Transient tracer applications in the Southern Ocean

Mario.Hoppema [ at ]


Transient tracers can be used to constrain the Inverse-Gaussian transit time distribution (IG-TTD) and thus provide information about ocean ventilation. Individual transient tracers have different time and application ranges which are defined by their atmospheric history (chronological transient tracers) or their decay rate (radioactive transient tracers). The classification ranges from tracers for highly ventilated water masses, e.g. sulfur hexafluoride (SF6), the decay of Tritium (�3H) and to some extent also dichlorodifluoromethane (CFC-12) to tracers for less ventilated deep ocean basins, e.g. CFC-12, Argon-39 (39Ar) and radiocarbon (14C). The IG-TTD can be empirically constrained by using transient tracer couples with sufficiently different input functions. Each tracer couple has specific characteristics which influence the application limit of the IG-TTD. Here we provide an overview of commonly used transient tracer couples and their validity areas within the IG-TTD by using the concept of tracer age differences (TAD). New measured CFC-12 and SF6 data from a section along 10°E in the Southern Ocean in 2012 are presented. These are combined with a similar data set of 1998 along 6°E in the Southern Ocean as well as with 39Ar data from the early 1980s in the western Atlantic Ocean and theWeddell Sea for investigating the application limit of the IG-TTD and to analyze changes in ventilation in the Southern Ocean.We found that the IG-TTD can be constrained south to 46°S which corresponds to the Subantarctic Front (SAF) denoting the application limit. The constrained IG-TTD north of the SAF shows a slight increase in mean ages between 1998 and 2012 in the upper 1200 m between 42–46°S. The absence of SF6 inhibits ventilation analyses below this depth. The time lag analysis between the 1998 and 2012 data shows an increase in ventilation down to 1000m and a steady ventilation between 2000m-bottom south of the SAF between 51–55°S.

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DOI 10.5194/osd-11-2289-2014

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Stöven, T. , Tanhua, T. and Hoppema, M. (2014): Transient tracer applications in the Southern Ocean , Ocean Science Discussions, 11 (5), pp. 2289-2335 . doi: 10.5194/osd-11-2289-2014

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