Pathways of the Agulhas waters poleward of 29°S

Wang, Jinbo; Mazloff, Matthew R.; Gille, Sarah T.

doi:10.1002/2014jc010049

Cited by 17 publications

(17 citation statements)

References 42 publications

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“…Tracer‐weighted properties help quantify when and where changes in water mass properties take place during tracer transport [e.g., Qu et al ., ; Wang et al ., ]. For instance, tracer‐weighted potential temperature

\bar{θ}

can be used as a proxy for tracer heat content:

\overset{θ false(t false)}{true} = \frac{\int ϕ θ d V}{\int ϕ d V},

where

ϕ

is a tracer field and the integral is over a volume V [ Wang et al ., ]. The time series

\overset{θ false(t false)}{true}

gives us information on how the tracer heat content changes as the tracer (which represents a particular collection of water mass parcels) mixes with other water masses and interacts with the mixed layer.…”

Section: Model Setup and Experiments Designmentioning

confidence: 99%

How does Subantarctic Mode Water ventilate the Southern Hemisphere subtropics?

et al. 2016

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In several regions north of the Antarctic Circumpolar Current (ACC), deep wintertime convection refreshes pools of weakly stratified subsurface water collectively referred to as Subantarctic Mode Water (SAMW). SAMW ventilates the subtropical thermocline on decadal timescales, providing nutrients for low‐latitude productivity and potentially trapping anthropogenic carbon in the deep ocean interior for centuries. In this work, we investigate the spatial structure and timescales of mode water export and associated thermocline ventilation. We use passive tracers in an eddy‐permitting, observationally‐informed Southern Ocean model to identify the pathways followed by mode waters between their formation regions and the areas where they first enter the subtropics. We find that the pathways followed by the mode water tracers are largely set by the mean geostrophic circulation. Export from the Indian and Central Pacific mode water pools is primarily driven by large‐scale gyre circulation, whereas export from the Australian and Atlantic pools is heavily influenced by the ACC. Export from the Eastern Pacific mode water pool is driven by a combination of deep boundary currents and subtropical gyre circulation. More than 50% of each mode water tracer reaches the subtropical thermocline within 50 years, with significant variability between pools. The Eastern Pacific pathway is especially efficient, with roughly 80% entering the subtropical thermocline within 50 years. The time required for 50% of the mode water tracers to leave the Southern Ocean domain varies significantly between mode water pools, from 9 years for the Indian mode water pool to roughly 40 years for the Central Pacific mode water pool.

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\bar{θ}

can be used as a proxy for tracer heat content:

\overset{θ false(t false)}{true} = \frac{\int ϕ θ d V}{\int ϕ d V},

where

ϕ

is a tracer field and the integral is over a volume V [ Wang et al ., ]. The time series

\overset{θ false(t false)}{true}

Section: Model Setup and Experiments Designmentioning

confidence: 99%

How does Subantarctic Mode Water ventilate the Southern Hemisphere subtropics?

et al. 2016

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“…This procedure makes the inherent assumption that the profiles collected by the floats while under the ice represent the properties of the water column at horizontal scales larger than the distance that the float traverses over the winter. In tests using measured summertime positions and particle simulation experiments in models similar to Wang et al (), Chamberlain et al () found that such interpolation might yield uncertainties of up to 100 km in the estimated location of floats by the end of winter, with the error being cumulative from the period of ice formation to ice melting; some improvement in the linearly‐interpolated position estimates can possibly be found using a Kalman filter. Occasionally, it is possible to attempt to actually track the floats under the ice using acoustic methods; beginning in 2007, a suite of 17 UW Argo floats equipped with RAFOS receivers tested this concept by recording acoustic travel times in the Weddell Sea transmitted by an array of 8 moored acoustic sources maintained by colleagues at the Alfred Wegener Institute for Marine and Polar Research in Germany.…”

Section: The Sea Ice Regimementioning

confidence: 99%

Profiling Floats in SOCCOM: Technical Capabilities for Studying the Southern Ocean

2018

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We report on profiling float technology used in the Southern Ocean Carbon and Climate Observations and Models (SOCCOM) program, a 6 year study of the interaction of ocean physics and the carbon cycle in the Southern Ocean. A central part of this program is to produce and deploy 200 profiling floats equipped with CTD units and chemical sensors capable of measuring dissolved oxygen, nitrate, pH, chlorophyll fluorescence, and particulate backscatter. The performance of the first 63 floats deployed in SOCCOM is examined, and examples of the design criteria used in producing these floats are shown. Some of the sensors require surface measurements to be made in the dark at regular intervals, and the probability of ascending to the sea surface in the dark is estimated as a function of year‐day and latitude. An energy budget derived from laboratory measurements shows that only about 25% of the total energy stored in the batteries is used by the biogeochemical sensors, which bodes well for the long‐term survivability of the floats. The ice‐avoidance algorithm is discussed in detail, and it is shown that it is working as designed and allowing unprecedented numbers of profiles to be collected beneath the wintertime ice cover. The overall reliability of the first group of SOCCOM floats is compared with a much larger ensemble of Argo floats; the results show that the SOCCOM floats are surviving at a rate similar to the Argo floats, which have been shown to have lifetimes in excess of 5 years.

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“…Wang et al . [] studied spreading of Agulhas waters into the Southern Ocean and found that although most of these waters end up in the Indian sector, a significant portion enters the South Atlantic through the boundary current along the southern tip of South Africa and via Agulhas rings. These processes are, however, outside of the scope of this paper and detailed analysis is not attempted here.…”

Section: Transient Surface Tracermentioning

confidence: 99%

Importance of mesoscale eddies and mean circulation in ventilation of the Southern Ocean

et al. 2017

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This study examines the relative importance of the mean advection and mesoscale currents in the property exchange between the Southern Ocean mixed layer and downstream in the upper 2000 m; this exchange is referred to as ventilation. A new, highly efficient off‐line tracer model employed here uses precalculated velocities to advect dynamically passive tracers. Two idealized tracers are considered: the Boundary Impulse Response (BIR) tracer, which helps to determine the ventilation pathways and time scales, and the Transient Surface Tracer (TST), which is relevant to transient atmospheric tracers. The importance of eddies is isolated by contrasting the control simulation with a simulation without mesoscale currents. The analysis reveals complex three‐dimensional ventilation pathways, controlled by the interplay between the mean advection and eddy‐induced spreading. The mean currents carry the tracers eastward within ACC and contribute to the formation of the Antarctic Intermediate Water (AAIW) in the South Pacific and South Atlantic. The main effect of eddies is to disperse tracers away from the mean pathways, and this dispersion acts to retain the BIR tracer in the Atlantic and Indian sectors and reduce the upstream influence of these regions on the South Pacific. In addition, the eddy‐induced along‐isopycnal spreading within ACC increases the ventilated depth and the inventory of TST. The results can be used to interpret distribution of tracers in the ocean in numerical simulations and observations.

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Pathways of the Agulhas waters poleward of 29°S

Cited by 17 publications

References 42 publications

How does Subantarctic Mode Water ventilate the Southern Hemisphere subtropics?

How does Subantarctic Mode Water ventilate the Southern Hemisphere subtropics?

Profiling Floats in SOCCOM: Technical Capabilities for Studying the Southern Ocean

Importance of mesoscale eddies and mean circulation in ventilation of the Southern Ocean

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