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Modeling the intense 2012–2013 dense water formation event in the northwestern M editerranean S ea: Evaluation with an ensemble simulation approach
Author(s) -
Waldman Robin,
Somot Samuel,
Herrmann Marine,
Bosse Anthony,
Caniaux Guy,
Estournel Claude,
Houpert Loic,
Prieur Louis,
Sevault Florence,
Testor Pierre
Publication year - 2017
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc012437
Subject(s) - thermohaline circulation , water mass , climatology , geology , isopycnal , deep sea , convection , mixing (physics) , north atlantic deep water , deep ocean water , mediterranean sea , convective mixing , structural basin , mediterranean climate , oceanography , bathymetry , paleontology , meteorology , physics , geography , archaeology , quantum mechanics
The northwestern Mediterranean Sea is a well‐observed ocean deep convection site. Winter 2012–2013 was an intense and intensely documented dense water formation (DWF) event. We evaluate this DWF event in an ensemble configuration of the regional ocean model NEMOMED12. We then assess for the first time the impact of ocean intrinsic variability on DWF with a novel perturbed initial state ensemble method. Finally, we identify the main physical mechanisms driving water mass transformations. NEMOMED12 reproduces accurately the deep convection chronology between late January and March, its location off the Gulf of Lions although with a southward shift and its magnitude. It fails to reproduce the Western Mediterranean Deep Waters salinification and warming, consistently with too strong a surface heat loss. The Ocean Intrinsic Variability modulates half of the DWF area, especially in the open‐sea where the bathymetry slope is low. It modulates marginally (3–5%) the integrated DWF rate, but its increase with time suggests its impact could be larger at interannual timescales. We conclude that ensemble frameworks are necessary to evaluate accurately numerical simulations of DWF. Each phase of DWF has distinct diapycnal and thermohaline regimes: during preconditioning, the Mediterranean thermohaline circulation is driven by exchanges with the Algerian basin. During the intense mixing phase, surface heat fluxes trigger deep convection and internal mixing largely determines the resulting deep water properties. During restratification, lateral exchanges and internal mixing are enhanced. Finally, isopycnal mixing was shown to play a large role in water mass transformations during the preconditioning and restratification phases.

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