Starting in 2011, coastal areas of the Caribbean Sea and tropical Atlantic Ocean began to experience extraordinary yearly accumulations of pelagic Sargasswn brown alga. Historical reports place large quantities of Scagassum only in the North Atlantic (mostly in the Gulf of Mexico and the Sargasso Sea). Accumulations of Sargassum in the tropical Atlantic have continued. We used a numerical particle-tracking system, wind and current reanalysis data, drifting buoy trajectories, and satellite imagery to determine the origin of the Sargasswn that is now found persistently in the tropical Atlantic. Our analyses suggest that during the extreme negative phase of the winter 2009-2010 North Atlantic Oscillation (NAO), unusually strong and southward-shifted westerly winds explain the transport of Scogassunt from the Sargasso Sea (similar to 20-40 degrees N, 80-20 degrees W) into the far eastern North Atlantic. Our hindcast Sargasswn distributions agree with surface current simulations with the inclusion of "windage". Windage is the additional, wind-induced drift of material floating at the free surface resulting from direct wind forcing on the sea surface, as well as on floating or partially-submerged objects. In our simulations, windage is included as an added vector (speed and direction) to the model-computed surface ocean currents equivalent to 1% of surface wind velocities. Lagrangian analysis of the regional circulation suggests that (1) part of the Sargassum subsequently drifted to the southwest in the North Equatorial Current (NEC) and entered the central tropical Atlantic, arriving in the Caribbean by the spring of 2011, with (2) another portion continuing southward along the coast of Africa hi the Canary Current, eventually joining the seasonally-varying system of tropical Atlantic currents and thereby delivering a large Sargassum population to the tropical Atlantic. Since then, Sargassum patches aggregate from March to September in massive windrows along the Inter-Tropical Convergence Zone (ITCZ) under the action of converging winds. The windrows follow the ITCZ in its seasonal northward migration in the central tropical Atlantic. They are stretched across the central tropical Atlantic as the ITCZ crosses the latitude of the seasonal formation of the North Equatorial Counter Current (NECC). These patches and windrows are exposed to high sunlight and open-ocean upward flux of nutrients due to eddy and wind-driven mixing in the central tropical Atlantic. During the northern spring and summer, as the Sargassum drifts farther north with the ITCZ, large portions of the population are advected into the eastern Caribbean Sea. Some of these patches remain dispersed as the ITCZ migrates southward, and re-aggregate into new windrows as the ITCZ intensifies the following March-April. If wind mixing is strong and the mixed layer is deeper than about 50-60 m in the southern tropical Atlantic at this time, the Sargasswn will bloom and form a massive windrow. Otherwise, the bloom will be inhibited. The extreme 2009-2010 NAO wind anomaly could be considered as triggering a biosphere "tipping point" that caused important ocean-scale ecosystem changes in the tropical Atlantic, with significant recurrent social and economic consequences. Understanding whether this new expanded geographic range of massive Sargassum blooms is temporary or whether it will revert to its pre-2009 distribution requires sustained monitoring and research.

Observations from five different systems provide a robust picture of the structure and variability of the Antilles Current, an important contributor to the oceanic flux budget, at 26.5 degrees N during 2005-2015. The analysis includes three direct measurement technologies (current meters, shipboard acoustic Doppler current profilers, and lowered acoustic Doppler current profilers) and two geostrophy-based measurement technologies (conductivity-temperature-depth profilers and pressure-equipped inverted echo sounders). The direct systems are shown to produce weaker, and less variable, Antilles Current transport estimates than the geostrophy-based systems. The record-length-mean geostrophic estimate for the Antilles Current is 4.7 Sverdrups (Sv; 1 Sv = 10(6) m(3)/s), and the daily temporal standard deviation is 7.5 Sv. The variations of the Antilles Current transport exceed those of the entire basin-wide meridional overturning circulation, illustrating the impact of this unusual current. Seasonal variability shows a maximum northward transport in August-September; however, the seasonal component of the variability is weak, and aliasing of higher frequencies is still a problem even with 10.5 years of data. The dominant time scales of variability in the spectra are at 70 and 180 days, and there is indication of westward propagation of Rossby Wave-like features into the region at a speed of 9 cm/s. There is no significant correlation between the Antilles Current transport variations and those of the Florida Current at 27 degrees N, in phase or at lags/leads of up to 5 years, likely reflecting the varying coastal wave/wall jet time scales for information to pass from the basin interior through the Bahamas Islands. Plain Language Summary The Antilles Current carries waters northward and northwestward around the Bahamas Islands. While scientists have known that the Antilles Current existed for decades, it has not been studied nearly as much as the stronger Florida Current to the west, even though studies have suggested that the Antilles Current plays a significant role in the north-south exchange of heat and salt within the North Atlantic. This study uses five different types of measurement systems to quantify how much water is being carried by the Antilles Current every day, how variable that flow is over a 10.5-year time period, and what typical salinity, temperature, and dissolved oxygen contents are for the waters carried by the flow. The study finds that on average, this current is carrying 4.7 x10(6) m(3) of water per second northward and that this flow can vary by more than 100% from day to day (i.e., some days the flow can actually reverse and go southward). The study reveals the time scales on which the current tends to vary, and it also provides some tantalizing evidence that the physics of the current may not be as simple as has been previously thought.

Since 2011, beach inundation of massive amounts of pelagic Sargassum algae has occurred around the Caribbean nations and islands. Previous studies have applied satellite ocean color to determine the origins of this phenomenon. These techniques, combined with complementary approaches, suggest that, rather than blooms originating in the Caribbean, they arrive from the Equatorial Atlantic. However, oceanographic context for these occurrences remains limited. Here, we present results from synthetic particle tracking experiments that characterize the interannual and seasonal dynamics of ocean currents and winds likely to influence the transport of Sargassum from the Equatorial Atlantic into the Caribbean Sea. Our findings suggest that Sargassum present in the western Equatorial Atlantic (west of longitude 50 degrees W) has a high probability of entering the Caribbean Sea within a year's time. Transport routes include the Guiana Current, North Brazil Current Rings, and the North Equatorial Current north of the North Brazil Current Retroflection. The amount of Sargassum following each route varies seasonally. This has important implications for the amount of time it takes Sargassum to reach the Caribbean Sea. By weighting particle transport predictions with Sargassum concentrations at release sites in the western Equatorial Atlantic, our simulations explain close to 90% of the annual variation in observed Sargassum abundance entering the Caribbean Sea. Additionally, results from our numerical experiments are in good agreement with observations of variability in the timing of Sargassum movement from the Equatorial Atlantic to the Caribbean, and observations of the spatial extent of Sargassum occurrence throughout the Caribbean. However, this work also highlights some areas of uncertainty that should be examined, in particular the effect of "windage" and other surface transport processes on the movement of Sargassum. Our results provide a useful launching point to predict Sargassum beaching events along the Caribbean islands well in advance of their occurrence and, more generally, to understand the movement ecology of a floating ecosystem that is essential habitat to numerous marine species.

The western Caribbean, a subarea of the Caribbean Sea Large Marine Ecosystem, includes the Mesoamerican Barrier Reef System, the Yucatan Basin, the Cayman Basin and the Yucatan Channel. Here we discuss the main oceanographic features of the western Caribbean Sea and present some examples of marine resources distributed throughout the western Caribbean Sea LME subarea along different spatial scales. Particular attention is given to their planktonic stages when physical oceanographic features (such as eddies and gyres, or current systems) can operate either as forces that promote larval dispersal or as barriers enhancing larval retention, as this determines their connectivity. Bluefin tuna, the early life stages (eggs and larvae) of reef fish, the Caribbean Spiny lobster, and the Queen conch are presented as examples. Dispersal distances depend on the oceanographic phenomena, with larger dispersals expected where intense currents occur, such as in the Yucatan Current. Conversely, retention can be expected in the presence of gyres such as the Honduras Gyre and Yucatan Basin eddies. There is a growing body of evidence supporting the need for a multi-scale approach in order to understand the complexity of LMEs. Moreover, the connectivity between regions in the western Caribbean Sea LME subarea, as shown by the exchange of marine resources and physical oceanographic processes, requires an international policy that supports collaborative efforts to monitor the dynamics of coastal and oceanic habitats together with marine resources.

Hydrographic data from two oceanographic cruises conducted during March 2006 and January/February 2007 are used to investigate the thermohaline structure related to the observed circulation along the Mesoamerican Barrier Reef System (MBRS). From our observations we identify three water masses in the MBRS: the Caribbean Surface Water (CSW), North Atlantic Subtropical Underwater (SUW), and Tropical Atlantic Central Water (TACW). Little vertical structure in temperature is observed in the upper 100m of the water column, but important differences are observed in the salinity distribution both horizontally and with depth. Freshwater inputs to the system from the mainland can be traced in the surface layer, with two possible sources: one from surface rivers located along the southern portion of the MBRS, and the other originating from an underground river system located along the northern portion of the MBRS. The thermohaline structure in the MBRS reflects the dynamics of the observed circulation. Uplifted isopycnals along most of the central and northern coastline of the MBRS reflect the effects of the strong geostrophic circulation flowing northward, i.e. the Yucatan Current. To the south along the MBRS, much weaker velocities are observed, with the Honduras Gyre dominating the flow in this region as presented during January/February 2007. These two regions are separated by onshore and divergent alongshore flow associated with the impingement of the Cayman Current on the shore and the MBRS.

The circulation and exchange processes controlling transport and water renewal within the western subregion of Florida Bay, USA, are presented and compared to our previous findings for the north-central and northeast subregions of the bay. We find there is a common bank/basin flow response to wind forcing that is the primary driver of water renewal for each of the regions studied. Florida Bay is a patchwork of shallow basins surrounded by very shallow banks that are cut through with deeper channels connecting to nearby basins. We observed that, for each subregion studied, there was a net downwind basin outflow through the larger channels that was approximately balanced by a net basin inflow over the surrounding shallow banks. The resulting basin throughflows are used to estimate exchange times for renewal of western basin waters of approximately 1 mo. This exchange time is sufficient to prevent hypersalinity and degradation of water quality in the western basin, in contrast to the north-central subregion, where hypersalinity development is an annual occurrence. Our results highlight the importance of wind induced water renewal in shallow coastal bays with weak to moderate tidal exchange. In addition, we have discovered a significant clockwise circulation pattern through the western basins from strong inflows of coastal waters through Flamingo Channel that turn southward through the western basins before rejoining the coastal flow toward the Florida Keys tidal passages and Atlantic coastal zone. A practical solution to control hypersalinity, sea grass die-off, and water quality degradation of Florida Bay is proposed.

Acoustic Doppler Current Profiler (ADCP) measurements and surface drifters released from two oceanographic cruises conducted during March 2006 and January/February 2007 are used to investigate the circulation off the Mesoamerican Barrier Reef System (MBRS). We show that the MBRS circulation can be divided into two distinct regimes, a northern region dominated by the strong, northward-flowing Yucatan Current, and a southern region with weaker southward coastal currents and the presence of the Honduras Gyre. The latitude of impingement of the Cayman Current onto the coastline varies with time, and creates a third region, which acts as a boundary between the northern and southern circulation regimes. This circulation pattern yields two zones in terms of dispersal, with planktonic propagules in the northern region being rapidly exported to the north, whereas plankton in the southern and impingement regions may be retained locally or regionally. The latitude of the impingement region shifts interannually and intra-annually up to 3° in latitude. Sub-mesoscale features are observed in association with topography, e.g., flow bifurcation around Cozumel Island, flow wake north of Chinchorro Bank and separation of flow from the coast just north of Bahia de la Ascencion. This third feature is evident as cyclonic recirculation in coastal waters, which we call the Ascencion-Cozumel Coastal Eddy. An understanding of the implications of these different circulation regimes on water mass distributions, population connectivity, and the fate of land-based pollutants in the MBRS is critically important to better inform science-based resource management and conservation plans for the MBRS coral reefs.

Circulation in the Gulf of Mexico (GOM) is dominated by mesoscale features that include the Loop Current (LC), Loop Current Rings (LCRs), and smaller frontal eddies. During May–June 2010, while oil was still flowing from the Macondo well following the Deepwater Horizon (DWH) platform explosion on April 20, 2010, drifter trajectories, satellite observations, and numerical simulations indicated a potential for direct connectivity between the northern Gulf and the Florida Straits via the LC system. This pathway could have potentially entrained particles, including northern GOM contaminants related to the oil spill, carrying them directly towards the coastal ecosystems of south Florida and northern Cuba. To assess this connectivity, and to evaluate the potential oil impacts on economically important GOM fisheries, an interdisciplinary shipboard survey was conducted in the eastern Gulf during July 2010. Analysis of the resulting hydrographic data confirmed that: (1) by July 2010 a large LCR had become separated from the main LC by a cyclonic eddy resulting in the loss of a direct transport mechanism from the northern GOM to the Florida Straits, leaving only indirect pathways available to potential contaminants; and (2) with the exception of four hydrographic stations occupied within 84km of the wellhead, no evidence of oil was found during the survey on the surface or within the water column. These results corroborated analysis of satellite altimetry observations of the GOM surface circulation and verified official surface oil coverage forecasts where they intersected with the survey track. This cruise sampled the LC, LCR, and frontal eddies to a depth of 2000m, with the results suggesting that any oil entrained by circulation features in prior months had either been weathered, consumed by bacteria, dispersed to undetectable levels, or was only present in unsurveyed areas. The assembled subsurface measurements represent one of only a few data sets collected across the dominant GOM mesoscale circulation features at a time when there was great concern about the potential long-range spreading of DWH related contaminants. Direct observations such as these are critical for the assessment of particle trajectory and circulation models utilized during the spill, and for the improvement of future numerical forecast products.

During April to June 2009, a large bolus of Amazon River water impacted the northeastern Caribbean Sea. Shipboard observations collected near Saba Bank, the U.S. and British Virgin Islands, and the Anegada Passage showed low surface salinity (35.76 ± 0.05 Practical Salinity Unit (PSU)), elevated surface temperature (26.77 ± 0.14°C), high chlorophyll-a (1.26 ± 0.21 mg m−3) and high dissolved oxygen (4.90 ± 0.06 mL L−1) in a 20- to 30-m thick surface layer in the riverine plume. The water was ~1°C warmer, 1 PSU fresher, 0.3 mL L−1 higher in oxygen and 1.2 mg m−3 higher in chlorophyll-a than Atlantic Ocean waters to the north, with Caribbean surface waters showing intermediate values. Plankton net tows obtained in the upper 100 m of the water column revealed larval fish assemblages within the plume that were significantly different from those of the surrounding waters and from those encountered in the area in previous years. The plume waters contained higher concentrations of mesopelagic fish larvae from the families Myctophidae and Nomeidae, which as adults typically inhabit offshore, deep water habitats. Concentrations of larvae from inshore and reef-associated families such as Scaridae, Serranidae, Labridae and Clupeidae were lower than those found outside the plume in similar shallow areas, particularly in near-surface waters. An event like the one observed in 2009 had not been documented in at least the past 30 yr, and yet it was followed by another similarly extreme event in 2010. The ecological implications, including any long-term consequences of such recent extreme events, are important and merit further study.

Author Posting. © The Oceanography Society, 2014. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 27, no. 2 (2014): 18-23, doi:10.5670/oceanog.2014.56.

A “black water” event, as observed from satellites, occurred off southwest Florida in 2012. Satellite observations suggested that the event started in early January and ended in mid-April 2012. The black water patch formed off central west Florida and advected southward towards Florida Bay and the Florida Keys with the shelf circulation, which was confirmed by satellite-tracked surface drifter trajectories. Compared with a previous black water event in 2002, the 2012 event was weaker in terms of spatial and temporal coverage. An in situ survey indicated that the 2012 black water patch contained toxic K. brevis and had relatively low CDOM (colored dissolved organic matter) and turbidity but high chlorophyll-a concentrations, while salinity was somewhat high compared with historical values. Further analysis revealed that the 2012 black water was formed by the K. brevis bloom initiated off central west Florida in late September 2011, while river runoff, Trichodesmium and possibly submarine groundwater discharge also played important roles in its formation. Black water patches can affect benthic coral reef communities by decreasing light availability at the bottom, and enhanced nutrient concentrations from black water patches support massive macroalgae growth that can overgrow coral reefs. It is thus important to continue the integrated observations where satellites provide synoptic and repeated observations of such adverse water quality events.

The Mesoamerican Barrier Reef System (MBRS) is of high ecological and economic importance to the western Caribbean region, and contains spawning sites for a number of reef fish species. Despite this, little is known of the distribution and transport of pelagic fish larvae in the area, and basic in situ information on larval fish assemblages is lacking. Here we describe the results of two biological oceanography research cruises conducted in winter-spring of 2006 and 2007, focusing on larval fish assemblages. We use multivariate assemblage analyses to examine vertical and horizontal distribution characteristics of larval fish assemblages, to highlight key distinguishing taxa, and to relate these to the observed oceanographic structure. Our results showed a general separation between the Gulf of Honduras region, which was characterized by weaker currents and high abundances of inshore and estuarine taxa (Eleotridae, Priacanthidae), and the northern MBRS, which was subject to strong northward flow and contained a mixture of mesopelagic and reef-associated taxa (Myctophidae, Sparidae). Although distinct patterns of vertical distribution were observed among taxa, both shallow and deep living larvae were broadly distributed throughout the study area. Analysis of historical drifter tracks highlighted the strong northward flow and low retention conditions typically present along the northern MBRS, as well as potential connectivity between the western Caribbean Sea, the Gulf of Mexico and the Atlantic Ocean.

Despite the importance of the West Florida Shelf (WFS) on regional ecology and local economy, systematic shelf-wide assessment of the ocean biology has not been conducted, primarily because of budgetary limitations for routine field campaigns and unknown accuracy of satellite-based data products. Here, using shipboard spectral normalized water-leaving radiance (nL(w)[lambda]) data and chlorophyll-a concentrations (Chl-a) collected regularly during two multiyear field programs spanning >10 years, the accuracies of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) standard data products were evaluated. The in situ data covered a wide dynamic range, with about one order of magnitude in nL(w)(490) (0.47 to 4.01 mW cm(-2) mu m(-1) sr(-1)) and two orders of magnitude in Chl-a (0.07 to 10.6 mg m(-3)). Near-concurrent in situ and satellite nL(w)(lambda 2) data showed absolute percent differences (APD) increasing from 7-9% to 10-14% when data with elevated aerosol optical thicknesses at 865 nm (tau(alpha)865) were included. Most of this uncertainty, however, canceled in the maximal blue-to-green reflectance band ratios traditionally used for estimating Chl-a. SeaWiFS OC4 Chl-a showed a root mean square (RMS) uncertainty of 0.106 for log-transformed data in waters offshore of the 20-m isobath that increased to 0.255 when all data were considered. The increased likelihood for nearshore SeaWiFS Chl-a greater than similar to 0.5 mg(-3) to be overestimated was shown to be caused by a variety of factors (colored dissolved organic matter [CDOM], suspended sediments, and bottom reflectance) that varied in both time and space. In the future, more sophisticated algorithms capable of taking these factors into consideration are required to improve remote determinations of Chl-a in nearshore waters of the WFS.

Ocean acidification (OA) is expected to reduce the calcification rates of marine organisms, yet we have little understanding of how OA will manifest within dynamic, real-world systems. Natural CO2, alkalinity, and salinity gradients can significantly alter local carbonate chemistry, and thereby create a range of susceptibility for different ecosystems to OA. As such, there is a need to characterize this natural variability of seawater carbonate chemistry, especially within coastal ecosystems. Since 2009, carbonate chemistry data have been collected on the Florida Reef Tract (FRT). During periods of heightened productivity, there is a net uptake of total CO2 (TCO2) which increases aragonite saturation state (Ωarag) values on inshore patch reefs of the upper FRT. These waters can exhibit greater Ωarag than what has been modeled for the tropical surface ocean during preindustrial times, with mean (± std. error) Ωarag-values in spring = 4.69 (±0.101). Conversely, Ωarag-values on offshore reefs generally represent oceanic carbonate chemistries consistent with present day tropical surface ocean conditions. This gradient is opposite from what has been reported for other reef environments. We hypothesize this pattern is caused by the photosynthetic uptake of TCO2 mainly by seagrasses and, to a lesser extent, macroalgae in the inshore waters of the FRT. These inshore reef habitats are therefore potential acidification refugia that are defined not only in a spatial sense, but also in time; coinciding with seasonal productivity dynamics. Coral reefs located within or immediately downstream of seagrass beds may find refuge from OA.

The northeast subregion of Florida Bay receives approximately 75% of the direct freshwater runoff to the bay, most of which is retained within the subregion and has little impact on the dilution of hypersalinity development in adjacent subregions. Using direct measurements of the volume transports through connecting channels and indirectly estimating the total transport to the subregion from mean sea level variability, we show that interior basin water exchanges are weak and controlled by local wind forcing. East-west winds produced seasonally averaged throughflows of 33 and 78 m(3) s(-1) during the El Nino-influenced wet and dry seasons of 2002 and 2003, respectively, and resulted in a one year residence time for the northeast subregion. The long residence time of the interior waters is due to the confining nature of the shallow banks and mangrove borders that surround the northeast subregion, as well as the lack of significant tidal exchange. Weak interbasin exchange results in the trapping of freshwater discharge from the Everglades within the northeast subregion. Development of hypersalinity within the north-central subregion of the bay has been associated with seagrass die-off and algal blooms that can cause water quality reduction in south Florida's coastal waters, including the Florida Keys reef tract. To reduce the development of hypersalinity within this region of the bay it will be necessary to divert a portion of the Everglades flow away from the northeast basin and into Whipray Basin during the dry season. Seasonal water balance estimates made for the northeast subregion and previous estimates from the north-central region indicate that groundwater inflows to Florida Bay are negligible and probably not a factor in water quality considerations.