CPD Climate of the Past Discussions CPD 1814-9359 Copernicus GmbH Göttingen, Germany 10.5194/cpd-7-1363-2011 Systematic study of the fresh water fluxes impact on the carbon cycle Bouttes N. 1 2 Roche D. M. 1 3 Paillard D. 1 Laboratoire des Sciences du Climat et de l'Environnement, IPSL-CEA-CNRS-UVSQ, UMR 8212, Centre d'Etudes de Saclay, Orme des Merisiers bat. 701, 91191 Gif Sur Yvette, France NCAS-Climate, Meteorology Department, University of Reading, Reading RG66BB, UK Faculty of Earth and Life Sciences, Section Climate Change and Landscape dynamics, Vrije Universiteit Amsterdam, De Boelelaan, 1085, 1081 HV Amsterdam, The Netherlands 26 04 2011 7 2 1363 1392 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.clim-past-discuss.net/7/1363/2011/cpd-7-1363-2011.html The full text article is available as a PDF file from http://www.clim-past-discuss.net/7/1363/2011/cpd-7-1363-2011.pdf

During glacial periods, atmospheric CO<sub>2</sub> concentration rapidly increases and decreases by around 15 ppm at the same time as climate experiments an abrupt cooling in the North Hemisphere and warming in the South Hemisphere. Such a climate change can be triggered in models by adding fresh water fluxes (FWFs) in the North Atlantic. Yet the impact on the carbon cycle is less straightforward, and previous studies give opposite results. Because both models and added fresh water fluxes were different in these studies, it prevents any direct comparison and hinders finding an explanation for these discrepancies. In this study we use the CLIMBER-2 coupled climate carbon model to explore the impact of different additional fresh water fluxes in various conditions, including the experiments previously performed with other models. We show that the CO<sub>2</sub> changes caused by the fresh water flux events should be interpreted as a combination of oceanic and terrestrial processes. The initial state of the Atlantic Meridional Overturning Circulation (AMOC) prior to the addition of fresh water fluxes appears to play a crucial role. The rapid increase of CO<sub>2</sub> observed in ice core data can only be accounted for when the export of North Atlantic Deep Water (NADW) is relatively slow. Additionally, the terrestrial and oceanic carbon reservoirs responses are a consequence of the climate change and most importantly of the "seesaw" effect. As the latter is different in the various models it results in widely different evolution of the vegetation and oceanic carbon reservoirs. The discrepancies between the different studies can thus be explained by a combination of these factors: initial climatic and carbon cycle states, characteristics of the added fresh water flux, AMOC initial state and model "seesaw" pattern.

 References Ahn, J. and Brook, E J.: Atmospheric CO<sub>2</sub> and Climate on Millennial Time Scales During the Last Glacial Period, Science, 322, 83–85, 2008. Alvarez-Solas, J., Charbit, S., Ritz, C., Paillard, D., Ramstein, G., and Dumas, C.: Links between ocean temperature and iceberg discharge during Heinrich events, Nature Geosc., 3, 122–126, http://dx.doi.org/10.1038/ngeo752doi:10.1038/ngeo752, 2010. Barker, S., Diz, P., Vautravers, M J., Pike, J., Knorr, G., Hall, I R., and Broecker, W S.: Interhemispheric Atlantic seesaw response during the last deglaciation, Nature, 457, 1097–1102, http://dx.doi.org/10.1038/nature07770doi:10.1038/nature07770, 2009. Berger, A L.: Long-term variations of daily insolation and Quaternary climatic changes, J. Atmos. Sci., 35, 2362–2368, 1978. Bond, G., Broecker, W., Johnsen, S., McManus, J., Labeyrie, L., Jouzel, J., and Bonani, G.: Correlations between climate records from North Atlantic sediments and Greenland ice, Nature, 365, 143–147, http://dx.doi.org/10.1038/365143a0doi:10.1038/365143a0, 1993. Bouttes, N., Paillard, D., and Roche, D M.: Impact of brine-induced stratification on the glacial carbon cycle, Clim. Past, 6, 575–589, http://dx.doi.org/10.5194/cpd-6-681-2010doi:10.5194/cpd-6-681-2010, 2010. Bouttes, N., Paillard, D., Roche, D M., Brovkin, V., and Bopp, L.: Last Glacial Maximum CO<sub>2</sub> and $\delta^13$C successfully reconciled, Geophys. Res. Lett., 38, L02705, http://dx.doi.org/10.1029/2010GL044499doi:10.1029/2010GL044499, 2011. Brovkin, V., Ganopolski, A., and Svirezhev, Y.: A continuous climate-vegetation classification for use in climate-biosphere studies, Ecol. Modell., 101, 251–261, 1997. Brovkin, V., Hofmann, M., Bendtsen, J., and Ganopolski, A.: Ocean biology could control atmospheric $\delta ^13$C during glacial-interglacial cycle, Geochem. Geophys. Geosyst., 3(5), 1027, http://dx.doi.org/10.1029/2001GC000270doi:10.1029/2001GC000270, 2002. Brovkin, V., Ganopolski, A., Archer, D., and Rahmstorf, S.: Lowering of glacial atmospheric CO<sub>2</sub> in response to changes in oceanic circulation and marine biogeochemistry, Paleoceanography, 22, PA4202, http://dx.doi.org/10.1029/2006PA001380doi:10.1029/2006PA001380, 2007. Clark, P U., Dyke, A S., Shakun, J D., Carlson, A E., Clark, J., Wohlfarth, B., Mitrovica, J X., Hostetler, S W., and McCabe, A M.: The Last Glacial Maximum, Science, 325, 710–714, http://dx.doi.org/10.1126/science.1172873doi:10.1126/science.1172873, 2009. Clement, A C. and Peterson, L C.: Mechanisms of abrupt climate change of the last glacial period, Rev. Geophys., 46, RG4002, http://dx.doi.org/10.1029/2006RG000204doi:10.1029/2006RG000204, 2008. Crowley, T J.: North Atlantic Deep Water cools the Southern Hemisphere, Paleoceanography, 7(4), 489–497, http://dx.doi.org/10.1029/92PA01058doi:10.1029/92PA01058, 1992. EPICA community members: One-to-one coupling of glacial climate variability in Greenland and Antarctica, Nature, 444, 195–198, http://dx.doi.org/10.1038/nature05301doi:10.1038/nature05301, 2006. Ganopolski, A. and Rahmstorf, S.: Rapid changes of glacial climate simulated in a coupled climate model, Nature, 409, 153–158, 2001. Ganopolski, A., Petoukhov, V., Rahmstorf, S., Brovkin, V., Claussen, M., Eliseev, A., and Kubatzki, C.: CLIMBER-2: A climate system model of intermediate complexity, part II: Model sensitivity, Clim. Dyn., 17, 735–751, 2001. Heinrich, H.: Origin and consequences of cyclic ice rafting in the Northeast Atlantic Ocean during the past 13 000~yr, Quat. Res., 29, 142–152, 1988. Kageyama, M., Paul, A., Roche, D M., and Meerbeeck, C. J V.: Modelling glacial climatic millennial-scale variability related to changes in the Atlantic meridional overturning circulation: a review, Quat. Sci. Rev., 20(21–22), 2931–2956, http://dx.doi.org/10.1016/j.quascirev.2010.05.029doi:10.1016/j.quascirev.2010.05.029, 2010. Köhler, P., Joos, F., Gerber, S., and Knutti, R.: Simulated changes in vegetation distribution, land carbon storage, and atmospheric CO<sub>2</sub> in response to a collapse of the North Atlantic thermohaline circulation, Climate Dyn., 25, 689–708, http://dx.doi.org/10.1007/s00382-005-0058-8doi:10.1007/s00382-005-0058-8, 2005. Lynch-Stieglitz, J., Adkins, J F., Curry, W B., Dokken, T., Hall, I R., Herguera, J C., Hirschi, J. J.-M., Ivanova, E V., Kissel, C., Marchal, O., Marchitto, T M., McCave, I N., McManus, J F., Mulitza, S., Ninnemann, U., Peeters, F., Yu, E.-F., and Zahn, R.: Atlantic Meridional Overturning Circulation During the Last Glacial Maximum, Science, 316(5821), 66–69, http://dx.doi.org/10.1126/science.1137127doi:10.1126/science.1137127, 2007. Mackintosh, A., Golledge, N., Domack, E., Dunbar, R., Leventer, A., White, D., Pollard, D., DeConto, R., Fink, D., Zwartz, D., Gore, D., and Lavoie, C.: Retreat of the East Antarctic ice sheet during the last glacial termination, Nature geoscience, 4, 195–202, http://dx.doi.org/10.1038/ngeo1061doi:10.1038/ngeo1061, 2011. Marchal, O., Stocker, T F., and Joos, F.: Impact of oceanic reorganizations on the ocean carbon cycle and atmospheric carbon dioxide content, Paleoceanography, 13, 225–244, 1998. McManus, J F., Francois, R., Gherardi, J.-M., Keigwin, L D., and Brown-Leger, S.: Collapse and rapid resumption of Atlantic meridional circulation linked to deglacial climate, Nature, 428, 834–837, http://dx.doi.org/10.1038/nature02494doi:10.1038/nature02494, 2004. Menviel, L., Timmermann, A., Mouchet, A., and Timm, O.: Meridional reorganizations of marine and terrestrial productivity during Heinrich events, Paleoceanography, 23, PA1203, http://dx.doi.org/10.1029/2007PA001445doi:10.1029/2007PA001445, 2008. Monnin, E., Indermühle, A., Daellenbach, A., Flueckiger, J., Stauffer, B., Stocker, T F., Raynaud, D., and Barnola, J.-M.: Atmospheric CO<sub>2</sub> concentrations over the Last Glacial Termination, Science, 291, 112–114, 2001. Peltier, W R.: Global glacial isostasy and the surface of the ice-age Earth: The ICE-5G (VM2) Model and GRACE, Annu. Rev. Earth Planet. Sci., 32, 111–49, http://dx.doi.org/10.1146/annurev.earth.32.082503.144359doi:10.1146/annurev.earth.32.082503.144359, 2004. Petoukhov, V., Ganopolski, A., Eliseev, A., Kubatzki, C., and Rahmstorf, S.: CLIMBER-2: A climate system model of intermediate complexity, part I: Model description and performance for present climate, Clim. Dyn., 16, 1–17, 2000. Rahmstorf, S.: Bifurcations of the Atlantic thermohaline circulation in response to changes in the hydrological cycle, Nature, 378, 145–149, http://dx.doi.org/10.1038/378145a0doi:10.1038/378145a0, 1995. Ruddiman, W.: Late Quaternary deposition of ice-rafted sand in the sub-polar North Atlantic (lat 40° to 65°), Geol. Soc. Am. Bull., 88, 1813–1821, 1977. Schmittner, A. and Galbraith, E D.: Glacial greenhouse-gas fluctuations controlled by ocean circulation changes, Nature, 456, 373–376, http://dx.doi.org/10.1038/nature07531doi:10.1038/nature07531, 2008. Stocker, T F.: Climate change – the seesaw effect, Science, 282(5386), 61–62, 1998. Stocker, T F. and Wright, D.: Rapid transitions of the ocean's deep circulation induced by changes in the surface water fluxes, Nature, 351, 729–732, 1991. Waelbroeck, C., Labeyrie, L., Michel, E., Duplessy, J C., McManus, J F., Lambeck, K., Balbon, E., and Labracherie, M.: Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records, Quat. Sci. Rev., 21(1–3), 295–305, http://dx.doi.org/10.1016/S0277-3791(01)00101-9doi:10.1016/S0277-3791(01)00101-9, 2002.