Partitioning of stable isotopes between scallop shell calcite and sea water and factors influencing shell growth and microgrowth patterns.

Abstract

There is great potential for establishing historical records of water temperature / the oxygen isotopic composition of sea water (0180 - H20) and the carbon isotopic composition of dissolved inorganic carbon (o13C - LC02) from oxygen and carbon isotopic records in scallop shell calcite (0180 and o13C)_ Variations in o13C - LC02in oceanic environments often reflect productivity cycles which may potentially be recorded within shell o13C records. The establishment of such records is based upon two fundamental assumptions_ These are that precipitation of shell calcite occurs in isotopic equilibrium with sea water and that growth occurs over an entire annual cycle_ Important information may also be gained from microgrowth patterns on the scallop shell surface ('striae') once factors governing their deposition are understood_ The above assumptions were tested for the scallop (Pecten maximus) by controlled experiment and in a year - long field study_ During periods of slow growth shell oxygen isotopes were found to be precipitated in isotopic equilibrium with sea water_ Shell carbon isotopes were found to be depleted with respect to isotopic equilibrium_ This was interpreted as resulting from a metabolic effect, probably reflecting incorporation of respiratory CO2 into the growing shell. At higher shell growth rates depletions / further depletions in 0180 / 013C with respect to isotopic equilibrium occurred, interpreted as reflecting kinetic effects_ Shell growth exhibited distinct seasonality, with growth cessation during the Winter months (below 8-9°C) and maximal growth rates in the Summer_ Stria deposition was found to be strongly related to shell growth rate_ The combined effects of growth cessation and precipitation of shell isotopes out of isotopic equilibrium with sea water precluded accurate determination of mean and annual ranges of water temperature / 0180 -H20 and o13C -LC02 from the shell isotopic record_ Shell 0180 / o13C and striae abundance records for Pecten maximus collected from an offshore site were interpreted in the context of the calibration work undertaken_

Date of Award	Sept 1998
Original language	English
Awarding Institution	Bangor University
Sponsors	Natural Environment Research Council (NERC)