Iron fertilization of surface waters along the northern Alaskan margin (mainly linked to Cordilleran Ice Sheet iceberg discharge) as an essential driver of phytoplankton growth during the past 54 ka. Occurrence of calcareous and siliceous primary producers was largely unaffected by low SST conditions during MIS 3 and MIS 2. Prominent role of tidewater glaciers in defining marine productivity dynamics of high-latitude coastal regions should be considered in understanding land-ocean interactions.