Estimating particle export using the Thorium-234 approach C/Th ratios Ken O. Buesseler Woods Hole Oceanographic Institution Idea is to set the stage & get certain images in your mind as we move in to workshop mode Think about what C/Th examples we have- new/unpublished/syntheses that might be useful for the group 2004 Thorium-234 workshop

C/Th ratio vs. size, depth, Outline  Introduction What is the “234Th approach?” Concept of C/Th ratio How did we get here?  C/Th variability- selected examples C/Th ratio vs. size, depth, region, collection device  How do we know it works? Comparisons with other methods

Carbon flux = 234Th flux  [C/234Th]sinking particles Thtot/U 234Th flux 1000 sinking particles C/Th 1:4 Empirical Approach Don’t need to know anything about process (but of course this is short sighted! C/Th tells you something about system) C flux 1000  1/4

Carbon flux = 234Th flux  [C/234Th]sinking particles Thtot/U 234Th flux 1000 1000 sinking particles C/Th 1:4 2:4 Thorium accociated with “recently produced, surface active, pollysaccharide-rich macromolecules” Quigley et al. 2002- OK, but does not limit empirical use of this tracer Trap = 3 days; filter = one point depth/time C flux 1000  1/4 1000  2/4

Carbon flux = 234Th flux  [C/234Th]sinking particles Thtot/U 234Th flux 1000 1000 500 sinking particles C/Th 1:4 2:4 1:2 Thorium accociated with “recently produced, surface active, polysaccharide-rich macromolecules” Quigley et al. 2002- OK, but does not limit empirical use of this tracer Trap = 3 days; filter = one point depth/time C flux 1000  1/4 1000  2/4 500  1/2 Assumptions - measure C/Th representative of sinking particles - sinking particles are only/major Th loss - sinking particles average over same time/space as flux

Carbon flux = 234Th flux  [C/234Th]sinking particles POC/234Th Empirical approach Must use site and depth appropriate ratio Decrease w/depth- due to C loss; increase in relative ratio acid polysaccharides which bind w/Th on surfaces Not appropriate to estimate 100m flux, from characteristics of surface derived particles i.e. variability in C/Th tells you nothing about accuracy/uncertainty in flux proxy Similar to Redfield Ratio; C/Chl Th flux on particles

How did we get here? Bhat et al., ‘69 & many others……….. What about using C/Th ratio and 234Th flux to determine sinking C export?  1st? JGOFS North Atlantic Bloom Experiment Kiel March 1990 PI meeting Claudia already reviewed history Kiel- personal story Kirk & myself (not in original proposal) asked for C flux but then at SCOR meeting met Tsunogai- 1976 abstract! C/Th = 5 uM/dpm & C flux @ 100m = 9 mMC/m2/d

How did we get here? Bhat et al., ‘69 & many others……….. What about using C/Th ratio and 234Th flux to determine sinking C export?  1st? JGOFS NABE Kiel March 1990 PI meeting DSRI 1992 Buesseler et al.  No, much earlier! 1976 Tsunogai & Minagawa (note C/Th ratio = 5 mM/dpm C flux @ 100m = 9 mmC/m2/d) Claudia already reviewed history Kiel- personal story Kirk & myself (not in original proposal) asked for C flux but then at SCOR meeting met Tsunogai- 1976 abstract! C/Th = 5 uM/dpm & C flux @ 100m = 9 mMC/m2/d

Early concepts on controls on C/Th ratio more to the story-C/Th tells you something about particle cycling & process that determine Th scavenging Acid Polysaccharides appear important- Santschi talk to follow Barg, Lee, Lal et al. ‘93 Santschi, Quigley, Honeyman, Baskaran et al Burd, Jackson, Moran et al. Usbeck et al. Michaels & Buesseler, ONR SIGMA proposal 1990

Early concepts on controls on C/Th ratio C/Th story more complicated - surface chemistry - ligands/APS & colloids - adsorption/aggregation Barg, Lee, Lal et al. Santschi, Quigley, Honeyman, Baskaran et al. Burd, Jackson, Moran et al. Usbeck et al. more to the story-C/Th tells you something about particle cycling & process that determine Th scavenging Acid Polysaccharides appear important- Santschi talk to follow Barg, Lee, Lal et al. ‘93 Santschi, Quigley, Honeyman, Baskaran et al Burd, Jackson, Moran et al. Usbeck et al. Michaels & Buesseler, ONR SIGMA proposal 1990

How does ratio vary w/size? - no simple relationship What if bottle POC to high? Often GFF from bottle used for 1um POC and pumps for larger size classes Diatoms in So. Ocean- primary producers, actively growing and exported intact w/o grazing Smaller cells/grazing, lower C/Th in other sites Guo et al., 2002 Savoye, Trull, Buesseler unpub. - watch out for comparisons of bottle POC (high) for 0.7um GFF and pumps for Th - also swimmer C/Th high- not passive sinking material - colloidal C/Th can be troublesome (sorptive losses)

How does ratio vary w/depth? - decreases with depth 0 m Depth (m) SOFeX- at depth, C/Th 1 vs. 53 um particle difference <factor of two Pump 1um 234Th & Bishop 1 um POC for Charette et al 200 m PAPA Coast POC/234Th (mM/dpm) Charette et al. 1999 POC/234Th (mM/dpm) SOFeX, Buesseler et al. 2004

How does ratio vary w/region? - C/Th higher in high latitudes & coastal settings Example from Ken’s SMP data on www Range of data sets, from n=2 to many years data at one site Trap = pump < bottle Murray, Dunne, Charette, Buesseler, Benitez-Nelson, Coppola, Fowler, Schmidt, Amiel, Cochran, Sarin, Shimmield, Moran, & more

How does ratio vary w/collection device? - is one method “best”? - what does range tell us? - more work is needed 400 mM/dpm Gustafsson et al. unpub. data Gullmar Fjord new methods- SPLITT; NBST; tube to tube variability; bottles vs. pumps Good news is not huge differences at any one site Variability between sampling periods, i.e. particle source term varies, so expect biases to vary BATS unpub. Data - Watch out for difference in methods e.g. trap C vs. filter C - Don’t expect single offset Cochran et al. 2004 MedFlux

Variations in C/Th are measured - What does this mean for accuracy of empirical method? look for oceanographic consistency direct comparisons to other methods (budgets & traps) - few data sets with appropriate space/time scales - hard to measure particle export by difference - comparison to other particle flux collectors- traps

- consistency of oceanographic trends ThE < 5% EQPAC- example of low export efficiency small cells, grazing controls & communities in “steady state”

- how does 234Th approach compare to other methods? Example of what we can/should do as group? Caveats w/each method & with space/time integral- 234Th no worse/better than others - watch out for averaging differences space/time/depth & lack of budget constraints

- how does 234Th approach compare to other methods? APF Buesseler et al., 2003 - example w/complete annual cycle

- example w/complete annual cycle APF APF Buesseler et al., 2003 - example w/complete annual cycle Nelson et al., 2003

Carbon fluxes determined from 234Th approach 1. show oceanographic consistency 2. generally agree with other methods 3. advantages over other methods SOFeX- at depth, C/Th 1 vs. 53 um particle difference <factor of two

Carbon fluxes determined from 234Th approach 1. show oceanographic consistency 2. generally agree with other methods 3. advantages over other methods Errors arise from both Th flux prediction & C/Th - need to quantify Th flux uncertainty (next talk!) - local C/Th variability at a specific site/depth < factor 2 (differences between particle size, filter vs. traps, etc.) - assumptions need to be clearly stated in each case e.g. steady state, character of sinking particles, spatial vs. temporal change, role of physical loss/supply

? Other examples of X/Y ratio variability in ocean sciences? Depth (m) 20 40 60 80 100 5 10 15 Depth (m) ? Found this data set- NOAA PMEL/AOML…. POC/234Th

Wanninkhof, 2003 Considerable research & debate on wind speed vs. gas transfer velocity relationship- but exact processes responsible for variability remains poorly understood

However we still use: F = k ∆ pCO2 to calculate global CO2 flux from site/time specific transfer velocity, k, and >1,400,000 measurements of surface ocean CO2 Wanninkhof, 2003 Like C/Th- many processes control ratio- gas transfer changes w/winds, bubble injection, surface films, physics, chemistry Make progress- community consensus important! Reason for this meeting Considerable research & debate on wind speed vs. gas transfer velocity relationship- but exact processes responsible for variability remains poorly understood Takahashi et al., 2002

C/Th ratios- status report We have made HUGE advances in our application of 234Th to determine upper ocean carbon flux since 1990 (oops, 1976!) Can’t imagine more progress in many other fields in last 15 years! 4L method- 18 profiles in SOFeX- 28 days Acid Polysacharide ligands 14C PProd- standardized method- argue over what it means, but helps to have one method

C/Th ratios- status report We have made HUGE advances in our application of 234Th to determine upper ocean carbon flux since 1990 (oops, 1976!) C/Th ratio is variable- w/size, depth, region- - fine for application as empirical tool - progress needed in sampling sinking particles Can’t imagine more progress in many other fields in last 15 years! 4L method- 18 profiles in SOFeX- 28 days Acid Polysacharide ligands 14C PProd- standardized method- argue over what it means, but helps to have one method

C/Th ratios- status report We have made HUGE advances in our application of 234Th to determine upper ocean carbon flux since 1990 (oops, 1976!) C/Th ratio is variable- w/size, depth, region- - fine for application as empirical tool - progress needed in sampling sinking particles Evaluate accuracy by comparison to other methods - proper space/time integration important- Can’t imagine more progress in many other fields in last 15 years! 4L method- 18 profiles in SOFeX- 28 days Acid Polysacharide ligands 14C PProd- standardized method- argue over what it means, but helps to have one method

C/Th ratios- status report We have made HUGE advances in our application of 234Th to determine upper ocean carbon flux since 1990 (oops, 1976!) C/Th ratio is variable- w/size, depth, region- - fine for application as empirical tool - progress needed in sampling sinking particles Evaluate accuracy by comparison to other methods - proper space/time integration important- Expand applications to other elements - PON, bSi, HOC’s, TM Can’t imagine more progress in many other fields in last 15 years! 4L method- 18 profiles in SOFeX- 28 days Acid Polysacharide ligands 14C PProd- standardized method- argue over what it means, but helps to have one method

C/Th ratios- status report We have made HUGE advances in our application of 234Th to determine upper ocean carbon flux since 1990 (oops, 1976!) C/Th ratio is variable- w/size, depth, region- - fine for application as empirical tool - progress needed in sampling sinking particles Evaluate accuracy by comparison to other methods - proper space/time integration important- Expand applications to other elements - PON, bSi, HOC’s, TM Better understanding of 234Th speciation needed - aggregation & scavenging; ligands & complexation Can’t imagine more progress in many other fields in last 15 years! 4L method- 18 profiles in SOFeX- 28 days Acid Polysacharide ligands 14C PProd- standardized method- argue over what it means, but helps to have one method

C/Th ratios- status report We have made HUGE advances in our application of 234Th to determine upper ocean carbon flux since 1990 (oops, 1976!) C/Th ratio is variable- w/size, depth, region- - fine for application as empirical tool - progress needed in sampling sinking particles Evaluate accuracy by comparison to other methods - proper space/time integration important- Expand applications to other elements - PON, bSi, HOC’s, TM Better understanding of 234Th speciation needed - aggregation & scavenging; ligands & complexation Learn from CO2 community - similar accuracy issues & unknowns - community workshops, organized field efforts, standardized protocols; synthesis of larger data sets Can’t imagine more progress in many other fields in last 15 years! 4L method- 18 profiles in SOFeX- 28 days Acid Polysacharide ligands 14C PProd- standardized method- argue over what it means, but helps to have one method

Thorium-234 approach & C/Th ratios - many to thank & credit for ideas, inspiration, challenges… Decided to take EndNote ref list and scramble first authors names to create this movie credit NASA, NOAA, DOE, ONR

Carbon flux = 234Th flux  [C/234Th]sinking particles Thtot/U 234Th flux 1000 1000 500 sinking particles C/Th 1/4 2/4 1/2 C flux 1000 x 1/4 2000 x 2/4 500 x 1/2 assumptions- measure C/Th representative of sinking particles - sinking particles are only/major Th loss - sinking particles average over same time/space as flux

EQPAC- 140W- boreal spring cruises - how does 234Th approach compare to other methods? EQPAC- 140W- boreal spring cruises Method Export C (mM C/m2/d) Reference Comments 234Th 1-4 (range 10N - 10S) Buesseler et al. ‘95 0-100m; C/Th pumps, varies with lat/long & season 3 (equator) Bacon et al. ‘96 0-100m; C/Th pumps 6 (equator) Murray et al. ‘96 0-100m; C/Th traps tCO2 & DOC <5 (1N - 1S budget) Feely/Peltzer et al. 0-100m; by difference New prod 15N <6-12 McCarthy et al. Flux at 100m Traps 4 - 36 (equator) Murray, Dunne et al. Flux at 100m; PITS uncorrected (overcollect- 234Th) XX Hernes et al. Flux at 120m; IRS trap

- how does 234Th approach compare to other methods? Ross Sea- JGOFS Method Export C (mM C/m2/d) Reference Comments 234Th 15 - 54 (two stations) Buesseler et al. ‘00 0-100m; summer to fall Orca & Minke; C/Th pumps Del-POC 150 Smith et al ‘00 0-50m; avg. for summer 40 Gardner et al. ‘00 0-100m; summer to fall Net Comm Prod 41 Sweeney et al ‘01 0-200m; summer to fall Traps 1.5 Collier et al. ‘00 Flux at 200m; (undercollect-Th/Pa)

North Atlantic Bloom Experiment - how does 234Th approach compare to other methods? North Atlantic Bloom Experiment Method Export C (mM C/m2/d) Reference Comments 234Th 30 - 60 Buesseler et al. ‘92 0-150m; varies with time and depth tCO2 70 Goyet et al. 0-125m; avg. for bloom Del-NO3 & O2 30-40 Bender et al. ‘92 Flux at 50m; early bloom only Traps 7-13 Martin et al. ‘92 Flux at 150m; invariant over bloom

How does ratio vary w/region? - C/Th higher in high lats & coastal (100m >50 or 70 mm) (90 to 200m traps) (50-100m >.5-1 mm) Different time integration Different number- single pt vs. whole year Murray, Dunne, Charette, Buesseler, Benitez-Nelson, Coppola, Fowler, Schmidt, Amiel, Cochran, Sarin, Shimmield, Moran, …….

How does ratio vary w/collection device? - is one method “best”? - if not, what does range tell us? - more work is needed new methods- SPLITT; NBST; tube to tube variability; bottles vs. pumps BATS unpub. data - watch out for difference in methods e.g. trap C vs. filter C