How much is the western Mediterranean really warming and salting?

Abstract

[1] Instrumental biases and data processing methods can modify temperature trend estimations and enhance decadal variability in the upper ocean. These questions have not been specifically addressed in the western Mediterranean (WMED), a region where warming and salting trends have been detected during the second half of the twentieth century. In this work we test the sensitivity of these trends and decadal variability in the WMED to the use of bathythermograph data and data processing methods. We analyze different subbasins in order to detect distinct local responses. Our results show that deep waters in the WMED are increasing their temperature and salinity at a rate of 0.002°C/yr and 9.2 Â 10 À4 yr À1 , respectively, from 1943. These trends are spatially homogeneous, not affected by instrumental biases, data processing methods, or changes in the period of time analyzed

Long-term monitoring programme of the hydrological variability in the Mediterranean Sea: a first overview of the HYDROCHANGES network

“…Further limitations in the use of time-and space-scattered (shiphandled CTD) data for trends estimates are: (i) the sensitivity of results to data analysis methods in the case of scarce data sets (Vargas-Yáñez et al, 2009); (ii) difficulty in detecting trends in shallow waters or in the surface layer, where short term variability is high and seasonal cycles are difficult to remove (Vargas-Yáñez et al, 2009); (iii) difficulty to properly estimate important statistical parameters, such as data significance and covariance between data sets, due to large gaps in time series; (iv) difficulty in comparing trends estimated in different places and/or different periods (Millot et al, 2006), preventing an analysis of propagation of signals through the sea (in terms of phase lags between time series); (v) high expensiveness of the experimental strategy, in terms of costs and logistics, preventing the measurements to be performed on e.g. a weekly basis, except for coastal regions (Pascual et al, 1995); (vi) instrumental biases in temperature time series (Vargas-Yáñez et al, 2010). Feedback mechanisms regulating the connections between climate, circulation and marine ecosystems, and possible alterations under future climate scenarios are not yet well understood.…”

The effect of interpolation methods in temperature and salinity trends in the Western Mediterranean

“…Second, we consider those results which are not sensitive to the interpolation process. We then compare such results with previous ones in Vargas-Yáñez et al (2009;2010) and check whether or not these results are also independent from other factors such as averaging methods or the use of bathythermograph data. In this way, it is established whether or not these results are robust, that is, independent of any possible change in the analysis process.…”

“…The candidate factors to have a major influence on the linear trend estimations are: 1) Averaging methods; 2) Instrumental biases; 3) Infilling techniques and 4) Using interpolated versus raw averaged data. The first three points have been analysed in Vargas-Yáñez et al (2010. Hereafter the fourth one will be considered.…”

Modelling the Pelagic Ecosystem Dynamics: The NW Mediterranean

“…However, the climate characteristics might be changing in the last decades as suggested by the increasing occurrence of tropical species (Bianchi, 2007) in line with indications of warming of Mediterranean waters (VargasYáñez et al, 2010). In fact, the connection of upper water layers of the pelagic ecosystem to the lower atmosphere allows the strong atmospheric changes recorded in the last years (Vargas-Yáñez et al, 2010;Camuffo et al, 2010) to produce still uncertain effects on the pelagic ecosystem, thus making even more difficult to understand the ecosystem dynamics.…”