Modelling present and future climate in the Mediterranean Sea: a focus on sea-level change (original) (raw)
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Journal of Physical Oceanography, 2004
Aspects of the sea level changes in the western Mediterranean Sea are investigated using a numerical tidal model of the Strait of Gibraltar. As a prerequisite, the performance of this model, that is, a two-dimensional, nonlinear, two-layer, boundary-fitted coordinate numerical model based on the hydrostatic approximation on an f plane, is assessed in the simulation of mean and tidal circulation of the Strait of Gibraltar. The model is forced by imposing mean interface and surface displacements as well as M 2 , S 2 , O 1 , and K 1 tidal components along the Atlantic and Mediterranean model open boundaries. Model results are compared with observations and with results obtained from a tidal inverse model for the eastern entrance of the Strait of Gibraltar. In general, good agreement is found. A sensitivity study performed by varying different model parameters shows that the model behaves reasonably well in the simulation of the averaged circulation. The model is then used to investigate the climatological sensitivity of the simulated dynamics in the Strait of Gibraltar to changes in the density difference between Atlantic and Mediterranean waters. For this purpose, given a certain density difference between Atlantic and Mediterranean waters, the authors iteratively searched for that sea level drop between the Atlantic and the Mediterranean that fulfills the mass balance of the Mediterranean. It is found that an increase of the density difference leads to an increase of the exchange flow and to an increase of the sea level drop between the two basins. A trend in the sea level drop of O(1 cm yr Ϫ1), such as the one observed between 1994 and 1997, is explained by the model as the result of a trend of O(10 Ϫ4 yr Ϫ1) in the relative density difference between the Mediterranean and Atlantic waters. The observed north-south asymmetry in this trend is also captured by the model, and it is found to arise from changes in the along-strait velocity. Results suggest that the dynamics within the Strait of Gibraltar cannot be neglected when sea level changes in the western Mediterranean basin are investigated.
The climate change signal in the Mediterranean Sea in a regionally coupled ocean-atmosphere model
Ocean Science Discussions
We assess the role of ocean feedbacks in the simulation of the present climate and on the downscaled climate change signal in the Mediterranean Sea with the regionally coupled model REMO-OASIS-MPIOM (ROM). The ROM oceanic component is global with regionally high horizontal resolution in the Mediterranean Sea. In our setup the Atlantic and Black Sea circulations are simulated explicitly. Simulations forced by ERA-Interim show a good representation of the present Mediterranean climate. Our analysis of the RCP8.5 scenario driven by MPI-ESM shows that the Mediterranean waters will be warmer and saltier across most of the basin by the end of the century. In the upper ocean layer temperature is projected to have a mean increase of 2.73°C, while the mean salinity increases by 0.17 psu, presenting a decreasing trend in the Western Mediterranean, opposite to the rest of the basin. The warming initially takes place at the surface and propagates gradually to the deeper layers. 1 Introduction The Mediterranean Sea is expected to be among the world most prominent and vulnerable climate change "hot spots". In this context, climate change lies at the heart of sustainable development in the Mediterranean. As such, the region is an optimal test bed for new approaches to science-society partnership sustained by the provision of adequate climate information and applicable to a broad range of vulnerable sectors. The Mediterranean is a regional sea circumscribed by Africa, Europe and Asia and divided into two sub-basins (eastern and western) through a sill that does not exceed 400 m depth between Sicily and the African continent. The region is located in a transitional area between tropical and mid-latitudes and presents a complex orography and coastlines where intense local air-sea and land-sea interactions take place. The freshwater balance in the Mediterranean basin is negative, since the evaporation exceeds rainfall and river runoff (Sanchez-Gomez et al., 2011). This deficit is compensated by a net inflow of water through the Strait of Gibraltar. The region is located in a transitional area between tropical and mid-latitudes and presents a complex orography and coastlines where intense local air-sea and land-sea interactions take place. These intense local air-sea interactions together with the inflow of Atlantic water drive the
The climate change signal in the Mediterranean Sea in a regionally coupled atmosphere–ocean model
Ocean Science
We analyze the climate change signal in the Mediterranean Sea using the regionally coupled model REMO-OASIS-MPIOM (ROM; abbreviated from the regional atmosphere model, the OASIS3 coupler and the Max Planck Institute Ocean Model). The ROM oceanic component is global with regionally high horizontal resolution in the Mediterranean Sea so that the water exchanges with the adjacent North Atlantic and Black Sea are explicitly simulated. Simulations forced by ERA-Interim show an accurate representation of the present Mediterranean climate. Our analysis of the RCP8.5 (representative concentration pathway) scenario using the Max Planck Institute Earth System Model shows that the Mediterranean waters will be warmer and saltier throughout most of the basin by the end of this century. In the upper ocean layer, temperature is projected to have a mean increase of 2.7 • C, while the mean salinity will increase by 0.2 psu, presenting a decreasing trend in the western Mediterranean in contrast to the rest of the basin. The warming initially takes place at the surface and propagates gradually to deeper layers. Hydrographic changes have an impact on intermediate water characteristics, potentially affecting the Mediterranean thermohaline circulation in the future.
MODELING THE RESPONSE OF THE MEDITERRANEAN SEA LEVEL TO GLOBAL AND REGIONAL CLIMATIC PHENOMENA
Fluctuations of the sea level pose an issue of emerging importance, especially after scientific research revealed a clear rising trend. Since the early 80's, a new technique, satellite altimetry, resulted in an abundance of sea surface height measurements and these data are crucial to both oceanographic and geodetic applications. This work presents the results of a correlation study of the Sea Level Anomaly (SLA) with global and regional climatic phenomena that influence the ocean state as well. For this reason, three correlation indexes have been examined. The first one is the well-known Southern Oscillation Index (SOI) corresponding to the ocean response to El Niño/La Niña-Southern Oscillation (ENSO) events. The next index is the North Atlantic Oscillation (NAO) index, which corresponds to the fluctuations in the difference of atmospheric pressure at sea level between the Icelandic low and the Azores high. The last index is the Mediterranean Oscillation Index (MOI), which refers to the fluctuations in the difference of atmospheric pressure at sea level between Algiers and Cairo. The raw data used were SLA values from Jason-1 and Jason-2 satellite altimetry missions for a period of thirteen years (2002-2014) within the entire Mediterranean Basin. Regional multiple regression 1 MSc. Dimitrios A. NATSIOPOULOS, dnatsio@topo.auth.gr 41 and correlation analyses between sea level anomalies and these indexes were carried out in order to detect and model correlations between the Mediterranean sea level and the aforementioned global and regional climatic phenomena.
Sea level forcing in the Mediterranean Sea between 1960 and 2000
Global and Planetary Change, 2008
Sea level trends and inter-annual variability in the Mediterranean Sea for the period 1960-2000 is explored by comparing observations from tide gauges with sea level hindcasts from a barotropic 2D circulation model, and two full primitive equation 3D ocean circulation models, a regional one and the Mediterranean component of a global one,. In the 2D model, 50% of the sea level variance was found to result from the wind and atmospheric pressure forcing. In the 3D models, 20% of the sea level variance was explained by the steric effects. The sea level residuals at the tide gauges locations, calculated by subtraction of the 2D model output from the sea level observations are significantly correlated (r = 0.4) with the steric signals from the 3D models. After the removal of the atmospheric and the steric contributions the tide-gauge sea level records indicate a period where sea level was stable (1960-1975) and a period where sea level was rising (1975-2000) with rates in the range 1.1-1.8 mm/yr. A part of the residual trend can be explained by the contribution of local land movements (0.3 mm/yr) while its major part indicates a global signal, probably mass addition, appearing after 1975.
Global and Planetary Change, 2011
Two-dimensional reconstructions of the Mediterranean sea level corrected for the atmospheric effects are proposed at monthly interval over the period 1970-2006 using 14 tide gage records and 33-year long (1970-2002) sea level grids from the NEMOMED8 regional ocean circulation model (NM8) and the PROTHEUS System Atmosphere-Ocean coupled model (PS). They are compared with a similar reconstruction using decade-long sea level grids from altimetry (Topex/Poseidon and Jason1) and a published reconstruction by Calafat and Gomis (2009). Tests with extra tide gages, not used in the computation, show that interannual variability is better captured when using long (33-year) spatial grids. In particular the NM8-based reconstruction reproduces better the sea level variability at all independent tide gages. An empirical Orthogonal Function decomposition of this reconstruction over 1970-2006 shows that the temporal curve of the two first modes are highly correlated with the North Atlantic Oscillation. We note in particular different behaviors over the 1970-1994 and 1994-2006 time spans. Results suggest that the North Atlantic Oscillation forcing modified the spatial patterns of the Mediterranean sea level around the year 1993 close to the date of occurrence of the Eastern Mediterranean Transient (a major change in the deep water formation of the Levantine and Ionian basin that occurred in the early 1990s).
Oceanologia, 2015
We analyse recent Mediterranean Sea surface temperatures (SSTs) and their response to global change using 1/4-degree gridded advanced very-high-resolution radiometer (AVHRR) daily SST data, 1982SST data, -2012. These data indicate significant annual warming (from 0.24 • C decade −1 west of the Strait of Gibraltar to 0.51 • C decade −1 over the Black Sea) and significant spatial variation in annual average SST (from 15 • C over the Black Sea to 21 • C over the Levantine sub-basin). Ensemble mean scenarios indicate that the study area SST may experience significant warming, peaking at 2.6 • C century −1 in the Representative Concentration Pathways 85 (RCP85) scenario.
Earth-Science Reviews, 2023
2023, Marriner N., Kaniewski D., Pourkerman M., Vacchi M., Melini D., Seeliger M., Morhange C., Spada G., Forecasted weakening of Atlantic overturning circulation could amplify future relative sea-level rise in the Mediterranean: A review of climate and tide-gauge data links, Earth-Science Reviews, 242, 104456. Sea-level rise is one of the most significant and perceptible consequences of global warming because it affects natural environments and coastal anthroposcapes at human timescales, particularly in sediment-starved littoral contexts. Within this framework, improvements in understanding the projection of sea-level rise require better knowledge of regional changes. Here we focus on the recent sea-level history of the Mediterranean Sea, an area characterized by a densely populated coast and where climate variability is larger, and the rate of sea-level rise higher than the global average. We produce a spatially-averaged Mediterranean relative sea-level (RSL) time series, based on 138 tide-gauge records, stretching back to the late 1800s, indicating that Mediterranean RSL has risen by ~24 cm in the past ~140 years. At interdecadal timescales and beyond, we find that Mediterranean relative sea-level rising rates (RSLRR) are significantly influenced by the strength of the Atlantic Multidecadal Oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC). Climate-model predictions of a weakened Atlantic overturning circulation in the coming decades, slowing and diminishing North Atlantic heat transport, has the potential to accentuate Mediterranean rising rates, with significant implications for the basin's coastal societies, infrastructure and economies. We conservatively estimate that a 0.1 • C decrease in AMO sea surface temperatures can accentuate Mediterranean RSLRR by up to − 0.61 ± 0.5 mm yr − 1. Future coastal management and adaptation policies must assimilate these findings into local/regional-scale impact and vulnerability assessments.
Comparison of Several Geoid Models Over the Western Mediterranean Sea
The Mediterranean Sea is a semi-enclosed true ocean. Recent Mediterranean circulation and sea level studies using various observations and ocean general circulation models show good coherence and agreement. The satellite altimetry and tide gauge observed and model predicted sea level show good coherent with correlation coefficient of 0.6. The barotropic pressure response accounts for about 66% of the Mediterranean sea level rise (1948-2001). The estimated sea level trend (1.54 ± 0.75 mm/yr) using decadal altimetry (1985-2001) after correcting the interannual/decadal signals reconstructed using tide gauge data, agrees well with the long term trend (1948-2001) estimated using tide gauges (1.43 ± 0.09 mm/yr) in the Mediterranean Sea, and is in better agreement than before with the global long-term sea level trend (1.7 – 1.8 mm/yr). Simulation studies indicate that the time-varying mass variations of Mediterranean Sea likely are sensitive to GOCE at the few mEötvös level. One of GOCE...
Recent sea surface temperature trends and future scenarios for the Mediterranean Sea
OCEANOLOGIA, 2014
We analyse recent Mediterranean Sea surface temperatures (SSTs) and their response to global change using 1/4-degree gridded advanced very-high-resolution radiometer (AVHRR) daily SST data, 1982SST data, -2012. These data indicate significant annual warming (from 0.24 • C decade −1 west of the Strait of Gibraltar to 0.51 • C decade −1 over the Black Sea) and significant spatial variation in annual average SST (from 15 • C over the Black Sea to 21 • C over the Levantine sub-basin). Ensemble mean scenarios indicate that the study area SST may experience significant warming, peaking at 2.6 • C century −1 in the Representative Concentration Pathways 85 (RCP85) scenario.