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Rick Lumpkin and Kevin Speer

Hemisphere where the ocean gains heat in the Tropics and loses large amounts of heat in the northern North Atlantic. This heat loss is associated with the formation of mode waters, culminating in Labrador Sea Water, as well as the formation of dense overflows leading to North Atlantic Deep Water (NADW) and the development of the Atlantic overturning circulation. In the subpolar Southern Ocean, discrepancies between flux datasets are larger. The ocean appears to gain heat over a large zone near 45°–50°S

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Adele K. Morrison and Andrew McC. Hogg

1. Introduction The overturning of deep, carbon rich water masses in the Southern Ocean is closely linked to the outgassing rate of natural CO 2 , and hence future changes in upwelling may significantly impact the present-day global oceanic sink of atmospheric CO 2 . The strong link between outgassing and overturning ( Toggweiler et al. 2006 ) has led to the suggestion that the Southern Ocean sink has weakened in response to increased westerly winds, owing to an inferred enhancement of the

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C. S. Jones and Paola Cessi

1. Introduction In the current climate system, deep water is formed in the North Atlantic, but not in the North Pacific, resulting in a global meridional overturning circulation (MOC) that transports heat northward in the Atlantic and contributes to a more marked southward heat flux in the South Indo-Pacific. The MOC is a global cell, driven by the wind-induced upwelling in the circumpolar region ( Toggweiler and Samuels 1993 ; Wolfe and Cessi 2010 ), as well as by diffusive upwelling at the

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Paola Cessi

convergence zone ( Kang et al. 2009 ). The oceanic heat transport in the Atlantic sector, everywhere northward, causes this asymmetry: it arises from the interhemispheric meridional overturning circulation that occupies the middepths of the Atlantic basin. The conceptual framework for the maintenance of the middepth overturning circulation (MOC) and the associated stratification has changed in the last decades. The idea of a diffusive balance between advection of buoyancy by the global overturning and

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A. M. de Boer, J. R. Toggweiler, and D. M. Sigman

from sinking in the Pacific. Thus, how does the Atlantic basin come to dominate the ocean’s overturning and deep circulation? Warren (1983) and Broecker (1991) attribute the Atlantic’s dominance to the fact that the North Atlantic is saltier than the North Pacific. This argument calls upon special geographic factors that reduce the salinity of the North Pacific by excess precipitation ( Warren 1983 ) or increase the salinity of the North Atlantic by excess evaporation ( Broecker 1991 ). One of

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Thomas W. N. Haine

1. Introduction The global ocean overturning circulation is transformed in the high latitudes of both hemispheres. The transformation is achieved by extraction of heat to the atmosphere, addition of meteoric freshwater (from precipitation minus evaporation, river runoff, and iceberg calving), and interaction with ice. Understanding how warm salty inflows to polar oceans partition into different outflow components is primitive, however, and this question is important for oceanography and climate

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David P. Marshall and Helen R. Pillar

overturning circulation in a rectangular interhemispheric basin. We choose to focus on established problems for two reasons: (i) to instill confidence in the general approach by diagnosing the net rotational forces in problems that are familiar but also (ii) to identify new dynamical insights into certain aspects of these flows. There are several benefits to considering the rotational momentum balance: Many of our conceptual models of the ocean circulation are formulated in terms of vorticity due to the

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Stuart P. Bishop, Peter R. Gent, Frank O. Bryan, Andrew F. Thompson, Matthew C. Long, and Ryan Abernathey

1. Introduction It is currently estimated that more than 40% of the oceanic uptake of anthropogenic CO 2 takes place south of 40°S ( Sallée et al. 2012 ), and mesoscale eddies play an important role in the uptake ( Gnanadesikan et al. 2015 ). The oceanic uptake over the Southern Ocean is largely governed by the strength of the meridional overturning circulation (MOC) and the location of outcropping isopycnals at the surface ( Marshall and Speer 2012 ; Morrison et al. 2015 ). Over the past 50

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Christopher L. Wolfe and Paola Cessi

1. Introduction The meridional overturning circulation (MOC) is a planetary-scale pattern of oceanic flows, which is partially responsible for about 1.3 PW (1 PW = 10 15 W) of heat transport into the North Atlantic ( Ganachaud and Wunsch 2000 ). Changes in the North Atlantic climate have been accompanied by changes in the MOC ( McManus et al. 2004 ; Liu et al. 2009 ). The MOC is also responsible for the downwelling and upwelling that regulates the uptake of CO 2 into the ocean. In particular

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Michael A. Spall and David Nieves

1. Introduction The Atlantic meridional overturning circulation (AMOC) transports significant quantities of heat and freshwater and, as such, represents an important component of the global climate system ( Ganachaud and Wunsch 2003 ; Lumpkin and Speer 2007 ). Variability in the AMOC is correlated with variability in sea surface temperature, air–sea fluxes, and heat storage in the ocean ( Williams et al. 2014 ; Häkkinen et al. 2015 ; Evans et al. 2017 ). The mean AMOC at 26.5°N is

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