Marine fish carbonates – contribution to sediment production in temperate environments
Stephens, Christine Elizabeth
Thesis or dissertation
University of Exeter
Reason for embargo
To allow sufficient time for all the work in data chapters to be published.
In the past, oceans have strongly influenced atmospheric CO2 levels through organic and inorganic carbon cycling. The inorganic carbon pump relies on the formation of calcium carbonate which releases CO2 into the surface ocean and traps alkalinity in solid form which sinks to deeper ocean layers and sediments. After sinking, calcium carbonate can either then become trapped in the sediments or dissolve increasing the alkalinity of deeper ocean layers. The net effect is of acidifying surface oceans and encouraging release of CO2 to the atmosphere. The present thesis focuses on marine teleost (bony) fish in temperate areas as previously poorly understood but potentially major producers of calcium carbonate in the ocean. Fish in temperate areas may be contributing to carbonate sediment production and as such the inorganic carbon pump. Prior to this thesis only tropical fish have been investigated as major piscine sediment producers. The present thesis describes the composition and morphology of carbonates produced by many different species of temperate fish providing a basis for the understanding the fate of these carbonates in the environments and their potential contribution to sediment production and the inorganic carbon cycle. Characteristics of carbonates produced by fish in the wild were fairly consistent within a species upon examination of carbonates produced by poor cod (Trisopterus minutus) over the course of a year. However, despite the likely consistent and distinct characteristics of fish carbonates, little evidence of them was found in temperate shallow sediments beneath pens of farmed Atlantic salmon (Salmo salar) where there theoretically should be very high production rates. Reduced salinity, often a feature of temperate areas compared to tropical areas, was found to reduce production rates of carbonate from fish compared to higher salinities. However, salinity reductions below the ocean average of 35 psu (practical salinity units) had less impact on production rates than increases above 35 psu. As such it is argued that production rates in temperate environments should still be relatively high considering high fish biomasses in some temperate regions and could still mean fish in temperate areas are an important source of carbonate production and potential sediment production.
Natural Environment Research Council
PhD in Biological Sciences