@article {tooth_seasonal_2023,
	title = {Seasonal overturning variability in the eastern North Atlantic subpolar gyre: a Lagrangian perspective},
	journal = {Ocean Science},
	volume = {19},
	number = {3},
	year = {2023},
	note = {Publisher: Copernicus GmbH},
	month = {jun},
	pages = {769{\textendash}791},
	abstract = {Both observations and ocean reanalyses show a pronounced seasonality in the strength of the Atlantic meridional overturning circulation (MOC) within the eastern North Atlantic subpolar gyre (eSPG). However, attributing this overturning seasonality to seasonal dense water formation remains challenging owing to the wide distribution of recirculation timescales within the Iceland and Irminger basins. Here, we investigate the nature of seasonal overturning variability using Lagrangian water parcel trajectories initialised across the Overturning in the Subpolar North Atlantic Program (OSNAP) East section within an eddy-permitting ocean sea ice hindcast. By adopting a Lagrangian perspective, we show that the seasonal minimum of the Eulerian overturning at OSNAP East in autumn results from a combination of enhanced stratification and increased southward transport within the upper East Greenland Current. This convergence of southward transport within the MOC upper limb is explained by decreasing water parcel recirculation times in the upper Irminger Sea, consistent with a gyre-scale response to seasonal wind forcing. To account for the diversity of recirculation times within the eSPG, we also quantify the Lagrangian overturning (LMOC) as the total dense water formation along water parcel trajectories. The majority of water parcels, sourced from the central and southern branches of the North Atlantic Current, fail to return to OSNAP East prior to experiencing wintertime diapycnal transformation into the lower limb, and thus they determine the mean strength of the LMOC within the eSPG (8.9 {\textpm} 2.2 Sv). The strong seasonality of the LMOC is explained by a small collection of upper-limb water parcels, circulating rapidly (<= 8.5 months) in the upper Irminger and central Iceland basins, whose along-stream transformation is determined by their month of arrival at OSNAP East.},
	issn = {1812-0784},
	doi = {10.5194/os-19-769-2023},
	url = {https://os.copernicus.org/articles/19/769/2023/},
	author = {Tooth, Oliver John and Johnson, Helen Louise and Wilson, Chris and Evans, Dafydd Gwyn}
}
@article {RN289,
	title = {The Observation-Based Application of a Regional Thermohaline Inverse Method to Diagnose the Formation and Transformation of Water Masses North of the OSNAP Array from 2013 to 2015},
	journal = {Journal of Physical Oceanography},
	volume = {50},
	number = {6},
	year = {2020},
	pages = {1533-1555},
	type = {Journal Article},
	doi = {10.1175/jpo-d-19-0188.1},
	url = {https://app.dimensions.ai/details/publication/pub.1124867712 https://journals.ametsoc.org/downloadpdf/journals/phoc/50/6/JPO-D-19-0188.1.pdf},
	author = {Mackay, Neill and Wilson, Chris and Holliday, N. Penny and Zika, Jan D.}
}
@article {RN298,
	title = {Atlantic Meridional Overturning Circulation: Observed Transport and Variability},
	journal = {Frontiers in Marine Science},
	volume = {6},
	year = {2019},
	pages = {260},
	type = {Journal Article},
	doi = {10.3389/fmars.2019.00260},
	url = {https://app.dimensions.ai/details/publication/pub.1116893735 https://www.frontiersin.org/articles/10.3389/fmars.2019.00260/pdf},
	author = {Frajka-Williams, Eleanor and Ansorge, Isabelle J. and Baehr, Johanna and Bryden, Harry L. and Chidichimo, Maria Paz and Cunningham, Stuart A. and Danabasoglu, Gokhan and Dong, Shenfu and Donohue, Kathleen A. and Elipot, Shane and Heimbach, Patrick and Holliday, N. Penny and Hummels, Rebecca and Jackson, Laura C. and Karstensen, Johannes and Lankhorst, Matthias and Le Bras, Isabela A. and Lozier, M. Susan and McDonagh, Elaine L. and Meinen, Christopher S. and Mercier, Herl{\'e} and Moat, Bengamin I. and Perez, Renellys C. and Piecuch, Christopher G. and Rhein, Monika and Srokosz, Meric A. and Trenberth, Kevin E. and Bacon, Sheldon and Forget, Gael and Goni, Gustavo and Kieke, Dagmar and Koelling, Jannes and Lamont, Tarron and McCarthy, Gerard D. and Mertens, Christian and Send, Uwe and Smeed, David A. and Speich, Sabrina and van den Berg, Marcel and Volkov, Denis and Wilson, Chris}
}
@article {RN24,
	title = {Overturning in the Subpolar North Atlantic Program: A New International Ocean Observing System},
	journal = {Bulletin of the American Meteorological Society},
	volume = {98},
	number = {4},
	year = {2017},
	pages = {737-752},
	type = {Journal Article},
	abstract = {For decades oceanographers have understood the Atlantic meridional overturning circulation (AMOC) to be primarily driven by changes in the production of deep-water formation in the subpolar and subarctic North Atlantic. Indeed, current Intergovernmental Panel on Climate Change (IPCC) projections of an AMOC slowdown in the twenty-first century based on climate models are attributed to the inhibition of deep convection in the North Atlantic. However, observational evidence for this linkage has been elusive: there has been no clear demonstration of AMOC variability in response to changes in deep-water formation. The motivation for understanding this linkage is compelling, since the overturning circulation has been shown to sequester heat and anthropogenic carbon in the deep ocean. Furthermore, AMOC variability is expected to impact this sequestration as well as have consequences for regional and global climates through its effect on the poleward transport of warm water. Motivated by the need for a mechanistic understanding of the AMOC, an international community has assembled an observing system, Overturning in the Subpolar North Atlantic Program (OSNAP), to provide a continuous record of the transbasin fluxes of heat, mass, and freshwater, and to link that record to convective activity and water mass transformation at high latitudes. OSNAP, in conjunction with the Rapid Climate Change{\textendash}Meridional Overturning Circulation and Heatflux Array (RAPID{\textendash}MOCHA) at 26{\textdegree}N and other observational elements, will provide a comprehensive measure of the three-dimensional AMOC and an understanding of what drives its variability. The OSNAP observing system was fully deployed in the summer of 2014, and the first OSNAP data products are expected in the fall of 2017.},
	issn = {0003-0007 1520-0477},
	doi = {10.1175/bams-d-16-0057.1},
	url = {https://staging-ddpp.dimensions.ai/details/publication/pub.1038223668 http://darchive.mblwhoilibrary.org/bitstream/1912/9015/1/bams-d-16-0057.1.pdf},
	author = {Susan Lozier, M. and Bacon, Sheldon and Bower, Amy S. and Cunningham, Stuart A. and Femke de Jong, M. and de Steur, Laura and deYoung, Brad and Fischer, J{\"u}rgen and Gary, Stefan F. and Greenan, Blair J. W. and Heimbach, Patrick and Holliday, Naomi P. and Houpert, Lo{\"\i}c and Inall, Mark E. and Johns, William E. and Johnson, Helen L. and Karstensen, Johannes and Li, Feili and Lin, Xiaopei and Mackay, Neill and Marshall, David P. and Mercier, Herl{\'e} and Myers, Paul G. and Pickart, Robert S. and Pillar, Helen R. and Straneo, Fiammetta and Thierry, Virginie and Weller, Robert A. and Williams, Richard G. and Wilson, Chris and Yang, Jiayan and Zhao, Jian and Zika, Jan D.}
}
