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While data-driven approaches demonstrate great potential in atmospheric modeling and weather forecasting, ocean modeling poses distinct challenges due to complex bathymetry, land, vertical structure, and flow non-linearity. This study introduces OceanNet, a principled neural operator-based digital twin for regional sea-suface height emulation. OceanNet uses a Fourier neural operator and predictor-evaluate-corrector integration scheme to mitigate autoregressive error growth and enhance stability over extended time scales. A spectral regularizer counteracts spectral bias at smaller scales. OceanNet is applied to the northwest Atlantic Ocean western boundary current (the Gulf Stream), focusing on the task of seasonal prediction for Loop Current eddies and the Gulf Stream meander. Trained using historical sea surface height (SSH) data, OceanNet demonstrates competitive forecast skill compared to a state-of-the-art dynamical ocean model forecast, reducing computation by 500,000 times. These accomplishments demonstrate initial steps for physics-inspired deep neural operators as cost-effective alternatives to high-resolution numerical ocean models. [ABSTRACT FROM AUTHOR]

The Gulf Stream, a major ocean current in the North Atlantic ocean is a key component in the global redistribution of heat and is important for marine ecosystems. Based on 27 years (1993–2019) of wind reanalysis and satellite altimetry measurements, we present observational evidence that the path of this freely meandering jet after its separation from the continental slope at Cape Hatteras, aligns with the region of maximum cyclonic vorticity of the wind stress field known as the positive vorticity pool. This synchronicity between the wind stress curl maximum region and the Gulf Stream path is observed at multiple time-scales ranging from months to decades, spanning a distance of 1500 km between 70 and 55W. The wind stress curl in the positive vorticity pool is estimated to drive persistent upward vertical velocities ranging from 5 to 17 cm day−1 over its ~ 400,000 km2 area; this upwelling may supply a steady source of deep nutrients to the Slope Sea region, and can explain as much as a quarter of estimated primary productivity there. [ABSTRACT FROM AUTHOR]

The connection between atmospheric blocking over the North Atlantic and the diabatic influence of the Gulf Stream is investigated using potential vorticity and moist potential vorticity diagnostics in the ERA5 reanalysis data set during wintertime (1979 - 2020). In line with previous research, the reliance atmospheric blocking has on turbulent heat fluxes over the Gulf Stream and its extension, for induction and maintenance, is shown to be significant. The air-sea heat flux generates negative potential vorticity air masses in the atmospheric boundary layer. These air masses subsequently contribute to the block's negative potential vorticity anomaly at upper levels through ascending motion in the warm conveyor belt. It is shown that the block's size and frequency partially depends on oceanic preconditioning via anomalous oceanic heat transport and heat content, prior to the blocking event, both of which allow for stronger turbulent heat fluxes. It is further hypothesized that the block feeds back positively on itself through the advection of cold dry air over the Gulf Stream, sustaining this air-sea interaction. This in turn decreases ocean heat content, eventually halting this air-sea interaction and severing the atmospheric block from its maintenance pathway. [ABSTRACT FROM AUTHOR]

The Gulf Stream (GS) ocean front exhibits intense ocean–atmosphere interaction in winter, which has a significant impact on the genesis and development of extratropical cyclones in the North Atlantic. The atmospheric rivers (ARs), closely related with the cyclones, transport substantial moisture from the North Atlantic towards the Western European coast. While the influence of the GS front on extratropical cyclones has been extensively studied, its effect on ARs remains unclear. In this study, two sets of ensemble experiments are conducted using a high-resolution global Community Atmosphere Model forced with or without the GS sea surface temperature front. Our findings reveal that the inclusion of the GS front leads to approximately 25% enhancement of water vapor transport and precipitation associated with ARs in the GS region, attributed to changes in both AR frequency and intensity. Furthermore, this leads to a more pronounced downstream response in Western Europe, characterized by up to 60% (40%) precipitation increases (reductions) around Spain (Norway) for the most extreme events (exceeding 90 mm/day). The influence of the GS front on ARs is mediated by both thermodynamic and dynamic factors. The thermodynamic aspect involves an overall increase of water vapor in both the GS region and Western Europe, promoting AR genesis. The dynamic aspect encompasses changes in storm tracks and Rossby wave train, contributing to downstream AR shift. Importantly, we find the co-occurrence of ARs and the GS front is crucial for inducing deep ascending motion and heating above the GS front, which perturbs the deep troposphere and triggers upper-level Rossby wave response. These findings provide a further understanding of the complex interaction between the oceanic front in the western boundary current regions and extratropical weather systems and the associated dynamics behind them. [ABSTRACT FROM AUTHOR]

Knowledge of near-bottom ocean current velocities and especially their extreme values is necessary to understand geomorphology of the seafloor and composition of benthic biological communities and quantify mechanical energy dissipation by bottom drag. Direct measurements of near-bottom currents in deep ocean remain scarce because of logistical challenges. Here, we report the results of flow velocity and pressure fluctuation measurements at three sites with depths of 2573–4443 m in the area where the Gulf Stream interacts with the New England Seamounts. Repeated episodes of unexpectedly strong near-bottom currents were observed, with the current speed at 4443 m of more than 0.40 m/s. At 2573 m, current speeds exceeded 0.20 m/s approximately 5% of the time throughout the entire eight-week measurement period. The maximum flow speeds of over 1.10 m/s recorded at this site significantly surpass the fastest previously reported directly measured current speeds at comparable or larger depths. A strong correlation is found between the noise intensity in the infrasonic band and the measured current speed. The noise intensity and the characteristic frequency increase with the increasing current speed. Machine-learning tools are employed to infer current speeds from flow-noise measurements at the site not equipped with a current meter. [ABSTRACT FROM AUTHOR]

Recent studies found that on long time scales there are often unexplained opposite trends in sea level variability between the upper and lower Chesapeake Bay (CB). Therefore, daily sea level and temperature records were analyzed in two locations, Norfolk in the southern CB and Baltimore in the northern CB; surface currents from Coastal Ocean Dynamics Application Radar (CODAR) near the mouth of CB were also analyzed to examine connections between the CB and the Atlantic Ocean. The observations in the bay were compared with daily Atlantic Meridional Overturning Circulation (AMOC) observations during 2005–2021. Empirical Mode Decomposition (EMD) analysis was used to show that variations of sea level and temperature in the upper and lower CB are positively correlated with each other for short time scales of months to few years, but anticorrelated on low frequency modes representing decadal variability and long-term nonlinear trends. The long-term CB modes seem to be linked with AMOC variability through variations in the Gulf Stream and the wind-driven Ekman transports over the North Atlantic Ocean. AMOC variability correlates more strongly with variability in the southern CB near the mouth of the bay, where surface currents indicate potential links with AMOC variability. For example, when AMOC and the Gulf Stream were especially weak during 2009–2010, sea level in the southern bay was abnormally high, temperatures were colder than normal and outflow through the mouth of CB was especially high. Sea level in the upper bay responded to this change only 1–2 years later, which partly explains phase differences within the bay. A persistent trend of 0.22 cm/s per year of increased outflow from the CB, may be a sign of a climate-related trend associated with combination of weakening AMOC and increased precipitation and river discharge into the CB. [ABSTRACT FROM AUTHOR]

Changes in the Atlantic Meridional Overturning Circulation (AMOC) in the quadrupled CO2 experiments conducted under the sixth Coupled Model Intercomparison Project (CMIP6) are examined. Increased CO2 triggers extensive Arctic warming, causing widespread melting of sea ice. The resulting freshwater spreads southward, first from the Labrador Sea and then the Nordic Seas, and proceeds along the eastern coast of North America. The freshwater enters the subpolar gyre north of the separated Gulf Stream, the North Atlantic Current. This decreases the density gradient across the current and the current weakens in response, reducing the inflow to the deepwater production regions. The AMOC cell weakens in tandem, first near the North Atlantic Current and then spreading to higher and lower latitudes. This contrasts with the common perception that freshwater caps the convection regions, stifling deepwater production; rather, it is the inflow to the subpolar gyre that is suppressed. Changes in surface temperature have a much weaker effect, and there are no consistent changes in local or remote wind forcing among the models. Thus an increase in freshwater discharge, primarily from the Labrador Sea, is the precursor to AMOC weakening in these simulations. [ABSTRACT FROM AUTHOR]

Understanding the distribution and biodiversity of marine species is crucial for developing effective conservation strategies and maintaining the health of global ecosystems. Advancements in molecular data utilization have significantly improved our understanding of biodiversity within the genus Terebellides. In this study, we conducted a phylogenetic analysis on polychaete samples from the Kandalaksha Bay, White Sea, revealing their affiliation with a putative undescribed species of the genus Terebellides found in two locations of the North Sea. Interestingly, this species was not detected in the Norwegian and Barents Seas, leading us to propose a disjunct distribution scenario for this Terebellides species. This unique distribution pattern might be attributed to the succession of polychaetes by new species, facilitated by the Gulf Stream and a climate change role in driving shifts in species' ranges and altering marine ecosystem dynamics. [ABSTRACT FROM AUTHOR]

Molecular genetic analyses of Caribbean populations of the supposedly widespread intertidal oribatid mite Alismobates inexpectatus revealed the existence of a cryptic species. The new species, Alismobates piratus sp. n., shows considerable COI and 18S rRNA gene sequence divergences and although morphometric analyses indicate considerable variation between the taxa, no distinguishing morphological feature could be detected. The extreme intertidal environment is suggested to be responsible for the observed morphological stasis of the two species and vicariance is supposed to be responsible for their speciation. Alismobates piratus sp. n. was found on Hispaniola, Guadeloupe, Barbados and Curaçao indicating a predominant distribution on the Greater and Lesser Antilles, whereas the occurrence of A. inexpectatus is primarily restricted to Central America, the northern Caribbean and the Greater Antilles. Haplotype network analyses indicate distinct geographic structuring and the absence of recent gene flow among the Antillean A. piratus sp. n. populations. Central American and Antillean populations of A. inexpectatus show similar patterns but populations from Bermuda and the Bahamas are characterized by a common origin and subsequent expansion. Genetic landscape analysis demonstrates that vast stretches of open ocean, like the Caribbean Basin and the Western Atlantic, act as rather effective barriers, whereas the continuous continental coastline of Central and North America may facilitate dispersal. Genetic data also indicates that the Gulf Stream plays an important role for the biogeography of intertidal oribatid mites as it may be responsible for the strong link between Central and North American populations as well as for the colonization of Bermuda. [ABSTRACT FROM AUTHOR]

The Gulf Stream anchors a notable time-mean convergence zone during warm seasons, which produces strong precipitation and huge latent heat release in the free atmosphere. How the Gulf Stream front drives transient winds resulting in the convergence zone remains intensely debated. The oceanic-front-induced convergences are masked by strong synoptic disturbances. By synthesizing the 10-years high-frequency samplings by QuikSCAT, this study develops a novel procedure to isolate the subtle but climatically important convergence response to the oceanic front from the energetic synoptic disturbances. The binned convergence exhibits an evident cosine dependence on the angles between sea surface temperature (SST) gradients and transient winds and reaches its maximum when the winds deceleratingly blow down SST gradients, consistent with the so-called vertical mixing mechanism. The transient surface winds accelerate (decelerate) due to the enhanced (reduced) downward momentum transfer over the mesoscale warm (cold) waters. Thus, stronger down-SST-gradient winds cause stronger convergences over shaper SST gradients. The linear relationship between convergence and wind advection over SST gradients significantly contributes to the time-mean Gulf Stream convergence zone. The increased boundary-layer moisture acts to strengthen the SST-front-induced convergence and shifts convergence towards the Gulf Stream axis. As the synoptic disturbances frequent over the Gulf Stream, this study provides a potential pathway that the mesoscale SST gradients modulate synoptic disturbances through driving the surface wind convergences. [ABSTRACT FROM AUTHOR]

The surface-intensified, poleward-flowing Gulf Stream (GS) encounters the equatorward-flowing Deep Western Boundary Current (DWBC) at 36° N off Cape Hatteras. In this study, daily output from a data-assimilative, high-resolution (800 m), regional ocean reanalysis was examined to quantify variability in the velocity structure of the GS and DWBC during 2017–2018. The validity of this reanalysis was confirmed with independent observations of ocean velocity and density that demonstrate a high level of realism in the model's representation of the regional circulation. The model's daily velocity time series across a transect off Cape Hatteras was examined using rotated Empirical Orthogonal Function analysis, and analysis suggests three leading modes that characterize the variability of the western boundary currents throughout the water column. The first mode, related to meandering of the GS current, accounts for 55.3% of the variance, followed by a "wind-forced mode", which accounts for 12.5% of the variance. The third mode, influenced by the DWBC and upper-ocean eddies, accounts for 7.1% of the variance. [ABSTRACT FROM AUTHOR]

The eddy diffusivity in the ocean pycnocline K N = γ ε / N 2 is analyzed based on field measurements of the turbulent kinetic energy (TKE) dissipation rate ε z and buoyancy frequency N z profiles and an assumed mixing efficiency of γ = 0.2 . The microstructure measurements were taken between 2013 and 2019 in various regions of the Bay of Bengal (BoB) as well as the central Gulf Stream (GS) and deep waters of the Southern California Bight (SCB). The space–time variability of K N z , t observed in the pycnocline of the southeastern BoB is likely related to internal-wave generated turbulence, identified by its following of MacKinnon–Gregg scaling (MacKinnon and Gregg in J Phys Oceanogr 33(7):1476–1492, 2003). The probability distribution function of diffusivity CDF K N could be well fitted by generalized extreme value distribution (GEVD) for all regions of BoB and other oceans. Mixing rates in the upper pycnocline of BoB during extended southwestern monsoon period tend to be larger in the southern parts of the Bay compared to central and northern parts. Statistics of K N in the GS and SCB waters appear to be similar to those in the southern BoB with a characteristic median value ~ 2 × 10 - 6 m2/s, suggesting relatively low intensity of vertical mixing therein compared to the canonical pycnocline diffusivity of K N ≈ 10 - 5 m2/s. Article Highlights: Internal wave instabilities appear to be a dominant mechanism of generating energetic mixing events in the Bay of Bengal (BoB). Mixing rates (diffusivities) in the upper pycnocline tends to be larger in the southern BoB than in the northern part of the Bay. Generalized extreme value distribution approximates well the probability functions of the diffusivity in all tested regions of BoB as well as in the other oceans. [ABSTRACT FROM AUTHOR]

The Gulf of Mexico shifted from a colonial backwater to an active center of increasingly global maritime trade and commerce in the nineteenth century. This was due to the acquisition of the Gulf's northern territories by the United States as a result of the Louisiana Purchase and the transition of the region and the seas surrounding it into an American territory and economic center. The shipwrecks and maritime infrastructure of the Gulf from that period are a cohesive maritime cultural landscape. That landscape, however, also includes elements and sites that are non-American, but which relate to the other groups and nationalities in the region, as well as shipwrecks associated with Gulf trade that wrecked or were lost outside the geographic boundaries of the Gulf of Mexico while in active trade. [ABSTRACT FROM AUTHOR]

The Gulf of Mexico emerged as an American fishing frontier in the nineteenth century. Maritime activities expanded and matured in terms of technology, scope, and scale. This activity left a substantial archaeological record on the seabed in the Gulf. Two deep-water shipwrecks offer archaeologically well-preserved, essentially undisturbed opportunities to assess vessels likely engaged in the fishing industry in and around the Gulf in the nineteenth century: the 7000-Foot Wreck (c. 1890–1920), and the Green Lantern Wreck (c. 1890–1920). These two deep-water wreck sites are significant for their presumed archaeological integrity as sites associated with a type of vessel and trade not often studied archaeologically, and are worthy of further work. [ABSTRACT FROM AUTHOR]

Autoregressive spectral analysis revealed underlying cyclical trends in the highly variable biomass and mean body weight indices of two Northwest Atlantic squid species with opposing life histories. Doryteuthis pealeii attaches its egg masses to the seabed in shallow waters on the Northeast USA shelf. The broader-ranging Illex illecebrosus uses the Gulf Stream (GS) to transport its pelagic egg masses and paralarvae from the Southern (USA shelf) to the Middle (Scotian Shelf) and Northern (Grand Banks) Fishery Regions. We compared significant spectral peaks, or cycles, between the 1993–2016 survey indices, GS latitudinal positions (at 74°, 70°, 65°, 60°, 55° and 50°W) and winter North Atlantic Oscillation (NAO) indices to reveal any synchronicities. Positive NAO anomalies associated with northward GS position shifts were predominant. NAO indices exhibited 2–3-year, 4–5-year, and near-decadal cycles. GS position periodicities included 2–3-year, 3–4-year, and both timescales for west of 65°W (Western Segment), east of 60°W (Eastern), and from 65° to 60°W, respectively. I. illecebrosus indices exhibited stock-wide 3–4-year cycles and 2–3-year cycles for the Middle and Southern Fishery Regions that were synchronous with GS latitudinal positions for the Eastern and Western GS Segments, respectively. D. pealeii biomass cycles varied seasonally. Spring 4–5-year cycles were synchronous with the NAO, and fall near-decadal cycles were synchronous with the NAO and all GS locations analyzed. Our findings of inter-annual biomass and body weight cycles from 2 to 3 years to near-decadal are remarkable given the sub-annual lifespans of both species, but confirm the tight coupling between recruitment, body size, and cyclical environmental forcing factors. [ABSTRACT FROM AUTHOR]

The northern Indian River Lagoon (IRL) has been experiencing severe water quality degradation and phytoplankton blooms in the last decade or so. Two important factors for maintaining high water quality in estuaries are the water residence time and connectivity. Here we used a newly developed high-resolution hydrodynamic model to investigate both factors in this area. Two types of numerical experiments have been carried out: (1) tracer dilution experiments in which an inert tracer was released from selected sub-basins and tracked for 3 months, and (2) particle experiments in which a number of neutrally buoyant particles were released from selected areas and tracked for 1 month. The results indicate that surface winds may drive complex yet coherent residual circulation, including semi-enclosed re-circulation cells, within each subbasin, with the patterns mainly depending on the directions of prevailing winds. These patterns may promote retention of waters and transport barriers within sub-basins, leading to long water residence time with limited connectivity between sub-basins, and spatial heterogeneity of water properties such as salinity, nutrients, organic matter, and dissolved oxygen. Despite their transient nature (weekly to monthly), these dynamic features and associated processes may also significantly affect the development of phytoplankton blooms and marine habitats in this region. On the other hand, water throughout the lagoon was strongly influenced by the water level in the coastal oceans, especially the frontal position of the Gulf Stream. This suggests that water exchanges through the inlets, albeit limited, are important to the water quality and phytoplankton blooms in the lagoon. [ABSTRACT FROM AUTHOR]

This is the first high-resolution seismic study showing how the Chicxulub impact shaped the eastern slope of the Campeche Bank in the south-eastern Gulf of Mexico. The induced shock wave fractured Cretaceous strata causing the collapse of the upper slope and shelf over a length of ca. 200 km. Failed material was either transported downslope or remained in parts on the accommodation space created by the collapsed. In the Cenozoic, the East Campeche Plastered Drift developed within the created accommodation space, controlled by the inflowing surface current from the Caribbean, which forms the Loop Current. The internal reflection configuration of the drift shows that the closure of the Suwannee Strait in the Late Oligocene and the closure of the CAS in the Mid to Late Miocene controlled the variability of the southern Loop Current in time. Since the Loop Current transports heat and moisture from the western Atlantic warm water pool into the North Atlantic and further to NW Europe by the Gulf Stream, the drift represents an archive for controlling factors that influenced climate of the northern hemisphere. This first high-resolution seismic reflection study from the eastern Campeche Bank expands the understanding of destructive processes that a meteorite impact induces into the earth system. Furthermore, these data document that the East Campeche Plastered Drift bears the potential to understand the link between the climate variability of the northern hemisphere and oceanic processes in the equatorial western Atlantic. [ABSTRACT FROM AUTHOR]

Midlatitude atmospheric blocking events are important drivers of long-lasting extreme weather conditions at regional to continental scales. However, modern climate models consistently underestimate their frequency of occurrence compared to observations, casting doubt on future projections of climate extremes. Using the prominent and largely underestimated winter blocking events in Europe as a test case, this study first introduces a spatio-temporal approach to study blocking activity based on a clustering technique, allowing to assess models' ability to simulate both realistic frequencies and locations of blocking events. A sensitivity analysis from an ensemble of 49 simulations from 24 coupled climate models shows that the presence of a mesoscale eddy-permitting ocean model increases the realism of simulated blocking events for almost all types of patterns clustered from observations. This finding is further explained and supported by concomitant reductions in well-documented biases in Gulf Stream and North Atlantic Current positions, as well as in the midlatitude jet stream variability. [ABSTRACT FROM AUTHOR]

We present observational evidence of a significant increase in Salinity Maximum intrusions in the Northeast US Shelf waters in the years following 2000. This increase is subsequent to and influenced by a previously observed regime-shift in the annual formation rate for Gulf Stream Warm Core Rings, which are relatively more saline than the shelf waters. Specifically, mid-depth salinity maximum intrusions, a cross-shelf exchange process, has shown a quadrupling in frequency on the shelf after the year 2000. This increase in intrusion frequency can be linked to a similar increase in Warm Core Ring occupancy footprint along the offshore edge of the shelf-break which has greatly increased the abundance of warm salty water within the Slope Sea. The increased ring occupancy footprint along the shelf follows from the near doubling in annual Warm Core Ring formation rate from the Gulf Stream. The increased occurrence of intrusions is likely driven by a combination of a larger number of rings in the slope sea and the northward shift in the GS position which may lead to more interactions between rings and the shelf topography. These results have significant implications for interpreting temporal changes in the shelf ecosystem from the standpoint of both larval recruitment as well as habitability for various important commercial species. [ABSTRACT FROM AUTHOR]

The Labrador Current transports cold, relatively fresh, and well-oxygenated waters within the subpolar North Atlantic and towards the eastern American continental shelf. The relative contribution of these waters to either region depends on the eastward retroflection of the Labrador Current at the Grand Banks of Newfoundland. Here, we develop a retroflection index based on the pathway of virtual Lagrangian particles and show that strong retroflection generally occurs when a large-scale circulation adjustment, related to the subpolar gyre, accelerates the Labrador Current and shifts the Gulf Stream northward, partly driven by a northward shift of the wind patterns in the western North Atlantic. Starting in 2008, a particularly strong northward shift of the Gulf Stream dominates the other drivers. A mechanistic understanding of the drivers of the Labrador Current retroflection should help predict changes in the water properties in both export regions, and anticipate their impacts on marine life and deep-water formation. The authors find that whether the Labrador Current transports its cold, relatively fresh, and well oxygenated waters towards the subpolar North Atlantic or the eastern American coast depends on large-scale forcing, partly driven by winds over the North Atlantic. [ABSTRACT FROM AUTHOR]

An analysis of the variability of the winter surface temperature anomaly in the North Atlantic in decades of negative and positive values of the North Atlantic Oscillation Index is presented. It is found that, in a decade with negative values of the North Atlantic Oscillation Index, the slope waters of the Gulf Stream system and Labrador Current waters decrease the temperature of the Gulf Stream at the mixing zone on the Scotia Peninsula shelf and in the area of the quasi-stationary anticyclonic gyre to a maximum. In a decade with positive values of the North Atlantic Oscillation Index, the temperature of the slope waters is close to the climate normal. Taking into account the increased speed of the Gulf Stream in the years with positive values of the North Atlantic Oscillation Index, the spreading of the ocean surface temperature anomaly over the North Atlantic water area occurs for a shorter time than in the years with negative values. [ABSTRACT FROM AUTHOR]

The North Atlantic Warming Hole (NAWH) has been observed and predicted due to the increase in carbon dioxide (CO2) concentration. If sulphate aerosols, which have a cooling effect on the atmosphere, are reduced by air pollution control, the NAWH may form as it would if CO2 concentrations increased. In this study, sensitivity experiments using a coupled atmosphere–ocean-aerosol model were conducted by varying the amount of sulphur dioxide (SO2) emissions, a precursor of sulphate which is the primary anthropogenic aerosol in the atmosphere, to analyse the changes in the ocean temperature, salinity, and density. The results showed that although the spatial patterns of the NAWH due to the changes in SO2 emissions was similar to that due to the changes in the CO2 concentrations, the magnitude of the shifts in the ocean parameters due to the changes in SO2 emissions is larger even when changes in global mean temperature are comparable. This can be due to the spatial concentration of sulphate aerosols in the mid-latitudes of the Northern Hemisphere, resulting larger changes in the heat transport from the south on the Gulf Stream and the North Atlantic Current along with changes in freshwater inflow from the Arctic through the Labrador Sea. [ABSTRACT FROM AUTHOR]

Seawater temperature is one of the main variables that determines cold-water coral distribution worldwide. As part of an initiative to explore new areas of deep-sea habitats along the Southeast United States (SEUS) continental margin, a series of expeditions were carried out as part of the Deep-Sea Exploration to Advance Research on Corals/Canyons/Cold seeps (DEEP SEARCH) project. During these explorations, a cold-water coral reef complex composed mainly of Lophelia pertusa was located off the coast of South Carolina at 650–850 m depth. In this geographic area the species normally has a thermal tolerance between 6 and 12 °C with the capacity to form extensive calcium carbonate structures, thus creating complex habitat for a variety of associated species. Owing to the paucity of these structures and the unusual environmental conditions of this geographic area, with regular arrival of warm surface waters from the Gulf Stream, the main aim of this study was to understand the physiological response of L. pertusa to the variation in extreme temperature events in this region. Short-term experiments simulated the rate of temperature increase from the ambient temperature (8 °C) to the environmental maximum (14 °C) (heat-wave treatment). We found that temperature had a significant effect on the metabolic functions through an increase in respiration (0.108 to 0.247 µmol O2 g−1DW h−1) and excretion rates (0.002 to 0.011 µmol NH3 g−1DW h−1) at 14 °C. Oxygen to Nitrogen ratios (O:N) also showed an effect of temperature where corals switched from lipid-dominated toward a mix of lipid-protein and protein-dominated catabolism. To further characterize the metabolic response, feeding assays (capture rate of Artemia) were performed at the same temperature range with an overall three-fold decrease in capture rates under 14 °C compared to ambient temperature, thus increasing the probability of temperature-induced metabolic stress. Our results suggest that temperature variations affect the metabolic response of cold-water corals, particularly along the SEUS continental margin. Since the incursion of warm surface water to deeper zones is predicted to increase in frequency and duration due to climate change, L. pertusa may be implicated negatively, followed by ecological consequences for the survival and functionality for the ecosystem it supports. [ABSTRACT FROM AUTHOR]

Decline in winter sea-ice concentration (SIC) in the Barents-Kara Sea significantly impacts climate through increased heat release to the atmosphere. However, the past Barents-Kara SIC decrease rate is underestimated in the majority of Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models. Here we show that climate model simulations can reproduce the Barents-Kara SIC trend for 1970–2017 when sea surface temperature (SST) variability in the Gulf Stream region is constrained by observations. The constrained warming of the Gulf Stream strengthens ocean heat transport to the Barents-Kara Sea that enhances the SIC decline. The linear trends between the SIC and SST are highly correlated in the CMIP6 ensemble, suggesting that the externally forced component of the Gulf Stream SST increase explains up to 56% of the forced Barents-Kara SIC trend. Therefore, future warming of the Gulf Stream can be an essential pacemaker of the SIC decline. Climate model simulations show that for 1970-2017 externally-forced sea surface temperature increases in the Gulf Stream explain up to 56% of the sea-ice decline in the Barents-Kara Sea during winter via poleward oceanic heat transport. [ABSTRACT FROM AUTHOR]

We have investigated the horizontal resolution dependence of the ocean–atmosphere coupling along the Gulf Stream, of simulations made by six Global Climate Models according to the HighResMIP protocol, and compared it with reanalysis and remote sensing observations. Two ocean–atmosphere interaction mechanisms are explored in detail: The Vertical Mixing Mechanism (VMM) associated with the intensification of downward momentum transfer, and the Pressure Adjustment Mechanism (PAM) associated with secondary circulations driven by pressure gradients. Both VMM and PAM are found to be active even in the eddy-parameterized models. However, increasing ocean and/or atmosphere resolution leads to enhanced ocean–atmosphere coupling and improved agreement with reanalysis and observations. Our results indicate that while one part of the stronger air–sea coupling is attributable to the refinement of the oceanic component to eddy-permitting, optimal results are obtained only by further increase of the atmosphere resolution too. The use of the eddy-resolving model show weaker or same coupling strength over the eddy-permitting resolution. We conclude that at least eddy-permiting ocean resolution and comparable atmosphere resolution are required for a reliable ocean–atmosphere coupling along the Gulf Stream. [ABSTRACT FROM AUTHOR]

A regional numerical ocean model of the Gulf Stream (GS) and the US East Coast was used to conduct sensitivity experiments of the dynamic response to temperature anomalies originated at different Atlantic locations. In a series of experiments, temperature anomalies were injected into the model domain through inflow boundary conditions at either the Florida Current (FC), the Slope Current (SC), or the Sargasso Sea (SS), while holding all other inflows/outflows unchanged. The strong currents and meso-scale variability of the GS system result in fast transport of anomalies throughout the model domain and immediate response within days. During a period of 60 days, remote temperature anomalies of ± 2 °C induced about 5–12 cm change in coastal sea level, about 0.5–1.0 ms−1 change in velocity, and about 30–50 km shift in the GS position, and a significant increase in kinetic energy of the whole GS system. Warm anomaly entering into the GS from the south through the FC had the strongest impact, strengthening the GS and temporally lowering coastal sea level by as much as ~ 10 cm, compared with coastal sea level drop of ~ 2–3 cm when the same warm anomaly was coming from the SS. Cold or warm anomalies coming from the north through the SC caused a large shift in the GS path, which moved onshore in the Mid-Atlantic Bight (MAB) and offshore in the South Atlantic Bight (SAB). Observations taken in 2017 when 3 hurricanes disrupted the GS flow show similar links between temperature anomalies, the GS, and coastal sea level, as in the idealized model simulations. The results demonstrated how temperature anomalies due to storms or uneven climate warming can cause variations on the coast and increased kinetic energy near western boundary currents. Since coastal sea level is positively correlated with temperature, but negatively correlated with the strength of the GS, the non-linear combination of the two factors can result in unexpected spatiotemporal variability in coastal sea level. The study provides better understanding of how remote signals affect the coast. [ABSTRACT FROM AUTHOR]

This study investigates linear trends, variability and predictive skill of the upper ocean heat content (OHC) in the North Atlantic basin. This is a region where strong decadal variability superimposes the externally forced trends, introducing important differences in the local warming rates and leading in the case of the Central Subpolar North Atlantic to an overall long-term cooling. Our analysis aims to better understand these regional differences, by investigating how internal and forced variability contribute to local trends, exploring also their role on the local prediction skill. The analysis combines the study of three ocean reanalyses to document the uncertainties related to observations with two sets of CMIP6 experiments performed with the global coupled climate model EC-Earth3: a historical ensemble to characterise the forced signals, and a retrospective decadal prediction system to additionally characterise the contributions from internal climate variability. Our results show that internal variability is essential to understand the spatial pattern of North Atlantic OHC trends, contributing decisively to the local trends and providing high levels of predictive skill in the Eastern Subpolar North Atlantic and the Irminger and Iceland Seas, and to a lesser extent in the Labrador Sea. Skill and trends in other areas like the Subtropical North Atlantic, or the Gulf Stream Extension are mostly externally forced. Large observational and modeling uncertainties affect the trends and interannual variability in the Central Subpolar North Atlantic, the only region exhibiting a cooling during the study period, uncertainties that might explain the very poor local predictive skill. [ABSTRACT FROM AUTHOR]

Several ocean Western Boundary Currents (WBCs) encounter a lateral gap along their path. Examples are the Kuroshio Current penetrating into the South China Sea through the Luzon Strait and the Gulf of Mexico Loop Current leaping from the Yucatan peninsula to Florida as part of the Gulf Stream system. Here, we present results on WBC relevant flows, generated in the world's largest rotating platform, where the Earth's sphericity necessary to support WBCs is realized by an equivalent topographic effect. The fluid is put in motion by a pump system, which produces a current that is stationary far from the gap. When the jet reaches the gap entrance, time-dependent patterns with complex spatial structures appear, with the jet leaking, leaping or looping through the gap. The occurrence of these intrinsic self-sustained periodic or aperiodic oscillations depending on current intensity is well known in nonlinear dynamical systems theory and occurs in many real systems. It has been observed here for the first time in real rotating fluid flows and is thought to be highly relevant to explain low-frequency variability in ocean WBCs. [ABSTRACT FROM AUTHOR]

A new approach for analysis of spatiotemporal variability across ocean basins was tested using global 1° × 1° monthly sea level reconstruction (RecSL) for 1900–2015. Each sea level cross section η(x,t) was converted into a single time series that contains both spatial and temporal variabilities by connecting back and forth repeated monthly sections. For example, a single zonal section between 50°W and 50°E would create a time series of 116 years × 12 months × 100° = 139,200 data points. The long record allowed great statistical significance and direct comparison between energy in spatial variability and energy in temporal variability. Time and length scales found in 116 years of RecSL data are compared with 23 years of altimeter data. Empirical Mode Decomposition (EMD) was then used to break the record into high-frequency modes representing spatial variability across the section and lower frequency modes representing temporal variability (capturing time scales of a few months to multidecadal). Examples of the spatiotemporal analysis in the Pacific Ocean showed how the method detected an increase in El Niño amplitude in equatorial regions and characterized spatiotemporal changes in the Kuroshio Current in mid-latitudes. In the Atlantic Ocean, the analysis showed the latitudinal dependency of spatiotemporal variability: for example, sections near the Gulf Stream (GS) and the Antarctic Circumpolar Current (ACC) showed energy dominated by small-scale spatial variability while sections across equatorial and subpolar North Atlantic regions showed energy dominated by long-term temporal variability and diminishing energy in spatial variability. The impact of the North Atlantic Oscillation (NAO) index on spatiotemporal variability showed that interannual variations in NAO are highly correlated with subpolar sea level variability, while decadal and longer variations in NAO are linked with sea level variations at the equatorial South Atlantic and the Antarctic zone. This analysis can be useful for other observations and various climate data. [ABSTRACT FROM AUTHOR]

Interannual oscillatory modes, atmospheric and oceanic, are present in several large regions of the globe. We examine here low-frequency variability (LFV) over the entire globe in the Community Earth System Model (CESM) and in the NCEP-NCAR and ECMWF ERA5 reanalyses. Multichannel singular spectrum analysis (MSSA) is applied to these three datasets. In the fully coupled CESM1.1 model, with its resolution of 0.1 × 0.1 degrees in the ocean and 0.25 × 0.25 degrees in the atmosphere, the fields analyzed are surface temperatures, sea level pressures and the 200-hPa geopotential. The simulation is 100-year long and the last 66 yr are used in the analysis. The two statistically significant periodicities in this IPCC-class model are 11 and 3.4 year. In the NCEP-NCAR reanalysis, the fields of sea level pressure and of 200-hPa geopotential are analyzed at the available resolution of 2.5 × 2.5 degrees over the 68-years interval 1949–2016. Oscillations with periods of 12 and 3.6 years are found to be statistically significant in this dataset. In the ECMWF ERA5 reanalysis, the 200-hPa geopotential field was analyzed at its resolution of 0.25 × 0.25 degrees over the 71-years interval 1950–2020. Oscillations with periods of 10 and 3.6 years are found to be statistically significant in this third dataset. The spatio-temporal patterns of the oscillations in the three datasets are quite similar. The spatial pattern of these global oscillations over the North Pacific and North Atlantic resemble the Pacific Decadal Oscillation and the LFV found in the Gulf Stream region and Labrador Sea, respectively. We speculate that such regional oscillations are synchronized over the globe, thus yielding the global oscillatory modes found herein, and discuss the potential role of the 11-year solar-irradiance cycle in this synchronization. The robustness of the two global modes, with their 10–12 and 3.4–3.6 years periodicities, also suggests potential contributions to predictability at 1–3 years horizons. [ABSTRACT FROM AUTHOR]

Global sea level reconstruction (RecSL) for 1900–2015 was used to estimate the variations in oceanic kinetic energy (OKE) and compare OKE with changes in wind patterns and wind kinetic energy (WKE); the comparison was done for each latitude and for 5 western boundary currents (WBCs). Two contributors to variability in sea level were analyzed: gravitational, rotational and deformational effects (GRD) related to changes in water masses (barystatic sea level change), and changes in the sterodynamic sea level (SDSL), associated with changes in wind, steric sea level and ocean circulation. GRD changes were responsible for latitudinal multidecadal variations with time scale of ~ 60 to 80 years, while SDSL changes were responsible for interannual and decadal variability, and together with the Greenland ice melt, to sea level acceleration since the 1960s. Regional changes near WBCs show a coherent upward trend in OKE (+ 24% ± 3 increase per century), while trends in WKE over the same regions changed widely from -11% (decrease) over the Gulf Stream region to + 28% (increase) over the Brazil Current region. Low frequency oscillations of wind and oceanic kinetic energy are correlated in some WBCs (e.g., R = 0.5 in the Kuroshio region) but not in others (e.g., R = -0.05 in the Gulf Stream region). The study suggests that several forcing mechanisms contribute to the increased OKE, they include an increased wind-stress curl over subtropical gyres, local changes in wind patterns that impact some WBCs, and large uneven warming near WBCs that increased sea level gradients and thus intensified OKE. [ABSTRACT FROM AUTHOR]

Bycatch in fisheries is a major threat to many seabird species. Understanding and predicting spatiotemporal changes in seabird bycatch from fisheries might be the key to mitigation. Inter-annual spatiotemporal patterns are evident in seabird bycatch of the U.S. Atlantic pelagic longline fishery monitored by the National Marine Fisheries Service Pelagic Observer Program (POP) since 1992. A newly developed fast computing Bayesian approximation method provided the opportunity to use POP data to understand spatiotemporal patterns, including temporal changes in location of seabird bycatch hotspots. A Bayesian model was developed to capture the inherent spatiotemporal structure in seabird bycatch and reduce the bias caused by physical barriers such as coastlines. The model was applied to the logbook data to estimate seabird bycatch for each longline set, and the mid-Atlantic bight and northeast coast were the fishing areas with the highest fleet bycatch estimate. Inter-annual changes in predicted bycatch hotspots were correlated with Gulf Stream meanders, suggesting that predictable patterns in Gulf Stream meanders could enable advanced planning of fishing fleet schedules and areas of operation. The greater the Gulf Stream North Wall index, the more northerly the seabird bycatch hotspot two years later. A simulation study suggested that switching fishing fleets from the hindcasted actual bycatch hotspot to neighboring areas and/or different periods could be an efficient strategy to decrease seabird bycatch while largely maintaining fishers' benefit. [ABSTRACT FROM AUTHOR]

The Loop Current evolves in the Gulf of Mexico as a continuation of the Yucatan Current and its upstream Caribbean Current, entering through the Yucatan Channel from the Northwestern Caribbean Sea. The Loop Current system contains the associated rich eddy field and together with the Florida Current controls the exit of the Gulf Stream toward the Atlantic Ocean and its downstream evolution along the US coasts. We examine the consequences of this natural connectivity, focusing on the dynamical synergy of mesoscale circulation processes downstream (north) of the Yucatan Channel (Gulf interior, dominated by Loop Current variability) and upstream (south) of the Yucatan Channel (Northwestern Caribbean Sea). We focus on Caribbean Anticyclones, their characteristics and evolution as they feed into the Loop Current system. We employ observational (satellite altimetry and drifters) and simulated (ocean numerical model) data for a 9-year period (2010–2018). Several metrics related to the Loop Current (maximum latitude, axis), Yucatan Current (zonal position), and Caribbean Sea mesoscale circulation (vorticity) are used to quantify how the accurate representation of Caribbean eddies can improve the prediction of the Loop Current. The numerical results, the altimetry observational fields, and the respective drifter trajectories show a strong relationship between the Caribbean Anticyclones and the Loop Current variability, both at the base of the Loop Current (position of the Yucatan Current) and within the Gulf interior (northern Loop Current position and orientation). During retracted Loop Current periods, the evolution of anticyclones in the Yucatan Channel plays a role on the eastward tilt of the Loop Current axis and the zonal shift of the Yucatan Current close to the island of Cuba. Lagrangian analyses confirmed that coherent anticyclonic flux across the Yucatan Channel usually evolves closer to Cuba and is associated with retracted Loop Current phases. A lag of 5 to 10 days between the anticyclonic vorticity in the northwestern Caribbean and the Loop Current variability was identified. The evolution of Caribbean Anticyclones crossing the Yucatan Channel is thus an influencing factor on the interior dynamics of the Gulf of Mexico and the connectivity processes with the Caribbean Sea. [ABSTRACT FROM AUTHOR]

The bulk sea surface temperature (SST) simulated by COAMPS/NCOM [Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) and the Navy Coastal Ocean Model (NCOM)] compares reasonably well with the bulk SST measured on the North Carolina shelf during the October of 2015 field campaign of the CASPER Project (Wang et al. in Bull Amer Met Soc 99:1449–1471, 2018). The model slightly overestimates the field data by about 0.15 °C; a linear regression is strong with a coefficient of determination r2 > 0.9. In deep waters of the Gulf Stream core, COAMPS/NCOM typically underestimates the measured SST by less than 1 °C except in the cold lens or meander where the temperature gradients were smoothed by the model. It is evident that sub-mesoscale features like frontal eddies, meanders and filaments, require a resolution higher than the 3 km grid spacing adopted for modeling. [ABSTRACT FROM AUTHOR]

Pelagic Sargassum macroalgal rafts in the North Atlantic support sessile and motile epifauna that attract ecologically and economically important migratory organisms. Three prevalent pelagic Sargassum morphotypes vary in their degree of branching and foliation, and thus have different structural complexities that can influence their respective value as motile epifauna habitat. Sargassum fluitans III and S. natans I have denser foliation, creating a complex habitat; in contrast, S. natans VIII is more open and architecturally simple. In 2015/2016, 373 dip net samples of algae were collected from the Tropical Atlantic, Greater Caribbean, Gulf of Mexico, Gulf Stream, and Sargasso Sea. 20,975 individual motile epifauna from 32 taxa were recorded. Sargassum fluitans III supported higher densities of individuals and greater numbers of taxa than S. natans VIII or S. natans I, a pattern attributed to its more complex architecture and consistent with communities on benthic and floating macroalgae. Most assemblages comprised a few dominant and many rare motile epifauna; when compared to historical studies, dominant motile epifauna had shifted. These findings suggest important differences in ecological value between pelagic Sargassum morphotypes with implications for coastal and pelagic conservation strategies, which warrant consideration given recent shifts in morphotype distribution and recurring pelagic Sargassum inundation events. [ABSTRACT FROM AUTHOR]

The present study examined the relationship between turbulent surface heat flux (SHF) and sea surface temperature (SST) variations using daily observational data. The SHF and SST relationship displays notable differences between winter and summer and prominent time-scale dependence in both seasons. In the mid-latitude SST frontal regions, SST has a larger role in driving SHF in winter than in summer. In the subtropical gyre regions, SHF plays a larger role in the SST change in summer than in winter. In winter, SHF has a larger effect on the SST change in the South China Sea than in the Arabian Sea and Bay of Bengal. In summer, the SST effect on SHF is dominant in the Arabian Sea, whereas the SHF impact on SST is dominant in the Philippine Sea. In the Gulf Stream, Kuroshio Extension and Agulhas Return Current, the SST effect extends up to 90-day time scales in winter, the SHF impact is limited to time scales below 20 days and the SST effect is dominant on time scales above 20 days in summer. In winter, the SHF effect extends up to 90-day time scales in the Bay of Bengal, South China Sea, and Philippine Sea, but is limited to time scales below 40 days in the Arabian Sea. In summer, the SST effect extends up to 90-day time scales in the Arabian Sea, whereas the SHF and SST effect is large on time scales shorter and longer than 40 days, respectively, in the Philippine Sea. [ABSTRACT FROM AUTHOR]

Recent research suggests the widespread existence of the signal-to-noise paradox in seasonal-to-decadal climate predictions. The essence of the paradox is that the signal-to-noise ratio in models can be unrealistically small and models may make better predictions of the observations than they predict themselves. The paradox highlights a potentially serious issue with model predictions as previous studies may underestimate the limit of predictability. The focus of this paper is two-fold: the first objective is to re-examine decadal predictability from the lens of the signal-to-noise paradox in the context of CMIP5 models. We demonstrate that decadal predictability is generally underestimated in CMIP5 models possibly due to the existence of the signal-to-noise paradox. Models underestimate decadal predictability in regions where it is likely for the paradox to exist, especially over the Tropical Atlantic Ocean and Tropical Indian Ocean and eddy-rich regions, including the Gulf Stream, Kuroshio Current, and Southern Ocean. The second objective follows from the results of the first, attempting to determine if this underestimate of decadal predictability is, at least partially, due to missing ocean mesoscale processes and features in CMIP5 models. A suite of coupled model experiments is performed with eddying and eddy-parameterized ocean component. Compared with eddy-parameterized models, the paradox is less likely to exist in eddying models, particularly over eddy-rich regions. These also happen to be regions where increased decadal predictability is identified. We hypothesize that this enhanced predictability is due to the enhanced vertical connectivity in the ocean. The presence of mesoscale ocean features and associated vertical connectivity significantly influence decadal variability, predictability, and the signal-to-noise paradox. [ABSTRACT FROM AUTHOR]

The input of mechanical power to the ocean due to the surface wind stress, in regions which correspond to different regimes of ocean dynamics, is considered using data from satellites observations. Its dependence on the coarse-graining range of the atmospheric and oceanic velocity in space from 0.5 to 10∘ and time from 6 h to 40 days is determined. In the area of the Gulf Stream and the Kuroshio extensions, the dependence of the power input on space-time coarse-graining varies over tenfold for the coarse-graining considered. It decreases over twofold for the Gulf Stream extension and threefold for the Kuroshio extension, when the coarse-graining length scale passes from a few degrees to 0.5∘ at a temporal coarse-graining scale of a few days. It increases over threefold in the Gulf Stream and the Kuroshio extensions when the coarse-graining passes from several days to 6 h at a spatial coarse-graining of a few degrees. The power input is found to increase monotonically with shorter coarse-graining in time. Its variation with coarse-graining in space has no definite sign. Results show that including the dynamics at scales below a few degrees reduces considerably the power input by air-sea interaction in regions of strongly nonlinear ocean currents. When the ocean velocities are not considered in the shear calculation, the power input is considerably (up to threefold) increased. The dependence of the power input on coarse-graining in space and time is close to being multiplicatively separable in all regions and for most of the coarse-graining domain considered. [ABSTRACT FROM AUTHOR]

A dominant paradigm for mid-latitude air-sea interaction identifies the synoptic-scale atmospheric "noise" as the main driver for the observed ocean surface variability. While this conceptual model successfully holds over most of the mid-latitude ocean surface, its soundness over frontal zones (including western boundary currents; WBC) characterized by intense mesoscale activity, has been questioned in a number of studies suggesting a driving role for the small scale ocean dynamics (mesoscale oceanic eddies) in the modulation of air-sea interaction. In this context, climate models provide a powerful experimental device to inspect the emerging scale-dependent nature of mid-latitude air-sea interaction. This study assesses the impact of model resolution on the representation of air-sea interaction over the Gulf Stream region, in a multi-model ensemble of present-climate simulations performed using a common experimental design. Lead-lag correlation and covariance patterns between sea surface temperature (SST) and turbulent heat flux (THF) are diagnosed to identify the leading regimes of air-sea interaction in a region encompassing both the Gulf Stream system and the North Atlantic subtropical basin. Based on these statistical metrics it is found that coupled models based on "laminar" (eddy-parameterised) and eddy-permitting oceans are able to discriminate between an ocean-driven regime, dominating the region controlled by the Gulf Stream dynamics, and an atmosphere-driven regime, typical of the open ocean regions. However, the increase of model resolution leads to a better representation of SST and THF cross-covariance patterns and functional forms, and the major improvements can be largely ascribed to a refinement of the oceanic model component. [ABSTRACT FROM AUTHOR]

As the Gulf Stream separates from the coast, it sheds both Warm and Cold Core Rings between 75 ∘ and 55 ∘ W . We present evidence that this ring formation behavior has been asymmetric over both interannual and seasonal time-scales. After a previously reported regime-shift in 2000, 15 more Warm Core Rings have been forming yearly compared to 1980–1999. In contrast, there have been no changes in the annual formation rate of the Cold Core Rings. This increase in Warm Core Ring production leads to an excess heat transfer of 0.10 PW to the Slope Sea, amounting to 7.7–12.4% of the total Gulf Stream heat transport, or 5.4–7.3% of the global oceanic heat budget at 30 ∘ N . Seasonally, more Cold Core Rings are produced in the winter and spring and more Warm Core Rings are produced in the summer and fall leading to more summertime heat transfer to the north of the Stream. The seasonal cycle of relative ring formation numbers is strongly correlated (r = 0.82) with that of the difference in upper layer temperatures between the Sargasso and Slope seas. This quantification motivates future efforts to understand the recent increasing influence of the Gulf Stream on the circulation and ecosystem in the western North Atlantic. [ABSTRACT FROM AUTHOR]

Bear Seamount (39° 55′ N; 67° 30′ W) is the oldest and westernmost seamount in the New England Seamount Chain. It is located in the Marine National Monument on the continental slope south of Georges Bank and is influenced by unique ecological factors and currents. We enumerated and calculated the diversity, catch per unit effort (CPUE), and distribution of trawl-susceptible crustacean micronekton (2–20 cm) in the vicinity of Bear Seamount. Sixty-six species of pelagic Crustacea (Decapoda, Lophogastrida, and Euphausiacea) were taken with large, double-warp midwater trawls at 33 stations in the spring of 2003 and 2004 and fall of 2014. Oblique trawl sampling occurred from the surface to 2238 m, with most sampling concentrated between 600 and 1700 m depth. In 2003–2004, the assemblage on the south side of the seamount was the most diverse, while the summit assemblage had the greatest CPUE and species richness. In 2014, the summit assemblage was the most diverse and species rich while the assemblage on the west side had the greatest CPUE. Rarefaction curves did not reach an asymptote, suggesting increased sampling effort will yield more species at Bear Seamount. Eusergestes arcticus and Meganyctiphanes norvegica were numerically dominant. Two species Pasiphaea hoplocerca and P. merriami are new records for Northwest Atlantic waters. [ABSTRACT FROM AUTHOR]

The Florida Current marks the beginning of the Gulf Stream at Florida Straits, and plays an important role in climate. Nearly continuous measurements of Florida Current transport are available at 27°N since 1982. These data are too short for assessing possible multidecadal or centennial trends. Here I reconstruct Florida Current transport during 1909–2018 using probabilistic methods and principles of ocean physics applied to the available transport data and longer coastal sea-level records. Florida Current transport likely declined steadily during the past century. Transport since 1982 has likely been weaker on average than during 1909–1981. The weakest decadal-mean transport in the last 110 y likely took place in the past two decades. Results corroborate hypotheses that the deep branch of the overturning circulation declined over the recent past, and support relationships observed in climate models between the overturning and surface western boundary current transports at multidecadal and longer timescales. Understanding trends in ocean circulation and dynamics is hampered by a lack of long-term records. Here the author uses probabilistic reanalysis of available data to show that transport by the Florida Current has declined over the past 110 years, indicating a slowdown of Atlantic Ocean circulation. [ABSTRACT FROM AUTHOR]

The meandering of the Gulf Stream through the Straits of Florida is associated with eddy activity to the north (along the Florida Keys) and the south (along the Cuban coast). This study focuses on recently identified processes along the Cuban coast, namely anticyclonic eddies (Cuban ANticyclones: CubANs) and cyclonic activity characterized by cold-core eddies (cyclones) and coastal upwelling that enhances them. It is shown that these processes are an important factor for the evolution of the Loop Current/Florida Current (LC/FC) system. In particular, the Gulf Stream meandering inside the Straits (that is manifested as the position of the FC branch) is strongly related to CubANs either inside the retracted (closer to the Cuban coast) LC branch (CubAN "A") or outside the LC as independent eddies (CubAN "B"). There are also mixed cases that both types of CubANs can be present, sharing a common place of origin, but evolving differently. These anticyclones are found to be strongly related to cyclonic activity and resulting temperature gradients along Cuba, characterized by cold-core cyclonic eddies and additional pools of cold waters that have upwelled under wind influence. These processes are shown to influence Gulf Stream meandering and also largely control the offshore export of upwelled, generally cooler and more productive, coastal waters. High-resolution simulations, in tandem with a variety of observational data, are used during a period of 8 years (2010–2017) to describe the evolution of CubANs and their contribution to Gulf Stream variability and associated coastal to offshore interactions. These findings are important for connectivity pathways between US and Cuban marine protected areas and between US coasts and the main Cuban area of oil exploration. [ABSTRACT FROM AUTHOR]

The Gulf Stream (GS) transports a massive amount of heat northward to high latitudes and releases sensible and latent heat to the atmosphere, playing an important role in the North Atlantic and European climate change. The change trends of the GS transport and pathway are still uncertain to date. Our analyses of altimeter observations from 1993 to 2016 indicate that the linear trends in surface maximum speed, transport, and latitudinal location of the GS are significant east of 61° W at the 95% level while they are small and not significant between 72° W and 61° W. The weakening trend of the GS during the period from 1993 to 2016 is accompanied with a southward-shifting path, which is associated with the decline of the North Atlantic Oscillation (NAO) and possibly reduction in the Atlantic meridional overturning circulation (AMOC). [ABSTRACT FROM AUTHOR]

Characterizing deep-sea coral biodiversity is essential to evaluate the current state of deep-sea ecosystems and to assess vulnerability to anthropogenic threats such as offshore drilling and ocean acidification. Thousands of deep-sea coral records from the past 6 decades are compiled in the publicly accessible NOAA database, but few large-scale analyses of deep-sea coral biodiversity through time have been conducted. This study provides the longest temporal analysis of deep-sea coral generic biodiversity (58 yr), and the first such study for US waters. To mitigate missing temporal and spatial data, a machine learning model was employed to simulate deep-sea coral occurrences. Patterns of deep-sea coral generic biodiversity were calculated for observed and simulated data from 1960 to 2018 in the US marine ecoregions of the Gulf Stream Slope, Carolinian Atlantic Shelf and Slope, South Florida/Bahamian Atlantic Shelf and Slope, and Northern Gulf of Mexico (NGOM) Shelf and Slope. There were statistically significant decreases in deep-sea coral generic biodiversity for all ecoregion/depth pairs in simulated data and most ecoregion/depth pairs in observed data. There was relative stability in biodiversity from 1960 to the mid-2000s, followed by generally rapid decreases between 2007 and 2011. Biodiversity stabilized after 2011, though it remains at the lowest average level in the past 58 yr. Most ecoregions and depths show the lowest generic richness during the most recent time interval (2010–2018) compared to the preceding 5 decades. The most persistent deep-sea coral genera from 1960 to 2018 vary based on ecoregion and depth. Rapid decreases in biodiversity support previous work showing deep-sea corals can undergo biodiversity loss in less than 4 yr, which is alarming given their slow growth and decadal recovery times. This analysis provides a robust temporal framework for future researchers to evaluate casual mechanisms affecting deep-sea coral biodiversity and inform on conservation strategies. [ABSTRACT FROM AUTHOR]

The generation of lee waves in the Gulf Stream along the U.S. seaboard is investigated using high resolution realistic simulations. The model reproduces the surface signature of the waves, which compares favourably with observations from satellite sun glitter images in the region. In particular, a large number of internal waves are observed above the Charleston Bump. These waves match well with the linear theory describing topographically-generated internal waves, which can be used to estimate the associated vertical transport of momentum and energy extracted from the mean flow. Finally, small scale topographic features are shown to have a significant impact on the mean flow in this region of the Gulf Stream, and the specific role of lee waves in this context is outlined. [ABSTRACT FROM AUTHOR]

Sea level rise (SLR) is causing acceleration in the frequency and duration of minor tidal flooding (often called "sunny-day" or "nuisance" flooding) along the U.S. East Coast. Those floods have a seasonal pattern that often follows the monthly mean sea level anomaly which peaks in September–October for stations between New York and south Florida. However, there are large differences between coasts: for example, over 75% of the minor floods occur during the fall in Florida, but during the spring and winter in Boston. Various data and forcing, such as tide gauge records, surface temperatures, winds, long-term tidal cycles, and the Gulf Stream flow, were analyzed to examine potential drivers and mechanisms that can contribute to the seasonal pattern of floods. The seasonal water temperature cycle, with maximum temperatures in August, could not by itself explain the seasonal sea level pattern, but two mechanisms that significantly correlate with the seasonal sea level and flooding patterns are the annual and semi-annual tidal cycles (correlation of ~ 0.97) and changes in the Gulf Stream (GS) flow (correlation of − 0.6; the GS shows a maximum decline in September–October during the period of peak flooding). The combination of the seasonal pattern of tropical storms and high coastal sea level can explain the high frequency of fall flooding along the Southeastern U.S. coasts, while winter storms have more influence on the northeastern coasts. In recent decades however, the seasonal pattern seemed to have shifted so that increased flooding is seen on the northeastern coasts during spring and summer, while in the Mid-Atlantic and southeastern coasts, a dramatic increase in flooding is seen almost exclusively during the fall. A long-term change in the mean zonal wind pattern along the coast can contribute to the recent shift in the seasonal flooding pattern. The study can help regional adaptation and resilience planning for flood-prone coastal cities and communities. [ABSTRACT FROM AUTHOR]

Based on average monthly data of the ORAS4 ocean reanalysis, the spatial distribution and values of anomalies of the ocean surface temperature and the velocity of surface currents occurring in the North Atlantic at the meridional displacements of the north wall of the Gulf Stream in January–February are determined. Gulf Stream North Wall Index data are used as data on Gulf Stream movements. The spatial distributions of anomalies corresponding to the northern and southern positions of the North Wall are based on averaging the fields of ocean surface temperature and the velocity of currents corresponding to each phase of the Gulf Stream North Wall index. It has been revealed that for meridional displacements of the North Wall of the Gulf Stream, statistically significant anomalies of the modulus of current velocity (0.03 m/s) and ocean surface temperature (1°C) are not only in the area of the Wall, but also along the entire northern boundary of the Gulf Stream. Here the value of the correlation coefficient of velocity time series with the Gulf Stream North Wall index is 0.56. As for temperature, the same coefficient is 0.50. Significant temperature anomalies (0.3°C) are found off the coast of the Iberian Peninsula and in the central part of the subtropical gyre. The values of the correlation coefficients of time series of the surface temperature and the index of the Gulf Stream in these areas are 0.48 and 0.53 respectively. [ABSTRACT FROM AUTHOR]

The Oceanographic Modeling and Observation Network (REMO) focuses on scientific and technological development of operational oceanography in Brazil considering both numerical forecasting and observational systems. A key component of the forecasting system is the recently constructed REMO Ocean Data Assimilation System (RODAS) into the HYbrid Coordinate Ocean Model (HYCOM). Here, RODAS is presented for the first time with its full capability. RODAS employs a multivariate ensemble optimal interpolation scheme that is able to assimilate Argo temperature (T) and salinity (S) profiles, sea surface temperature (SST) analyses, and satellite along-track or gridded sea-level anomaly (SLA) data. RODAS is presented together with a series of Observing System Experiments (OSEs), in which components of the Global Ocean Observing System (GOOS) were systematically withheld from 3-year assimilation runs over the Atlantic Ocean. Using the same initial condition from a full assimilation run, OSEs were performed from 1 January 2010 to 31 December 2012 withholding (i) only Argo data; (ii) only UK MetOffice OSTIA SST analyses; (iii) only satellite along-track altimetry data; and (iv) all observation types. These runs were also compared with the full assimilation run and the model free run to evaluate the impact of different observations into the model state. The results show that each observation type brings complementary information into the analyses. Assimilation of SST is needed to better constrain the mixed layer temperature, while assimilation of SLA mainly improves the representation of circulation by adding mesoscale-like features, such as those found in the Gulf Stream and the Brazil-Malvinas Confluence. In the subsurface, only Argo observations are able to constrain the thermohaline state. When Argo data are withheld, the quality of S is seriously compromised and becomes worse than the free run in the upper ocean. Additionally, the run withholding all observation types shows that the model state in the surface almost reaches the free run state by the end of the third year. However, below 300 m, the memory of the Argo data assimilation is longer and the quality of T and S is only degraded by 35% in comparison with the full assimilation run. [ABSTRACT FROM AUTHOR]

Leptocephali of the shallow-water congrid eel Ariosoma balearicum are abundant during February–April in the Sargasso Sea, and larval and adult meristic data indicates this species includes several regional subpopulations/cryptic species. Four multiple-transect larval surveys (2011, 2014, 2015, 2017) were used to examine the geographic size distribution of two myomere-count types of A. balearicum leptocephali. High-count (HC) larvae were consistently mostly between 80 and 100 mm in size (60–132 mm; 87.9 ± 6.8 mm) as observed previously, and frequently had narrow size ranges. The usually larger LC larvae (78–176 mm; 111.4 ± 26.7 mm) were more abundant in western or central areas. HC larvae tended to decrease in size from west to east and increase from south to north. Catch rates were geographically variable relative to hydrographic structure/frontal positions across the wide 2015 sampling area. Mitochondrial 16 s rRNA sequences of HC and LC larvae show species-level differences, providing evidence of the existence of two cryptic species with different larval dispersal strategies in the Sargasso Sea subtropical gyre region. The HC larvae disperse widely into the gyre, seemingly through Gulf Stream recirculation or eastward frontal-jet flows, and apparently must use directional swimming to cross the Florida Current to recruit into the South Atlantic Bight. LC leptocephali may mostly be retained near the Bahamas, with few larvae dispersing into the gyre. This seems to indicate natural selection occurred for spawning location and larval behavior due to the powerful Florida Current/Gulf Stream, resulting in two completely different spawning and larval dispersal strategies within a local geographic region. [ABSTRACT FROM AUTHOR]