Experiments in reconstructing twentieth-century sea levels

One approach to reconstructing historical sea level from the relatively sparse tide-gauge network is to employ Empirical Orthogonal Functions (EOFs) as interpolatory spatial basis functions. The EOFs are determined from independent global data, generally sea-surface heights from either satellite altimetry or a numerical ocean model. The problem is revisited here for sea level since 1900. A new approach to handling the tide-gauge datum problem by direct solution offers possible advantages over the method of integrating sea-level differences, with the potential of eventually adjusting datums into the global terrestrial reference frame. The resulting time series of global mean sea levels appears fairly insensitive to the adopted set of EOFs. In contrast, charts of regional sea level anomalies and trends are very sensitive to the adopted set of EOFs, especially for the sparser network of gauges in the early 20th century. The reconstructions appear especially suspect before 1950 in the tropical Pacific. While this limits some applications of the sea-level reconstructions, the sensitivity does appear adequately captured by formal uncertainties. All our solutions show regional trends over the past five decades to be fairly uniform throughout the global ocean, in contrast to trends observed over the shorter altimeter era. Consistent with several previous estimates, the global sea-level rise since 1900 is 1.70 ± 0.26 mm yr⁻¹. The global trend since 1995 exceeds 3 mm yr⁻¹ which is consistent with altimeter measurements, but this large trend was possibly also reached between 1935 and 1950.     

Shoreline variability via empirical orthogonal function analysis: Part I temporal and spatial characteristics

Empirical orthogonal functions (EOFs) or principal components were used to extract the significant modes of shoreline variability from several data sets collected at three very different locations. Although EOFs have proven to be a valuable tool in the analysis of nearshore data, most applications have focused on the ability of the technique to describe cross-shore or profile variability. Here however, EOFs were used to help identify the dominant modes of longshore shoreline variability at Duck, North Carolina, the Gold Coast, Australia, and at several locations within the Columbia River Littoral Cell in the U.S. Pacific Northwest. In part one of this analysis, characteristic patterns of shoreline variability identified by the EOF analysis are described in detail. At each site, the dominant modes consisting of the first four eigenfunctions were found to describe nearly 95% of the total shoreline variability. At both Duck and the Gold Coast, several interesting longshore periodic features suggestive of sand waves were identified, while boundary effects related to natural headlands and navigational structures/entrances dominated the Pacific Northwest data sets.     

Basis functions for shallow-water temperature profiles based on the internal-wave eigenmodes

The shallow-water temperature profile is typically parameterized using a few empirical orthogonal function(EOF)coefficients. However, when the experimental area is poorly known or highly variable, the adaptability of the EOFs will be significantly reduced. In this study, a new set of basis functions, generated by combining the internal-wave eigenmodes with the average temperature gradient, is developed for characterizing the temperature perturbations. Temperature profiles recorded by a thermisto...     

Semidiurnal amphidrome of the North East Pacific: Where?

The degree to which satellite altimetry may extend its contributions to geophysics will depend on the accuracy of corrected altitudes, on the precision of orbit corrections, on exact geoid representation and on our ability to separate independent oceanic processes affecting sea surface elevations. The barotropic tide-namely the oceanic response to gravitational driving which maintains its phase lock with gravitational forces and which is always exactly predictable-constitutes a fundamental phenomenon in itself. Indirectly it tends to obscure in altimetric data other processes such as solid earth tides, large scale ocean circulation and climatic response of the ocean. The most realistic hope of obtaining the necessary predictive information on global oceanic tides resides in the construction of complete and accurate cotidal and corange maps. The importance of direct observations of open ocean tides in achieving this goal is stressed using an array of seafloor pressure data from the NE Pacific. Among more general results, the locations of long postulated semidiurnal amphidromes in the area are defined with an accuracy of one degree or less for M2 and S2. The importance of observations over a sufficient spatial coverage in tuning mathematical simulations of tides is illustrated. Ten new sets of tidal constants for the NE Pacific are tabulated.     

大洋富钴结壳实时开采切削深度优化分级模型研究

根据统计分形理论对大量实验测得的微地形数字高程数据进行了分维空间、无标度区和分形维数等分析和计算,并求出了各自的地形特征数据,同时建立了单个微地形在控制废石混入率时富钴结壳开采的最优切削深度的遗传寻优算法。在此基础上,利用实验所得各种分形特征数据及微地形的自相似性、各向异性及分形布朗函数,通过计算机自动生成了大量仿真微地形,并求出了各相应仿真微地形的地形特征数值和在控制废石混入率时富钴结壳开采的最优切削深度,再通过对此大样本的统计回归分析,建立了大洋富钴结壳实时开采切削深度的优化分级模型。该模型经实验数据的验证,其结果达到了满意的要求。     

Impacts of Kelvin wave forcing in the Peru Humboldt Current system: Scenarios of spatial reorganizations from physics to fishers

Because climate change challenges the sustainability of important fish populations and the fisheries they support, we need to understand how large scale climatic forcing affects the functioning of marine ecosystems. In the Humboldt Current system (HCS), a main driver of climatic variability is coastally-trapped Kelvin waves (KWs), themselves originating as oceanic equatorial KWs. Here we (i) describe the spatial reorganizations of living organisms in the Humboldt coastal system as affected by oceanic KWs forcing, (ii) quantify the strength of the interactions between the physical and biological component dynamics of the system, (iii) formulate hypotheses on the processes which drive the redistributions of the organisms, and (iv) build scenarios of space occupation in the HCS under varying KW forcing. To address these questions we explore, through bivariate lagged correlations and multivariate statistics, the relationships between time series of oceanic KW amplitude (TAO mooring data and model-resolved baroclinic modes) and coastal Peruvian oceanographic data (SST, coastal upwelled waters extent), anchoveta spatial distribution (mean distance to the coast, spatial concentration of the biomass, mean depth of the schools), and fishing fleet statistics (trip duration, searching duration, number of fishing sets and catch per trip, features of the foraging trajectory as observed by satellite vessel monitoring system). Data sets span all or part of January 1983 to September 2006. The results show that the effects of oceanic KW forcing are significant in all the components of the coastal ecosystem, from oceanography to the behaviour of the top predators – fishers. This result provides evidence for a bottom-up transfer of the behaviours and spatial stucturing through the ecosystem. We propose that contrasting scenarios develop during the passage of upwelling versus downwelling KWs. From a predictive point of view, we show that KW amplitudes observed in the mid-Pacific can be used to forecast which system state will dominate the HCS over the next 2–6 months. Such predictions should be integrated in the Peruvian adaptive fishery management.     

Efficiency of reduced-order, time-dependent adjoint data assimilation approaches

Applications of adjoint data assimilation, which is designed to bring an ocean circulation model into consistency with ocean observations, are computationally demanding. To improve the convergence rate of an optimization, reduced-order optimization methods that reduce the size of the control vector by projecting it onto a limited number of basis functions were suggested. In this paper, we show that such order reduction can indeed speed up the initial convergence rate of an assimilation effort in the eastern subtropical North Atlantic using in situ and satellite data as constraints. However, an improved performance of the optimization was only obtained with a hybrid approach where the optimization is started in a reduced subspace but is continued subsequently using the full control space. In such an experiment about 50% of the computational cost can be saved as compared to the optimization in the full control space. Although several order-reduction approaches seem feasible, the best result was obtained by projecting the control vector onto Empirical Orthogonal Functions (EOFs) computed from a set of adjusted control vectors estimated previously from an optimization using the same model configuration.     

An ocean model for climate variability studies

Models of the time dependent ocean circulation can be simplified considerably by filtering out all short term, small scale motions which are unimportant for climatic processes. For time scales large compared with a day and space scales large compared with the internal Rossby radius of deformation (～50 km), the currents in most of the interior ocean can be determined diagnostically as quasi-equilibrium fields, so that only the salinity and temperature fields need be treated prognostically.Regions of closed f/h contours, however, represent exceptions. Here trapped vorticity gyres exist as free flow solutions without external forcing, and in the presence of forcing the barotropic velocity field must therefore be determined prognostically through a potential vorticity equation for the gyres.Lateral boundary layers and the equatorial regions also require separate treatment. These were not considered specifically, but it is suggested that integrated (parametrical) models analogous in structure to mixed-layer models or the integrated boundary layer models of aerodynamics may be the most appropriate technique for coupling these regions to the interior ocean in a comprehensive ocean model suitable for climate studies.A coupled multi-region model of the global ocean circulation based on these scale considerations could be sufficiently cost-effective to permit systematic investigation of the role of the oceanic heat storage and transport in climate variability studies over a wide spectrum of space and time scales.The analysis of the seasonal variations of the interior ocean circulation represents a simple example in which the filtered model yields considerably simpler and more readily interpretable results than a fully three-dimensional, unfiltered model.     

一种基于声速剖面展开的内波监测新方法

声速剖面时空分布的获取是利用声学方法监测内波的核心问题。在反演算法中，声速剖面通常是采用展开的方式用若干个参数来表示的。这就导致了有时很难从反演结果中直接获得内波的相关信息。本文的目标是找到一种通过展开系数直接获取内波特性的方法。通过推导内波水动力方程，可以从较少的声速剖面样本中提取出水动力简正模态（Hydrodynamic Normal Modes，HNMs）作为声速剖面展开的正交基。较之广泛采用的正交经验函数（Empirical Orthogonal Functions, EOFs），HNMs直接与内波活动相关，具有更明确的物理含义。然后，基于HNMs对声速剖面的时间序列进行展开，获得展开系数。最后，从前两阶展开系数的时间导数中可以获取内波活动的信息。将方法应用于受内波影响而具有明显时空扰动的南海北陆架区温度链数据，结果表明：只用前两节模态就可以在较好的精度范围内重构声速剖面。前两阶系数的时间导数具有独特的双震荡结构可以用于探测内孤立波。从展开系数也可以获得幅度以及波长信息。理论推导和实验分析证明了本文方法在内波监测中的有效性。HNMs方法使用便利且对样本的依赖性较小，可以在内波活跃海域作为EOFs的有效补充用于声速剖面的展开。     

Coupling global and regional circulation models in the coastal Gulf of Alaska

As part of the US GLOBEC NE Pacific program, we are simulating currents in the Coastal Gulf of Alaska (CGOA) to explore sources of interannual and interdecadal variability. To do so, we have developed a coupled modeling system composed of linked regional and global circulation models. The regional model, configured with 13–22 km resolution in the CGOA, is forced at the surface by observed heat fluxes and wind stresses, at the continental boundaries by observed runoff, and at the open ocean boundaries by a combination of tracer climatologies and sub-tidal velocity and tidal elevation provided by a global finite element model. In this communication, we describe the coupled system, including its present method of intermodel coupling, describe a series of multi-year model hindcasts, compare hindcast results with Eulerian and Lagrangian field data obtained in the CGOA in fall 1996, and assess the impact of global information (barotropic sub-tidal velocities and tidal elevations) on the regional model under the present coupling strategy. We find that the regional model produces appropriate current systems (Alaskan Stream, Alaska Coastal Current) and scalar fields, but with mesoscale variability (of SSH and velocities) at somewhat reduced strength relative to data, and with temperature gradients somewhat larger than those observed. Barotropic sub-tidal information from the global model penetrates the regional model interior, supplying additional mesoscale variability, and modifying regional velocity and scalar fields in both shallow and deep areas. Tidal information exerts a significant influence on sub-tidal scalar and velocity structure only in specific shallow areas, where the tides (and tidal mixing) are strongest. Pending the exploration of alternate coupling schemes, we infer from these results that on a time scale of months, purely barotropic information from outside the CGOA will have a modest impact on its mean regional circulation, but a potentially stronger impact on the statistics and details of mesoscale eddies.     

Dynamics of the long-period tides

The long-period tides are a tool for understanding oceanic motions at low frequencies and large scales. Here we review observations and theory of the fortnightly, monthly and pole tide constitutents. Observations have been plagued by low signal-to-noise ratios and theory by the complex lateral geometry and great sensitivity to bottom slopes. A new spectral element model is used to compute the oceanic response to tidal forcing at 2-week and monthly periods. The general response is that of a heavily damped (Q ≈ 5) system with both the energy input from the moon and the dissipation strongly localized in space. The high dissipation result is probably generally applicable to all low frequency barotropic oceanic motions. Over much of the ocean, the response has both the character of a large-scale and a superposed Rossby wave-like character, thus vindicating two apparently conflicting earlier interpretations. To the extent that free waves are excited they are consistent with their being dominated by Rossby and topographic Rossby wave components, although gravity modes are also necessarily excited to some degree. In general, a modal representation is not very helpful. The most active regions are the Southern Ocean and the western and northern North Atlantic. These results are stable to changes in geometry, topography, and tide period. On a global average basis, the dynamical response of Mm is closer to equilibrium than is Mf.     

Design of an adaptive controller for submersibles via multimodel gain scheduling

An adaptive autopilot for submarines via gain scheduling is introduced. The procedure used in the design is based on the stochastic controller and observer techniques. The autopilot is designed to operate in various sea conditions. Steady-state estimator gains corresponding to different wave heights are calculated and utilized in estimating the real wave height by switching the gain sets. Since large perturbations require large hydroplane angles which cannot be realizable due to their physical limits, different controller gain sets are employed for the appropriate operation of the hydroplanes. The presented controller is not confined to a particular sea state, and possesses robustness against possible changes in the external environment, exploiting the multimodel representation of the sea state.     

基于正交匹配追踪的声层析方法

声速剖面的变化会对声传播产生较大的影响，经验正交函数模型经常用来实现对声速剖面数据的简化描述。然而在内波、湍流等海水不均匀性存在时，这种正则化操作会造成声速重构精度的大幅降低。本文利用字典学习生成声速剖面的非正交原子，在稀疏编码时采用正交匹配追踪（OMP，Orthogonal Matching Pursuit）算法，更新字典则使用KSVD （Kernel Singular Value Decomposition）的字典更新算法。由于字典学习不需要强制使用正交条件，对于训练数据更加灵活，从而可以使用少数的原子组合达到更高的重构精度。利用一次浅海声学实验多次测量的声速剖面研究了海水声速剖面的经验正交函数表示和字典学习，研究表明：相比于正交函数表示，学习字典可以利用少数原子（甚至一个原子）更好的解释声速剖面扰动。字典学习可以提高声速剖面的稀疏性，从而提高声速剖面的反演精度。     

An intercomparison of GEOSAT, TOPEX and ERS1 measurements of wind speed and wave height

Mean monthly values of altimeter wind speed and wave height are compared with data from NDBC buoys. As a result of these comparisons, corrections are made to the raw data products available from these satellites. Data from the GEOSAT, TOPEX and ERS1 missions corrected in this fashion are used to show that there have been no measurable changes in the global wind and wave climate during the 10 years spanned by these various missions. It is proposed that the corrected values of wind speed and wave height provide the basis for the formation of a long-term global data base which spans the periods of these multiple missions.     

Automated cleaning and uncertainty attribution of archival bathymetry based on a priori knowledge

Hydrographic offices hold large valuable historic bathymetric data sets, many of which were collected using older generation survey systems that contain little or no metadata and/or uncertainty estimates. These bathymetric data sets generally contain large outlier (errant) data points to clean, yet standard practice does not include rigorous automated procedures for systematic cleaning of these historical data sets and their subsequent conversion into reusable data formats. In this paper, we propose an automated method for this task. We utilize statistically diverse threshold tests, including a robust least trimmed squared method, to clean the data. We use LOESS weighted regression residuals together with a Student-t distribution to attribute uncertainty for each retained sounding; the resulting uncertainty values compare favorably with native estimates of uncertainty from co-located data sets which we use to estimate a point-wise goodness-of-fit measure. Storing a cleansed validated data set augmented with uncertainty in a re-usable format provides the details of this analysis for subsequent users. Our test results indicate that the method significantly improves the quality of the data set while concurrently providing confidence interval estimates and point-wise goodness-of-fit estimates as referenced to current hydrographic practices.     

Seismostratigraphic analysis of the Transkei Basin: A history of deep sea current controlled sedimentation

The Earth's climate is controlled by various factors, with large scale ocean currents playing a significant role. In particular, the global thermohaline circulation of water masses like the Antarctic Bottom Water (AABW), or the North Atlantic Deep Water (NADW), is a global motor for maintaining the exchange of water masses. The AABW and NADW have met and interacted off South Africa since Oligocene times. Here, the narrow deep Agulhas Passage gateway, located between South Africa and the submarine Agulhas Plateau, constrains bottom water exchange between the southeast Atlantic and the southwest Indian Ocean. A seismostratigraphic analysis of sedimentary structures in the Transkei Basin, which opens up at the eastern end of the Agulhas Passage, was carried out, to reconstruct the palaeocurrents off South Africa. The analysis of newly collected high resolution seismic reflection data showed the effect of large scale current deposition. There are at least 5 major sedimentary phases to observe, some of which seem to be influenced by NADW and AABW. The first stage represents ongoing deep sea sedimentation from middle Cretaceous to middle Tertiary times. Later stages are separated by discordances, which represent the onset of AABW and NADW, among others, triggered by the opening of the Drake Passage gateway ( 35 Ma) and the closure of the Isthmus of Panama ( 3 Ma). We found two large drift bodies located one above the other. Corresponding to their shape and position, the older drift is inferred to have been deposited by currents flowing in a north–southerly direction, whereas the younger drift lies perpendicular to it and seems to be built up by west–east flowing currents.     

Decline of brown trout (Salmotrutta) in Switzerland - how to assess potential causes in a multi-factorial cause-effect relationship.

A considerable decline in fish catch in Switzerland triggered a 5-year project (Fischnetz) to investigate potential causes. The results of many field and laboratory studies, together with literature and historical data, indicated a need for a concise synthesis of the results. Therefore, Bayesian probability network (BPN) and weight-of-evidence (WOE) approaches were applied. Here, these both approaches are compared and evaluated. In addition, the potential reasons for the (mis)match in the two approaches were evaluated. In both studies, proliferative kidney disease (PKD), caused by a parasite, and the clinical outbreak supported by various factors, was a very probable single parameter. WOE assessed habitat and streambed quality as likely for contributing to impaired health, recruitment and abundance at single sites only, but this parameter was assessed to be the most important and ubiquitous stressor in the BPN. Mismatches suggested that these factors were either not considered or not equally assessed by the different models, which is due to different endpoints, incomplete data sets and different handling of these various data sets by the applied synthesis approaches.     

An Electronic Chart Display and Information System

This article introduces the most advanced form of electronic chart display and information systems (ECDIS) which complies with the performance standards for ECDIS established by the International Maritime Organization (IMO) and International Hydrographic Organization (IHO). It also describes the key features and the important functions of ECDIS, which we developed. This system is different from the productions developed by C-map, Seven-cs, offshore, and others. It is more suitable for China Marine Safety Administration Bureau to manage the navigation marks real-time. Using this system charts were located and accessed rapidly, and displayed smoothly. This article also discusses in ECDIS application system how to dynamically access and desert charts data in a limited memory (limited computer memory and resource). We constructed a tridimensional structure to manage a large amount of charts data. Vertically, according to the scale range, all charts were divided into eight levels, and a data structure called as “Multiple Scale Quad-tree” was constructed. And horizontally, a grid (every unit has a fixed size) was given to a certain scale level. We call this data structure a “Regular Page.” We explore the implementation of such a structure on the worldwide charts management utilizing quad-trees. Then we discuss the future development of ECDIS and its application system in marine agencies in China.     

Nutrient chemistry of the Ob' and Yenisey Rivers,Siberia: results from June 2000 expedition and evaluation of long-term data sets

Although containing only ∼1% of global ocean volume, the arctic Ocean receives almost 10% of global river discharge. Nutrients carried by arctic rivers influence the productivity of their estuaries and coastal seas and may serve as important indicators of changing conditions in their watersheds. The three largest arctic rivers (Yenisey, Ob', and Lena) enter the arctic Ocean from Siberia and together account for nearly 35% of river-water inputs to the arctic Ocean. Although several nutrient flux estimates have been published for Eurasian arctic rivers, recent publications have highlighted uncertainties in these estimates and have cautioned against their uncritical use, particularly with respect to ammonium data. In order to help clarify the situation and evaluate the validity of existing long-term data sets, we went to Siberia during June 2000 to collect and analyze new nutrient samples from the downstream reaches of the Yenisey and Ob' rivers. Samples were independently analyzed by as many as four groups/laboratories in order to maximize confidence in analytical results. Whereas long-term data sets report average ammonium concentrations of 710 and 360 μg N/l in the Ob' and Yenisey rivers, respectively, we measured concentrations of only 10–15 μg N/l in both rivers in June 2000. We conclude that existing long-term data sets for these two rivers are grossly in error with respect to ammonium concentrations, and by extension that other surprisingly high values of ammonium reported for Russian arctic rivers (for example Pur, Taz, Nadym, and Pechora rivers) must be considered extremely doubtful. The situation is better for nitrate and phosphate, but our one-time sampling is insufficient to fully evaluate the reliability of existing data sets for these nutrients. Because a substantial percentage of the total freshwater input to the arctic Ocean comes from Russian rivers, the large revisions in ammonium concentrations needed for the Ob', Yenisey, and probably other Eurasian arctic rivers will significantly reduce estimates of dissolved inorganic nitrogen (DIN) fluxes to the arctic Ocean as a whole.     

Possible causes of the underestimation of paleoclimate low-frequency variability by statistical methods

The Northern Hemisphere mean surface temperature has shown a significant positive trend over the past two centuries. On the basis of the well-known reconstructions of global climate from proxy data, the conclusion is made that the current warming has been unprecedented during at least the past two millennia. On the other hand, it was demonstrated in [6] that the existing statistical models strongly underestimate the low-frequency variability of global annual mean temperature, thus making the conclusion drawn above questionable. At present, the results of [6] are interpreted as evidence that the Mann reconstruction is invalid [1]. To our knowledge, however, it is too early to draw such conclusions. What is the cause of smoothing low-frequency variability? To what extent are various statistical models used for paleoclimate reconstruction that is subject to this effect? To answer these questions, numerical experiments are performed with data sets of annual mean surface temperature over the past millennium that are simulated with the ECHO-G coupled ocean-atmosphere general circulation model.