The flow of Antarctic bottom water to the southwest Indian Ocean estimated using CFCs

Haine, Thomas W. N.; Watson, Andrew J.; Liddicoat, M.I.; Dickson, Robert R.

doi:10.1029/98jc02476

Cited by 64 publications

(57 citation statements)

References 62 publications

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“…(Note that because this calculation is based on a concentration gradient, the exact positions of where the slope is calculated can differ, making such estimations amenable to paleo-reconstructions where end-members may not be well constrained.) This effective transport rate estimate is, as was the case for our NADW estimate, lower than the CFC estimate of ∼1.2 cm/s for AABW (Haine et al, 1998). We can predict that the benthic fluxes affecting AABW must be more complex, because linear extrapolation of the rate of change in ε Nd over latitude as shown in Figures 3, 4 would imply that AABW has an ε Nd of −6 at 60 • S, which it does not .…”

Section: Implications Of a Benthic Flux In The Atlanticcontrasting

confidence: 38%

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

Haley

Abbott

et al. 2017

Front. Mar. Sci.

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Neodymium (Nd) isotopes are considered a valuable tracer of modern and past ocean circulation. However, the promise of Nd isotope as a water mass tracer is hindered because there is not an entirely self-consistent model of the marine geochemical cycle of rare earth elements (REEs, of which Nd is one). That is, the prevailing mechanisms to describe the distributions of elemental and isotopic Nd are not completely reconciled. Here, we use published [Nd] and Nd isotope data to examine the prevailing model assumptions, and further compare these data to emergent alternative models that emphasize benthic processes in controlling the cycle of marine REEs and Nd isotopes. Our conclusion is that changing from a "top-down" driven model for REE cycling to one of a "bottom-up" benthic source model can provide consistent interpretations of these data for both elemental and isotopic Nd distributions. We discuss the implications such a benthic flux model carries for interpretation of Nd isotope data as a tracer for understanding modern and past changes in ocean circulation.

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Section: Implications Of a Benthic Flux In The Atlanticcontrasting

confidence: 38%

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

Haley

Abbott

et al. 2017

Front. Mar. Sci.

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“…Eastward spreading of WSBW into the Indian Ocean is apparent with a decreasing tracer concentration due to mixing with the overlying CDW. The bottom flow from the Weddell Basin into the Mozambique and Crozet Basins is consistent with the findings of Mantyla and Reid (1995) and Haine et al (1998). Although the model deep and bottom waters are not as saline or dense as in the real ocean (Hirst et al 2000), the model overall reproduces key features of Weddell Sea deep and bottom water ventilation rates and pathways.…”

Section: B Modeled Aabwsupporting

confidence: 77%

Antarctic Bottom Water Variability in a Coupled Climate Model

Santoso

England

2008

Journal of Physical Oceanography

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The natural variability of the Weddell Sea variety of Antarctic Bottom Water (AABW) is examined in a long-term integration of a coupled climate model. Examination of passive tracer concentrations suggests that the model AABW is predominantly sourced in the Weddell Sea. The maximum rate of the Atlantic sector Antarctic overturning ( atl ) is shown to effectively represent the outflow of Weddell Sea deep and bottom waters and the compensating inflow of Warm Deep Water (WDW). The variability of atl is found to be driven by surface density variability, which is in turn controlled by sea surface salinity (SSS). This suggests that SSS is a better proxy than SST for post-Holocene paleoclimate reconstructions of the AABW overturning rate. Heat-salt budget and composite analyses reveal that during years of high Weddell Sea salinity, there is an increased removal of summertime sea ice by enhanced wind-driven ice drift, resulting in increased solar radiation absorbed into the ocean. The larger ice-free region in summer then leads to enhanced air-sea heat loss, more rapid ice growth, and therefore greater brine rejection during winter. Together with a negative feedback mechanism involving anomalous WDW inflow and sea ice melting, this results in positively correlated -S anomalies that in turn drive anomalous convection, impacting AABW variability. Analysis of the propagation of -S anomalies is conducted along an isopycnal surface marking the separation boundary between AABW and the overlying Circumpolar Deep Water. Empirical orthogonal function analyses reveal propagation of -S anomalies from the Weddell Sea into the Atlantic interior with the dominant modes characterized by fluctuations on interannual to centennial time scales. Although salinity variability is dominated by along-isopycnal propagation, variability is dominated by isopycnal heaving, which implies propagation of density anomalies with the speed of baroclinic waves.

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“…The values we derive are significantly different from those of Haine et al [1998], who made such an assumption in their simple plume model, indicating that (as shown previously for the North Atlantic DWBC) the Southern Hemisphere boundary current flows cannot be construed as exhibiting tracer-free mixing. We acknowledge that the model we used for this study is highly idealized and simple and subject to many of the untested assumptions made previously by Haine et al [ 1998]; see section 4 for discussion. However, it produced reasonable statistical matches to the measured CFC concentrations along the plume, indicating that at lea,st some of the main elements of the flow were captured.…”

Section: Discussionmentioning

confidence: 99%

Chlorofluorocarbon‐derived formation rates of the deep and bottom waters of the Weddell Sea

Meredith¹,

Watson²,

Scoy³

et al. 2001

J. Geophys. Res.

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Abstract. The spreading and mixing of deep and bottom waters from the Weddell Sea (originating with potential temperature <0øC) are investigated through analysis of new and historical CFC measurements. We investigate the component that enters the southern Indian Ocean with a simple one-dimensional advection-diffusion model of the deep boundary current. This model does not require a condition of mixing solely with tracer-free water to be imposed. As boundary conditions, we derive time histories for the CFC concentrations of newly formed Weddell Sea deep and bottom waters. A range of best fit velocities is obtained by determining which model velocities produce model tracer concentrations closest to measured concentrations. From this, we derive a formation rate of 3.24-1.5 Sv for the waters originating with temperatures lower than 0øC that subsequently enter the southern Indian Ocean. This compares to an upper limit for these waters of 5.7 Sv derived from the CFC-11/CFC-12 ratio. Whilst the former value is dependent on the highly idealized concepts of the model used, the latter is a more robust upper limit. Using the CFC-11/CFC-12 ratio measured at Vema Channel during the World Ocean Circulation Experiment cruise A23, an upper limit of 0.9 Sv is derived for the formation rate of waters colder than 0øC that enter the South Atlantic. Overall, an upper limit of 6.6 Sv is derived for the rate of formation of the deep and bottom waters of the Weddell Sea. A better representation is obtained by combining the upper limit to the South Atlantic component with the model-derived southern Indian Ocean estimate; we thus estimate the formation rate of the deep and bottom waters in the Weddell Sea to be 3.74-1.6 Sv. Whilst the range obtained is large and the assumptions implicit in the calculations are potentially significant, we believe this more realistically represents the true formation rate than estimates derived using an imposed condition of tracer-free mixing. The range can be narrowed in future as more data become available.

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The flow of Antarctic bottom water to the southwest Indian Ocean estimated using CFCs

Cited by 64 publications

References 62 publications

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

The Impact of Benthic Processes on Rare Earth Element and Neodymium Isotope Distributions in the Oceans

Antarctic Bottom Water Variability in a Coupled Climate Model

Chlorofluorocarbon‐derived formation rates of the deep and bottom waters of the Weddell Sea

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