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In response to quadrupled CO2, the Southern Ocean primarily uptakes excess heat around 60°S, which is then redistributed by the northward ocean heat transport (OHT) and mostly stored in the ocean or released back to the atmosphere around 45°S. However, the relative roles of mean ocean circulation and ocean circulation change in the uptake and redistribution of heat in the Southern Ocean remain controversial. Here, a set of climate model experiments embedded with a novel partial coupling technique are used to separate the roles of mean ocean circulation (passive component) and ocean circulation change (active component). For the ocean heat uptake (OHU) response, the mean ocean circulation and ocean circulation change are of equal importance. The OHT response south of 50°S is mainly determined by mean ocean circulation, while the ocean circulation change generates an anomalous southward OHT north of 50°S. A heat budget analysis finds that the divergence of passive OHT acts to balance the passive surface heat gain to the south of ∼50°S, while the convergence of active OHT acts to balance the active surface heat loss to the north of ∼50°S. Intriguingly, all the increase in ocean heat storage (OHS) is attributable to the passive component, with the ocean circulation change playing almost no role. In the Southern Ocean, both the active and the passive ocean heat transports are overcompensated by the reverse atmospheric heat transport via the Bjerknes compensation.

Mesoscale eddies play an important role in both momentum and heat balances in the Southern Ocean. Previous studies have documented an increasing intensity of the Southern Ocean eddy field during recent decades; however, it is still unclear whether the mesoscale eddies with different lifetimes have different temporal variations. Using satellite altimeter observations from 1993 to 2020, we find that the increasing trend in the intensity of eddies is dominated by long-lived eddies (with lifetimes ≥ 90 days), whose amplitude has increased at a rate of ~2.8% per decade; the increase is concentrated downstream of topography. In contrast, short-lived eddies (with lifetimes < 90 days) do not appear to have a significant trend in their amplitudes since the early 1990s. An energy conversion analysis indicates that the increased baroclinic instabilities of the mean flows associated with topography are responsible for the amplitude increase of the long-lived eddies.

Ocean mesoscale eddies are observed to influence mixed layer depth (MLD) with a deepening by anticyclonic eddies (AEs) and a shoaling by cyclonic eddies (CEs). By using Argo profiles, satellite altimeter data and eddy-resolving model data, this study investigates how the AEs and CEs alongside the Kuroshio Extension jet (KEJ) modulate the winter MLD. Results show that although the modulations by the AEs and CEs are roughly symmetric over the whole region on the winter MLD, their impacts are strongly asymmetric to the north and south of the KEJ. The deepening effect by the AEs is much more than the shoaling effect by the CEs to the north of the KEJ, while the shoaling effect by the CEs is much more than the deepening effect by the AEs to the south of the KEJ. Therefore, their overall effect results in a net deepening to the north and a net shoaling to the south of the KEJ. A further analysis finds that this asymmetric feature is closely related to the distribution of eddy amplitudes which implies more energetic AEs to the north but CEs to the south of the KEJ. This study highlights the importance of the distribution of energetic eddies on the modulation of MLD.

This study investigates the responses of the meridional ocean heat transport (OHT) to heat fluxes of equal amplitude but opposite sign into the global ocean surface using the Community Earth System Model (CESM). Results show that the poleward OHT in both hemispheres are weakened in response to the positive forcing (i.e., warming) and strengthened in response to the negative forcing (i.e., cooling), with the latter change exceeding the former, manifesting an overall asymmetric response. The OHT responses in the Indo-Pacific to both the warming and the cooling and thus their asymmetry are dominated by its Eulerian-mean component, due primarily to changes in the Indo-Pacific Subtropical Cells. Similarly, the OHT responses in the Atlantic are determined by changes in the Atlantic Meridional Overturning Circulation, yet their asymmetry is small due to the mediation from the nonlinear effect of temperature and velocity changes. For the Southern Ocean, the Eulerian-mean component still controls the total OHT responses, yet the largest contribution is from changes in vertical temperature structure. In addition, the asymmetric response in the Southern Ocean is a joint effort among the overturning circulation cells, horizontal gyres, eddies, as well as temperature changes.

Under external heating forcing in the Southern Ocean, climate models project anomalous northward atmosphere heat transport (AHT) across the equator, accompanied by a southward shift of the intertropical convergence zone (ITCZ). Comparison between a fully coupled and a slab ocean model shows that the inclusion of active ocean dynamics tends to partition the cross-equatorial energy transport and significantly reduce the ITCZ shift response by a factor of 10, a finding which supports previous studies. To understand how ocean dynamics damps the ITCZ’s response to an imposed thermal heating in the Southern Ocean, we examine the ocean heat transport (OHT) and ocean circulation responses in a set of fully coupled experiments. Results show that both the Indo-Pacific and the Atlantic contribute to transport energy across the equator mainly through its Eulerian-mean component. However, different from previous studies that linked the changes in OHT to the changes in the wind-driven subtropical cells or the Atlantic meridional overturning circulation (AMOC), our results show that the cross-equatorial OHT anomaly is due to a broad clockwise overturning circulation anomaly below the subtropical cells (approximately bounded by the 5°C to 20°C isotherms and 50°S to 10°N). Further elimination of the wind-driven component, conducted by prescribing the climatological wind stress in the Southern Ocean heat perturbation experiments, leads to little change in OHT, suggesting that the OHT response is predominantly thermohaline-driven by air-sea thermal interactions.

Climate models project an enhancement in SST seasonal cycle over the midlatitude oceans under global warming. The underlying mechanisms are investigated using a set of partially coupled experiments, in which the contribution from direct CO2 effects (i.e., the response in the absence of wind change) and wind feedbacks can be isolated from each other. Results indicate that both the direct CO2 and wind effects contribute to the enhancement in the SST seasonal cycle, with the former (latter) being more important in the Northern Hemisphere (Southern Hemisphere). Further decomposition of the wind effect into the wind stress feedback and wind speed feedback reveals the importance of the wind stress–driven ocean response in the change of SST seasonal cycle, a result in contrast to a previous study that ascribed the midlatitude SST seasonal cycle change to the thermodynamic wind speed feedback. The direct CO2 effect regulates the SST seasonal cycle through the warming-induced shoaling in the annual mean mixed layer depth (MLD) as well as the MLD difference between winter and summer. Moreover, the surface wind seasonal cycle changes due solely to the direct CO2 effect are found to bear a great resemblance to the full wind response, suggesting that the root cause for the enhancement of the midlatitude SST seasonal cycle resides in the direct CO2 effect. This notion is further supported by an ocean-alone experiment that reproduces the SST seasonal cycle enhancement under a spatially and temporally homogeneous surface thermal forcing.

Tryptophol (TOL) is a metabolic derivative of tryptophan (Trp) and shows pleiotropic effects in humans, plants and microbes. In this study, the effect of Trp and phenylalanine (Phe) on TOL production in Saccharomyces cerevisiae was determined, and a systematic interpretation of TOL accumulation was offered by transcriptomic and metabolomic analyses. Trp significantly promoted TOL production, but the output plateaued (231.02-266.31 mg/L) at Trp concentrations ≥ 0.6 g/L. In contrast, Phe reduced the stimulatory effect of Trp, which was strongly dependent on the Phe concentration. An integrated genomic, transcriptomic, and metabolomic analysis revealed that the effect of Trp and Phe on TOL production was mainly related to the transamination and decarboxylation of the Ehrlich pathway. Additionally, other genes, including thiamine regulon genes (this), the allantoin catabolic genes dal1, dal2, dal4, and the transcriptional activator gene aro80, may play important roles. These findings were partly supported by the fact that the thi4 gene was involved in TOL production, as shown by heterologous expression analysis. To the best of our knowledge, this novel biological function of thi4 in S. cerevisiae is reported here for the first time. Overall, our findings provide insights into the mechanism of TOL production, which will contribute to TOL production using metabolic engineering strategies.

Atlantic Meridional Overturning Circulation (AMOC) exhibits interdecadal to multidecadal variability, yet the role of surface freshwater flux (FWF) variability in this AMOC variability remains unclear. This study isolates the contribution of FWF variability in modulating AMOC through a partially coupled experiment, in which the effect of the interactive FWF is disabled. It is demonstrated that the impact of the coupled FWF variability enhances the persistence of density and deep convection anomalies in the Labrador Sea (LS), thus lengthening the period of the AMOC oscillation on multidecadal timescale and suppressing its ∼30-year periodicity. Further lead-lag regressions illuminate that the more persistent LS density anomalies are maintained by two mechanisms: (a) The local temperature-salinity coupling through the evaporation and (b) a downstream propagation along the East Greenland Current of the extra salinity anomaly due to the sea ice melting changes associated with an atmosphere forcing over the southern Greenland tip.

Seasonal-to-decadal variability of spice injection in the upper ocean of the subtropical southeastern Pacific (SEP) is investigated using 3-day and 0.25° simulations spanning from 1992 to 2016 in the Consortium for Estimating the Circulation and Climate of the Ocean. The spice injection refers to convective mixing through which saline water in the mixed layer is injected into the interior to generate positive temperature and salinity anomalies or spiciness anomaly (SPA). Results show that the spice injection in the SEP occurs during austral winter when the mixed layer is deep, and it leads to a positive SPA in the interior. The interior SPA is found to experience significant interannual variability, which is well correlated with winter mixed layer depth (MLD), with more interior SPA corresponding to deeper MLD. During a strong winter of injection, the interior spiciness change rate can reach up to ~ 0.005 kg m−3 day−1 and the gain of spiciness in the interior ~ 0.2 kg m−3 over the SEP region. The interannual-decadal variability of interior SPA in the SEP has a significantly negative correlation to the low-frequency El Nino–Southern Oscillation index, with larger (smaller) SPA during La Nina (El Nino) conditions.

This study investigates the contribution of mesoscale eddies to the subduction and transport of North Pacific Eastern Subtropical Mode Water (ESTMW) using the high-frequency output of an eddy-resolved ocean model spanning the period 1994–2010. Results show that the subduction induced by mesoscale eddies accounts for about 31% of the total subduction of ESTMW formation. The volume of ESTMW trapped by anticyclonic eddies is slightly larger than that trapped by cyclonic eddies. The ESTMW trapped by all eddies in May reaches up to about 2.8 × 1013 m3, which is approximately 16% of the total ESTMW volume. The eddy-trapped ESTMW moves primarily westward, with its meridional integration at 18°–30°N reaching about 0.17 Sv, which is approximately 18% of the total zonal ESTMW transport in this direction, at 140°W. This study highlights the important role of eddies in carrying ESTMW westward over the northeastern Pacific Ocean.

This study investigates the response of the subtropical gyre circulation in the North Pacific Ocean to quadrupled CO2 using the Community Earth System Model, version 1 (CESM1). In particula...

The response of the eastern tropical Indian Ocean (ETIO) to heat fluxes of equal amplitude but opposite sign is investigated using the Community Earth System Model (CESM). A significant positive asymmetry in sea surface temperature (SST) is found over the ETIO—the warming responses to the positive forcing exceeds the cooling to the negative forcing. A mixed layer heat budget analysis is carried out to identify the mechanisms responsible for the SST asymmetry. Results show that it is mainly ascribed to the ocean dynamical processes, including vertical advections and diffusion. The net surface heat flux, on the contrary, works to reduce the asymmetry through its shortwave radiation and latent heat flux components. The former is due to the nonlinear relationship between SST and cloud, while the latter is resulted mainly from Newtonian damping and air-sea stability effects. Changes in the SST skewness are also evaluated, with more enhanced negative SST skewness over the ETIO found for the cooling than heating scenarios due to the asymmetric thermocline-SST feedback.

Subantarctic Mode Water (SAMW) forms in deep mixed layers just north of the Antarctic Circumpolar Current in winter, playing a fundamental role in the ocean uptake of heat and carbon. Using a gridded Argo product and the ERA-Interim reanalysis for years 2004-2018, the seasonal evolution of the SAMW volume is analyzed using both a kinematic estimate of the subduction rate and a thermodynamic estimate of the air-sea formation rate. The seasonal SAMW volume changes are separately estimated within the monthly mixed layer and in the interior below it. We find that the variability of SAMW volume is dominated by changes in SAMW volume in the mixed layer. The seasonal variability of SAMW volume in the mixed layer is governed by formation due to air-sea buoyancy fluxes (45%, lasting from July to August), entrainment (35%), and northward Ekman transport across the Subantarctic Front (10%). The interior SAMW formation is entirely controlled by exchanges between the mixed layer and the interior (i.e. instantaneous subduction), which occurs mainly during August-October. The annual mean subduction estimate from a Lagrangian approach shows strong regional variability with hotspots of large SAMW subduction. The SAMW subduction hotspots are consistent with the distribution and export pathways of SAMW over the central and eastern parts of the south Indian and Pacific Oceans. Hotspots in the south Indian Ocean produce strong subduction of 8 and 9 Sv for the light and southeast Indian SAMW, respectively, while SAMW subduction of 6 and 4 Sv occurs for the central and southeast Pacific SAMW, respectively.

BackgroundTryptophol (TOL) is a metabolic derivative of tryptophan (Trp) and shows pleiotropic effects in humans, plants and microbes. The mechanisms of TOL biosynthesis were first explored several decades ago. Nonetheless, a systematic interpretation of TOL over-accumulation is still lacking.ResultsBased on TOL yield, a suitable transformation medium (TM1) was used to culture Saccharomyces cerevisiae strain KMLY1-2. The dynamics of TOL production, cell growth, and gene transcription revealed that TOL production was dependent on cell density and the expression of key genes. Additionally, the effects of Trp and phenylalanine (Phe) on TOL production were tested, and the results showed that Trp can significantly facilitate TOL accumulation, but output plateaued (231.02−266.31 mg/L) at Trp concentrations ≥0.6 g/L. In contrast, Phe reduced the stimulatory effect of Trp, which strongly depended on the Phe concentration. To elucidate the molecular basis and regulatory mechanism of TOL overproduction, an integrated analysis of metabolomics, genomics, and transcriptomics was performed. The results revealed that 1) both the Ehrlich pathway and tryptamine-dependent pathway were involved in S. cerevisiae TOL biosynthesis; 2) Trp increased TOL production by enhancing the Ehrlich pathway, in which the steps of transamination (including aminotransferase genes aro9, aat1, bat2 and his5) and decarboxylation (including decarboxylase genes aro10 and pdc5) played important roles. Of course, this process was assisted by amino acid permease genes agp1 and tat2, dihydrolipoyl dehydrogenase gene lpd1, and transcriptional activator gene aro80, etc.; 3) Phe restricted TOL biosynthesis by repressing the transcript levels of genes such as aat1, his5, aro10, pdc5 and aro80, thus interfering with the transamination and decarboxylation reactions; and 4) under sufficient Trp conditions, the de novo Trp biosynthetic pathway and central carbon metabolism (glycolysis, pentose phosphate pathway, and citrate cycle) of S. cerevisiae were weakened, while the content of some amino acids increased, which may be related to the promotion of yeast cell growth by Trp.ConclusionsIn this study, TOL production of S. cerevisiae was significantly improved, and our integrated multi-omics analyses have provided insights into the understanding of TOL over-accumulation, which will be useful for future production of TOL using metabolic engineering strategies.

Lactobacillus plantarum is one of common probiotics in fermented foods. Quorum sensing (QS) is a common communication way within bacteria. It is not clear whether the probiotic properties of L. plantarum mediated by QS. Here, Lb. plantarum YM-4-3 was examined for resistance of pH, bile, antimicrobial and luxS gene expression pattern. The study found that: (1) the supernatant of YM-4-3 had bacteriostatic effect to Escherichia coli O157:H7, Listeria monocytogenes and Staphylococcus aureus; (2) Lb. plantarum YM-4-3 shown tolerance property to the strongest acid culture that pH value of 3; (3) the bile tolerance of Lb. plantarum YM-4-3 was significant difference with the growth stage, the early exponential phase of the growth culture can tolerate bile of 0.4% (w/v), while the stationary growth stage can only tolerate bile of 0.2%; (4) Lb. plantarum YM-4-3 luxS gene was contrary expression along with the growth. (5) Compared with the wild-type strain, the adhesion ability of Lb. plantarum YM-4-3 ΔluxS was decreased obviously. These results showed that AI-2 LuxS quorum sensing system mediating Lb. plantarum acid, bile tolerance, antimicrobial and adhesion of probiotics.

Global Navigation Satellite System (GNSS) is now widely used for continuous ionospheric observations. Three-dimensional computerized ionospheric tomography (3DCIT) is an important tool for the reconstruction of electron density distributions in the ionosphere through effective use of the GNSS data. More specifically, the 3DCIT technique is able to resolve the three-dimensional electron density distributions over the reconstructed area based on the GNSS slant total electron content (STEC) observations. We present an Improved Constrained Simultaneous Iterative Reconstruction Technique (ICSIRT) algorithm that differs from the traditional ionospheric tomography methods in 3 ways. First, the ICSIRT computes the electron density corrections based on the product of the intercept and electron density within voxels so that the assignment of corrections at different heights becomes more reasonable. Second, an Inverse Distance Weighted (IDW) interpolation is used to restrict the electron density values in the voxels not traversed by GNSS rays, thereby ensuring the smoothness of the reconstructed region. Also, to improve the reconstruction accuracy around the HmF2 (the peak height of the F2 layer) altitude, a multiresolution grid is adopted in the vertical direction, with a 10-km resolution from 200 to 420 km and a 50-km resolution at other altitudes. The new algorithm has been applied to the GNSS data over the European and North American regions in different case studies that involve different seasonal conditions as well as a major storm. In the European region experiment, reconstruction results show that the new ICSIRT algorithm can effectively improve the reconstruction of the GNSS data. The electron density profiles retrieved from ICSIRT are much closer to the ionosonde observations than those from its predecessor, namely, the Constrained Simultaneous Iteration Reconstruction Technique (CSIRT). The reconstruction accuracy is significantly improved. In the North American region experiment, the electron density profiles in ICSIRT results show better agreement with incoherent scatter radar observations than CSIRT, even for the topside profiles.

A large set of Green’s function-type experiments is performed with q-flux forcings mimicking the effects of the ocean heat uptake (OHU) to examine the global surface air temperature (SAT) sensitivities to the location of the forcing. The result of the experiments confirms the earlier notion derived from experiments with different model complexities that the global mean SAT is far more sensitive to the oceanic forcing from high latitudes than the tropics. Remarkably, no matter in which latitude the q-flux forcings are placed, the SAT response is always characterized by a feature of polar amplification, implicating that it is intrinsic to our climate system. Considerable zonal asymmetry is also present in the efficacy of the tropical OHU, with the tropical eastern Pacific being much more efficient than the Indian Ocean and tropical Atlantic in driving global SAT warming by exciting the leading neutral mode of the SAT that projects strongly onto global mean warming. Using a radiative kernel, feedback analysis is also conducted to unravel the underlying processes responsible for the spatial heterogeneity in the global OHU efficacy, the polar amplification structures, and the tropical altruism of sharing the warmth with remote latitudes. Warming “altruism” for a q flux at a given latitude is also investigated in terms of the ratio of the induced remote latitudes versus the directly forced local warming. It is found that the tropics are much more altruistic than higher latitudes because of the high-energy transport efficiency of the Hadley circulation.

Climate models project a significant shoaling of the thermocline over the western equatorial Pacific Ocean under global warming, which has been generally regarded as a direct response to surface wind change. This study investigates the formation processes for the equatorial Pacific thermocline response to CO2 quadrupling using the Community Earth System Model version 1 (CESM1). In particular, an overriding method is applied to isolate and quantify the wind stress effect and the direct radiative effect of CO2 emissions. Results show that both effects of the wind stress and direct radiative forcing are equally important for shoaling the equatorial thermocline, with the former responsible for its upper portion change and the latter for its lower portion change. Further passive tracer experiments with the ocean component of the CESM1 verify the role of ocean surface warming in shoaling the equatorial thermocline and identify the ocean circulation change in response to the surface warming as its dynamic cause of formation.

The response of ENSO amplitude to climate warming and cooling is investigated using the Community Earth System Model (CESM), in which the warming and cooling scenarios are designed by adding heat fluxes of equal amplitude but opposite sign onto the ocean surface, respectively. Results show that the warming induces an increase of the ENSO amplitude but the cooling gives rise to a decrease of the ENSO amplitude, and these changes are robust in statistics. A mixed layer heat budget analysis finds that the increasing (decreasing) SST tendency under climate warming (cooling) is mainly due to an enhancement (weakening) of dynamical feedback processes over the equatorial Pacific, including zonal advective (ZA) feedback, meridional advective (MA) feedback, thermocline (TH) feedback, and Ekman (EK) feedback. As the climate warms, a wind anomaly of the same magnitude across the equatorial Pacific can induce a stronger zonal current change in the east (i.e., a stronger ZA feedback), which in turn produces a greater weakening of upwelling (i.e., a stronger EK feedback) and thus a larger thermocline change (i.e., a stronger TH feedback). In response to the climate warming, in addition, the MA feedback is also strengthened due to an enhancement of the meridional SST gradient around the equator resulting from a weakening of the subtropical cells (STCs). It should be noted that the weakened STCs itself has a negative contribution to the change of the MA feedback which, however, appears to be secondary. And vice versa for the cooling case. Bjerknes linear stability (BJ) index is also evaluated for the linear stability of ENSO, with remarkably larger (smaller) BJ index found for the warming (cooling) case.

This paper explores the use of the linear response function (LRF) to relate the mean sea surface temperature (SST) response to prescribed ocean heat convergence (q flux) forcings. Two methods for constructing the LRF based on the fluctuation–dissipation theorem (FDT) and Green’s function (GRF) are examined. A 900-yr preindustrial simulation by the Community Earth System Model coupled with a slab ocean model (CESM–SOM) is used to estimate the LRF using FDT. For GRF, 106 pairs of CESM–SOM simulations with warm and cold q-flux patches are performed. FDT is found to have some skill in estimating the SST response to a q-flux forcing when the local SST response is strong, but it fails in inverse estimation of the q-flux forcing for a given SST pattern. In contrast, GRF is shown to be reasonably accurate in estimating both SST response and q-flux forcing. Possible degradation in FDT may be attributed to insufficient data sampling, significant departure of the SST distribution from Gaussianity, and the nonnormality of the constructed operator. The GRF-based LRF is then used to (i) generate a global surface temperature sensitivity map that shows the q-flux forcing in higher latitudes to be 3–4 times more effective than low latitudes in producing global surface warming, and (ii) identify the most excitable SST mode (neutral vector) that shows marked resemblance to the interdecadal Pacific oscillation (IPO). The latter discovery suggests that the IPO-like fluctuation exists in the absence of the coupling to the ocean dynamics. Coupling to the ocean dynamics in CESM, on the other hand, only enhances the spectral power of the IPO at interannual time scales.

The response of the tropical Indian Ocean (TIO) to greenhouse gases (GHGs) and aerosols are investigated based on historical single-forcing and all-forcing simulations using the Geophysical Fluid D...

The role of ocean dynamics in the response of the equatorial Pacific Ocean to climate warming is investigated using both an atmosphere–ocean coupled climate system and its ocean component. Results show that the initial response (fast pattern) to an uniform heating imposed on the ocean is a warming centered to the west of the date line owing to the conventional ocean dynamical thermostat (ODT) mechanism in the eastern equatorial Pacific—a cooling effect arising from the up-gradient upwelling. In time, the warming pattern gradually propagates eastward, becoming more El Niño–like (slow pattern). The transition from the fast to the slow pattern likely results from 1) the gradual warming of the equatorial thermocline temperature, which is associated with the arrival of the relatively warmer extratropical waters advected along the subsurface branch of the subtropical cells (STCs), and 2) the reduction of the STC strength itself. A mixed layer heat budget analysis finds that it is the total ocean dynamical effect rather than the conventional ODT that holds the key for understanding the pattern of the SST in the equatorial Pacific and that the surface heat flux works mainly to compensate the ocean dynamics. Further passive tracer experiments with the ocean component of the coupled system verify the role of the ocean dynamical processes in initiating a La Niña–like SST warming and in setting the pace of the transition to an El Niño–like warming and identify an oceanic origin for the slow eastern Pacific warming independent of the weakening trade wind.

Enhanced mesoscale eddy activities or tropical instability waves (TIWs) exist along the northern front of the cold tongue in the eastern equatorial Pacific Ocean. In this study, we investigate seasonal variability of eddy kinetic energy (EKE) over this region and its associated dynamic mechanism using a global, eddy-resolving ocean general circulation model (OGCM) simulation, the equatorial mooring data and satellite altimeter observations. The seasonal-varying enhanced EKE signals are found to expand westward from 100°W in June to 180°W in December between 0°−6°N. This westward expansion in EKE is closely connected to the barotropically-baroclinically unstable zonal flows that are in thermal-wind balance with the seasonal-varying thermocline trough along 4°N. By adopting an 1½-layer reduced-gravity model, we confirm that the seasonal perturbation of the thermocline trough is dominated by the anti-cyclonic wind stress curl forcing, which develops due to southerly winds along 4°N from June to December.

The goal of this study was to explore the regulatory mechanisms of phenyllactic acid (PLA) overaccumulation in

Previous observations suggest periodic freshwater patches separating from the Block Island Sound (BIS) estuarine plume. In this study, the dynamics of the separation process is investigated through a series of numerical experiments using the Regional Ocean Modeling System (ROMS). In addition, we explore the seasonal variability of the freshwater patches and their response to river discharge and ambient current. The model results indicate that episodic freshwater patches are triggered by small changes in tidal currents over the spring-neap tidal cycle. The spring-neap variation in tidal currents causes significant, monthly fluctuations in turbulent mixing and vertical stratification in BIS, modulating the freshwater discharge thereby generating episodic freshwater patches that move both downstream along the southern shore of Long Island and toward Rhode Island Sound (RIS). The realistically configured model shows that the freshwater patches experience strong seasonal variability. They are largest in spring when the river discharge peaks, and smallest in summer due to the weak river discharge and a robust upstream ambient current from RIS. According to the analysis of the freshwater transport out of BIS, we conclude that such detachment occurs at tidal mixing fronts.

The Regional Ocean Modeling System (ROMS) is used to study the summer circulation in the southwestern Yellow Sea (SWYS). The modeled currents show good agreement with observations from both drifters and moorings. While the summer current in the SWYS flows consistently northeastward on the surface with large magnitude offshore, the current below the surface layer features a cyclonic circulation roughly along the 25 m isobath. The effect of a surface wind stress and bottom thermal fronts on the circulation is investigated through a series of process-oriented numerical experiments. It is found that the southeasterly wind dominates the surface current, whereas the bottom thermal fronts, which are formed in a transition area between the vertically well-mixed region and the stratified region, are responsible for the cyclonic circulation below the surface.

Observations reveal a near-surface circulation around the periphery of Rhode Island Sound (RIS) that occurs in summer stratified conditions and disappears in winter when weak solar insolation and wind stirring result in strong vertical mixing. According to a series of numerical simulations and theoretical analysis, we attribute the summer intensification of this “periphery current” to a circulation produced by seasonal bottom thermal fronts often observed from May to September. The strength of the thermal fronts is proportional to the surface solar radiation. Meanwhile, the simulations capture a continuous topographically rectified tidal residual current in RIS and a pair of opposite-sign headland eddies around Montauk Point in Block Island Sound (BIS). Our analysis suggests the importance of nonlinear vorticity advection and frictional torques in BIS. On the other hand, the vorticity balance shows the importance of velocity torque by contributing to the opposite headland gyres, while the effect by planetary vorticity stretching is negligible over BIS but important in RIS.

A numerical simulation using the Regional Ocean Modeling System (ROMS) indicates that there was significant interannual-to-interpentadal variability of along-shelf transport and water properties over the Middle Atlantic Bight (MAB) from 2004 to 2013. To examine the relative contribution from local atmospheric forcing versus remote oceanic open boundary forcing to such low-frequency variability, we implement a suite of process oriented numerical experiments. Results show that the interannual variability is dominated by remote forcing from the open boundaries of the region rather than by local atmospheric forcing. The penetration of the Labrador Current into the region contributes to a significant increase of along-shelf transport in the winters of 2009 and 2010. By contrast, the anti-cyclonic mesoscale eddies associated with the Gulf Stream decrease the background along-shelf jet and, in certain cases, even reverse the along-shelf transport. In addition, the along-shelf transport appears to possess an interpentadal variation, i.e., weaker during 2004–2008 but stronger during 2009–2013, which is found caused by the migration of the Gulf Stream.

Buoyant discharge of freshwater from Long Island Sound (LIS) forms a seasonal buoyant plume outside Block Island Sound (BIS) between the coast of Long Island and the denser shelf waters. The plume’s seasonal variability and its response to tides, winds, and surface heating are investigated through a series of process-oriented experiments using the Regional Ocean Modeling System (ROMS). Results show the importance of river discharge, wind directions, and surface heating in the seasonal variation of the BIS buoyant plume. In winter and spring, the plume is intermediate with a large surface offshore extension detached from the bottom. From winter to spring, the river discharge increases; meanwhile, upwelling-favorable winds keep dominating. They compete with the increase of surface heating and generate a broader buoyant plume in spring than in winter. In summer, the plume is bottom advected with most of its width in contact with the bottom and is featured with the steepest isopycnals and narrowest plume, which is driven by a combination of strong insolation, weak buoyant discharge from LIS, and feeble winds. In fall, although the river discharge is comparable to that in winter, the upwelling-favorable wind is relatively weaker, corresponding to a narrower intermediate plume.