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Landrum, LL, Gammon RH, Feely RA, Murphy PP, Kelly KC, Cosca CE, Weiss RF.  1996.  North Pacific Ocean CO2 disequilibrium for spring through summer, 1985-1989. Journal of Geophysical Research-Oceans. 101:28539-28555.   10.1029/96jc02100   AbstractWebsite

Extensive measurements of CO2 fugacity in the North Pacific surface ocean and overlying atmosphere during the years 1985-1989 are synthesized and interpreted to yield a basin-wide estimate of Delta fCO(2). The observations, taken from February through early September, suggest that the subtropical and subarctic North Pacific is a small sink for atmospheric CO2 (0.07 to 0.2 Gton C (half year)(-1) for the region north of 15 degrees N). Objective analysis techniques are used to estimate uncertainty fields resulting from constructing basin-wide contours of oceanic fCO(2) on the basis of individual cruise transects. The uncertainties are significant and imply that future sampling programs need to recognize that estimating oceanic uptake of anthropogenic CO2 from ship-transect observations of oceanic fCO(2) alone will require very extensive sampling.

LeBel, DA, Smethie WM, Rhein M, Kieke D, Fine RA, Bullister JL, Min DH, Roether W, Weiss RF, Andrie C, Smythe-Wright D, Jones EP.  2008.  The formation rate of North Atlantic Deep Water and Eighteen Degree Water calculated from CFC-11 inventories observed during WOCE. Deep-Sea Research Part I-Oceanographic Research Papers. 55:891-910.   10.1016/j.dsr.2008.03.009   AbstractWebsite

The accumulation of man-made chlorofluorocarbons (CFCs) in subsurface water masses is directly related to their formation rate, and the water mass formation rate can be calculated from its CFC inventory. CFC-11 inventories between 65 degrees N and 10 degrees S in the Atlantic Ocean have been calculated for Eighteen Degree Water (EDW) and the components of North Atlantic Deep Water (NADW) from data collected primarily between 1996 and 1998 as part of the World Ocean Circulation Experiment (WOCE). CFC-11 inventories for individual water masses are 5.4 million moles for EDW, 10.5 million moles for Upper Labrador Sea Water (ULSW) (4.6 million moles south of 42 degrees N), 23.4 million moles for Classical Labrador Sea Water (CLSW), 10.4 million moles for Iceland-Scotland Overflow Water (ISOW), and 8.3 million moles for Denmark Strait Overflow Water (DSOW). The estimated error for these inventories is about +/- 10%. The sum of the NADW components (ULSW, CLSW, ISOW, DSOW) is 53.2 million moles which is about half of the total CFC-11 inventory, 103.8 million moles, in the North Atlantic Ocean. Maps of water column inventories illustrate the formation mechanisms and spreading pathways within these water masses. The inventories directly reflect the input of newly formed water in the North Atlantic over the time scale of the CFC transient, about 3 decades. The interior regions of the North Atlantic contain most (75-80%) of the CFC-11 inventory in NADW indicating strong recirculation and mixing of newly formed NADW from the DWBC into the interior with a time scale of 2-3 decades. Average water mass formation rates between 1970 and 1997 are: 3.3Sv for EDW, 3.5Sv for ULSW (2.0Sv from the central Labrador Sea and 1.5 Sv from the southern Labrador Sea), 8.2 Sv for CLSW, 5.7 Sv for ISOW, and 2.2 Sv for DSOW. Estimated errors are +/- 20% for CLSW and +/- 16% for the other water masses. The total for NADW, which forms the deep limb of the North Atlantic Meridional Overturning Circulation, is 19.6 Sv. An extensive test of the effects of temporal variability on the average formation rate calculated from the CFC inventory indicates that the error introduced by the assumption of a constant water mass formation rate is no greater than 15% for CLSW and 10% for the other water masses. (c) 2008 Elsevier Ltd. All rights reserved.

Lefevre, N, Watson AJ, Cooper DJ, Weiss RF, Takahashi T, Sutherland SC.  1999.  Assessing the seasonality of the oceanic sink for CO2 in the northern hemisphere. Global Biogeochemical Cycles. 13:273-286.   10.1029/1999gb900001   AbstractWebsite

Seasonal CO2 fluxes are estimated from quarterly maps of Delta pCO(2) (difference between the oceanic and atmospheric partial pressure of CO2) and associated error maps. Delta pCO(2) maps were interpolated from pCO(2) measurements in the North Atlantic and the North Pacific Oceans using an objective mapping technique. Negative values correspond to an uptake of CO2 by the ocean. The CO2 flux for the North Atlantic Ocean, between 10 degrees N and 80 degrees N, ranges from -0.69 GtC/yr, for the first quarter (January-March), to -0.19 GtC/yr for the third quarter (July-September) using the gas exchange coefficient of Tans et al. [1990], satellite wind speeds, and a correction for the skin effect. On annual average, the North Atlantic ocean (north of 10 degrees N) is a sink of CO2 ranging from -0.23 +/- 0.08 GtC/yr (gas exchange coefficient of Liss and Merlivat [1986] with Esbensen and Kushnir [1981] wind field) to -0.48 +/- 0.17 GtC/yr (gas exchange coefficient of Tans et al. with satellite wind field). The CO2 flux for the North Pacific, between 15 degrees N and 65 degrees N, ranges from -0.66 GtC/yr from April to June to zero from July to September. For the Atlantic, the errors are generally small, that is, less than 0.19 GtC/yr, but for the Pacific considerably larger uncertainties are generated due to the less extensive data coverage. The northern hemisphere ocean (north of 10 degrees N) is a net sink of CO2 to the atmosphere which is stronger in spring (April-June), due to the biological activity, with an estimate of -1.23 +/- 0.40 GtC/yr averaged over this period. The annual mean northern hemisphere ocean flux is -0.86 +/- 0.61 GtC/yr.

Li, S, Park S, Lee JY, Ha KJ, Park MK, Jo CO, Oh H, Mühle J, Kim KR, Montzka SA, O’Doherty S, Krummel PB, Atlas E, Miller BR, Moore F, Weiss RF, Wofsy SC.  2018.  Chemical evidence of inter-hemispheric air mass intrusion into the Northern Hemisphere mid-latitudes. Scientific Reports. 8:4669.   10.1038/s41598-018-22266-0   AbstractWebsite

The East Asian Summer Monsoon driven by temperature and moisture gradients between the Asian continent and the Pacific Ocean, leads to approximately 50% of the annual rainfall in the region across 20–40°N. Due to its increasing scientific and social importance, there have been several previous studies on identification of moisture sources for summer monsoon rainfall over East Asia mainly using Lagrangian or Eulerian atmospheric water vapor models. The major source regions for EASM previously proposed include the North Indian Ocean, South China Sea and North western Pacific. Based on high-precision and high-frequency 6-year measurement records of hydrofluorocarbons (HFCs), here we report a direct evidence of rapid intrusion of warm and moist tropical air mass from the Southern Hemisphere (SH) reaching within a couple of days up to 33°N into East Asia. We further suggest that the combination of direct chemical tracer record and a back-trajectory model with physical meteorological variables helps pave the way to identify moisture sources for monsoon rainfall. A case study for Gosan station (33.25°N, 126.19°E) indicates that the meridional transport of precipitable water from the SH accompanying the southerly/southwesterly flow contributes most significantly to its summer rainfall.

Li, JL, Cunnold DM, Wang HJ, Weiss RF, Miller BR, Harth C, Salameh P, Harris JM.  2005.  Halocarbon emissions estimated from advanced global atmospheric gases experiment measured pollution events at Trinidad Head, California. Journal of Geophysical Research-Atmospheres. 110   10.1029/2004jd005739   AbstractWebsite

The emissions of halogenated gases from the West Coast region of the United States are estimated from measurements from 1995 to 2003 at the Advanced Global Atmospheric Gases Experiment site at Trinidad Head, California. The emissions estimation procedure uses pollution events combined with population densities integrated along back trajectories, and the estimates are constrained by independent estimates of CH4 and N2O emissions from the U. S. West Coast region. The best fit, average emissions of CH4 and N2O and the average chloroform emissions in California, Oregon, and Washington combined from 1996 to 2002 are 44, 3.7, and 0.07 kg person(-1) yr(-1), respectively. The emissions per person of CFC-11 (CCl3F), CFC-2 (CCl2F2), CFC-113 (CCl2FCClF2), and methyl chloroform (CH3CCl3) from California in 1996-1998 are calculated to be factors of approximately 2.2, 1.3, 0.7, and 1.6, respectively, less (more for CFC-113) than those reported for the northeastern United States by Barnes et al. (2003). The emission per person of all these gases in the U. S. West Coast region decreased from 1998 to 1999 by a factor of 2 or more, but from 1999 to 2002 the estimated emissions of all four gases have remained fairly constant and are 0.016, 0.048, 0.002, and 0.006 kg person(-1) yr(-1), respectively. The methyl chloroform estimates suggest a delay of up to 1 year in the decline of the emissions from 1996 to 1998, but otherwise, and in 1999-2000, in contrast to the Millet and Goldstein (2004) results, they are in agreement with the average methyl chloroform emissions per person for the United States based on the UNEP country by country consumption figures (A. McCulloch, private communication, 2004). Averaging the Trinidad Head and the Barnes et al. (2003) per person estimates and multiplying by the U. S. population suggests average methyl chloroform emissions in the United States of 18 Gg yr(-1) in 1996 to 1998. In 2001-2002, if the ratio of the emissions per person in these two regions was the same as in 1996-1998, we estimate U. S. emissions of 2.2 Gg yr(-1), which is one half of the Millet and Goldstein (2004) estimate.

Li, PY, Muhle J, Montzka SA, Oram DE, Miller BR, Weiss RF, Fraser PJ, Tanhua T.  2019.  Atmospheric histories, growth rates and solubilities in seawater and other natural waters of the potential transient tracers HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116. Ocean Science. 15:33-60.   10.5194/os-15-33-2019   AbstractWebsite

We present consistent annual mean atmospheric histories and growth rates for the mainly anthropogenic halogenated compounds HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116, which are all potentially useful oceanic transient tracers (tracers of water transport within the ocean), for the Northern and Southern Hemisphere with the aim of providing input histories of these compounds for the equilibrium between the atmosphere and surface ocean. We use observations of these halogenated compounds made by the Advanced Global Atmospheric Gases Experiment (AGAGE), the Scripps Institution of Oceanography (SIO), the Commonwealth Scientific and Industrial Research Organization (CSIRO), the National Oceanic and Atmospheric Administration (NOAA) and the University of East Anglia (UEA). Prior to the direct observational record, we use archived air measurements, firn air measurements and published model calculations to estimate the atmospheric mole fraction histories. The results show that the atmospheric mole fractions for each species, except HCFC-14 lb and HCFC-142b, have been increasing since they were initially produced. Recently, the atmospheric growth rates have been decreasing for the HCFCs (HCFC-22, HCFC-141b and HCFC-142b), increasing for the HFCs (HFC-134a, HFC-125, HFC-23) and stable with little fluctuation for the PFCs (PFC-14 and PFC-116) investigated here. The atmospheric histories (source functions) and natural background mole fractions show that HCFC-22, HCFC-141b, HCFC-142b, HFC-134a, HFC-125 and HFC-23 have the potential to be oceanic transient tracers for the next few decades only because of the recently imposed bans on production and consumption. When the atmospheric histories of the compounds are not monotonically changing, the equilibrium atmospheric mole fraction (and ultimately the age associated with that mole fraction) calculated from their concentration in the ocean is not unique, reducing their potential as transient tracers. Moreover, HFCs have potential to be oceanic transient tracers for a longer period in the future than HCFCs as the growth rates of HFCs are increasing and those of HCFCs are decreasing in the background atmosphere. PFC-14 and PFC-116, however, have the potential to be tracers for longer periods into the future due to their extremely long lifetimes, steady atmospheric growth rates and no explicit ban on their emissions. In this work, we also derive solubility functions for HCFC-22, HCFC-14 lb, HCFC-142b, HFC-134a, HFC-125, HFC-23, PFC-14 and PFC-116 in water and seawater to facilitate their use as oceanic transient tracers. These functions are based on the Clark-Glew-Weiss (CGW) water solubility function fit and salting-out coefficients estimated by the poly-parameter linear free-energy relationships (pp-LFERs). Here we also provide three methods of seawater solubility estimation for more compounds. Even though our intention is for application in oceanic research, the work described in this paper is potentially useful for tracer studies in a wide range of natural waters, including freshwater and saline lakes, and, for the more stable compounds, groundwaters.

Li, S, Kim J, Kim KR, Muhle J, Kim SK, Park MK, Stohl A, Kang DJ, Arnold T, Harth CM, Salameh PK, Weiss RF.  2011.  Emissions of halogenated compounds in East Asia determined from measurements at Jeju Island, Korea. Environmental Science & Technology. 45:5668-5675.   10.1021/es104124k   AbstractWebsite

High-frequency in situ measurements at Gosan (Jeju Island, Korea) during November 2007 to December 2008 have been combined with interspecies correlation analysis to estimate national emissions of halogenated compounds (HCs) in East Asia, including the chlorofluorocarbons (CFCs), halons, hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF(6)), and other chlorinated and brominated compounds. Our results suggest that overall China is the dominant emitter of HCs in East Asia, however significant emissions are also found in South Korea, Japan and Taiwan for HFC-134a, HFC-143a, C(2)F(6), SF(6), CH(3)CCl(3), and HFC-365mfc. The combined emissions of CFCs, halon-1211, HCFCs, HFCs, PFCs, and SF(6) from all four countries in 2008 are 25.3, 1.6, 135, 42.6, 3.6, and 2.0 kt/a, respectively. They account for approximately 15%, 26%, 29%, 16%, 32%, and 26.5% of global emissions, respectively. Our results show signs that Japan has successfully phased out CFCs and HCFCs in compliance with the Montreal Protocol (MP), Korea has started transitioning from HCFCs to HFCs, while China still significantly consumes HCFCs. Taiwan, while not directly regulated under the MP, is shown to have adapted the use of HFCs. Combined analysis of emission rates and the interspecies correlation matrix presented in this study proves to be a powerful tool for monitoring and diagnosing changes in consumption of HCs in East Asia.

Liang, Q, Chipperfield MP, Fleming EL, Abraham LN, Braesicke P, Burkholder JB, Daniel JS, Dhomse S, Fraser PJ, Hardiman SC, Jackman CH, Kinnison DE, Krummel PB, Montzka SA, Morgenstern O, McCulloch A, Mühle J, Newman PA, Orkin VL, Pitari G, Prinn RG, Rigby M, Rozanov E, Stenke A, Tummon F, Velders GJM, Visioni D, Weiss RF.  2017.  Deriving Global OH Abundance and Atmospheric Lifetimes for Long-Lived Gases: A Search for CH3CCl3 Alternatives. Journal of Geophysical Research: Atmospheres. 122:11,914-11,933.   10.1002/2017JD026926   Abstract

An accurate estimate of global hydroxyl radical (OH) abundance is important for projections of air quality, climate, and stratospheric ozone recovery. As the atmospheric mixing ratios of methyl chloroform (CH3CCl3) (MCF), the commonly used OH reference gas, approaches zero, it is important to find alternative approaches to infer atmospheric OH abundance and variability. The lack of global bottom-up emission inventories is the primary obstacle in choosing a MCF alternative. We illustrate that global emissions of long-lived trace gases can be inferred from their observed mixing ratio differences between the Northern Hemisphere (NH) and Southern Hemisphere (SH), given realistic estimates of their NH-SH exchange time, the emission partitioning between the two hemispheres, and the NH versus SH OH abundance ratio. Using the observed long-term trend and emissions derived from the measured hemispheric gradient, the combination of HFC-32 (CH2F2), HFC-134a (CH2FCF3, HFC-152a (CH3CHF2), and HCFC-22 (CHClF2), instead of a single gas, will be useful as a MCF alternative to infer global and hemispheric OH abundance and trace gas lifetimes. The primary assumption on which this multispecies approach relies is that the OH lifetimes can be estimated by scaling the thermal reaction rates of a reference gas at 272 K on global and hemispheric scales. Thus, the derived hemispheric and global OH estimates are forced to reconcile the observed trends and gradient for all four compounds simultaneously. However, currently, observations of these gases from the surface networks do not provide more accurate OH abundance estimate than that from MCF.

Lucas, DD, Yver Kwok C, Cameron-Smith P, Graven H, Bergmann D, Guilderson TP, Weiss R, Keeling R.  2015.  Designing optimal greenhouse gas observing networks that consider performance and cost. Geosci. Instrum. Method. Data Syst.. 4:121-137.: Copernicus Publications   10.5194/gi-4-121-2015   AbstractWebsite
Lueker, TJ, Walker SJ, Vollmer MK, Keeling RF, Nevison CD, Weiss RF, Garcia HE.  2003.  Coastal upwelling air-sea fluxes revealed in atmospheric observations of O2/N2, CO2 and N2O. Geophysical Research Letters. 30   10.1029/2002gl016615   AbstractWebsite

[1] We capture water column ventilation resulting from coastal upwelling in continuous records of O-2/N-2, CO2, and N2O at Trinidad, California. Our records reveal the gas exchange response time of the ocean to the upwelling and ensuing biological production. Satellite and buoy wind data allow extrapolation of our records to assess coastal upwelling air-sea fluxes of O-2 and N2O. We improve on previous regional estimates of N2O flux in coastal and continental shelf region of the western U. S. We characterize the source of N2O as being predominately from nitrification based on the O-2/N2O emissions ratio observed in our atmospheric records.

Lunt, MF, Park S, Li S, Henne S, Manning AJ, Ganesan AL, Simpson IJ, Blake DR, Liang Q, O'Doherty S, Harth CM, Mühle J, Salameh PK, Weiss RF, Krummel PB, Fraser PJ, Prinn RG, Reimann S, Rigby M.  2018.  Continued emissions of the ozone-depleting substance carbon tetrachloride from Eastern Asia. Geophysical Research Letters. : Wiley-Blackwell   10.1029/2018GL079500   Abstract

Abstract Carbon tetrachloride (CCl4) is an ozone-depleting substance, accounting for about 10% of the chlorine in the troposphere. Under the terms of the Montreal Protocol, its production for dispersive uses was banned from 2010. In this work we show that, despite the controls on production being introduced, CCl4 emissions from the eastern part of China did not decline between 2009 and 2016. This finding is in contrast to a recent bottom-up estimate, which predicted a significant decrease in emissions after the introduction of production controls. We find eastern Asian emissions of CCl4 to be 16 (9?24) Gg/year on average between 2009 and 2016, with the primary source regions being in eastern China. The spatial distribution of emissions that we derive suggests that the source distribution of CCl4 in China changed during the 8-year study period, indicating a new source or sources of emissions from China's Shandong province after 2012.

Lunt, MF, Rigby M, Ganesan AL, Manning AJ, Prinn RG, O'Doherty S, Muhle J, Harth CM, Salameh PK, Arnold T, Weiss RF, Saito T, Yokouchi Y, Krummel PB, Steele LP, Fraser PJ, Li SL, Park S, Reimann S, Vollmer MK, Lunder C, Hermansen O, Schmidbauer N, Maione M, Arduini J, Young D, Simmonds PG.  2015.  Reconciling reported and unreported HFC emissions with atmospheric observations. Proceedings of the National Academy of Sciences of the United States of America. 112:5927-5931.   10.1073/pnas.1420247112   AbstractWebsite

We infer global and regional emissions of five of the most abundant hydrofluorocarbons (HFCs) using atmospheric measurements from the Advanced Global Atmospheric Gases Experiment and the National Institute for Environmental Studies, Japan, networks. We find that the total CO2-equivalent emissions of the five HFCs from countries that are required to provide detailed, annual reports to the United Nations Framework Convention on Climate Change (UNFCCC) increased from 198 (175-221) Tg-CO2-eq.y(-1) in 2007 to 275 (246-304) Tg-CO2-eq.y(-1) in 2012. These global warming potential-weighted aggregated emissions agree well with those reported to the UNFCCC throughout this period and indicate that the gap between reported emissions and global HFC emissions derived from atmospheric trends is almost entirely due to emissions from nonreporting countries. However, our measurement-based estimates of individual HFC species suggest that emissions, from reporting countries, of the most abundant HFC, HFC-134a, were only 79% (63-95%) of the UNFCCC inventory total, while other HFC emissions were significantly greater than the reported values. These results suggest that there are inaccuracies in the reporting methods for individual HFCs, which appear to cancel when aggregated together.

Lupton, JE, Klinkhammer GP, Normark WR, Haymon R, Macdonald KC, Weiss RF, Craig H.  1980.  Helium-3 and manganese at the 21°N East Pacific Rise hydrothermal site. Earth and Planetary Science Letters. 50:115-127.   10.1016/0012-821x(80)90123-5   AbstractWebsite

Water samples collected at the 21°N hydrothermal site on the East Pacific Rise crest, including Deep-Tow and hydrocast samples collected in 1977 and three hot vent water samples collected recently with the submersible “Alvin”, contain significant additions of3He,4He, and Mn. Although the vent water collections were at least 50-fold diluted with ambient seawater, they are up to 53 times enriched in3He and 7.4 times enriched in4He relative to saturated seawater, with concentrations of total dissolvable manganese (TDM) up to 310 μg/kg.3He and4He covary in the vent samples, with3He/4He about 8 times the atmospheric ratio, reflecting a mantle helium source. In contrast to the helium isotopes the Mn/3He ratio in the vent samples is variable, ranging from 4.3 × 104 up to 1.0 × 105 g/cm3. Profiles of3He/4He and TDM in the water column at 21°N show a sharp maximum ofδ(3He) = 47%and TDM= 0.69 μg/kg, much higher than the average values of 34% and 0.2 μg/kg for the deep water in this region. This spike in3He and Mn occurs at 2400 m depth, 200 m above the level of the 21°N vents, and 100 m higher than any local bathymetry, evidence for upward transport of the hydrothermal discharge via rising plumes of hot vent water. Two of the 21°N Deep-Tow samples associated with small (⩽0.010°C) temperature anomalies hadδ(3He) = 38%and TDM= 0.28 and 0.58 μg/kg, also slightly elevated relative to background. The Deep-Tow and hydrocast samples have lower Mn/3He ratios than average vent samples due to Mn removal by scavenging. Comparison of vent samples and water column measurements at 21°N indicate that the pure vent water could be detected using3He and Mn even when diluted ∼105 times with seawater, confirming that these two tracers are extremely sensitive indicators of submarine hydrothermal activity.

Lupton, JE, Weiss RF, Craig H.  1977.  Mantle helium in hydrothermal plumes in the Galapagos Rift. Nature. 267:603-604.   10.1038/267603a0   AbstractWebsite

THE 3He/4He ratio in deep Pacific water is 20–30% higher than in atmospheric helium because of injection of primordial helium from the mantle1,2. The largest 3He enrichments in the Pacific have been found in water on the crest of the East Pacific Rise where the isotopic ratios indicate2 that the excess helium component has a 3He/4He ratio about ten times the atmospheric ratio, in agreement with the ratios measured in trapped helium in the glassy rims of oceanic tholeiites3,4. Recent measurements in this laboratory5 have shown that the hot brines in the axial rift of the Red Sea are very highly enriched in mantle helium. 3He and 4He are respectively 3300 and 380 times supersaturated relative to atmospheric solubility equilibrium in seawater, with a 3He/4He ratio of 1.2×10−5, or 8.6 times the ratio in atmospheric helium. Comparison of the enrichments of various elements in the Red Sea brines and in brines associated with salt domes6 shows that helium is the only component in the Red Sea brines which unequivocally requires derivation from hydrothermal circulation of seawater in basalts. The helium isotopes are thus an extremely powerful and sensitive tracer for the detection and mapping of hydrothermal systems in oceanic spreading centres.

Lupton, JE, Weiss RF, Craig H.  1977.  Mantle helium in the Red Sea brines. Nature. 266:244-246.   10.1038/266244a0   AbstractWebsite

HELIUM isotope studies on terrestrial samples have revealed the existence of two helium components which are clearly distinct from atmospheric helium. The first of these, which we term ‘crustal helium’, was identified in 1946 in natural gas wells1. This crustal component is produced by radioactive decay of U and Th to 4He, with 3He production by (n, α) reactions on Li; the resulting helium is characterised by 3He/4He ≃ 10−7, one-tenth of the atmospheric ratio2. The second component, ‘mantle helium’, was discovered as ‘excess 3He’ in deep ocean water, attributed to a flux of primordial helium from the mantle3. Studies of the 3He/4He ratio in deep water on the East Pacific Rise4 and in helium trapped in submarine basalt glasses5,6 have shown that this mantle component is characterised by 3He/4He ≃ 10−5, about 10 times the atmospheric ratio and 100 times the ratio in crustal helium. Basalt glasses from the Western Pacific Lau Basin, the East Pacific Rise, and the Mid-Atlantic Ridge contain trapped helium with similar 3He/4He ratios, indicating that mantle helium in at least three areas in which new lithosphere is being formed has a unique and uniform isotopic signature.