Moana-Maty: Iron and the Marquesas Island Mass Effect


The Marquesas Islands archipelago is located northeast of French Polynesia, in the central South Pacific. One of the most remarkable features of this environment is the presence of recurrent hotspot of productivity in the vicinity of the islands, a process commonly referred to as the Island Mass Effect. However, the underpinning physical and biogeochemical mechanisms that drive the enhanced phytoplankton growth observed in this region relative to surroundings High Nutrient Low Chlorophyll waters are still unclear. While various investigators have postulated that the surface waters near the islands are naturally fertilized with iron, there are very few iron observations at sufficient spatial and temporal resolution to corroborate this hypothesis and to determine the origin of the presumed iron enrichment.

In collaboration with colleagues from the French IRD, the Chemical Oceanography lab will participate in the MOANA-MATY expedition aboard the RV L’Alis. We will collect water samples at 15 stations along several transects in the vicinity of the Marquesas Islands in Sept-Oct 2018 and once again in Feb-March 2019. We will analyze these samples for dissolved Fe and total dissolvable Fe back at MLML and use these data to: (1) investigate the seasonality in Fe concentrations in relation to the Marquesas bloom dynamics and local circulation, and (2) determine the source of the Fe enrichment (e.g., local sources, vertical inputs from subsurface waters).