1. Planktic Foraminiferal Shell Thinning due to Anthropogenic CO 2 Emissions? Hans de Moel, Gerald M. Ganssen, Frank J.C. Peeters, Simon J.A. Jung, Dick Kroon, Geert-Jan A. Brummer, Richard E. Zeebe

2. IPCC 4AR Working Group 2 states in its Summary for Policymakers: ACIDIFICATION

3. Source: Zeebe and Wolf-Gladrow 2001

4. CALCIFICATION Laboratory experiments confirm relationship [CO 3 2- ] and calcification: Source: Riebesell et al. (2000)‏ Corals Coccolithophorids Forams

5. CALCIFICATION Laboratory experiments confirm relationship [CO 3 2- ] and calcification: Source: Langdon and Atkinson (2005)‏ Corals Coccolithophorids Forams

6. CALCIFICATION Laboratory experiments confirm relationship [CO 3 2- ] and calcification: Corals Coccolithophorids Forams Source: Bijma et al. (1999)‏

7. Atmospheric CO 2 over the last 4 Glacial Cycles Source: Petit et al. 1999 Vostok ice-core 90 ppm GEOLOGICAL PAST

8. Source: Barker and Elderfield 2002 Shell weights of planktic foraminifera drop on Glacial-Interglacial transition due to higher CO 2, and thus lower [CO 3 2- ] GEOLOGICAL PAST

9. 90 ppm Source: Etheridge et al. (1996)‏ Anthropogenic increase in CO 2 comparable to G-IG changes Has a decrease in shell weight already taken place in the last century? PRESENT

10. METHOD Studied planktic foraminifera (G. ruber) shells in the top of the sediment offshore Somalia. Have shells in the top lower shell weights? Are light/thin shells younger than heavy/thick shells?

11. RESULTS – shell weight downcore Shell weight was measured for the 250-300 µm and the 300-355 µm fraction, measuring the average weight over 80 tests each. The two averages were averaged using the distribution found in the core-top (0.75 vs. 0.25) to calculate the 250-355 µm fraction weight displayed in the graph. F = dissolution index: intact vs. broken shells ~1000 years b.p.

12. RESULTS – upper cm of sediment Mean Foram Weight* (µg)‏ Shell Wall Thickness (µm)‏ δ 18 O (‰)‏ δ 13 C (‰)‏ F 14 C 14 C Age (yr BP)‏ 13.42 (n = 657)‏ 10.08 (n = 795)‏ 17 (n = 8)‏ 12 (n = 6)‏ -1.98 ±0.39 -1.78 ±0.63 0.83 ±0.33 0.47 ±0.36 0.9834 1.0415 135 ±25 -325 ±25 * 250 – 500 μm fraction

13. Source: Bohm et al. (2002)‏ Caribbean Sponge Stable Carbon Isotopes (δ 13 C)‏ RESULTS – stable carbon isotopes δ 13 C (%)‏ 0.83 ±0.33 0.47 ±0.36

14. RESULTS – age Source: Grumet et al. (2002)‏ Radiocarbon ( 14 C)‏ F 14 C 0.9834 1.0415

15. Shell weights are lower in sediment mixed layer Transparent/light tests have lower δ 13 C and higher F 14 C, in line with our hypothesis that they are younger than the opaque/thick ones. Both observations are in line with the acidification hypothesis But… CONCLUSIONS FROM RESULTS

16. Other mechanisms could theoretically be responsible for the observed differences in shell weight/thickness:  Post-depositional calcification - no sign in δ 18 O of colder bottom water : NO  Habitat & symbiont variations - doesn’t explain lower shell weights within sediment ML : NO  Selective removal, fragmentation/dissolution - shells look well preserved (see also dissolution index F) and doesn’t explain lower weights within ML : NO DISCUSSION

17. Upwelling: thick and thin shells as a seasonal feature (upwelling = thin; non = thick): - is not in line with radiocarbon data and would not explain increased weight below sediment ML However, looking at additional data rises some doubts… DISCUSSION

18. Shell weights from surface water and sediment trap* * 250-355 μm fraction ** Site 906, february ’93 (intra-monsoon)‏ *** flux-corrected average over whole series (9 months)‏ DISCUSSION Avg. Weight* (μg)‏ Plankton tow**11.5 Sediment trap***11.8 Sediment ML11.8 Below ML13.6 Top: thin vs. thick9.7 – 12.9

19. Sediment trap data monsoon versus intermonsoon season DISCUSSION Weight (μg)‏ δ 18 Oδ 13 C Trap – Monsoon11.1-1.70.6 Trap – Intermonsoon12.6-2.11.1 Top – Thin9.7-1.780.47 Top - Thick12.9-1.980.83

20. Seasonal upwelling thus produces: –Significant differences in shell weight –Changes in δ 18 O and δ 13 C similar to thin vs. thick Shells from plankton tows and traps are not particularly light Weights from water sampling and sediment mixed layer are strikingly similar However, plankton-tows are snapshots in time and traps do not record annual variability. DISCUSSION

21. Furthermore, 14 C age would theoretically be higher (old upwelling water) for shells produced during upwelling, while the thin shells have lower 14 C age. Upwelling does not explain the increase in weight below the sediment mixed layer. DISCUSSION

22. Both, acidification and seasonal upwelling do not fully explain our data: –Plankton tow and sediment trap samples are not well explained by an acidification hypothesis, yet –Radiocarbon measurements and high shell weights cannot be explained by seasonal upwelling Additional information is needed in order to deconvolve the different processes and unambiguously interpret the data. CONCLUSION

23. Measure weights on single specimens together with single specimen δ 13 C and δ 18 O to unravel the upwelling signal (this paper)‏ Measure weight distributions based on single specimen weights and thin/thick ratio down-core (this paper)‏ Measure weights from long-term (xx years) sediment trap records (our part within EPOCA)‏ Look at other sites with less pronounced seasonal variations (started up and additional funding: PhD to be proposed this summer to NWO)‏ WAY FORWARD

24. Thank you for your attention