A window on the deep ocean: The special value of ocean bottom pressure for monitoring the large-scale, deep-ocean circulation

Hughes, Chris W.; Williams, Joanne; Blaker, Adam T.; Coward, Andrew C.; Stepanov, V. N.

doi:10.1016/j.pocean.2018.01.011

Cited by 42 publications

(57 citation statements)

References 68 publications

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“…For example, Hughes et al () demonstrate how the geostrophic portion of the meridional overturning circulation can be monitored using only boundary measurements, while others (e.g., Duchez et al, ; Frajka‐Williams, ) lean on established theory such as Sverdrup balance to develop metrics for the overturning circulation that may allow us to reconstruct its variability over a longer time period. Hughes et al () show that mesoscale energy is suppressed in bottom pressure on the continental slope, such that variations in pressure along boundaries are coherent over large distances, with likely implications for the coherence of the AMOC.…”

Section: Monitoring and Understanding Observed Amoc Variability At 26°nmentioning

confidence: 99%

Recent Contributions of Theory to Our Understanding of the Atlantic Meridional Overturning Circulation

et al. 2019

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Revolutionary observational arrays, together with a new generation of ocean and climate models, have provided new and intriguing insights into the Atlantic Meridional Overturning Circulation (AMOC) over the last two decades. Theoretical models have also changed our view of the AMOC, providing a dynamical framework for understanding the new observations and the results of complex models. In this paper we review recent advances in conceptual understanding of the processes maintaining the AMOC. We discuss recent theoretical models that address issues such as the interplay between surface buoyancy and wind forcing, the extent to which the AMOC is adiabatic, the importance of mesoscale eddies, the interaction between the middepth North Atlantic Deep Water cell and the abyssal Antarctic Bottom Water cell, the role of basin geometry and bathymetry, and the importance of a three‐dimensional multiple‐basin perspective. We review new paradigms for deep water formation in the high‐latitude North Atlantic and the impact of diapycnal mixing on vertical motion in the ocean interior. And we discuss advances in our understanding of the AMOC's stability and its scaling with large‐scale meridional density gradients. Along with reviewing theories for the mean AMOC, we consider models of AMOC variability and discuss what we have learned from theory about the detection and meridional propagation of AMOC anomalies. Simple theoretical models remain a vital and powerful tool for articulating our understanding of the AMOC and identifying the processes that are most critical to represent accurately in the next generation of numerical ocean and climate models.

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Section: Monitoring and Understanding Observed Amoc Variability At 26°nmentioning

confidence: 99%

Recent Contributions of Theory to Our Understanding of the Atlantic Meridional Overturning Circulation

et al. 2019

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“…However, it fails when the integral is right across the ocean, because the measurement at the end points is then of bottom pressure, and mesoscale eddies have little influence on bottom pressure on a steep continental slope. In a model context, this was demonstrated by Hughes et al (), who showed that bottom pressures on the continental slope do reflect large‐scale dynamics and the AMOC very clearly and that the model variability is consistent with satellite sea level measurements and bottom pressures in the WAVE array. Hughes et al () explain this with a simple scaling argument, based on the inability of vorticity balance to produce large vertical velocities.…”

Section: Additional Technologiesmentioning

confidence: 60%

“…In a model context, this was demonstrated by Hughes et al (), who showed that bottom pressures on the continental slope do reflect large‐scale dynamics and the AMOC very clearly and that the model variability is consistent with satellite sea level measurements and bottom pressures in the WAVE array. Hughes et al () explain this with a simple scaling argument, based on the inability of vorticity balance to produce large vertical velocities. The suppression of mesoscale energy at the boundary was also observed and justified in a vertical sidewall context, by Kanzow et al ().…”

Section: Additional Technologiesmentioning

confidence: 60%

Sustainable Observations of the AMOC: Methodology and Technology

McCarthy¹,

Brown

Flagg

et al. 2020

Reviews of Geophysics

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“…Correlations between the other mooring BP records and the ocean BP from the nearest GRACE mascon vary from weak (WB4, r = 0.26 and not significant) to moderate (EB1, r = 0.45). It should be noted that both WB2 and WB4 BP are compared with BP from the same GRACE mascon and that the difference in correlation is likely due to mesoscale variability being suppressed by the steep continental slope at WB2 but not at WB4 (Hughes et al, ; Kanzow et al, ). Overall, we conclude that while some GRACE BP records agree with the in situ measurements, this depends on the location.…”

Section: Resultsmentioning

confidence: 99%

“…Near the western boundary of the North Atlantic, variability in sea surface height and eddy kinetic energy at WB4 has been found to be higher than that of moorings close to the continental slope such as WB2 (Kanzow et al, ). Hughes et al () showed that, in the NEMO ocean model, mesoscale variability in BP is suppressed on the continental slope. The suppression of small‐scale variability by the steep western continental slope may explain the difference in correlation of in situ BP at WB2 and WB4 with the same GRACE mascon BP.…”

Section: Discussionmentioning

confidence: 99%

Estimating the Deep Overturning Transport Variability at 26°N Using Bottom Pressure Recorders

2019

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The RAPID mooring array at 26 • N in the Atlantic has been observing the Atlantic meridional overturning circulation (AMOC) since 2004, with estimates of AMOC strength suggesting that it has declined over the 2004-2016 period. When AMOC transport is estimated, an external transport is added to the observed Ekman, Florida Straits, and baroclinic geostrophic transports to ensure zero net mass transport across the section. This approach was validated using the first year of RAPID data by estimating the external component directly from in situ bottom pressure data. Since bottom pressure recorders commonly show low-frequency instrument drift, bottom pressure data had to be dedrifted prior to calculating the external component. Here we calculate the external component from 10 years of in situ bottom pressure data and evaluate two choices for dedrifting the records: traditional and adjusted using a Gravity Recovery and Climate Experiment (GRACE) bottom pressure solution. We show that external transport estimated from GRACE-adjusted, in situ bottom pressure data correlates better with the RAPID compensation transport (r = 0.65, p < 0.05) than using individually dedrifted bottom pressure recorders, particularly at low frequencies on timescales shorter than 10 years, demonstrating that the low-frequency variability added from GRACE is consistent with the transport variability at RAPID. We further use the bottom pressure-derived external transport to evaluate the zonal distribution of the barotropic transport variability and find that the transport variability is concentrated west of the Mid-Atlantic Ridge rather than uniformly distributed across the basin, as assumed in the RAPID calculation.Plain Language Summary Differences in bottom pressure between locations in the ocean can tell us how water moves between them. We can measure it using recorders at the seabed, but because of the great depth and pressure, the measurements record a "drift" as well as changes in pressure. Removing this drift can also remove genuine longer-term signals. We try to use a completely separate measure of ocean bottom pressure, derived from satellite data, to remove this drift but keep all the real changes in pressure. To see how well this works, we compare the large-scale ocean transport we estimate using our satellite-adjusted bottom pressures, to estimates of the same transport in the North Atlantic measured by a permanent mooring array between 2004 and 2014.

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A window on the deep ocean: The special value of ocean bottom pressure for monitoring the large-scale, deep-ocean circulation

Cited by 42 publications

References 68 publications

Recent Contributions of Theory to Our Understanding of the Atlantic Meridional Overturning Circulation

Recent Contributions of Theory to Our Understanding of the Atlantic Meridional Overturning Circulation

Sustainable Observations of the AMOC: Methodology and Technology

Estimating the Deep Overturning Transport Variability at 26°N Using Bottom Pressure Recorders

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