Growth Characteristics and Susceptibility to Bleaching in the Massive Porites Corals, South Thailand

Extensive bleaching of corals occurred around Phuket, South Thailand, in the summer of 1991, accompanied by sea surface temperatures of 3 1" C (ca. 2" C above normal). During this episode we noted a marked variation in the degree of bleaching of adjacent, but otherwise similar, mas- sive Porites coral colonies. During a previous study we had found large within-site variations in the growth rates of P. lutea in this area. To see if sus- ceptibility to bleaching could be related to growth characteristics of the colonies prior to the bleaching event, 8 bleached and 9 unbleached colonies were sampled from 1-2 m water depth on the front of a fringing reef. We measured the linear extension and skeletal bulk density of each coral for an annual giowth increment prior to the bleaching event (ap- proximately December 1989-December 1990). For this period we found no significant differences in linear extension rate, skeletal bulk density or cal- cification rate between colonies which subsequently bleached and those which remained unbleached. From this we conclude that these two aspects of coral biology (ie, skeletogenesis and tendency to bleach) are controlled by substantially different parameters

The petrography and microstructure of medieval lime mortars from the west of Scotland: Implications for the formulation of repair and replacement mortars

Twelfth and thirteenth Century lime mortars from the west of Scotland were examined using optical polarising microscopy and SEM on impregnated, polished thin sections, and of fracture surfaces by secondary electron SEM. The non-hydraulic calcite binder in these mortars is locally inhomogeneous, exhibiting variations in texture and density. Spongiform binder with porosity of size 10-20gm has sharp transitions with neighbouring zones of dense binder. Sub-isopachus concentrically accreted calcite pore linings delineate extensive areas of secondary porosity created by dissolution of binder. Common lime inclusions (lime lumps) suggest that hot mixing processes were used. Textural characteristics of lime lumps are similar to reaction rims on partially burnt primary source limestone suggesting that provenance for the lime can be deduced from the petrographic features of incompletely burnt relics. The evidence for the dissolution and reprecipitation of carbonate binder materials suggests the need for a careful reconsideration of practical historic mortar analysis. These historic mortars are texturally and compositionally more complex than their modern equivalents. These textures provide evidence for historic lime burning and mortar mixing practices in Scotland during the middle ages, as well as ageing processes, and allows the possibility of a more sophisticated approach to formulating compatible replacement mortars