Percorrer por autor "Escobar, Jaime"
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- Nutrient inputs and net ecosystem productivity in the mouth of the Magdalena River, ColombiaPublication . Torregroza-Espinosa, Ana Carolina; Camilo Restrepo, Juan; Escobar, Jaime; Brenner, Mark; Newton, AliceNutrient inputs and biogeochemical cycles in estuaries are strongly influenced by river discharge and suspended particulate matter (SPM). We evaluated temporal differences in nutrient bioavailability and net ecosystem productivity (NEP) and analyzed the effect of SPM on nutrient availability and estuary NEP in the mouth of the Magdalena River, Colombia. In this study, we used the stratified Muddy LOICZ model. Calculated water residence times in the estuary were low (similar to 0.9-2.1 days), as were proportions of dissolved nitrogen (DIN) and phosphorus (DIP) forms (similar to 10-30%) in the total nutrient pool. Dissolved nutrient proportions displayed differences between seasons (transition period [June 2018] and wet [November 2018]), and between the upper and lower, density-stratified water layers. Nutrient adsorption and desorption, associated with SPM in the estuary, determined bioavailable nutrient concentrations. When SPM was incorporated in the Muddy LOICZ model, the output indicated that NEP in the estuary was positive, i.e. gross primary productivity exceeded community respiration (autotrophic), and that there was net retention of nitrogen and phosphorus in the estuary. Primary producers in the autotmphic ecosystem fix sufficient carbon to supply higher tmphic levels. Prevalence of fine sediment with high organic matter (OM) content in the Magdalena River, along with turbulence that results in vertical water column mixing, suggest conditions conducive to flocculation. This investigation highlights the importance of the Magdalena River mouth in the transport and processing of sediments and nutrients being discharged to the Caribbean Sea.
- Spatial and temporal variability of temperature, salinity and chlorophyll-a in the Magdalena River mouth, Caribbean SeaPublication . Carolina Torregroza-Espinosa, Ana; Camilo Restrepo, Juan; Escobar, Jaime; Pierini, Jorge; Newton, AliceVariations in the physico-chemical characteristics of estuaries, such as surface water salinity and temperature, lead to the establishment of gradients that are closely related with the distribution of nutrients and suspended sediment. This affects light penetration, which in turn influences Chlorophyll-a (Chl-a) concentration and primary productivity. We used MODIS imagery to identify spatio-temporal patterns of sea surface salinity, temperature, and Chl-a concentrations from 2003 to 2017, to explore relationships between these variables and oceanographic factors, such as streamflows, winds and currents in the mouth of Colombia's Magdalena River, which discharges to the Caribbean Sea. Sea surface salinity (SSS) in the study zone varied in time and space from estuarine to marine. Mean SSS was 10.8 +/- 3.4 at Bocas de Ceniza, and 28.4 +/- 0.4 in the Caribbean Sea, with the horizontal salinity gradient providing evidence for the existence of a salinity plume. Mean monthly sea surface temperatures (SST) averaged across all years were 27.6 +/- 1.5 degrees C at Bocas de Ceniza, and 27.6 +/- 1.3 degrees C in the Caribbean Sea. A significant, increasing trend in temperature was observed throughout the years of the study period. Average Chl-a values were 3.3 +/- 1.4 mg m(-3) at Bocas de Ceniza, and 1.5 +/- 1.2 mg m(-3) in the Caribbean Sea and the calculated average Trophic State Index (TSI) for Bocas de Ceniza indicated that the estuary trophic state varied between oligo-mesotrophic (30 < TSI <= 40) and mesotrophic (40 < TSI <= 50). The highest concentrations of Chl-a were found in intermediate salinities in the estuarine zone. Outside the saline plume, there is a considerable decrease in Chl-a concentrations (<0.5 mg m(-3)). Winds played the most important role in influencing spatio-temporal distribution of chemical and physical variables in the study zone. Our results emphasize the importance of physical processes on biological dynamics in the Magdalena River mouth.
- Tropical ecosystem shifts at the Eocene–Oligocene transition in the southwestern Caribbean regionPublication . Trejos-Tamayo, Raúl; Garzón, Darwin; Ochoa, Diana; Plata-Torres, Angelo; Frontalini, Fabrizio; Vallejo-Hincapié, Felipe; Abrantes, Fatima; Magalhães, Vitor; Arias-Villegas, Viviana; Jaramillo, Carlos; Escobar, Jaime; Curtis, Jason H.; Flores, José-Abel; Osorio-Tabares, Constanza; Duque Castaño, Monica Liliana; Bedoya, Erika; Pardo-Trujillo, AndrésThe Eocene-Oligocene transition (EOT; similar to 34 Ma) marks a pivotal climatic shift from a warm, ice-free world to a cooler, glaciated climate driven by a significant decline in atmospheric pCO2 levels. This global cooling event, characterized by the first major Antarctic glaciation and a similar to 50 m sea-level fall, triggered selective extinctions in marine ecosystems and restructured sedimentary processes, making it one of the most significant climatic events of the Cenozoic. While the global impacts of the EOT are well documented, its effects on the marine environment of NW South America remain poorly understood. This region's unique position as a connection between the Pacific and Atlantic oceans before the closure of the Central American Seaway provides a valuable window into tropical ecosystem responses during this period. This study integrates micropaleontological and geochemical data from the ANH-SJ-1 drill core in the Colombian Caribbean to evaluate the impacts of global climatic shifts on tropical marine ecosystems. Palynological indicators, including the terrestrial/marine (T/M) index, along with XRF-derived elemental ratios (Zr/Rb, Ti/Al, K/Al, and K/Rb), reflect enhanced continental input during the EOT. These patterns suggest intensified erosion and detrital transport to bathyal depths, likely driven by rapid sea-level fall and hypopycnal flows. Calcareous nannofossil trophic indices reveal elevated surface productivity, likely fueled by increased continental nutrient influx, supported by higher Ba/Ti ratios that indicate enhanced organic matter export to the seafloor. The resulting oxygen depletion favored infaunal over epifaunal benthic foraminifera, marking a shift in community structure. Improved carbonate preservation across the transition, evidenced by a shift from agglutinated to calcareous benthic foraminifera and higher Ca/Ti ratios, reflects a deepening of the carbonate compensation depth (CCD), likely due to enhanced alkalinity from continental weathering. A positive delta 13Corg excursion (similar to 0.84 parts per thousand) aligns with global records and supports contributions from organic carbon oxidation, volcanic inputs, and weathering. Although limited by the number of available samples and low fossil abundances in some intervals, our multiproxy approach enables a coherent reconstruction of environmental dynamics. The ANH-SJ-1 record highlights the sensitivity of tropical systems to global climatic shifts and reinforces the importance of tropical data for understanding Cenozoic climate evolution and anticipating future ecosystem responses.