We present and assess the distribution of neon in South Atlantic and South Pacific waters, on the basis of more than 3000 mostly new neon data which were obtained primarily under the hydrographic program of the World Ocean Circulation Experiment (predominantly southern summer to fall cruises). Data precision is better than±0.5%, and the set is internally consistent within±0.3% and partly better, and compatible with reported high-quality neon values. Using suitably averaged data (precision 0.1–0.3%), we find that the total range of neon anomalies relative to a solubility equilibrium with atmospheric neon at the observed potential temperature and salinity (using the solubilities of Weiss, J. Chem. Eng. Data 16 (1971) 235) is approximately 0–4%, and below 2000m depth, 3–4% only. We consistently observe two types of neon depth profiles, one for the temperate-latitudes ocean, which is characterized by a near-surface maximum and a minimum in Antarctic Intermediate Water, and one for the Southern Ocean that essentially displays a steady increase with depth. The neon distribution reflects the influence of air injected by submerged air bubbles, the areal distribution of atmospheric pressure, seasonal temperature changes in the mixed layer and solar heating below it, and interaction with sea ice and glacial ice, largely in keeping with previous work. However, it appears that interaction with sea ice reduces neon anomalies distinctly less than the literature suggests. The temperate-ocean shallow maxima point to widespread subsurface heating in the course of the summer season by roughly 1K. Among the major source water masses of the deep waters, the neon anomalies are lowest in Antarctic Intermediate Water (∼1.5%), intermediate in North Atlantic Deep Water (∼3%, confirming previous work) and similarly in Circumpolar Deep Water, and highest in Antarctic Bottom Water (∼3.8%). The anomalies in Southeast Pacific deep waters (>2500m) are comparatively less (only∼3.3%), as a result of the contribution of Antarctic Intermediate Water. The present study is the first attempt to deal with the oceanic distribution of neon in a systematic fashion. The results can serve to assist assessments of the oceanic distributions of other dissolved gases.

We present 3He data from a repeat section across Drake Passage, from three sections off the South American continent in the Pacific, at 28°S, 35°S, and 43°S, and from three sections in the Atlantic, eastward of the Malvinas, close to 35°W, and near the Greenwich Meridian. In Drake Passage, a distinct high-3He signal is observed that is centered just above the boundary of the Lower and the Upper Circumpolar Deep Water (LCDW, UCDW), and is concentrated towards the northern continental slope. 3He concentrations in the Antarctic Circumpolar Current (ACC) upstream of Drake Passage (World Ocean Circulation Experiment section P19 at 88°W) are markedly lower than those found in Drake Passage, and a regional source of primordial helium in the path of the ACC that might cause the high-3He feature can be ruled out. We explain the feature by addition of high-3He waters present at the 43°S Pacific section. This supports a previous, similar interpretation of a low-salinity anomaly in Drake Passage (Naveira Garabato et al., Deep-Sea Research I 49 (2002) 681), that is strongly related to the high-3He feature. Employing multiparameter water mass analysis (including 3He as a parameter), we find that deep waters as met at the 43°S Pacific section, flowing south along the South American continental slope, contribute substantially to the ACC waters in Drake Passage (fractions exceed 50% locally). Lesser, but laterally more extended contributions are found east of the Malvinas, and still smaller ones are present at 35°W and at the Greenwich Meridian. Using velocity measurements from one of the two Drake Passage sections, we estimate the volume transport of these waters to be 7.0±1.2Sv, but the average transport may be somewhat lower as the other realization had a less pronounced signal. The enhanced 3He signature in Drake Passage is essentially confined north of the Polar Front. Further downstream the signature crosses this front, to the extent that at 35°W the contributions south and north of it are of similar magnitude. At the same time, the 3He levels north of the front are reduced due to a substantial admixture of low-3He North Atlantic Deep Water, such that 3He becomes highest south of the front. The flow of Southeast Pacific deep slope waters entering the ACC constitutes the predominant exit pathway of the primordial helium released in the deep Pacific, and represents a considerable fraction of the deep water return flow from the Pacific into the ACC. Therefore and also because the density range of the added deep slope waters is intermediate between those of UCDW and LCDW, they must be considered a distinct water mass.

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

We have analyzed deep helium isotope data from World Ocean Circulation Experiment section P17 along 135°W in the Pacific Ocean. Combining these data with neon data, we have derived the isotopic ratio (Rt) of the nonatmospheric part of helium (terrigenic helium). The calculated Rt values are significantly lower than helium isotope ratios from mid‐ocean ridge (MOR) sources (RMOR ≈ 8Ra; Ra: = (3He/4He)air), which are generally presumed to dominate the isotope characteristics of helium of nonatmospheric origin. For the depths most influenced by the southern East Pacific Rise (EPR) helium plume the isotopic ratio of terrigenic helium is ∼7.4 Ra. However, both the northern EPR plume and the Juan de Fuca Ridge (JdFR) plume show significantly lower Rt values of ∼6.8 Ra. We find minimum Rt values of ∼5.6 Ra at about 20°N to 30°N from 2000 m depth to the ocean floor. We conclude that in addition to the EPR and JdFR helium sources (having MOR isotope characteristics) there is a flux of radiogenic 4He out of deep‐sea sediments and the oceanic crust which causes a significant deviation of Rt toward values lower than RMOR. Using our calculated terrigenic 4He concentrations and isotope ratios Rt and the helium isotope ratios of the two end‐members (MOR helium and crustal helium), we derive concentrations and ocean bottom fluxes of crustal 4He (4Hecrust). Maximum concentrations of 4Hecrust (up to ∼30 pmol kg−1) are found at about 20°N to 30°N between 2000 m and 4000 m along the P17 section. The mean crustal 4He flux is obtained as 1.0 (±0.4) 109 atoms m−2Earth s−1.

Rates of oxygen consumption are determined by fitting simulated oxygen concentrations to observations from a medium-resolution survey of the Eastern Mediterranean in 1987 (METEOR cruise M5/6). The simulations are obtained with a previously described two-dimensional kinematic model of the sea, which is newly calibrated using concurrent hydrographic and tracer data, and with oxygen consumption as a function of depth being parameterized following previous work. The consumption rate is obtained as R(z)=22(z/100)−2+0.31μmol/(kgyr) for z<1000m, and R=0.53μmol/(kgyr) for z⩾1000m. For the waters below about 700 m depth, the uncertainty in R is approximately ±35%. Significant error contributions arise from the oxygen concentration of the waters newly supplied to the deep waters, and from possible deviations from a steady state in circulation and in oxygen cycling. The upper ocean rates are rather more uncertain, but they are compatible with rates from the literature. The deduced deep-water oxygen consumption rate is considerably higher than the rates found in previous deep-ocean work. Such rather high rates, which possibly are related to the comparatively high temperatures of the deep waters, have repercussions in various contexts, e.g. in the assessment of environmental conditions in the past that led to the formation of sapropel layers. The updated circulation model yields a deep-water renewal rate for the Eastern Mediterranean only moderately different from a previous value. The rate actually replenishing the deep regime amounts to 5.1×105 m3/s (±20%), of which 2.8×105 m3/s (±30%) are recirculated deep water. Convective renewal of the deep regime (>1200 m depth) by the combined addition of surface and intermediate waters requires 150 years (±30%).

Helium isotope data from three zonal WOCE sections (11 degrees S, 19 degrees S and 30 degrees S) in the South Atlantic are presented. Among other features we find a distinct delta(3)He-maximum above the Mid-Atlantic Ridge (MAR) at all three latitudes. Using a hydrographic multiparameter analysis, we separate He-3 emanating from the MAR from the large-scale He-3 background. To our knowledge, this is the first confirmation of input of primordial He-3 at the MAR in the South Atlantic. The source appears to be weak compared with the Pacific sources, causing He-3 elevations (relative to background values) of only 2-3% directly above the MAR. This exceeds by several times the statistical and systematic data uncertainties, which amount to 0.35% each, so that detailed contouring of the MAR-derived He-3 is possible. At 30 degrees S and 11 degrees S, a significant signal extends westward over at least 2000 km, whereas at 19 degrees S the signal is more confined to the ridge area. The westward extensions indicate westward flow at depths near the ridge crest elevation, contradicting flow directions deduced previously by Reid (1989). (C) 2000 Elsevier Science Ltd. All rights reserved.

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.

Available distributions of certain tracers (the CFC F 12, tritium, tritiugenic 3He, terrigenic helium released from the ocean floor) throughout the Eastern Mediterranean provide information on the turnover of deep and intermediate waters. Terrigenic helium is used as an independent ocean tracer for the first time. Information on rates of water mass formation, recirculation, and mixing is obtained by evaluating the tracer data and salinity data by means of a two-dimensional, low-resolution kinematic advection/diffusion model. Results from a previous evaluation (Roether and Schlitzer, 1991) are reinforced, and interplay of ventilation and upwelling of “older” waters from deeper layers becomes apparent. A second topic is the use of tracer data to diagnose, as well as to correct, deep water formation and spreading in an ocean general circulation model (OGCM, GFDL type) for the Eastern Mediterranean. The potential of this approach is demonstrated by F 12 simulations. These show that climatological forcing definitely falls short of generating correct deep water formation and that realistic OGCM simulation of an overflow process is difficult to achieve.