bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical tools for ocean monitoring and research
Authors: Moore C. , Barnard A. , Fietzek P. , Lewis M. R. , Sosik H. M. , White S. , Zielinski O.
Published: April 2010

Abstract. Requirements for understanding the relationships between ocean color and suspended and dissolved materials within the water column, and a rapidly emerging photonics and materials technology base for performing optical based analytical techniques have generated a diverse offering of commercial sensors and research prototypes that perform optical measurements in water. Through inversion, these tools are now being used to determine a diverse set of related biogeochemical and physical parameters. Techniques engaged include measurement of the solar radiance distribution, absorption, scattering, stimulated fluorescence, flow cytometry, and various spectroscopy methods. Selective membranes and other techniques for material isolation further enhance specificity, leading to sensors for measurement of dissolved oxygen, methane, carbon dioxide, common nutrients and a variety of other parameters. Scientists are using these measurements to infer information related to an increasing set of parameters and wide range of applications over relevant scales in space and time.
"Scale oriented" embedded modeling of the North-Western Mediterranean in the frame of MFSTEP
Authors: Estournel C. , Auclair F. , Lux M. , Nguyen C. , Marsaleix P.
Published: April 2010

Abstract. An embedded forecasting system was developed for the North-Western Mediterranean at 3-km resolution. The system is based on the Symphonie hydrodynamic free surface model and on the variational initialization and forcing platform VIFOP. The regional model is initialized and forced at its open lateral boundaries by the MFS GCM and forced at the surface by the ALADIN numerical weather prediction model. Once a week, a five-day forecast is produced after a hindcast of seven days. This pre-modeling period of 7 days before beginning the forecast allows the development of the small scale features associated to the high resolution. The relevance of the 5-day forecast strategy has been examined by comparing the forecasted fields to hindcast fields (forced by meteorological and oceanic analyses) considered as a reference. Mismatches remain at a very low level indicating a good quality of the forecasted forcing fields and also possibly to the strong wind conditions which prevailed during the period. The embedded forecasts have been compared to the MFS observing system (SST and MedArgo) during 6 forecast cycles between September 2004 and February 2005. It was basically found that in the North-Western Mediterranean, the MFS basin-scale model and thus the regional model forecasts are characterized by large negative biases of salinity in the first 100 m under the surface leading thus to too light subsurface waters. The underestimation of temperature by the regional model just below the surface and its overestimation at 30m deep can be attributed to an overestimation of the turbulent mixing. The regional model allows to represent a number of processes especially those induced by the wind as coastal upwelling under stratified conditions, dense water formation over the Gulf of Lion shelf, deep mixing in the convection zone or influence on the Northern Current penetration in the Gulf of Lion.
Ensemble perturbation smoother for optimizing tidal boundary conditions by assimilation of High-Frequency radar surface currents – application to the German Bight
Authors: Barth A. , Alvera-Azcárate A. , Gurgel K.-W. , Staneva J. , Port A. , Beckers J.-M. , Stanev E. V.
Published: April 2010

Abstract. High-Frequency (HF) radars measure the ocean surface currents at various spatial and temporal scales. These include tidal currents, wind-driven circulation, density-driven circulation and Stokes drift. Sequential assimilation methods updating the model state have been proven successful to correct the density-driven currents by assimilation of observations such as sea surface height, sea surface temperature and in-situ profiles. However, the situation is different for tides in coastal models since these are not generated within the domain, but are rather propagated inside the domain through the boundary conditions. For improving the modeled tidal variability it is therefore not sufficient to update the model state via data assimilation without updating the boundary conditions. The optimization of boundary conditions to match observations inside the domain is traditionally achieved through variational assimilation methods. In this work we present an ensemble smoother to improve the tidal boundary values so that the model represents more closely the observed currents. To create an ensemble of dynamically realistic boundary conditions, a cost function is formulated which is directly related to the probability of each boundary condition perturbation. This cost function ensures that the boundary condition perturbations are spatially smooth and that the structure of the perturbations satisfies approximately the harmonic linearized shallow water equations. Based on those perturbations an ensemble simulation is carried out using the full three-dimensional General Estuarine Ocean Model (GETM). Optimized boundary values are obtained by assimilating all observations using the covariances of the ensemble simulation.
Variability of scaling time series in the Arctic sea-ice drift dynamics
Authors: Chmel A. , Smirnov V. N. , Sheikin I. B.
Published: April 2010

Abstract. The motion of an individual ice floe in the Arctic Ocean was monitored at the Russian research station North Pole 35 established on the ice pack in 2008. The ice floe speed (V) was found to be correlated with wind speed (v) in main features, such as the positions of maxima and minima of V and v. However, the fine structure of the V-variation cannot be explained by the wind forcing alone. There were periods of time when the floe drift was affected by the interactions of ice floes between each other or by the periodical forcing due to either the Coriolis inertia effect or the tidal activity. These data were compared with the "waiting times" statistics that are the distributions of time intervals between subsequent, sufficiently strong changes in the kinetic energy of drifting ice floe. These distributions were measured in several time windows differing in the average wind speed and wind direction, and/or in the mechanical state of the ice pack. The distribution functions N (t>τ), where N is the number of successive events of energy change separated by the time interval t that exceeds τ, constructed in different time windows demonstrate fractal or a multifractal nature of the time series during motion in the consolidated ice pack but were truly random when the ice floe drifted in the highly fragmented sea ice. The latter result shows the existence of a relationship between the long-range mechanical interactions in the pack and long-term memory (time scaling behaviour) of the sea-ice motion.
Assessment of sensor performance
Authors: Waldmann C. , Tamburri M. , Prien R. D. , Fietzek P.
Published: April 2010

Abstract. There is an international commitment to develop a comprehensive, coordinated and sustained ocean observation system. However, a foundation for any observing, monitoring or research effort is effective and reliable in situ sensor technologies that accurately measure key environmental parameters. Ultimately, the data used for modelling efforts, management decisions and rapid responses to ocean hazards are only as good as the instruments that collect them. There is also a compelling need to develop and incorporate new or novel technologies to improve all aspects of existing observing systems and meet various emerging challenges. Assessment of Sensor Performance was a cross-cutting issues session at the international OceanSensors08 workshop in Warnemünde, Germany, which also has penetrated some of the papers published as a result of the workshop (Denuault, 2009; Kröger et al., 2009; Zielinski et al., 2009). The discussions were focused on how best to classify and validate the instruments required for effective and reliable ocean observations and research. The following is a summary of the discussions and conclusions drawn from this workshop, which specifically addresses the characterisation of sensor systems, technology readiness levels, verification of sensor performance and quality management of sensor systems.
Impact of global ocean model resolution on sea-level variability with emphasis on interannual time scales
Authors: Penduff T. , Juza M. , Brodeau L. , Smith G. C. , Barnier B. , Molines J.-M. , Treguier A.-M. , Madec G.
Published: April 2010

Abstract. Four global ocean/sea-ice simulations driven by the same realistic 47-year daily atmospheric forcing were performed by the DRAKKAR group at 2°, 1°, ½°, and ¼° resolutions. Simulated mean sea-surface heights (MSSH) and sea-level anomalies (SLA) are collocated over the period 1993–2004 onto the AVISO dataset. MSSH fields are compared with an inverse estimate. SLA datasets are filtered and compared over various time and space scales with AVISO regarding three characteristics: SLA standard deviations, spatial correlations between SLA variability maps, and temporal correlations between observed and simulated band-passed filtered local SLA timeseries. Beyond the 2°−1° transition whose benefits are moderate, further increases in resolution and associated changes in subgrid scale parameterizations simultaneously induce (i) strong increases in SLA standard deviations, (ii) strong improvements in the spatial distribution of SLA variability, and (iii) slight decreases in temporal correlations between observed and simulation SLA timeseries. These 3 effects are not only clear on mesoscale (14–180 days) and quasi-annual (5–18 months) fluctuations, but also on the slower (interannual), large-scale variability ultimately involved in ocean-atmosphere coupled processes. Most SLA characteristics are monotonically affected by successive resolution increases, but irregularly and with a strong dependance on frequency and latitude. Benefits of enhanced resolution are greatest in the 1°−½° and ½°−¼° transitions, in the 14–180 day range, and within eddy-active mid- and high-latitude regions. In the real ocean, most eddy-active areas are characterized by a strong SLA variability at all timescales considered here; this localized, broad-banded temporal variability is only captured at ¼° resolution.
Western Iberian winter wind indices based on significant wind events
Authors: Mason E. , Santos A. M. P. , Peliz Á J.
Published: April 2010

Abstract. Wind speed data obtained from the National Centers for Environmental Prediction (NCEP) Reanalysis project are used to construct winter (November–March) wind indices for the western Iberian Peninsula. The data used represent a 2.5° square area, centred at 41.0° N, 9.4° W, over the period 1948-2003. The NCEP data are well correlated with a time-series (1980–2001) of wind measurements from the Cape Carvoeiro lighthouse on the western Portuguese coast (39.4° N, 9.4° W). The new indices, of which there are four corresponding to northerlies, easterlies, southerlies and westerlies, constitute measures of numbers of significant wind event days, where a significant wind event is defined to be 4 or more consecutive days of wind speeds exceeding 4 m s-1. Results show both intra- and inter-annual variations in the numbers of significant wind event days, as well as clear decadal trends. A comparison between a hybrid index, composed of the numbers of significant northerly and easterly wind event days - both promote offshore transport, which is thought to have a negative impact on pelagic fish recruitment - and western Iberian sardine catch data, reveal an extensive period of significant negative correlation. The relationship over the most recent period, ~1999–2000, is unclear.
Transient residence and exposure times
Authors: Delhez E. J. M.
Published: April 2010

Abstract. The residence time measures the time spent by a water parcel or a pollutant in a given water body and is therefore widely used in environmental studies. The adjoint method introduced by Delhez et al. (Estuarine Coastal and Shelf Sciences, 2004) to compute this diagnostic is revised here to take into account the effect of the initialisation and of the boundary conditions. In addition to the equation for the mean residence time, it is suggested to solve a simple advection-diffusion problem to quantify the effect of the initialisation and clarify the interpretation of the results. Using the two same equations but with modified boundary conditions, the method can also be used to quantify the accumulated time spent by water/tracer parcels in a control domain. This diagnostic is called "exposure time".
El Niño in a changing climate: a multi-model study
Authors: van Oldenborgh G. J. , Philip S. , Collins M.
Published: April 2010

Abstract. In many parts of the world, climate projections for the next century depend on potential changes in the properties of the El Niño - Southern Oscillation (ENSO). The current staus of these projections is assessed by examining a large set of climate model experiments prepared for the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Firstly, the patterns and time series of present-day ENSO-like model variability in the tropical Pacific Ocean are compared with that observed. Next, the strength of the coupled atmosphere-ocean feedback loops responsible for generating the ENSO cycle in the models are evaluated. Finally, we consider the projections of the models with, what we consider to be, the most realistic ENSO variability. Two of the models considered do not have interannual variability in the tropical Pacific Ocean. Three models show a very regular ENSO cycle due to a strong local wind feedback in the central Pacific and weak sea surface temperature (SST) damping. Six other models have a higher frequency ENSO cycle than observed due to a weak east Pacific upwelling feedback loop. One model has much stronger upwelling feedback than observed, and another one cannot be described simply by the analysis technique. The remaining six models have a reasonable balance of feedback mechanisms and in four of these the interannual mode also resembles the observed ENSO both spatially and temporally. Over the period 2051-2100 (under various scenarios) the most realistic six models show either no change in the mean state or a slight shift towards El Niño-like conditions with an amplitude at most a quarter of the present day interannual standard deviation. We see no statistically significant changes in amplitude of ENSO variability in the future, with changes in the standard deviation of a Southern Oscillation Index that are no larger than observed decadal variations. Uncertainties in the skewness of the variability are too large to make any statements about the future relative strength of El Niño and La Niña events. Based in this analysis of the multi-model ensemble, we expect very little influence of global warming on ENSO.
Water mass transformation in the North Atlantic over 1985–2002 simulated in an eddy-permitting model
Authors: Marsh R. , Josey S. A. , Nurser A. J. G. , de Cuevas B. A. , Coward A. C.
Published: April 2010

Abstract. Water mass transformation in the North Atlantic is examined in an eddy-permitting simulation with the OCCAM ocean general circulation model, forced by realistic surface fluxes over the period 1985–2002. Three regions are considered: the Subtropics, the Mid-latitudes and the Northeast Atlantic. The oceanic boundaries of each region coincide with hydrographic sections occupied in recent years. These regions broadly represent the formation sites of Subtropical Mode Water (STMW) and Subpolar Mode Water (SPMW). A water mass budget is obtained for each region and year. Terms in the budget comprise surface-forced transformation rates, boundary exchanges and unsteadiness. Unsteadiness is relatively small, so that regional net water mass transformation is largely balanced by net boundary exchanges. Transformation rates due to mixing are then obtained as the difference between net and surface transformation rates. Transports at the boundaries are compared with recent observations, and reasonable agreement is obtained. For the period 1985-1993, model surface transformation rates are broadly in agreement with equivalent rates computed using the globally-balanced SOC fluxes of heat and freshwater, derived from ship observations. In each Atlantic region, surface transformation rates reach 10-15 Sv, based on both model and SOC fluxes. Higher spatial and temporal resolution in the OCCAM surface fluxes may improve the realism of surface transformation rates in some regions, notably the Labrador Sea. However, the unrealistic location of the North Atlantic Current too far south leads to spurious surface heating east of the Grand Banks in OCCAM. Period-mean transformation rates due to mixing reveal the formation of intermediate waters in each region due to the "consumption" of lighter and denser waters formed by surface fluxes, and are comparable with recent inverse estimates. There is, however, strong interannual-to-decadal variability in the consumption rates. In the subtropics, STMW consumption rates co-vary with STMW formation rates. In the subpolar gyre, anomalies in SPMW consumption rate appear to lag anomalies in the surface formation rate by up to 4 years.
Effects of mesoscale eddies on global ocean distributions of CFC-11, CO2 and Δ14C
Authors: Lachkar Z. , Orr J. C. , Dutay J.-C. , Delecluse P.
Published: April 2010

Abstract. Global-scale tracer simulations are typically made at coarse resolution without explicitly modeling eddies. Here we ask what role do eddies play in ocean uptake, storage, and meridional transport of transient tracers. We made global anthropogenic transient-tracer simulations in non-eddying (2°cosφ×2°, ORCA2) and eddying (½°cosφ×½°, ORCA05) versions of the ocean general circulation model OPA9. We focus on the Southern Ocean where tracer air-sea fluxes are largest. Eddies have little effect on global and regional bomb Δ14C uptake and storage. Yet for anthropogenic CO2 and CFC-11, increased eddy activity reduces southern extratropical uptake by 28% and 25% respectively. There is a similar decrease in corresponding inventories, which provides better agreement with observations. With higher resolution, eddies strengthen upper ocean vertical stratification and reduce excessive ventilation of intermediate waters by 20% between 60° S and 40° S. By weakening the Residual Circulation, i.e., the sum of Eulerian mean flow and the opposed eddy-induced flow, eddies reduce the supply of tracer-impoverished deep waters to the surface near the Antarctic divergence, thus reducing the air-sea tracer flux. Consequently, inventories for both CFC-11 and anthropogenic CO2 decrease because their mixed layer concentrations in that region equilibrate with the atmosphere on relatively short time scales (15 days and 6 months, respectively); conversely, the slow air-sea equilibration of bomb Δ14C of 6 years, gives surface waters little time to exchange with the atmosphere before they are subducted.
Mechanisms controlling primary and new production in a global ecosystem model – Part I: The role of the large-scale upper mixed layer variability
Authors: Popova E. E. , Coward A. C. , Nurser G. A. , de Cuevas B. , Fasham M.J.R. , Anderson T. R.
Published: April 2010

Abstract. A global general circulation model coupled to a simple six-compartment ecosystem model is used to study the extent to which global variability in primary and export production can be realistically predicted on the basis of advanced parameterizations of upper mixed layer physics, without recourse to introducing extra complexity in model biology. The ''K profile parameterization'' (KPP) scheme employed, combined with 6-hourly external forcing, is able to capture short-term periodic and episodic events such as diurnal cycling and storm-induced deepening. The model realistically reproduces various features of global ecosystem dynamics that have been problematic in previous global modelling studies, using a single generic parameter set. The realistic simulation of deep convection in the North Atlantic, and lack of it in the North Pacific and Southern Oceans, leads to good predictions of chlorophyll and primary production in these contrasting areas. Realistic levels of primary production are predicted in the oligotrophic gyres due to high frequency external forcing of the upper mixed layer (accompanying paper Popova et al., 2006) and novel parameterizations of zooplankton excretion. Good agreement is shown between model and observations at various JFOFS time series sites: BATS, KERFIX, Papa and station India. One exception is that the high zooplankton grazing rates required to maintain low chlorophyll in high-nutrient low-chlorophyll and oligotrophic systems lessened agreement between model and data in the northern North Atlantic, where mesozooplankton with lower grazing rates may be dominant. The model is therefore not globally robust in the sense that additional parameterizations were needed to realistically simulate ecosystem dynamics in the North Atlantic. Nevertheless, the work emphasises the need to pay particular attention to the parameterization of mixed layer physics in global ocean ecosystem modelling as a prerequisite to increasing the complexity of ecosystem models.
The low-resolution CCSM2 revisited: new adjustments and a present-day control run
Authors: Prange M.
Published: April 2010

Abstract. The low-resolution (T31) version of the Community Climate System Model CCSM2.0.1 is revisited and adjusted by deepening the Greenland-Scotland ridge, changing oceanic mixing parameters, and applying a regional freshwater flux adjustment at high northern latitudes. The main purpose of these adjustments is to maintain a robust Atlantic meridional overturning circulation which collapses in the original model release. The paper describes the present-day control run of the adjusted model which is brought into climatic equilibrium by applying a deep-ocean acceleration technique. The accelerated integration is extended by a 100-year synchronous phase. The simulated meridional overturning circulation has a maximum of 14×106 m3 s−1 in the North Atlantic. Most shortcomings found in the control run are identified as "typical problems" in global climate modelling. Given its good simulation skills and its relatively low resource demands, the adjusted low-resolution version of CCSM2.0.1 appears to be a reasonable alternative to the latest low-resolution Community Climate System Model release (CCSM3.0) if runtime is a critical factor.
The M3A multi-sensor buoy network of the Mediterranean Sea
Authors: Nittis K. , Tziavos C. , Bozzano R. , Cardin V. , Thanos Y. , Petihakis G. , Schiano M. E. , Zanon F.
Published: April 2010

Abstract. A network of three multi-sensor timeseries stations able to deliver real time physical and biochemical observations of the upper thermocline has been developed for the needs of the Mediterranean Forecasting System during the MFSTEP project. They follow the experience of the prototype M3A system that was developed during the MFSPP project and has been tested during a pilot pre-operational period of 22 months (2000–2001). The systems integrate sensors for physical (temperature, salinity, turbidity, current speed and direction) as well as optical and chemical observations (dissolved oxygen, chlorophyll-a, PAR, nitrate). The south Aegean system (E1-M3A) follows a modular design using independent mooring lines and collects biochemical data in the upper 100 m and physical data in the upper 500 m of the water column. The south Adriatic buoy system (E2-M3A) uses similar instrumentation but on a single mooring line and also tests a new method of pumping water samples from relatively deep layers, performing analysis in the protected ''dry'' environment of the buoy interior. The Ligurian Sea system (W1-M3A) is an ideal platform for air-sea interaction processes since it hosts a large number of meteorological sensors while its ocean instrumentation, with real time transmission capabilities, is confined in the upper 50 m layer. Despite their different architecture, the three systems have common sampling strategy, quality control and data management procedures. The network operates in the Mediterranean Sea since autumn 2004 collecting timeseries data for calibration and validation of the forecasting system as well for process studies of regional dynamics.
Improved quality check procedures of XBT profiles in MFS-VOS
Authors: Reseghetti F. , Borghini M. , Manzella G. M. R.
Published: April 2010

Abstract. Sippican T4/DB XBT profiles, collected in the framework of Mediterranean Forecasting System – Toward Environmental Prediction, are analysed, namely the possible influence of launching position height, ship speed and of probes' characteristics. Comparison of XBT vs CTD profiles have suggested some changes in quality control procedures and, more important, in the values of fall rate coefficients customised for the Mediterranean. The effects of these new procedures on the overall uncertainty on depth and on temperature measurements are estimated.
An oceanographer’s guide to GOCE and the geoid
Authors: Hughes C. W. , Bingham R. J.
Published: April 2010

Abstract. A review is given of the geodetic concepts necessary for oceanographers to make use of satellite gravity data to define the geoid, and to interpret the resulting product. The geoid is defined, with particular attention to subtleties related to the representation of the permanent tide, and the way in which the geoid is represented in ocean models. The usual spherical harmonic description of the gravitational field is described, together with the concepts required to calculate a geoid from the spherical harmonic coefficients. A brief description is given of the measurement system in the GOCE satellite mission, scheduled for launch shortly, followed by a description of a reference ellipsoid with respect to which the geoid may be calculated. Finally, a recipe is given for calculation of the geoid relative to any chosen ellipsoid, given a set of spherical harmonic coefficients and defining constants.
Atmospheric forcing of DSOW salinity
Authors: Holfort J. , Albrecht T.
Published: April 2010

Abstract. The temporal evolution of the characteristics of Denmark Strait Overflow Water (DSOW) is reconstructed using hydrographic data and compared with possible atmospheric forcing mechanisms. It is concluded that the main factor influencing the DSOW characteristics at a time scale of one to several years is the difference in mean sea level pressure across, respective wind along Denmark Strait. The main process which leads to salinity changes in the DSOW is therefore changing percentages of the different water masses involved in the DSOW formation and not the changes of the characteristics of these water masses.
Physical response of the coastal ocean to Hurricane Isabel near landfall
Authors: Bingham F. M.
Published: April 2010

Abstract. Hurricane Isabel made landfall near Drum Inlet, North Carolina on 18 September 2003. In nearby Onslow Bay an array of 5 moorings captured the response of the coastal ocean to the passage of the storm by measuring currents, surface waves, bottom pressure, temperature and salinity. Temperatures across the continental shelf decreased by 1–3°C, consistent with a surface heat flux estimate of 750 W/m2. Salinity decreased at most mooring locations. A calculation at one of the moorings estimates rainfall of 11 cm and a net addition of fresh water at the surface of 8 cm. The low-pass current field shows a shelf-wide movement of water, first to the southwest, with an abrupt reversal to the northeast along the shelf after landfall. Close analysis of this reversal shows it to be a disturbance propagating offshore at a speed somewhat less than the local shallow water wave speed. The high-pass current field at one of the moorings shows a significant increase in kinetic energy at periods between 10 min and 2 h during the approach of the storm. This high-pass flow is isotropic and has a short (<5 m) vertical decorrelation scale. It appears to be closely associated with the winds, Finally we examined the surface wave field at one of the moorings. It shows the swell energy peaking well before the winds waves. At the height of the storm, as the winds rotated rapidly in the cyclonic sense, the wind wave direction rotated as well, with a lag of 45–90°.
The improvements of the Ships Of Opportunity Program in MFSTEP
Authors: Manzella G. M. R. , Reseghetti F. , Coppini G. , Borghini M. , Crusado A. , Galli C. , Gertman I. , Gervais T. , Hayes D. , Millot C. , Özsoy E. , Tziavos C. , Velasquez Z. , Zodiatis G.
Published: April 2010

Abstract. The Ships Of Opportunity Program in the Mediterranean Sea was established at the end of 1999, in the framework of the Mediterranean Forecasting System – Pilot Project (MFS-PP). Many improvements have been made in data collection, transmission and management. Calibration of selected XBTs and a comparison of XBTs vs. CTDs during some research cruises have assured the quality of the data. Transmission now allows receiving data in full resolution by using GSM or satellite telecommunication services; management is offering access to high quality data and view services. The effects of technological and methodological improvements in the observing system are assessed in terms of capability to represent the most important circulation features. The improved methodologies have been tested during the Mediterranean Forecasting System – Toward Environmental Prediction (MFS-TEP) – Targeted Operational Period (MFS-TOP), lasting from September 2004 to February 2005. In spite of the short period of measurements, several important aspects of the Mediterranean Sea circulation have been verified, such as eddies and gyres in the various sub-basins, and dense water formation processes in some of them (vertical homogeneous profiles of about 13°C down to ~800 m in the Provencal, and of about 14.9°C down to ~300 m in the Levantine have allowed defining an index of dense water formation).
Assessment of one year of high-resolution operational forecasts for the southeastern Mediterranean shelf region in the MFSTEP project
Authors: Brenner S. , Murashkovsky A. , Gertman I.
Published: April 2010

Abstract. Within the framework of the MFSTEP project an operational ocean forecasting system for the Southeastern Mediterranean Sea has been implemented and evaluated through a series of preoperational tests and subsequently for one year of operational forecasts. The system is based on the Princeton Ocean Model (POM). The high-resolution shelf model is nested in a coarser resolution regional model, which is in turn nested in a coarser resolution full Mediterranean model. The respective grid sizes of the three models are 1.25, 3, and 6 km. Lateral boundary conditions are taken from the daily mean fields of the regional model while the surface forcing is taken from the hourly values of a regional atmospheric forecast model. When compared to satellite derived sea surface temperatures and the MFSTEP analysis fields, the high-resolution shelf model forecasts are significantly more skillful than the coarser model forecasts for the relevant domain. In the four-day forecasts, most of the error appears to be due to the analysis error inherent in the initial conditions. Future development of the system will therefore focus on improving the specification of the initial conditions.
Temporal and spatial characteristics of sea surface height variability in the North Atlantic Ocean
Authors: Cromwell D.
Published: April 2010

Abstract. We investigate the spatial and temporal variability of sea surface height (SSH) in the North Atlantic basin using altimeter data from October 1992–January 2004. Our primary aim is to provide a fuller description of such variability, particularly that associated with propagating signals. We also investigate possible correlations between SSH variability and climate indices. We first investigate interannual SSH variations by deriving the complex empirical orthogonal functions (CEOFs) of altimeter data lowpass-filtered at 18 months. We determine the spatial structure of the leading four modes (both in amplitude and phase) and also the associated principal components (PCs). Using wavelet analysis we derive the time-varying spectral density of the PCs revealing when particular modes are strongest between 1992–2004. The spatial pattern of the leading CEOF, comprising 30% of the total variability, has a 5-year period. Signal propagation with a 5-year period is also observed in the Labrador Sea. The second mode, with a dominant 3-year signal, has strong variability in the eastern basin. We next focus on the Azores subtropical frontal region. The leading mode (35%) is strong in the south and east of this region. The second mode (21%) has a near-zonal band of low variance between ~22°–27° N sandwiched between two regions of high variance. We then lowpass filter the altimeter data at a cutoff of 30 days, instead of 18 months, in order to retain signals associated with propagating baroclinic Rossby waves. The leading mode is the annual steric signal, around 46% of the SSH variability. The third and fourth CEOFs, 11% of the remaining variability, are associated with westward propagation which is particularly dominant in a ''waveband'' between 32°–36° N. No significant cross-correlation is found between the North Atlantic Oscillation index and the amplitude of the leading two principal components of interannual SSH variability. The East Atlantic Pattern index, however, is correlated with the principal components of the two leading modes of SSH variability, particularly with PC2 in the Azores subtropical frontal region. Further investigation of forcing mechanisms is suggested using hindcasts from ocean general circulation models.
How does ocean ventilation change under global warming?
Authors: Gnanadesikan A. , Russell J. L. , Zeng F.
Published: April 2010

Abstract. Since the upper ocean takes up much of the heat added to the earth system by anthropogenic global warming, one would expect that global warming would lead to an increase in stratification and a decrease in the ventilation of the ocean interior. However, multiple simulations in global coupled climate models using an ideal age tracer which is set to zero in the mixed layer and ages at 1 yr/yr outside this layer show that the intermediate depths in the low latitudes become younger under global warming. This paper reconciles these apparently contradictory trends, showing that a decrease in upwelling of old water from below is responsible for the change. Implications for global biological cycling are considered.
A fishery observing system for the collection of fishery and oceanographic data
Authors: Falco P. , Belardinelli A. , Santojanni A. , Cingolani N. , Russo A. , Arneri E.
Published: April 2010

Abstract. Fishery Observing System (FOS) was developed as a first and basic step towards fish stock abundance nowcasting/forecasting within the framework of the EU research program Mediterranean Forecasting System: Toward an Environmental Prediction (MFSTEP). The study of the relationship between abundance and environmental parameters also represents a crucial point towards forecasting. Eight fishing vessels were progressively equipped with FOS instrumentation to collect fishery and oceanographic data. The vessels belonged to different harbours of the Central and Northern Adriatic Sea. For this pilot application, anchovy (Engraulis encrasicolus, L.) was chosen as the target species. Geo-referenced catch data, associated with in-situ temperature and depth, were the FOS products but other parameters were associated with catch data as well. MFSTEP products numerical circulation models provide many of these data. In particular, salinity was extracted from re-analysis data of numerical circulation models. Satellite-derived sea surface temperature (SST) and chlorophyll were also used as independent variables. Catch and effort data were used to estimate an abundance index (CPUE – Catch per Unit of Effort). Considering that catch records were gathered by different fishing vessels with different technical characteristics and operating on different fish densities, a standardized value of CPUE was calculated. A spatial and temporal average CPUE map was obtained together with a monthly mean time series in order to characterise the variability of anchovy abundance during the period of observation (October 2003–August 2005). In order to study the relationship between abundance and oceanographic parameters, Generalized Additive Models (GAM) were used. Preliminary results revealed a complex scenario: the southern sector of the domain is characterised by a stronger relationship than the central and northern sector where the interactions between the environment and the anchovy distribution are hidden by a higher percentage of variability within the system which is still unexplained. GAM analysis showed that increasing the number of explanatory variables also increased the portion of variance explained by the model. Data exchange and interdisciplinary efforts will therefore be crucial for the success of this research activity.
Effects of the 2003 European heatwave on the Central Mediterranean Sea surface layer: a numerical simulation
Authors: Olita A. , Sorgente R. , Ribotti A. , Natale S. , Gaberšek S.
Published: April 2010

Abstract. The effects of anomalous weather conditions on the sea surface layer over the Central Mediterranean were studied with an eddy resolving regional ocean model by performing a 5-year long simulation from 2000 to 2004. The focus was on surface heat fluxes, temperature and dynamics. The analysis of the time series of the selected variables permitted us to identify and quantify the anomalies of the analysed parameters. In order to separate the part of variability not related to the annual cycle and to locate the anomalies in the time-frequency domain, we performed a wavelet analysis of anomalies time series. We found the strongest anomalous event was the overheating affecting the sea surface in the summer of 2003. This anomaly was strictly related to a strong increase of air temperature, a decrease of both wind stress and upward heat fluxes in all their components. The simulated monthly averages of the sea surface temperature were in a good agreement with the remotely-sensed data, although the ocean regional model tended to underestimate the extreme events. We also found, on the basis of the long-wave period of the observed anomaly, this event was not limited to the few summer months, but it was probably part of a longer signal, which also includes negative perturbations of the involved variables. The atmospheric parameters responsible for the overheating of the sea surface also influenced the regional surface and sub-surface dynamics, especially in the Atlantic Ionian Stream and the African Modified Atlantic Water current, in which flows seem to be deeply modified in that period.
Distribution and transport processes of marine particulate matter off Cape Blanc (NW-Africa): results from vertical camera profiles
Authors: Nowald N. , Karakas G. , Ratmeyer V. , Fischer G. , Schlitzer R. , Davenport R. A. , Wefer G.
Published: April 2010

Abstract. In this study, we present vertical particle profiles acquired with the deep-sea camera system ParCa. The profiles were obtained during three campaigns in the spring seasons of 2001–2003 off NW-Africa (Cape Blanc). The camera profiles showed interannual and spatial variabilities regarding the particle concentrations in the ocean surface which were related to changes in the Chl-a biomass concentration. Although particle concentrations varied, all profiles showed rather similar distribution patterns. They were characterised by a subsurface particle maximum layer, around 200 m at stations close to the coast and around 400 m at stations further offshore. We argue, that at least a portion of the material seen in the subsurface maximum originates from the coast, and was laterally advected towards the open ocean by filament activity. Apart from this offshore transport, increased concentrations of particulate matter above the seafloor suggest a downslope transport of particulate matter near the seafloor. Both hypothesis were tested with model computations, described in a companion paper. A special sedimentation event was observed during a field campaign in 2001. The particle abundance patterns and the size distributions most likely reflect a sinking event, where particulate matter is transferred on very short time scales from the surface to the seafloor. We assume, that the fast sinking particle cloud preferably scavenges the more abundant small particles, resulting in larger particles sizes above and within the sinking cloud.
Three decades of research on the greater Agulhas Current
Authors: Lutjeharms J. R. E.
Published: April 2010

Abstract. The greater Agulhas Current has been shown to be a key link in the global thermohaline circulation and an increased understanding of this current system is therefore of more than just local interest. Knowledge on the Agulhas Current system has in fact increased enormously over the past 30 years. This review covers some aspects of what has been learnt on the northern and the southern parts of the Agulhas Current proper and their influence on the waters and circulation of the adjoining continental shelf. It also discusses the Natal Pulse and new information that has been gained on how it is triggered and what influence it has. It deals with the Agulhas retroflection, the shedding of Agulhas rings and the movement and characteristics of these rings. The Agulhas Return Current forms the final outflow of the system and current knowledge on that current is appraised. The sources of the Agulhas Current have been a controversial subject for many years and this dispute continues. This is described and discussed, based on what information has been gained from research over the past three decades. Building on what is currently known, some suggestions are given on the most important remaining knowledge gaps and how these could most efficaciously be filled.
Design of an automatic multiple launcher for expendable probes
Authors: Zappalà G. , Reseghetti F. , Manzella G. M. R.
Published: April 2010

Abstract. A main goal of a ships of opportunity program is the provision of near real time temperature profiles. The use of expandable probes allows the reduction of costs, in comparison to usual scientific cruises. A major cost effectiveness can be achieved by using an automated multiple launcher, that can be used with a minimum personnel effort. A multiple launcher, developed in the framework of the Mediterranean Forecasting System – Toward Environmental Prediction, allows to collect eight temperature profiles, with a sampling strategy that can be monitored automatically by means of a software. The data acquisition system is controlled internally in all functionalities, and data can be transmitted by GSM or satellite telephone systems.
Internal tides and energy fluxes over Great Meteor Seamount
Authors: Gerkema T. , van Haren H.
Published: April 2010

Abstract. Internal-tide energy fluxes are determined halfway over the southern slope of Great Meteor Seamount (Canary Basin), using data from combined CTD/LADCP yoyoing, covering the whole water column. The strongest signal is semi-diurnal and is concentrated in the upper few hundred meters of the water column. An indeterminacy in energy flux profiles is discussed; it is argued that a commonly applied condition used to uniquely determine these profiles does in fact not apply over sloping bottoms. However, the vertically integrated flux can be established unambiguously. The observed results are compared to the outcome of a numerical internal-tide generation model. For the semi-diurnal internal tide, the vertically integrated flux found in the model corresponds well to the observed one. For the diurnal tide, however, the former is much smaller; this points to non-tidal origins of the diurnal signal, which is indeed to be expected at this latitude (30°), where near-inertial and diurnal periods coincide.
LIDAR vs. GEODAS land elevation data in hurricane induced inundation modelling
Authors: Peng M. , Pietrafesa L. J. , Bao S. , Liu H. , Xia M. , Yan T.
Published: April 2010

Abstract. LIDAR (Light Detection and Ranging) and GEODAS (GEOphysical DAta System) are respectively taken as the land elevation data for a 3-D storm surge and inundation model to investigate the subsequent inundation differences. Hilton Head, South Carolina, and Croatan-Albemarle-Pamlico Estuary System (CAPES), North Carolina, are the two investigated regions. Significant inundation differences with LIDAR versus GEODAS are found in both regions. The modeled inundation area with GEODAS is larger than with LIDAR. For Category 2–3 hypothetical hurricanes, the maximum inundation difference in Hilton Head region is 67%, while the difference in the CAPES is 156%. Generally, vertical precision difference of the two databases is the major reason for the inundation difference. Recently constructed man-made structures, not included in the GEODAS, but included in the LIDAR data sets may be another contributing reason.
Seasonal variability of phytoplankton fluorescence in relation to the Straits of Messina (Sicily) tidal upwelling
Authors: Azzaro F. , Decembrini F. , Raffa F. , Crisafi E.
Published: April 2010

Abstract. In the Straits of Messina the large gradients of tidal displacements as well as the topographic constrictions determine the upwelling of deeper waters in the surface layer. This work describes the seasonal variability of surface distribution of phytoplankton biomass depending on upwelling phenomena. Temperature, salinity, nitrates and phytoplankton fluorescence were measured in 1994 and 1995 by continuous underway surface real-time measurements on board dedicated research boats. Each survey was performed following the dynamic phases of flooding and ebbing tides. Tidal currents are essentially southward during the high tide and northward during the low tide. During the low water slack, large spatial gradients of physical-chemical and biological parameters were mainly found, while in the high water slack a diffused phytoplankton fluorescence was observed only in autumn, in coincidence of a seasonal thermocline. Salinity, nitrate and chlorophyll-a fluorescence data revealed a significant positive intercorrelation, whereas they are inversely correlated with temperature. Generally, during winter, the upwelling distribution was limited to narrow zones, while in summer it involved the middle of the Straits and southern zones. During spring in the southern zone of the Straits, maximum of chlorophyll-a fluorescence was detected (May 1995, 0.32 µg-Chla l-1); in summer, when back and forth tidal movements become intense between the Tyrrhenian and the Ionian seas, values was everywhere lower. The data set from continuous and repeatable acquisition has allowed the study of different time-space scales in the Straits of Messina, a very strong dynamic environment. The Straits system can be compared to an "intermittent pump" which, during the different seasons, before enriched itself and then it provides nutrients to the surrounding basins.