Total organic carbon distribution and budget through the Strait of Gibraltar in April 1998

In order to investigate total organic carbon (TOC) exchange through the Strait of Gibraltar, samples were taken along two sections from the western (Gulf of Cádiz) and eastern (Western Alboran Sea) entrances of the Strait and at the middle of the Strait in April 1998. TOC was measured by using a high-temperature catalytic oxidation method. The results referenced here are based on a three-layer model of water mass exchange through the Strait, which includes the Atlantic inflow, Mediterranean outflow and an interface layer in between. All layers were characterised by a decrease of TOC concentrations from the Gulf of Cádiz to the Western Alboran Sea: from 60–79 to 59–66 μM C in the Atlantic inflow and from 40–60 to 38–52 μM C in the Mediterranean waters, respectively. TOC concentrations in the modified North Atlantic Central Water varied from 43 to 55 μM C. Intermediate TOC values were measured in the interface layer (43–60 μM C). TOC concentrations increased from the middle of the Strait towards continents indicating a contribution of organic carbon of photosynthetic origin along Spain and Morocco coasts or TOC accumulation due to upwelling in the northeastern part of the Strait. Our results indicate that the short-term variability caused by the tide greatly impacts the TOC distribution, particularly in the Gulf of Cádiz. The TOC input from the Atlantic Ocean to the Mediterranean Sea through the Strait of Gibraltar varies from 0.9×10⁴ to 1.0×10⁴ mol C s⁻¹ (or 0.28×10¹² to 0.35×10¹² mol C year⁻¹, respectively). This estimate suggests that the TOC inflow and outflow through the Strait of Gibraltar are two and three orders of magnitude higher than reported via the Turkish Straits and Mediterranean River inputs.     

Fortnightly and monthly variability of the exchange through the Strait of Gibraltar

The fortnightly and monthly variability of the exchange through the Strait of Gibraltar has been studied from two simultaneous five-month long moored datasets, at Camarinal Sill and the East Section. The study focuses on the M_sf and M_m tidal components and their role for the subinertial exchange. A significant monthly signal is observed in the upper layer transport. Also, a significant fortnightly signal is observed in the lower layer transport, which minimum (maximum flow toward the Atlantic) takes place approximately on spring tides. In consequence the net transport has both signals, with maximum taking place during neap tides and a small monthly inequality. Fortnightly and monthly variability in the interface depth is also observed at Camarinal Sill, the interface being deeper on neap and shallower on spring tides. At the East Section the interface depth signals are not significant.The subinertial variability of the transports is separated in two contributions. The first one is called quasistatic transport and arises from the subinertial fluctuations of currents. The second contribution, called tidally rectified transports, arise from the non-linear correlation of currents and interface depth at tidal frequencies. The tidally rectified transports are important at Camarinal but not at the East Section. An apparent contradiction between the fortnightly signals of the subinertial currents and subinertial transports is resolved when the fortnightly signal of the tidally rectified transports are considered. The fortnightly signal of the quasistatic and tidally rectified transports mutually cancel in the upper layer, but not in the lower layer where the rectified transports dominate. A simple model for the spring-tide mixing forcing accounts for the fortnightly variability of the lower layer quasistatic transports but underestimates it for the upper layer. Finally, the observed lower layer transport is compatible with the hydraulic control condition at Camarinal Sill except for certain periods during intense spring tides.     

Estimation of the transports through the Strait of Gibraltar

An acoustic doppler current profiler (ADCP) is used to measure the currents and estimate the transports over the Camarinal Sill at the Strait of Gibraltar. The deepest measurements of the ADCP compare well with an underlying conventional current meter. The exchange interface between the Atlantic and the Mediterranean water is defined as the depth of the maximum vertical shear. The mean depth of the shear interface is 147 m. The time series of the depth of the interface and the currents are used to estimate the transports across the Strait. The resulting values are 0.78 Sv for the Atlantic inflow and −0.67 Sv for the Mediterranean outflow. The time series of the shear interface include fortnightly oscillations of 19 m. The time series of the transports are compared with the pressure and sea level difference records across the Strait. Linear multiple regression is used to estimate the (statistical) contribution of each parameter on the variation of transports. The cross strait sea level difference is well correlated with the Atlantic inflow and accounts for 57% of the variability of the transport records which improves to 78% when the fortnightly and monthly cycles are included in the linear regression. The Mediterranean outflow is best correlated with the along strait sea level difference which accounts for only 10% of the variability of the transport record. Again the addition of the M_sf and the MM cycles improves the percentage of the variance accounted for to 37%. The local, along strait wind component is significantly correlated with, both the Atlantic inflow and the across strait sea level difference.     

Biogeochemical patterns in the Atlantic Inflow through the Strait of Gibraltar

The effects of tidal forcing on the biogeochemical patterns of surface water masses flowing through the Strait of Gibraltar are studied by monitoring the Atlantic Inflow (AI) during both spring and neap tides. Three main phenomena are defined depending on the strength of the outflowing phase predicted over the Camarinal Sill: non-wave events (a very frequent phenomenon during the whole year); type I Internal wave events (a very energetic event, occurring during spring tides); and type II Internal wave events (less intense, occurring during neap tides).During neap tides, a non-wave event comprising oligotrophic open-ocean water from the Gulf of Cádiz is the most frequent and clearly dominant flow through the Strait. In this tidal condition, the inflow of North Atlantic Central Water (NACW) provides the main nutrient input to the surface layer of the Alboran Sea, supplying almost 70% of total annual nitrate transport to the Mediterranean basin. A low percentage of active and large phytoplankton cells and low average concentrations of chlorophyll (0.3–0.4 mg m⁻³) are found in this tidal phase. Around 50% of total annual phytoplankton biomass transport into the Mediterranean Sea through the Strait presents these oligotrophic characteristics.In contrast, during spring tides, patches of water with high chlorophyll levels (0.7–1 mg m⁻³) arrive intermittently, and these are recorded concurrently with the passage of internal waves coming from the Camarinal Sill (type I internal wave events). When large internal waves are arrested over the Camarinal Sill this implies strong interfacial mixing and the probable concurrent injection of coastal waters into the main channel of the Strait. These processes result in a mixed water column in the AI and can account for around 30% of total annual nitrate transport into the Mediterranean basin. Associated with type I internal wave events there is a regular inflow of large and active phytoplankton cells, transported in waters with relatively high nutrient concentrations, which constitutes a significant supply of planktonic resources to the pelagic ecosystem of the Alboran Sea (almost 30% of total annual phytoplankton biomass transport).     

台湾海峡1997年夏季和1998年冬季两航次颗粒有机碳研究

1997～1998年台湾海峡两个航次的数据表明,颗粒有机碳(POC)的平均含量为0．120±0．009mg/dm3,表层POC浓度在夏季和冬季分别存在几个高值区。POC在随深度变化的剖面分布图中,最大值出现在10m层,底层水明显受再悬浮影响,这一剖面的变化规律普遍存在于整个海区及不同季节。夏季POC的深度变化幅度要显著大于冬季,这与垂直混合作用有关。POC与Chl－a相关性较差,暗示以Chl－a估算浮游植物的不确定性及POC产生及来源的复杂性。     

Total inorganic carbon in sea ice

The method proposed for determining the total inorganic carbon (TC) concentrations in sea ice (Arctic region, North Pole-35 expedition) based on the measurement of the total alkalinity (TA) and the pH in the melt waters without the CO₂ exchange with the atmosphere is considered. It is shown that the TC/Sal and TA/TC values through the entire ice section remain similar to these parameters in the subice water. The surface snow and the uppermost ice layers are characterized by elevated TA/TC values, which indicate the reaction Ca²⁺ + 2HCO₃⁻ = ↓CaCO₃ + ↑CO₂ + H₂O. The release of CO₂ to the atmosphere due to the decomposition of calcium hydrocarbonate is as high as ∼20 mmol/m². The meltwater of the examined ice is undersaturated with CO₂, which may result in a sink of atmospheric CO₂ (∼30 mmol/m²).     

Modelling of seasonal exchange flows through the Dardanelles Strait

The Dardanelles Strait is a remarkable example of a long, narrow, shallow, and strongly stratified strait with bidirectional exchange that is governed by both baroclinic and barotropic forcing with a wide spectrum of variability. A three-dimensional free surface primitive equation model is applied to study seasonal hydrodynamics variability in this strait. The calculated vertical structure of temperature, salinity, and velocity fields agrees well with available survey data. Seasonal monthly values of the volume exchange at the Aegean and Marmara exits are estimated. It is found that the seasonal exchange dynamics is governed by the turbulent friction and entrainment at the Nara Passage area. The mean annual water transport in the upper layer is increased by 80% after the Nara Passage. About 25% of water entering in the Dardanelles bottom layer reaches the Marmara Sea in winter, and 50% reaches it in summer. The estimate of the Dardanelles hydrodynamics according to hydraulic and viscous–advective–diffusive regime classification shows significant deviation from the two-layer hydraulic asymptotic. However, according to three-layer hydraulic theory, the flow is found to be critical in the Nara Passage area.     

台湾海峡南部夏季的颗粒有机碳

根据2004年夏季、2005年夏季和2006年夏季3个航次观测的颗粒有机碳(POC)数据,表层POC含量的分布表现出近岸高、远岸低的特点,表层和次表层POC含量的高值区出现在东山以东以及南澳附近上升流区。沿岸流较强的2005年和2006年航次具有相对丰富的总悬浮颗粒物(TSM)含量。浮游植物是该区POC的主要来源。各航次的POC含量与叶绿素a(Chl a)含量正相关,所有航次统计的Chl a/POC与Chl a呈正相关,上升流区Chl a/POC偏小,上升流较强的航次高Chl a区的Chl a/POC也偏小,反映了上升流与高营养转换效率浮游生物生态在空间和时间上的联系。根据Chl a/POC~Chl a关系图判断,台湾海峡南部海域1988年、1998年和2004年夏季航次的浮游生物营养转换效率受到相对抑制,而在上升流信号较强的2005年和2006年夏季航次,上升流区的浮游生物高营养转换效率状态得以强化。各航次的POC含量和Chl a/POC比值与TSM含量正相关,POC/TSM比值与TSM负相关,沿岸流带来的陆源悬浮颗粒物通量波动,并没明显干扰台湾海峡南部以海洋浮游生物生态主导的颗粒有机碳生物地球化学循环格局。     

Non-linear interaction between tidal and subinertial barotropic flows in the Strait of Gibraltar

The present work establishes clear relationships of the amplitude and phase variation of the barotropic M₂ signal in the velocity of the current with the barotropic subinertial flow in the Strait of Gibraltar. The analytical procedure is applied on data from Gibraltar Experiment in order to obtain barotropic subinertial series and the amplitude and phase variation of the M₂ signal series involves harmonic analysis, empirical orthogonal function analysis and complex demodulation. In addition, cross-spectral analysis has been applied to study these relationships, concerning which non-linear interaction between M₂ and the subinertial oscillation is proposed as the responsible physical mechanism. An analytical solution characterizing this type of non-linear interaction is offered in explanation of the experimental results.     

Metal fluxes through the Strait of Gibraltar: the influence of the Tinto and Odiel rivers (SW Spain)

A large set of new data concerning dissolved metal concentrations has been acquired in the Gulf of Cadiz and in the Strait of Gibraltar from 1996 to 1999. These data, associated with models (hydrodynamic, tracer advection–dispersion and mixing), have been used to assess the influence of rivers draining the South Iberian Pyrite Belt on the Gulf of Cadiz and on the Atlantic inflow in the Strait of Gibraltar.Metal concentrations in surface waters from the Gulf of Cadiz are maximal near the mouth of the Tinto/Odiel rivers with values exceeding 50 nmol/kg (Mn), 5 nmol/kg (Ni), 30 nmol/kg (Cu), 100 nmol/kg (Zn), 0.9 nmol/kg (Cd) and 45 nmol/kg (As). From the Tinto/Odiel river, a plume of contamination follows the coast in the direction of the Strait of Gibraltar. The computation of a tracer advection–dispersion model confirms that the coastal currents carry the metals discharged from the Tinto and Odiel to the Strait of Gibraltar.From temperature–salinity and metal–salinity plots, four water masses can be recognised in the Gulf of Cadiz and in the Strait of Gibraltar: North Atlantic Surface Water (NASW), North Atlantic Central Water (NACW) and metal-enriched Spanish Shelf Waters from the Gulf of Cadiz (SSW). The Mediterranean Outflow Water (MOW) is also clearly seen at depths greater than 300 m.The chemical characteristics of these various water masses have been used in a mixing model to evaluate their relative contribution to the Atlantic inflow through the Strait of Gibraltar. These contributions are seasonally variable. In June 1997, the contribution was: 80±20%, 5±5% and 15±10% for NASW, NACW and SSW, respectively. In September, the SSW contribution was apparently negligible.Finally, these relative contributions allow the evaluation of the metal fluxes in the Strait of Gibraltar. The presence of SSW in the Strait increases the metal flux to the Mediterranean Sea by a factor of 2.3 (Cu), 2.4 (Cd), 3 (Zn) and 7 (Mn). It does not modify significantly As and Ni fluxes.     

A sediment and organic carbon budget for the greater Strait of Georgia

Recent efforts to construct global ocean budgets for carbon have recognized the importance of continental margins. In this study, we constructed budgets for the Strait of Georgia, a temperate, North American west coast basin that receives the inflow of one of the world's major rivers. Drawing from published and unpublished data, we have estimated the magnitude of the various sources and sinks of fresh water, sediment and organic carbon.The Fraser River is the dominant source of fresh water and particles to the strait, contributing approximately 73% of the 158×10⁹ m³ year⁻¹ of water and 64% of the 30×10⁹ kg year⁻¹ of particles. Other rivers supply most of the remainder, while rain, groundwater and anthropogenic sources of water and particles are negligible in comparison. Fresh water escapes the Strait of Georgia through Juan de Fuca Strait, but particulate inputs are approximately balanced by sedimentation within the greater Strait of Georgia, implying almost complete trapping of particles.Dissolved and particulate organic carbon are derived mainly from in situ primary production (855×10⁶ kg year⁻¹) and from the Fraser River (550×10⁶ kg year⁻¹). Other rivers contribute 200×10⁶ kg year⁻¹ of organic carbon, and anthropogenic sources (ocean dumping, sewage, pulp mills and aquaculture) a further 119×10⁶ kg year⁻¹. Particulate organic carbon is predominantly buried (428×10⁶ kg year⁻¹) or oxidized (90×10⁶ kg year⁻¹) in the sediments of the strait. About 70% of the organic carbon that enters or is produced in the strait is dissolved. Most of the dissolved organic carbon is oxidized within the strait (784×10⁶ kg year⁻¹), but the remainder (400×10⁶ kg year⁻¹) is exported to the Pacific Ocean. Although the particulate organic carbon budget by itself implies net autotrophy, dissolved organic carbon oxidation may make the Strait of Georgia slightly net heterotrophic.     

Mediterranean outflow through the Strait of Gibraltar since 18,000 Years B.P.: Mineralogical and geochemical arguments

Data obtained from mineralogical and geochemical analyses of piston and gravity cores, recovered from an area off Lisbon (Portugal) to the Alboran Sea (Mediterranean), serve as a basis for better understanding the past 18,000 years of hydrological exchanges at Gibraltar. Tracers used in this study are smectite, kaolinite, Ta, Th, La. One of the primary sources of particles both into and out of the Mediterranean is the Guadalquivir River. These particles are transported back into the Atlantic in the Mediterranean outflow water, and deposited along the Iberian slope. No evidence for reversal of this outflow current was found in those cores, since 18,000 years B.P.     

渤海海峡冬季表层海水中溶解无机碳分布特征分析

根据2010 年2 月—2010 年3 月的调查数据, 探讨了冬季渤海海峡及其附近表层海水中溶解无机碳体系的分布特征。结果表明: 表层水体中TA、DIC 和HCO₃^- 的浓度分布总体上呈现出海峡西南部高东北部低的分布趋势。西南部出现的高值区, 与该区域靠近莱州湾, 受莱州湾水体污染影响有关。调查海域TA 与表层水的温度相关性明显, pH 与叶绿素的相关性较高。水温和Chl-a 浓度是影响水体中无机碳体系分布变化的重要因素。其中, 水温对HCO₃^- 的影响要明显强于DIC。海峡南北两侧水体交换的差异, 是导致海峡南部东西两端无机碳体系各参数监测数值的差异明显大于海峡北部的主要原因。     

南日群岛东部海域岩芯沉积物有机碳含量和δ13CTOC值的变化特征及古气候环境意义

2008年在南日群岛东部海域用钻机采集长度为1 004 cm的岩芯样品,测试沉积物中总有机碳（TOC）含量、稳定碳同位素比值（δ13CTOC）、碳氮比值（C/N）、碳酸盐含量以及14C数据,分析其垂直剖面上的变化特征,阐明其沉积环境和古气候的指示意义.沉积物TOC含量变化范围为0.44%～0.74%,垂直剖面上总体显示出末次冰期和全新世中期TOC含量较高,全新世早期相对稳定,而全新世中后期TOC波动范围明显增大.C/N值在5.3～14.9之间变化,平均值为8.1;δ13CTOC值范围为-23.07‰～-21.04‰,表明沉积物中的有机质以海洋自生为主,同时混有部分陆源有机质.碳酸盐含量在3.3%～10.9%之间.TOC含量、C/N比值、δ13CTOC值在岩芯垂直剖面上具有很好的相关性.14C测年数据以及各要素测值在垂直剖面上的变化特征表明：自11 250 aBP以来该海域附近古气候有可能经历了以下4个演化阶段：①11 500～9 000 aBP期间气候寒冷、海平面下降,采样点可能为浅水区或潮间带;②9 000～8 000 aBP期间为升温期,气候由寒冷转向温暖;③8 000～4 300 aBP期间,为相对稳定的暖湿期,在后期气候出现小幅的波动;④4 300 aBP至今,气候进入明显的周期性波动期,暖湿和干冷气候多次交替变化;4 300～3 000 aBP期间为相对寒冷的时期;3 000～1 800 aBP期间为较稳定温暖期,1 800～1 000 aBP期间气温快速降低,标志着研究区进入一个新的寒冷阶段,但是自1 000 aBP以来,气候又再次出现转暖的趋势.     

Effect of the along-strait wind on the volume transport through the Tsushima/Korea Strait in September

Recent investigation suggests that volume transport through the Tsushima/Korea Strait often has double peaks during the summer to autumn period with decreasing transport in September. The satellite-observed wind changes from weak northwestward (across-strait) in summer to strong southwestward (along-strait) in early autumn (September) in the strait. Such a strong along-strait wind is related to tropical cyclones, which frequently pass through the East China Sea in September. The effect of the along-strait wind component on the transport variation is examined using a three-dimensional numerical model. The simulated volume transport through the Tsushima/Korea Strait shows realistic seasonal and intra-seasonal variations. According to sensitivity experiments on local winds, the transport variations in September are mainly generated by strong along-strait (southwestward) wind rather than weak across-strait wind. The strait transport responds to the along-strait wind (southeastward), which produces a sea level increase along the Korean coast, resulting in the geostrophic balance across the strait. The transport minimum through the Tsushima/Korea Strait in September can be determined by the combination of the across-strait geostrophic and along-strait ageostrophic balances. The Editor-in-Chief does not recommend the usage of the term “Japan/East Sea” in place of “Sea of Japan”.     

渤海海峡冬季无机碳的立体分布特征及其源汇变化

根据2010年2月至2010年3月对渤海海峡3个断面39个站位表层、10 m层和30 m层水体中盐度、水温、叶绿素a以及无机碳等参数的测定数据,分析了该季节溶解无机碳的分布特征以及源汇变化状况,探讨了影响其分布的主要因素。结果显示,调查期间渤海海峡水体中各水层溶解无机碳(DIC)及其组分浓度分布较一致,其中DIC及HCO₃-的浓度等值线分布均呈现出从西南向东北梯度降低的趋势,且受温度影响明显;二氧化碳分压[p(CO₂)]则表现出与叶绿素a含量成明显负相关的分布特征;位于渤海海峡东部的H断面垂直方向上,由于受黄海、渤海水团在海峡中部交汇混合形成的水体紊流影响,DIC及其组分在断面中部等值线分布较两边曲折。冬季渤海海峡表现出明显的源、汇分区分布特征,整个调查区海-气二氧化碳通量为3.52 mmol/(m2·d),表现为大气CO₂的弱源。冬季流经渤海海峡的DIC通量约为(130±2)×103 mol/s。     

东海中北部海域秋季表层海水中无机碳与海气界面碳的迁移

基于2010 年11 月对长江口外东海中北部海域的综合调查, 系统研究了该海域的无机碳体系参数的分布特征、海?气界面二氧化碳通量及其影响因素。研究结果表明, 该海域秋季溶解无机碳(DIC)高值区主要出现在调查海域东北部及长江口附近海域, 而调查海域南部DIC 含量较少且变化平缓, 其主要是受台湾东部流向东北方向的黑潮支流及长江冲淡水的影响; 表层海水CO₂分压(pCO₂)值变化范围为40.8～63.5 Pa, 呈现沿黑潮支流流入方向由东南向西北逐渐增高的趋势。秋季表层海水pCO₂与温度(T)、盐度(S)有较好的负相关性, 说明海水温度升高和盐度增加, pCO₂降低, 反之亦然。另外, 通过估算得出, 秋季CO₂海-气交换通量为2.69～33.66 mmol/(m²·d), 平均值为(14.35 ± 7.06 )mmol/(m²·d),其在长江口邻近海域相对较大, 而在调查海域南部相对较小; 2010 年秋季水体向大气释放CO₂的量(以碳计)为(2.35 ± 1.16)×104 t/d, 是大气CO₂较强的源, 说明东海中北部海域秋季总体上是CO₂的源。     

Water,salt, and heat exchange through the Kinburn Strait of the Dnieper-Bug Estuary

Based on the multiannual observations (1965–2011), the diurnal, seasonal, and annual variabilities of the water, salt, and heat exchange rates in the Kinburn Strait of the Dnieper-Bug Estuary are studied. A method for calculation of the water, salt, and heat exchange rates through the strait is proposed, and the respective values are specified to be used for solving the practical problems related to efficient use of the water resources in this near-mouth region.     

Flow variability in the Strait of Gibraltar: The Mediterranean adjustment to tidal forcing

The vertical structure of the flow variability through the Strait of Gibraltar is studied based on the Gibraltar Experiment and the Word Ocean Circulation Experiment data sets. An analysis of the leading modes of velocity and density variability at the Strait of Gibraltar showed an adjustment of the water masses exchanged through the Strait. Mediterranean mass variations resulting from the water exchanged by barotropic tidal oscillations generate changes of the baroclinic component of the flow that damp these mass variations. This adjustment explains the previously observed fortnightly variation of the shear. Moreover, the adjustment is found to operate for the subinertial time scale flow variability forced by the atmospheric pressure. An analytical model aimed at reproducing variations of the velocity with time and in the vertical is derived. The model includes a depth-varying parameterisation of friction and takes into account density gradient fluctuations across the Strait. The model reproduces the main features of the flow, in particular the shear and the interface depth variations with the tide phase.     

Nutritional analysis of freshwater and marine amphipods from the Strait of Gibraltar and potential aquaculture applications

Four gammarid and four caprellid amphipod species from the Strait of Gibraltar were analyzed to study their nutritional contents: Caprella dilatata, Caprella equilibra, Caprella grandimana, Caprella penantis, Elasmopus rapax, Hyale perieri and Jassa sp. from marine water habitats and Echinogammarus sp. from freshwater habitats. Lipids, proteins, carbohydrates, ash and water contents were measured. Proteins and ash were the most abundant components in all the species, ranging between 37.9 and 44.6% and 29.3 and 39.7% dry weight, respectively. The lipid and carbohydrate contents showed lower levels (5.1–9.6% and 3.1–9.1% dry weight, respectively). No significant differences in general biochemical composition were found between gammarid and caprellid species. The most abundant fatty acids were the polyunsaturated ones (38.3%) with high levels of EPA (20:5(n-3)) with 8.5 to 17.7%, DHA (22:6(n-3)) with 0.9 to 13.6% and ARA (20:4(n-6)) with 1.7 to 5.8%. Caprellid species were characterized by a higher percentage of polyunsaturated fatty acids, while the freshwater gammarid species showed the lowest levels. According to lipid classes, caprellids had higher phospholipids levels and lower triacylglycerol levels, as well as a higher content of polar lipids than the gammarids, being more suitable for their use in aquaculture. Differences in the general biochemical composition between species can be related to habitat characteristics, diets and environmental conditions. Advantages and disadvantages of the use of these organisms in aquaculture are discussed.