Decadal-scale variations of water mass properties in the deep Weddell Sea

Fahrbach, Eberhard; Hoppema, Mario; Rohardt, Gerd; Schröder, Michael; Wisotzki, Andreas

doi:10.1007/s10236-003-0082-3

Cited by 124 publications

(125 citation statements)

References 57 publications

(86 reference statements)

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“…The model domain covers the Weddell Sea from 40 • W to 0 • and 78 • S to 66 • S (Figure 1) and is forced with (a) a climatological monthly wind field (Kottmeier and Sellmann, 1996), (b) prescribed vertically integrated mass transport stream function values along the open boundaries at the western, northern, and eastern model domain (Thoma et al, 2006a), (c) restoring of temperature and salinity to observations at the lateral open boundaries (Gouretski et al, 1999;Fahrbach et al, 2004), and (d) surface restoring of temperature and salinity according to reasonably adjusted observations (Gouretski et al, 1999;Thoma et al, 2006a). The simplified surface restoring, applied instead of a coupled sea ice model, allows us to investigate the mere impact of warmed ocean waters onto the cavity's freshwater production rate, assuming fixed atmospheric conditions.…”

Section: Methodsmentioning

confidence: 99%

“…Scenario S 10y 0.1 is featured by a temperature increase of 0.1 • C, evenly distributed over 10 years. This scenario is based upon observations by Robertson et al (2002), Fahrbach et al (2004), andSmedsrud (2005), who described a 0.01 • C increase per year along the prime meridian by means of hydrographic stations and mooring data. However, the articles are nonuniform with respect to the warming depth.…”

Section: Methodsmentioning

confidence: 99%

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Modelling the impact of ocean warming on melting and water masses of ice shelves in the Eastern Weddell Sea

et al. 2010

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The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate the impact on the temperature-salinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical experiments the warming is imposed homogeneously along the open inflow boundaries of the model domain, leading to a warming of the Warm Deep Water (WDW) further downstream. Our modelling results indicate a weak quadratic dependence of the melt rate at the ice shelf base on the imposed amount of warming, which is consistent with earlier studies. The total melt rate has a strong dependence on the applied ocean warming depth. If the warming is restricted to the upper ocean (above 1000 m), the water column (aside from the mixed surface layer) in the vicinity of the ice shelves stabilises. Hence, reduced vertical mixing will reduce the potential of Antarctic Bottom Water formation further downstream with consequences on the global thermohaline circulation. If the warming extends to the abyss, the WDW core moves significantly closer to the continental shelf break. This sharpens the Antarctic Slope Front and leads to a reduced density stratification. In contrast to the narrow shelf bathymetry in the EWIS region, a wider continental shelf (like in the southern Weddell Sea) partly protects ice shelves from remote ocean warming. Hence, the freshwater production rate of, e.g., the Filchner Ronne Ice Shelf increases much less compared to the EWIS for identical warming scenarios. Our study therefore indicates that the iceocean interaction has a significant impact on the temperature-salinity distribution and the water column stability in the vicinity of ice shelves located along a narrow continental shelf. The effects of ocean warming and the impact of increased freshwater fluxes on the circulation are of the same order of magnitude and superimposed. Therefore, a consideration of this interaction in large-scale climate studies is essential.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Modelling the impact of ocean warming on melting and water masses of ice shelves in the Eastern Weddell Sea

et al. 2010

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“…Underneath the surface layer, the Warm Deep Water (WDW; Carmack and Forster, 1975), characterized by an intermediary temperature maximum of about 1.1°C and a salinity maximum of about 34.7, is found. In the south, the surface mixed layer of about 100-120 m depth deepens towards the shelf break to more than 600 m near the Antarctic Slope Front (Jacobs 1991), which separates the WW and the WDW from the colder and less saline shelf waters near the Antarctic continent (Fahrbach et al, 2004). along the 6°W transect and at the southernmost stations of the 0°E and 3°E transects no measurements were possible because of severe ice conditions.…”

Section: Hydrographymentioning

confidence: 99%

Acoustic insights into the zooplankton dynamics of the eastern Weddell Sea

Cisewski

Strass

2016

Progress in Oceanography

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The success of any efforts to determine the effects of climate change on marine ecosystems depends on understanding in the first instance the natural variations, which contemporarily occur on the interannual and shorter time scales. Here we present results on the environmental controls of zooplankton distribution patterns and behaviour in the eastern Weddell Sea, Southern Ocean. Zooplankton abundance and vertical migration are derived from the mean volume backscattering strength (MVBS) and the vertical velocity measured by moored acoustic Doppler current profilers (ADCPs), which were deployed simultaneously at 64°S, 66.5°S and 69°S along the Greenwich Meridian from February, 2005, until March, 2008 While these time series span a period of full three years they resolve hourly changes.A highly persistent behavioural pattern found at all three mooring locations is the synchronous diel vertical migration (DVM) of two distinct groups of zooplankton that migrate between a deep residence depth during daytime and a shallow depth during nighttime. The DVM was closely coupled to the astronomical daylight cycles. However, while the DVM was symmetric around local noon, the annual modulation of the DVM was clearly asymmetric around winter solstice or summer solstice, respectively, at all three mooring sites. DVM at our observation sites persisted throughout winter, even at the highest latitude exposed to the polar night. Since the magnitude as well as the relative rate of change of illumination is minimal at this time, we propose that the ultimate causes of DVM separated from the light-mediated proximal cue that coordinates it. In all three years, a marked change in the migration behaviour occurred in late spring (late October/early November), when DVM ceased. The complete suspension of DVM after early November is possibly caused by the combination of two factors: (1) increased availability of food in the surface mixed layer provided by the phytoplankton spring bloom, and (2) vanishing diurnal enhancement of the threat from visually oriented predators when the illumination is quasi-continuous during the polar and subpolar summer. 3Zooplankton abundance in the water column, estimated as the mean MVBS in the depth range 50 -300 m, was highest end of summer and lowest mid to end winter on the average annual cycle. However, zooplankton abundance varied several-fold between years and between locations. Based on satellite and in situ data of chlorophyll and sea ice as well as on hydrographic measurements, the interannual and spatial variations of zooplankton mean abundance can be explained by differences in the magnitude of the phytoplankton spring bloom, which develops during the seasonal sea ice retreat. Whereas the vernal ice melt appears necessary to stimulate the blooming of phytoplankton, it is not the determinator of the blooms magnitude, its areal extent and duration. A possible explanation for the limitation of the phytoplankton bloom in some years is top-down control. We hypothesize that the phytoplankton spring ...

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“…However, this does not necessarily mean that this water is entering south of Maud Rise at 65°S, 3°E, but may just be time-dependent eddies which seem to develop in the flow in the lee of the Rise. The character of the WDW is known to vary in time, and there has been some debate about the causes of this (Fahrbach et al 2004Smedsrud 2005Smedsrud , 2006.…”

Section: Introductionmentioning

confidence: 99%

Modification by lateral mixing of the Warm Deep Water entering the Weddell Sea in the Maud Rise region

2010

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Deep water originating in the North Atlantic is transported across the Antarctic Circumpolar Current by eddies and, after circumnavigating of the Antarctic, enters the Weddell Gyre south of Africa. As it does so, it rises up from mid-depth towards the surface. The separate temperature and salinity maxima, the Upper and Lower Circumpolar Deep Waters, converge to form the Warm Deep Water. Cores of this water mass on the southern flank of the eastern Weddell Gyre show a change in characteristic as they flow westward in the Lazarev Sea. Observations have been made along four meridional sections at 3°E, 0°, 3°W and 6°W between 60 and 70°S during the Polarstern Cruise ANTXXIII/2 in 2005/2006. These show that a heterogeneous series of warm and salty cores entering the region from the east both north and south of Maud Rise (65°S, 3°W) gradually merge and become more homogeneous towards the west. The gradual reduction in the variance of potential temperature on isopycnals is indicative of isopycnic mixing processes. A multiple regression technique allows diagnosis of the eddy diffusivities and, thus, the relative importance of isopycnic and diapycnic mixing. The method shows that the isopycnic diffusivity lies in the range 70-140 m 2 s −1 and the diapycnic diffusivity reaches about 3×10 −6 m 2 s −1 . Scale analysis suggests that isopycnic diffusion dominates over diapycnic diffusion in the erosion of the Warm Deep Water cores.

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Decadal-scale variations of water mass properties in the deep Weddell Sea

Cited by 124 publications

References 57 publications

Modelling the impact of ocean warming on melting and water masses of ice shelves in the Eastern Weddell Sea

Modelling the impact of ocean warming on melting and water masses of ice shelves in the Eastern Weddell Sea

Acoustic insights into the zooplankton dynamics of the eastern Weddell Sea

Modification by lateral mixing of the Warm Deep Water entering the Weddell Sea in the Maud Rise region

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