Carbonate sediment production by marine fish: quantifying production across carbonate provinces and applications to global marine carbonate modelling

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A major component of the marine-atmospheric carbon cycle is the precipitation and dissolution of calcium carbonate in seawater. Calcium carbonate is the mineral that makes up rocks such as limestone and chalk. Detailed knowledge of this component is important to our understanding of the global carbon cycle, and to the earth system as a whole. This proposal builds upon recent findings that represent a fundamental and previously unexpected change to our understanding of one aspect of marine carbon cycling, namely carbonate sediment production. Specifically, we have recently discovered an entirely new source of carbonate sediment derived from marine bony fish (like barracuda, flatfish and grouper, collectively known as 'teleosts'). All teleosts precipitate carbonates within their guts as a by-product of continuously drinking Ca- and Mg-rich seawater, excreting the ingested marine Ca and Mg as insoluble carbonate into the marine environment. Funded through a NERC small grant in 2008 (NE/G010617/1) we made a series of remarkable discoveries regarding the significance of these fish-derived carbonates within shallow tropical marine environments, and which have major implications for the field of carbonate sedimentology. Specifically, we showed that in that region fish produce and excrete, in very large amounts, a wide range of fine-grained (mostly <30 micron) precipitated calcium carbonates. This carbonate is in the form of both 'low' and 'high' Mg-calcite, and aragonite. Additionally, using site specific fish biomass and measured carbonate excretion rate data, we estimated that fish produce ~6.1 million kg of calcium carbonate sediment per year across the Bahamian archipelago, and that estimated contributions from fish to total carbonate mud production average ~14 % overall, and exceed 70 % in specific habitats. Finally, we made the crucial observation that the crystals produced by fish occur commonly in the finest sediment fractions of surface sediments from all sedimentary environments examined in the Bahamas, thus demonstrating that such material does indeed represent both a novel and quantitatively important source of marine carbonate sediment.The above discoveries thus have direct application to conceptual ideas of how shallow marine carbonate factories function both today and in the past. Arising from this however are a series of fundamental questions about the wider global significance of this carbonate sediment source in different marine carbonate depositional environments:Q1. Do fish produce similar types of fine-grained carbonate sediment (morphologically and compositionally) in different marine environments and what is the range in variability of these carbonate sediments across tropical to cool temperate environmental gradients? Q2. How do rates of fish-derived carbonate sediment production derived from sites in The Bahamas compare to those in other tropical, subtropical and temperate regions, and can this be reliably predicted from temperature and body size? Q3. How variable is the preservation (and dissolution) potential of the range of carbonate sedimentary phases produced by fish in different marine environments? Q4. How do overall rates and phases of carbonate produced in different environments vary as a function of local fish community structure and abundance? To address these questions we propose to collect data on the types and rates of carbonate sediment produced by fish across a latitudinal gradient (14o to 43oS) that spans tropical through to cool temperate marine environments (~30 to ~12oC), and to use this data: (i) to determine the dissolution/ preservation potential of fish-derived carbonate sediments (as a function of composition and morphology) across these environments; and (ii) to model, at regional and global scales, the volumes and phases of fish-derived sediment that are initially produced, and then either preserved or dissolved in different marine environments.