Sverdrup Lecture 2008 Chlorofluorocarbons: The Oceans’ Inadvertent Canary Rana A. Fine Rosenstiel School of the University of Miami

Harold Sverdrup , on the submarine Nautilus in 1931 (Munk, Polar Res., 2001) Volume transport: 1 Sverdrup (Sv) = 10 6 m 3 /s Sverdrup Dynamics- Relationship between the large scale ocean circulation and the wind stress curl

Chlorofluorocarbons, CFCs Gases Synthetic halogenated methanes Chemical structure: CFC-11 CCl 3 F, CFC-12 CCl 2 F 2, Sources: anthropogenic Environmental: GHG, threat to ozone layer

Analytical Background for Oceanic CFCs: Shipboard measurement using gas chromatograph Solubility measurements in laboratory Chemical stability Atmospheric time history – ALE/GAGE/AGAGE network

Walker et al., JGR, 2000; Geller et al., 1997; Maiss and Brenninkmeijer, 1998 ALE/GAGE/AGAGE network R. Weiss Lab SF 5 CF 3 for purposeful release instead of SF 6, Smethie et al., 2006; Ho et al Atmospheric time histories of CFCs, SF 6

Age- an elapsed time since a subsurface water mass was last in contact with the atm Partial pressure age, pCFC = C(CFC) / F(CFC), pSF 6, matched to atmospheric time history. "Average" age, application to upper ocean processes. Assuming equilibrium with present atm. Ratio age, pCFC-11/pCFC-12 and pSF 6 /pCFC-11,12. Age of the tracer bearing component.

Caveats for using CFC ages CFC ages are subject to biases due to mixing Recent work offers promise for separating effects of mixing on CFC ages (and improving estimates of anthropogenic CO 2 inventories) via use of – CFCs and SF 6 –transit time distributions (TTD): there is a continuous range of time scale for the movement from a source to a remote region (e.g., Hall, Haine, Waugh, Khatiwala, Peacock, Maltrud, Steinfeldt, et al.)

Highest CFC inv (and CO 2 ) downstream of NADW formation, 60% in SH, 82% upper 1000 m- area- (includes deep water source regions) Willey, Fine, et al., GRL, 2004 NADW SAMW/AAIW, ACC 1994

Applications for CFCs: Biogeochemistry anthropogenic CO2 inventories oxygen utilization rates denitrification and nitrogen fixation rates dissolved organic carbon decay rates Calibration for ARGO sensors

Applications for CFCs continued: Added dimension of time Circulation Pathways Independent test for models Thermocline ventilation- understand and monitor ocean gas uptake and the global CO 2 cycle water mass in contact with atmosphere and gas exchange is occurring MOC circulation and formation rates- flux of water into water mass leading to an increase in water mass volume

Where do internal natural ocean variability affect the representativeness of a CFC measurement? Strong CFC gradients Rossby waves (e.g., Rogers et al.) High EKE

P16 150W North Pacific: no overall net change in ventilation time scales Sonnerup et al., JGR, 2008 measured along 150W in 2006: σ θ < < σ θ < 26.6 σ θ >26.6 → increases in pCFC-12 ages contoured as function of Δ pCFC-12-pSF6 ages in 1D transport model → 6-10 year mixing induced increase in pCFC ages; uncertainties in pSF6 ages ± years Most of measured-modeled pCFC-12 age change can be explained by 1D transport model

MOC Climatic Importance : Transport and storage of climatically important properties: effects on global heat, freshwater, CO 2 budgets Natural variability-NAO: change in formation of Labrador Sea Water- heat loss to atm => warms Europe Past climate variations have been linked to changes in MOC Deep waters sink, they are transported equatorward by Deep Western Boundary Current, and are replenished by shallow poleward transport

MOC from CFCs: Identification of 2 well ventilated components Upper North Atlantic Deep Water UNADW Lower North Atlantic Deep Water LNADW Pathways Deep Western Boundary Current DWBC continuity deep circulation gyres interior pathways along the equator Timescales Quantification/Sverdrups from Inventories Variability in rates

Maximum CFC-11 in DWBC, CLSW spreads from its source to subtropics in ~10 years. Molinari, Fine et al., GRL, 1998 NADW: ULSW CLSW MNADW/ ISOW LNADW/ DSOW

Smethie et al., AGU Monogr DWBC DWBC continuous into tropics 24.5N

Using CFC Inventories to Estimate MOC Formation Rates (R) Transport of newly formed water that sinks across the upper boundary of a water mass I CFC = ∫ R  C S (t)dt C S = E F  F  C A assuming R constant over period of CFC input R = I CFC / ∫ C S (t)dt R is an integral from beginning of major CFC input ~1970 Deeper convection, longer it lasts => higher inventory. Errors ~ 20% : lateral intergration, E F can vary with time, R constant over time Smethie & Fine, 2001; Rhein et al., 2002, Keike et al., 2006; Lebel et al., 2008

MOC Rates from CFC Inventories AMOC = ± 4.0 Sv (10 6 m 3 /s) average for ULSW* = 3.5 ± 0.6 Sv CLSW* = 8.2 ± 1.6 Sv ISOW = 5.7 ± 0.9 Sv DSOW = 2.2 ± 0.4 Sv (LeBel et al., DSR, 2008) SO = 14 Sv + (7.4 ± 2.4 Sv LCDW) = 21 Sv average for (Orsi et al., 1999, 2002) + Moorings at 26.5N in 2004: 18.7 ± 5.6 Sv, range 4-35 Sv! Cunningham et al., 2007 CFCs in NADW not yet affected by mixing with other water masses, inventory method useful for next several decades. NADW: 53.2 x 10 6 moles ± 10%, ~50% total NA