Eddy contributions to the meridional transport of salt in the North Atlantic

Tréguier, Anne‐Marie; Deshayes, Julie; Lique, Camille; Dussin, Raphaël; Molines, Jean‐Marc

doi:10.1029/2012jc007927

Cited by 60 publications

(97 citation statements)

References 51 publications

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“…At 26.5°N the uncorrected value for M ov was -0.55 Sv, while after applying the velocity bias correction it becomes -0.67 Sv. One of the reasons for velocity biases might be that eddies play an important role in the total freshwater budget and they are underestimated in coarse resolution models (Tréguier et al, 2012;Mecking et al, 2016). The latter study also found that freshwater transport by the gyre can become much stronger in an eddy-permitting model, allowing for a stronger negative M ov .…”

Section: Conclusion and Discussionmentioning

confidence: 49%

The effect of model bias on Atlantic freshwater transport and implications for AMOC bi-stability

Mecking¹,

Drijfhout²,

Jackson³

et al. 2017

Tellus A: Dynamic Meteorology and Oceanography

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Evidence from paleo-proxy records suggests that the Atlantic Meridional Overturning Circulation (AMOC) can be in both an AMOC on state, the AMOC as we observe it today, and an AMOC off state, where the AMOC becomes extremely weak or even collapses. The freshwater transport due to the AMOC (M ov ) at 34°S in the Atlantic has often been used as an indicator for bi-stability, with a positive M ov suggesting a monostable AMOC and a negative M ov suggesting a bi-stable AMOC. Often studies have shown that the sign of the divergence of the M ov might be a good indicator of AMOC bi-stability. In this study we investigate how model bias affects the sign of M ov across all latitudes in the Atlantic basin, through a detailed analysis of the Coupled Model Inter-Comparison Project 5 (CMIP5) model ensemble. M ov , in the CMIP5 models is generally too positive in the southern Atlantic due to a salinity bias, while in the subtropical North Atlantic the values of M ov are influenced by a combination of velocity and salinity biases. We compare these results to observations, reanalysis products and Hadley Centre Global Environmental Model version 3 global configuration version 2, a current generation coupled model which exhibits a stable AMOC off state, and discuss the differences that can lead to the possibility of a bi-stable AMOC as opposed to a monostable AMOC.

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Section: Conclusion and Discussionmentioning

confidence: 49%

The effect of model bias on Atlantic freshwater transport and implications for AMOC bi-stability

Mecking¹,

Drijfhout²,

Jackson³

et al. 2017

Tellus A: Dynamic Meteorology and Oceanography

View full text Add to dashboard Cite

show abstract

“…However, HEDDY and HADV may also vary in phase during some events (the 1999 freshening, Figure 9b). Gross negative correlation between eddy and mean horizontal salt transport is a very striking characteristic also present in other eddy resolving ocean simulations [Treguier et al, 2012]. Although the magnitude of interannual variations of the surface salt flux (SSF) is weaker than that of the other term, its contribution cannot be quantified as negligible (Figure 9b).…”

Section: Modelmentioning

confidence: 84%

Interannual Caribbean salinity in satellite data and model simulations

et al. 2015

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Aquarius sea surface salinity (SSS) reveals the presence of interannual variations in the Caribbean with about 0.5 psu change between salty and fresh events, which propagate westward across that basin at an average speed of 11 cm/s and are preceded by corresponding SSS anomalies east of the Lesser Antilles. These upstream SSS anomalies are produced by interannual changes in the Amazon plume. Their presence is verified using in situ measurements from the northwest tropical Atlantic station. In contrast to SSS, which displays westward propagation, SST changes almost immediately across the Caribbean, suggesting large-scale atmospheric processes have a primary role in regulating interannual SST in contrast to SSS. A global 1/10 mesoscale ocean model is used to quantify possible origination mechanisms of the Caribbean salinity anomalies and their fate. Simulations confirm that they are produced by anomalous horizontal salt advection, which conveys these salinity anomalies from an area east of the Lesser Antilles across the Caribbean. Anomalous horizontal advection is dominated by mean currents acting on anomalous salinity. The model suggests that interannual Caribbean salinity anomalies eventually enter the Florida Current and reach the Gulf Stream 6-12 months after crossing the central Caribbean. Previous studies link the origin of salinity anomalies in the Amazon plume to variations in the annual freshwater discharge from the continent. In this model interannual discharge variations are absent while simulated SSS variability is in line with observations. This suggests that interannually forced ocean dynamics plays a key role in river plume variability and its spatial dispersion.

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“…It is worth noting that this feature, present in many coarse and eddy-permitting models (e.g. Danabasoglu et al, 2014;Grist et al, 2010), is absent in GLOB16, likely due to a correct path of the simulated North Atlantic Current (Dan- abasoglu et al, 2014; Treguier et al, 2012), as described in Sect. 3.6.…”

Section: Volume and Heat Transportsmentioning

confidence: 99%

A 1/16° eddying simulation of the global NEMO sea-ice–ocean system

et al. 2016

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Abstract. Analysis of a global eddy-resolving simulation using the NEMO general circulation model is presented. The model has 1/16 • horizontal spacing at the Equator, employs two displaced poles in the Northern Hemisphere, and uses 98 vertical levels. The simulation was spun up from rest and integrated for 11 model years, using ERA-Interim reanalysis as surface forcing. Primary intent of this hindcast is to test how the model represents upper ocean characteristics and sea ice properties.Analysis of the zonal averaged temperature and salinity, and the mixed layer depth indicate that the model average state is in good agreement with observed fields and that the model successfully represents the variability in the upper ocean and at intermediate depths. Comparisons against observational estimates of mass transports through key straits indicate that most aspects of the model circulation are realistic. As expected, the simulation exhibits turbulent behaviour and the spatial distribution of the sea surface height (SSH) variability from the model is close to the observed pattern. The distribution and volume of the sea ice are, to a large extent, comparable to observed values.Compared with a corresponding eddy-permitting configuration, the performance of the model is significantly improved: reduced temperature and salinity biases, in particular at intermediate depths, improved mass and heat transports, better representation of fluxes through narrow and shallow straits, and increased global-mean eddy kinetic energy (by ∼ 40 %). However, relatively minor weaknesses still exist such as a lower than observed magnitude of the SSH variability. We conclude that the model output is suitable for broader analysis to better understand upper ocean dynamics and ocean variability at global scales. This simulation represents a major step forward in the global ocean modelling at the Euro-Mediterranean Centre on Climate Change and constitutes the groundwork for future applications to short-range ocean forecasting.

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Eddy contributions to the meridional transport of salt in the North Atlantic

Cited by 60 publications

References 51 publications

The effect of model bias on Atlantic freshwater transport and implications for AMOC bi-stability

The effect of model bias on Atlantic freshwater transport and implications for AMOC bi-stability

Interannual Caribbean salinity in satellite data and model simulations

A 1/16° eddying simulation of the global NEMO sea-ice–ocean system

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