Abstract
One century of oceanographic measurements has evidenced gradual increases in temperature and salinity of western Mediterranean water masses, even though the vertical stratification has basically remained unchanged. Starting in 2005, the basic structure of the intermediate and deep layers abruptly changed. We report here evidence of reinforced thermohaline variability in the deep western basin with significant dense water formation events producing large amounts of warmer, saltier and denser water masses than ever before. We provide a detailed chronological order to these changes, giving an overview of the new water masses and following their route from the central basin interior to the east (toward the Tyrrhenian) and toward the Atlantic Ocean. As a consequence of this climate shift, new deep waters outflowing through Gibraltar will impact the North Atlantic in terms of salt and heat input. In addition, modifications in the Mediterranean abyssal ecosystems and biogeochemical cycles are to be expected.
Highlights
One century of oceanographic measurements has evidenced gradual increases in temperature and salinity of western Mediterranean water masses, even though the vertical stratification has basically remained unchanged
We report here evidence of reinforced thermohaline variability in the deep western basin with significant dense water formation events producing large amounts of warmer, saltier and denser water masses than ever before
In the northern part of the Western Mediterranean Sea (WMED) open ocean convection occasionally occurs, driven by atmospheric cooling due to strong northerly winds, and by the general cyclonic circulation that uplifts isopycnals in the centre of the gyre[2], bringing a salty layer of Levantine Intermediate Water (LIW), which comes from the Eastern Mediterranean (EMED), closer to the surface and to the influence of the atmospheric forcing
Summary
One century of oceanographic measurements has evidenced gradual increases in temperature and salinity of western Mediterranean water masses, even though the vertical stratification has basically remained unchanged. The Mediterranean region is recognized as a hot-spot for future climatic changes[1] and can be described as a “miniature ocean”, since most oceanographic processes of the global ocean occur with a turnover timescale about one tenth of the global ocean’s. This makes it a convenient laboratory, more accessible and controlled because of its semi-enclosed nature and its smaller size, where climate changes happen faster and can be observed on scales of human lifetime.
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