VERtical Transport In the Global Ocean VERTIGO VERTIGO project web site Agenda Sunday- Intro/Nature papers Processes in the surface layer a. who/what’s there b. rates Monday-Processes in the mesopelagic a. sinking/suspended particles- characteristics b. heterotrophic processing c. rates of remineralization Tuesday-Data management What gets to the bottom Models DSRII plans/Finalizing Nature ms Breakout groups * Dinner- Clam bake! Wednesday-How well have we answered key VERTIGO questions Remaining questions & what is coming next w/in VERTIGO & beyond

What controls the efficiency of particle transport between the surface? Observation- Higher shallow fluxes and more efficient transport to depth at K2 holds for all elements Why? Character of source differs - seeing end of diatom bloom vs. picoplankton - sinking rates, ballast, pellets vs. aggregates Mesopelagic processes differ - zooplankton grazing - bacterial processing - ambient oxygen, temp Focus discussion on addressing VERTIGO observations & hypotheses

Revisiting Carbon Flux through the Ocean’s Twilight Zone Buesseler, Lamborg, Boyd, Lam, Trull, Bishop, Casciotti, Dehairs, Elskens, Honda, Karl, Siegel, Silver, Steinberg, Valdes, Van Mooy, Wilson VERTIGO differs from prior study in use of NBST & combination of physical, biological, geochemical studies

1. variations in vertical attenuation of POC flux (high ALOHA b=1.3; K2 low b=0.5) exceed range of b’s found in Martin et al. - impact on deep ocean chemistry/C sequestration - not parameterized in models (e.g. Howard et al.)

2. Variation in transfer efficiency (b’s) holds for all elements and relative pattern consistent between sites - ballast elements do reach greater depth/less attenuation - silica pump at K2 efficient for all elements

Reasons for ALOHA vs. K2 difference in flux attenuation - structure of food web K2- PProd decreases & fraction PProd in large phyto decreases (30 to 20%) e-ratio (20 to 11%) b- remains the same ALOHAK2 e & b are decoupled - large pellets/efficient transport K2 vs. ALOHA Zoo size- 42% >2mm K2 upper 150m vs. 18% >2mm ALOHA Pellet size ug C/pellet K2 150m vs at ALOHA

What we still don’t fully understand (talking points for meeting) Why at K2 we observe less POC flux attenuation? colder- lower Q10 theory incubation data- less rapid bacterial degradation higher biomineral content (density) and thus faster sinking bigger pellets and thus faster sinking production includes more large diatoms Why K2 is expected to have more rapid POC flux attenuation? colder- slower stokes sinking rates higher bacterial C demand below 150m 10x higher zoo biomass and higher ZCD more rapid pellet attenuation with depth (?) higher remineralization signal – Ba data ? Sinking rates vs. remineralization rates

ALOHA

ALOHA characteristics - warm waters >25C surface - ML 40-50m - low ML Chl (<0.5 ug/l) - low macronutrients nutrients - deep Chl max (120m) - variable/high PAR - picoplankton & N2 fixers - Fv/Fm low N & P limitation - anticylonic currents during VERTIGO - baroclinic currents vary with depth - No big spatial/temporal trends

Satellite chlorophyll April-Sept 2005 (one month avg) AprilMayJune JulyAugSept

K2 CTD 24

Increasing N:Si with removal of bSi by diatom growth and export ? Seasonal drawdown of nutrients - diatom bloom K2 mooring Honda et al. results K2 VERTIGO cruise results

All data- surface only (steep nutriclines below 10-20m & 60-80m) K2 nutrient data more complicated- spatial variability

CTD 4-39 CTD <10 m K2 Surface N:Si (M) Fronts/eddies w/different nutrients/biota?

Nutrients are removed by biological uptake and export - those waters where nutrients are lowest, have lower phyto biomass (post “bloom”) - this holds for fucoxanthanin & 234Th (i.e. we are looking at the net result of export post “bloom”) - spatial variability in stage of bloom

K2 characteristics - cold waters 2C surface - ML 20-30m - low ML Chl (0.5 ug/l) - high macronutrients nutrients (10-15 mM DIN; 1-2 mM DIP; 5-25mM Si) - Chl max (60m) - constant/low PAR - Large diatoms shallow & deeper Chl max - Radiolarians deep- > m - Fv/Fm low Fe limitation - currents to east during VERTIGO - barotropic similar flow surface to depth - temporal shift toward lower nutrients [Si], lower fluxes - spatial gradients significant?

What a trap samples… Origins Collections Siegel et al trap

From last slide Particle collection funnel (closed circles) = region where particles originate that reach trap during a given deployment time Particle source funnel (open circles) = region where particles have originated from euphotic zone - overlap if sinking rate fast and/or time is long enough to reach depth Siegel et al. 2006

Blue = 500m; Green = 300m; Red = 150m Solid line = path of NBST Dotted line = path of tethered “Clap” trap Shallow traps sample different parts of a 30-60km source region Particle source summary

Blue = 500m; Green = 300m; Red = 150m Solid line = path of NBST Dotted line = path of tethered “Clap” trap Shallow traps sample different parts of a 30-60km source region Does this matter? Not at ALOHA- uniform biogoechemistry (surface Chl shown here) Particle source summary

Blue = 500m; Green = 300m; Red = 150m Solid line = path of NBST Dotted line = path of tethered “Clap” trap Particle source summary

K2 D1 Blue = 500m; Green = 300m; Red = 150m Solid line = path of NBST Dotted line = path of tethered “Clap” trap

K2 D2 Blue = 500m; Green = 300m; Red = 150m Solid line = path of NBST Dotted line = path of tethered “Clap” trap

K2 D1K2 D2

Calculate 234 Th flux from the measured 234 Th activities d 234 Th/dt = ( 238 U Th) * l - P Th + V where l = decay rate; P Th = 234 Th export flux; V = sum of advection & diffusion low 234 Th = high flux Th>U indicates remineralization need to consider non-steady state and physical transport Thorium-234 approach for export production half-life = 24.1 days source = 238 U parent is conservative sinks = attachment to sinking particles and decay depth (m) [ 234 Th] 238 U       Th

ALOHA higher 234Th, lower particle flux K2 lower 234Th, higher particle flux

ALOHA- Small Th:U deficits down to m

Large Th:U deficits down to 60m Excess 234Th immediately below Chl & at deep nutricline

ALOHA all 234Th data No evidence of clear temporal or spatial trends

K2- all data (upper 50m) Weak relationship between waters with lower nutrients and lower 234Th (correlation between removal of macronutrients & sinking particle flux)

K2 234Th- Weak evidence of regional increase in 234Th in upper 60m (implies decreasing particle flux vs. time & need for non- steady state models

CTD 4-39CTD m 150m K2 234Th (dpm/l)

Carbon flux = 234 Th flux  [C/ 234 Th] sinking particles Empirical approach Must use site and depth appropriate ratio POC/ 234 Th

C/Th in trap decreases with depth and relatively constant

C/Th decreases with depth- all samples Trap particles most similar to 10-53um filtered material >53um can be higher (esp. at depth)

C/Th in trap decreases with depth and relatively constant

C/Th decreases with depth- all sample types Trap particles most similar to 5-53um filtered material >350 um can be higher (esp. at depth)- zooplankton?

Predicted fluxes from watercolumn profiles and measured trap fluxes similar for 234Th (and are low). Trap averages out spatial variability? POC fluxes match and are low Avg. 1-2 mM/m2/d ALOHA

K2 Predicted and measured 234Th fluxes agree deploy 1, not D2, unless we consider decreasing Th with time (large uncertainty in dTh/dt) POC fluxes match D1 but not D2 Avg. D1 = 5 mM/m2/d D2 = 2 in trap 5 w/1D SS model 2.5 w/NSS

CTD 4-39CTD m 150m K2 Scale 2x smaller POC flux (mM/m2/d)

K2 234Th export production story- Evidence of spatial and temporal variability in 234Th correlated to nutrient drawdown C/Th story is less complicated- decreasing w/z & constant POC = 10 +/- 2 mM/m2/d =10.1/9.1 D1/D2 central stations only (can decrease D2 if we believe Th increasing w/time) New production D1= /- 3.5 ; D2= 5.8 +/- 1.9 POC = 6 +/- 2 mM/m2/d =5.1/5.6 D1/D2 central stations only (can decrease D2 if we believe Th increasing w/time) - Watch out for differences in integration time 234Th vs. stocks, biota, etc.

Excess 234Th immediately below Chl & at deep nutricline

Excess 234Th due to shallow remineralization between m is common at same density surface ( )

Excess 234Th due to shallow remineralization & nutrient gradients increase and N:Si change (preferential remineralization of N over Si)

CTD 4-39CTD m – 150m K2 Delta- POC flux (mM/m2/d) Estimate shallow remineralization from difference in 234Th predicted POC flux vs. depth Average del-POC flux 60m to 150m D1 = 5.0 mM/m2/d D2 = 3.5 mM/m2/d

Deep moored traps collects over larger source area (95% from 220km range at 100m/d) 3 yr estimate of particle source “streaks”

Deep moored traps collects over larger source area (95% from 220km range at 100m/d) Does this matter? At ALOHA, 2004 source region in west with up to 50% higher Chl Connections between shallow and deep flux need to consider the different source regions 3 yr estimate of particle source “streaks” Siegel et al. 2006

ALOHA POC fluxes VERTIGO cruise dates 500m = 3.6 mg/m2/d 2800 = =2.4 August 4000m > 2800m Is this indication of efficient transport >500m or lateral source?