the duration and severity of hypoxia prior to sampling rather than at the time of sampling helps to better understand benthic community responses to hypoxia.     

Progress in the Energy Closure of Eddy Covariance Systems

The sum of turbulent fluxes measured by the eddy-covariance method is often 10%~30% lower than available energy (i.e., the net radiation minus the ground heat flux). This systematic bias in the EC method is called the "EC energy closure problem" and has been one of the biggest challenges in micrometeorology. In the past decades, lots of studies have focused on this problem and have found extensive knowledge about it. In this paper, we introduced the reasons to the EC energy closure problem and systematically summarized the understandings on this problem with a discussion regarding the merits and limitations of possible correction methods. Compared with previous overview studies, our study focused on the methods and progresses on the EC energy closure problem using the Large Eddy Simulation (LES). The existing problem, e.g., the lack of high quality and high spatial density of "surface true fluxes" observations (e.g., matric observations), the failure of fully emulating the EC using the LES and how to mechanistically understand that large eddies affect turbulence structures and lead to non-closure problem, hinder the further understanding of the EC energy closure problem. Thus, in the future, focus should be put on the mechanistic understanding of how large eddies affect the non-closure problem and some dense field observations to obtain the high quality "surface true fluxes".     

典型森林生态系统碳交换的机理模拟及其与观测的比较研究

CEVSA模型是一个基于生理生态过程模拟植物—土壤—大气系统能量交换和水碳氮耦合循环及其对环境变化响应和适应的机理模型,在区域和全球尺度上得到广泛应用,但缺乏在生态系统尺度上的验证。本研究对CEVSA模型中碳循环关键过程的定量表达进行了重要改进：将模型的模拟时间步长由“旬”改为“日”;增加了物候参数化的子程序;调整了生物量的分配方案;基于碳平衡模拟叶面积指数的季节动态等。分别使用改进前后的CEVSA模型模拟了3类典型森林生态系统碳交换的季节动态,模拟的结果与通量观测进行了比较分析。结果表明,改进后的CEVSA模型能更好地模拟不同类型森林生态系统碳交换的季节动态,但在不同生态系统的不同时段,模型模拟的结果与通量观测相比还有一定的偏差,模型在碳交换关键过程对环境变化的响应和适应,尤其是针叶林光合作用对温度变化的响应和适应,以及生态系统对高温和水分亏缺的响应和适应等方面的模拟还需要进一步的改进和验证。     

Development of Productivity Models for the Northern Gulf of Mexico Based on Oxygen Concentrations and Stable Isotopes

Oxygen concentrations have been used for decades to estimate primary production (P) and respiration (R) in aquatic ecosystems. Yet, this approach cannot separate the effects of biological and physical processes affecting oxygen dynamics; therefore, it is now often complemented with the analysis of stable oxygen isotopes. Existing algorithms for calculating primary production and P/R have been developed for closed systems and steady-state open systems. None of these formulations are applicable to productive aquatic ecosystems where diurnal changes in oxygen concentrations and isotope values are usually large. Here, we describe a novel P/R model that includes algorithms for air–sea gas exchange and is not constrained by steady-state conditions. Our objective was to test model sensitivity to variations in input parameters for values commonly observed in coastal waters of the northern Gulf of Mexico. The model was highly sensitive to variations in fractionation factor for respiration (ε) but less sensitive to variations in wind speed, oxygen isotope values of source-water, or oxygen flux through the picnocline. This model is easily transferable to other coastal ecosystems, with a caveat that system-specific values for ε are needed to obtain realistic estimates of P/R.     

Benthic Phosphorus Dynamics in the Gulf of Finland, Baltic Sea

Benthic fluxes of soluble reactive phosphorus (SRP) and dissolved inorganic carbon (DIC) were measured in situ using autonomous landers in the Gulf of Finland in the Baltic Sea, on four expeditions between 2002 and 2005. These measurements together with model estimates of bottom water oxygen conditions were used to compute the magnitude of the yearly integrated benthic SRP flux (also called internal phosphorus load). The yearly integrated benthic SRP flux was found to be almost 10 times larger than the external (river and land sources) phosphorus load. The average SRP flux was 1.25?±?0.56?mmol?m^?2?d^?1 on anoxic bottoms, and ?0.01?±?0.08?mmol?m^?2?d^?1 on oxic bottoms. The bottom water oxygen conditions determined whether the SRP flux was in a high or low regime, and degradation of organic matter (as estimated from benthic DIC fluxes) correlated positively with SRP fluxes on anoxic bottoms. From this correlation, we estimated a potential increase in phosphorus flux of 0.69?±?0.26?mmol?m^?2?d^?1 from presently oxic bottoms, if they would turn anoxic. An almost full annual data set of in situ bottom water oxygen measurements showed high variability of oxygen concentration. Because of this, an estimate of the time which the sediments were exposed to oxygenated overlying bottom water was computed using a coupled thermohydrodynamic ocean?Csea and ecosystem model. Total phosphorus burial rates were calculated from vertical profiles of total phosphorus in sediment and sediment accumulation rates. Recycling and burial efficiencies for phosphorus of 97 and 3%, respectively, were estimated for anoxic accumulation bottoms from a benthic mass balance, which was based on the measured effluxes and burial rates.     

海气CO2通量与涡动相关法应用研究进展

海气CO2交换速率及通量的测定、估算是碳循环研究的重要内容。测定、估算海气CO2交换速率及通量有多种方法,但都有其局限性,准确定量海气碳通量的大小仍是碳循环研究的热点问题。当前应用最广泛的海气界面分压差法需要通过间接手段测定海气交换速率,交换速率和风速的关系基于经验公式,不确定性较大;而涡动相关法（eddy covariance / eddy correlation）是一种直接测量方法,理论上不需要任何经验参数,在近年来取得较大进展。综述了近年来国内外CO2海气交换速率及通量的测定、估算方法的研究进展,并对各种方法的原理、应用、优缺点进行了分析,着重介绍了涡动相关法测量CO2通量的原理、国内外研究现状、相对传统方法的优缺点以及发展前景等,对未来海气CO2交换速率及通量研究发展趋势和研究方法作了展望。     

The distribution of dibenzothiophenes in Gulf of Mexico sediments

Sediment extracts from 81 piston cores taken in water depths between 70 and 1200 m on the Gulf of Mexico continental shelf and slope were analyzed for dibenzothiophenes by capillary gas chromatography with flame photometric detection (FPD). The major aromatic sulfur compounds detected were dibenzothiophene; methyl, ethyl and propyl dibenzothiophenes; two unidentified sulfur compounds; and a series of benzothiophenes. In general, benzothiophenes (BTs) were detected at only trace levels though this may be due to loss during the analysis. Dibenzothiophenes (DBTs) concentrations ranged from <1 to 1725 ng/g, with an average of 139 ng/g. Vertical distributions generally showed significant increases in DBTs concentrations with depth. DBTs distributions in sediment extracts were similar to oils produced in the northern Gulf of Mexico. Variations from this composition may be due to microbial degradation in the near subsurface. The vertical and molecular distribution of DBTs suggests that the source of DBTs in the Gulf of Mexico sediments studied is upward migrating petroleum. Two unidentified compounds are speculated to be derivatives of DBTs, caused by indigenous microbial activity. This study suggests that DBTs may be useful for detecting seepage from deeper, more mature, source rocks and/or reservoired petroleum.     

Contaminants in sediments from the central Gulf of Mexico

Surface sediment samples at 89 locations and 300-cm cores from 43 sites in the Mississippi Sound were examined for evidence of pollutant impact upon this coastal environment. Chemical variables determined were total organic carbon, Kjeldahl nitrogen, phenols, and hydrocarbons. Values of these pollutant indicators were about the same or lower in Gulf of Mexico samples compared to Missippi Sound sediments and considerably lower than those from rivers and bays emptying into the sound, indicating limited impact from sites of pollutant sources into the sound. Concentrations of sedimentary pollutants peaked in the Pascagoula River where levels of total organic carbon (TOC), Kjeldahl nitrogen (TKN), phenols, and hydrocarbons exceeded sound values by one to three orders of magnitude. Analysis of cores shows pollutant intrusion to sediment strata predating industrial development. The level of pollution varies from site to site but fortunately is only serious at localized sites within the sound.     

Numerical analysis of meteotsunamis in the Northeastern Gulf of Mexico

Natural Hazards - Although relatively rare, meteotsunamis are capable of causing coastal infrastructure damage and casualties. Analyses of water level and meteorological data in the U.S. show that...     

Use of Shallow Lagoon Habitats by Nekton of the Northeastern Gulf of Mexico

We compared nekton use of prominent habitat types within a lagoonal system of the northeastern Gulf of Mexico (GoM). These habitat types were defined by combinations of structure (cover type) and location (distance from shore) as: Spartina edge (≤1 m from shore), Spartina (3 m from shore); Juncus edge (≤1 m from shore); seagrass located 3, 5, and 20 m from shore; and shallow non-vegetated bottom at various distances from shore. Although seagrass and Spartina edge sites differed little in environmental characteristics, the density and biomass of most abundant taxa, including pink shrimp (Farfantepenaeus duorarum), were higher in seagrass. Most species within seagrass and Spartina did not differ in abundance or biomass with distance from shore. Our study revealed a shift in peak habitat use in the northeastern GoM to seagrass beds from the pattern observed to the west where nekton is concentrated within shoreline emergent vegetation.     

Petroleum drilling and production operations in the Gulf of Mexico

Decades of offshore and inland petroleum drilling and production in the Gulf of Mexico and on the Gulf coast have provided the much needed energy and chemical feedstocks to the nation, and also have made an impact on the environment in the area. Our study showed deposits of contaminated sediment on the ocean floor around offshore platforms, old reserve pits, and dump sites next to many surface facilities and compressor stations. The substances found on the ocean floor and in dump sites are simple or emulsified mixtures of silt, hydrocarbons, and water. The cleaning of the ocean floor and pits is an economic and technical challenge. Hydrocarbons are from crude oil and chemical additions for various operational necessities, including additions of biocides, corrosion inhibitors, antifreezes, and coagulants. When the new government regulations lower the allowable maximum total organic carbon level to the 50 ppm range, these hydrocarbons can no longer be ignored by drilling and production operators.     

Benthic Respiration and Inorganic Nutrient Fluxes in the Estuarine Region of Patos Lagoon (Brazil)

In situ benthic flux chamber experiments were performed during late austral spring and early summer of 1996 at eleven nearshore locations in the southern Patos Lagoon, Brazil. The Patos Lagoon is the largest lagoonal system in South America and is a very important nursery ground for local fin fish and shell fish fisheries. These are the first benthic flux measurements made in Patos Lagoon and they suggest that remineralizationwithin the sediments may dominate the recycling of organic matter and nutrients in thelagoon. Measured oxygen benthic fluxes (45–160 mmol m^-2 d^-1) are sufficientto remineralize reported mean water column carbon fixation while phosphate and fixednitrogen benthic fluxes (-0.4–2 and -1.1–4.2 mmol m^-2 d^-1, respectively)are sufficient to supply 100% and 25% of the required water column nutrient demand,respectively. Although of limited areal and temporal coverage, these initial studiesdemonstrate that sediments play a major role in the metabolism and nutrient cyclingwithin the Patos Lagoon Estuary and that future studies of lagoonal biogeochemistrymust consider exchange with the bottom.     

Examination of Winter Circulation in a Northern Gulf of Mexico Estuary

Numerical model experiments were conducted to examine how estuarine circulation and salinity distribution in the Calcasieu Lake Estuary (CLE) of southwest Louisiana respond to the passage of cold fronts. River runoff, local wind stress, and tides from December 20, 2011, to February 1, 2012, were included as input. The experiments showed an anticyclonic circulation in the eastern CLE, a cyclonic circulation in West Cove, and a saltwater conduit in the navigation channel between these circulation cells. Freshwater from the river and wetlands tends to flow over the shallow shoals toward the ocean, presenting a case of the conventional estuarine circulation with shallow water influenced by river discharge and with weak tidally-induced motion, enhanced by wind. The baroclinic pressure gradient is important for the circulation and saltwater intrusion. The effect of remote wind-driven oscillation plays an important role in circulation and salinity distribution in winter. Unless it is from the east, wind is found to inhibit saltwater intrusion through the narrow navigation channel, indicating the effect of Ekman setup during easterly wind. A series of north-south oriented barrier islands in the lake uniquely influenced water level and salinity distribution between the shallow lake and deep navigation channel. The depth of the navigation channel is also crucial in influencing saltwater intrusion: the deeper the channel, the more saltwater intrusion and the more intense estuarine circulation. Recurring winter storms have a significant accumulated effect on the transport of water and sediment, saltwater intrusion, and associated environmental and ecosystem effects.     

Distribution and Fluxes of Calcium Carbonatealong the Continental Margin in the Gulf of Biscay

Compositions of major components in suspended matter,collected by centrifugation, in situ pumping andsediment traps, in the Gulf of Biscay during the OMEXproject were determined and compared. The resultsshow a strong and rapid decrease in the concentrationof biogenic fraction in the upper 200 m of the watercolumn which may be attributed to the preferentialremoval of this component due to the production offaecal pellets and to the formation of marine snow. Concurrent decrease with depth of the organic andinorganic carbon contents demonstrate the importanceof the respiration of organic matter and thedissolution of calcium carbonate in the oceanic carboncycling. Lithogenic and carbonate fluxes across thecontinental slope in the Goban Spur area wereevaluated based on sediment trap records. The rate ofproduction of calcium carbonate in the surface waters(100 g CaCO3 m-2y-1), deduced from theprimary production measurements, is much largercompared to the fluxes of this component observed inthe sediment traps (5–21 g CaCO3 m-2y-1)and to its rate of burial (9–31 gCaCO3 m-2y-1). It strongly suggeststhe occurrence of carbonate dissolution, even inwaters oversaturated with respect to the mineral phaseconsidered. This is likely to be associated with therespiration of organic matter within the faecalpellets, or at the surface of biogenic calcite oraragonite     

Land-derived organic matter in surface sediments from the Gulf of Mexico

Lignin oxidation products and ¹³C/¹²C ratios were compared as indicators of land-derived organic matter in surface sediments from the western Gulf of Mexico. Whole sediments were reacted with cupric oxide to yield phenolic oxidation products that indicated the types and relative amounts of the lignins that were present.Measurements of lignin concentration and carbon isotope abundances both indicated a sharp offshore decrease of land-derived organic matter in most areas of the western Gulf. This decrease results primarily from mixing of terrestrial and marine organic matter. The terrestrially derived material in these sediments has a lignin content similar to that of grasses and tree leaves. Flowering plants contribute most of the sedimented lignin compounds. These lignins apparently occur in the form of well-mixed plant fragments that are transported to sea by rivers and deposited primarily on the inner continental shelf.