Seasonality of the Meridional Overturning Circulation in the subpolar North Atlantic

Fu, Yao; Lozier, Susan; Biló, Tiago Carrilho; Bower, Amy S.; Cunningham, Stuart A.; Cyr, Frédéric; Jong, M. Femke de; deYoung, Brad; Drysdale, Lewis A.; Fraser, Neil; Fried, Nora; Furey, Heather H.; Handmann, Patricia; Holliday, N. Penny; Holte, James; Inall, Mark; Johns, William E.; Jones, Sam; Karstensen, Johannes; Li, F.; Pacini, Astrid; Pickart, Robert S.; Rayner, Darren; Straneo, Fiammetta; Yashayaev, Igor

doi:10.1038/s43247-023-00848-9

Cited by 22 publications

(33 citation statements)

References 52 publications

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“…The strongest AMOC volume transports appear from August to November, the weakest in January. This agrees with other observations of the seasonal cycle in the subpolar North Atlantic at the OSNAP array (Fu et al., 2023), finding a minimum AMOC volume transport in winter (NDJ). The shape of the seasonal cycle does not depend on whether it is calculated over the whole period, the RAPID measuring period, or the OSNAP measuring period.…”

Section: Resultssupporting

confidence: 92%

Meridional Connectivity of a 25‐Year Observational AMOC Record at 47°N

Wett,

Rhein,

Kieke

et al. 2023

Geophysical Research Letters

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Since climate model studies project a decline of the Atlantic Meridional Overturning Circulation (AMOC) in the 21st century, monitoring AMOC changes remains essential. While AMOC variability is expected to be coherent across latitudes on longer than decadal timescales, connectivity on inter‐annual and seasonal timescales is less clear. Model studies and observational estimates disagree on the regions and timescales of meridional connectivity and AMOC observations at multiple latitudes are needed to study its connectivity. We calculate basin‐wide AMOC volume transports (1993–2018) from measurements of the North Atlantic Changes (NOAC) array at 47°N, combining data from moored instruments with hydrography and satellite altimetry. The mean NOAC AMOC is 17.2 Sv exhibiting no long‐term trend. Both the unfiltered and low‐pass filtered NOAC AMOC show a significant correlation with the RAPID‐MOCHA‐WBTS AMOC at 26°N when the NOAC AMOC leads by about one year.

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Section: Resultssupporting

confidence: 92%

Meridional Connectivity of a 25‐Year Observational AMOC Record at 47°N

Wett,

Rhein,

Kieke

et al. 2023

Geophysical Research Letters

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“…MOC in the density space is the maximum of the stream function,

\text{MOC}(t)={\max }_{{\sigma }_{0}}\left[\psi \left({\sigma }_{0},t\right)\right]=\int \nolimits_{{\sigma }_{\max }}^{{\sigma }_{\text{MOC}}(t)}\int \nolimits_{{x}_{w}}^{{x}_{e}}v\left(x,\sigma ,t\right)dx\,d\sigma ,

where σ MOC represents the density at which the overturning stream function reaches its maximum. To maintain consistency with the observational results reported by the OSNAP team (e.g., Fu et al., 2023; Lozier et al., 2019), the density employed here is σ 0 , that is, the potential density referenced to the sea surface. The comparison of the ECCO data set and the OSNAP observation is detailed in Text S1 of Supporting Information .…”

Section: Methodsmentioning

confidence: 83%

“…Despite the limited overlap in time span between ECCO v4r3 (1992between ECCO v4r3 ( -2015 and the OSNAP observation (2014 onwards), the performance of ECCO in capturing the OSNAP MOC can still be evaluated by examining its ability to reproduce the long-term mean and seasonal variability. Following previous studies, it is more proper to define the subpolar MOC in the density space than the depth space (e.g., Fu et al, 2023;Li et al, 2021;Lozier et al, 2019). The overturning stream function in the density space, written as ψ(σ 0 ,t), is obtained by integrating from a high-density extreme (σ max ) over the zonal section extending from x w to x e ,…”

Section: Data: Ecco V4r3mentioning

confidence: 99%

“…Moreover, a new insight gained from the OSNAP observations has brought about a contrasting viewpoint on the Labrador Sea's role in shaping the AMOC variability. A diagram based on models suggested that the Labrador Sea plays a primary role in modulating the AMOC variability (e.g., Jackson et al., 2016; Menary et al., 2020; Roberts et al., 2013; Robson et al., 2014), while the observations indicated that the Labrador Sea contributes weakly to the overturning in terms of both mean and variability across the OSNAP line (Fu et al., 2023; Lozier et al., 2019). Efforts to reconcile such disparity have suggested that the density anomalies observed in the Labrador Sea, as well as the temperature and salinity anomalies, originate from the eastern subpolar gyre (e.g., Lozier et al., 2019; Menary et al., 2020; Rousselet et al., 2022; Zou et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

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Exploring the AMOC Connectivity Between the RAPID and OSNAP Lines With a Model‐Based Data Set

Han

2023

Geophysical Research Letters

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Two major trans‐basin mooring arrays, the Rapid Climate Change‐Meridional Overturning Circulation and Heatflux Array (RAPID) at 26.5°N since 2004 and the Overturning in the Subpolar North Atlantic Program (OSNAP) situated at 53°–60°N since 2014, have been continuously monitoring the Atlantic Meridional Overturning Circulation (AMOC). This study explores the connectivity of AMOC across these two mooring lines from a novel adiabatic perspective utilizing a model‐based data set. The findings unveil significant in‐phase connections facilitated by the adiabatic basinwide redistribution of water between the two lines on a monthly timescale. This adiabatic mode is a possible cause for the observed subpolar AMOC seasonality by OSNAP. Furthermore, the Labrador Sea was identified as a hotspot for adiabatic forcing of the overturning circulations, primarily attributed to its dynamic isopycnal movements.

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“…The OSNAP data used for this work are available online at https://www.o-snap.org/observations/data/ (Fu et al, 2023a(Fu et al, , 2023b.…”

Section: Data Availability Statementmentioning

confidence: 99%

Propagation and Transformation of Upper North Atlantic Deep Water From the Subpolar Gyre to 26.5°N

et al. 2023

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Because new observations have revealed that the Labrador Sea is not the primary source for waters in the lower limb of the Atlantic Meridional Overturning Circulation (AMOC) during the OSNAP period, it seems timely to re‐examine the traditional interpretation of pathways and property variability for the AMOC lower limb from the subpolar gyre to 26.5°N. In order to better understand these connections, Lagrangian experiments were conducted within an eddy‐rich ocean model to track upper North Atlantic Deep Water (uNADW), defined by density, between the OSNAP line and 26.5°N as well as within the Labrador Sea. The experiments reveal that 77% of uNADW at 26.5°N is directly advected from the OSNAP West section along the boundary current and interior pathways west of the Mid‐Atlantic Ridge. More precisely, the Labrador Sea is a main gateway for uNADW sourced from the Irminger Sea, while particles connecting OSNAP East to 26.5°N are exclusively advected from the Iceland Basin and Rockall Trough along the eastern flank of the Mid‐Atlantic Ridge. Although the pathways between OSNAP West and 26.5°N are only associated with a net formation of 1.1 Sv into the uNADW layer, they show large density changes within the layer. Similarly, as the particles transit through the Labrador Sea, they undergo substantial freshening and cooling that contributes to further densification within the uNADW layer.

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Seasonality of the Meridional Overturning Circulation in the subpolar North Atlantic

Cited by 22 publications

References 52 publications

Meridional Connectivity of a 25‐Year Observational AMOC Record at 47°N

Meridional Connectivity of a 25‐Year Observational AMOC Record at 47°N

Exploring the AMOC Connectivity Between the RAPID and OSNAP Lines With a Model‐Based Data Set

Propagation and Transformation of Upper North Atlantic Deep Water From the Subpolar Gyre to 26.5°N

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