The northern North Atlantic Ocean mean circulation in the early 21st century

Abstract

The decadal mean circulation in the northern North Atlantic was assessed for the early 21st century from repeated ship-based measurements along the Greenland-Portugal OVIDE line, from satellite altimetry and from earlier reported transports across 59.5°N and at the Greenland-Scotland sills. The remarkable quantitative agreement between all data sets allowed us to draw circulation pathways with a high level of confidence. The North Atlantic Current (NAC) system is composed of three main branches, referred to as the northern, central and southern branches, which were traced from the Mid-Atlantic Ridge (MAR), to the Irminger Sea, the Greenland-Scotland Ridge and the subtropical gyre. At OVIDE, the northern and central branches of the NAC fill the whole water column and their top-to-bottom integrated transports were estimated at 11.0 ± 3 Sv and 14.2 ± 6.4 Sv (1 Sv = 106 m3 s-1), respectively. Those two branches feed the cyclonic circulation in the Iceland Basin and the flow over the Reykjanes Ridge into the Irminger Sea. This cross-ridge flow was estimated at 11.3 ± 4.2 Sv westward, north of 58.5°N. The southern NAC branch is strongly surface-intensified and most of its top-to-bottom integrated transport, estimated at 16.6 ± 2 Sv, is found in the upper layer. It is composed of two parts: the northern part contributes to the flow over the Rockall Plateau and through the Rockall Trough towards the Iceland-Scotland Ridge; the southern part feeds the anticyclonic circulation towards the subtropical gyre. Summing over the three NAC branches, the top-to-bottom transport of the NAC across OVIDE was estimated at 41.8 ± 3.7 Sv.

Dissolved Organic Nitrogen Production and Export by Meridional Overturning in the Eastern Subpolar North Atlantic

“…The horizontal stream function of the depth-integrated volume transport illustrates the main features of the circulation across the OVIDE 2002 section ( Figure 2a) described in detail elsewhere (Daniault et al, 2016;Lherminier et al, 2007). The basin-scale transport in the eSPNA was constituted by the northward flow of the NAC located at ∼1,600 km from Greenland in the eastern rim of the gyre and by the southward flow of the EGC, in the western rim of the gyre along the Greenland slope.…”

“…The subpolar North Atlantic (SPNA) is a key region for the Meridional Overturning Circulation (MOC) (Daniault et al, 2016). The North Atlantic Current (NAC) carries warm and saline thermocline waters of subtropical origin into the SPNA gyre along its southeastern rim, constituting the northward flowing upper limb of the MOC in the region (Figure 1a).…”

The GEOVIDE cruise in May–June 2014 reveals an intense Meridional Overturning Circulation over a cold and fresh subpolar North Atlantic

“…1). A careful study of the ADT stream- Daniault et al (2016). Note that the errors given for the GEOVIDE estimates come from the covariance matrix resulting from the inverse model.…”

“…5324 P. Zunino et al: The GEOVIDE cruise in May-June 2014 adapted from Daniault et al (2016), which will be referred to as D2016 hereafter.…”

“…2b); both water masses were advected together by the ERRC, but probably issued from different ventilation regions. According to de Boisséson et al (2012), the SPMW is formed by air-sea interactions on its way around the Iceland Basin. The sign of all the anomalies described above is consistent with vertical mixing in the winter before the GEOVIDE cruise, transferring the cold, fresh, and oxygenated anomalies imprinted locally by the atmosphere into the whole mixed layer.…”