Abstract
Seawater pH is undergoing a decreasing trend due to the absorption of atmospheric CO2, a phenomenon known as ocean acidification (OA). Biogeochemical processes occurring naturally in the ocean also change pH and hence, for an accurate assessment of OA, the contribution of the natural component to the total pH variation must be quantified. In this work, we used 11 years (2005–2015) of biogeochemical measurements collected at the Strait of Gibraltar to estimate decadal trends of pH in two major Mediterranean water masses, the Western Mediterranean Deep Water (WMDW) and the Levantine Intermediate Water (LIW) and assess the magnitude of natural and anthropogenic components on the total pH change. The assessment was also performed in the North Atlantic Central Water (NACW) feeding the Mediterranean Sea. Our analysis revealed a significant human impact on all water masses in terms of accumulation of anthropogenic CO2. However, the decadal pH decline found in the WMDW and the NACW was markedly affected by natural processes, which accounted for by nearly 60% and 40% of the total pH decrease, respectively. The LIW did not exhibit a significant pH temporal trend although data indicated natural and anthropogenic perturbations on its biogeochemical signatures.
Highlights
Seawater pH is undergoing a decreasing trend due to the absorption of atmospheric CO2, a phenomenon known as ocean acidification (OA)
In the current study we examined the relative contribution of both CANT uptake and biology on temporal pH trends in two major Mediterranean water masses, the Western Mediterranean Deep Water (WMDW) and the Levantine Intermediate Water (LIW)
The depth and thickness of each water mass varied along the Strait, which is due to the influence of physical mechanisms that act at different temporal scales, such as tidal currents, winds, atmospheric pressure variations and circulation processes forced by bathymetry that determine the vertical position of water masses[20]
Summary
Seawater pH is undergoing a decreasing trend due to the absorption of atmospheric CO2, a phenomenon known as ocean acidification (OA). Some works have provided a total pH decline between −0.055 and −0.156 pH units[9,12] whereas other studies reported values ranging from −0.005 to −0.06 pH10,13 These discrepancies are based on the simulation of the quantity of CANT that is taken up by Mediterranean water masses. The accurate assessment of the actual extent of ocean acidification requires the identification of the fraction of the total pH change that is purely due to natural processes and discriminate it from the anthropogenic fraction. This analysis is relevant in the MedSea where biogeochemistry is closely linked to water circulation patterns[18,19]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
