Nova Acta Leopoldina NF 121, Nr. 408, 305 –309 (2015) 305 New Carbonate System Proxies: Foram Culturing and Pteropod Potentials Nina Keul, Gerald Langer, Lennart de Nooijer, Gernot Nehrke, Gert-Jan Reichart, Jelle Bijma, and Ralph Schneider (Kiel) Global climate change is one of the most pressing challenges our society is facing currently. Climate sensitivity due to atmospheric CO 2 doubling will most likely increase global tempera- tures by 2.0 – 4.5 °C (IPCC 2007). While some direct effects of increasing CO 2 are straightfor- ward (e.g. ocean acidiication, atmospheric temperature rise), the mid- and long-term impacts of increasing CO 2 levels are less easily predicted due to poorly qualiied contribution from various potential positive and negative feedbacks in the climate system. Palaeoreconstruc- tions combining temperature reconstructions and atmospheric paleo-CO 2 levels are necessary to validate models that aim at predicting future global temperature increases. Reconstructions of atmospheric CO 2 from ice-cores are conined to the last 800 ka (Lüthi et al. 2008), while reconstruction of atmospheric pCO 2 on longer timescales rely largely on marine sedimentary archives (e.g. Hönisch et al. 2012). Within the latter, foraminifera play a central role, since the chemical and isotopic composition of their shells relect the physicochemical properties of the seawater that these organisms grew in (Emiliani 1955). Palaeo atmospheric CO 2 con- centrations can be estimated from past seawater CO 2 (aq), which in turn can be reconstructed when two out of six parameters are known of the oceans carbonate system (“C-system”; CO 2 , HCO 3 – , CO 3 2– , pH, DIC [dissolved inorganic carbon] and total alkalinity). Currently established, foraminifera-based C system proxies include boron isotopes (pH), B/Ca (CO 3 2– ) or the reconstruction of total alkalinity via salinity variations (Hemming and Hanson 1992, Hönisch and Hemming 2005, Hönisch et al. 2009, Sanyal et al. 1995, Yu et al. 2010). However, these proxies do not allow the reconstruction of the complete C sys- tem by themselves, due to various limitations and uncertainties associated with the different methods used (e.g. Yu and Elderfield 2007). Despite much recent progress in the ield of paleoclimatology aiming at overcoming these limitations and uncertainties, accurate and pre- cise reconstructions of past pCO 2 levels remains challenging. Here we present the potential of culturing studies with foraminifera and ield studies using pteropods to establish new C system proxy relationships. Culturing living foraminifera is a valuable tool to precisely calibrate new and existing proxies. In some species, asexual reproduction can be triggered in the laboratory, resulting in 50 to 300 one-chambered juveniles that can be placed into experiments under controlled con- ditions (e.g. various pH’s, [DIC]s, TAs). After maintaining them at a range of environmental conditions until they have grown into maturity, the resulting isotope and element composition of their calcium carbonate can be measured and related to these environmental conditions. 62 Keul.indd 305 11.02.2015 14:24:09