In 1997, a unique hydrographic and chlorofluorocarbon (CFC: component CFC-11) dataset was obtained in the subpolar North Atlantic. To estimate the synopticity of the 1997 data, the recent temporal evolution of the CFC and Labrador Sea Water (LSW) thickness fields are examined. In the western Atlantic north of 50degreesN, the LSW thickness decreased considerably from 1994-97, while the mean CFC concentrations did not change much. South of 50degreesN and in the eastern Atlantic, the CFC concentration increased with little or no change in the LSW thickness. On shorter timescales, local anomalies due to the presence of eddies are observed, but for space scales larger than the eddies the dataset can be treated as being synoptic over the 1997 observation period.The spreading of LSW in the subpolar North Atlantic is described in detail using gridded CFC and LSW thickness fields combined with Profiling Autonomous Lagrangian Circulation Explorer (PALACE) float trajectories. The gridded fields are also used to calculate the CFC-11 inventory in the LSW from 40degrees to 65degreesN, and from 10degrees to 60degreesW. In total, 2300 +/- 250 tons of CFC-11 (equivalent to 16.6 million moles) were brought into the LSW by deep convection. In 1997, 28% of the inventory was still found in the Labrador Sea west of 45degreesW and 31% of the inventory was located in the eastern Atlantic.The CFC inventory in the LSW was used to estimate the lower limits of LSW formation rates. At a constant formation rate, a value of 4.4-5.6 Sv (Sv = 10(6) m(3) s(-1)) is obtained. If the denser modes of LSW are ventilated only in periods with intense convection, the minimum formation rate of LSW in 1988-94 is 8.1-10.8 Sv, and 1.8-2.4 Sv in 1995-97.

Increased values of trichlorofluoromethane (CFC-11), tritium and stable tritium in the depth range from 2500 to 3500m at the eastern flank of the Mid-Atlantic Ridge at 48°N (WHP section A2) indicate an influence of newly ventilated water. Water with similar Θ, S and tracer properties is found on the WHP section A1 (55°N) situated north of the Gibbs Fracture Zone in the Iceland Basin. The high tracer concentrations are due to the influence of Iceland Scotland Overflow Water (ISOW). The ISOW-influenced water found in the Iceland Basin partially passes by the Gibbs Fracture Zone (52°N) and flows southward along the topography of the Mid-Atlantic Ridge. A quantitative analysis of the transport from the Iceland Basin to the Westeuropean Basin is carried out based on the assumption that the water with enhanced tracer values is a two-component mixture of recirculating North East Atlantic Deep Water from the eastern part of the Westeuropean Basin and ISOW-influenced water as found on A1 in the Iceland Basin (NEADWIB). The composition of the mixture and the transport time for the NEADWIB are deduced from the temporal evolution of the tracer values. From the distance between the two sections and the area with enhanced tracer values, a transport of NEADWIB from the Iceland Basin to the Westeuropean Basin of 1.63±0.32Sv111Sv=106m3/s. is calculated for the density range 41.37<σ3<41.475. Transports between 2.4 and 3.5Sv result if the transport in the former density range is extrapolated to 41.35<σ3<41.52 (corresponding to σΘ>27.8) in different ways.

Journal of Geophysical Research: OceansVolume 106, Issue C3 p. 4679-4679 CorrectionsFree Access Correction to “Component separation of oceanic helium” by Wolfgang Roether, Roland Well, Alfred Putzka, and Christine Rüth Wolfgang Roether, Wolfgang RoetherSearch for more papers by this authorRoland Well, Roland WellSearch for more papers by this authorAlfred Putzka, Alfred PutzkaSearch for more papers by this authorChristine Rüth, Christine RüthSearch for more papers by this author Wolfgang Roether, Wolfgang RoetherSearch for more papers by this authorRoland Well, Roland WellSearch for more papers by this authorAlfred Putzka, Alfred PutzkaSearch for more papers by this authorChristine Rüth, Christine RüthSearch for more papers by this author First published: 15 March 2001 https://doi.org/10.1029/1999JC000080Citations: 13AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article.Citing Literature Volume106, IssueC315 March 2001Pages 4679-4679 RelatedInformation

Chlorofluorocarbon (CFC) and hydrographic data collected in the North Atlantic in the late 1980s and early 1990s are used to confirm and add to earlier work on the large-scale circulation pathways and timescales for the spreading of North Atlantic Deep Water (NADW) components and how these components relate to the hydrographic structure. Throughout the western North Atlantic, high CFC concentrations are coincident with newly formed NADW components of Upper Labrador Sea Water (ULSW), Classical Labrador Sea Water (CLSW), and Overflow Waters (OW). ULSW is marked by a CFC maximum throughout the western subtropical and tropical Atlantic, and CLSW is marked by a CFC maximum north of 38 degrees N in data collected in 1990-1992. Iceland-Scotland Overflow Water (ISOW) splits into two branches in the eastern basin, with one branch entering the western basin where it mixes with Denmark Strait Overflow Water (DSOW) and the densest branch flows southward along the bottom in the eastern basin. DSOW contributes the largest portion of the CFC signal in OW. It is estimated that these NADW components are at 60-75% equilibrium with the CFC concentration in the atmosphere at the time of formation. The large-scale data set confirms that NADW spreads southward by complex pathways involving advection in the Deep Western Boundary Current (DWBC), recirculation in deep gyres, and mixing. Maps of the CFC distribution show that properties within the gyres are relatively homogeneous, particularly for OW, and there is a profound change at the gyre boundaries. The density of the core of ULSW increases in the equatorward direction because of entrainment by overlying northward flowing Upper Circumpolar Water and at the equator, ULSW has the same density as CLSW in the subtropics but is warmer and saltier. The density of OW decreases between the subpolar region and the subtropics. This is caused by the least dense part of OW exiting the subpolar region in the DWBC, while the densest component recirculates in the subpolar basins. Some variability is observed in OW density in the subtropics and tropics because of variability in mixing with Antarctic Bottom Water and changes in the subtropics that are probably related to the transport of different vintages of DSOW. Ages derived from CFC ratios show that the NADW components of northern origin spread throughout the western North Atlantic within 25-30 years. This corresponds to a spreading rate of 1-2 cm s(-1) and is comparable to the time a climate anomaly introduced into the subpolar North Atlantic will take to penetrate the entire western North Atlantic Ocean.

We describe and evaluate the distribution of the transient tracer tritium in the Eastern Mediterranean, on the basis of approximately 700 data points obtained from cruise M5/6 of F/S METEOR, Aug.–Sept. 1987. The horizontal resolution provided by the dataset is limited, but the vertical resolution is sufficient to resolve most of the principal features of the tritium distribution, and the data quality is good. Previous results concerning the thermohaline circulation of the Eastern Mediterranean based on tracer data are confirmed. Up to 1987 Eastern Mediterranean Deep Water (EMDW) was replenished from the Adriatic Sea, a near-bottom replenishment from the Aegean Sea contributing at most about 10%. A comparison with tritium data from a 1978 METEOR cruise gives evidence of a transfer of near-surface waters into the EMDW during the period between the two surveys. Cretan Intermediate Water (CIW) with a core depth of approximately 700 m and replenished from the Aegean Sea is found to be a prominent water mass. CIW spreads primarily westward, and is bordered in the Levantine Sea by EMDW which in this region extends to about 500 m depth. We infer that CIW replenishment has been rather steady since at least some decades, with a turnover time on the order of 10 years, and we name evidence that suggests a possible contribution of CIW to the dense water formation in the Adriatic Sea. Specific differences between the distribution of tritium and that of the chlorofluorocarbon tracer CFC 12 are noted. Tritium concentrations in the near-surface waters are found to be somewhat variable. The explanation is that for this tracer redistribution within the water column is particularly relevant.

A new procedure to quantify the components of oceanic helium (“terrigenic” 3He and 4He released from the ocean floor and “tritiugenic” 3He from tritium decay) is described. Terrigenic He and nonatmospheric 3He (i.e., terrigenic and tritiugenic combined) are obtained in terms of measured concentrations of the He isotopes and also of neon (Ne) (which improves the separation considerably), assuming terrigenic He to vanish in the mixed layer. For the subsequent separation of terrigenic and tritiugenic 3He, additional information is required and 3He due to natural tritium represents a complication. The procedure is applied to data from a hydrographic section in the South Atlantic (19°S, 1991) and one in the Eastern Mediterranean (1987). The 1σ data precisions and a systematic error accounting for uncertainties in mixed‐layer He are approximately 0.3%. Sections of the new representations of oceanic He and 3He and comparisons to the nearest classical quantities (i.e., 3He, He) are presented. In the South Atlantic the 3He distribution reflects the hydrographic structure. East of 20°W the average 3He/4He ratio of terrigenic He below 800 m is 4.5±0.8 times the atmospheric ratio, which implies a substantial contribution of crustal He. In the upper waters, tritiugenic 3He (0.5 tritium units, ±20%) is separated from terrigenic 3He. In the Eastern Mediterranean, tritiugenic 3He is quantified throughout the water column in the presence of substantial levels of terrigenic He; the release rate of terrigenic He from the sea floor is found to be 3.1±1.2 1010 atoms m−2 s−1, similar to the rate for continental crust, with a mantle He contribution of 5±1.2% only. Recommendations for future work are to reduce the mentioned systematic error and the uncertainty margins of the He and Ne solubilities and of 3He due to natural tritium.

We describe a new gas chromatographic analytical system for the joint measurement of the chlorofluorocarbons CFC‐11, CFC‐12, and CFC‐113 and of CC14 in ocean waters. From measurements at sea and in the laboratory we find overall precisions for surface waters of ±0.6, 0.6, 1.5, and 2.4% and detection limits of 0.002, 0.002, 0.008, and 0.003 pmol/kg, for CFC‐12, CFC‐11, CFC‐113, and CC14, respectively (1‐σ equivalents). The measurement repeat period is 17 min. A purge‐and‐trap approach, and other details, pay tribute to the work of Bullister and Weiss [1988]. A capillary column in combination with a low‐volume trap yields higher resolution than reported for other systems. There is füll separation of CFC‐12 from N2O and a satisfactory one of CFC‐113 from CH3I; to achieve the latter, a short packed column is operated in series with the main column. Slow purging of CC14 from the water samples contributes to its analytical error. The system is fully automated, allowing eight water samples and associated calibration measurements to be carried out unattented. Water samples are transferred into the system by means of flow‐through containers incorporating glass ampoules. Alternatively, the ampoules can be flame‐sealed, allowing sample storage for later analysis ashore. The performance of the system is assessed in some detail to serve as reference information for other CFC measurement systems and to direct future system tuning and developments. The system has been successfully employed at sea repeatedly. Sections from cruise M30/2, 1994 (Atlantic, 48° N), are presented as an example.

Ocean temperature, salinity and chlorofluorocarbon concentration data are used to track the recent spreading of cold intermediate-depth water masses from the Labrador Sea across the northern North Atlantic Ocean. These water masses, which are formed from surface waters by deep convection in the Labrador Sea, spread three to four times faster than previously estimated, with associated consequences for the North Atlantic thermohaline circulation.

We report distributions of the chlorofluorocarbon CFC 11, of CCl4, and of terrigenic He-3, along three zonal sections across the South Atlantic (WOCE WHP sections A8 - A10, 11.7 degrees S, 19 degrees S, 30 degrees S). The distributions fully reflect the water mass structure of the sections. They reveal a region of comparably much slower water renewal in the range of the Central and Antarctic Intermediate Waters, northeast of the Angola-Benguela Front. For all water masses further down, the distributions demonstrate that renewal is very much slower still, and that it occurs via advective cores adjacent to the respective western boundaries of the basins. The oldest waters are found to be present in a wedge centered in about 3000 m depth and extending from the African slope westward across the Midatlantic Ridge. The tracers are characterized by different input time scales, and these are well apparent in their distributions. The observed correlation between tracers indicates rather steady formation of Upper North Atlantic Deep Water over the past several decades. CCl4 is powerful in tracing relatively older waters, but in the upper South Atlantic waters our data confirm the decomposition of CCl4 reported previously.

Exploratory measurements of a suite of anthropogenic halocarbon compounds (CCl 4 , CCl 2 FCClF 2 (CFC‐113), CH 3 CCl 3 , CCl 3 F (CFC‐11)) were made using a new analytical technique on RV Meteor cruise 15 along 19°S (World Ocean Circulation Experiment (WOCE) Line A9)) in the Atlantic Ocean during February–March 1991. A separate analytical system was used to determine CCl 2 F 2 (CFC‐12) and CCl 3 F (CFC‐11). A limited number of CFC‐113 profiles indicated that it was undetectable below 400–500 m. The CCl 4 data indicate that the entire Brazil Basin contains readily measurable levels of CCl 4 (>0.05 pmol kg −1 ), whereas the deep Angola Basin contains very low levels (≤0.02 pmol kg −1 ). Slightly higher levels were found close to the bottom in the deep Angola Basin: possibly an anthropogenic signature. In contrast, most of the deep Brazil Basin and all of the deep Angola Basin (>1000 m) had undetectable levels of CFC‐11, CFC‐12, and CFC‐113. Preindustrial levels of CCl 4 in the atmosphere were therefore negligible (atmospheric mixing ratio <0.1 pptv). CCl 4 /CFC‐11 ratios are used to estimate apparent ages and dilution factors for the North Atlantic Deep Water and Antarctic Bottom Water. Whereas CCl 4 /CFC‐11/CFC‐12 levels are internally consistent in deep waters, suggesting near‐conservative behavior, there is evidence for very rapid removal of CCl 4 in the thermocline. Removal rates suggest that in addition to neutral hydrolysis, some other loss pathway must be involved.

New hydrographic and nutrient data obtained on a section across Drake Passage (F/S Meteor January 1990, World Ocean Circulation Experiment Hydrographic Program section S1) are in close agreement with property sections reported previously. The chlorofluoromethanes CFM 11 and CFM 12 were measured in Drake Passage for the first time. CFM concentrations are found to decrease from the surface down into the Upper Circumpolar Deep Water, for which they confirm water renewal from the south. For the Lower Circumpolar Deep Water, in which CFM concentrations were above detection limit only south of the Polar Front, very little water renewal on the CFM time scale is implied. Nonvanishing CFM is again found in the Weddell Sea Deep Water and the Southeast Pacific Deep Water toward the bottom in the south, but recent ventilation for the latter water mass is rejected. CFM 11 and CFM 12 concentrations vary essentially in constant proportion down to very low concentrations, questioning the possibility of using CFM ratios as “age” markers. The observed ratios are shown to be a natural feature of the upwelling regime of the southern ocean. Property concentrations on isopycnal surfaces display large undulations, reaching down into the Upper Circumpolar Deep Water. Their extrema, due to varying contribution of young water of southern origin, are situated at the boundaries of the current bands of the Antarctic Circumpolar Current The feature is ascribed to property advection by rings and is taken to support previous claims that rings are an important transport mechanism across the Antarctic Circumpolar Current and that they might assist in maintaining its fronts.

The supermatrix-Liouville formalism to compute Mössbauer relaxation spectra leads, applied to the6S5/2-state of57Fe(III) to a 288-dimensional nonhermitian matrix. Provided that an axial crystal field acts on the electronic states, only few of the states described by the supermatrix are necessary to simulate theoretical spectra and the dimension of this matrix can be reduced to at least 1/3. This confinement implies no approximation for the description of the six electronic states of Fe(III) and for the interactions of them with environment and nucleus.