Caribbean Water Research Articles

Recent records of thermohaline profiles and water depth in the Taam ja’ Blue Hole (Chetumal Bay, Mexico)

Coastal karst structures have been recently explored and documented in Chetumal Bay, Mexico, at the southeast of the Yucatan Peninsula. These structures, recognized as blue holes, stand out for their remarkable dimensions within a shallow estuarine environment. Particularly the Taam Ja’ Blue Hole (TJBH), revealed a depth of ~274 mbsl based on echo sounder mapping, momentarily positioning it as the world's second-deepest blue hole. However, echo sounding methods face challenges in complex environments like blue holes or inland sinkholes arising from frequency-dependent detection and range limitations due to water density vertical gradients, cross-sectional depth variations, or morphometric deviations in non-strictly vertical caves. Initial exploration could not reach the bottom and confirm its position, prompting ongoing investigation into the geomorphological features of TJBH. Recent CTD profiler records in TJBH surpassed 420 mbsl with no bottom yet reached, establishing the TJBH as the deepest-known blue hole globally. Hydrographic data delineated multiple water layers within TJBH. Comparison with Caribbean water conditions at the Mesoamerican Barrier Reef System, reef lagoons, and estuaries suggests potential subterranean connections. Further research and implementation of underwater navigation technologies are essential to decipher its maximum depth and the possibilities of forming part of an interconnected system of caves and tunnels.

Thermohaline and current variability off the west Yucatan peninsula coast

Thermohaline and current variability for a certain period in the first ∼40 km off the western Yucatan Peninsula were analyzed, from five hydrographic campaigns carried out between 2017 and 2018, and 2.5 years of two moored current meters and satellite wind observations. Three different coastal environments in the study region create local particularities important to the thermohaline variations: mangrove forests, coastal lagoons, and river or groundwater discharges. The thermohaline variability presented a seasonality marked principally by the salinity balances and by the temperature heating/cooling cycles. Seawater was commonly saltier near the coast, principally in spring (dry epoch) when there is an increase in evaporation. The type of waters identified were modified versions of the Caribbean water masses, where precipitation/evaporation balances, along with the wind forcing, mixed them with the near-coastal local fluxes. Dimensional analysis showed that bottom friction was not negligible (Ek > 1), and that water column stratification constrained the flow (Ri > 1). Currents off Campeche and Sisal flowed west-southwest and showed low coherency between sites, due to the different coastline orientations. Their predominant force was the wind stress, but bottom friction affected them, supported by the Ekman surface and bottom layers intersection. Ekman surface layer was commonly deeper than the actual depth, therefore Ekman spiral cannot develop completely, hence currents had an angle to the right of the direction of the winds of 72° (42°) in Campeche (Sisal). These flows were moderately coherent and in phase with the wind stress, at periods of 5 (18) days, respectively.

Effect of Caribbean Water incursion into the Gulf of Mexico derived from absolute dynamic topography, satellite data, and remotely sensed chlorophyll <i>a</i>

Abstract. The dynamics of the Loop Current (LC) and the detached Loop Current eddies (LCEs) dominate the surface circulation of the Gulf of Mexico (GoM) and transport Caribbean Water (CW) into the gulf. In this work, 25 years (1993–2017) of daily satellite data are used to investigate the variability of these physical processes and their effect on chlorophyll a (Chl a) concentrations from 1998 to 2017, including temporal changes, mean differences, and regional concentration tendencies. The physical variables analyzed are absolute dynamic topography (ADT) and oceanic currents. From the ADT and oceanic current monthly climatologies, it is shown that there is an annual intrusion of CW with an inward incursion that starts in spring, peaks in the summer, reaches to 28∘ N and 90.45∘ W, and then retreats in winter to approximately 26.5 ∘ N and 88.3 ∘ W. Minimum surface Chl a concentrations (< 0.08 mg m−3) are found during the summer–autumn period inside the region of maximum incursion of CW; the opposite is observed during the winter period when Chl a concentrations were at a maximum, e.g., > 0.14 mg m−3. The 3-year running averages of the ADT 40 cm isoline qualitatively reproduce the climatological pattern of 25 years showing that before 2002 CW was less intrusive. This suggests that from 2003 onward, larger volumes of oligotrophic waters from the Caribbean Sea have invaded the western GoM and reduced mean surface Chl a concentrations. A direct comparison between the 1998–2002 and 2009–2014 periods indicates that in the latter time interval, the Chl a concentration above waters deeper than 250 m has decreased significantly.

The Harderian gland transcriptomes of Caraiba andreae, Cubophis cantherigerus and Tretanorhinus variabilis, three colubroid snakes from Cuba

The Harderian gland is a cephalic structure, widely distributed among vertebrates. In snakes, the Harderian gland is anatomically connected to the vomeronasal organ via the nasolacrimal duct, and in some species can be larger than the eyes. The function of the Harderian gland remains elusive, but it has been proposed to play a role in the production of saliva, pheromones, thermoregulatory lipids and growth factors, among others. Here, we have profiled the transcriptomes of the Harderian glands of three non-front-fanged colubroid snakes from Cuba: Caraiba andreae (Cuban Lesser Racer); Cubophis cantherigerus (Cuban Racer); and Tretanorhinus variabilis (Caribbean Water Snake), using Illumina HiSeq2000 100 bp paired-end. In addition to ribosomal and non-characterized proteins, the most abundant transcripts encode putative transport/binding, lipocalin/lipocalin-like, and bactericidal/permeability-increasing-like proteins. Transcripts coding for putative canonical toxins described in venomous snakes were also identified. This transcriptional profile suggests a more complex function than previously recognized for this enigmatic organ.

Evaluating weather observations and the Climate Forecast System Reanalysis as inputs for hydrologic modelling in the tropics

AbstractCorrectly representing weather is critical to hydrological modelling, but scarce or poor quality observations can often compromise model accuracy. Reanalysis datasets may help to address this basic challenge. The Climate Forecast System Reanalysis (CFSR) dataset provides continuous, globally available records, and CFSR data have produced satisfactory hydrological model performance in some temperate and monsoonal locations. However, the use of CFSR for hydrological modelling in tropical and semi‐tropical basins has not been adequately evaluated. Taking advantage of exceptionally high rainfall station density in the catchments of the Rio Grande de Loiza above San Juan, Puerto Rico, we compared model performance based on CFSR records with that based on publicly available weather stations in the Global Historical Climate Network (GHCN, n = 21) and on a dataset of rainfall records maintained by the United States Geological Survey Caribbean Water Science Center (USGS, n = 24). For an implementation of the Soil and Water Assessment Tool (SWAT) with subbasins defined at 11 streamflow gages, uncalibrated measures of Nash–Sutcliffe efficiency (NSE) were >0 at 8 of 11 gages using USGS precipitation data for daily simulations over the period 1998–2012, but were <0 using GHCN weather station records (8 of 11) and CFSR reanalysis data (9 of 11). Autocalibration of individual SWAT models for each of the 11 basins against each of the available weather datasets yielded NSE values > 0 using all precipitation inputs, including CFSR. However, the ground weather station closest to the geographic basin centre produced the highest NSE values in only 5 of 11 cases. The spatially interpolated CFSR data performed as well or better than single ground observations made further than 20–30 km, and sometimes better than individual weather stations <10 km from the basin centroid. In addition to demonstrating the need to evaluate available weather inputs, this research reinforces the value of CFSR data as a means to supplement ground records and consistently determine a baseline for hydrologic model performance. Copyright © 2016 John Wiley & Sons, Ltd.

Kinematic metrics of the Loop Current in the Gulf of Mexico from satellite altimetry

We analyzed a 20-year time series (January 1st, 1993 through December 31st, 2012) of Loop Current (LC) surface area derived from satellite altimetry in the eastern Gulf of Mexico to estimate kinematical metrics of this potent flow. On average the LC intrudes to its maximum northward position about 216±126 days after the previous eddy separation; and ∼30±31 days later sheds a large anticyclonic eddy. When the northern extent of the LC intrusion following the previous eddy separation is greater than 27°N, the current retreats very quickly until it sheds another eddy with the entire separation process occurring on the order of 30 days. To first order the change in areal extent of the LC during intrusion into the Gulf occurs at an average rate of 225km2day−1, which corresponds to an intrusion velocity of 1.7cms−1 of the LC front, and adds Caribbean water to the Gulf at a rate of 2.6±0.7Sv.

Tools for the implementation of integrated water resources management (IWRM) in the Caribbean

While many countries and regional authorities in the Caribbean have embraced the concept of integrated water resources management (IWRM) and recognized its guiding principles as beneficial, few have possessed the capacity to implement it since its enunciation in the Dublin Principles of 1992. The Caribbean Water Initiative (CARIWIN) endeavoured over a 6-year period, 2006–2012, to build capacity in a collaborative process with national governments and regional and international agencies. The result of this collaborative process was the selection of three Caribbean-specific tools to support the implementation of the key components of IWRM. These tools were National Water Information Systems, the Caribbean Drought and Precipitation Monitoring Network, and Community Water Strategies. This paper describes these three tools and the process promoted through CARIWIN for their successful adoption and implementation, i.e. a program including professional development, institutional partnerships, research, and dissemination of knowledge.

Standing stocks and body size of deep-sea macrofauna: Predicting the baseline of 2010 Deepwater Horizon oil spill in the northern Gulf of Mexico

A composite database encompassing 6 benthic surveys from years 1983 to 2003 was constructed to evaluate the distribution of macrofaunal biomass in the deep Gulf of Mexico (GoM) prior to the Deepwater Horizon oil spill. Predictive models based on optimal scaling of ocean color data and high resolution bathymetry were employed to map the benthic biomass in the vicinity of spill site because no previous sampling had been conducted at that exact location. The predicted biomass declines with water and mixed layer depth and is an increasing function of surface primary production and temporal variation of sea surface temperature. The decline of animal size with depth, however, was a function of a shift of dominant abundance from large to small taxa. At a local scale, high benthic biomass in the N GoM was associated with the enhanced productivity by the nutrient-laden Mississippi River outflows, offshore transport of the river plumes, and upwelling along the northern edge of the Loop Current. The apparent biomass enhancement at the Mississippi and De Soto Canyon and deep sediment fan was presumably related to lateral down-slope advection of organic carbon from the surrounding continental margin. Except for the Campeche Bank, the meager biomass of the Mexican margin may reflect the characteristic low-productivity Caribbean water that enters the GoM through Yucatan Strait. Benthic biomass in the N GoM was not statistically different between comprehensive surveys in the years 1983–1985 and 2000–2002. The stock assessment and biomass predictions from 669 cores at 170 locations throughout the deep GoM provide an important baseline of the sediment-dwelling fauna that may be subjected to immediate or long-term impacts from the oil spill or from climate change.

Late Neogene planktonic foraminifera of the Cibao Valley (northern Dominican Republic): Biostratigraphy and paleoceanography

An assemblage of planktonic foraminifera is described from 125 samples taken from the Cercado, Gurabo, and Mao Formations in the Cibao Valley, northern Dominican Republic. The primary objectives of this study are to establish a biochronologic model for the late Neogene of the Dominican Republic and to examine sea surface conditions within the Cibao Basin during this interval. The Cercado Formation is loosely confined to Zones N17 and N18 (∼ 7.0–5.9 Ma). The Gurabo Formation spans Zones N18 and N19 (∼ 5.9–4.5 Ma). The Mao Formation is placed in Zone N19 (∼ 4.5–3.6 Ma). Changes in the relative abundances of indicator species are used to reconstruct sea surface conditions within the basin. Increasing relative abundances of Globigerinoides sacculifer and Globigerinoides ruber, in conjunction with a decreasing relative abundance of Globigerina bulloides, suggests the onset of increasing sea surface temperature and salinity in conjunction with diminishing primary productivity at ∼ 6.0 Ma. Abrupt increases in the relative abundances of G. sacculifer and G. ruber at ∼ 4.8 Ma suggest a major increase in sea surface temperature and salinity in the early Pliocene. The most likely mechanism for these changes is isolation of the Caribbean Ocean through progressive restriction of Pacific–Caribbean transfer via the Central American Seaway. Periods of high productivity associated with upwelling events are recorded in the upper Cercado Formation (∼ 6.1 Ma) and in the middle Mao Formation (∼ 4.2 Ma) by spikes in G. bulloides and Neogloboquadrina spp. respectively. The timing of major increases in sea surface salinity and temperature as well as decreasing productivity (∼ 4.8 Ma) and periods of upwelling (∼ 6.1and 4.2 Ma) in the Cibao Basin generally corroborate previously suggested Caribbean oceanographic changes related to the uplift of Panama. Changes in sea surface conditions depicted by paleobiogeographic distributions in the Cibao Basin suggest that shoaling along the Isthmus of Panama had implications in a shallow Caribbean basin as early as 6.0 Ma. Major paleobiologic changes between ∼ 4.8 and 4.2 Ma likely represent the period of final closure of the CAS and a nearly complete disconnection between Pacific and Caribbean water masses. This study illustrates the use of planktonic foraminifera in establishing some paleoceanographic conditions (salinity, temperature, productivity, and upwelling) within a shallow water basin, outlining the connection between regional and localized oceanographic changes.

Closing of the Central American Seaway and the Ice Age: A critical review

What role did the closing of the Central American Seaway play in enabling continental ice sheets to wax and wane over North America and Fennoscandia? A summary of relevant evidence presented here permits a causal relationship between them but can be interpreted to show none. The common denominator of such evidence is the approximate simultaneity of that closing with global cooling and the first major ice advance. At the resolution of paleoclimate, however, geologic evidence from Central America places only weak constraints on when interchange between Pacific and Caribbean water ceased. The strongest evidence for when North and South America became connected by a continuous land bridge, the “Great American Exchange” of vertebrates, assigns climate change the causal role, for an arid Central American climate, typical of glacial times, seems necessary for animals that inhabited savannas to pass through Panama. Paleoceanographic and geochemical studies of environments and water masses in the eastern Pacific, western Caribbean, and Atlantic in general call for continual change since ∼6 Ma or earlier, if evidence concurrent with global change near 3.5–3 Ma seems more widespread than for other times. Hypothesized connections between a closed seaway and glaciation commonly call for profoundly different North Atlantic Ocean circulation, but simulations using general circulation models provide a spectrum of differences in circulation for open and closed seaways. Might much (not all) of the evidence implicating the closing of the seaway in global climate change in fact be a consequence of that change and blind to Central America's tectonic development?

Government Watch: EU funds African, Caribbean water cleanup

ADVERTISEMENT RETURN TO ISSUEPREVDepartmentsNEXTGovernment Watch: EU funds African, Caribbean water cleanupMaria BurkeCite this: Environ. Sci. Technol. 2004, 38, 11, 200APublication Date (Web):June 1, 2004Publication History Published online1 June 2004Published inissue 1 June 2004https://doi.org/10.1021/es040510jRIGHTS & PERMISSIONSArticle Views111Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (52 KB) Get e-Alerts Get e-Alerts

Aspectos morfodinámicos de la bahía de Cartagena de Indias

The oceanographic characteristics of the oceanic waters over the Providencia Depression (Lat. 12.8 N, Long. 81.7 W) were investigated by means of a physical, chemical and biological study made on board the oceanographic vessel ARC “Providencia” from May 25 to June 17, 2004. Analysis of the physical parameters showed the modification of the mixed layer that deepen from 35 to 55m in 8 days due to the arrival of an atmospheric easterly wave. Geostrophic estimations indicated a mainly southward flux of ~0.12m/s. Surface layers were not occupied by Surface Caribbean Water indicating the little influence of the larger south American rivers in the area during this epoch. The core of Subtropical Underwater had salinities above 37.0 in 125m depth, these are high values according to the climatology. Intermediate Antarctic Water showed a minimum salinity of 34.795 in 700m depth and Deep Atlantic Water was found deeper. Chemical and nutrient measurements were within known ranks for the studied area. Surface and bentic macrofauna alive during the survey were reported. The studied parameters indicated that the waters in the Depression were well ventilated at the moment of the measurements.

Millennial‐ to century‐scale variability in Gulf of Mexico Holocene climate records

Proxy records from two piston cores in the Gulf of Mexico (GOM) provide a detailed (50–100 year resolution) record of climate variability over the last 14,000 years. Long‐term (millennial‐scale) trends and changes are related to the transition from glacial to interglacial conditions and movement of the average position of the Intertropical Convergence Zone (ITCZ) related to orbital forcing. The δ18O of the surface‐dwelling planktic foraminifer Globigerinoides ruber show negative excursions between 14 and 10.2 ka (radiocarbon years) that reflect influx of meltwater into the western GOM during melting of the Laurentide Ice Sheet. The relative abundance of the planktic foraminifer Globigerinoides sacculifer is related to transport of Caribbean water into the GOM. Maximum transport of Caribbean surface waters and moisture into the GOM associated with a northward migration of the average position of the ITCZ occurs between about 6.5 and 4.5 ka. In addition, abundance variations of G. sacculifer show century‐scale variability throughout most of the Holocene. The GOM record is consistent with records from other areas, suggesting that century‐scale variability is a pervasive feature of Holocene climate. The frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability, indicating that at least some of the century‐scale climate variability during the Holocene is due to external (solar) forcing.

Upwelling on the Yucatan Shelf: hydrographic evidence

Hydrographic data gathered during four cruises are used to evidence upwelling on the Yucatan Shelf, and describe its structure. Subsurface Caribbean water (characterized by 16 to 20°C, 36.1 to 36.5 S, and 8 to 14 μmol 1 −1 nitrate concentrations) upwells along the eastern slope of the Yucatan Shelf. This water, which originates at depths of about 220–250 m in the Yucatan Channel, rises at about 10 −2 cm s −1 to dome into the euphotic zone, but only occasionally breaks the ocean surface. This upwelling appears to follow a seasonal cycle. During spring and summer the upwelled water intrudes over the Yucatan Shelf to create a two-layered water column. Strong stratification between Caribbean surface water (CSW) and the Yucatan upwelling water (YUW) layer on the shelf is likely to prevent mixing between them, except during the winter periods of northern winds. The YUW layer moves westward across the shelf and contributes to the formation of a cyclonic gyre north of Cape Catoche. The curl of the prevailing wind stress is not likely to induce upwelling along the eastern Yucatan slope. The observations imply that the upwelling is probably caused by bottom friction or other topographical mechanisms. A subsurface countercurrent runs southward along the eastern slope of the Yucatan Shelf, and appears to be closely related to the upwelling process. The Salinity Maximum is ruptured on the western side of the Yucatan Channel as a consequence of the upwelling. The data presented support the hypothesis that Yucatan is one of the most important upwelling regions on a western oceanic margin.

234Th:238U disequilibria in the Gulf of Mexico: the importance of organic matter and particle concentration

We have measured the concentrations of dissolved and particulate234Th, suspended particulate matter, dissolved organic carbon, nutrients and a suite of pigments along a transect in the shelf and slope waters of the Gulf of Mexico. The deep water station samples were collected in the presence (summer 1992) and absence (spring 1992) of a warm-core ring. In the summer, the station was at the periphery of a warm-core ring containing more oligotrophic, Caribbean water, while in the spring, only Gulf water was present. The234Th deficiency, which extends throughout a 1500 m water column in spring, indicates active lateral exchange of dissolved and particulate species. This study provides insight into the role of particles for234Th scavenging and differences in the scavenging intensities in the presence and absence of a warm-core ring. In addition, the possibility that the major carrier phase of thorium cycling could be dissolved organic carbon is suggested from the correlation between234Th (dissolved and total) and dissolved organic carbon concentrations. The average particle residence time for the whole water column in spring, seven days, was significantly shorter than that for summer, 21 days. This longer residence time in the summer is attributed to the presence of a warm-core ring which resulted in lower particle, DOC, and nutrient concentrations. Values of scavenging and particle residence times and234Th fluxes, and the significance of the correlations of these values with concentrations of particle mass and various pigments are discussed.

Hydrographic properties and circulation of the North Carolina shelf and slope waters

Processes affecting the renewal of the North Carolina Shelf Waters are discussed on the basis of temperature, salinity, dissolved oxygen, nutrients, runoff and wind data collected during 1965–1967. These consist of horizontal advection near the coast from the north, meanders of the Gulf Stream, subsurface intrusion, cascading and runoff.The wind-driven Virginia Water transport past Cape Hatteras may markedly reduce the temperature and salinity, and accelerate the freshwater exchange. The runoff from the watershed north of Cape Hatteras, when driven south by northerly winds, especially during the peak period in early spring, has a much greater influence on the circulation in Raleigh and Onslow Bays that does that from the adjacent rivers south of Cape Hatteras. Meanders in the Gulf Stream may renew the shelf waters with warm, saline water. Intrusion of subsurface Caribbean Water on to the outer part of the shelf takes place most frequently during the late summer following a period of southerly winds. It is postulated that during the cold part of the year when the surface layers are only partly stratified, such an intrusion may lead to upwelling near the shelf break. Cascading from the shelf down the slope may occur during the cold season following periods of low air temperature. Intrusion of subsurface water replenishes nutrients in the area, while cascading reduces the available supply of nutrients.

NUTRIENT‐DENSITY RELATIONSHIPS IN THE WESTERN NORTH ATLANTIC BETWEEN CAPE LOOKOUT AND BERMUDA1

A study of the nutrient‐density relationships of Sargasso Sea water reveals a close correlation; Gulf Stream waters are anomalously higher and more variable in nutrients for a given density. Nutrient anomalies can be used in the same way as oxygen anomalies to map the distribution of Caribbean water in sections across the Gulf Stream. They show that contributions of Caribbean water to the Gulf Stream vary greatly from time to time. Oxidative ratios of ΔO : ΔN : ΔP = (−233) : 16.3 : 1.0 were derived from the correlation between oxygen anomalies and nutrients anomalies of Gulf Stream water in the sigma‐t range 25.0–26.8.

Observations of deep-water renewal in the Caribbean Sea

Observations with bottom-moored current meters in the Jungfern passage show that, contrary to previous conclusions, deep water in the Venezuela basin is being renewed. During a 5-day record, the flow was mainly oscillatory at tidal frequency, with a net inflow by the tidal mechanism of only 6×103 m3 sec−1. During a single 11-hour surge the inflow rate was 50 to 200 × 103 m3 sec−1. Steady-state heat-budget and oxygen-budget calculations require a renewal rate of about 100×103 m3 sec−1. The sill depth is 1860 meters. STD observations near the sill reveal a sharp interface between Caribbean water above and oceanic water below sill depth. The north-south hydrographic sections of IGY data show an abrupt change in vertical temperature gradient near 2600 to 2800 meters. This feature, also found in other basins, is interpreted to result from differences in renewal between tidal inflow and stronger sporadic surges, with the earth's rotation being an important controlling parameter.

Mineral Source and Transport in Waters of the Gulf of Mexico and Caribbean Sea

Mineral particles suspended in the Gulf of Mexico and Caribbean Sea were analyzed in relation to clay mineral distributions in bottom sediments, to sedimentation processes active in the region, and to the prevailing currents. Circulation in the upper layers of water flowing from the Caribbean, carrying a micaceous-rich mineral assemblage, has exercised an influence on mineral transport into the Gulf of Mexico, different from the montmorillonite-rich load delivered by the Mississippi River. Particulate matter, suspended in North Atlantic water and Amazon River discharge, enters the Caribbean through the Lesser Antilles and contributes to the detrital mineral content of Caribbean water, as does that carried by the wind.

Some chemical and hydrographic observations along the north coast of South America—I. Cabo Tres Puntas to Curaçao, including the Cariaco Trench and the Gulf of Cariaco

Chemical and hydrographic observations were made on five north-south sections along the Caribbean coast of Venezuela in October and November, 1958. In addition, 15 stations were occupied in the Gulf of Cariaco. Chemical determinations included dissolved oxygen, total and inorganic phosphorus, nitrate, silicate and, in the anaeric waters of the Gulf of Cariaco and the Cariaco Trench, hydrogen sulphide.Except for some low-salinity near-surface water, these waters frrm a single mass, on the basis of the temperature-salinity diagram, in agreement with the findings of Parr (1937). Minimu salinities are found at 700–800 m and can be attributed to Antarctic Intermediate sources. Maximum salinities are in the upper 200 m, at depths which increase to the north.Near the coats, isopleths of salinity, temperature, density and the nutrient ions generally slope upward toward the south, particularly in the eastern sections. This is interpreted as evidence of upwelling along this coast, a phenomenon which appears to be the only important source of nutrients in the photic zone, and which accounts for the high biological productivity of the region.The Gulf of Cariaco was filled with nearly isohaline water having the same temperature correlations as the Caribbean water outside at the time of the observations. Upwelling at the eastern end of the Gulf is clearly evident from the temperature, oxygen and nutrient distributions. The water deeper than about 54 m is isolated from, and is colder than, water at equal depths outside. Past observations indicate that this deep water may be renewed some (and possibly all) years, in February. These deep waters are isolated, vertically, by a sharp temperature gradient, as stagnant, and contain sulphides. The upwelling in the east results in high biological productivity in the region, which is evident from the rich flora and fauna.An estimate of the productivity of the region has been made from the fixation of phosphate-phosphorous which upwells near the coast, north of Puerto La Cruz. The calculation indicates a production of 0·14 gm C/m2/day, a figur which is consistent with estimates made in the region by other methods. An estimate made in the Gulf of Cariaco, also on the basis of the fixation of inorganic phosphate, indicated a daily production of 2·8 to 5·7 gm C/m2.