A Review on the Role of Reactive Iron Phases in the Stabilization of Organic Carbon in Sediments Ian A. Navarrete* a Gerald Dicen a Ma. Carmela A. Garcia a Kyla Marie I. Castro a Efren J. Sta. Maria b Severino G. Salmo III a * Corresponding author; Email: inavarrete@ateneo.edu a Department of Environmental Science, Ateneo de Manila University, Loyola Heights, 1108 Quezon City b Chemistry Research Section, Philippine Nuclear Research Institute, Commonwealth Avenue, Diliman, 1101 Quezon City Abstract There is a continual rivers influx of dissolved organic carbon (DOC; 0.25 × 10 15 g yr -1 ) and particulate organic carbon (POC; 0.15 × 10 15 g yr -1 ) from continents to the ocean and this constitutes a significant flux of carbon (C) and a major pathway that marine ecosystem sequester C. Once in the ocean, complex abiotic and biotic processes affect the residence time of these C, wherein some of these processes result in the immediate release of these C into the atmosphere, whereas others can effectively stabilize organic carbon (OC) in sediments for decadal or millennial scale. Uncertainty remains, however, the underlying mechanisms of OC stabilizations and preservations in sediments, which cast shadows in predicting the response of OC in sediments to climate change. This paper reviews the long-term stabilization (e.g. co- precipitation, direct chelation, sorption, etc.) of OC in sediments and discusses the sorptive interaction of OC with mineral phases. We argue that iron (Fe), which is derived from dust, coastal and shallow sediments exerted significant control over OC stabilization in sediments (‘rusty sink’) and thus, contributing to the global cycles of C. Lastly, protecting the remaining natural mangrove vegetation could reduce sediments and OC losses from these areas and thus, will increase the resilience of OC to the anticipated more extreme hydrological events. Introduction Understanding how ecosystem store or release carbon (C) is one of ecology's greatest challenges in the 21st century. Of the 5 global C pools (i.e. pedologic, biotic, fossil fuel and atmospheric pools), the oceanic pool which is estimated at 38,000 Pg (1 Pg = 1 billion metric tons) is 5 times higher than the four C pools combine (Lal, 2008). About 96% of this C is deposited in the deep layer (inorganic C and is a very stable form of C), while about 670 Pg is located in the surface layer and about 1,000 Pg are in the organic form. The atmospheric pool is connected to the ocean pool which absorbs (sink) 92.3 Pg C yr -1 and releases (source) 90 Pg C yr -1 resulting in a net positive balance of 2.3 Pg C yr -1 . However, complex abiotic and biotic processes affect the residence time of these C, wherein some of these processes result in the immediate release of these C into the atmosphere, whereas others can effectively stabilize OC in sediments for decadal