The Bremen ocean bottom tiltmeter (OBT) – a technical article on a new instrument to monitor deep sea floor deformation and seismicity level

The Bremen ocean bottom tiltmeter is a new 6000 m-depth deep sea instrument for autonomous observation of sea floor tilt with signal periods longer than 7.5 s. The instrument also records vertical acceleration in the frequency range from DC to 1 Hz. The tiltmeter has an Applied Geomechanics Inc. 756 wide angle biaxial bubble tilt sensor with a resolution of 1.0μ rad (0.2 arc second). A Kistler Corp. MEMS accelerometer of type Servo K-Beam 8330A2.5 with about 10⁻⁵m/s² resolution is used for the acceleration measurements. An Oceanographic Embedded Systems AD24 24 bit Sigma-Delta converter, which is controlled by a low-power Persistor Inc. embedded computer system of type CF 2, samples the data. The duration of tiltmeter operation is more than one year, which is controlled by the battery life. In our design the tiltmeter does not need active leveling devices, i.e., servo motors or other moving components to adjust sensors or frame. We designed the instrument for deployments by means of a remote operated vehicle. Since May 2005 the Bremen ocean bottom tiltmeter has recorded sea floor deformation and seismicity level in the Logatchev hydrothermal vent field, Mid-Atlantic Ridge. The tiltmeter is a part of the monitoring system of project ‘Logatchev Long-Term Environmental Monitoring,’ called LOLEM, of the German research program with the name ‘Schwerpunktprogramm 1144: Vom Mantel zum Ozean.’     

Seasonal variations in the total content of hydrogen fluoride in the atmosphere

The results of ground-based measurements of the total content (TC) of hydrogen fluoride in the atmosphere in Peterhof near St. Petersburg for one year (from April 2009 through April 2010) using a Bruker IFS125 Fourier spectrometer with a high spectral resolution (0.005 cm^?1) are presented. The well-known computer code SFIT2 (Zephyr-2) was used for the radiation data inversion. Random measurement errors were 1–5% and the systematic error was 5–10%. The seasonal trend of the HF TC in Peterhof is characterized by a minimum in summer and a maximum in winter through early spring and is very close to the seasonal HF TC trend obtained at the Harestua Network for the Detection of Atmospheric Composition Change (NDACC) station located at about the same latitude. A comparison of the St. Petersburg State University (SPbSU) ground-based measurements with the data of satellite HF TC measurements (with an ACE-FTS instrument) showed a good quantitative agreement of the results for the entire period of observations. According to our ground-based measurements and the satellite measurements with the ACE-FTS instrument, the mean values of the HF TC and its rms variations during the period under investigation are 1.77 × 10¹⁵ and 1.80 × 10¹⁵ cm^?2 (difference 1.5%) and 21 and 18%, respectively.     

A three-component ocean bottom seismograph for controlled source and earthquake seismology

A three-component pop-up ocean-bottom seismograph was built at the Institute of Oceanographic Sciences in 1978. It is constructed around a buoyant 71 cm diam aluminium alloy forged sphere which contains three 4.5 Hz orthogonal geophones and an external hydrophone. The instrument will record continuously in analogue mode for over eight days using a modified reel-to-reel tape-recorder running at 1.5 mm s^-1. The geophones have a bandwidth of 2–25 Hz and the hydrophone bandwidth is 5–40 Hz. Ballast release is by pre-set clock or by acoustic command.Fifty-four deployments have been carried out in five cruises for the loss of only one instrument. Good recordings of dropped weights, airguns, explosions and earthquakes have been obtained.     

An inexpensive instrument for measuring benthic current velocity and direction at sea

An instrument which measures the velocity and direction of benthic water currents at depths of up to 80 m is described. Characteristics of this meter include: (i) readings are not affected by water flow during sinking or retrieval; (ii) it is portable; (iii) it operates unattended; (iv) it is inexpensive; and (v) it requires only simple maintenance. A timing circuit which operates two time periods in succession is used to activate and de-activate a revolution counter and a fluidfilled compass which are mounted on a special frame and vane system. In the field, the instrument accurately measured average current velocities of up to 6 m s⁻¹. Data are presented which illustrate the usefulness of this instrument in describing the velocity and direction of benthic currents along the east coast of Australia and demonstrate a positive correlation between benthic current velocity and catch rates of the commercially-exploited spanner crab Ranina ranina.     

A towed near-surface optical reflectance meter for measuring ocean colour in support of remote sensing

An underwater optical instrument, the Lighfish, measures near-surface irradiance reflectance in six spectral channels while it is towed from a research vessel at a depth of a few metres. The detectors are configured such that all downward-looking detectors observe the same instrument shadow. Effects of self-shading are negligible for waters and wavelengths having absorption coefficients less than 0.3 m⁻¹. Variance in the derived spectral reflectance ratios is shown to be significantly reduced compared with that in single channel irradiance measurements. The instrument can be used to develop remote sensing algorithms as well as for other oceanographic applications.     

Return to ranger submarine slide,Baja California,Mexico

Ranger Slide is a modest (12 km³) slide deposit of Pliocene and younger sediment on the continental slope in northern Sebastian Vizcaino Bay, Mexico. A limited survey using a deeply-towed instrument shows that hummocky terrain immediately downslope from the slide scar consists of large blocks of semiconsolidated sediment, some exceeding a kilometer in length and 10⁷ m³ in volume. Most blocks have rotated, fallen apart, and/or deformed during movement. The form, structure, and processes related to emplacement of the blocks within the hummocky topographic zone of Ranger Slide may be common to many submarine slides on slopes involving semiconsolidated, terrigenous sediment.     

海水叶绿素a现场测量仪研究

采用荧光测量方法研究成功的海水叶绿素a现场测量仪，是用于海上现场实时测量海洋中浮游植物体内叶绿素a含量的新型海洋仪器。本仪器采用低功耗、高强度、低重复频率、窄脉冲宽度的脉冲氙灯，为激发光源及相应的脉冲检测技术测量荧光信号。该仪器可在海表层至50m水深内任一日光强度下工作；测量海洋中浮游植物体内叶绿素a的浓度范围为1×10-6—1×10-9g／cm3；当仪器走航拖曳速度为2m／s时，其空间分辨度为1m，仪器具有海上现场测量实用价值。     

Near bottom magnetic profile across the Red Sea

Results are presented from a high precision geophysical profile made at an altitude of about 100 m above the sea floor with the Deep Two instrument package, crossing the Red Sea at 17°30N. The emphasis is on the analysis and interpretation of the magnetic field, including an inversion which removes the distortions due to bathymetry and the orientation with respect to the earth's main field vector. The spreading rates are determined precisely and found to be highly asymmetric: only 5 mm yr^-1 to the east and up to 10 mm yr^-1 to the west. We conclude that the axis of spreading is located on a volcanic ridge, rather than on the axial graben, based on the presence of a zone of high magnetization. The magnetization high (40 Am^-1) is about twice as great as found on the Mid-Atlantic Ridge with the same instrument and analysis. The quality of the recording of the magnetic anomalies in the oceanic crust is much greater than expected for such a low spreading rate.     

Determining the total ozone from geostationary earth satellites

A method for determining the total ozone (TO) with high spatial (3×3 km²) and temporal (15 min) resolutions by using measurements of the Earth’s outgoing thermal radiation from Meteosat geostationary satellites is proposed. The method is based on measurements with a SEVIRI instrument (eight IR channels) and involves additional information on the three-dimensional field of the atmospheric temperature and on the surface temperature obtained from polar satellites (AIRS instrument). The inverse problem of TO determination is solved by the method of neural networks. TO measurements with the AIRS instrument are also used for training the neural networks. Ground-based TO measurements at the international ozonometric network are used for controlling the quality of AIRS data and detecting the errors of the proposed method of TO determination from SEVIRI data. The mean and rms differences between TO values obtained with the use of the proposed method and from the results of measurements at the international ozonometric network are shown to be 1.5 and 6.5%, respectively. Examples of TO distributions reconstructed with high spatial and temporal resolutions are presented. These examples show that the elaborated method for solving various scientific and applied problems and, in particular, for investigating stratospheric dynamics is promising.     

光谱法测定海水中溶解态无机氮的研究进展

溶解态无机氮（dissolved inorganic nitrogen, DIN）主要由亚硝酸盐-氮（NO^-₂-N）、硝酸盐-氮（NO^-₃-N）和铵氮（NH⁺₄-N）组成,它们在海洋的生物地球化学循环过程中起重要作用。但人类活动向海洋输入了大量无机氮,导致一系列环境问题。为了更好地开展海洋氮循环研究和环境污染管理,需对海水中的DIN进行测定。在众多分析方法中,光谱法因其通用性好、适用范围广、所需设备简单,成为测定海水DIN的首选。本文总结了近10年来基于光谱法测定海水DIN的研究进展,包括紫外分光光度法测定NO^-₃-N、萘乙二胺分光光度法测定NO^-₂-N和NO^-₃-N、次溴酸盐氧化-分光光度法测定NH⁺₄-N、靛酚蓝分光光度法测定NH⁺₄-N、酸碱指示剂-分光光度法测定NH⁺₄-N、荧光法和化学发光法测定DIN等,比较了各分析方法的特点,并展望了光谱法测定海水DIN的发展趋势。总的来说,在分析方法上,新试剂的使用以及一些新合成材料的出现,丰富了DIN的分析手段;在分析仪器上,以流动分析技术为基础的分析仪器在DIN的实验室及现场分析中得到了广泛应用。DIN的分析方法均朝着简单便捷、全自动化、分析速度快、精确度高、可适用范围广的方向发展。     

海水油荧光测量方法实验研究

根据荧光测量方法的原理,采和双光路,双通道及单片微机控制,数据自动采集的技术,于１９９７年研制成功用于海洋现场探测的单波段水中油荧光计。应用该水中油荧光计进行了海水中微量油份的测量实验研究。     

Instruments for investigating shore and nearshore processes

Abstract

On shingle beaches, changes in foreshore elevation and sediment distribution landward of the break point are produced largely by variations in the uprush and backwash of waves. However, very little is known about the forces active in this zone.

A field instrument system which senses and records some of the parameters thought to influence beach erosion and deposition in this zone has been constructed. The equipment is also suitable for the investigation of a number of other shore and nearshore processes including erosion on sandy and rocky shores, and flow processes affecting littoral biological communities.

In the swash zone two sensing heads, a dynamometer and a depth recorder, sense variations in uprush and backwash velocities, energies, discharges, and depths of flow. Both devices are electromechanical and are coupled to a recording unit on land by PVC‐insulated cable. The dynamometer (two force plates mounted back‐to‐back on a compression spring and coupled to variable resistances) has been calibrated, statically and in a flume, to obtain velocity determinations accurate to within 10 cm . sec^?1 of true flow speed. Average swash zone velocities lie between 100 and 300 cm . sec^?1.

A parallel‐wire resistance gauge mounted an a stilling tube records flow depths. As water level rises and falls in the tube it alters resistance in a control circuit. The land unit, amplifiers and a strip‐chart recorder, receives the output from the dynamometer and flow depth gauge. The recorder is equipped with a trip‐pen so that analysis of wave periods or other variables is possible in the field. With poles at known spacings across the shore and the trip‐pen records, velocity distributions across the swash zone can be obtained. Measurements of velocity made near the bed with the dynamometer can then be related to the local surface velocity profile.

Problems with the instrument system include inability to record velocities at several points simultaneously, and unreliable records of backwash parameters with low breakers on shingle beaches because of the small volume of flow and rapid percolation of water into the beach face.     

First measurements from a deep-tow transient electromagnetic sounding system

An electromagnetic sounding system has been developed to map the shallow electrical conductivity structure of the deep sea floor. The instrument consists of a magnetic source and several colinear magnetic receivers forming an array which is towed along the seafloor. The source generates a time varying magnetic field; the shape of the resulting magnetic field waveform at the receivers depends on the electrical conductivity below the seafloor between the receivers and the source. The instrument can be towed systematically over a study area under acoustic transponder or GPS navigation to construct a map of the electrical conductivity. Towing speeds of greater than 1 m s^–1 (2 knots) can be achieved without adversely effecting data quality. The instrument is sufficiently robust to survive continual contact with thinly sedimented, abrasive basalt. We present the first results from a deployment in August, 1990 near the Cleft Segment of the Juan de Fuca Ridge along an 8 km track to the west of the spreading center. Unforeseen problems with the instrument restricted the utility of the measurements for constructing detailed vertical conductivity profiles, but the measurements were adequate to determine an average conductivity in the upper 25 m, at more than 70 stations. The conductivity was found to vary from 0.1 to 0.4 S/m along the track.     

CHEMINI: A new in situ CHEmical MINIaturized analyzer

“CHEMINI” is a new instrument developed for the measurement of seawater chemical parameters. It is a mono-parameter in situ chemical analyzer based on flow injection analysis and colorimetric detection. The deep-sea version of CHEMINI combines two modules to perform the analysis of dissolved iron [Fe (II) or Fe (II+III)] and total sulphide (H₂S+HS^?+S^2?) up to 6000 m depth. Detection limits are, respectively, 0.3 and 0.1 μM for iron and sulphide. The system proved highly reliable during the MoMARETO cruise on the Mid-Atlantic Ridge. The two CHEMINIs were used to describe the chemical environment in 12 mussel beds on the Tour Eiffel hydrothermal edifice.     

A new benthic aqueous flux meter for very low to moderate discharge rates

Significant quantities of fluids and dissolved geochemical components are expelled through the sediment surface in ocean margin and sedimented ridge environments. Recently, significant interest has been generated in constraining hydrological processes in these environments, but direct measurement of fluid flow in the marine environment has proven to be difficult and many aspects of marine hydrogeology remain poorly understood. To address the need for a means to make a significant number of direct measurements in a wide range of low to moderate flow environments, we have developed a new type of benthic aqueous flux meter that is capable of measuring diffuse fluid flow through the sediment surface on the order of 0.1 mm yr⁻¹–15 m yr⁻¹ when the flow is through sediments with permeabilities of less than 10⁻⁸ cm² (typical seafloor sediments). The instrument measures fluid flow by determining the degree of dilution of a chemical tracer that is injected by an osmotic pump at a known rate into the fluids venting into or out of a collection chamber situated on the sea bed. The pump also withdraws a subsample of this tracer/fluid mix into sample coils allowing a serial record of the flow rates to be determined. Both upward and downward flow can be measured and, when flux rates are high enough to effectively flush the collecting chamber, the instruments also act as geochemical samplers. Three years of laboratory testing and field use have constrained the effects of (1) temperature, pressure, and deployment duration on osmotic pump performance, (2) dispersion/diffusion in the sample coils, and (3) deflection of flow under a range of sediment permeabilities. Recent deployments on the Kodiak and Cascadia accretionary prisms document the range and capabilities of the instrument in the field.     

Development and assessment of an analytical system for the accurate and continual measurement of total dissolved inorganic carbon

An automated coulometric titration system based on that described by Johnson, Sieburth, Williams and Brandstrom (1987, Mar. Chem., 21: 117–133) has been evolved for the accurate and continual measurement of total dissolved inorganic carbon (TCO₂). The instrument achieves an analytical precision (1 SD) of ±0.5–1.0 μmol kg⁻¹ (0.025–0.05%). The accuracy of the system has been examined by a limited comparison with other coulometric-based titrators and with a manometric-based system; agreement was to 1 μmol kg⁻¹. The capability for automatic continual analysis allows surface mapping of TCO₂; a sample rate of 10 analyses h⁻¹ gives a mapping resolution of 1–2 km. Provision for frequent standardization with a liquid substandard has been included in the development. The ability to achieve high-density analyses while maintaining interlaboratory consistency and standardization constitutes a vital contribution to surveys of ocean carbon chemistry (e.g. Joint Global Ocean Flux Study, World Ocean Circulation Experiment).     

SEDVEL: An underwater balance for measuring in situ settling velocities and suspended cohesive sediment concentrations

An automated instrument (SEDVEL—Sedimentation Velocity) was developed to directly measure the mass-concentration and the mass-distribution of settling velocities of suspended particulate matter (SPM) in situ. This instrument consists of an underwater balance, which directly measures the variation in time of the immersed weight of particulate matter (PM) as it settles on a plate located at the bottom of a settling tube, under quiescent conditions. SEDVEL operates underwater and samples in situ for deployment periods of a few days. SEDVEL produced consistent and reproducible results when tested both in the laboratory and in the field under SPM dry-concentrations of 5 to 200 mg l^− 1. Errors in the estimates of maximum dry-concentrations from SEDVEL measurements were less than 30% in 69% of the cycles analysed in the laboratory. The corresponding figure for in situ measurements was 50%. These errors are likely related to uncertainties in the calculation of the dry-density of flocs and in the definition of the zero position (ZP) of the SEDVEL balance. The slow settling particles/flocs (W_s < 1 mm s^− 1) represented 32–98% of the total mass of SPM at two sites of deployment in Cleveland Bay (Australia). Distinct settling behaviours were observed between the two sites and among different tidal stages associated with differences in the floc population; the aggregation of which probably varied as a function of the bottom grain size, shear stress, resuspension, advection and organic content of SPM.     

Coulometric total carbon dioxide analysis for marine studies: Automation and calibration

An automated instrument for the coulometric detection of total carbon dioxide (TCO₂) was developed from the manual prototype of Johnson et al. Pure CO₂ was used to calibrate the detector, the whole analytical procedure was controlled by a microcomputer, and the unit was compact enough for field and shipboard use. Some 67 samples from the Askö field station on the Baltic Sea (salinity = 6; TCO₂ ranging from 1224.3 to 1276.1 μmol l⁻¹ with a mean of 1245.6 μmol l⁻¹) and 31 samples from Swedish lakes (TCO₂ ranging from 19.5 to 252.3 μmol l⁻¹ with a mean of 72.9 μmol l⁻¹) were analyzed. The pooled standard deviation of these analyses was ± 1.0 μmol l⁻¹ (% CV of 0.08 and 1.3%, respectively). Precisions of < 0.1% were routine for waters exceeding 1000 μmol l⁻¹ TCO₂. At Askö on the Baltic Sea, the mean absolute difference between coulometric and pH-alkalinity determinations of TCO₂ on 22 parallel samples was 6.7 μmol kg⁻¹ or 0.5% of the mean. Community metabolism studies gave maximum rates of net production (TCO₂ uptake) and respiration (TCO₂ production) of 0.9-1.2 and 0.3-0.5 μmol l⁻¹ b⁻¹, respectively. The results of this study provide solutions to the problems observed with the earlier manual prototype.     

A rapid birefringence method for measuring suspended CaCO3 concentrations in seawater

The extreme birefringence of calcium carbonate (CaCO₃) relative to other major components of marine particulate matter provides a basis for making optical in situ measurements of particulate inorganic carbon (PIC) in seawater. This concept was tested with a benchtop spectrophotometer equipped with a 1- and 10-cm path length sample cell and modified with linear polarizers to measure the birefringence of suspended particles. Sample suspensions containing 3–100% CaCO₃ (by weight) were prepared from calcareous marine sediment material and varying amounts of non-birefringent diatomaceous earth. The samples ranged in total suspended material from 0.003 to 249 mg l⁻¹ and PIC from 0.03 to 1820 μmol CaCO₃ l⁻¹. A positive relationship was observed between birefringence and PIC, with response falling off as the total particle concentration and the relative abundance of non-CaCO₃ particles in the sample increased. Sensitivity increased linearly with optical path length, and absolute detection limits of 0.2–0.4 and 0.04–0.08 μmol CaCO₃ l⁻¹, respectively, were determined for path lengths of 1- and 10-cm based on the intrinsic signal noise of the modified spectrophotometer. Conventional (i.e., non-polarized) transmittance measurements were used to correct the birefringence signal for the sensitivity loss due to interference from scattering and absorption. Without further modification, this spectrophotometer-based method can be used (with a 10-cm cell) to quantify PIC in most surface ocean waters—including those influenced by coccolithophore blooms. The spectrophotometer results define performance requirements and design parameters for an in situ instrument capable of operating over the oceanic range of PIC.