Effects of the 2003 European heatwave on the Central Mediterranean Sea: surface fluxes and the dynamical response

Abstract

Abstract. The effects of the 2003 European heatwave on the sea surface layer of the Central Mediterranean were studied using a regional 3-D ocean model. The model was used to simulate the period 2000 to 2004 and its performance was validated using remotely-sensed and in situ data. Analysis of the results focused on changes in the Sea Surface Temperature (SST) and on changes to the surface and sub-surface current field. This permitted us to identify and quantify the anomalies of atmospheric and sea surface parameters that accompanied the heatwave. The dominant annual cycle in each variable was first removed and a wavelet analysis then used to locate anomalies in the time-frequency domain.We found that the excess heating affecting the sea surface in the summer of 2003 was related to a significant increase in air temperature, a decrease in wind stress and reduction of all components of the upward heat flux. The monthly averages of the model SST were found to be in good agreement with remotely-sensed data during the period studied, although the ocean model tended to underestimate extreme events. The spatial distribution of SST anomalies as well as their timefrequency location was similar for both the remotely-sensed and model temperatures. We also found, on the basis of the period of the observed anomaly, that the event was not limited to the few summer months of 2003 but was part of a longer phenomenon. Both the model results and experimental data suggest the anomalous heating mainly affected the top 15 m of ocean and was associated with strong surface stratification and low mixing.The skill of the model to reproduce the sub-surface hydrographic features during the heatwave was checked by comparison with temperature and salinity measurements. ThisCorrespondence to: A. Olita (a.olita@iamc.cnr.it) showed that the model was generally in good agreement with observations. The model and observations showed that the anomalous warming also modified the currents in the region, most noticeably the Atlantic Ionian Stream (AIS) and the Atlantic Tunisian Current (ATC). The AIS was reduced in intensity and showed less meandering, mainly due to the reduced density gradient and low winds, while the ATC was enhanced in strength, the two currents appearing to modulate each other in order to conserve the total transport of Modified Atlantic Water.

Frequency of marine heatwaves in the North Atlantic and North Pacific since 1950

“…These events have been referred to as marine heatwaves and have been described as regions of large-scale and persistent positive sea surface temperature (SST) anomalies [Pearce et al, 2011]. Well-known marine heatwaves have occurred in the Mediterranean Sea [Black et al, 2004;Olita et al, 2007], off Western Australia [Pearce and Feng, 2013], in the northwest Atlantic [Mills et al, 2013;Chen et al, 2014Chen et al, , 2015, and in the northeast Pacific [Bond et al, 2015;Hartmann, 2015]. Like heatwaves on land, marine heatwaves are likely to become more frequent and intense under continued anthropogenic warming assuming fixed temperature thresholds [Solomon et al, 2007].…”

SLA–chlorophyll-a variability and covariability in the Algero-Provençal Basin (1997–2007) through combined use of EOF and wavelet analysis of satellite data

“…The main mechanism explaining this relationship is the shoaling/deepening of the isopycnae due to the action of dynamical features, having a SLA signature, which produces the increase/decrease of nutrients injection into the euphotic layer. The study of the relationships between hydrodynamical processes and the dynamics of the first trophic levels are topical from a theoretical point of view as well as to understand (and possibly to predict) the ecological effects of hydrodynamic shifts in a climate change scenario (Turley 1999;Schär et al 2004;Somot et al 2006;Olita et al 2007). This study becomes more important in highly dynamic seas, like the Western Mediterranean, where the hydrodynamic processes may strongly influence the phytoplankton distribution and concentration (Moran et al 2001;Taupier-Letage et al 2003;Isern-Fontanet et al 2004;Ribotti et al 2004;Kahru et al 2007).…”

Impact of SLA assimilation in the Sicily Channel Regional Model: model skills and mesoscale features

“…The Sicily Channel (sub-)Regional Model (SCRM Sorgente et al, 2003;Gaberšek et al, 2007;Olita et al, 2007;Sorgente et al, 2011) has produced, since 2003, forecasts and simulations of the central Mediterranean Sea including the southern Tyrrhenian Sea, the Sardinia Channel, the Sicily Channel, the western part of the Ionian Sea and a wide area over the Tunisian and Libyan continental shelves. SCRM is part of the national and Mediterranean networks of operational oceanography, namely GNOO (Italian National Group of Operational Oceanography) and MOON (Mediterranean Operational Oceanography Network).…”