major water mass components flow epsilon Nd [Nd] [Sverdrup] (10^-12g/g) Labrador Sea Water (LSW) LSW 4 -13.9 ± 0.4 2.5 ± 0.2 Northeast Atlantic 6 -11.3* Deep Water (NEADW) Iceland-Scotland- 2 -8.2 ± 0.6 3.1 ± 0.3 Overflow Water (ISOW) Modified North 1 -13.1 ± 0.3 2.4 ± 0.2 Atlantic Water (MNAW) LSW 1 -13.9 ± 0.4 2.5 ± 0.2 Eastern Lower 2 -12.5 ± 0.4 3.4 ± 0.4 Deep Water (LDW) Northwest Atlantic 6 -10.9* Bottom Water (NWABW) Denmark Strait 3 -8.4 ± 1.2 3.2 ± 0.5 Overflow Water LSW 1.5 -13.9 ± 0.4 2.5 ± 0.2 Subpolar Mode Water 1.5 -13.9 ± 0.2 2.7 ± 0.1 (SPMW) * calculated values (all other Nd isotopic compositions reported in the table are derived from direct seawater measurements on various locations across the North Atlantic). A hypothetical value of epsilon Nd of -11.7 for proto-NADW north of 50°N can be calculated assuming that water mass mixing is the only process by which NADW acquires its Nd isotopic composition from the different contributors. Proportions of contributing water masses are taken from Schmitz [1996] and measured Nd isotopic compositions and concentrations for these contributors are taken from Lacan and Jeandel [2005a] and are reported here. Since mature NADW has an isotopic composition of -13.5 [Piepgras and Wasserburg, 1987], a value which can already be observed in the proto-NADW region of the southwest Labrador Sea, a process different than water mass mixing must be involved in the formation of the Nd isotopic composition of NADW. This process has been identified by Lacan and Jeandel [2005b] as boundary exchange, which is the reversible exchange of Nd between bottom sediments and seawater at the land-ocean interface.