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N. P. Holliday, S. Bacon, J. Allen, and E. L. McDonagh

1. Introduction The details of circulation pathways and transport in the western boundary currents (WBCs) of the northwest North Atlantic are an aspect of the global circulation that remains imperfectly understood. The general nature of the currents around Greenland and northeast Canada has been known for some time: shallow components transport both freshwater from the high latitudes and salinity from the subpolar regions into the Labrador Sea. There, they combine with the underlying cold

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Chaojiao Sun, Ming Feng, Richard J. Matear, Matthew A. Chamberlain, Peter Craig, Ken R. Ridgway, and Andreas Schiller

1. Introduction Ocean boundary currents are poorly represented in the current climate models that contribute to the Coupled Model Intercomparison Project phase 3 (CMIP3), an initiative by the World Climate Research Programme (WCRP). This representation is partly due to an insufficient horizontal resolution of about 1°–2° (about 100–200km) in the ocean component of climate models, too large to realistically simulate these narrow jets. As a result there is limited confidence in the structural

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Hajime Nishigaki and Humio Mitsudera

1. Introduction The Kuroshio south of Japan, which is a part of the subtropical western boundary current in the North Pacific, has a bimodal nature having two types of paths, the nonlarge meander (NLM) paths and the large meander (LM) paths ( Fig. 1 ; also see Kawabe 1995 ). This study is motivated by the nature of the nearshore NLM (nNLM; in Fig. 1 ) path of the Kuroshio. It detaches from the coastline and the bottom slope downstream of Cape Shiono-misaki. A region with weak current is

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Erwin Lambert, Tor Eldevik, and Michael A. Spall

; Eldevik and Nilsen 2013 ; Lambert et al. 2016 ). The transformation of AW that results in a net density increase occurs primarily in the boundary current as postulated by Mauritzen (1996) , who attributed this transformation to surface heat loss from the boundary region. Spall (2004) indicated that lateral heat loss from the boundary due to eddy fluxes could contribute significantly to net densification. The downstream buoyancy loss can induce a shoreward flow onto the continental shelves, forming

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Veit Lüschow, Jin-Song von Storch, and Jochem Marotzke

focused on those occurring near the surface, while deep eddies and their interaction with deep ocean currents has received little attention. Here, we address one such current, namely, the deep western boundary current (DWBC) in the Atlantic, and describe its interplay with mesoscale eddy fluxes. The DWBC is expected to constitute the deep limb of the Atlantic meridional overturning circulation (AMOC; Fine 1995 ). Yet, recent observational studies question the continuous nature of the DWBC, in

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Wenjing Jia, Dong Wang, Nadia Pinardi, Simona Simoncelli, Andrea Storto, and Simona Masina

1. Introduction Featured by mesoscale activities and strong carbon uptake (e.g., Takahashi et al. 2002 ; Yu and Weller 2007 ), the western boundary current (WBC) region plays a key role in the ocean heat transport and overturning circulation. Being characterized by a frontal structure and by mesoscale and ring dynamics, the WBC and its associated recirculation subregions are challenging in terms of observational and modeling requirements for climatological studies. Even with coordinated in

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Gordon E. Swaters

1. Introduction The deep western boundary currents (DWBCs) in the Atlantic Ocean are an important pathway for the equatorward flow of deep cold waters produced in the Labrador and Norwegian/Greenland Seas. In midlatitudes, these currents correspond to grounded equatorward flows on a sloping bottom with distinct upslope and downslope incroppings or groundings (locations where the isopycnal or height field intersects the bottom; e.g., see Fig. 3 in Toole et al. 2011 ). (It is important to point

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Kathryn A. Kelly, R. Justin Small, R. M. Samelson, Bo Qiu, Terrence M. Joyce, Young-Oh Kwon, and Meghan F. Cronin

1. Introduction In the strong Northern Hemisphere midlatitude western boundary current (WBC) systems—the Gulf Stream (GS) in the North Atlantic and the Kuroshio Extension (KE) in the North Pacific—there is a complex interaction between dynamics and thermodynamics and between the atmosphere and ocean ( Fig. 1 ). A precipitous drop in the meridional transport of heat in the Northern Hemisphere ocean occurs where these warm WBCs separate from the coast and flow into the ocean interior ( Trenberth

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Aviv Solodoch, James C. McWilliams, Andrew L. Stewart, Jonathan Gula, and Lionel Renault

. 3), and influencing the CO 2 sink in the North Atlantic ( Takahashi et al. 2009 ). Despite its importance, the characterization of three-dimensional AMOC pathways remains incomplete, as does the understanding of their driving mechanisms ( Lozier 2012 ). A significant portion of the deep (southward) AMOC branch occurs within the deep western boundary current (DWBC). The occurrence and role of the DWBC was predicted by Stommel and Arons (1959) , albeit on the basis of assumptions now partially

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Xuebin Zhang, Bruce Cornuelle, and Dean Roemmich

model ( Heimbach et al. 2005 ). The adjoint model calculates the sensitivity (i.e., the partial derivative) of the cost function J with respect to the control variable υ , which is simply . The model dynamics are contained in the chain rule of partial derivatives. The control variables can be model state, forcing fields, model parameters, and initial or open boundary conditions. For the current study, we are interested in the variability of the meridional boundary transport east of the

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