Ocean Circulation Model Research Articles

Variability of nutrient transport and associated upper ocean primary production induced by Kuroshio meanders in the Enshu-nada Sea, Japan

Towards the desirable preservation of the marine environment under a changing global climate, this study aims to investigate the coastal biological response to varying oceanic conditions, namely the Kuroshio meander, and associated nitrate transport on the Pacific coast of Japan around the Enshu-nada Sea, using a coupled three-dimensional regional ocean circulation model with a nitrogen-based ecosystem model. A prominent difference was found in nitrate transport processes between for a period when the Kuroshio took a meandering path and for a non-meandering period, leading to about 1.5 times higher surface primary production measured by chlorophyl-a concentration during the non-meandering period than during the meandering period. The upper ocean nitrate flux budget analysis showed that the subsurface nitrate was transported upward as a vertical diffusive flux around the north (shoreward) of the Kuroshio path and as a mean vertical advective flux in the Kuroshio downstream region around the Izu-Ogasawara Ridge. In contrast, high-frequency eddy vertical advective fluxes caused downward transport, but to a degree about 20% smaller than the other fluxes. After nitrate was supplied to the upper layer, it was transported horizontally by the counterclockwise rotating cyclonic eddy formed between the coast and the Kuroshio and supplied to phytoplankton in the Enshu-nada Sea. These results suggest that carbon sequestration due to biological pump may also vary in response to the Kuroshio that is influenced by basin-scale oceanic conditions.

Three-dimensional transport of coral larvae and associated population connectivity in the coastal area of Okinawa Island, Japan

In recent years, global warming has intensified coral bleaching worldwide. The mesophotic zone (MPZ) at depths of 30-150 meters, where photosynthesis is viable and water temperatures are stable, is expected to serve as a refuge and gene resupply source for shallow-water corals. This study quantitatively evaluates the 3D population connectivity between shallow-water corals and MPZ corals in the potential coral habitats surrounding Okinawa Island. Utilizing a triple-nested high-resolution 3D ocean circulation model, an offline, 3D Lagrangian advection-dispersion model for planktonic coral larvae was developed. Results show that 3D intra-island coral connectivity is strongly influenced by topographically constrained residual currents around the island. Coral larvae released from shallow areas are transported in a clockwise direction around the island. While the larvae released from the west coast are transported to the east coast by crossing the northern tip of the island, their movement is significantly hindered at the southern tip by a shallow channel as a topographic barrier. Conversely, this clockwise transport is much less pronounced in the MPZ, resulting in lower connectivity between the west and east coasts. In addition, potential source areas of coral larvae were analyzed to determine an island-wide coral network that could support coral conservation efforts in Okinawa.

The Effect of Southern Ocean Topography on the Global MOC and Abyssal Water Mass Distribution

Abstract We investigate the role of Southern Ocean topography and wind stress in the deep and abyssal ocean overturning and water mass composition using a suite of idealized global ocean circulation models. Specifically, we address how the presence of a meridional ridge in the vicinity of Drake Passage and the formation of an associated Southern Ocean gyre influence the water mass composition of the abyssal cell. Our experiments are carried out using a numerical representation of the global ocean circulation in an idealized two-basin geometry under varying wind stress and Drake Passage ridge height. In the presence of a low Drake Passage ridge, the overall strength of the meridional overturning circulation is primarily influenced by wind stress, with a topographically induced weakening of the middepth cell and concurrent strengthening of the abyssal cell occurring only after ridge height passes 2500 m. Passive tracer experiments show that a strengthening middepth cell leads to increased abyssal ventilation by North Atlantic water masses, as more North Atlantic Deep Water (NADW) enters the Southern Ocean and then spreads into the Indo-Pacific. We repeat our tracer experiments without restoring in the high-latitude Southern Ocean in order to identify the origin of water masses that circulate through the Southern Ocean before sinking into the abyss as Antarctic Bottom Water. Our results from these “exchange” tracer experiments show that an increasing ridge height in Drake Passage and the concurrent gyre spinup lead to substantially decreased NADW-origin waters in the abyssal ocean, as more surface waters from north of the Antarctic Circumpolar Current (ACC) are transferred into the Antarctic Bottom Water formation region. Significance Statement The objective of this study is to investigate how topographic features in the Southern Ocean can affect the overall structure of Earth’s large-scale ocean circulation and the distribution of water masses in the abyssal ocean. We focus on the Southern Ocean because the region is of central importance for exchange between the Atlantic and Indo-Pacific Ocean basins and for CO2 and heat uptake into the abyssal ocean. Our results indicate that Southern Ocean topography plays a major role in the overall circulation by 1) controlling the direct transfer of abyssal waters from the Atlantic to the Indo-Pacific via its influence on the Atlantic meridional overturning circulation and 2) controlling the coupling between the abyssal ocean and surface waters north of the Antarctic Circumpolar Current via the Southern Ocean gyre.

Assimilation of Surface Geostrophic Currents in the East Sea Using the Ensemble Kalman Filter

The conventional ocean data assimilation process typically involves assimilating hydrographic data, such as temperature and salinity measurements, obtained from both satellites and in-situ observations. This study introduces a novel approach to enhance ocean circulation modeling by assimilating surface geostrophic currents derived from satellite altimetry data using the ensemble Kalman filter. To match the time scales for the variability in the observed surface geostrophic currents and the model currents, the current velocities from the model were low-pass filtered. The optimal cut-off period for the low-pass filter was determined to be 31 days in the East Sea. Eight sensitivity experiments were then conducted to examine the effects of observation error and low-pass filtering during the assimilation of surface geostrophic current data. Assimilation experiments with surface geostrophic current data improved surface currents but had minor negative impacts on the temperature and salinity when compared with assimilation experiments without surface geostrophic current data. Notably, the experiment with an observation error of 10 cm/s for the geostrophic current outperformed the other experiments. Surface geostrophic current assimilation improved the sea surface temperature during winter and effectively modified surface current patterns during autumn in the East Sea. Assimilating satellite-derived surface geostrophic currents in the ocean circulation model thus enhanced the accuracy of surface circulation simulation. This improvement in ocean analysis data offers significant benefits for understanding ocean climate change and for developing marine management strategies.

The vortex splitting process from interaction between a mesoscale vortex and two islands

Mesoscale vortices are major carriers of oceanic material and energy transfer, transporting large amounts of high-energy, temperature-anomalous water bodies during their movement. This significantly impacts both the ocean and the atmosphere. Based on the distribution of the North Brazil Curren rings and the Lesser Antilles in the eastern Caribbean Sea, we use the Regional Ocean Model System ocean circulation model to construct an idealized vortex. Simulations are conducted by varying the distances between the two islands and the scales of the islands to analyze how different parameters affect the vortex path and structural evolution. Using theoretical derivation and numerical simulation results, we construct a dimensionless parameter involving vortex diameter, island diameter, and the distance between the islands to determine the conditions under which vortex splitting occurs. The reliability of this dimensionless parameter is verified using experimental data and satellite data from St. Vincent and Barbados from April 6 to May 6, 2000.

Deep Mesoscale and Submesoscale Circulations Around the Atlantis II Seamount

AbstractThis study investigates the complex interactions between the North Atlantic Current (NAC) and the New England Seamount chain, focusing on the Atlantis II seamount. Employing a high‐resolution submesoscale permitting regional ocean circulation model nested within a basin‐wide simulation, it explores three distinct periods, each 2 weeks long, showcasing varied deep mesoscale and submesoscale circulations around the seamount. The analysis includes Eulerian statistics and Lagrangian particle tracing experiments to explore the transport and mixing impacts of the highly dynamic flow around the seamount. The results reveal significant density variations across the water column, attributed to the seamount's influence on local ocean currents. Specifically, mesoscale and submesoscale vortices, a seamount wake, and lee waves form during periods of increased near‐bottom current flow. These findings highlight the critical role of topographic features in modulating oceanic flows and ocean mixing, which have implications, among others, for nutrient distribution, acoustic propagation, and climate modeling. The variety and variability of the mesoscale and submesoscale circulations that arise in response to the variability in the NAC strength and position in relation to the New England Seamount Chain demonstrate the difficulty in extrapolating general behaviors from isolated observational campaigns.

Assessing impacts of observations on ocean circulation models with examples from coastal, shelf, and marginal seas

Ocean observing systems in coastal, shelf and marginal seas collect diverse oceanographic information supporting a wide range of socioeconomic needs, but observations are necessarily sparse in space and/or time due to practical limitations. Ocean analysis and forecast systems capitalize on such observations, producing data-constrained, four-dimensional oceanographic fields. Here we review efforts to quantify the impact of ocean observations, observing platforms, and networks of platforms on model products of the physical ocean state in coastal regions. Quantitative assessment must consider a variety of issues including observation operators that sample models, error of representativeness, and correlated uncertainty in observations. Observing System Experiments, Observing System Simulation Experiments, representer functions and array modes, observation impacts, and algorithms based on artificial intelligence all offer methods to evaluate data-based model performance improvements according to metrics that characterize oceanographic features of local interest. Applications from globally distributed coastal ocean modeling systems document broad adoption of quantitative methods, generally meaningful reductions in model-data discrepancies from observation assimilation, and support for assimilation of complementary data sets, including subsurface in situ observation platforms, across diverse coastal environments.

Water budget of the Caspian Sea by numerical experiments with ocean circulation model INMIO-CICE in the last glacial maximum and pre-industrial period

We used the hydrodynamic model of the Caspian Sea, INMIO-CICE, to calculate equilibrium river runoff and evaporation from the sea surface over a wide range of sea levels (from –85 to +50 m asl) for different climatic conditions: the Last Glacial Maximum (about 21kyr) and pre-industrial climate (~1850 CE). Data from the climate model INMCM4.8 were used as boundary conditions. It was found that to maintain sea level at 35–50 m asl, corresponding to the maximum values of the Khvalynian transgression, a river runoff of about 400 km3/year was required in the Last Glacial Maximum. In the Last Glacial Maximum evaporation from the sea surface decreased by 105–170 mm (12–22%), and precipitation, according to the INMCM4.8 model, by 50–70 mm (15–30%). This caused the equilibrium runoff to decrease by about 10–20% compared to pre-industrial conditions. Smaller absolute and relative changes correspond to lower sea levels. The maximum decrease in evaporation occurred at 5 m asl.

Subspace time series clustering of meteocean data to support ocean and coastal hydrodynamic modeling

High-quality ocean and coastal circulation predictions strongly rely on the availability of accurate time series of main meteocean forcing, e.g. wind velocity, atmospheric air pressure. In this study, we formulated and tested on a real case a new approach for generating medium term time series of meteocean data from available reanalysis database. We used the fifth generation reanalysis (ERA5) of global climate and weather data. The methodology is based on the K-means clustering technique, which groups unlabeled data into different clusters. In particular, we implemented a subspace clustering method that includes an automatic weighting of the meteocean variables of interest. To test the performance, we apply the algorithm to the Pearl River Estuary (China). By comparing the proposed methodology with standard clustering analysis, our results suggest that the obtained meteocean scenarios (clusters) better reproduce the time trends of the main variables, in terms of typical indexes used for evaluating the goodness of clustering. Moreover, we showed how using climatological averages, commonly adopted for circulation and wave models, could lead to loosing the important local variability of the meteocean signals. The present approach could represent an advancement in time series clustering to be coupled with ocean and regional circulation models in ocean engineering applications.

Quantifying the accuracy of acoustic arrival-time predictions using high-resolution ocean circulation models

Accurately modeling acoustic propagation in dynamic ocean environments exhibiting sub-mesoscale variability is challenging. Such environments require high-resolution ocean circulation model to accurately predict local sound speed variability at sub-mesoscales. This study focuses on high-resolution rendition of the De Soto canyon area, located in the Gulf of Mexico. Predicted sound speed profiles were found at times to exhibit very strong vertical gradients (e.g. with sharp “elbows”) reflecting the small-scale vertical variations of ocean layer properties. If used as raw inputs for ray-tracingsimulations, such sound speed profiles were found to generate inconsistent estimation of eigenray paths and spurious paths appearing intermittently caused by the inherent limitations of the ray-tracing methods. Nevertheless, we show that such artefacts can be mitigated by appropriately smoothing the input sound speed profile spatial variability especially if only low to mid-frequency (<1 kHz) propagation is predicted. To do so, the accuracy of arrival-times predictions using ray-tracing predictions with spatially smoothed sound speed profiles as a function of center frequency (<1 kHz) will be quantified against parabolic equations simulations used here as reference solution. We hypothesize that this smoothing approach for the input sound speed variations will enable to retain the numerical advantage of ray-tracing predictions while maintaining sufficient accuracy.

ALBATROSS: Advancing Southern Ocean tide modelling with high resolution and enhanced bathymetry

The knowledge of bathymetry and ocean tides plays a pivotal role at the crossroads of various scientific fields, especially in the Polar regions. Its significance extends to ocean circulation modeling and understanding the coupled dynamical response of the ocean, sea-ice and ice-sheet systems. In the Southern Ocean, conventional satellite altimetry measurements are rare below the 66° parallel. Hydrodynamic models are thus useful tools to provide spatially continuous information about ocean tides. However, the accuracy of ocean tide models around the Antarctic continent is currently limited by the quality of bathymetry. Recent reprocessing of decade-long CryoSat-2 data has facilitated a new computation of bathymetry around Antarctica, bringing innovative information on bathymetry gradients. This, combined with new compilations of bathymetry, ice draft, coastline, and grounding line datasets in ice-shelf regions, allows improving models and knowledge of ocean tides in the Southern Ocean. We developed a new high-resolution tidal model that implements the improved bathymetry data and includes data assimilation of satellite-altimetry tidal retrievals computed from CryoSat-2, filling the gap between the 66°S-limited coverage of the TOPEX-Jason suite missions and the Antarctic coast. Comparisons with tidal estimates derived from tide gauge measurements showed very good consistencies with an RMSE of 3 cm.

Quantifying three-dimensional effects on sound propagation near the New England Sea Mount Chain using ray-tracing

This study investigates the impact of three-dimensional (3-D) bathymetry and sound speed variability on sound propagation, utilizing 3-D ray tracing compared to simple two-dimensional ray tracing (Nx2-D) within the New England seamount chain, focusing on the Atlantis II seamount area. The research has three main objectives. First, it examines the differences between 3-D and 2-D acoustic propagation modeling of bathymetric reflections. Second, it evaluates the impact of physical oceanographic effects on 3-D versus 2-D acoustic modeling, employing a high-resolution regional ocean circulation model with a horizontal resolution of 1 km and 100 terrain-following vertical layers. Third, it compares the modeled acoustic propagation to experimental data collected by a surface autonomous vehicle (wave glider) fully instruments for measuring local physical ocean variables (e.g., CTD data) and equipped with a compact tetrahedron hydrophone array (capable of profiling the water column from ∼10 to ∼150m) which recorded low and mid-frequency transmissions from moored acoustic sources deployed near Atlantis II seamount. The need for full 3-D ray-tracing modeling (instead of using simpler Nx2-D simulations) for accurately predicting shadow zones and understanding regional acoustic propagation paths in areas with rapid and diverse bathymetric changes, such as isolated seamounts, will be quantified.

Ocean warming as a trigger for irreversible retreat of the Antarctic ice sheet

Warmer ocean conditions could impact future ice loss from Antarctica due to their ability to thin and reduce the buttressing of laterally confined ice shelves. Previous studies highlight the potential for a cold to warm ocean regime shift within the sub-shelf cavities of the two largest Antarctic ice shelves—the Filchner–Ronne and Ross. However, how this impacts upstream ice flow and mass loss has not been quantified. Here using an ice sheet model and an ensemble of ocean-circulation model sub-shelf melt rates, we show that transition to a warm state in those ice shelf cavities leads to a destabilization and irreversible grounding line retreat in some locations. Once this ocean shift takes place, ice loss from the Filchner–Ronne and Ross catchments is greatly accelerated, and conditions begin to resemble those of the present-day Amundsen Sea sector—responsible for most current observed Antarctic ice loss—where this thermal shift has already occurred.

The impact of coupling a dynamic ocean in the Hurricane Analysis and Forecast System

Coupling a three-dimensional ocean circulation model to an atmospheric model can significantly improve forecasting of tropical cyclones (TCs). This is particularly true of forecasts for TC intensity (maximum sustained surface wind and minimum central pressure), but also for structure (e.g., surface wind-field sizes). This study seeks to explore the physical mechanisms by which a dynamic ocean influences TC evolution, using an operational TC model. The authors evaluated impacts of ocean-coupling on TC intensity and structure forecasts from NOAA’s Hurricane Analysis and Forecast System v1.0 B (HFSB), which became operational at the NOAA National Weather Service in 2023. The study compared existing HFSB coupled simulations with simulations using an identical model configuration in which the dynamic ocean coupling was replaced by a simple diurnally varying sea surface temperature model. The authors analyzed TCs of interest from the 2020–2022 Atlantic hurricane seasons, selecting forecast cycles with small coupled track-forecast errors for detailed analysis. The results show the link between the dynamic, coupled ocean response to TCs and coincident TC structural changes directly related to changing intensity and surface wind-field size. These results show the importance of coupling in forecasting slower-moving TCs and those with larger surface wind fields. However, there are unexpected instances where coupling impacts the near-TC atmospheric environment (e.g., mid-level moisture intrusion), ultimately affecting intensity forecasts. These results suggest that, even for more rapidly moving and smaller TCs, the influence of the ocean response to the wind field in the near-TC atmospheric environment is important for TC forecasting. The authors also examined cases where coupling degrades forecast performance. Statistical comparisons of coupled versus uncoupled HFSB further show an interesting tendency: high biases in peak surface winds for the uncoupled forecasts contrast with corresponding low biases, contrary to expectations, in coupled forecasts; the coupled forecasts also show a significant negative bias in the radii of 34 kt winds relative to National Hurricane Center best track estimates. By contrast, coupled forecasts show very small bias in minimum central pressure compared with a strong negative bias in uncoupled. Possible explanations for these discrepancies are discussed. The ultimate goal of this work will be to enable better evaluation and forecast improvement of TC models in future work.

Surface Currents and Relative-Wind Stress in Coupled Ocean–Atmosphere Simulations of the Northern California Current System

Abstract The dependence of surface-current damping on the definition of surface current for the relative wind is examined in coupled ocean–atmosphere numerical simulations of the northern California Current System (nCCS) during March–October 2009. The model response is analyzed for wind stress computed from relative wind for six different choices of effective model surface velocity. Simulations without surface-current coupling are also considered. As a function of the geographically varying uppermost grid-level depth, the model uppermost grid-level velocity is found to have a wind-drift component with a log-layer structure. Mean geostrophic wind work is concentrated in the shelf and slope regions during March–May (MAM) and in the deep offshore region in June–September (JJAS). The surface-current damping effect on ocean kinetic energy depends more strongly on the parameterization of atmospheric planetary boundary layer (PBL) turbulence than on the surface-current coupling formulation: weaker PBL mixing gives stronger surface-current damping. The damping effect is stronger in the less energetic offshore region than in the more energetic region closer to the coast. During MAM, the changes in kinetic energy and geostrophic wind work in the shelf and slope regions are spatially correlated, while during JJAS, the changes in geostrophic wind work are strongly modulated by SST–stress coupling. The wind-drift-corrected surface-current formulations result in large changes in the effective wind work based on the product of stress and relative-wind surface current but result in only small changes in the kinetic energy of the circulation. Significance Statement Ocean currents and atmospheric winds are coupled by the exchange of momentum across the air–sea interface, the strength of which depends on the relative wind, the difference between the surface wind and surface current. The purpose of this work was to examine the dependence of a coupled ocean–atmosphere model of the northern California Current System (nCCS) on the representations of the relative-wind surface current and turbulent mixing in the lower atmosphere. The model surface current was found to have a shallow wind-drift response. The model ocean circulation was driven primarily by near-coast winds during the spring and by offshore winds during the summer. The ocean response depended more strongly on the atmospheric turbulent mixing than on the surface current representation.

A comprehensive investigation of storm surge-induced urban flooding in Macao during Typhoon Hato in 2017

A comprehensive understanding of the processes of storm surge and flooding induced by typhoons is crucial for the development of effective emergency plans and risk management strategies. This study employed the three-dimensional coastal ocean circulation model FVCOM to simulate the storm surge in the Pearl River Estuary (PRE) during Typhoon Hato in 2017. In addition, the storm surge predictions are integrated with the InfoWorks 2D-1D hydrologic network drainage model to study urban flooding in the Inner Harbor district in Macao for the first time. Typhoon's wind and pressure fields were reconstructed based on parametric models, and numerical experiments were conducted to investigate the effects of tide-surge interaction. A thorough comparison between observed and simulated wind and water levels demonstrated a high degree of agreement. The results reveal that nonlinear tide-surge interactions are not uniformly distributed across the PRE. In the Lingdingyang waters, the impact of tide-surge interaction on the total water level ranges from 1% offshore to 30% upstream. In the coastal waters near Macao, this impact varies from 5% to 25%, with a peak impact of 25% observed near Hac Sa Bay in Macao, indicating a significant influence of tide-surge interaction in this area. Predicted city flood levels during HATO are well-validated against field data. The Inner Harbor of Macao is identified as the zone most severely affected by flooding induced by storm surge, with the highest flood depths recorded at its northern and southern ends.

Assessing total mortality following seabird wrecks given variable data quantity and quality: the Cassin’s auklet die-off

Mass mortality events (MMEs) of seabirds are becoming more frequent as the global climate warms. Often documented via beached bird surveys, methods for estimating event-wide mortality are needed that can accommodate regional differences in carcass deposition and data quality/quantity. We develop a framework for estimating mortality from beached bird counts, extending existing approaches through the novel application of ocean circulation modeling to assess beaching likelihood. We applied our framework to the 2014/15 Cassin’s auklet ( Ptychoramphus aleuticus) MME, which spread across three regions (central California, northern California-through-Washington, British Columbia) with varying data quality/quantity. Our best mortality estimate of ∼400 000 (estimates ranged from 265 000 to 700 000 depending on model uncertainty and extent) places this seabird MME as one of the largest on record. However, we caution that much uncertainty exists surrounding model parameterization and deposition in British Columbia where beached bird data were sparse. We suggest that the application of ocean circulation models, combined with process-based modeling of carcass persistence and detection, can improve estimates of MME magnitude.

Singular Phenomenon Analysis of Wind-Driven Circulation System Based on Galerkin Low-Order Model

Ocean circulation plays an important role in the formation and occurrence of extreme climate events. The study shows that the periodic variation of ocean circulation under strong wind stress is closely related to climate oscillation. Ocean circulation is a nonlinear dynamic system, which shows complex nonlinear characteristics, so the essence behind ocean circulation has not been clearly explained. Therefore, the response and evolution of the circulation system to wind stress are studied based on the bifurcation and catastrophe theories in nonlinear dynamics. First, the quasi-geostrophic gyre equation and the normalized gravity model are introduced and developed to study ocean circulation driven by wind stress, and solved using the Galerkin method. Then, the bifurcation and catastrophe behaviors of the system governed by the low-order ocean circulation model during the change in wind stress intensity and the coexistence of multiple equilibria in the circulation system are studied in detail. The results show that saddle and unstable nodes appear in the system after a cusp catastrophe. With the change in model parameters, the unstable node becomes the unstable focus, and then the subcritical Hopf bifurcation occurs. The system forms a bistable interval when the system undergoes a catastrophe twice, and the system shows hysteresis. In addition, multiple equilibrium states are coexisting in the circulating system, and the unstable equilibrium state always changes into a stable equilibrium state through vortex movement. Therefore, there is a route for the system to induce short-term climate oscillation, that is, in the multi-stable equilibrium state of the system, the vortex oscillates after being subject to small disturbances, and then triggers climate oscillation.

Coupling of potential habitat models with particle tracking experiments to examine larval fish dispersal and connectivity in deep water regions.

Computing Lagrangian trajectories with ocean circulation models is a powerful way to infer larval dispersal pathways and connectivity. Defining release areas and timing of particles to represent larval habitat realistically is critical to obtaining representative dispersal pathways. However, it is challenging due to spatial and temporal variability in larval density. Forward-tracking particle experiments were conducted to study larval connectivity of four species (neritic or mesopelagic) in the Gulf of Mexico's (GoM) deep-water region. A seasonal climatology coupled with predicted potential larval habitat models based on generalized additive models was used to delimit the particle dispersal origin. Two contrasting mesoscale circulation patterns were examined: (1) high Loop Current (LC) intrusion, absence of recently detached LC anticyclonic eddies (LC-ACE), and no interaction between LC-ACEs and the semi-permanent cyclonic eddy (CE) in the Bay of Campeche (BoC), and (2) limited LC intrusion, a recently detached LC-ACE, and interaction between LC-ACEs and the BoC's CE. To simulate larval transport, virtual larvae were randomly released in the potential habitats and advected for 30 days with the velocity fields of the HYbrid Coordinate Ocean Model with hourly-resolution assimilation. Potential habitat location and size played a major role in dispersal and connectivity. A greater percentage of particles were retained in potential habitats restricted to the southern BoC, suggesting lower connectivity with other GoM regions than those encompassing most of the BoC or the central Gulf. Mesoscale feature interactions in the western GoM and BoC led to greater dispersion along the western basin. By contrast, the absence of ACE-CE interaction in the BoC led to greater retention and less connectivity between the southern and northern GoM. Under high LC intrusion, particles seeded north of the Yucatan Shelf were advected through the Florida Straits and dispersed within the GoM. Coupling potential habitat models with particle experiments can help characterize the dispersal and connectivity of fish larvae in oceanic systems.

Impacts of glacial discharge on the primary production in a Greenlandic fjord

Subglacial discharge from marine-terminating glaciers in Greenland injects large volumes of freshwater and suspended sediment into adjacent fjord environments. Although the discharge itself is nutrient poor, the formation of meltwater plumes can enhance marine biological production by stimulating upwelling of nutrient-rich fjord water. Despite the importance of meltwater discharge to marine ecosystems, little is known of the quantitative impact of discharge processes on phytoplankton growth, including the effects of local plumes, fjord-wide stirring and mixing, and suspended sediments on net primary production (NPP). Here, we report simulations of Bowdoin Fjord in northwestern Greenland using coupled non-hydrostatic ocean circulation and lower-trophic level ecosystem models, developed using field data. Our findings demonstrate that subglacial discharge plays a crucial role in NPP by stirring and mixing the entire fjord water system, which has a greater effect on NPP than local plume upwelling. Sensitivity tests suggest a 20% increase in NPP under conditions of enhanced discharge anticipated in the future. However, if glacier discharge and retreat exceed critical levels, NPP is predicted to decline by 88% relative to present values. This pattern reflects the negative impact of increased sediment flux on photosynthesis and weakened fjord stirring and mixing resulting from shallower outlet depths.