Influence of the Hawaiian Islands on Biogeochemistry in the Pacific

Abstract

This study explores how the Hawaiian Islands impact biogeochemistry in the Pacific Ocean, focusing on how far the islands influence on biologically important variables, namely nutrients and phytoplankton, extends into the west Pacific. In the nutrient-poor (oligotrophic) waters around Hawaiʻi, the islands play a critical role in generating productivity through eddies and other ocean disturbances, supporting plankton, fisheries, and carbon export. Previous research indicates far-reaching effects of the Hawaiian Islands on physical variables such as winds, currents, vertical advection, and sea surface temperatures up to 3000 km west of the islands (Xie et al., 2001). However, the impacts of this wake on nutrients and biological variables remain underexplored, with most studies focusing only on waters near the Main Hawaiian Islands. Using the Regional Ocean Modeling System (ROMS) coupled with the Carbon, Ocean, and Lower Tropics (COBALT) model, the study investigates how physical and biological processes interact west of Hawaiʻi. ROMS was run from 2000 to 2020 over a region extending west to approximately 175ºE. This study found a significant wake of eddy kinetic energy (EKE) extending to roughly 185ºE, showing that eddies generated by the islands have far-reaching impacts. Both cyclonic (upwelling) and anticyclonic (downwelling) eddies appear to influence nutrient transport and productivity far from the islands, and these effects vary based on depth. Nitrate and phosphate have wakes that extend across the entire domain, while iron and phytoplankton do show elevated levels near the islands, but do not have as far-reaching wakes. These findings highlight Hawaiʻi’s broader ecological significance in structuring productivity patterns across the Pacific, with implications for ecosystem management and conservation efforts. Further research is needed to better understand the mechanisms driving these biological responses and to predict how changing climate conditions may alter Hawaiʻi’s ecological influence.