ALBERT

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: 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: The Miocene to Pleistocene Limon Group of Costa Rica is a mixed carbonate–siliciclastic succession that formed in association with the emergence of the Central American Isthmus. Our study focuses on a lower Late Pliocene reef unit, the newly excavated Contact Cut, which is located at the contact between the siliciclastic sediments of the Rio Banano Formation and the mixed reefal and coral bearing deposits and siliciclastic sediments of the Quebrada Chocolate Formation. The siliciclastic sediments were deposited in a thick, deltaic setting sourced by erosion of the Cordillera de Talamanca. Deposits of the Limon Group preserve a sequence of progressively shallowing, near-shore sediments that were exposed by uplift during the early to middle Pleistocene. The Contact Cut outcrop shows the first reef sequence in the stratigraphic sequence and thus illustrates the reestablishment of Caribbean coral reef predominance in the Neogene. It shows extensive reef growth during a rise in sea level and a slight progradation during the succeeding sea-level highstand. Three stages of reef evolution are recognized based on faunal diversity. The Contact Cut reef complex is comparable to the time equivalent reef of the Las Islas roadcut, situated west of Limon, which shows a rapid burial of the corals by siliciclastics. Both reefs document a distinct facies diversification during the final stages of the closing of the Central American Seaway. The reefs developed in an environment stressed by siliciclastic input, which ultimately caused a decrease in coral diversity and abundance followed by a temporary demise of the reefs. The biotic composition of the patch reefs that occurred during the sea-level rise, Las Islas and Contact Cut, did not differ from the reefs that developed during the final highstand in sea level, the reefs of the overlying Moin formation (Limon Group). Differences in the position on the shelf relative to the source of the siliciclastics might have been the cause for the different response to the rise in sea level of the transgressive reefs, with a very fast give up scenario for Las Islas reef and a catch up followed by a give up phase for Contact Cut reef.

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 Chiriquı´ 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; Chiriquı´ is mesotrophic throughout the year, whereas the Gulf of Panama is eutrophic due to intense seasonal upwelling. Coralline algal carbonate production is 103 greater in the Gulf of Chiriquı´ (11.258 3 1010 gr CaCO3 yr21) than in the Gulf of Panama (1.69 3 1010 gr CaCO3 yr21), which is characterized mostly by siliciclastics with minor carbonates. Corallines display a patchy distribution in both gulfs being concentrated mainly around the islands. In Chiriquı´, they occur as thin crusts as well as massive-nodular and openbranching 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: In a sediment core from the leeward side of the Great Bahama Bank (Ocean Drilling Program ODP-Leg 166, 1006A-24H, early Pliocene) several paleoceanographic proxies were compared with carbonate mineralogy. The proxies measured on the planktonic foraminifera species Globigerinoides sacculifer are Mg/Ca and Sr/Ca elemental ratios, and δ18O values. These proxies are widely used in pelagic sediments to derive parameters of water masses, such as paleo-temperature and -salinity. To produce quantitative estimates it is necessary to verify that the primary shell mineralogy of the foraminifera was not altered diagenetically. Diagenetic alteration can be rapid in periplatform settings relative to pelagic deep-sea sediments, since the meta-stable carbonate phases provide an additional driving force for recrystallisation. We show that the Sr/Ca ratio of foraminiferal calcite can be used to assess the degree of diagenetic alteration of their shell chemistry. Using this method, we demonstrate that the primary signal in the oxygen-isotope ratios is preserved in the studied core. In the Mg/Ca record, the relative change of foraminiferal Mg/Ca ratios seems to be preserved, but absolute values are influenced by diagenesis. The second set of proxies comprises δ13C and C/N ratios of organic carbon. These are used in pelagic sediments in order to assess the origin of organic carbon (terrestrial or marine phytoplankton). It is demonstrated here that a simple two-end mixing model cannot explain the observed co-occurrence of relatively high δ13Corg and C/N values. As the δ13Corg values co-vary with the aragonite content, we attribute this signature to varying contribution of organic carbon from benthic algae, which are also the major aragonite producers on the platform top.

Description: After the closure of the Central American Seaway around 3.6 Ma, the benthic carbonate ecosystems developed differently in the Caribbean and on the Pacific side of the Isthmus of Panama. In this thesis, fossil and recent carbonate systems were studied and a comparison was made between fossil and present-day carbonate ecosystems from the same paleolatitude. This opens up the possibility to document the evolution of these sedimentation systems through time.