Southwest Caribbean Research Articles

The Influence of Caribbean Current Eddies on Coastal Circulation in the Southwest Caribbean Sea

Abstract Westward-propagating Caribbean Current eddies modify the volume-integrated potential vorticity (PV) balance in the western Caribbean Sea, influencing the circulation of the Panamá–Colombia Gyre (PCG) and coastal currents hundreds of kilometers to the south of the eddies’ mean trajectory. Using 22 years of output from the Hybrid Coordinate Ocean Model, we apply a volume-integrated eddy phase-averaged 1.5-layer PV balance, showing that PV fluxes into the PCG region are balanced by frictional PV dissipation represented by linear drag along the coastline. Coastal currents in the PCG region vary by a factor of 2 in phase with the passage of a Caribbean Current eddy over the 116-day average eddy period. Flow separation at the Isthmus of Panamá results in a vortex shed from the Darien Gulf, which slows the coastal currents in the gyre region from their maximum during eddy events. An annual ensemble average PV balance in the gyre region shows that the mean PV influx to this region is higher from August to October. Correspondingly, the range of coastal currents in the gyre region over an eddy event is modestly influenced by the PV influx magnitude. Eddy-influenced reversals in the coastal current can occur between November and July at Bocas del Toro and year-round at Colón. Such coastal current reversals are important for the alongshore transport of larvae, freshwater, and chemical tracers.

Weak Temperature Gradient Modeling of Convection in OTREC

AbstractConvection observed in the OTREC field program in the tropical east Pacific and southwest Caribbean is simulated using a cloud‐resolving model employing the weak temperature gradient approximation. Simulations are made using reference profiles derived from three‐dimensional variational analyses of dropsonde data selected for different ranges of saturation fraction, a kind of column relative humidity. For each of these humidity ranges, two simulations are performed, one with ventilation of the model domain by the ambient wind (a new model feature) and one without this ventilation. The model results using ventilation are much closer to observation than those without ventilation, especially for drier environments. These results have strong implications for the distribution of ITCZ convection in the east Pacific and for the construction of cumulus parameterizations.

OTREC2019: Convection Over the East Pacific and Southwest Caribbean

AbstractWe present preliminary results from the field program Organization of Tropical East Pacific Convection (OTREC), with measurements during August and September of 2019 using the NSF/NCAR Gulfstream V over the tropical East Pacific and Southwest Caribbean. We found that active convection in this region has predominantly bottom‐heavy vertical mass fluxes, while decaying systems exhibit top‐heavy fluxes characteristic of stratiform rain regions. As in other regions that have been studied, a strong anti‐correlation exists between the low to mid‐level moist convective instability and the column relative humidity or saturation fraction. Finally, the characteristics of convection as a function of latitude differ greatly between the Southwest Caribbean and Colombian Pacific coast on one hand, and the intertropical convergence zone to the west. In particular, the strongest convection in the former is to the south, while it is to the north in the latter, in spite of similar latitudinal sea surface temperature distributions.

Metabolic Profiling of the Soft Coral Erythropodium caribaeorum (Alcyonacea: Anthothelidae) from the Colombian Caribbean Reveals Different Chemotypes.

The Caribbean soft coral Erythropodium caribaeorum is a rich source of erythrolides—chlorinated briarane diterpenoids. These compounds have an ecological role as feeding deterrents, with a wide variation in their composition depending on the location where the sample is collected. In Colombia, this soft coral can be found at different locations in the Caribbean Sea including Santa Marta, Islas del Rosario, and Providencia—three environmentally different coral reef areas in the south and southwest Caribbean Sea. In order to evaluate differences in erythrolide composition, the metabolic profiles of samples from each of these locations were analyzed by HPLC-MS. Principal component analysis showed changes in the diterpene composition according to the sample origin. Diterpenes from samples collected at each location were isolated to describe the three chemotypes. The chemotype from Santa Marta was highly diverse, with the new erythrolides W and X together with eight known erythrolides. The sample from Islas del Rosario showed a low diversity chemotype constituted by high amounts of erythrolide A and B. The chemotype from Providencia showed low chemical diversity with only two main compounds—erythrolide V and R. Evaluation of cytotoxic activity against the human cancer cell lines PC-3, MCF7, and A549 showed erythrolides A and B as the more active compounds with IC50 values in the range from 2.45 to 30 μM.

Crustal deformation in the northern Andes – A new GPS velocity field

We present a velocity field for northwestern South America and the southwest Caribbean based on GPS Continuously Operating Reference Stations in Colombia, Panama, Ecuador and Venezuela. This paper presents the first comprehensive model of North Andean block (NAB) motion. We estimate that the NAB is moving to the northeast (060°) at a rate of 8.6 mm/yr relative to the South America plate. The NAB vector can be resolved into a margin-parallel (035°) component of 8.1 mm/yr rigid block motion and a margin-normal (125°) component of 4.3 mm/yr. This present-day margin-normal shortening rate across the Eastern Cordillera (EC) of Colombia is surprising in view of paleobotanical, fission-track, and seismic reflection data that suggest rapid uplift (7 km) and shortening (120 km) in the last 10 Ma. We propose a “broken indenter” model for the Panama-Choco arc, in which the Choco arc has been recently accreted to the NAB, resulting in a rapid decrease in shortening in the EC. The Panama arc is colliding eastward with the NAB at approximately 15–18 mm/yr, and the Panama-Choco collision may have been responsible for much of the uplift of the EC. The present on-going collision poses a major earthquake hazard in northwestern Colombia from the Panama border to Medellin area. Since the northeastward margin-parallel motion of the NAB is now greater than the rate of shortening in the EC, northeast trending right-lateral strike-slip faulting is the primary seismic hazard for the 8 million inhabitants of Bogota, the capital city of Colombia. There continues to be a high risk of a great megathrust earthquakes in southern Colombia along the Ecuador-Colombia trench. Trench earthquakes have only released a fraction of the energy accumulated in the Ecuador-Colombia trench since the 1906 Ecuador earthquake, and interseismic strain is accumulating rapidly at least as far north as Tumaco, the rupture area of the 1979 earthquake.

Shell shape variation of queen conch Strombus gigas (Mesograstropoda: Strombidae) from Southwest Caribbean

The endangered species Strombus gigas is a marine gastropod of significant economic importance through the Greater Caribbean region. In contrast to phenotypic plasticity, the role of genetics on shell variations in S. gigas has not been addressed so far, despite its importance in evolution, management and conservation of this species. This work used geometric morphometrics to investigate the phenotypic variation of 219 shells of S. gigas from eight sites of the Colombian Southwest Caribbean. Differences in mean size between sexes and among sites were contrasted by analysis of variance. Allometry was tested by multivariate regression and the hypothesis of common slope was contrasted by covariance multivariate analysis. Differences in the shell shape among sites were analyzed by principal component analysis. Sexual size dimorphism was not significant, whereas sexual shape dimorphism was significant and variable across sites. Differences in the shell shape among sites were concordant with genetic differences based on microsatellite data, supporting its genetic background. Besides, differences in the shell shape between populations genetically similar suggest a role of phenotypic plasticity in the morphometric variation of the shell shape. These outcomes evidence the role of genetic background and phenotypic plasticity in the shell shape of S. gigas. Thus, geometric morphometrics of shell shape may constitute a complementary tool to explore the genetic diversity of this species.

Variación fenotípica de la langosta espinosa Panulirus argus (Decapoda: Paniluridae) en el Caribe Suroccidental

The spiny lobster Panulirus argus is an important fishery species in the Western Central Atlantic. Changes in the dispersion range through its life cycle and heterogeneous habitats, suggest that P. argus exhibit phenotypic plasticity. However, the morphometric variation of this species is unknown so far, although this information is relevant in evolutionary studies as well as to solve questions of fishery interest. Thus, the aim of this study was to determine whether P. argus exhibit phenotypic variation between sexes, among five geographic origins and three oceanographic conditions of Southwest Caribbean (Colombian archipelago San Andrés, Providencia y Santa Catalina). A total of 193 P. argus adults were submitted to geometric morphometrics using six landmarks that delimit one half of the sternal plate. The differences in sternal plate size were compared with Kruskal-Wallis and Mann-Whitney Tests. The allometric effect was estimated using Multivariate Regression Analysis, the model of allometric slopes was tested by Multivariate analysis of covariance and the sternal plate shape differences was explored using non-parametric comparisons of Euclidian distances and Neighbour Joinnig trees. The results showed that the morphometric variation of sternal plate of this spiny lobster varied according to the gender since the sexual size and shape dimorphisms were significant. In both sexes, the sternal plate shape differed among oceanographic scenarios as it was evidenced by significant differences among Euclidian distances, and the tendency to cluster by North, Centre and South sections of San Andrés archipelago. Additionally, the morphometric variation resulting from phenotypic plasticity to variable ecological contexts may explain the phenotypic differences among genetically similar populations. This information permits to define management units, support the selection of regulatory policies of this fishery and complement the genetic analysis of the species in this Caribbean region.

Changes in bivalve functional and assemblage ecology in response to environmental change in the Caribbean Neogene

We documented changes in the relative abundance of bivalve genera and functional groups in the southwest Caribbean over the past 11 Myr to determine their response to oceanographic changes associated with the closure of the Central American Seaway ca. 3.5 Ma. Quantitative bulk samples from 29 localities yielded 106,000 specimens in 145 genera. All genera were assigned to functional groups based on diet, relationship to the substrate, and mobility. Ordinations of assemblages based on quantitative data for functional groups demonstrated strong shifts in community structure, with a stark contrast between assemblages older than 5 Ma and those younger than 3.5 Ma. These changes are primarily due to an increase in the abundance of attached epifaunal bivalves (e.g.,Chama,Arcopsis, andBarbatia) and a decrease in infaunal bivalves (e.g.,VaricorbulaandCaryocorbula). Taxa associated with seagrasses, including deposit-feeding and chemosymbiotic bivalves (e.g.,Lucina), also increased in relative abundance compared to suspension feeders. The composition of bivalve assemblages is correlated with the carbonate content of sediments and the percentage of skeletal biomass that is coral. Our results strongly support the hypothesis that increases in the extent of coral reefs andThalassiacommunities were important drivers of biologic turnover in Neogene Caribbean benthic communities.

Cytotoxic and Antimicrobial Activity of Pseudopterosins and seco-Pseudopterosins Isolated from the Octocoral Pseudopterogorgia elisabethae of San Andrés and Providencia Islands (Southwest Caribbean Sea)

To expand the potential of pseudopterosins and seco-pseudopterosins isolated from the octocoral Pseudopterogorgia elisabethae of San Andrés and Providencia islands (southwest Caribbean Sea), we report the anti-microbial profile against four pathogenic microorganisms (Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Candida albicans) and report a more complete cytotoxic profile against five human cells lines (HeLa, PC-3, HCT116, MCF-7 and BJ) for the compounds PsG, PsP, PsQ, PsS, PsT, PsU, 3-O-acetyl-PsU, seco-PsJ, seco-PsK and IMNGD. For the cytotoxic profiles, all compounds evaluated showed moderate and non-selective activity against both tumor and normal cell lines, where PsQ and PsG were the most active compounds (GI50 values between 5.8 μM to 12.0 μM). With respect to their anti-microbial activity the compounds showed good and selective activity against the Gram-positive bacteria, while they did not show activity against the Gram-negative bacterium or yeast. PsU, PsQ, PsS, seco-PsK and PsG were the most active compounds (IC50 2.9–4.5 μM) against S. aureus and PsG, PsU and seco-PsK showed good activity (IC50 3.1–3.8 μM) against E. faecalis, comparable to the reference drug vancomycin (4.2 μM).

Subduction in the southern Caribbean: Images from finite‐frequency P wave tomography

The eastern boundary of the Caribbean plate is marked by subduction of the Atlantic under the Lesser Antilles. The southeastern plate boundary is characterized by a strike‐slip margin, while different configurations of subduction of the southwest Caribbean under South America have been proposed. We investigate the slab geometry in the upper mantle using multiple‐frequency, teleseismic P wave tomography. Waveforms from P and PKPdf phases from 285 (Mb > 5.0) events occurring at epicentral distances from 30° to 90° and greater than 150° were bandpass filtered and cross‐correlated to obtain up to three sets of delay times for each event. The delay times were inverted using approximate first Fresnel zone sensitivity kernels. Our results show the subducting Atlantic slab, as well as a second slab in the west of the study area that we interpret as a subducting fragment of the Caribbean plate. Both slabs have steep dips where imaged and can be traced to depths greater than 600 km. These results are consistent with transition zone boundary topography as determined by receiver function analysis. The Atlantic slab extends continent‐ward south of the plate bounding strike‐slip margin. We interpret this extension as continental margin lithospheric mantle that is detaching from beneath South America and subducting along with the oceanic Atlantic slab. The steep subduction of the Caribbean occurs ∼500 km landward from the trench, implying an initial stage of shallow subduction as far to the east as the Lake Maracaibo‐Mérida Andes region, as has been inferred from intermediate depth seismicity.

Ecology of extreme faunal turnover of tropical American scallops

The marine faunas of tropical America underwent substantial evolutionary turnover in the past 3 to 4 million years in response to changing environmental conditions associated with the rise of the Isthmus of Panama, but the ecological signature of changes within major clades is still poorly understood. Here we analyze the paleoecology of faunal turnover within the family Pectinidae (scallops) over the past 12 Myr. The fossil record for the southwest Caribbean (SWC) is remarkably complete over this interval. Diversity increased from a low of 12 species ca. 10–9 Ma to a maximum of 38 species between 4 and 3 Ma and then declined to 22 species today. In contrast, there are large gaps in the record from the tropical eastern Pacific (TEP) and diversity remained low throughout the past 10 Myr. Both origination and extinction rates in the SWC peaked between 4 and 3 Ma, and remained high until 2–1 Ma, resulting in a 95% species level turnover between 3.5 and 2 Ma. The TEP record was too incomplete for meaningful estimates of origination and extinction rates. All living species within the SWC originated within the last 4 Myr, as evidenced by a sudden jump in Lyellian percentages per faunule from nearly zero up to 100% during this same interval. However, faunules with Lyellian percentages near zero occurred until 1.8 Ma, so that geographic distributions were extraordinarily heterogeneous until final extinction occurred. There were also striking differences in comparative diversity and abundance among major ecological groups of scallops. Free-swimming scallops constituted the most diverse guild throughout most of the last 10 Myr in the SWC, and were always moderately to very abundant. Leptopecten and Argopecten were also highly diverse throughout the late Miocene and early Pliocene, but declined to very few species thereafter. In contrast, byssally attaching scallops gradually increased in both diversity and abundance since their first appearance in our samples from 8–9 Ma and are the most diverse group today. Evolutionary turnover of scallops in the SWC was correlated with strong ecological reorganization of benthic communities that occurred in response to declining productivity and increased development of corals reefs.

Eocene-Pliocene planktonic foraminifera biostratigraphy from the continental margin of the southwest Caribbean

Biostratigraphy in northern Colombia has traditionally been done using foraminifera. Quantitative biostratigraphic techniques could improve the zonations that have been proposed for the region. We analyze the biostratigraphic information from 190 planktonic foraminifera species, and 1961 ditch-cutting samples from 26 oil wells in northern Colombia to produce a zonation for the region. A quantitative biostratigraphic technique known as Constrained Optimization was used to analyze the data. The proposed zonation relies exclusively on last occurrences, which are readily applied to petroleum exploration. It has thirteen zones and eight subzones for the Eocene to Pliocene interval. Three zones and two subzones are defined for the Eocene, three zones for the Oligocene, six zones and six subzones for the Miocene, and one zone for the Pliocene. The zonation reveals three major unconformities: (1) a late Eocene - early Oligocene hiatus; (2) a late Oligocene - early Miocene hiatus; and (3) a late Miocene hiatus; the hiatuses are related to the collision of the Caribbean with the South American plate.

Vegetation Structure, Composition, and Species Richness Across a 56‐year Chronosequence of Dry Tropical Forest on Providencia Island, Colombia1

ABSTRACTWe compared vegetation structure and species richness across a 56‐yr chronosequence of six replicated age classes of dry tropical forest on the island of Providencia, Colombia, in the Southwest Caribbean. Stand age classes were determined using sequential, orthorectified panchromatic aerial photos acquired between 1944 and 1996 and Landsat 7 ETM + satellite imagery from 2000. Along the chronosequence we established 59 plots of 2 × 50 m (0.01 ha) to document changes in species richness, basal area, tree height, stem density, and sprouting ability. All woody trees and shrubs >2.5 cm diameter at breast height (DBH) were censused and measured. Although woody species density reached a peak in stands from 32 to 56 yr old, rarefaction analysis showed that species richness increased linearly with stand age and was highest in stands 56 yr old or greater. Nonparametric, abundance‐based estimators of species richness also showed positive and linear associations with age. Basal area and mean tree height were positively associated with age since abandonment, while sprouting ability showed a negative relationship. Our results indicate rapid recovery of woody species richness and structural characteristics along this tropical dry forest chronosequence.

Morphology, Sediments, and Depositional Environments of a Small Carbonate Platform: Serranilla Bank, Nicaraguan Rise, Southwest Caribbean Sea

Serranilla Bank (16 degrees N, 80 degrees W) is located on the Nicaraguan Rise, a major structural-topographic high on the Caribbean Plate. This bank is one of several small, detached platforms upon which carbonate accretion is failing to keep pace with Holocene sea-level rise. High-resolution seismic profiling, sediment sampling, SCUBA-diver observations, and dredge hauls show that this relatively deep (10 to 40 m) bank is bounded by steep escarpments, lacks coral-reefs, and has few islands and minimal Holocene sediment cover. Hardgrounds populated by brown algae and sponges predominate in the southeastern sector; sediments are thin and coarse-grained. On the remainder of the bank, Halimeda /molluscan-dominated sediments are more common and finer-grained. Sediment cover on about 80% of the banktop is too thin to resolve seismically (< 2 m), though some topographic lows have slightly thicker accumulations that occur as large (3-8 m high) bedforms indicating northwestward transport. The largest field of bedforms is located near the northwestern margin of the platform. Platform-margin sediment deposits are limited in thickness and areal extent. Muds are scarce and are winnowed off-shelf by strong currents. Factors limiting Holocene sediment accretion on Serranilla Bank include the platform's small size, strong currents that promote off-bank sediment transport, rapid flooding during Holocene sea-level rise, lack of active frame-building benthic communities, and ubiquitous bioerosion.

Multiple Megabreccia Shedding from Low-Relief Carbonate Platforms in an Active Tectonic Setting: Nicaraguan Rise, Southwest Caribbean Sea: ABSTRACT

Multiple Megabreccia Shedding from Low-Relief Carbonate Platforms in an Active Tectonic Setting: Nicaraguan Rise, Southwest Caribbean Sea: ABSTRACT

Rhodolite and Encrusted-Grain Sedimentation, Thunder and Lightning Knolls, Southwest Caribbean Sea: ABSTRACT

Rhodolite and Encrusted-Grain Sedimentation, Thunder and Lightning Knolls, Southwest Caribbean Sea: ABSTRACT

Extreme Variation in Settlement of the Caribbean Triggerfish Balistes vetula in Panama

In Spring 1985 a mass settlement of pelagic juveniles of the triggerfish Balistes vetula occurred in the eastern half of the southwest Caribbean, but not elsewhere in the tropical western Atlantic. This distribution of recruitment is correlated with major surface water currents: the southwest Caribbean is partly isolated from the rest of the Caribbean and has separate eastern and western current eddies. Settlers were 4.9-7.0 cm long, and estimated to be 66-86 d old. At Punta de San Bias (Panama) the abundance of settlers that arrived in 1985 was at least 50-100 times greater than in any other year since at least 1979. The mass settlement produced a 1.5 fold increase in the adult population at that site, but B. vetula adults remained uncommon (at about 5% the density which can occur elsewhere). ( ), p. 698-703

Experiments on the strength of materials

We present a velocity field for northwestern South America and the southwest Caribbean based on GPS Continuously Operating Reference Stations in Colombia, Panama, Ecuador and Venezuela. This paper presents the first comprehensive model of North Andean block (NAB) motion. We estimate that the NAB is moving to the northeast (060°) at a rate of 8.6 mm/yr relative to the South America plate. The NAB vector can be resolved into a margin-parallel (035°) component of 8.1 mm/yr rigid block motion and a margin-normal (125°) component of 4.3 mm/yr. This present-day margin-normal shortening rate across the Eastern Cordillera (EC) of Colombia is surprising in view of paleobotanical, fission-track, and seismic reflection data that suggest rapid uplift (7 km) and shortening (120 km) in the last 10 Ma. We propose a “broken indenter” model for the Panama-Choco arc, in which the Choco arc has been recently accreted to the NAB, resulting in a rapid decrease in shortening in the EC. The Panama arc is colliding eastward with the NAB at approximately 15–18 mm/yr, and the Panama-Choco collision may have been responsible for much of the uplift of the EC. The present on-going collision poses a major earthquake hazard in northwestern Colombia from the Panama border to Medellin area. Since the northeastward margin-parallel motion of the NAB is now greater than the rate of shortening in the EC, northeast trending right-lateral strike-slip faulting is the primary seismic hazard for the 8 million inhabitants of Bogota, the capital city of Colombia. There continues to be a high risk of a great megathrust earthquakes in southern Colombia along the Ecuador-Colombia trench. Trench earthquakes have only released a fraction of the energy accumulated in the Ecuador-Colombia trench since the 1906 Ecuador earthquake, and interseismic strain is accumulating rapidly at least as far north as Tumaco, the rupture area of the 1979 earthquake.