Comments by Mary Jane Perry University of Maine 6 November 2012 EURO-BASIN WP2 The Biological Carbon Pump Disclaimer – my comments are based on a very limited knowledge of the full suite of EURO BASIN extensive activities. Some slides are based on an earlier version of Adrian Martin’s presentation. Apologies in advance for any incorrect statements.

WP2 Aim – important and very challenging Produce new observations of particle formation, aggregation, sinking, and decomposition for a range of marine ecosystems in the North Atlantic, through lab, mesocosm and field studies. Combine results with literature data to generate new particle flux algorithms. BASIN scale – proceeds dynamic range of community structure and of physical/chemical forcing Correct parameterize key to realistic models.

WP2 Key Questions How much is sinking? (is that the reason for discrepancy observed by Steinberg?) What is sinking? What controls the speed of sinking? What controls the rate of attenuation?

AS WAY OF BACKGROUND – I will reference the Autonomous North Atlantic Bloom experiment – Eric D’Asaro, Craig Lee, and myself. Evolution of the Bloom from early April through late June Process cruise in May (3 weeks). Perry et al., OCB News, Fall 2012

We successfully captured the start of the bloom with one float and 4 gliders. Similar to satellite. PATCHY bloom. Mahadevan et al., 2012, Science

2 months of Lagrangian float data in upper 230 m. NCP from changes in NO 3 and O 2 ; export flux from difference between NCP and POC. Alkire et al., 2012, DRS

How much is sinking? What is sinking? What controls the speed of sinking? What controls the rate of attenuation? WP2 Key Questions

Marine snow catcher Allows fractionation of export. 33 deployments 7 profiles of 4 depths between 50 – 600 m ~ 300 particles analysed Mid-term Synthesis Workshop, Lisbon 6-8 th Nov Very nice approach How much sinks out of upper100m, sinks slowly, and is respired? (Alkire et al., 2012, DSR) Would be good to couple with sediment traps; also with optical spikes (more later) for projecting results to broader spatial scale.

How much is sinking? What is sinking? What controls the speed of sinking? What controls the rate of attenuation? WP2 Key Questions

Mid-term Synthesis Workshop, Lisbon 6-8 th Nov Small aggregates containing large, heavy foram tests (light green)collide with slower sinking aggregates (dark green), fragmenting them and preventing large aggregates from growing Aggregates incorporating coccoliths (blue) sink quickly for their size, relative to aggregates formed in the absence of the coccoliths (red). aggs w/foram tests aggs w/coccos aggs w/o foram but from foram exp diatom aggs not exposed to calcite ballast De La Rocha, in prep Very nice result Role of TEP  physiology is important

Question on formation of aggregates, in lab and mesoscom experiments – how much does concentration affect aggregate size, magnitude of flux and aggregate sinking rate? These are high particle concentrations; can results be scaled to field concentrations that are only ~ 10% ? Treatment Integrated chl (mg) Day 8 Day 17 N+P+Si6 ± 317 ± 14 N+P+Si+copepods20 ± 748 ± 16 N+P2 ± ± 5 N+P+copepods4 ± 220 ± 11

Marine snow catcher sinking speed Mid-term Synthesis Workshop, Lisbon 6-8 th Nov Velocity ~ a*ESD b + c*Transparency Transparency:  > 60%   40-60%   20-40%   < 20% Giering, in prep Beautiful data, but bit of a puzzle – speeds are much higher than mesocosm, but few coccoliths. Denser big particles do sink faster.

Iceland Basin 2008 North Atlantic – sudden appearance of ‘spikes’ in all optics; spikes are caused by sinking aggregates. (from Briggs et al. 2011, DSR)

Spikes appeared suddenly, and were observed by all four gliders, as a ‘sinking front’. Hence, could compute sinking rates ~ 75 m/d. (similar to rates from the Snow Catcher). (from Briggs et al. 2011, DSR) Make sure gliders measure optics deeper than 300 m

How much is sinking? What is sinking? What controls the speed of sinking? What controls the rate of attenuation? WP2 Key Questions Very interesting relationship by UNI on C/N ratio of suspended material

Marine snow catcher Slow sinking flux vs previous estimates Mid-term Synthesis Workshop, Lisbon 6-8 th Nov Giering, in prep Other estimates are from Thorium and C: Th ratios; is that a reason for discrepancy? How do these compare to other NA estimates? Or, are measurements from early bloom? Does flux scale w/NCP?

Iceland Basin 2008 North Atlantic bloom – comparison of flux from different approaches (from Briggs et al. 2011, DSR)

Phytoplankton and zooplankton community composition makes a difference in flux Station 3 – Norwegian Sea Small flagellates but few diatoms Lots of microzooplankton Station 1 – Iceland Basin Lots of large diatoms Few microzooplankton Calanus

Alkire et al., 2012, DRS Sieracki, pers. comm. Iceland Basin 2008 North Atlantic bloom community composition evolved, and with it the rate of carbon export. Export additionally scaled with magnitude of NCP.

Patchy ocean – use information about the community structure to project export rates to a larger scales.

How much is sinking? What is sinking? What controls the speed of sinking? What controls the rate of attenuation? *** WP2 Key Questions

Marine snow catcher Decomposition of slow-sinking flux Mid-term Synthesis Workshop, Lisbon 6-8 th Nov Giering, in prep Chlorophyll is a proxy for labile POC. Is this microbial?

Estimated sinking rate ~ 75 m/day.Exponent b =1.03 +/ Similar pattern from Iceland Basin 2008 North Atlantic bloom, based on optical spikes ~~ in situ proxy for sinking aggregates (from Briggs et al. 2011, DSR)

Nature of material that sinks matters for attenuation. Chaetoceros resting spores comprised 10-60% of POC in PELAGRA sediment traps. Spores are more resistant to microbial degradation. (and why spores in the deep sea?) C Rynearson et al. – manuscript; graphics- Poulton & Sieracki

EURO BASIN WP2 is focussing on export control processes that vary in different regions/ communities. This work represents a major step forward in the understanding of mechanisms in the BCP. Knowing space and time scales when a particular mechanism operates is crucial for accurately and adequately representing the BCP in models, and for predictions under various climate change scenarios.