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Estimating changes in ocean ventilation from early 1990s CFC‐12 and late 2000s SF 6 measurements
Author(s) -
Tanhua Toste,
Waugh Darryn W.,
Bullister John L.
Publication year - 2013
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/grl.50251
Subject(s) - tracer , chlorofluorocarbon , sulfur hexafluoride , environmental science , mixing (physics) , atmospheric sciences , ventilation (architecture) , mixing ratio , offset (computer science) , climatology , meteorology , oceanography , geology , chemistry , physics , organic chemistry , quantum mechanics , computer science , nuclear physics , programming language
Transient tracer measurements can constrain the rates and pathways of ocean ventilation and act as proxies for biogeochemically relevant gases such as CO 2 and oxygen. Various techniques have deduced changes in ocean ventilation over decadal timescales using transient tracer measurements made on repeat sections, but these require a priori assumptions about mixing in the ocean interior. Here, we introduce a simple, direct observational method that takes advantage of the similar atmospheric increase rates of chlorofluorocarbon‐12 and sulfur hexafluoride, but with a time lag (offset) of 14–15 years. Such repeat measurements can be directly compared without prior assumptions about mixing. A difference larger than ~2 years between modern sulfur hexafluoride and historical chlorofluorocarbon‐12 tracer ages implies a change in ventilation, although lack of difference does not necessarily imply no change. Several tracer data sets are presented, which suggest changes in ventilation in the South Pacific and North Atlantic Oceans.