We compare a compilation of 220 sediment core d13C data from the glacial Atlantic Ocean with three-dimensional ocean circulation simulations including a marine carbon cycle model. The carbon cycle model employs circulation fields which were derived from previous climate simulations. All sediment data have been thoroughly quality controlled, focusing on epibenthic foraminiferal species (such as Cibicidoides wuellerstorfi or Planulina ariminensis) to improve the comparability of model and sediment core carbon isotopes. The model captures the general d13C pattern indicated by present-day water column data and Late Holocene sediment cores but underestimates intermediate and deep water values in the South Atlantic. The best agreement with glacial reconstructions is obtained for a model scenario with an altered freshwater balance in the Southern Ocean that mimics enhanced northward sea ice export and melting away from the zone of sea ice production. This results in a shoaled and weakened North Atlantic Deep Water flow and intensified Antarctic Bottom Water export, hence confirming previous reconstructions from paleoproxy records. Moreover, the modeled abyssal ocean is very cold and very saline, which is in line with other proxy data evidence.

We combined carbon isotope data from various compilations [Sarnthein et al., 1994, Bickert and Mackensen, 2004, Curry and Oppo, 2005, Marchal and Curry, 2008], and from the PANGAEA and NCDC databases (https://pangaea.de and http://www.ncdc.noaa.gov/paleo). As far as possible the original authors within the compilations were traced back and referenced. We only considered sediment cores containing Cibicidoides wuellerstorfi which is known to be the most reliable conserver of d13C (DIC) in the ocean [Woodruff et al., 1980, Belanger et al., 1981, Zahn et al., 1986, Hodell etal., 2001]. Some cores include a few other benthic species (Planulina ariminensis or Cibicidoides kullenbergi), which are also used in this study, as they are thought to have an epibenthic habitat, too [Lutze and Thiel, 1989].For each core we calculated the average d13C value of the Late Holocene and Last Glacial Maximum time slice. Our definitions of the Late Holocene and the Last Glacial Maximum are 0-4 ka BP and 18-24 ka BP, respectively. Phytodetritus corrections like those used in Bickert and Mackensen [2004] were not applied to any of the data.

Supplement to: Hesse, Tilman; Butzin, Martin; Bickert, Torsten; Lohmann, Gerrit (2011): A model-data comparison of d13C in the glacial Atlantic Ocean. Paleoceanography, 26, PA3220