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- Jeansson, Emil, 1972, et al.
(författare)
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Recent changes in the Greenland Sea: Tracers and Hydrography
- 2008
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Ingår i: Geophysical Research Abstracts. ; 10
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Konferensbidrag (refereegranskat)abstract
- Time series of chemical and hydrographic parameters from mid-90s to 2006 in the central Greenland Sea are presented. In addition to potential temperature and salinity, oxygen and transient tracers (CFC-12 and CFC-11) have been measured between 1995 and 2006. The lack of deep convection since the 80s has changed the properties of the Greenland Sea Deep Water, which has become more or less continuously warmer and more saline during, at least, the last two decades. The change in temperature and salinity during the 90s has previously been reported as 0.01°C yr−1 and 0.001°C yr−1, respectively. The change from the mid-90s to 2006 shows the same trend, and might now even increase more rapidly. At the same time, the levels of oxygen have decreased while the transient tracer concentrations have more or less levelled out, indicating that the deep water now has a larger contribution of Arctic Ocean Deep Water. The ventilation depth of the Greenland Sea was larger in the 2000s, compared with the 90s. In accordance with this the transient tracer concentrations of the intermediate waters, down to 1500 m, has increased.
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| 2. |
- Messias, M. J, et al.
(författare)
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The Greenland Sea tracer experiment 1996–2002: Horizontal mixing and transport of Greenland Sea Intermediate Water
- 2008
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Ingår i: Progress In Oceanography. - : Elsevier BV. - 0079-6611. ; 78:1, s. 85-105
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Tidskriftsartikel (refereegranskat)abstract
- In summer 1996, a tracer release experiment using sulphur hexafluoride (SF6) was launched in the intermediate-depth waters of the central Greenland Sea (GS), to study the mixing and ventilation processes in the region and its role in the northern limb of the Atlantic overturning circulation. Here we describe the hydrographic context of the experiment, the methods adopted and the results from the monitoring of the horizontal tracer spread for the 1996–2002 period documented by 10 shipboard surveys. The tracer marked “Greenland Sea Arctic Intermediate Water” (GSAIW). This was redistributed in the gyre by variable winter convection penetrating only to mid-depths, reaching at most 1800 m depth during the strongest event observed in 2002. For the first 18 months, the tracer remained mainly in the Greenland Sea. Vigorous horizontal mixing within the Greenland Sea gyre and a tight circulation of the gyre interacting slowly with the other basins under strong topographic influences were identified. We use the tracer distributions to derive the horizontal shear at the scale of the Greenland Sea gyre, and rates of horizontal mixing at 10 and 300 km scales. Mixing rates at small scale are high, several times those observed at comparable depths at lower latitudes. Horizontal stirring at the sub-gyre scale is mediated by numerous and vigorous eddies. Evidence obtained during the tracer release suggests that these play an important role in mixing water masses to form the intermediate waters of the central Greenland Sea. By year two, the tracer had entered the surrounding current systems at intermediate depths and small concentrations were in proximity to the overflows into the North Atlantic. After 3 years, the tracer had spread over the Nordic Seas basins. Finally by year six, an intensive large survey provided an overall synoptic documentation of the spreading of the tagged GSAIW in the Nordic Seas. A circulation scheme of the tagged water originating from the centre of the GS is deduced from the horizontal spread of the tracer. We present this circulation and evaluate the transport budgets of the tracer between the GS and the surroundings basins. The overall residence time for the tagged GSAIW in the Greenland Sea was about 2.5 years. We infer an export of intermediate water of GSAIW from the GS of 1 to 1.85 Sv (1 Sv = 106 m3 s−1) for the period from September 1998 to June 2002 based on the evolution of the amount of tracer leaving the GS gyre. There is strong exchange between the Greenland Sea and Arctic Ocean via Fram Strait, but the contribution of the Greenland Sea to the Denmark Strait and Iceland Scotland overflows is modest, probably not exceeding 6% during the period under study.
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| 3. |
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| 4. |
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| 5. |
- Olsson, Anders, 1970, et al.
(författare)
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The East Greenland Current studied with CFCs and released sulphur hexafluoride
- 2005
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963. ; 55:1-2, s. 77-95
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Tidskriftsartikel (refereegranskat)abstract
- The distribution and evolution of water masses along the East Greenland Current (EGC) from south of the Fram Strait to the Denmark Strait were investigated using chlorofluorocarbons (CFCs) and the released tracer sulphur bexafluoride (SF6) together with hydrographic data. Water masses contributing to the Denmark Strait overflow, and to some extent also contributions to the Iceland-Scotland over-flow, are discussed from observations in 1999. Special emphasis is put on the advection and mixing of Greenland Sea Arctic Intermediate Water (GSAIW), which could be effectively traced thanks to the release of sulphur hexafluoride in the Greenland Sea Gyre in 1996. By means of the dispersion of the tracer, Greenland Sea Arctic Intermediate Water was followed down to the Denmark Strait Sill as well as close to the Faroe-Shetland Channel. The results indicate that this water mass can contribute to both overflows within 3 years from leaving the Greenland Sea. The transformation of Greenland Sea Arctic Intermediate Water was dominated by water from the Arctic Ocean, especially by isopycnal mixing with upper Polar Deep Water (uPDW) but, to a less extent, also by Canadian Basin Deep Water. A mixture of Greenland Sea Arctic Intermediate Water and upper Polar Deep Water was lifted 500 m on its way through southwestern Iceland Sea, to a depth shallow enough to let it reach the sill of the Denmark Strait from where it can be incorporated in the densest layer of the overflow. The observations show contributions to the Denmark Strait overflow from both the East Greenland Current and the Iceland Sea. (c) 2004 Elsevier B.V. All rights reserved.
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| 6. |
- Tanhua, Toste, 1965, et al.
(författare)
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A first study of SF6 as a transient tracer in the Southern Ocean
- 2004
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Ingår i: Deep-Sea Research Part Ii-Topical Studies in Oceanography. ; 51:22-24, s. 2683-2699
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Tidskriftsartikel (refereegranskat)abstract
- Halogenated transient tracers such as the chlorofluorocarbons CFC-11, CFC-12 and CFC-1 13 are commonly used in oceanographic studies. These compounds enter the ocean via the atmosphere and their triansient atmospheric concentrations make them valuable as oceanic tracers. The trends of rapidly rising atmospheric concentrations of these tracers are however broken, and the oceanic signal becomes increasingly more difficult to decipher. There is a need for a new transient tracer to complement the existing suit of tracers, especially for recently ventilated water masses. One compound that looks promising in this respect is sulphur hexafluoride (SF6), an inert gas whose atmospheric concentration is rising rapidly. In this paper, the use of SF6 as a transient tracer in recently ventilated waters is discussed and the method for determination of SF6 in seawater is described. Tracer data from a section in the Atlantic sector of the Southern Ocean along 6degreesE, from 60degreesS to 40degreesS, occupied during January 1998, are presented. The Antarctic Polar Front, found close to 50degreesS, was studied with a densely sampled section down to 400 m depth and SF6/CFC-12 ratios are used to deduce ventilation ages and dilution factors. A comparison of apparent ages derived from a variety of tracers is presented together with the uncertainties in these estimates. This work demonstrates that SF6 is a useful and valuable transient tracer for waters ventilated during the last 20 years. (C) 2004 Elsevier Ltd. All rights reserved.
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| 7. |
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| 8. |
- Tanhua, Toste, 1965, et al.
(författare)
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Formation of Denmark Strait overflow water and its hydro-chemical composition
- 2005
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963. ; 57:3-4, s. 264-288
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Tidskriftsartikel (refereegranskat)abstract
- The dense overflow across the Denmark Strait is investigated with hydrographic and hydro-chemical data and the water mass composition of the Denmark Strait Overflow Water (DSOW) is determined by multivariate analysis. Hydrographical properties, the transient tracers CFC-11 and CFC-12, oxygen and nutrients are utilized for the water mass definitions. Distribution and characteristics of water masses north of Denmark Strait are described, the important water masses at the sill and the variability on weekly time-scales are discussed, and the entrainment and mixing of water into the overflow plume in the northern Irminger Basin is calculated. The analysis indicates that water masses both from the Nordic Seas and the Arctic Ocean are important for the formation of DSOW. It is found that water masses transported with the East Greenland Current make up about 75% of the overflow at the sill. The overflow at, and shortly south of, the sill is inhomogeneous with a low-salinity component dominated by Polar Intermediate Water. The high-salinity component of the overflow is mainly of Arctic origin. The water mass composition, and the short-term variability for 7 repeats of sections close to the sill are described, and these illustrate that the overflow is in fact a composite of a number of water masses with different formation and transport histories. This indicate that the overflow is a robust feature, but that it responds to variations in the circulation or atmospheric forcing that influences the formation of intermediate and deep water masses within the Arctic Mediterranean and the North Atlantic. At a section about 400 kin south of the sill the overflow is well mixed and modified by entrainment of, mainly, Iceland-Scotland Overflow Water and Labrador Sea Water, together constituting 30% of the overflow plume. The entrainment of Middle Irminger Water dominates shortly downstream of the sill, before the overflow plume reaches too deep but the entrainment seems to be intermittent in time. (c) 2005 Elsevier B.V. All rights reserved.
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| 9. |
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| 10. |
- Tanhua, Toste, 1965, et al.
(författare)
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Removal and bioaccumulation of anthropogenic, halogenated transient tracers in an anoxic fjord
- 2005
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Ingår i: Marine Chemistry. - : Elsevier BV. - 0304-4203. ; 94:1-4, s. 27-41
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Tidskriftsartikel (refereegranskat)abstract
- The persistence of the anthropogenic halogenated tracers, CFC-11 (CCl3F), CFC-12 (CCl2F2), CFC-113 (CCl2FCClF2), carbon tetrachloride (CCl4) and methyl chloroform (CH3CCl3) in oxygen-depleted waters was investigated in the anoxic fjord Framvaren in southern Norway. A model for the ventilation of the water in the fjord was created based on tritium and CFC-12 profiles. The results suggest that CFC-12 is stable in this environment, although still affected by particulate scavenging, while the other four halocarbon species shows signs of significant removal in the oxic/anoxic interface. The first-order removal coefficients were calculated to be 0.35, 0.19, 1.23 and 0.31 year(-1) for CFC-11, CFC-113, CCl4 and CH3CCl3, respectively. Significant downward flux of halogenated tracers by sinking organic matter is suggested by the model; the tracers are subsequently released to the water column by the remineralisation of the particles. This process acts as a sink of halogenated tracers in the surface waters, whereas it is a source for the deep waters. Our results points to bioaccumulation factors (BF) for the CFC tracers in the order of 4.4-5.4 (log BF), which is 100-600 times those previously reported. This might be of significance to near-shore, semi-enclosed, basins with a high flux of organic matter, but would still have little importance in open ocean basins. (c) 2004 Elsevier B.V. All rights reserved.
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