The Water Mass Transformation in the Upper Limb of the Overturning Circulation in the Southern Hemisphere

Abstract

The warming and salinification of the northwards flowing water masses from the Southern Ocean to the tropics are studied with Lagrangian trajectories simulated using fields from an Earth System Model. The trajectories are used to trace the geographical distribution of the water mass transformation and connect it with the pathways of the upper limb of the overturning circulation in the Southern Hemisphere. In the Antarctic Circumpolar Current water gains heat just below the mixed layer, mainly when the layer is thin during Austral spring and summer. This gain is therefore suggested to be a consequence of heat flux from the atmosphere and mixing processes at the base of the mixed layer. In the Southern Hemispheric subtropical gyres on the other hand, a large warming and salinification of the northwards flowing water results from internal mixing with other warmer and more saline water masses. Close to the Antarctic shelf waters are getting fresher as a result of ice melting, whereas further north, in the Antarctic Circumpolar current, waters are getting more saline as a result of evaporation. Our results show that it is not only the heat and freshwater fluxes through the sea surface that control the heat and salt changes of the upper limb of the overturning circulation in the Southern Hemisphere. In fact, internal mixing accounts for 25% of the heat change, and 22% of the salinity change.

Identification of the atmospheric water sources and pathways responsible for the East Asian summer monsoon rainfall

“…The three‐dimensional mass‐conserving Lagrangian particle tracing algorithm TRACMASS v7.0 (Aldama‐Campino et al, 2020; Döös, 1995) is used in the present study to identify the water sources and pathways responsible for East Asian rainfall. TRACMASS has been used to trace water in the ocean (Berglund et al, 2017; Berglund et al, 2021; Berglund et al, 2022; Döös et al, 2008) and air in the atmosphere (Kjellsson & Döös, 2012; Schumacher et al, 2022). Recently, TRACMASS was modified to trace atmospheric water (Dey & Döös, 2020).…”

North Atlantic Ocean Circulation and Related Exchange of Heat and Salt Between Water Masses

“…However, only 5.3% of the trajectories needed this looping; the remaining 94.7% exited through a boundary withing the 1850-2014 period. Looping data when simulating trajectories has been discussed in previous studies and do not generate large errors (e.g., Berglund et al, 2017Berglund et al, , 2021Thomas et al, 2015;Van Sebille et al, 2018). Trajectories that exited through the sea surface during the simulation were treated separately and gave rise to a total of 0.9 Sv for all water in the Atlantic Ocean.…”