The RAPID-MOCHA-WBTS (hereafter RAPID) array is an observing system designed to study the Atlantic Meridional Overturning Circulation (AMOC). It is an international collaboration between the National Oceanography Centre, University of Miami, and NOAA. The primary goals of the RAPID array are to observe and understand changes in the AMOC over time, and improve our understanding of how changes in the ocean circulation system may influence regional and global climate patterns. The array consists of a network of moored instruments, which measure ocean temperature, salinity, dissolved oxygen, and flow velocities. The AMOC at 26◦N has now been continuously measured by the RAPID array over the period April 2004 to present (20 years of observing). This record provides unique insight into the variability of the large-scale ocean circulation, previously only measured by sporadic snapshots of basin-wide transport from hydrographic ship sections. The continuous measurements have unveiled striking variability on timescales of days to a decade, driven largely by wind forcing, contrasting with previous expectations about a slowly varying buoyancy-forced overturning circulation. We will present the history of the RAPID observational array and its contribution to AMOC science.

The Florida Current (FC) provides the majority of the northward volume and heat transports for both the meridional overturning and the horizontal gyre circulations in the subtropical North Atlantic. A unique, sustained observing system in the Florida Straits at about 27°N, consisting of voltage measurements recorded from a submarine telecommunication cable installed between Florida and Grand Bahama Island, paired with regular calibration and validation cruises, was established in 1982. Since then, the recorded cable voltage time series has enabled over 40 years of quasi-continuous, daily estimates of the FC volume transport. The cable data constitutes the longest observational record of any boundary current and a key component of the Atlantic Meridional Overturning Circulation (AMOC) in existence. By this measure, it can be representative of the AMOC weakening, suggested by climate models and proxy-based reconstructions.Here, we reassess the record-long change in the FC strength by revising the processing of voltages measured on the submarine cable. With the increased length of the cable record, we show that it has become necessary to account for the secular change in the Earth’s geomagnetic field, especially when studying processes on decadal and longer time scales. We calculate the corrected estimates of the FC volume transport and show that (i) the FC strength has not declined as reported recently, but has remained remarkably stable since 1982, and (ii) with the corrected FC record, the AMOC at ~26.5°N exhibits a decadal-scale variability rather than a long-term decline.The results of this study indicate that, if climate models are correct that the AMOC is slowing or will soon slow down, this slowdown has not yet been reflected in the FC, or the observational record is still too short to detect it with confidence. The existing records are just starting to resolve decadal-scale signals relevant to climate variability. Continued observations are thus necessary for detection and mechanistic understanding of climate-related changes and for validating and improving ocean and climate models.

Direct measurements of the Atlantic Meridional Overturning Circulation (AMOC) and meridional heat transport (MHT) are necessary to better understand the impact of anthropogenic greenhouse gas emissions for the global climate system. The RAPID-MOCHA-WBTS array at 26°N is the only trans-Atlantic observing system to provide 20 years of continuous measurements of the AMOC and MHT. While the design of the array has continuously evolved as our understanding of the AMOC has advanced and as new technologies have become available, the goal of the RAPID-evolution project is now to design a lower cost and sustainable observing system to continue the measurements at the accuracy required by users. Using the dataset gathered since 2004 and ocean reanalysis, a first objective seeks to evaluate the sensitivity of the AMOC estimate to the choice of methodology and data included in the calculation. The project includes the development of a new high-resolution ocean model to identify the short and longer term impacts of incorporating these datasets in the AMOC estimation. Recent technological developments also enable new approaches that could provide better and more cost-effective calculation of the AMOC. The RAPID-Evolution project investigates these approaches and develops methodologies to make use of them, including a new variation of the stepping method using glider deployments and the telemetry of mooring data via an autonomous vehicle.

Radiosondes are important for calibrating satellite sensors and assessing sounding retrievals. Vaisala RS41 radiosondes have mostly replaced RS92 in the Global Climate Observing System (GCOS) Reference Upper Air Network (GRUAN) and the conventional network. This study assesses RS41 and RS92 upper tropospheric humidity (UTH) accuracy by comparing with Infrared Atmospheric Sounding Interferometer (IASI) upper tropospheric water vapor absorption spectrum measurements. Using single RS41 and RS92 soundings at three GRUAN and DOE Atmospheric Radiation Measurement (ARM) sites and dual RS92/RS41 launches at three additional GRUAN sites, collocated with cloud-free IASI radiances (OBS), we compute Line-by-Line Radiative Transfer Model radiances for radiosonde profiles (CAL). We analyze OBS-CAL differences from 2015 to 2020, for daytime, nighttime, and dusk/dawn separately if data is available, for standard (STD) RS92 and RS41 processing, and RS92 GRUAN Data Processing (GDP; RS41 GDP is in development). We find that daytime RS41 (even without GDP) has ~1% smaller UTH errors than GDP RS92. RS41 may still have a dry bias of 1–1.5% for both daytime and nighttime, and a similar error for nighttime RS92 GDP, while standard RS92 may have a dry bias of 3–4%. These sonde humidity biases are probably upper limits since “cloud-free” scenes could still be cloud contaminated. Radiances computed from European Centre for Medium-Range Weather Forecasts (ECMWF) analyses match better than radiosondes with IASI measurements, perhaps because ECMWF assimilates IASI measurements. Relative differences between RS41 STD and RS92 GDP, or between radiosondes and ECMWF humidity profiles obtained from the radiance analysis, are consistent with their differences obtained directly from the RH measurements.

The accuracy of Vaisala RS92 versus RS41 global radiosonde soundings, emphasizing stratospheric temperature, is assessed from January 2015 to June 2017 using similar to 311 500 RS92 and similar to 65 800 RS41 profiles and three different reference data sources. First, numerical weather prediction (NWP) model outputs are used as a transfer medium to produce relative RS92 and RS41 comparisons by analyzing observation minus NWP model background (OB-BG) and observation minus analysis (OB-AN) differences using the NOAA Climate Forecast System Reanalysis (CFSR; both comparisons) and the operational European Centre for Medium-Range Weather Forecasts (ECMWF) model (OB-AN comparison only). Second, GPS radio occultation (GPSRO) dry temperature profiles are directly compared with radiosondes, using GPSRO data from the University Corporation for Atmospheric Research (UCAR) Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) and EUMETSAT Radio Occultation Meteorology (ROM) Satellite Application Facility (SAF). Third, dual launches (RS92 and RS41 suspended from the same balloon) at five sites allow direct assessments. Comparisons of RS92 versus RS41 from all reference data sources are basically consistent. These two sondes agree well with global average temperature differences <0.1-0.2 K in the lower stratosphere from 51.5 to 26.1 hPa based on global stations and the dual launches. RS41 appears to be less sensitive than RS92 to changes in solar elevation angle. This study indicates that nighttime RS92 and RS41 radiosonde temperature biases are negligible, but infers a stratospheric cold bias (<0.5 K) in the CFSR and ECMWF model data.

The atmospheric temperature and water vapour profile products, derived from the hyperspectral cross-track infrared sounder/advanced technology microwave sounder (CrIS/ATMS) on board the Suomi national polar orbiting partnership (S-NPP) satellite and the Infrared Atmospheric Sounding Interferometer (IASI) on board MetOP-B satellite, were assessed using radiosonde data as the target. This is achieved by leveraging the strengths of satellite synchronized dedicated, Global Reference Upper Air Network (GRUAN), and conventional radiosonde observations (RAOBs) in the analysis of satellite-radiosonde collocation data, compiled through the NOAA sounding Products Validation System (NPROVS). One of the results found in the study is water vapour profiles of both the NOAA Unique Combined Atmospheric Processing System (NUCAPS) and EUMETSAT IASI L2 products are comparable to or even better than numerical model prediction (NWP) outputs, when dedicated ship RAOBs were used as the benchmark.

Using historical (1994–2017) satellite-tracked surface drifter trajectory data, we conduct a probabilistic Lagrangian circulation study which sheds light on the connectivity of Pulley Ridge with other locations in the Gulf of Mexico and adjacent areas. The analysis reveals that Pulley Ridge is connected with the North Atlantic, the Caribbean Sea, and most of the Gulf of Mexico. Preferred connecting pathways are identified and arrival times to potential reef sites computed. The study demonstrates the importance of Pulley Ridge as a source for neighboring regions like the Dry Tortugasa, the Florida Keys, Campeche Bank, and the east Florida coast as well as a self-recruitment area for species with short competence time. The study further suggests that the reefs in the Caribbean Sea, the Dry Tortugas, the western Florida Keys, and the West Florida Shelf can act as sources for Pulley Ridge, indicating the importance of Pulley Ridge as a central refugium for species in the Gulf of Mexico.

The Pulley Ridge and Dry Tortugas coral reefs are among the most pristine, but also fragile, marine ecosystems of the continental United States. Understanding connectivity processes between them and with surrounding shelf and deep areas is fundamental for their management. This study focuses on the physical processes related to the connectivity of these reefs. Unprecedented in situ time series were used at these specific reef locations, together with satellite observations and numerical simulations, to investigate the dynamics controlling local circulation on the Southwestern Florida Shelf (SWFS) under oceanic influence. The approach of the Loop Current and Florida Current (LC/FC) system to the SWFS slope can induce 0.5 to 1 m/s offshore flows impacting the Pulley Ridge and Dry Tortugas reefs. On the other hand, when the LC/FC system retreats from the slope, onshore flows can carry open-sea waters over the coral reefs. Local formation of cyclonic eddies is possible near the Dry Tortugas reefs in the LC approach case and passage of upstream LC Frontal Eddies is possible in the LC retreat case. Offshore currents 1 m/s over the SWFS slope were also found during periods of anticyclonic LC Eddy separation. A novel finding is the shedding and northward propagation of mesoscale anticyclonic eddies from the core of the LC along the West Florida Shelf. Eddy shedding may have a broader effect on the dynamics of the shelf around the study reef areas. Long periods of LC/FC domination over these coral reefs (reaching several weeks to months) are characterized by strong (similar to 1 m/s) along-shelf currents and continuous upwelling processes, which may weaken the slope stratification and bring colder, deeper waters over the shelf-break and toward the shallower shelf region.

Using historical (1994-2017) satellite-tracked surface drifter trajectory data, we conduct a probabilistic Lagrangian circulation study which sheds light on the connectivity of Pulley Ridge with other locations in the Gulf of Mexico and adjacent areas. The analysis reveals that Pulley Ridge is connected with the North Atlantic, the Caribbean Sea, and most of the Gulf of Mexico. Preferred connecting pathways are identified and arrival times to potential reef sites computed. The study demonstrates the importance of Pulley Ridge as a source for neighboring regions like the Dry Tortugasa, the Florida Keys, Campeche Bank, and the east Florida coast as well as a self-recruitment area for species with short competence time. The study further suggests that the reefs in the Caribbean Sea, the Dry Tortugas, the western Florida Keys, and the West Florida Shelf can act as sources for Pulley Ridge, indicating the importance of Pulley Ridge as a central refugium for species in the Gulf of Mexico.

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.

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.