The Weddell Gyre (WG) is one of the main oceanographic features of the Southern Ocean south of the Antarctic Circumpolar Current which plays an influential role in global ocean circulation as well as gas exchange with the atmosphere. We review the state‐of‐the art knowledge concerning the WG from an interdisciplinary perspective, uncovering critical aspects needed to understand this system's role in shaping the future evolution of oceanic heat and carbon uptake over the next decades. The main limitations in our knowledge are related to the conditions in this extreme and remote environment, where the polar night, very low air temperatures, and presence of sea ice year‐round hamper field and remotely sensed measurements. We highlight the importance of winter and under‐ice conditions in the southern WG, the role that new technology will play to overcome present‐day sampling limitations, the importance of the WG connectivity to the low‐latitude oceans and atmosphere, and the expected intensification of the WG circulation as the westerly winds intensify. Greater international cooperation is needed to define key sampling locations that can be visited by any research vessel in the region. Existing transects sampled since the 1980s along the Prime Meridian and along an East‐West section at ~62°S should be maintained with regularity to provide answers to the relevant questions. This approach will provide long‐term data to determine trends and will improve representation of processes for regional, Antarctic‐wide, and global modeling efforts—thereby enhancing predictions of the WG in global ocean circulation and climate.

[1] A total of 232 samples were analyzed for concentrations of dissolved aluminum ([Al]) and manganese ([Mn]) in Drake Passage. Both [Al] and [Mn] were extremely low ($0.3 and 0.1 nM, respectively) in the surface layer of the middle Drake Passage, most likely due to limited input and biological uptake/scavenging.

cannot be related to the known sources in the south, the Filchner-Ronne Ice Shelf. We show that this bottom water is formed in the western Weddell Sea, most likely in interaction with the Larsen C Ice Shelf. By applying an Optimum Multiparameter Analysis (OMP) using temperature, salinity, and noble gas observations (helium isotopes and neon), we obtained mean glacial melt water fractions of about 0.1% in the bottom water. On sections across the Weddell Gyre further north melt water fractions are still in the order of 0.04%. Using chlorofluorocarbons (CFCs) as age tracers, we deduced a mean transit time between the western source and the bottom water found on the slope toward the north (9 ± 3 years). This transit time is larger and the inferred transport rate is small in comparison to previous findings. But accounting for a loss of the initially formed bottom water volume due to mixing and renewal of Weddell Sea Deep Water, a formation rate of 1.1 ± 0.5 Sv in the western Weddell Sea is

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The World Ocean takes up a large portion of the anthropogenic CO 2 emitted into the atmosphere. Determining the resulting increase in dissolved inorganic carbon (C T , expressed in mmol kg À 1) is challenging, particularly in the sub-surface and deep Southern Ocean where the time rate of change of C T (in mmol kg À 1 decade À 1) is commonly expected to be low. We present a determination of this time trend of C T in a dataset of measurements that spans 35 years comprising 10 cruises in the 1973-2008 period along the 01-meridian in the Weddell Gyre. The inclusion of many cruises aims to generate results that are more robust than may be obtained by taking the difference between only one pair of cruises, each of which may suffer from errors in accuracy. To further improve consistency between cruises, data were adjusted in order to obtain time-invariant values of C T (and other relevant parameters) over the 35 years in the least ventilated local water body, this comprising the deeper Warm Deep Water (WDW) and upper Weddell Sea Deep Water (WSDW). It is assumed that this normalization procedure will allow trends in C T in the more intensely ventilated water masses to be more clearly observed. Time trends were determined directly in measurements of C T , and alternatively in back-calculated values of preformed C T (C T 0 ; i.e., the C T of the water at the time that it lost contact with the atmosphere). The determined time trends may be attributed to a combination of natural variability (in hydrography or biogeochemistry) and increased uptake of anthropogenic CO 2 from the atmosphere. In order to separate these natural and anthropogenic components, an analysis of the residuals of a multivariate linear regression (MLR), involving the complete time series of all 10 cruises, was additionally performed. This approach is referred to as the Time Series Residuals (TSR) approach. Using the direct method, the time trends of C T in the WSDW are quite small and non-significant at þ 0.176 7 0.321 mmol kg À 1 decade À 1. On the other hand, the measured concentration of C T in the Weddell Sea Bottom Water (WSBW) is shown to rise slowly but significantly over the period from 1973 to 2008 at a rate of þ 1.1517 0.563 mmol kg À 1 decade À 1. The spatial distribution of these determined increases of C T in the deep Weddell Gyre closely resembles that of the increase of the anthropogenic tracer CFC-12, this strong similarity supporting a mostly anthropogenic cause for the increasing trend of C T. Time trends in back-calculated values of C T 0 appear to be obscured due to uncertainties in the measurements of O 2. Finally, the shallow waters (o200 m depth) do not allow for interpretation since these are strongly affected by seasonality. Due to the small time trend signal in the WSBW, the TSR approach does not allow for unambiguous attribution of the observed trend in C T in the WSBW. The residuals of the TSR method do exhibit a time trend (considered representative of the time trend of C ant) of þ 0.445 7 0.405 mmol kg À 1 decade À 1 (i.e., o...