Perspectives of transient tracer applications and limiting cases

Abstract

Abstract. Currently available transient tracers have different application ranges that are defined by their temporal input (chronological transient tracers) or their decay rate (radioactive transient tracers). Transient tracers range from tracers for highly ventilated water masses such as sulfur hexafluoride (SF 6 ) through tritium ( 3 H) and chlorofluorocarbons (CFCs) up to tracers for less ventilated deep ocean basins such as argon-39 ( 39 Ar) and radiocarbon ( 14 C). In this context, highly ventilated water masses are defined as water masses that have been in contact with the atmosphere during the last decade. Transient tracers can be used to empirically constrain the transit time distribution (TTD), which can often be approximated with an inverse Gaussian (IG) distribution. The IG-TTD provides information about ventilation and the advective/diffusive characteristics of a water parcel.Here we provide an overview of commonly used transient tracer couples and the corresponding application range of the IG-TTD by using the new concept of validity areas. CFC-12, CFC-11 and SF 6 data from three different cruises in the South Atlantic Ocean and Southern Ocean as well as 39 Ar data from the 1980s and early 1990s in the eastern Atlantic Ocean and the Weddell Sea are used to demonstrate this method. We found that the IG-TTD can be constrained along the Greenwich Meridian south to 46 • S, which corresponds to the Subantarctic Front (SAF) denoting the application limit. The Antarctic Intermediate Water (AAIW) describes the limiting water layer in the vertical. Conspicuous high or lower ratios between the advective and diffusive components describe the transition between the validity area and the application limit of the IG-TTD model rather than describing the physical properties of the water parcel. The combination of 39 Ar and CFC data places constraints on the IG-TTD in the deep water north of the SAF, but not beyond this limit.

Transient tracer distributions in the Fram Strait in 2012 and inferred anthropogenic carbon content and transport

“…The method of validity areas, introduced in Stöven et al (2015), is used to determine the applicability of the tracer couple. For this purpose, the tracer age is calculated from the transient tracer concentrations (Waugh et al, 2003) which provide the tracer age relationship of the tracer couple.…”

Temporal changes in ventilation and the carbonate system in the Atlantic sector of the Southern Ocean

“…The 2012 data set contains CFC-12 and SF 6 measurements of a meridional section along 10°E between 44-53°S as recently discussed by Stöven et al (2015). The distribution patterns of CFC-12 and SF 6 are similar and generally close to saturation in the mixed layer and with decreasing concentrations with increasing depth.…”

“…The measurements during the ANT-XXVIII/3 cruise include the transient tracers SF 6 and CFC-12 (Stöven et al, 2015), the carbonate system variables Dissolved Inorganic Carbon (DIC) and Total Alkalinity (TA) (Jones et al, 2016) , the inorganic macronutrients silicate, nitrate and phosphate (Hoppe et al, 2016) as well as dissolved oxygen. Oxygen was measured using a standard automated Winkler technique with photometric endpoint detection with a precision of 0.7 mol/kg, or 0.3%.…”

“…. (Stöven et al, 2015) For this study we also use modern and historic transient tracer data for the survey area. This includes: SF 6 and CFC-12 data from the ANT-XXVIII/3 expedition in 2012 (discussed below); historic CFC-12 data from the SWEDARP expedition in 1998 (Tanhua et al, 2004) and the ANT-XV/4 expedition in 1998 (Hoppema et al, 2001).…”

Meteorology and oceanography of the Atlantic sector of the Southern Ocean—a review of German achievements from the last decade

“…Waugh et al (2013) estimated that CDW aged in all Southern Ocean sectors between 30 and 60 % in the period of the early 1990s to the late 2000s (~60 % in the Atlantic sector) and attributed this age increase or ventilation decrease to an intensified westerly wind field over the ACC. A new concept of validity areas for tracer couples may help to identify and validate future changes in ventilation in these regions (Stöven et al 2015).…”