Continental shelves are important land-ocean interfaces where natural and anthropogenic processes, as well as sediment geochemistry regulate the sequestration of organic matter (OM) in the sediment. In the Northern Gulf of Mexico, along the Louisiana shelf, the Mississippi River discharge asserts strong seasonal controls over primary production and sedimentary reserves of minerals. Recent studies have shown the importance of mineral-organic matter interactions in the sedimentary OM preservation, both of which are abundant in this region. Thus, the major objective of this work is to understand the spatial and temporal variability of the sediment organic carbon (OC) directly bound to the reactive iron (rFe) mineral phases such as goethite, ferrihydrite, lepidocrocite and hematite. Sediment samples were collected from five sites along the river plume during periods of low (August/September 2016) and high (May 2017) river discharge. Average rFe content in the top 20 cm of sediment was significantly higher at all sites in May (6.9 ±1.5 mg gdw-1) compared to August (4.3± 0.6 mg gdw-1), while particulate OC content in these sediments was higher in August (11.9 ± 3.7 mg gdw-1) compared to May (7.4± 4.7 mg gdw-1). However, the bulk OC bound to rFe in these sediments did not vary significantly between the two seasons and ranged between 2.3 - 3.4 mg gdw-1. Molar OC: Fe ratios in the OC associated with rFe ranged between 0.9-6.2, with higher ratios in the deeper sediment sections (5-20 cm) than at the top (0-5 cm). Our results indicate that 27- 32% of the total OC in sediment is associated with rFe phase and preserved in these recent shelf sediments. A combination of X-ray diffractometry and Fe-K Edge X-ray absorption near edge structure spectroscopy analyses were carried out to identify the mineralogical composition of rFe bound to the organic carbon in the sediments. Preliminary findings indicate that most of the iron is found as non-reactive iron in clay mineral smectite, but the dominant form of rFe associated with OC is goethite.