Marine barite (BaSO4) is produced in the water column in association with decaying organic matter; its distribution in the water column and in core-top sediments closely corresponds with the organic carbon flux from the surface ocean to the deep ocean (export production). Barite preservation in non-sulfate-reducing sediments is high, compared to other proxies used to reconstruct both export carbon fluxes (export production) and carbon burial rates. Thus the accumulation rate of marine barite is one of the most promising methods (or proxy variables) for export production and has been used to understand and reconstruct past biogeochemical processes in the ocean, including export productivity. Like any other paleoceanographic proxy, there are assumptions and complications associated with the application of barite accumulation rates in reconstructing export production. Specifically, because barite constitutes only a small fraction of the total sediment (o1%), computing precise barite accumulation rates depends on accurate estimates of bulk sediment mass accumulation rates which are hard to determine, particularly at high temporal resolution. Moreover, the significance of variable barite preservation depends on seawater saturation levels with respect to barite and sedimentation rates, which have not yet been fully investigated. Several studies have demonstrated the utility of this proxy, and if used wisely, marine barite accumulation rates in marine sediments can provide valuable information about changes in carbon export to depth and the response of the carbon cycle to climate perturbations in the geological record. Ideally, to achieve higher confidence in paleo-reconstructions of export production, several independent proxies should be applied simultaneously at any given site or time interval. r 2007 Elsevier Ltd. All rights reserved.

Marine barite: Recorder of variations in ocean export productivity

The 18S ribosomal DNA molecular phylogeny and lipid composition of over 120 marine diatoms showed that the capability to biosynthesize highly branched isoprenoid (HBI) alkenes is restricted to two specific phylogenetic clusters, which independently evolved in centric and pennate diatoms. The molecular record of C25 HBI chemical fossils in a large suite of well-dated marine sediments and petroleum revealed that the older cluster, composed of rhizosolenid diatoms, evolved 91.5 ± 1.5 million years ago (Upper Turonian), enabling an accurate dating of the pace of diatom evolution that is unprecedented. The rapid rise of the rhizosolenid diatoms probably resulted from a major reorganization of the nutrient budget in the mid-Cretaceous oceans, triggered by plate tectonics.

https://science.sciencemag.org/content/sci/304/5670/584.full.pdf

The Rise of the Rhizosolenid Diatoms

Early diagenesis of biogenic silica in the Amazon delta: alteration, authigenic clay formation, and storage

Marine sponges are able to process a variety of carbon (C), nitrogen (N), phosphorous (P), and silicon (Si) dissolved compounds, in addition to the particulate C, N, and P obtained through regular feeding. While Si fluxes through sponges are exclusively related to the elaboration of their skeleton of biogenic silica, C, N, and P fluxes derive from a complex combination of metabolic processes that include feeding, respiration, egestion, excretion, as well as hosting of large microbial populations within the sponge body. Because of the remarkable abundance of sponges in many benthic marine communities, they have the potential to impact the availability of the compounds they take up and release, affecting the benthic-pelagic coupling and cycling rates of chemical elements that are crucial to determine growth of bacterioplankton and primary producers at the ecosystem level. Unfortunately, our knowledge and understanding of the magnitude of the sponge-meditated nutrient fluxes and their ecological implications depends much on the compound type (i.e. C, N, P, or Si). Herein, we review the available knowledge on the subject with emphasis on recent developments.

/pdf/nutrient-fluxes-through-sponges-biology-budgets-and-4csx7l4i09.pdf

Nutrient fluxes through sponges: biology, budgets, and ecological implications.

Institute of Bioanalytical Chemistry, Dresden University of Technology, D-01069 Dresden, Germany, Crystal Engineering, Growth and Design Laboratory, Department of Chemistry, University of Crete, Voutes Campus, GR-71003 Heraklion, Crete, Greece, Laboratory of Mechanisms and Transfer in Geology, Observatory Midi-Pyrenees (OMP), UMR 5563, CNRS, 14 Avenue Edouard Belin, 31400 Toulouse, France, and FORTH-ICEHT and Laboratory of Inorganic and Analytical Chemistry, Department of Chemical Engineering, University of Patras, GR-265 04 Patras, Greece[007f]

A.Johan van Bennekom

Papers

Processes controlling solubility of biogenic silica and pore water build-up of silicic acid in marine sediments