| 1. |
- 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. |
- Lauvset, Siv K., et al.
(författare)
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The annual update GLODAPv2.2023: the global interior ocean biogeochemical data product
- 2024
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Ingår i: Earth System Science Data. - 1866-3591. ; 16, s. 2047-2072
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Tidskriftsartikel (refereegranskat)abstract
- The Global Ocean Data Analysis Project (GLODAP) is a synthesis effort providing regular compilations of surface to bottom ocean biogeochemical bottle data, with an emphasis on seawater inorganic carbon chemistry and related variables determined through chemical analysis of seawater samples. GLODAPv2.2023 is an update of the previous version, GLODAPv2.2022 (Lauvset et al., 2022). The major changes are as follows: data from 23 new cruises were added. In addition, a number of changes were made to the data included in GLODAPv2.2022. GLODAPv2.2023 includes measurements from more than 1.4 million water samples from the global oceans collected on 1108 cruises. The data for the now 13 GLODAP core variables (salinity, oxygen, nitrate, silicate, phosphate, dissolved inorganic carbon, total alkalinity, pH, chlorofluorocarbon-11 (CFC-11), CFC-12, CFC-113, CCl4, and SF6) have undergone extensive quality control with a focus on the systematic evaluation of bias. The data are available in two formats: (i) as submitted by the data originator but converted to World Ocean Circulation Experiment (WOCE) exchange format and (ii) as a merged data product with adjustments applied to minimize bias. For the present annual update, adjustments for the 23 new cruises were derived by comparing those data with the data from the 1085 quality-controlled cruises in the GLODAPv2.2022 data product using crossover analysis. SF6 data from all cruises were evaluated by comparison with CFC-12 data measured on the same cruises. For nutrients and ocean carbon dioxide (CO2), chemistry comparisons to estimates based on empirical algorithms provided additional context for adjustment decisions. The adjustments that we applied are intended to remove potential biases from errors related to measurement, calibration, and data-handling practices without removing known or likely time trends or variations in the variables evaluated. The compiled and adjusted data product is believed to be consistent to better than 0.005 in salinity, 1% in oxygen, 2% in nitrate, 2% in silicate, 2% in phosphate, 4µmolkg−1 in dissolved inorganic carbon, 4µmolkg−1 in total alkalinity, 0.01–0.02 in pH (depending on region), and 5% in the halogenated transient tracers. The other variables included in the compilation, such as isotopic tracers and discrete CO2 fugacity (fCO2), were not subjected to bias comparison or adjustments. The original data, their documentation, and DOI codes are available at the Ocean Carbon and Acidification Data System of NOAA National Centers for Environmental Information (NCEI), which also provides access to the merged data product. This is provided as a single global file and as four regional ones – the Arctic, Atlantic, Indian, and Pacific oceans – under https://doi.org/10.25921/zyrq-ht66 (Lauvset et al., 2023). These bias-adjusted product files also include significant ancillary and approximated data, which were obtained by interpolation of, or calculation from, measured data. This living data update documents the GLODAPv2.2023 methods and provides a broad overview of the secondary quality control procedures and results.
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| 3. |
- 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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| 4. |
- Montagna, Paolo, et al.
(författare)
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Dissolved neodymium isotopes in the Mediterranean Sea
- 2022
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier BV. - 0016-7037. ; 322, s. 143-169
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Tidskriftsartikel (refereegranskat)abstract
- The neodymium isotopic composition (εNd) of seawater is one of the most important geochemical tracers to investigate water mass provenance, which can also serve as a proxy to reconstruct past variations in ocean circulation. Nd isotopes have recently also been used to reconstruct past circulation changes in the Mediterranean Sea on different time scales. However, the modern seawater εNd dataset for the Mediterranean Sea, which these reconstructions are based on, is limited and up to now only 160 isotopic measurements are available for the entire basin. The lack of present-day data also limits our understanding of the processes controlling the Nd cycle and Nd isotopic distribution in this semi-enclosed basin. Here we present new εNd data from 24 depth profiles covering all Mediterranean sub-basins, which significantly increases the available dataset in the Mediterranean Sea. The main goal of our study is to better characterize the relationship between the dissolved Nd isotope distributions and major water masses in the Mediterranean Sea and to investigate the impact and relative importance of local non-conservative modifications, which include input of riverine particles and waters, aeolian-derived material and exchange with the sediments at continental margins. This comprehensive εNd dataset reveals a clear εNd – salinity correlation and a zonal and depth gradient with εNd systematically increasing from the western to the eastern Mediterranean basin (average εNd = −8.8 ± 0.8 and −6.7 ± 1 for the entire water column, respectively), reflecting the large-scale basin circulation. We have evaluated the conservative εNd behaviour in the Mediterranean Sea and quantified the non-conservative components of the εNd signatures by applying an Optimum Multiparameter (OMP) analysis and results from the Parametric Optimum Multiparameter (POMP) analysis of Jullion et al. (2017). The results of the present study combined with previously published Nd isotope values indicate that dissolved εNd behaves overall conservatively in the open Mediterranean Sea and show that its water masses are clearly distinguishable by their Nd isotope signature. However, misfits between measured and OMP- and POMP-derived εNd values exist in almost all sub-basins, especially in the eastern Levantine Basin and Alboran Sea at intermediate-deep depths, which can be explained by the influence of detrital lithogenic εNd signatures through interaction with highly radiogenic Nile sourced volcanic fractions and unradiogenic sediments, respectively.The radiogenic signature acquired in the eastern Levantine Basin is carried by the Levantine Intermediate Water and transferred conservatively to the entire Mediterranean at intermediate depths. Our measured εNd values and OMP- and POMP-derived results indicate that non-conservative contributions originating from sediment sources are then propagated by water mass circulation (with distinct preformed εNd) along the Mediterranean Sea through advection and conservative mixing. Mediterranean εNd effectively traces the mixing between the different water masses in this semi-enclosed basin and is a suitable water mass tracer.
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| 5. |
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| 6. |
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| 7. |
- 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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| 8. |
- Sloyan, Bernadette M., et al.
(författare)
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The global ocean ship-base hydrographic investigations program (GO-SHIP): A platform for integrated multidisciplinary ocean science
- 2019
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Ingår i: Frontiers in Marine Science. - : Frontiers Media SA. - 2296-7745. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- The Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP) provides a globally coordinated network and oversight of 55 sustained decadal repeat hydrographic reference (core) lines as part of the global ocean/climate observing systems (GOOS/GCOS) for study of physical oceanography, the ocean carbon, oxygen and nutrient cycles, and marine biogeochemistry. GO-SHIP enables assessment of the ocean sequestration of heat and carbon, changing ocean circulation and ventilation patterns, and their effects on ocean health and Earth's climate. Rapid quality control and open data release along with incorporation of the GO-SHIP effort in the Joint Technical Commission for Oceanography and Marine Meteorology (JCOMM) in situ Observing Programs Support Center (JCOMMOPS) have increased the profile of, and participation in, the program and led to increased data use for a range of efforts.
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| 9. |
- 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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| 10. |
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| 11. |
- 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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| 12. |
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| 13. |
- 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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| 14. |
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| 15. |
- Tanhua, Toste, et al.
(författare)
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Ventilation of the Arctic Ocean: Mean ages and inventories of anthropogenic CO2 and CFC-11
- 2009
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Ingår i: J. Geophys. Res.. ; 114
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Tidskriftsartikel (refereegranskat)abstract
- The Arctic Ocean constitutes a large body of water that is still relatively poorly surveyed because of logistical difficulties, although the importance of the Arctic Ocean for global circulation and climate is widely recognized. For instance, the concentration and inventory of anthropogenic CO2 (C ant) in the Arctic Ocean are not properly known despite its relatively large volume of well-ventilated waters. In this work, we have synthesized available transient tracer measurements (e.g., CFCs and SF6) made during more than two decades by the authors. The tracer data are used to estimate the ventilation of the Arctic Ocean, to infer deep-water pathways, and to estimate the Arctic Ocean inventory of C ant. For these calculations, we used the transit time distribution (TTD) concept that makes tracer measurements collected over several decades comparable with each other. The bottom water in the Arctic Ocean has CFC values close to the detection limit, with somewhat higher values in the Eurasian Basin. The ventilation time for the intermediate water column is shorter in the Eurasian Basin (∼200 years) than in the Canadian Basin (∼300 years). We calculate the Arctic Ocean C ant inventory range to be 2.5 to 3.3 Pg-C, normalized to 2005, i.e., ∼2% of the global ocean C ant inventory despite being composed of only ∼1% of the global ocean volume. In a similar fashion, we use the TTD field to calculate the Arctic Ocean inventory of CFC-11 to be 26.2 ± 2.6 × 106 moles for year 1994, which is ∼5% of the global ocean CFC-11 inventory.
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