Effects of Atolls on the Distribution and Composition of Suspended Particles in the Western Tropical Pacific

Abstract

Atolls are unique geomorphic structures that influence suspended sediment dynamics and microbial communities through their interaction with wave energy, currents, and limited landmass. These factors create localized patterns of suspended particles, yet their impacts on microbial activity and nutrient cycling remain poorly understood. This study investigates how atolls influence suspended sediments' vertical distribution and composition by examining differences in organic and inorganic particle concentrations at varying depths. I hypothesize that atolls promote the accumulation of fine organic matter and microbial activity near the reef, while larger inorganic sediments dominate farther away due to hydrodynamic forces. Fieldwork was conducted near Nam2 Atoll in the western Pacific, where transmissometer data, Conductivity, Temperature, and Depth (CTD) profiles, and water samples were collected across different locations. The composition of suspended particles was determined through microscopy while the proportion between organic and inorganic materials was quantified by the Loss on Ignition (LOI) method. Results indicate a significant decrease in the organic-to-inorganic ratio with depth, with the highest organic concentrations occurring in surface waters (20–100 m) and inorganic sediments increasing at deeper layers (>500 m). Statistical analysis revealed a T-statistic was 0.4129 while the p-value was 0.6889 however, showed no significant difference in organic-inorganic ratios between shallow and deep samples. The observed organic-to-inorganic ratio trends help clarify how organic carbon is stored and transported in marine environments which can inform climate models and global carbon budget estimates.