Crustal helium in deep Pacific waters

Well, Roland; Lupton, J. E.; Roether, Wolfgang

doi:10.1029/1999jc000279

Cited by 23 publications

(18 citation statements)

References 59 publications

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“…. This estimate is broadly similar to the analysis of Well et al (Well et al, 2001) but significantly smaller than that of Roether et al (Roether et al, 1998). The relatively clear imprint on the noble gas estimated CXS 4 He suggests that more regional scale evaluations of that quantity may be useful for discerning the importance of this phenomenon.…”

supporting

confidence: 73%

The deep distributions of helium isotopes, radiocarbon, and noble gases along the U.S. GEOTRACES East Pacific Zonal Transect (GP16)

et al. 2018

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We report the deep distributions of noble gases, helium isotopes, and radiocarbon measured during the U.S. GEOTRACES GP16 East Pacific Zonal Transect between 152 and 77°W at 12-15°S in the South Pacific. The dominant feature is an intense tongue of hydrothermal effluent that extends more than 4,000 km westward from the East Pacific Rise (EPR) at ~2500m depth. The patterns reveal significant "downstream" variations in water mass structure, advection, and mixing that belie the simple perception of a continuous plume extending westward from the EPR. For example, one feature observed at 120°W, 14°S has tracer signatures that are consistent with a water mass originating from an area as much as 2,000 km south of this section, suggesting a quasi-permanent northward flow on the western flank of the EPR. Helium isotope variations in the plume show a uniquely high In the western end of the section, incoming bottom waters have relatively less hydrothermal hydrothermal helium, more radiocarbon, and more oxygen, as well as negative saturation anomalies for the heavy noble gases (Ar, Kr, and Xe). During the basin-scale upwelling of this water, diapycnal mixing serves to erase these negative anomalies. The relative magnitudes of the increases for the heavy noble gases (Ar, Kr, and Xe) are quantitatively consistent with this process. This leads us to estimate the relatively smaller effects on He and Ne saturations, which range from near zero to 0.2% and 0.3% respectively. With this information, we are able to refine our estimates of the magnitude of He ratio of non-atmospheric helium introduced into deep Pacific waters.pg. 2

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confidence: 73%

The deep distributions of helium isotopes, radiocarbon, and noble gases along the U.S. GEOTRACES East Pacific Zonal Transect (GP16)

et al. 2018

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“…The separation of tritiugenic 3 He followed a procedure described elsewhere (Roether et al, 1998b, which makes use of concurrent He and Ne concentration data. Under the special conditions of the Mediterranean Sea there is, fortunately, much less interference by 3 He released from the ocean floor than elsewhere in the ocean (Roether et al, 1998b;Well et al, 2001). Furthermore, the volcanic 3 He observed by Lupton et al (2011) is released at rather shallow depths, so that much of it is removed with the LIW outflow from the Tyrrhenian Sea.…”

Section: Discussionmentioning

confidence: 91%

Tracers confirm downward mixing of Tyrrhenian Sea upper waters associated with the Eastern Mediterranean Transient

Roether

2011

Ocean Sci.

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Abstract. Observations of tritium and 3 He in the Tyrrhenian Sea, 1987Sea, -2009, confirm the enhanced vertical mixing of intermediate waters into the deep waters that has been noted and associated with the Eastern Mediterranean Transient in previous studies. Our evidence for the mixing rests on increasing tracer concentrations in the Tyrrhenian deep waters, accompanied by decreases in the upper waters, which are supplied from the Eastern Mediterranean. The downward transfer is particularly evident between 1987 and 1997. Later on, information partly rests on increasing tritium-3 He ages; here we correct the observed 3 He for contributions released from the ocean floor. The Tyrrhenian tracer distributions are fully compatible with data upstream of the Sicily Strait and in the Western Mediterranean. The tracer data show that mixing reached to the bottom and confirm a cyclonic nature of the deep water circulation in the Tyrrhenian. They furthermore indicate that horizontal homogenization of the deep waters occurs on a time scale of roughly 5 years. Various features point to a reduced impact of Western Mediterranean Deep Water (WMDW) in the Tyrrhenian during the enhanced-mixing period. This is an important finding because it implies less upward mixing of WMDW, which has been named a major process to enable the WMDW to leave the Mediterranean via the Gibraltar Strait. On the other hand, the TDW outflow for several years represented a major influx of enhanced salinity and density waters into the deep-water range of the Western Mediterranean.

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“…For helium isotopes, we neglected for simplicity a source of 3 He from the decay of naturally occurring tritium (Bayer & Schlosser, ) and a source of 4 He from crustal sediments (Well et al, ). The 3 He source from natural tritium would tend to produce higher δ 3 He values and is likely most important in recently ventilated waters, while the crustal 4 He source would tend to produce lower δ 3 He values and is likely most important in older waters such as the North Pacific (Well et al, ). The effect of neglecting these sources on the inferred mantle‐ 3 He injection rates is likely smaller than the uncertainties due to the subgrid‐scale diffusivities reported here.…”

Section: Remaining Uncertaintiesmentioning

confidence: 99%

Radiocarbon and Helium Isotope Constraints on Deep Ocean Ventilation and Mantle‐³He Sources

DeVries

Holzer

2019

JGR Oceans

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Radiocarbon (Δ14C) and helium isotopes (δ3He) have long been used to constrain the ocean's ventilation rates and to trace regional deep ocean circulation pathways, but they have not been fully exploited together to constrain the deep circulation in global models. Here we assimilate Δ14C and δ3He measurements into a global ocean circulation inverse model (OCIM) to jointly constrain the deep ocean circulation and the rate of mantle‐helium injection at seafloor spreading ridges. We find that the new version of the inverse model (OCIM2) matches the observed Δ14C and δ3He distributions much better than a previous version (OCIM1) that assimilated objectively mapped Δ14C but not δ3He. OCIM2 features faster‐ventilated bottom waters and slower‐ventilated intermediate‐depth waters in the Pacific and Indian Oceans. The mean time since last ventilation (ideal mean age) in Pacific bottom waters is up to 150 years younger, while middepth Pacific waters are up to several hundred years older. The δ3He constraints are shown to be important for estimates of the mean time to next ventilation in the Pacific Ocean. The δ3He constraints also favor jet‐like currents in the deep equatorial Pacific to capture realistic westward propagating helium plumes emanating from the East Pacific Rise. The globally integrated mantle‐helium source is 585–672 mol/year, compared to 400–1,000 mol/year from previous estimates. The major regional difference occurs in the Southern Ocean, where the OCIM2 mantle‐helium source is up to threefold smaller than estimates based on ridge spreading rates.

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Crustal helium in deep Pacific waters

Cited by 23 publications

References 59 publications

The deep distributions of helium isotopes, radiocarbon, and noble gases along the U.S. GEOTRACES East Pacific Zonal Transect (GP16)

The deep distributions of helium isotopes, radiocarbon, and noble gases along the U.S. GEOTRACES East Pacific Zonal Transect (GP16)

Tracers confirm downward mixing of Tyrrhenian Sea upper waters associated with the Eastern Mediterranean Transient

Radiocarbon and Helium Isotope Constraints on Deep Ocean Ventilation and Mantle‐³He Sources

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Crustal helium in deep Pacific waters

Cited by 23 publications

References 59 publications

The deep distributions of helium isotopes, radiocarbon, and noble gases along the U.S. GEOTRACES East Pacific Zonal Transect (GP16)

The deep distributions of helium isotopes, radiocarbon, and noble gases along the U.S. GEOTRACES East Pacific Zonal Transect (GP16)

Tracers confirm downward mixing of Tyrrhenian Sea upper waters associated with the Eastern Mediterranean Transient

Radiocarbon and Helium Isotope Constraints on Deep Ocean Ventilation and Mantle‐3He Sources

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Product

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About

Radiocarbon and Helium Isotope Constraints on Deep Ocean Ventilation and Mantle‐³He Sources