Atmospheric Fe supply has a negligible role in promoting marine productivity in the Glacial North Pacific Ocean

Abstract. Iron is a key element in the Earth climate system as it can enhance the marine primary productivity in the High-Nutrient Low-Chlorophyll (HNLC) regions where, despite a high concentration of major nutrients, the chlorophyll production is low due to iron limitation. One of the main Fe sources to the ocean is Aeolian dust. For this reason, ice cores provide a sensitive and continuous archive for reconstructing Fe fluxes over the last millennia. Here we show the first Northern Hemisphere Fe record retrieved from the NEEM ice core, which offers a unique opportunity to reconstruct the past Fe fluxes in the Arctic region over the last 108 kyr. Holocene Fe fluxes to the Arctic were three times lower than the average recorded over the last glacial period. They were greater during the Last Glacial Maximum (LGM) and the Marine Isotope Stage 4 (MIS 4). Comparing our data with palaeoceanographic records retrieved from the HNLC North Pacific, we demonstrated that during the coldest periods, characterized by the highest Fe fluxes, marine productivity in the subarctic Pacific Ocean did not increase due to a greater sea-ice extent and the absence of upwelling nutrient supply. This supports the hypothesis that Fe-fertilization was more effective in other regions, such as the transition zone of the North Pacific, where a closer relationship between marine productivity and the Aeolian Fe fluxes was observed.