Description: In this study two carbonate environments are compared and contrasted; the Gulf of Panama and the Gulf of Chiriquı´ on the Pacific side of Panama. These two embayments are in close geographic proximity at latitudes between 7° N and 9° N. The Gulf of Panama and the Gulf of Chiriquı´ are characterized by contrasting oceanographic conditions with year-round stable non-upwelling conditions in the Gulf of Chiriquı´ and strong seasonal upwelling in the dry season (December to April) in the Gulf of Panama. The upwelling variations only have a limited influence on the amount of carbonate produced; however, they do have a major impact on the occurrence of specific carbonate producing biota. In addition, carbonate production and distribution is influenced in both gulfs by the occurrence of islands and by terrigenous input. Terrigenous material is found mainly in the smaller grain sizes (〈63 to 250 lm) that can be transported easily by currents and waves. Carbonate dominant sediments (carbonate sands and mixed carbonate–siliciclastic sands) mainly occur around the islands and are dominated by larger grain-sizes (〉500 lm). The Gulf of Panama and the Gulf of Chiriquı´ both show warm and temperate carbonate-producing biota, with carbonate producers from tropical (corals) to mixed tropical to cool-water (coralline red algae) and cold-water (balanids) environments. The Gulf of Chiriquı´ is characterized by oligotrophic to mesotrophic conditions resulting in a photozoan (coral) and/or rhodolith- facies in shallow-water areas surrounding the islands and a molluscdominated facies in deeper waters towards the shelf edge. Seasonal upwelling causes temporary eutrophic conditions in the Gulf of Panama, which results in a heterozoan facies around the islands dominated by balanids, echinoderms and molluscs. Thus a ‘cool-water’ carbonate fauna and eutrophic conditions can exist in the tropics within an area prone to seasonal upwelling. The distinct facies differences found on the Pacific shelf of Panama stress the importance of variations in oceanographic conditions, upwelling versus nonupwelling, in determining carbonate production and associated facies patterns in the tropics.

Description: Distribution, growth rate, and carbonate production of non-geniculate and unattached coralline red algal beds (rhodoliths) were studied in the Gulfs of Panama and Chiriqui along the Pacific coast of Panama. This is the first attempt to quantify coralline carbonate production in this region based on a newly developed algorithm. Although situated at the same latitude, the two gulfs are characterized by distinctly different environmental conditions; Chiriqui is mesotrophic throughout the year, whereas the Gulf of Panama is eutrophic due to intense seasonal upwelling. Coralline algal carbonate production is [~]10x greater in the Gulf of Chiriqui (11.258 x 1010 gr CaCO3 yr-1) than in the Gulf of Panama (1.69 x 1010 gr CaCO3 yr-1), which is characterized mostly by siliciclastics with minor carbonates. Corallines display a patchy distribution in both gulfs being concentrated mainly around the islands. In Chiriqui, they occur as thin crusts as well as massive-nodular and open-branching growth types; encrusting types are most common in the Gulf of Panama. Growth rates of branching corallines were calculated based on annual growth bands matched to their skeletal Mg/Ca ratios. Ratios are higher in the less dense portions of growth bands corresponding to higher growth rates during the dry season, whereas both Mg/Ca ratios and growth rates in the dense portions (wet season) drop. Growth rates of branch tips in both sites are similar to those reported from other temperate-subtropical regions. Extremely slow growth rates combined with the old ages of individual thalli document the overall stability of this algal ecosystem.

Description: A piston core from the Maldives carbonate platform was investigated for carbonate mineralogy, grain-size distributions, calcium carbonate content and organic carbon. The sedimentary record was linked to Late Pleistocene sea-level variations, using an age model based on oxygen isotopes obtained from planktonic foramanifera, nannofossil biostratigraphy and 14C age determinations. The correlation between the sedimentary record and Late Pleistocene sea-level showed that variations in aragonite and mud during the past 150 000 years were clearly related to flooding and sea floor exposure of the main lagoons of the atolls of the Maldives carbonate platform. Platform flooding events were characterized by strongly increased deposition of aragonite and mud within the Inner Sea of the Maldives. Exposure events, in contrast, can be recognized by rapid decreases in the values of both proxy records. The results show that sediments on the Maldives carbonate platform contain a continuous record of Pleistocene sea-level variations. These sediments may, therefore, contribute to a better understanding of regional and even global sea-level changes, and yield new insights into the interplay between ocean currents and carbonate platform morphology.