Redrawing the Iceland−Scotland Overflow Water pathways in the North Atlantic

Zou, Sijia; Bower, Amy S.; Furey, Heather H.; Lozier, M. Susan; Xu, Xiaobiao

doi:10.1038/s41467-020-15513-4

Cited by 20 publications

(22 citation statements)

References 31 publications

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“…These OSNAP observations reveal that changes in the western boundary current in the subpolar North Atlantic are not, by themselves, indicators of subpolar MOC variability on monthly to interannual time scales. The MOC lower limb in the subpolar North Atlantic has a complex circulation 3 , 39 and changes in the full set of pathways combine to describe the MOC and its variability. Thus, a partial measurement (or proxy) of the DWBC transport or density variations in a limited geographical area (e.g., in the central Labrador Sea or within the Labrador Sea western boundary) is insufficient to reconstruct MOC changes in the subpolar region on these time scales.…”

Section: Discussionmentioning

confidence: 99%

Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation

et al. 2021

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Changes in the Atlantic Meridional Overturning Circulation, which have the potential to drive societally-important climate impacts, have traditionally been linked to the strength of deep water formation in the subpolar North Atlantic. Yet there is neither clear observational evidence nor agreement among models about how changes in deep water formation influence overturning. Here, we use data from a trans-basin mooring array (OSNAP—Overturning in the Subpolar North Atlantic Program) to show that winter convection during 2014–2018 in the interior basin had minimal impact on density changes in the deep western boundary currents in the subpolar basins. Contrary to previous modeling studies, we find no discernable relationship between western boundary changes and subpolar overturning variability over the observational time scales. Our results require a reconsideration of the notion of deep western boundary changes representing overturning characteristics, with implications for constraining the source of overturning variability within and downstream of the subpolar region.

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Section: Discussionmentioning

confidence: 99%

Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation

et al. 2021

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“…ISOW flows close to the bottom from the Iceland Sea to the North Atlantic in the region east of Iceland, mainly through the Faroe Bank Channel (Swift, 1984;Lacan et al, 2004;Zou et al, 2020). ISOW turns into two main branches before passing the Charlie-Gibbs Fracture Zone (CGFZ), with the first one flowing through the Mid-Atlantic Ridge, into the Irminger Basin, where it meets and mixes with DSOW (Fig.…”

Section: Iceland-scotland Overflow Watermentioning

confidence: 99%

Water masses in the Atlantic Ocean: characteristics and distributions

Liu

Tanhua

2021

Ocean Sci.

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Abstract. A large number of water masses are presented in the Atlantic Ocean, and knowledge of their distributions and properties is important for understanding and monitoring of a range of oceanographic phenomena. The characteristics and distributions of water masses in biogeochemical space are useful for, in particular, chemical and biological oceanography to understand the origin and mixing history of water samples. Here, we define the characteristics of the major water masses in the Atlantic Ocean as source water types (SWTs) from their formation areas, and map out their distributions. The SWTs are described by six properties taken from the biased-adjusted Global Ocean Data Analysis Project version 2 (GLODAPv2) data product, including both conservative (conservative temperature and absolute salinity) and non-conservative (oxygen, silicate, phosphate and nitrate) properties. The distributions of these water masses are investigated with the use of the optimum multi-parameter (OMP) method and mapped out. The Atlantic Ocean is divided into four vertical layers by distinct neutral densities and four zonal layers to guide the identification and characterization. The water masses in the upper layer originate from wintertime subduction and are defined as central waters. Below the upper layer, the intermediate layer consists of three main water masses: Antarctic Intermediate Water (AAIW), Subarctic Intermediate Water (SAIW) and Mediterranean Water (MW). The North Atlantic Deep Water (NADW, divided into its upper and lower components) is the dominating water mass in the deep and overflow layer. The origin of both the upper and lower NADW is the Labrador Sea Water (LSW), the Iceland–Scotland Overflow Water (ISOW) and the Denmark Strait Overflow Water (DSOW). The Antarctic Bottom Water (AABW) is the only natural water mass in the bottom layer, and this water mass is redefined as Northeast Atlantic Bottom Water (NEABW) in the north of the Equator due to the change of key properties, especially silicate. Similar with NADW, two additional water masses, Circumpolar Deep Water (CDW) and Weddell Sea Bottom Water (WSBW), are defined in the Weddell Sea region in order to understand the origin of AABW.

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“…Traditionally it was thought that the principal origin of ISOW found in the boundary current along the western flank of the Reykjanes Ridge (Daniault et al, 2016) was the Charlie Gibbs Fracture Zone. However, there is growing evidence from modelled and observed float trajectories that Bight Fracture Zone is a very important pathway of ISOW into the western flank of the ridge (Bower et al, 2002;Xu et al, 2010;Zou et al, 2017;Zou et al, 2020). For example, some floats deployed at ISOW densities in the Bight Fracture Zone (Bower et al, 2002;Lankhorst and Zenk, 2006;Zou et al, 2017) have described northward flows connecting with the boundary current while the majority of RAFOS and Deep Argo floats released at the Charlie Gibbs Fracture Zone followed westnorthwest interior pathways or took a southward direction along the Mid Atlantic Ridge (Racapéet al, 2019;Zou et al, 2020).…”

Section: Observed Isow Pathways In 2017-2018mentioning

confidence: 99%

“…However, there is growing evidence from modelled and observed float trajectories that Bight Fracture Zone is a very important pathway of ISOW into the western flank of the ridge (Bower et al, 2002;Xu et al, 2010;Zou et al, 2017;Zou et al, 2020). For example, some floats deployed at ISOW densities in the Bight Fracture Zone (Bower et al, 2002;Lankhorst and Zenk, 2006;Zou et al, 2017) have described northward flows connecting with the boundary current while the majority of RAFOS and Deep Argo floats released at the Charlie Gibbs Fracture Zone followed westnorthwest interior pathways or took a southward direction along the Mid Atlantic Ridge (Racapéet al, 2019;Zou et al, 2020). To check whether there was ISOW at the Bight Fracture Zone during OVIDE 2018 we collected a near-bottom seawater sample at 2280 m depth in station OV104 (Figure 4A).…”

Section: Observed Isow Pathways In 2017-2018mentioning

confidence: 99%

“…However, there is growing evidence from numerical simulations and field observations (e.g., Zou et al, 2020) to portray a more complex circulation scheme in which ISOW travels, more often than previously thought, off boundary currents (magenta dotted lines in Figure 1). For example, a number of Lagrangian floats deployed at the Reykjanes Ridge and programmed to drift at ISOW levels showed trajectories that detach from the boundary current to travel westward into the Irminger Sea, southward along the flanks of the Mid Atlantic Ridge, or eastward to the afar West European Basin (Bower et al, 2002;Lankhorst and Zenk, 2006;Xu et al, 2010;Zou et al, 2017;Racapéet al, 2019;Zou et al, 2020).…”

Section: Introductionmentioning

confidence: 98%

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Rapidly Increasing Artificial Iodine Highlights Pathways of Iceland-Scotland Overflow Water and Labrador Sea Water

et al. 2022

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Iceland-Scotland Overflow Water (ISOW) and Labrador Seawater (LSW) are major water masses of the lower Atlantic Meridional Overturning Circulation (AMOC). Therefore, the investigation of their transport pathways is important to understand the structure of the AMOC and how climate properties are exported from the North Atlantic to lower latitudes. There is growing evidence from Lagrangian model simulations and observations that ISOW and LSW detach from boundary currents and spread off-boundary, into the basin interior in the Atlantic Ocean. Nuclear fuel reprocessing facilities of Sellafield and La Hague have been releasing artificial iodine (129I) into the northeastern Atlantic since the 1960ies. As a result, 129I is supplied from north of the Greenland-Scotland passages into the subpolar region labelling waters of the southward flowing lower AMOC. To explore the potential of 129I as tracer of boundary and interior ISOW and LSW transport pathways, we analyzed the tracer concentrations in seawater collected during four oceanographic cruises in the subpolar and subtropical North Atlantic regions between 2017 and 2019. The new tracer observations showed that deep tracer maxima highlighted the spreading of ISOW along the flanks of Reykjanes Ridge, across fracture zones and into the eastern subpolar North Atlantic supporting recent Lagrangian studies. Further, we found that 129I is intruding the Atlantic Ocean at unprecedented rate and labelling much larger extensions and water masses than in the recent past. This has enabled the use of 129I for other purposes aside from tracing ISOW. For example, increasing tracer levels allowed us to differentiate between newly formed 129I-rich LSW and older vintages poorer in 129I content. Further, 129I concentration maxima at intermediate depths could be used to track the spreading of LSW beyond the subpolar region and far into subtropical seas near Bermuda. Considering that 129I releases from Sellafield and La Hague have increased or levelled off during the last decades, it is very likely that the tracer invasion will continue providing new tracing opportunities for 129I in the near future.

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Redrawing the Iceland−Scotland Overflow Water pathways in the North Atlantic

Cited by 20 publications

References 31 publications

Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation

Subpolar North Atlantic western boundary density anomalies and the Meridional Overturning Circulation

Water masses in the Atlantic Ocean: characteristics and distributions

Rapidly Increasing Artificial Iodine Highlights Pathways of Iceland-Scotland Overflow Water and Labrador Sea Water

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