Preparation and calibration of the 1978 National Bureau of Standards tritiated-water standards

Abstract. Ventilation is the primary pathway for atmosphere-ocean boundary perturbations, such as temperature anomalies, to be relayed to the ocean interior. It is also a conduit for gas exchange between the interface of atmosphere and ocean. Thus it is a mechanism whereby, for instance, the ocean interior is oxygenated and enriched in anthropogenic carbon. The ventilation of the Mediterranean Sea is fast in comparison to the world ocean and has large temporal variability. Here we present transient tracer data from a field campaign in April 2011 that sampled a unique suite of transient tracers (SF 6 , 3 H and 3 He) in all major basins of the Mediterranean. We apply the transit time distribution (TTD) model to the data in order to constrain the mean age, the ratio of the advective / diffusive transport and the number of water masses significant for ventilation.We found that the eastern part of the eastern Mediterranean can be reasonably described with a one-dimensional inverse Gaussian TTD (IG-TTD), and thus constrained with two independent tracers. The ventilation of the Ionian Sea and the western Mediterranean can only be constrained by a linear combination of IG-TTDs. We approximate the ventilation with a one-dimensional, two inverse Gaussian TTD (2IG-TTD) for these areas and demonstrate a possibility of constraining a 2IG-TTD from the available transient tracer data. The deep water in the Ionian Sea has a mean age between 120 and 160 years and is therefore substantially older than the mean age of the Levantine Basin deep water (60-80 years). These results are in contrast to those expected by the higher transient tracer concentrations in the Ionian Sea deep water. This is partly due to deep water of Adriatic origin having more diffusive properties in transport and formation (i.e., a high ratio of diffusion over advection), compared to the deep water of Aegean Sea origin that still dominates the deep Levantine Basin deep water after the Eastern Mediterranean Transient (EMT) in the early 1990s. The tracer minimum zone (TMZ) in the intermediate of the Levantine Basin is the oldest water mass with a mean age up to 290 years. We also show that the deep western Mediterranean has contributed approximately 40 % of recently ventilated deep water from the Western Mediterranean Transition (WMT) event of the mid-2000s. The deep water has higher transient tracer concentrations than the mid-depth water, but the mean age is similar with values between 180 and 220 years.

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“…(4). A generally accepted value for the decay constant of tritium is λ = 0.05576/a (Unterweger et al, 1980;Taylor and Roether, 1982).…”

Section: Tracer Age and The Transit Time Distributionmentioning

confidence: 99%

Ventilation of the Mediterranean Sea constrained by multiple transient tracer measurements

Stöven

Tanhua

2014

Ocean Sci.

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“…where the TTD-derived tracer concentrations at a given point in space, r, and a given time, t, are a function of c o (the input function of CFC-12 or 3 H at the sea surface) and, for 3 H , e −λ t (the radioactive decay term of 3 H into 3 He), where λ is the decay rate of tritium into tritogenic He (0.05576 yr −1 ; Unterweger et al, 1980). The data shown in Fig.…”

Section: Appendix a Description Of The Transit Time Distribution (Ttdmentioning

confidence: 99%

Nitrous oxide dynamics in low oxygen regions of the Pacific: insights from the MEMENTO database

et al. 2012

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Abstract. The eastern tropical Pacific (ETP) is believed to be one of the largest marine sources of the greenhouse gas nitrous oxide (N 2 O). Future N 2 O emissions from the ETP are highly uncertain because oxygen minimum zones are expected to expand, affecting both regional production and consumption of N 2 O. Here we assess three primary uncertainties in how N 2 O may respond to changing O 2 levels: (1) the relationship between N 2 O production and O 2 (is it linear or exponential at low O 2 concentrations?), (2) the cutoff point at which net N 2 O production switches to net N 2 O consumption (uncertainties in this parameterisation can lead to differences in model ETP N 2 O concentrations of more than 20 %), and (3) the rate of net N 2 O consumption at low O 2 . Based on the MEMENTO database, which is the largest N 2 O dataset currently available, we find that N 2 O production in the ETP increases linearly rather than exponentially with decreasing O 2 . Additionally, net N 2 O consumption switches to net N 2 O production at ∼ 10 µM O 2 , a value in line with recent studies that suggest consumption occurs on a larger scale than previously thought. N 2 O consumption is on the order of 0.01-1 mmol N 2 O m −3 yr −1 in the Peru-Chile Undercurrent. Based on these findings, it appears that recent studies substantially overestimated N 2 O production in the ETP. In light of expected deoxygenation and the higher than previously expected point at which net N 2 O production switches to consumption, there is enough uncertainty in future N 2 O production that even the sign of future changes is still unclear.

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“…Two types of water samples were collected from each gushing site: a 45-liter sample for 14 C dating and a 1-liter sample for 3 H ( t 1/2 =12 43 . yr; Unterweger et al 1980;Lucas and Unterweger 2000) measurement. Dissolved inorganic carbon (DIC) was precipitated in the field.…”

Section: Sampling and Radiometric Analysis Methodsmentioning

confidence: 99%

Tritium Concentrations and Radiocarbon Ages of Gushing Groundwater from Hsuehshan Tunnel, Northern Taiwan

Liu¹,

Chen²,

Yang³

et al. 2005

Terr. Atmos. Ocean. Sci.

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Preparation and calibration of the 1978 National Bureau of Standards tritiated-water standards

Cited by 119 publications

References 6 publications

Ventilation of the Mediterranean Sea constrained by multiple transient tracer measurements

Ventilation of the Mediterranean Sea constrained by multiple transient tracer measurements

Nitrous oxide dynamics in low oxygen regions of the Pacific: insights from the MEMENTO database

Tritium Concentrations and Radiocarbon Ages of Gushing Groundwater from Hsuehshan Tunnel, Northern Taiwan

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