Mesoscale Eddies Research Articles

Mesoscale eddy in situ observation and characterization via underwater glider and complex network theory.

Mesoscale eddies have attracted increased attention due to their central role in ocean energy and mass transport. The observations of their three-dimensional structure will facilitate the understanding of nonlinear eddy dynamics. In this paper, we propose a novel framework, the mesoscale eddy characterization from ordinal modalities recurrence networks method (MeC-OMRN), that utilizes a Petrel-II underwater glider for in situ observations and vertical structure characterization of a moving mesoscale eddy in the northern South China Sea. First, higher resolution continuous observation profile data collected throughout the traversal by the underwater glider are acquired and preprocessed. Subsequently, we analyze and compute these nonlinear data. To further amplify the hidden structural features of the mesoscale eddy, we construct ordinal modalities sequences rich in spatiotemporal characteristics based on the measured vertical density of the mesoscale eddy. Based on this, we employ ordinal modalities recurrence plots (OMRPs) to depict the vertical structure inside and outside the eddy, revealing significant differences in the OMRPs and the unevenness of density stratification within the eddy. To validate our intriguing findings from the perspective of complex network theory, we build the multivariate weighted ordinal modalities recurrence networks, through which network measures exhibit a more random distribution of vertical density stratification within the eddy, possibly due to more intense vertical convection and oscillations within the eddy's seawater micelles. These framework and intriguing findings are anticipated to be applied to more data-driven in situ observation tasks of oceanic phenomena.

Influence of mesoscale eddies on wind retrieval from C-band synthetic aperture radar images

ABSTRACT Synthetic Aperture Radar (SAR) is an innovative technique for monitoring sea surface dynamics and has a large swath coverage (>200 km). In this paper, we investigate the characteristics of anticyclonic and cyclonic eddies on SAR and the influence of mesoscale eddies on SAR wind retrieval. Mesoscale eddies in the global oceans are identified from daily sea level anomaly (SLA) data in 2022–2023, which are integrated by the Haiyang-2B/2C/2D (HY-2B/2C/2D) altimeters. A total of 1000 Sentinel-1 (S-1) images acquired in interferometric-wide (IW) and extra-wide (EW) modes are available, and they cover the mesoscale eddies. In addition, swath wind products from HY-2 scatterometers and sea surface temperature (SST) data from Haiyang-1C (HY-1C) are collected. Co-polarized (vertical–vertical (VV) and horizontal–horizontal (HH)) Geophysical Model Function (GMF) C-SARMOD2 was applied to invert the wind speed with reference to the scatterometer-measured wind direction. The variation in the difference (SAR retrievals minus scatterometer measurements) indicates that the SST of below 11°C has a certain impact on the SAR wind retrieval. The influence is weak at higher SSTs, and the difference increases with increasing eddy kinetic energy (EKE). It is concluded that the shear current associated with mesoscale eddies is a significant factor that affects the accuracy of SAR-derived winds.

Movement behavior of satellite-tagged leatherback turtles from Panama in response to chlorophyll, primary productivity, temperature, and eddy kinetic energy

Leatherback turtles Dermochelys coriacea are globally endangered. This study tracked 30 individuals from the North Atlantic population tagged on the Caribbean Panama rookery (San San Pond Sak protected area, Bocas del Toro) over a period of 3 yr. We used satellite telemetry to investigate the probability that turtles switched between migration and foraging behavioral states as a function of environmental variables. We mapped the extensive migratory routes of these turtles and analyzed these using data derived from remote sensing, including chlorophyll, productivity, and sea surface temperature (SST), to assess how these influence their migratory and foraging behaviors. We also considered oceanographic processes, i.e. mesoscale eddies coinciding with the turtles’ migration paths, to understand their behavioral responses. Our observations revealed that while some turtles undertook extensive migrations to high-use areas in the Northeast and Northwest Atlantic, the majority remained within the boundaries of the Gulf of Mexico. The study effectively differentiated migration and feeding behavior, noting a clear positive relationship between feeding activities and chlorophyll concentration, while productivity played only a marginal role, and no influence was found for SST and mesoscale eddies. This study advances knowledge of North Atlantic leatherback turtle migrations, underscoring the importance of integrated, multidisciplinary marine conservation efforts. Understanding the impact of climate warming on migration paths and food source availability necessitates a holistic approach encompassing changes in physical oceanography, nutrient dynamics, and interactions from plankton to higher trophic levels. Additionally, as leatherback turtles traverse various international territories, the research emphasizes the need for collaborative data collection for their effective protection.

Oceanic eddy with submesoscale edge drives intense air-sea exchanges and beyond

Oceanic mesoscale eddies influence air-sea interaction and atmosphere dynamics through ventilating heat and moisture upward. However, whether the sea surface temperature (SST) gradient on the eddy edge could affect the heat and moisture release is still unknown because of the limited observations and coarse-resolution climate models. Using high-resolution atmospheric simulations, this study compares the atmospheric response to the mesoscale (~ 40 km) and submesoscale (~ 4 km) SST gradients at the edge of an eddy. Results show that submesoscale SST gradient drives stronger surface heat and moisture fluxes, enhancing the vertical mixing intensity by 2–3 times within and above the marine atmospheric boundary layer. As a result, one local precipitation event is found to be an order of magnitude larger overlying the eddy. Our findings highlight the importance of resolving oceanic submesoscale features for accurately predicting atmosphere dynamics and precipitation over the ocean.

The formation and ventilation of an oxygen minimum zone in a simple model for latitudinally alternating zonal jets

Abstract. An advection–diffusion model coupled to a simple dynamical ocean model is used to illustrate the formation and ventilation of an oxygen minimum zone. The advection–diffusion model carries a passive tracer with a source at the western boundary and a Newtonian damping term to mimic oxygen consumption. The dynamical model is a non-linear one-and-a-half-layer reduced-gravity model. The latter is forced by an annually oscillating mass flux confined to the near-equatorial band that, in turn, leads to the generation of mesoscale eddies and latitudinally alternating zonal jets at higher latitudes. The model uses North Atlantic geometry and develops a tracer minimum zone remarkably similar in location to the observed oxygen minimum zone in the eastern tropical North Atlantic (ETNA). This is despite the absence of wind forcing for a subtropical gyre and the shadow zone predicted by the ventilated thermocline theory. Although the model is forced only at the annual period, the model nevertheless exhibits decadal and multidecadal variability in its spun-up state. The associated trends are comparable to observed trends in oxygen within the ETNA oxygen minimum zone. Notable exceptions are the multi-decadal decrease in oxygen in the lower-oxygen minimum zone and the sharp decrease in oxygen in the upper-oxygen minimum zone between 2006 and 2013.

Resolving the ubiquitous small-scale semi-permanent features of the general ocean circulation: a multiplatform observational approach

Abstract Based on twenty years of Argo and ship/animal-borne/glider hydrographic profile data, we derive a new high resolution hydrographic Atlas and associated circulation field for the oceans above 2000 dbar. Satellite altimetric observations are used to explicitly regress out eddy noise in the fit, greatly reducing one of the major sources of noise. Geostrophic shears are found from the fitted geopotential anomaly fields. Ekman velocities are estimated using satellite wind stresses. Both Argo trajectory observations at 1000 dbar and surface drifter observations are used to reference geostrophic shears derived from the Atlas hydrography. Surface drifter velocities are analyzed with an additional wind-friction term to remove the wind-related flow. Agreement between the surface geostrophic (referenced to Argo trajectories) and drifter-based surface velocity is high at both large and mesoscales, lending confidence to the derived geostrophic circulation fields. The Atlas reveals standing mesoscale eddies and meanders in western boundary systems, and the braided jet structure of the Antarctic Circumpolar Current. In the interior, the upper ocean flow consists of a highly baroclinic large-scale Sverdrup flow and smaller scale (~200 km width) semi-zonal jets, which are more barotropic (low vertical shear) and have an average zonal width of around 2000 km. These semi-zonal jets are globally ubiquitous - found in all basins pole-to-pole. The many permanent mesoscale features of the mean general circulation contrasts with that predicted by theories of the large-scale flow in simplified flat-bottomed domains. The new Atlas presents a new opportunity to benchmark modern high resolution ocean and climate models.

Role of mesoscale eddies in the biogeochemistry of the Mozambique Channel

This study aims to characterize how eddies shape the biogeochemistry of the Mozambique Channel using a physical-biogeochemical model that realistically simulates its interannual dynamics. The 20-year-long numerical simulation provides a comprehensive dataset for robust statistical analysis of thousands of mesoscale features using an eddy detection method. We show that all eddy types significantly shape the biogeochemical landscape over the Mozambique Channel, with varying effects across different areas: (1) Sofala Bank and Delagoa Bay: Cyclonic eddies enhance diatom production. (2) Comoros Basin: Cyclonic eddies favor diatom growth via nutrient-rich waters from the NEMC. (3) Central Mozambique Channel: Anticyclonic eddies and rings promote nanophytoplankton through eddy-topography interactions. (4) Southern Mozambique Channel: A mix of eddies from the MC and South Madagascar influences diverse responses due to coastal upwelling. This diversity of processes results in distinct biological signatures of eddy types, leading to diverse ecosystem assemblages with a clear oligotrophic signature.

Common occurrences of subsurface heatwaves and cold spells in ocean eddies

Extreme ocean temperature events are becoming increasingly common due to global warming, causing catastrophic ecological and socioeconomic impacts1–5. Despite extensive research on surface marine heatwaves (MHWs) and marine cold spells (MCSs) based on satellite observations6,7, our knowledge of these extreme events and their drivers in the subsurface ocean—home to the majority of marine organisms—is very limited8,9. Here we present global observational evidence for the important role of mesoscale eddies in the occurrence and intensification of subsurface MHWs and MCSs. We found that 80% of measured MHWs and MCSs below a depth of 100 m do not concur with surface events. In contrast to the weak link between surface MHWs (MCSs) and ocean eddies, nearly one-third of subsurface MHWs (MCSs) in the global ocean, and more than half of such events in subtropical gyres and mid-latitude main current systems, occur within anticyclonic (cyclonic) eddies. These eddy-associated temperature extremes have intensified at rates greater than background level in past decades, suggesting a growing impact of ocean eddies on subsurface MHWs and MCSs with ongoing global warming.

Nitrogen fixation in the North Atlantic supported by Gulf Stream eddy-borne diazotrophs

AbstractMesoscale oceanic eddies contribute to the redistribution of resources needed for plankton to thrive. However, due to their fluid-trapping capacity, they can also isolate plankton communities, subjecting them to rapidly changing environmental conditions. Diazotrophs, which fix dinitrogen (N2), are key members of the plankton community, providing reactive nitrogen, particularly in large nutrient-depleted regions such as subtropical gyres. However, there is still limited knowledge about how mesoscale structures characterized by specific local environmental conditions can affect the distribution and metabolic response of diazotrophs when compared with the large-scale dynamics of an oceanic region. Here we investigated genetic diazotroph diversity and N2 fixation rates in a transect across the Gulf Stream and two associated eddies, a region with intense mesoscale activity known for its important role in nutrient transport into the North Atlantic Gyre. We show that eddy edges are hotspots for diazotroph activity with potential community connectivity between eddies. Using a long-term mesoscale eddy database, we quantified N2 fixation rates as up to 17 times higher within eddies than in ambient waters, overall providing ~21 µmol N m−2 yr−1 to the region. Our results indicate that mesoscale eddies are hotspots of reactive nitrogen production within the broader marine nitrogen cycle.

Observation of Statistical Characteristics and Vertical Structures of Surface Warm Cyclonic Eddies and Cold Anticyclonic Eddies in the North Pacific Subtropical Countercurrent Region

Conventional wisdom about mesoscale eddies is that cyclonic (anticyclonic) eddies are commonly associated with cold(warm) surface cores. Nevertheless, plenties of surface warm cyclonic eddies (WCEs) and cold anticyclonic eddies (CAEs) in the North Pacific Subtropical Countercurrent (STCC) region are observed by a synergistic investigation based on data from satellite altimetry, microwave radiometer, and Argo float profiles in this study. The results indicate that these two types of abnormal eddies (WCEs and CAEs) are prevalent in the STCC region, comprising approximately 30% of all eddies detected via satellite observations. We then analyze their spatial-temporal distribution characteristics and composite vertical structures. A statistical comparison with surface cold cyclonic eddies (CCEs) and warm anticyclonic eddies (WAEs) reveals notable differences between the anomalous and typical eddies. Additionally, we present the composite vertical structures of temperature and salinity anomalies for the anomalous eddies across five delineated subregions within an eddy-coordinate system. Furthermore, the close relationship between these abnormal eddies and subsurface-intensified mesoscale eddies are discussed.

Analysis and prediction of mesoscale eddy kinetic energy variations in the Kuroshio extension

The Kuroshio Extension (KE) region, a crucial area in the Northwest Pacific Ocean, exhibits eddy kinetic energy with various scales of periodicity. Understanding how to extract its characteristic features and analyze and predict their periodic correlations has become vital for studying the regulatory mechanisms of eddy kinetic energy in the KE region. This paper first introduces a mesoscale eddy hybrid identification algorithm based on the flow field vector and the closed flow field. Using this algorithm, we gather mesoscale eddy identification data from the KE region to extract the monthly average series of five typical features of the KE region. Subsequently, wavelet theory is applied to analyze the cycles of these main features, identifying the common cycles of the KE region as the primary focus for analyzing the vorticity kinetic energy. This analysis includes cycle correlations with globally recognized indices, and it predicts these correlations. Further analysis of the main characteristic cycles through wavelet theory reveals that the KE region's eddy kinetic energy is significantly influenced by solar activity over long periods and by the North Pacific ocean-atmosphere interaction over shorter, interannual periods. Finally, this paper introduces a W-LSTM (Wavelet Decomposition based Long Short-term Memory Networks) prediction model based on wavelet decomposition for the KE region, covering January 2023–December 2023. The model demonstrates its effectiveness, achieving a Root Mean Square Error (RMSE) of 0.2530 and a correlation coefficient of 0.8259 between the predicted data and the actual observations.

A Stable Implementation of a Data‐Driven Scale‐Aware Mesoscale Parameterization

AbstractOcean mesoscale eddies are often poorly represented in climate models, and therefore, their effects on the large scale circulation must be parameterized. Traditional parameterizations, which represent the bulk effect of the unresolved eddies, can be improved with new subgrid models learned directly from data. Zanna and Bolton (2020), https://doi.org/10.1029/2020gl088376 (ZB20) applied an equation‐discovery algorithm to reveal an interpretable expression parameterizing the subgrid momentum fluxes by mesoscale eddies through the components of the velocity‐gradient tensor. In this work, we implement the ZB20 parameterization into the primitive‐equation GFDL MOM6 ocean model and test it in two idealized configurations with significantly different dynamical regimes and topography. The original parameterization was found to generate excessive numerical noise near the grid scale. We propose two filtering approaches to avoid the numerical issues and additionally enhance the strength of large‐scale energy backscatter. The filtered ZB20 parameterizations led to improved climatological mean state and energy distributions, compared to the current state‐of‐the‐art energy backscatter parameterizations. The filtered ZB20 parameterizations are scale‐aware and, consequently, can be used with a single value of the non‐dimensional scaling coefficient for a range of resolutions. The successful application of the filtered ZB20 parameterizations to parameterize mesoscale eddies in two idealized configurations offers a promising opportunity to reduce long‐standing biases in global ocean simulations in future studies.

Seasonality of Submesoscale Vertical Heat Transport Modulated by Oceanic Mesoscale Eddies in the Kuroshio Extension

AbstractEnergetic mesoscale eddies are often accompanied by strong submesoscale variability, which plays a significant role in connecting mesoscale and turbulent motions in the ocean and leads to strong vertical motions. The product of a high‐resolution (1/48°) oceanic numerical model, the LLC4320, is employed to investigate the seasonal variations of vertical heat transport induced by submesoscale processes within multiple mesoscale eddies in the Kuroshio Extension (KE) region. In different seasons, the submesoscale vertical heat transport exhibits a consistent upward pattern, with notably higher magnitudes observed during winter. In winter, the maxima value of submesoscale vertical heat flux (SVHF) can account for approximately 60% of the total vertical heat flux (VHF). This is equivalent to the average net sea surface heat flux in a single eddy region. In summer and autumn, the maxima absolute value of submesoscale vertical heat flux can account for approximately 30% of the total VHF. Energy analysis reveals that baroclinic instability associated with vertical buoyancy flux has a crucial effect on generating submesoscale processes within the eddy region. The submesoscale motions are influenced by the mixed layer instability, strain‐induced frontogenesis, turbulent thermal wind and turbulent thermal wind‐induced frontogenesis within the upper mixed layer, while they are largely associated with the strain‐induced frontogenesis in the ocean interior. Furthermore, the upward low‐frequency submesoscale vertical heat transport is generated by submesoscale secondary circulation at eddy peripheries.

Remote Impacts of Cyclonic Eddies on Productivity Around the Main Hawaiian Islands

AbstractThe Hawaiian Island chain lies on the southern limb of the oligotrophic North Pacific Subtropical Gyre, an area characterized by low productivity. In this region, productivity is controlled by several factors, including the island mass effect and mesoscale eddies generated by wind stress curl in the lee of the islands. This study identifies high‐chlorophyll events that occur periodically off the northern coasts of the Main Hawaiian Islands. These events are present in the satellite record and can be reproduced using a regional dynamical model. Model results indicate events are characterized by increases in total phytoplankton and total zooplankton, and a shift in phytoplankton size structure. We show these events are uniquely driven by the presence of cyclonic mesoscale eddies located downstream, on the opposite side of the island chain. While these eddies are known to impact productivity locally, we reveal that nutrients upwelled by these eddies can also be transported around the islands, counter to the mean background flow. These results demonstrate how leeward cyclonic eddies can have far‐reaching, remote impacts on productivity around the Hawaiian Islands.

Modulation of Internal Solitary Waves by One Mesoscale Eddy Pair West of the Luzon Strait

Abstract The characteristics of modulated internal solitary waves (ISWs) under the influence of one mesoscale eddy pair in the Luzon Strait, involving one anticyclonic eddy (AE) and one cyclonic eddy (CE) induced by the Kuroshio intrusion, were investigated using a nested high-resolution numerical model in the northeastern South China Sea (SCS). The presence of mesoscale eddies greatly impacts the nonlinear evolution of type-a and type-b ISWs. The eddy pair contributes to distinct wave properties and energy evolutions. Compared to type-b waves, type-a waves display more pronounced modulatory characteristics with a larger spatial scale. CE currents and horizontal inhomogeneous stratification are crucial in modulating the wave behaviors, which induce extremely large-amplitude depression ISWs. The AE thereafter yields retardation effects on the wave energy evolution. The average depth-integrated available potential and kinetic energy showed relative growth rates of −66.12% and −46.07%, respectively, for type-a waves, and −24.26% and −20.15%, respectively, for type-b waves along the propagation path up to the AE core. The deformed and distorted ISW crest lines propagating further northward exhibit a more dramatic shoaling evolution. The maximum total energies of type-a and type-b waves at the north station are approximately 13.5 and 3.5 times, respectively, greater than those at the south station on the continental shelf of the Dongsha Atoll. This work provides essential insights into modulated ISW dynamics under the mesoscale eddy pair within the northeastern SCS deep basin.

Subsurface Marine Heatwaves in the South China Sea

AbstractMarine heatwaves (MHWs), extreme warm ocean temperature events, greatly impact marine ecosystems. While most MHW studies in the South China Sea (SCS) focus on the sea surface, subsurface characteristics remain less explored. This study uses high‐resolution (1/12°) ocean reanalysis data sets to assess MHW properties with depth in the SCS from 1993 to 2022. We find that MHW intensities are typically stronger at subsurface levels (30–150 m) than at the surface, with significant spatial variations. The vertical structures of MHW maximum and cumulative intensities peak between 70 and 100 m with 2.7°C and 63°C days, respectively; MHW annual days and duration increase gradually from 10 to 2,000 m with duration peaks at 2,000 m (∼60 days), four times longer than that at the surface. The SCS experienced two major periods of extensive El Niño‐related subsurface MHWs from 1997 to 2002 and 2008 to 2014, with MHWs reaching depths of 150 m and covering 70% of the upper 40 m. Strong El Niño events strengthen the western Pacific subtropical high, reducing summer monsoon winds, weakening coastal upwelling east of Vietnam, and increasing water temperatures. Regions of elevated eddy kinetic energy in the SCS suggest that significant mesoscale eddy activities are situated east of Vietnam. In addition, notable eddy heat transport was observed in the above region and west of the Luzon Strait in the upper 1,000 m. This may help to explain the high maximum and cumulative intensities of MHWs exceeding 100 m in the northern SCS.

Distinct Impacts of Topographic versus Planetary PV Gradients on Baroclinic Turbulence

Abstract The impacts of topographic versus planetary potential vorticity (PV) gradients on fully developed geostrophic turbulence are often treated as dynamically equivalent in theoretical understanding and parameterizations of ocean mesoscale turbulence. Using a suite of homogeneous, two-layer quasigeostrophic (QG) turbulence simulations, we identify similarities and distinctions of topographic versus planetary PV gradients in modulating turbulent eddy energy and fluxes. We show that, while an elevated background PV gradient can suppress geostrophic turbulence, a positive (negative) bottom slope with respect to the orientation of isopycnal slope barotropizes (debarotropizes) the turbulent energy at large scales, which contrasts with a dynamically inert planetary PV gradient in the modewise energy transfer. Then, in the presence of weak bottom drag, a positive slope energizes large-scale along-slope jets and limits small-scale barotropic eddies, both of which yield stronger eddy suppression effects than from a planetary PV gradient; by contrast, a negative slope hinders along-slope jet formation by enhancing the dual-energy cascade cycling, which alleviates the topographic suppression on eddies. In the presence of strong bottom drag, a positive slope elevates barotropic eddy energy, which further enhances the eddy-driven fluxes; by contrast, a negative slope confines turbulent energy to the baroclinic mode, which is strongly damped, causing further weakened turbulent energy and eddy fluxes. A flow regime captured by linear QG theories also emerges as the turbulent energy cascade is jointly suppressed by negative slopes and strong bottom drag. This study provides insights into parameterizing mesoscale eddy effects across sloping bathymetry in predictive ocean models.

Mesoscale eddies inhibit intensification of the Subantarctic Front under global warming

Abstract Oceanic mesoscale eddies are important dynamical processes in the Southern Ocean. Using high-resolution (~0.1○ for the ocean) Community Earth System Model (CESM-HR) simulations under a high-carbon emission scenario, we investigate the role of mesoscale eddies in regulating the response of the Subantarctic Front (SAF) to global warming. The CESM-HR simulates more realistic oceanic fronts and mesoscale eddies in the Southern Ocean than a coarse-resolution (~1○ for the ocean) CESM. Under global warming, the SAF is projected to intensify. The mean flow temperature advection intensifies the front, whereas the mesoscale-eddy-induced temperature advection and atmospheric dampening play primary (~67%) and secondary (~28%) roles in counteracting the effect of mean flow temperature advection. Our study suggests the importance of mesoscale eddies on inhibiting the SAF intensification under global warming and necessity of mesoscale-eddy-resolving simulations for faithful projection of future climate changes in the Southern Ocean.

Kuroshio path variability inferred from satellite-derived sea surface topography in the northwestern Pacific

The Kuroshio has a fundamental impact on the regional oceanography of the northwestern Pacific. But identification of the Kuroshio path (KP), an abstraction of the course along which the Kuroshio mainstream moves, has not yet been established in a systematic manner. We optimally track the KP and study its variability in the northwestern Pacific south of ~31°N, where eddy activity is rich. An automatic contour method based on maximum surface geostrophic velocity along a given satellite-derived dynamic topographic isoline is applied and its performance is evaluated. Our results are robust and can be further used to derive kinematical, statistical, and spectral properties of the flow field of the Kuroshio upstream. We improve the identification method by tracing two separate KPs in different subdomains. The existence of an alignment or mismatch of these two retrieved KPs hints at the arrival of an approaching eddy. The highly variable and distorted KP east of Luzon Strait and Taiwan is due to eddy impingement. Most of the variability along the KP stems from energy with time scales of ~30–200 days and 1 year. A more consistent KP is seen north of ~26°N, with increasing surface currents of up to ~1 m s−1 before entering through the Tokara Strait. Such regional differences result from the various impacts of impinging mesoscale eddies on the Kuroshio, mainly due to blockage by the Ryukyu Islands. Our optimally determined KP is in line with the historical shipborne subsurface velocity measurements revealing the Kuroshio velocity core and observations of strong surface currents of > ~0.5 m s−1 by shore-based high-frequency radar (HFR) from locations along the east coast of Taiwan. Supportive evidence of concurrent KP distortion shows that HFR-derived vortex-like flow patterns are related to mesoscale eddies impinging from regions east of the radar footprint. Our work has value as a supplement to the data from radar operational routines, and will help interpret and diagnose these complicated HFR observations east of Taiwan.

The role of mesoscale-driven connectivity patterns in coral recovery around Moorea and Tahiti, French Polynesia

Coral reefs are declining due to anthropogenic warming. Nonetheless, some have recovered quickly from repeated bleaching events. Coral recovery depends on adaptation capabilities, fishing pressure, overall number of stressors, reef conditions before the event, and degree of connectivity. Coral reefs that are connected to many others can receive viable larvae and regain coverage faster. Around Moorea and Tahiti, within the Society Islands of French Polynesia, coral cover has regained its previous levels rapidly, despite several mass bleaching events over the past three decades. Here it is explored whether the connectivity with distant reefs may support such recovery by modeling the transport of coral larvae around the islands over 28 years. Ocean currents enable connectivity with the Tuamotu Islands, ~ 250 km to the northeast, that act as sources to Moorea and Tahiti for pelagic larval durations of three weeks or longer. The circulation around Moorea and Tahiti is very dynamic; mesoscale eddies can also halt the connectivity with the Tuamotu Islands and sporadically transport larvae from reefs to the west and southeast instead. With many undisturbed coral reefs within a 300 km radius and strong mesoscale variability, a dynamic, long-range connectivity may explain the recovery of reefs around Moorea and Tahiti.