Flow of bottom water in the northwestern Weddell Sea

Fahrbach, Eberhard; Harms, S. L.; Rohardt, Gerd; Schröder, Michael; Woodgate, Rebecca A.

doi:10.1029/2000jc900142

Cited by 84 publications

(68 citation statements)

References 24 publications

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“…The finding in the present model that the production rates of deep and bottom waters in the North Atlantic and Southern Oceans are of about the same magnitude (about 16 Sv) is consistent with the study of Orsi et al (2002), who exploited CFC inventories in the Southern Ocean for the estimation of watermass production rates, and is also in agreement with the postulations of Broecker et al (1998) on the basis of the PO* 4 parameter. Many previous AABW production estimates (see Fahrbach et al 2001;Foldvik et al 2004 and references therein) are much smaller; however, values are often difficult to compare because of differences in the watermass definitions used and because most studies focus on specific regions and do not provide circum-Antarctic production rates. Garabato et al (2002) find significant AABW production in the Weddell Sea and a northward transport into the Scotia Sea of 9.7 Ϯ 3.7 Sv.…”

Section: Deep and Bottom Water Circulationmentioning

confidence: 99%

Assimilation of Radiocarbon and Chlorofluorocarbon Data to Constrain Deep and Bottom Water Transports in the World Ocean

Schlitzer

2007

Journal of Physical Oceanography

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A coarse-resolution global model with time-invariant circulation is fitted to hydrographic and tracer data by means of the adjoint method. Radiocarbon and chlorofluorocarbon data are included to constrain deep and bottom water transport rates and spreading pathways as well as the strength of the global overturning circulation. It is shown that realistic global ocean distributions of hydrographic parameters and tracers can be obtained simultaneously. The model correctly reproduces the deep ocean radiocarbon field and the concentrations gradients between different basins. The spreading of CFC plumes in the deep and bottom waters is simulated in a realistic way, and the spatial extent as well as the temporal evolution of these plumes agrees well with observations. Radiocarbon and CFC observations place upper bounds on the northward transports of Antarctic Bottom Water (AABW) into the Pacific, Atlantic, and Indian Oceans. Long-term mean AABW transports larger than 5 Sv (Sv ϵ 10 6 m 3 s Ϫ1) through the Vema and Hunter Channels in the South Atlantic and net AABW transports across 30°S into the Indian Ocean larger than 10 Sv are found to be incompatible with CFC data. The rates of equatorward deep and bottom water transports from the North Atlantic and Southern Ocean are of similar magnitude (15.7 Sv at 50°N and 17.9 Sv at 50°S). Deep and bottom water formation in the Southern Ocean occurs at multiple sites around the Antarctic continent and is not confined to the Weddell Sea. A CFC forecast based on the assumption of unchanged abyssal transports shows that by 2030 the entire deep west Atlantic exhibits CFC-11 concentrations larger than 0.1 pmol kg Ϫ1, while most of the deep Indian and Pacific Oceans remain CFC free. By 2020 the predicted CFC concentrations in the deep western boundary current (DWBC) in the North Atlantic exceed surface water concentrations and the vertical CFC gradients start to reverse.

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Section: Deep and Bottom Water Circulationmentioning

confidence: 99%

Assimilation of Radiocarbon and Chlorofluorocarbon Data to Constrain Deep and Bottom Water Transports in the World Ocean

Schlitzer

2007

Journal of Physical Oceanography

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“…Significant seasonal variations have been observed in near-bottom properties near the Adélie Coast [Fukamachi et al, 2000], extending at least as far offshore as the 2660 m isobath. Strong seasonal variability has also been observed in the outflow of bottom water from the Weddell Sea [e.g., Fahrbach et al, 2001]. The only way to remove the ambiguity introduced by temporal and spatial aliasing is to compare observations made at the same locations and in the same season.…”

Section: Introductionmentioning

confidence: 99%

Freshening of the Adélie Land Bottom Water near 140°E

Aoki

Rintoul

Ushio

et al. 2005

Geophysical Research Letters

119

103

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[1] Repeat summer hydrographic observations along 140°E are used to document significant changes in the properties of the Adélie Land Bottom Water (ALBW) between the mid-1990s and 2002-2003. Water on the 28.35 kgÁm À3 neutral density surface cooled by 0.2°C and freshened by 0.03 psu between 1994 and 2002. By reoccupying the same stations in the same season, the effects of seasonal variability and spatial variability were minimised allowing the signal of water mass changes to be clearly identified. Comparison of the recent data to high quality historical observations shows that the ALBW also freshened between the late 1960s and the mid-1990s. Although there is insufficient data to construct a continuous time series, the simplest explanation of the observed changes is that there has been a long-term (>30 year) and continuing freshening of the source waters supplying bottom water to the Australian-Antarctic basin.

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“…Current-meter moorings have confirmed the presence of a DWBC carrying dense water equatorward in the northwest Weddell Sea 11,14 and north of the Falkland Islands 8 (Supplementary Table 1 The horizontal coherence and duration of the array allowed accurate estimates of the transport and structure of the Kerguelen DWBC.…”

mentioning

confidence: 99%

“…In comparison, the net transport of water with θ < 0.2°C by the Kerguelen DWBC is 8.0 Sv (16.4 Sv to the northwest and an 8.4 Sv recirculation to the southeast). Incoherent multi-year moored measurements in the northwest Weddell Sea reveal relatively weak currents (deep mean flows < 7 cm s -1 ) 11 . Combining these 6 current-meter data with CTD sections gives a net export of 3.8 Sv of AABW (θ < 0°C) from the Weddell Sea 14 ; based on an inverse model, an additional 4.7 Sv may leave the Weddell Sea across the Scotia Ridge 21 .…”

mentioning

confidence: 99%

Strong export of Antarctic Bottom Water east of the Kerguelen plateau

et al. 2010

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The horizontal coherence and duration of the array allowed accurate estimates of the transport and structure of the Kerguelen DWBC.The DWBC forms a narrow (~50 km wide), intense, bottom-intensified flow to the northwest over the lower flank of the plateau, with a flow to the southeast further offshore (Fig. 2). The currents are remarkably strong for these depths: maximum two-year mean speed exceeds 20 cm s -1 at ~3500 m depth at M6 (the largest DWBC speeds yet observed at similar depths; Supplementary Table 1 The similarity between the moored results and the synoptic snapshots indicates that the limited vertical resolution of the moored instruments is sufficient to capture the DWBC structure.The daily velocity and potential temperature data are used to calculate the 4 AABW transport per unit width (Fig. 3a). The northwestward transport of AABW is concentrated between M4 and M6, with the largest value observed at M5 where the velocities are large and the AABW layer is thick (Fig. 2). Northwestward transport is commonly observed to extend offshore as far as M3 (~38 km is within the 95% confidence intervals of the mean after 9 months, indicating that the records are of sufficient length to establish a stable mean. The overall impression is of a narrow, intense and relatively steady deep boundary current, modulated by topographic waves and the episodic influence of fronts and meanders of the ACC.This DWBC is associated with a mean temperature transport of -2.52±0.26 Sv °C 5 northwestward.Snapshot estimates based on CTD/ADCP measurements are in agreement with the observations from the moored array, with the exception of the deployment cruise (Fig. 3b, Supplementary Table 2). However, these estimates sampled periods of larger than average transport (Fig. 3b) Several factors make it difficult to assess the relative contribution of the Kerguelen DWBC to the Southern Ocean overturning. These include the presence of recirculation gyres, interaction between the DWBC and other circulation regimes (e.g., the ACC and subpolar gyres) 8 , the fact that mixing and entrainment change the volume and properties of AABW along the export pathway 13 , and the lack of coherent long-term observations in other DWBCs. The only previous coherent current meter measurements of AABW export by a DWBC south of 45°S were obtained north of the Falkland Plateau, where a net transport of 1.9 Sv of Weddell Sea Deep Water (θ < 0.2°C) was found to enter the Argentine Basin (the difference between 8.2 Sv westward and 6.3 Sv recirculating to the east) 8 . In comparison, the net transport of water with θ < 0.2°C by the Kerguelen DWBC is 8.0 Sv (16.4 Sv to the northwest and an 8.4 Sv recirculation to the southeast). Incoherent multi-year moored measurements in the northwest Weddell Sea reveal relatively weak currents (deep mean flows < 7 cm s -1 ) 11 . Combining these 6 current-meter data with CTD sections gives a net export of 3.8 Sv of AABW (θ < 0°C) from the Weddell Sea 14 ; based on an inverse model, an additional 4.7 Sv may leave the Weddell Sea ac...

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Flow of bottom water in the northwestern Weddell Sea

Cited by 84 publications

References 24 publications

Assimilation of Radiocarbon and Chlorofluorocarbon Data to Constrain Deep and Bottom Water Transports in the World Ocean

Assimilation of Radiocarbon and Chlorofluorocarbon Data to Constrain Deep and Bottom Water Transports in the World Ocean

Freshening of the Adélie Land Bottom Water near 140°E

Strong export of Antarctic Bottom Water east of the Kerguelen plateau

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