Colombian Basin Research Articles

Fracture evaluation of the plutonic basement in the Upper Magdalena Basin: Implications for the development of naturally fractured reservoirs in the Northern Andes

Plutonic rocks typically have negligible matrix porosity and permeability. However, fractures and mineral alterations create storage space and flow pathways that turn plutonic rocks into fluid reservoirs. Despite significant hydrocarbon discoveries, naturally fractured reservoirs in plutonic rocks have been poorly studied. In most Colombian basins, the crystalline basement has undergone multiple deformational events and is thrust over the Cretaceous to Cenozoic source and reservoir rocks of the conventional petroleum system. This structural configuration is ideal for the migration of oil into a fractured basement. A multiscale fracture analysis, including field, petrographical and petrophysical techniques was conducted on the Permian and Jurassic plutonic basement of Upper Magdalena Basin in order to understand the controls on brittle deformation, the development of fracture networks and their potential to form hydrocarbon reservoirs. The results indicate that protolith textures and structures, including magmatic and mylonitic foliation, favours fracturing. Dykes exhibit higher fracture density (7–48 fractures/m), porosity (mean = 0.4%) and permeability (mean = 125,818.75 mD) than the host rock (2–25 fractures/m; 0.23%; 12,066.09 mD). Intersection zones from regional faults, are characterized by the highest fracture and lineament intensity. Our results suggest that dyke swarms and interacting damage zones can significantly enhance the reservoir quality of plutonic rocks by providing storage in fractures and fluid pathways to the host rock.

Ocean tides in the colombian basin and atmospheric contribution to S2

The tidal behavior in the Colombia basin is described based on the analysis of eighteen tide gauge time series, fourteen in the Colombian coasts and four placed in neighboring countries. Tidal constituents are published for the first time at nine of these stations. Harmonic analysis shows that the main constituents in the Caribbean correspond to three diurnals (K1, O1, P1); three semidiurnals (M2, N2, S2), and one long period harmonic (Mf), showing amplitudes and phase lag that correspond to previous tidal reports in the basin. In Turbo, due to the shallow and extensive continental shelf in the Urabá gulf, M2 is amplified, and shallow water harmonics appear. The amplitude and phase of each observed constituent are compared with global tide models FES2014, TPXO9 and DTU10, showing good agreement. The most significant differences occur with semidiurnal harmonics at stations close to the amphidromic point in the eastern Caribbean. In Mf, considerable interannual variations are found, supporting the need of over one year of sea level data to assess this constituent in the Colombia basin accurately. The radiational component of S2 is assessed using barometric pressure in thirteen stations, confirming its importance when compared to the gravitational contribution to the observed sea level harmonic. A trend in the atmospheric S2 is found in Cartagena, which supports those trends in sea-level S2, previously reported in the Caribbean Sea, are caused by variations in the radiational forcing.

Performance of high-resolution precipitation datasets CHIRPS and TerraClimate in a Colombian high Andean Basin

High-resolution reanalysis products could improve the representativeness of rainfall on high Andean basins, but their performance must be locally validated. We addressed the performance, accuracy, and ability of TerraClimate and CHIRPSv.2 to represent 36 years of rainfall (1985–2020) from 23 stations in the Upper Chicamocha River, a Colombian basin of complex terrain and tropical hydrometeorology. Using several statistical metrics at monthly, seasonal and annual scales, we found how both datasets overestimate rainfall as a function of elevation, with better performance and accuracy from CHIRPS (r ∼0.76, R2 ∼0.58, NSE ∼0.56, and low RMSE ∼33.7 mm/month, MAE ∼25.2 mm/month, ME ∼6.4 mm/month, and PBIAS ∼9.3), while TerraClimate overestimates inter-annual variability, especially between June and August. Seasonally, the datasets exhibit different spatial patterns and magnitudes, even after bias correction. The findings highlight the potential use and challenges of high-resolution datasets in basins with similar topography and hydrometeorology in the Andean region.

Numerical modeling of oil spills in the Gulf of Morrosquillo, Colombian Caribbean

This study encompasses the analysis of oil spills occurred in the Gulf of Morrosquillo during the loading procedures of oil tankers in the Coveñas maritime Terminal, by means of numerical simulation experiments of the trajectories and weathering processes of oil spilled, which occurred under specific wind, waves, and ocean currents conditions. A three-dimensional (3D) modelling system, OpenOil, which is part of the open-source OpenDrift trajectory framework was used to simulate two contingencies occurred in July and August 2014. During each event, different volumes of Vasconia crude oil spilled on the sea surface were simulated. The resulting slicks were subject to wind drift, Stokes drift from wave forcing, and ocean currents transporting the oil spilled towards the coast. Oil weathering effects (evaporation, emulsification, and biodegradation) are included in the analysis. To calculate weathering of the oil, OpenOil interfaces with the latest version of the open source ADIOS oil library. It should be noted that meteorological and ocean conditions contribute to the oil pathways that in both periods forced the oil slick towards the central coast of the Gulf. The wind speed is an important factor contributing to the rapid evaporation rates of the oil spilled in the warm waters of the Caribbean Sea; hence, allowing a gradual increase of the water fraction, which could lead to the formation of tar balls found in the affected coasts in the areas simulated by the model. The implementation of OpenOil to predict the oil fate and weathering processes in the Colombian basin prove to be a valuable tool that should be used in this maritime terminal to improve planning and preparedness in case of an oil spill. The simulations could be enhanced with higher resolution databases.

Horizontal/vertical motion and wedge geometry of the Sinú Fold Belt, South-Caribbean accretionary prism, NW Colombia: Implications for a morphostructural zoning

The Sinú Fold Belt, located in the southwestern part of the South Caribbean Deformed Belt, northwest Colombia, has been interpreted as the outer portion of an accretionary wedge resulting from the subduction of the Caribbean Plate under the South American Plate. Several geological sections, across and along the offshore portion of the Sinú Fold Belt, have been constructed through geological interpretation of 2D seismic sections constrained by a few exploration wells. Their analysis has allowed us to quantify the amount of horizontal motion (shortening responsible for the structures and basal detachment displacement) and vertical motion (tectonic subsidence/uplift and wedge vertical thickening) undergone by the belt over time; unravel its recent evolution consisting of almost no active structures in the south edge and a large amount of active structures northwards; quantify its pore pressure, coefficient of friction and strength using its wedge geometry consisting of high taper angles in the lower continental slope near the deformation front and lower taper angles in the upper continental slope away from it; and understand the aseismic and trench-lacking character of the belt. These observations have been crucial to identify the main features of the morphostructural zones across the belt (Colombian Basin, lower continental slope, upper continental slope and continental shelf) and establish a new along-strike zoning (north region influenced by the Magdalena Fan/Canoas Oblique Ramp, Sinú Fold Belt s.s., and south salient influenced by the Uramita Fault).

Seismic analysis of the geological occurrence of gas hydrate in the Colombian Caribbean offshore

The bottom-simulating reflector (BSR) recognized in seismic sections represents the division between free gas and gas hydrate. This reflector has been identified in the permafrost and several petroliferous marine basins worldwide, including the Colombia offshore basins. Using high quality three-dimensional (3D) seismic data from the Sinú offshore basin (southern Caribbean), the BSR was exceptionally well-imaged within two geomorphological settings, including the Southern Caribbean Deformed Belt and the Colombia Basin, indicating possible gas hydrate presence in the study area. The BSR occurrence was mapped and categorized following existing nomenclature developed off Taiwan into three (3) categories: Basin-type, Ridge-type and Submarine Canyon-type. The BSR occurrence was dominated by the Ridge type category that was mainly found in the accretionary prism within modern and ancient anticlinal structures, followed by the Basin-type BSR found mainly at the Colombia Basin margin and a few intraslope sub-basins. The Submarine Canyon-type was found on small segments of the main drainage routes that cut through anticlinal structures. BSR distribution and characterization was also correlated with a seabed geomorphologic map, including thrusts with bathymetric expression, revealing that the BSR typology map closely resembled the N–S trend of subsurface structures in the south, as well as their NE-SW trend in the central portion of the accretionary prism. We suggest the dimensions (width and depth) of the seafloor features does influence BSR occurrence, tending to parallel major anticlines, and wider/deeper portions of intraslope sub-basins and submarine canyons, while omitting small-scale features.

Can We Better Constrain the Timing of GNAIW/UNADW Variability in the Western Equatorial Atlantic and Its Relationship to Climate Change During the Last Deglaciation?

AbstractWe have revisited the well‐trod VM28‐122 core retrieved from the deep Colombian Basin, which includes sediments that reflect modern Upper North Atlantic Deep Water and extends through the last deglaciation into the last glacial period when the site was bathed in Glacial North Atlantic Intermediate Water. Here, we leverage the nearby Cariaco Basin's surface water radiocarbon reconstruction (reservoir age, and ΔR) on the IntCal20 timescale to recast the period of the last deglaciation with a newly constrained age model. Based on the revised age model, we observe that the multimillennial decrease in benthic δ13C and B/Ca (which record δ13C of dissolved inorganic carbon and Δ[CO3−2], respectively) began at 18,100 ± 240 (95% CI) calibrated years BP, synchronous with Termination 1, as identified by changes in the Antarctic Ice Sheet composite and by the onset of rapid glacier recession in the Southern Hemisphere (Denton et al., 2010, https://doi.org/10.1126/science.1184119; Denton et al., 2021, https://10.1016/j.quascirev.2020.106771). The beginning of the decrease in benthic δ18O is concurrent with the changes in carbon chemistry or at most, a few hundred years later. It is no later than 17,700 ± 300 (95% CI) yrs BP in our record, at the putative start of Heinrich Stadial 1. With sufficient data density (more than 2–3 control points per kyr) and an independent record of past surface water radiocarbon variations, it is possible to achieve late glacial and deglacial chronologies with fidelities similar to those of ice cores. Doing so in more oceanographic locations should shed light more broadly on the mechanisms instrumental to abrupt climate change.

Structure, age, and origin of the Caribbean Plate unraveled

Our compilation of marine magnetics of the Caribbean Plate allows us to identify magnetic anomalies from the Cretaceous Normal Superchron (CNS) in the Colombia and Venezuela basins, from which we propose a model for the age and origin of the Caribbean Plate and its Large Igneous Province (CLIP). The comparison of selected marine magnetic profiles across these basins with high resolution profiles from other areas across the CNS indicates that the Colombia Basin formed 73-92 million years ago (Ma) and the Venezuela Basin 92-108 Ma. The two basins and the older part of the CLIP formed at a ridge axis in the Pacific Ocean, near the Central American Seaway. These results strongly constrain regional plate tectonic models for America and the Pacific Ocean.

Mass balance of Neogene sediments in the Colombia basin relationship with the evolution of the Magdalena and Cauca River basins

The Colombia basin contains large volumes of sediment accumulated during the last 17 My. The use of isochore maps, exploratory wells, micropaleontological and geochronological dates has enabled us to estimate the volumes of sediment and accumulation rates in this basin. The analysis of source of sediments and exhumation data from the Northern Andes of South America led to the definition of areas and thicknesses of material eroded during the Neogene - Quaternary, to obtain volumes or material eroded from the continent that can be correlated with sediment volumes accumulated in the Colombia Basin. The analyzed sediment volumes suggest that during the last 17 My ~72.06x1015 Tons accumulated in the Colombia Basin, while ~ 7.16x1013 Tons accumulated in the continental catchment areas. The sedimentation in the Colombian Basin has occurred at variable rates, with values ranging from 55 MTons/My to 295 MTons/My, with a peak of 803 MTons/My in the early Pleistocene (between 2.4 and 2.2 Ma). The evaluation between the total volumes of sediment accumulated in the offshore and onshore, suggests that in the continental part of the basin less than 4% of the total volume of eroded sediment is trapped and, therefore, the behavior of the accumulation rates calculated in the offshore directly reflect the relief evolution of South America’s Northern Andes. It seems, at large, that the lithospheric convergence rates and subduction angle (South America vs Nazca and Meso Atlantic opening) have controlled the regional exhumation of the Northern Andes, with the exception of the Pleistocene high sedimentation event, which seems to coincide with local events such as the collision of the Panama Arch against Western Antioquia. It may be concluded that thanks to this collision, drainage systems such as those of the Magdalena and Cauca rivers were modified, which resulted in the formation of the Magdalena Submarine Fan.

Submarine geomorphology, tectonic features and mass wasting processes in the archipelago of San Andres, Providencia and Santa Catalina (western Caribbean)

Recent acquisition of multibeam bathymetric data in western Caribbean allowed illuminating for the first time the submarine morphology of the Archipelago of San Andres, Providencia and Santa Catalina (ASAPSC), and surrounding areas. Our results show that the nine islands of the archipelago (San Andres, Providencia, Albuquerque, Este-Sureste, Roncador, Quitasueño, Serrana, Serranilla and Bajo Nuevo) correspond to the emerged portions of a belt of volcanic edifices extending along the ASAPSC seafloor. Overall, the submarine slopes are characterized by having steep flanks that extend to depths greater than −2000 m and are frequently cut by linear gullies and canyons. The submarine volcanic buildings are aligned in specific directions, parallel to the trends of the main fault systems in the area, indicating that the genesis and evolution of the archipelago have been strongly influenced by the interplay between volcanism and tectonics. Moreover, the presence of several pull-apart basins (Providencia, Albuquerque, Nutibara, Cunas and Guambiano depressions) related to S-shaped releasing bends in the Albuquerque-Providencia, Pedro and Serrana fault systems evidences that an intraplate transtensional tectonics is currently operating in this sector of the Caribbean plate. We propose that the ASAPSC belongs to the Northwestern Caribbean Volcanic Province (NCVP), which corresponds to a province made of an oceanic crust highly affected by volcanism sandwiched between a block composed of continental crust (Upper Nicaraguan Rise) and a block underlain by a CLIP-type to normal oceanic crust (Colombia Basin). Finally, the identification of massive debris avalanche deposits and large-scale bedforms shows that mass wasting processes have been common in the most recent history of the ASAPSC. This implies that collapses of the seamount flanks and the subsequent generation of tsunamis should be considered as a new threat to the coastal zones of the western Caribbean Sea.

Modelling the transport of sediment discharged by Colombian rivers to the southern Caribbean Sea

The three-dimensional transport of sediments released by the main rivers in the Colombian Caribbean basin is investigated using numerical model simulations. Different types of sediments (fine sands, very fine sands and coarse silts) were tracked by implementing SedimentDrift software, a subclass of the OpenDrift open-source trajectory framework. The simulations were forced with climatological winds from ERA-5 and currents from the Copernicus Marine Environment Monitoring Service (CMEMS). In situ measurements from the area were utilised in the evaluation of the forcing fields. The diagnostic analysis of ERA-5 and CMEMS at the evaluated stations in the Colombian basin led to the conclusion that these datasets are reliable; hence, they can be used for several oceanographic and coastal engineering studies. The sediment transport of non-cohesive particles at each river mouth is subject to the variability of local hydrodynamics, morphological features and the grain size, which determines the settling velocities. These factors were considered and evaluated in detail. Given the lack of available in situ information, the performance of the Lagrangian model is evaluated by comparing the resulting simulations with previous studies reported in the area for river plume dynamics. However, this study presents an initial analysis of the pathways that sediments of different sizes follow, from the river mouth to the seafloor. This approach is convenient given that the Colombian rivers deliver large amounts of sediment of various grain sizes, there are insufficient in situ data to assess the seasonal cycle of sediment transport and many aspects of the sediment dynamics are not fully resolved. The resulting simulations provide evidence of the importance of high-resolution ocean current data, given that this is the main factor determining the trajectories and dispersion patterns at seasonal scales.

Development of microsatellite loci and population genetics in the bumblebee catfish species Pseudopimelodus atricaudus and Pseudopimelodus magnus (Siluriformes: Pseudopimelodidae)

ABSTRACT The Neotropical freshwater catfish Pseudopimelodus atricaudus and Pseudopimelodus magnus are two recently discovered species endemic to the Colombian Magdalena-Cauca River basin. In this study, a set of 13 microsatellite loci were developed by using next generation sequence technology to assess the genetic diversity and population structure in P. atricaudus and test for cross-species amplification in P. magnus. Both species exhibited high genetic diversity (P. atricaudus: Na: 9.000 - 9.769 alleles/locus, Ho: 0.760 - 0.804, HE: 0.804 - 0.840; P. magnus: Na: 12.8 - 5.4 alleles/locus, Ho: 0.638 - 0.683, HE: 0.747 - 0.755) compared to the mean levels of genetic diversity reported for Neotropical Siluriformes, and lack of genetic differentiation among sampling sites within the Cauca River (P. atricaudus: F’ST=0.013 - 0.017, P > 0.05, D’est= -0.004 - 0.023, P > 0.05; P. magnus: F’ST= 0.031, P= 0.055; D’est= 0.045, P= 0.058). This work is the first insight on the diversity and the population genetics of species of the family Pseudopimelodidae and provides a framework to further population genetic and conservation analyses needed in this poorly studied family at the microevolutionary level.

Structural style and evolution of the offshore portion of the Sinu Fold Belt (South Caribbean Deformed Belt) and adjacent part of the Colombian Basin

The Sinu fold belt, located in northwestern Colombia, is the southwesternmost part of the South Caribbean Deformed Belt, which has been interpreted as an accretionary wedge resulting from the subduction of the Caribbean Plate under the South American Plate. The geological interpretation of 2D seismic surveys and bathymetric maps, with the aid of a few exploration wells, has been the basis to construct a structural map and several geological sections to illustrate the offshore part of the Sinu Fold Belt and the portion of the Colombian Basin adjacent to the belt. Their analysis has allowed us to characterize different structural styles (thrusts and related folds in the outer part of the belt, and normal faults and shale diapirs in the inner one), the timing of the structures, as well as the kinematic evolution from a Cretaceous-Paleocene extensional event responsible for the Colombian Basin structure to the Pliocene-Quaternary contractional event which caused the Sinu Fold Belt.

Structure, stratigraphy, and petroleum potential of the deepwater Colombian Basin, offshore northern Colombia

We have defined the structure and stratigraphy of the central area of the Colombian Basin — offshore of the northern Caribbean coast of Colombia — using approximately 8400 line km of depth-converted 2D seismic data assembled from academic and industry sources. We integrate information from offset deep sea drilling program and ocean drilling program wells into a structural and stratigraphic model of the Colombian Basin, identifying the key elements of a petroleum system. These elements are (1) Upper Cretaceous marine shale source rock, (2) Middle to Upper Miocene (16–5.3 Ma) basin-floor fans associated with the Magdalena fan turbidite system, (3) structural traps and stratigraphic traps, and (4) sealing intervals formed by Miocene hemipelagic marine shale associated with sea-level high-stands. We extend a previously recognized trap type for the Colombian margin to include stratigraphic traps within the distal Miocene Magdalena fan section. We base our interpretations upon seismic observations of amplitude anomalies conformant with structures; fluid migration pathways along faults; and bright, laterally continuous, and low-impedance seismic reflectors. The primary risk for the exploration potential of the area is the presence of a laterally extensive Upper Cretaceous source rock within the main Colombian basin depocenter. The 1D burial history models and 3D basin modeling indicate that a source rock of this age and at this stratigraphic level would have expelled hydrocarbons during Middle to Late Miocene from the deepest part of the basin and may continue to expel hydrocarbons in the present day.

Genetic Diversity of the Cichlid Andinoacara latifrons (Steindachner, 1878) as a Conservation Strategy in Different Colombian Basins.

Cichlids constitute a diverse monophyletic group that have developed adaptive strategies to thrive in diverse environments. Andinoacara represents an example of diversification on the South American Andean uplift, providing a key model for understanding the evolution of biogeographic patterns. In this study, we analyzed the species Andinoacara latifrons using two mitochondrial markers (COI, cytb) and one nuclear marker (RAG1) in a populational level. Sequences were obtained through tissue collection and from the GenBank database. Populational analysis showed significant structuration among populations, also corroborated with population pairwise Fst results. Fu’s Fs and Tajima’s D results showed populations that seems to be under populational expansion. We identified 22 haplotypes using cytb. The population associations in the Cauca haplotype are related to the Momposina depression and the mixture of the Cauca-Magdalena river basins in the lower Cauca-Magdalena region. We constructed a new phylogenetic tree, which grouped mainly two A. latifrons lineages: (1) an upper Magdalena and Catatumbo clade and (2) an upper Cauca and upper Magdalena clade. Thus, A. latifrons represents a diverse entity that contributes to our understanding of the evolutionary history of northern South America. Our findings provide insight into devising public policies in determining refuges for the preservation of biodiversity in the lower Cauca and Magdalena regions in Colombia.

Basin modeling of Late Cretaceous / Mio-Pliocene (.) petroleum system of the deep-water eastern Colombian Basin and South Caribbean Deformed Belt

Previous interpretation of 2D and 3D seismic reflection data have shown widespread, direct hydrocarbon indicators from deep-water successions of the eastern Colombian Basin (ECB) and adjacent South Caribbean Deformed Belt (SCDB) that suggest the presence of an extensive - but poorly defined - petroleum system. We integrate Rock-Eval analysis, seismic interpretation, and 1D/2D thermal and basin modeling to better understand the origin of gas chimneys and bright spots identified in the ECB. Our dataset consists of 36 Rock-Eval samples of Coniacian to Santonian source rocks from the DSDP well sites 153, 151, and 146 located in the Beata Ridge tied to a 270 km-long composite 2D seismic line covering the ECB. Rock-Eval analyses reveal intervals of immature source rocks containing 1) kerogen types II and III; 2) an average TOC of 3.70% with a maximum TOC of 11.4%; 3) an average HI of 241; and 4) an average OI of 124. Seismic interpretation reveals: 1) wedging of post-Coniacian, organic-rich successions from the Beata Ridge (35–73 m thick) towards the ECB (500–1700 m thick); 2) Late Cretaceous to Eocene slow sedimentation rate of 38 m/my, followed by faster Oligocene to Recent sedimentation rate of 149 m/my from the Magdalena River; and 3) Late Oligocene to Recent thrusting and propagation of the SCDB. Thermal and basin modeling show: 1) mature Cretaceous source rocks in the SCDB and ECB; 2) Miocene to Pliocene, Magdalena Fan-derived deltaic and turbiditic reservoir and seal rocks, and Plio-Pleistocene sealing mass transport deposits.; 3) Late Oligocene to present-day trap formation related to thrust front structures, compaction folds, and stratigraphic traps; 4) hydrocarbon expulsion since Pliocene times; 5) vertical and lateral up-dip seaward migration occurs in the ECB while a secondary landward migration takes place toward the SCDB; and 6) hydrocarbon accumulation and preservation may be affected by remobilization due to biodegradation in the ECB and trap breaching in the SCDB.

Heavy oil in-situ upgrading evaluation by a laboratory-calibrated EoS-based reservoir simulator

A laboratory-calibrated numerical model was designed and computationally accelerated that allows for evaluating the performance of the in-situ upgrading technology applied to heavy oil reservoirs during steamflooding operations. The kinetic model, based on SARA measurements, represents aquathermolysis reactions and the thermodynamic oil behavior. Mass and energy transport equations were coupled to a rigorous three-phase equation of state, including the nanoparticle transport and retention by non-equilibrium equations. The coupling was validated employing available information such as PVT data before upgrading, the evolution of composition during a batch-reactor test, and residual oil saturation reduction by nanocatalyst retention. This approach allows for reproducing the API gravity enhancement and the oil viscosity reduction during a steamflooding experiment under the presence of a metallic-composed nanocatalyst. Considering uncertainty upon retention and wettability alteration, laboratory parameters were up-scaled to simulate steam and nanocatalyst co-injection in an analogous model based on a heavy oil reservoir located in the Magdalena Medio Valley Colombian basin. Simulations predict that the oil recovery factor can be increased up to 5% more than typical steamflooding and sets a precedent for the upscaling of this type of technology for pilot test designing. . The laboratory-based numerical model presented in this work suggests that the kinetic scheme based on SARA measurements along with residual oil saturation reduction by non-equilibrium nanoparticle retention captures the main mechanisms occurring during in-situ upgrading.

Interannual variability of wave climate in the Caribbean Sea

Low-frequency interannual climatic oscillations have been reported to influence the precipitation regimes, river discharges, winds, and sea level in the Caribbean Sea. Here, we analyzed the presence and relevance of low-frequency oscillations in the waves’ climate of the Caribbean Sea using data from WAVEWATCH III (NOAA) reanalysis and applying frequency domain wavelet transform technique. Results show a clear sectorization of the Caribbean Sea according to the presence and relevance of interannual oscillations in wave climate, where the southwestern region (Colombian basin) exhibits a larger number of statistically significant oscillations (at 95% confidence levels) with recurrence periods of 2–4, 4–8, and 8–12 years. Only some of these frequencies are observed in the rest of Caribbean basin. Two climatic events occurring in the periods 1997–1998 and 2010–2011 stand out in the study zone for their high energy in wavelet analysis. These events have been associated with the occurrence of the warm and cold phases of the El Nino Southern Oscillation (ENSO), respectively, and are well known due to their strong global effects on hydroclimatology. Thus, an additional analysis was performed in the time domain to investigate the effect of the two events on Caribbean Sea waves. The results revealed an influence of ENSO on significant wave height and peak period comparing with multi-year average conditions, producing highly variable spatial and temporal wave patterns, with more evident effects during the cold phase of ENSO (La Nina). These results confirm the sectorization of the Caribbean Sea regarding the energy and interannual variability of waves.

The First Botanical Exploration to the Upper Cuiarí (Cuyarí) and Isana Rivers, Upper Río Negro Basin, Guainía Department, Colombia

This account reports a journey of ca. 500 km from the city of Inírida to the Colombian basins of the Cuiarí and Isana Rivers (Guianía department) in April–May 2014, the first botanical expedition to this region. This area exemplifies one of the last innermost and botanically unexplored regions of the northwestern corner of the Amazon basin (the upper Río Negro basin), aside from the fieldwork started some 234 years ago with the exploration of the middle and lower portion of the Isana basin in Brazil (where it is called Içana) by the Portuguese naturalist Alexandre Rodrigues Ferreira. On our expedition we collected 1301 botanical numbers, which resulted in eight new species (two already published), two new families, and 24 species new to the Flora of Colombia. Another noteworthy feature is the high diversity of the forests in the upper Isana River, represented by between 108 and 162 spp. with a diameters ≥ 2.5 cm in different 40 × 40 m plots (1600 m2). The Isana River is a white-water basin (with high levels of sediments), with large areas covered by the vegetation typical of black-water rivers (Amazon Caatinga forests, lower forests, savannas and sclerophyllous shrubby vegetation over white-sand soils). This feature results from the influence of several black-water rivers, the headwaters of which drain from Precambrian Guiana shield outcrops. This account of the first botanical exploration in the Colombian portion of the Cuiarí and Isana Rivers is yet another example of the need for continued floristic studies in regions where there are large geographic gaps in the knowledge of Amazonian flora. Advances in documentation of this flora can be achieved through institutional and private partnerships, improved training, and continued fieldwork in collaboration with local inhabitants. A discussion of demarcation issues regarding the frontier between Brazil and Colombia in this northwestern corner of the Amazon basin, its physical and biological environments, and its ancestral and current inhabitants is presented.

Methodological approach for hydroacoustic seabed characterization in Serrana Bank (Seaflower Biosphere Reserve)

Hydroacoustic methods provide rapid and extensive access to seabed characteristics, which is not possible using other underwater technologies. Currently, hydroacoustics are widely used to determine seabed topography and sediment type, but significant developments have not occurred for detecting and classifying structures above the seabed, such as coral reefs and marine meadows, which are very important ecosystems. In the present study, we propose a new methodological approach to characterize the seabed at Serrana Bank (14.27°–14.48° N and 80.10°–80.23° W), located in the Colombian Basin of the Caribbean Sea, by combining acoustic information (split-beam echosounder) and underwater imagery. In all, 49 acoustic transects were created using a BioSonics DT-X scientific echosounder (with a 38-kHz split-beam transducer and a FURUNO differential GPS) during the Seaflower Scientific Expedition III (Colombian Ocean Commission, Colciencias) from August 12–15, 2016. Using cluster analysis with the Spearman correlation distance, 14 different Typical Acoustic Reflectance Profiles (TARPs) were identified at a distance of 0.80. These TARPs result from the natural acoustic signals produced by the sediment types and ecological structures present on the seabed. When comparing these TARPs with the photographic records and previous ecological maps, various ecological structures above the seabed were acoustically identified, such as coral debris, octocorals, macroalgae meadows, and several associations among coral and different sizes of macroalgae. The potential of this approach to generate a low-cost, automated method for mapping seabed ecosystems and to enable feasible assessments in marine protected areas is discussed.