| Summary: | The rise in the atmospheric CO2 levels due to human activities (CANT) is softened by its oceanic uptake. But this absorption leads to a suite of chemical changes collectively known as ocean acidification. Although acidification occurs in the world ocean, its impacts tend to be stronger in the high latitude oceans. Moreover, in some regions where vertical movements are relatively fast, i.e., in regions of water mass formation such as the Subpolar North Atlantic, the timescale for deep penetration of CANT is on the order of decades, thus being faster exposed to the acidification effects. This thesis focuses on the acidification and transports of water masses and CO2 in the North Atlantic Subpolar Gyre (NASPG). The changes in CANT, pH, total alkalinity (AT) and aragonite saturation were evaluated in the main water masses of the Irminger and Iceland Basins for the period 1981–2014. The CANT uptake in both basins led to significant acidification rates in the whole water column, which drive the shoaling of the aragonite saturation horizon. The impact of acidification on the CaCO3 pump led to an AT increase in intermediate and deep waters of the Irminger Sea, although models predict that the AT increase would not be detectable until 2040. pH was decomposed in two terms: one derived from the CANT penetration (DpHCant) and another not directly related to the CANT uptake (DpHVar). At steady state, DpHVar would be constant and all the pH changes would be explained through DpHCant. However, in the intermediate waters of the Irminger Basin DpHCant only explains 64-92% of the observed pH decrease and DpHVar contributes to explain up to 28% of the pH change, driven mainly by ventilation changes. To determine the effect of the circulation changes in the oceanic uptake and storage of CANT, the water mass distribution, transport and transformation in the NASPG are discussed for the first decade of the 2000s (2002–2010), as well as the inter-annual variability of the water mass structure from 1997 to 2010. The reduction of the ...
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