We tested the sensitivity of the vertical distributions and shell dissolution patterns of thecosome pteropods to spatial gradients associated with an eddy-associated front in the southern California Current System. The aragonite saturation horizon ($Ømega$arag = 1.0) shoaled from \textgreater200 to \textless75 m depth across the front. The vertical distribution of thecosome pteropods tracked these changes, with all 5 species showing reduced occurrence at depths below 100 m where waters were less saturated with respect to aragonite. Shell dissolution patterns of the numerically dominant thecosome Limacina helicina corresponded to the cross-frontal changes in $Ømega$arag saturation state. Severe shell dissolution (categorized here as Type II and Type III) was low in near-surface waters where $Ømega$arag \textgreater 1.4, while peak dissolution occurred in depths where $Ømega$arag = 1.0 to 1.4. Vertical habitat compression and increased shell dissolution may be expected to accompany future shoaling of waters that are undersaturated with respect to aragonite.
