Model Thermohaline Trends in the Mediterranean Sea during the Last Years: A Change with Respect to the Last Decades?

Temperature and salinity outputs from ECCO (years 93–09) and GLORYS (years 03–09) models have been used to compute the thermohaline and steric sea level trends in the surface (0–150 m), intermediate (150 m–600 m), and deep (600 m–bottom) layers of the Mediterranean Sea. Some changes with respect to the second half of the 20th century have been observed: the cooling of the upper waters of the entire eastern basin since 1950 seems to have vanished; the warming of WMDW historically reported for the second half of the last century could have reversed, although there is no agreement between both models at this point (trends of different sign are predicted); the salinification of WMDW reported for the previous decades is not observed in the south-westernmost area in the period 93–09, and a clear change from positive to negative in the steric sea level trend with respect to the period 93–05 is detected due to the sharp decreasing steric sea level of years 02–06

The Numerical Solution of the External Dirichlet Generalized Harmonic Problem for a Sphere by the Method of Probabilistic Solution

In the present paper, an algorithm for the numerical solution of the external Dirichlet generalized harmonic problem for a sphere by the method of probabilistic solution (MPS) is given, where “generalized” indicates that a boundary function has a finite number of first kind discontinuity curves. The algorithm consists of the following main stages: (1) the transition from an infinite domain to a finite domain by an inversion; (2) the consideration of a new Dirichlet generalized harmonic problem on the basis of Kelvin’s theorem for the obtained finite domain; (3) the numerical solution of the new problem for the finite domain by the MPS, which in turn is based on a computer simulation of the Weiner process; (4) finding the probabilistic solution of the posed generalized problem at any fixed points of the infinite domain by the solution of the new problem. For illustration, numerical examples are considered and results are presented.Partial funding for open access charge: Universidad de Málag

A Method to Extract Measurable Indicators of Coastal Cliff Erosion from Topographical Cliff and Beach Profiles: Application to North Norfolk and Suffolk, East England, UK

Recession of coastal cliffs (bluffs) is a significant problem globally, as around 80% of Earth’s coastlines are classified as sea cliffs. It has long been recognised that beaches control wave energy dissipation on the foreshore and, as a result, can provide protection from shoreline and cliff erosion. However, there have been few studies that have quantified the relationship between beach levels and cliff recession rates. One of the few quantitative studies has shown that there is a measurable relationship between the beach thickness (or beach wedge area (BWA) as a proxy for beach thickness) and the annual cliff top recession rate along the undefended coast of North Norfolk and Suffolk in eastern England, United Kingdom (UK). Additionally, previous studies also found that for profiles with low BWA, the annual cliff top recession rate frequency distribution follows a bimodal distribution. This observation suggests that as BWA increases, not only does cliff top recession rate become lower, but also more predictable, which has important implications for coastal stakeholders particularly for planning purposes at decadal and longer time scales. In this study, we have addressed some of the limitations of the previous analysis to make it more transferable to other study sites and applicable to longer time scales. In particular, we have automatised the extraction of cliff tops, toe locations, and BWA from elevation profiles. Most importantly, we have verified the basic assumption of space-for-time substitution in three different ways: (1) Extending the number or years analysed in a previous study from 11 to 24 years, (2) extending the number of locations at which cliff top recession rate and BWA are calculated, and (3) exploring the assumption of surface material remaining unchanged over time by using innovative 3D subsurface modelling. The present study contributes to our understanding of a poorly known aspect of cliff–beach interaction and outlines a quantitative approach that allows for simple analysis of widely available topographical elevation profiles, enabling the extraction of measurable indicators of coastal erosion

Assessment of the spawning habitat, spatial distribution, and Lagrangian dispersion of the European anchovy (Engraulis encrasicolus) early stages in the Gulf of Cadiz during an apparent anomalous episode in 2016

Modelling the environmental factors influencing the spatial variation of fish early life stages density and their drift history can identify the key biological and physical processes for the recruitment variability. Distance-based linear multivariate techniques were used to characterize the spawning areas of the European anchovy Engraulis encrasicolus in the Gulf of Cadiz (GoC). Chlorophyll is the environmental variable that best characterized its spawning areas with a time-lag of three days. The use of Lagrangian models to simulate the dispersal of small pelagic species more dependent on advection such as the European anchovy early life stages (early larvae and eggs) in the GoC could provide the degree of connectivity between spawning and nursery areas and identify the physical drivers of the recruitment variability. The larval final destination is critical for the survival of a marine species which is coastal-dependent during its early life stages. Simulations with a Lagrangian transport model in the Southwest Iberian Peninsula were performed during the most intense spawning peak of 2016, when a strong and persistent countercurrent event developed. Most of the simulated early life stages were transported to the western Portuguese coast and, to a lesser extent, to the Atlantic oligotrophic waters, suggesting an increase in the connectivity between the subdivision 9a South and West components. Although different environmental processes occurring during ontogenetic stages, as well as overfishing, among others, can explain part of the variability observed in recruitment, events such as the development of coastal countercurrents during the spawning season could partly account for an increase of anchovy on the western Portuguese coast and a decrease in the Gulf of Cadiz one year laterFinancial support was given by ECOCADIZ 2016 (Spanish Institute of Oceanography, Spain) . The authors thank the crews of the R/V Miguel Oliver for technical assistance on the field. ATM acknowledges project 'SARDINHA2020Abordagem Ecossistemica para a gestAo da pesca da sardinha (MAR01.04.02FEAMP0009) ', from the Programa Operacional MAR 2020 (Portugal) . Open Access has been partly financed by the University of Cadiz (Spain) , the Campus de Excelencia Internacional/Global del Mar (CEI MAR, Spain) , and the research group RNM337 Oceanograflia y Teedeteccion (Spain) . The authors are also grateful to Dr. Morais and to another anonymous reviewer for their constructive comments

Understanding the patterns of biological response to physical forcing in the Alboran Sea (western Mediterranean)

A singular value decomposition (SVD) analysis was performed to determine the coupled modes of variability of satellite surface chlorophyll (CHL) and absolute dynamic topography (ADT) data for the Alborán Sea (western Mediterranean) during a 12-year period (1998–2009). From this analysis we have been able to detect features of the Alborán Sea dynamics that had not been recognized in previous research on the primary production of this basin. We have found that the two leading SVD modes represent more than 97% of the total squared covariance. The first mode is associated with the inverse barometer and its impact on chlorophyll distribution, whereas the second physical mode can explain the distribution of eutrophic and oligotrophic waters in the Alborán Sea. The results also confirm that the phytoplankton in the basin is very tightly controlled by meteorological and physical processes, via the advection of properties through the Strait, by the influence of Atlantic Jet intensity, which controls the gyres of the basin, and by the activation of up- or down-welling coastal processes by wind

The effect of Mediterranean exchange flow on European time mean sea level

Using a suite of ocean model simulations and a set of dedicated twin experiments, we show that the exchange flow between the Mediterranean and the North Atlantic leads to a drop in time mean European coastal sea level along the Atlantic coast north of Gibraltar. The drop is about 7 cm along the Portuguese coast and remains apparent (though reduced) as far north as the Norwegian coast. We also show that Mediterranean time and spatial mean sea level is about 9 cm lower than it would be without the exchange flow (but assuming a small supply from the Atlantic to balance evaporation). Each of these relationships makes possible an estimate of the magnitude of the exchange flow based on sea level measurements, and estimates of 0.8 and 0.91 sverdrups are made consistent with previous determinations based mainly on current measurements in the Strait of Gibraltar

The upper-oceanic response to overflows : a mechanism for the Azores Current

Author Posting. © American Meteorological Society, 2008. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 38 (2008): 880–895, doi:10.1175/2007JPO3750.1.The oceanic response to overflows is explored using a two-layer isopycnal model. Overflows enter the open ocean as dense gravity currents that flow along and down the continental slope. While descending the slope, overflows typically double their volume transport by entraining upper oceanic water. The upper oceanic layer must balance this loss of mass, and the resulting convergent flow produces significant vortex stretching. Overflows thus represent an intense and localized mass and vorticity forcing for the upper ocean. In this study, simulations show that the upper ocean responds to the overflow-induced forcing by establishing topographic β plumes that are aligned more or less along isobaths and that have a transport that is typically a few times larger than that of the overflows. For the topographic β plume driven by the Mediterranean overflow, the occurrence of eddies near Cape St. Vincent, Portugal, allows the topographic β plume to flow across isobaths. The modeled topographic β-plume circulation forms two transatlantic zonal jets that are analogous to the Azores Current and the Azores Countercurrent. In other cases (e.g., the Denmark Strait overflow), the same kind of circulation remains trapped along the western boundary and hence would not be readily detected.SK’s support during the time of his Ph.D. research in the MIT/WHOI Joint Program was provided by the National Science Foundation through Grant OCE04-24741. JP and JY have also received support from the Climate Process Team on Gravity Current Entrainment, NSF Grant OCE-0611530

Aragonite saturation state in a continental shelf (Gulf of Cádiz, SW IberianPeninsula): Evidences of acidification in the coastal area

The spatiotemporal variability of aragonite saturation state (ΩAr) has been studied in the eastern shelf of the Gulf of Cádiz (GoC) (SW Iberian Peninsula). The study was carried out during the years 2014 and 2016 aboard twelve oceanographic cruises, along three or five transects, located between Cape Trafalgar and the Guadiana River. The GoC exhibited oversaturated of calcium carbonate with ΩAr mean values of 2.68 ± 0.30 in surface and 2.05 ± 0.15 in deep waters. pH, total alkalinity (TA), calcium concentration (Ca2+) and ΩAr showed a high variability within the surface mixed layer (SML, z 100 m), TA and Ca2+ concentration presented a conservative behaviour related to the distribution of the different water masses located in the GoC. The vertical variation of ΩAr also depends on the degree of mineralization of these water masses, obtaining the maximum values in the Subtropical North Atlantic Central Water (100–200 m), minimum values in the Subpolar North Atlantic Central Water (about 400 m), and intermediate values associated to the presence of the Mediterranean Water (>500 m). Results showed a significative acidification of the coastal areas, for those depths lower than 100 m from 2006 to 2016, with a mean decrease of pH and ΩAr of −0.0089 and −0.0552 yr−1, respectively. © 2021 The AuthorsThis work was funded by the Spanish CICYT (Spanish Program for Science and Technology) under the contract RTI2018-100865-B-C21 . Dolores Jiménez-López was financed by the University of Cádiz with a FPI fellowship (FPI-UCA) and Ana Sierra was financed by the Spanish Ministry of Education with a FPU fellowship (FPU2014-04048)

Circulation and oxygen cycling in the Mediterranean Sea: Sensitivity to future climate change

Climate change is expected to increase temperatures and decrease precipitation in the Mediterranean Sea (MS) basin, causing substantial changes in the thermohaline circulation (THC) of both the Western Mediterranean Sea (WMS) and Eastern Mediterranean Sea (EMS). The exact nature of future circulation changes remains highly uncertain, however, with forecasts varying from a weakening to a strengthening of the THC. Here we assess the sensitivity of dissolved oxygen (O2) distributions in the WMS and EMS to THC changes using a mass balance model, which represents the exchanges of O2 between surface, intermediate, and deep water reservoirs, and through the Straits of Sicily and Gibraltar. Perturbations spanning the ranges in O2 solubility, aerobic respiration kinetics, and THC changes projected for the year 2100 are imposed to the O2 model. In all scenarios tested, the entire MS remains fully oxygenated after 100 years; depending on the THC regime, average deep water O2 concentrations fall in the ranges 151–205 and 160–219 µM in the WMS and EMS, respectively. On longer timescales (>1000 years), the scenario with the largest (>74%) decline in deep water formation rate leads to deep water hypoxia in the EMS but, even then, the WMS deep water remains oxygenated. In addition, a weakening of THC may result in a negative feedback on O2 consumption as supply of labile dissolved organic carbon to deep water decreases. Thus, it appears unlikely that climate-driven changes in THC will cause severe O2 depletion of the deep water masses of the MS in the foreseeable future