From Nano-Gels to Marine Snow: A Synthesis of Gel Formation Processes and Modeling Efforts Involved with Particle Flux in the Ocean.

Antonietta Quigg,Kai Ziervogel,Adrian Burd,Manoj Kamalanathan,Wei-Chun Chin,Peter H Santschi,Chen Xu

doi:10.3390/gels7030114

Abstract

Marine gels (nano-, micro-, macro-) and marine snow play important roles in regulating global and basin-scale ocean biogeochemical cycling. Exopolymeric substances (EPS) including transparent exopolymer particles (TEP) that form from nano-gel precursors are abundant materials in the ocean, accounting for an estimated 700 Gt of carbon in seawater. This supports local microbial communities that play a critical role in the cycling of carbon and other macro- and micro-elements in the ocean. Recent studies have furthered our understanding of the formation and properties of these materials, but the relationship between the microbial polymers released into the ocean and marine snow remains unclear. Recent studies suggest developing a (relatively) simple model that is tractable and related to the available data will enable us to step forward into new research by following marine snow formation under different conditions. In this review, we synthesize the chemical and physical processes. We emphasize where these connections may lead to a predictive, mechanistic understanding of the role of gels in marine snow formation and the biogeochemical functioning of the ocean.

Highlights

IntroductionPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
Considering the rich and ubiquitous presence of phytoplankton in the ocean and high-yield secretory activity [36,86,87,88], these results suggest that microalgae might be a major source of reduced organic carbon and may release amphiphiles that can induce dissolved organic matter (DOM) assembly
The formation of marine snow from biopolymers secreted by microbes is a dynamic progression that relies on biological, physical, and chemical processes

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Once nanogels have formed in the oceans, they can interact with each other to form larger, supramolecular networks or microgels (Figure 1) which are ~4–5 μm in size [4,46,58,59] or 3D polymer hydrogel networks [16,60,61] known as physical gels The latter are stabilized by hydrophobic or ionic bonds as gels are mostly water and so they can interpenetrate [14,49]. The distinctive sugar and amino acid compositions of the colloidal fraction are relatively uniform throughout the ocean such that these chemical signatures are used to test for selective assembly of biomacromolecules into gels [57] These biopolymers are either released by phytoplankton primary production, bacterial activity, or are the end products of the degraded detritus of marine biota [16,39,59]. Considering the rich and ubiquitous presence of phytoplankton in the ocean and high-yield secretory activity [36,86,87,88], these results suggest that microalgae might be a major source of reduced organic carbon and may release amphiphiles that can induce DOM assembly

TEP and CSP

Marine Snow

Modeling Efforts

Marine Gels and the Ocean’s Carbon Cycle

Findings

Conclusions