Float Data Research Articles

Deep Floats Reveal Complex Ocean Circulation Patterns

Acoustically tracked floats drift far below the ocean’s surface, providing fresh discoveries about deep-sea currents. A new archive gathers decades’ worth of float data into a central repository.

Observing the Ice‐Covered Weddell Gyre With Profiling Floats: Position Uncertainties and Correlation Statistics

AbstractArgo‐type profiling floats do not receive satellite positioning while under sea ice. Common practice is to approximate unknown positions by linearly interpolating latitude‐longitude between known positions before and after ice cover, although it has been suggested that some improvement may be obtained by interpolating along contours of planetary‐geostrophic potential vorticity. Profiles with linearly interpolated positions represent 16% of the Southern Ocean Argo data set; consequences arising from this approximation have not been quantified. Using three distinct data sets from the Weddell Gyre—10‐day satellite‐tracked Argo floats, daily‐tracked RAFOS‐enabled floats, and a particle release simulation in the Southern Ocean State Estimate—we perform a data withholding experiment to assess position uncertainty in latitude‐longitude and potential vorticity coordinates as a function of time since last fix. A spatial correlation analysis using the float data provides temperature and salinity uncertainty estimates as a function of distance error. Combining the spatial correlation scales and the position uncertainty, we estimate uncertainty in temperature and salinity as a function of duration of position loss. Maximum position uncertainty for interpolation during 8 months without position data is 116 ± 148 km for latitude‐longitude and 92 ± 121 km for potential vorticity coordinates. The estimated maximum uncertainty in local temperature and salinity over the entire 2,000‐m profiles during 8 months without position data is 0.66 ∘C and 0.15 psu in the upper 300 m and 0.16 ∘C and 0.01 psu below 300 m.

The Open‐Ocean Side of the Malvinas Current in Argo Floats and 24 Years of Mercator Ocean High‐Resolution (1/12) Physical Reanalysis

AbstractDownstream of Drake Passage, the northern branches of the Antarctic Circumpolar Current, the Polar Front and the Subantarctic Front, veer northward and the latter forms the Malvinas Current (MC). The MC flows along the continental slope up to 38°S where it loops southward as the Malvinas Return Flow. Using 24 years of Mercator Ocean physical reanalysis outputs and Argo float data, we explore the open‐ocean side of the MC. We observe the occurrence of blocking events at 49°S, a region where the MC is exposed to the warm and salty anticyclonic anomalies propagating westward along the steep slope of the Malvinas Escarpment. During these events, the MC is cut off from its source, and the MC transport is considerably reduced at 49°S. The open‐ocean side of the MC is regularly supplied with cold polar waters from the Polar front.The polar waters accumulate and recirculate between the MC and the Malvinas Return Flow. The water characteristics of the recirculation region change over time. The recirculation region hosts significantly lighter and fresher waters during the period 1997–2003 compared with prior and later years. The 1997–2003 salinity minimum in the recirculation region corresponds to a period with reduced feeding events at 49°S.

Inferring and Removing a Spurious Response in the Optical Backscattering Signal from an Autonomous Profiling Float

AbstractDevelopment of autonomous profiling floats, allowing for long-term continuous measurement of bio-optical variables, promises to significantly increase our knowledge of the variability of the particulate optical backscattering coefficient bbp in marine environments. However, because autonomous floats are designed for unattended data collection and only rarely are recovered for analysis of the condition of the sensors in situ, the quality-control analysis of float data streams is of paramount importance in both a particular dataset and the larger understanding of the response of sensors over the lifetime of the floats. Anomalous data from a backscattering sensor (MCOMS) mounted on autonomous profiling floats are reported here. The observed sensor behavior, which presents itself as significant differences in the values observed at the parking depth between profiles, caused by a steady increase in the signal during the profiling time, is neither common to all sensors nor can it be a function of changes in the particle population. A simple quality-control procedure that is able to detect this spurious sensor response is proposed. Further characterization of this effect will require laboratory experimentation under controlled conditions of temperature and pressure.

A \u201cmirror layer\u201d of temperature and salinity in the ocean

Using the newly available 13-year Argo float data for the period 2004–2016, a three-dimensional temperature–salinity (T–S) correlation field is constructed for the global upper ocean. It is revealed that the layer-averaged correlation between T and S time series has a significant peak (~ 0.7) at a depth of approximately 300 m, suggesting that the density-compensated thermohaline covariation may lead to a maximum T–S coupling in the vicinity of the pycnocline. This argument is supported by subsequent findings that the spatial distributions of temperature and salinity have excellent consistencies in terms of both climatology and seasonality around this depth, which we call a “T-S mirror layer”. Since mass, heat and salt are mainly transported by dynamic events and processes, dominant currents and prevailing eddies in the pycnocline zone are found to determine the fundamental patterns of the global T/S climatologies which are characterized by a unified pattern of six well-defined warm/salty pools with collocated centroids and a clear west preference. Our results also suggest that the climatological ocean circulations transport heat/salt as a conveyor belt, meanwhile heat and salt parcels are discretely transported by numerous migrating mesoscale eddies, the combined effects of which lead to the formation of six well-defined “warm/salty pools” in the western subtropical oceans with a core depth of ~ 300 m at the “mirror layer”.

Argo Observations of the Deep Mixing Band in the Southern Ocean: A Salinity Modeling Challenge

AbstractThe Southern Ocean plays an important role in mediating oceanic uptake of CO2 and heat due to a strong meridional overturning circulation. Gridded Argo float data for 2004–2017 were used to evaluate subsurface processes at the mixed layer depth (MLD) that occur in a narrow deep mixing band. Shifts in the value of the Turner Angle at the MLD indicate that early in the season the MLD deepens slowly as it encounters and is stabilized by a subsurface salt maximum. By September mixing has penetrated this salinity feature and the rate of deepening is faster once the MLD is deeper than the depth where the maximum salinity occurs (~150–200 m). This distinctive salinity layer is the result of surface Ekman transport of fresh water from the south and subsurface advection of high‐salinity water from the north. Two configurations of the Community Earth System Model (CESM) ocean‐ice forced hindcast experiments—one with 1° and the other with 0.1° horizontal resolution (Parallel Ocean Program low and high resolutions [POP‐LR and POP‐HR], respectively)—are compared with the Argo data for 2005–2009. POP‐LR has a shallow MLD bias common to many Fifth Coupled Models Intercomparison Project (CMIP5) models, while POP‐HR has a mix of deep and shallow MLD biases. While both models were able to replicate the large‐scale processes leading to formation of a high‐salinity layer, the salinity feature in POP‐HR is too strong and deep. Neither model was able to replicate the vertical mixing processes leading to penetration of the subsurface salt maximum.

Argo Floats as a Novel Part of the Monitoring the Hydrography of the Bothnian Sea

We made an assessment of the hydrography in the Bothnian Sea based on data collected by the Argo floats during the first six years of operation in the Bothnian Sea (2012–2017). We evaluated the added value of Argo data related to the pre-existing monitoring data. The optimal usage and profiling frequency of Argo floats was also evaluated and the horizontal and vertical coverage of the profiles were assessed. For now we lose 4m of data from the surface due to sensor design and some meters from the bottom because of the low resolution of available bathymetry data that is used to avoid bottom collisions. Mean monthly temperature and salinity close to surface and below halocline from the float data were within the boundaries given in literature, although some variation was lost due to scarcity of winter profiles. The temporal coverage of the Argo data is much better than that of ship monitoring, but some spatial variability is lost since the floats are confined in the over 100m deep area of the Bothnian Sea. The possibility to adjust the float profiling frequency according to weather forecasts was successfully demonstrated and found a feasible way to get measurements from storms and other short term phenomena unreachable with research vessels. First six years of operation have shown that Argo floats can be successfully operated in the challenging conditions of the Bothnian Sea and they are shown to be an excellent addition to the monitoring network there. With multiple floats spread in the basin we can increase our general knowledge of the hydrographic conditions and occasionally get interesting data related to intrusions and mixing during high wind events and other synoptic scale events.

Large-scale impacts of the mesoscale environment on mixing from wind-driven internal waves

Oceanic mesoscale structures such as eddies and fronts can alter the propagation, breaking and subsequent turbulent mixing of wind-generated internal waves. However, it has been difficult to ascertain whether these processes affect the global-scale patterns, timing and magnitude of turbulent mixing, thereby powering the global oceanic overturning circulation and driving the transport of heat and dissolved gases. Here we present global evidence demonstrating that mesoscale features can significantly enhance turbulent mixing due to wind-generated internal waves. Using internal wave-driven mixing estimates calculated from Argo profiling floats between 30° and 45° N, we find that both the amplitude of the seasonal cycle of turbulent mixing and the response to increases in the wind energy flux are larger to a depth of at least 2,000 m in the presence of a strong and temporally uniform field of mesoscale eddy kinetic energy. Mixing is especially strong within energetic anticyclonic mesoscale features compared to cyclonic features, indicating that local modification of wind-driven internal waves is probably one mechanism contributing to the elevated mixing observed in energetic mesoscale environments. Mesoscale ocean features can alter the magnitude of turbulent mixing caused by wind-driven internal waves, an analysis of Argo float and model data suggests.

Estimating Currents From Argo Trajectories in the Bothnian Sea, Baltic Sea

Argo floats have been used in the environmental monitoring of the Bothnian Sea, a sub-basin of the Baltic Sea, for five years as part of the Finnish Euro-Argo programme. The Bothnian Sea is considered to be an environmentally healthy part of the Baltic Sea because the deep waters of the basin are well-ventilated by inflowing oxygen-rich saltier and heavier surface layer waters of the Baltic Sea proper. Thus the deep water flow is of interest in the Bothnian Sea. In this study, we used Argo float data from six different long-term missions, from 111 to 512 days, to analyze the deep-water flow in the Bothnian Sea where no continuous monitoring of currents exist. We estimated mainly the flow below the expected halocline from the paths of the floats. We analyzed the movements statistically and estimated the error caused by the surface drift of the floats during their stay at the surface by using 3D hydrodynamic model results as reference data. Our results show a cyclonic resultant current in the deep trench of the Bothnian Sea. There seemed to be very little exchange between coastal zone and open-sea waters in deeper layers. The drifting speed of the floats in the deep layers of Bothnian Sea generally was around 2 cm/s but instantaneous speeds of tens of centimeters up to 30 cm/s in the middle-layer (50 dbars) were observed. In the Bothnian Sea deep, the deep trench on the Finnish side of the Bothnian Sea, the vast majority of the observations showed deep currents from south to north, with the same average speed of around 2 cm/s but the instantaneous maximum was smaller at 13 cm/s. Our study indicates that the routine Argo float observations can be used to get information on the deep currents in the basin in addition to traditional hydrographic observations. This helps in improving our understanding of the oxygen dynamics of the bottom layers of the Bothnian Sea, and the living conditions of the benthic phyto- and zooplankton communities there.

Water masses in the far western equatorial Pacific during the winters of 2010 and 2012

Conductivity-temperature-depth (CTD) data obtained during the 2010 La Nina winter and the 2012 normal winter, combined with concurrent Argo profiling float data, provide a quasi-synoptic description of the water mass distributions and their variations in the far western equatorial Pacific Ocean. The water mass connection between the western Pacific and the east Indonesian seas is emphasized. Analysis indicates that the North Pacific Tropical Water (NPTW, S >34.9) carried by the Mindanao Current southward and the South Pacific Tropical Water (SPTW, S >35.1) from the southern hemisphere meet in the area. Observations suggest that the southward transport of the NPTW is stronger in 2010 than in 2012 due to enhanced advection of the Mindanao Current. The distribution of SPTW, which crosses the equator in the northwest direction and retroflects back to the interior Pacific Ocean, is found to retreat from 4°–5°N in 2012 to 2°–3°N in 2010 La Nina peak in the 130°E section. A relatively fresh tropical subsurface water is identified in between the NPTW and the SPTW, moving eastward with the North Equatorial Countercurrent into the equatorial Pacific Ocean. However, the salinity maximum of this subsurface fresh water is found to decrease eastward, suggesting that the salinity maximum is generated either by strong diapycnal mixing or by isopycnal mixing of temporally entrained Indonesian sea water into the area.

Transport, properties, and life cycles of mesoscale eddies in the eastern tropical South Pacific

Abstract. The influence of mesoscale eddies on the flow field and the water masses, especially the oxygen distribution of the eastern tropical South Pacific, is investigated from a mooring, float, and satellite data set. Two anticyclonic (ACE1/2), one mode-water (MWE), and one cyclonic eddy (CE) are identified and followed in detail with satellite data on their westward transition with velocities of 3.2 to 6.0 cm s−1 from their generation region, the shelf of the Peruvian and Chilean upwelling regime, across the Stratus Ocean Reference Station (ORS; ∼20∘ S, 85∘ W) to their decaying region far west in the oligotrophic open ocean. The ORS is located in the transition zone between the oxygen minimum zone and the well oxygenated South Pacific subtropical gyre. Velocity, hydrographic, and oxygen measurements at the mooring show the impact of eddies on the weak flow region of the eastern tropical South Pacific. Strong anomalies are related to the passage of eddies and are not associated with a seasonal signal in the open ocean. The mass transport of the four observed eddies across 85∘ W is between 1.1 and 1.8 Sv. The eddy type-dependent available heat, salt, and oxygen anomalies are 8.1×1018 J (ACE2), 1.0×1018 J (MWE), and -8.9×1018 J (CE) for heat; 25.2×1010 kg (ACE2), -3.1×1010 kg (MWE), and -41.5×1010 kg (CE) for salt; and -3.6×1016 µmol (ACE2), -3.5×1016 µmol (MWE), and -6.5×1016 µmol (CE) for oxygen showing a strong imbalance between anticyclones and cyclones for salt transports probably due to seasonal variability in water mass properties in the formation region of the eddies. Heat, salt, and oxygen fluxes out of the coastal region across the ORS region in the oligotrophic open South Pacific are estimated based on these eddy anomalies and on eddy statistics (gained out of 23 years of satellite data). Furthermore, four profiling floats were trapped in the ACE2 during its westward propagation between the formation region and the open ocean, which allows for conclusions on lateral mixing of water mass properties with time between the core of the eddy and the surrounding water. The strongest lateral mixing was found between the seasonal thermocline and the eddy core during the first half of the eddy lifetime.

Comparison of interpolation methods for sea surface temperature data D

Interpolation methods have been used in many applications to produce continuous surface data based on point data. The common interpolation methods for Sea Surface Temperature (SST) data are Inverse Distance Weighted (IDW), Kriging, Natural Neighbor Interpolation (NNI), and Spline. In this study, those four interpolation methods will be reviewed and compared to find the satisfactory method. The Argo float data was chosen as SST point data and Aqua MODIS image as validation data. Each method will be reviewed and compared to Aqua MODIS data to find the best performance. The assessment for testing the best interpolation model is smooth performance, Maximum and Minimum comparison, mean comparison, Root Mean Square Error (RMSE) and Standard Deviation Difference. The result shows that IDW interpolation is the best way to make spatial interpolation for SST.

Impact of 2015–2016 ENSO on the winter bloom and associated phytoplankton community shift in the northeastern Arabian Sea

Abstract The present study explores the impact of 2015–16 El-Nino Southern Oscillation (ENSO) on the winter phytoplankton bloom in the northeastern Arabian Sea (NEAS). In situ Chlorophyll a (Chla) from the bio-Argo float (2013–2016) and phytoplankton pigment data collected onboard R.V. Sindhu Sankalp (February 2013 and 2016) have been used to decipher the 2015–2016 ENSO modulated variability. During a normal winter, convective mixing deepens the mixed layer (ML) and increases the availability of nutrients in the euphotic zone. During the 2015–16 ENSO, the intensity of the convection (evaporation) was weaker than normal and this, in turn, weakened the convective mixing in the following winter. However, during the 2015–16 ENSO event, a warm core eddy deepened the ML further by pushing the nutracline downwards, thereby reducing the availability of nutrients. Changes in the physical condition during the 2015–16 ENSO altered the nutrient availability which in turn affected the Chla production and associated phytoplankton community structure. The Bio-Argo observations show 50% reduction in Chla during February 2016 compared to a normal year, which we attribute to the ENSO event of 2015–2016. Additionally, pigment data shows a reduction in the abundance of microplankton (diatoms and dinoflagellates) and an increase in abundance of picoplankton in the NEAS. Our results clearly indicate that 2015 ENSO played a dominant role in altering the phytoplankton community composition and in turn the productivity of the Arabian Sea.

On the assimilation of absolute geodetic dynamic topography in a global ocean model: impact on the deep ocean state

General ocean circulation models are not perfect. Forced with observed atmospheric fluxes they gradually drift away from measured distributions of temperature and salinity. We suggest data assimilation of absolute dynamical ocean topography (DOT) observed from space geodetic missions as an option to reduce these differences. Sea surface information of DOT is transferred into the deep ocean by defining the analysed ocean state as a weighted average of an ensemble of fully consistent model solutions using an error-subspace ensemble Kalman filter technique. Success of the technique is demonstrated by assimilation into a global configuration of the ocean circulation model FESOM over 1 year. The dynamic ocean topography data are obtained from a combination of multi-satellite altimetry and geoid measurements. The assimilation result is assessed using independent temperature and salinity analysis derived from profiling buoys of the AGRO float data set. The largest impact of the assimilation occurs at the first few analysis steps where both the model ocean topography and the steric height (i.e. temperature and salinity) are improved. The continued data assimilation over 1 year further improves the model state gradually. Deep ocean fields quickly adjust in a sustained manner: A model forecast initialized from the model state estimated by the data assimilation after only 1 month shows that improvements induced by the data assimilation remain in the model state for a long time. Even after 11 months, the modelled ocean topography and temperature fields show smaller errors than the model forecast without any data assimilation.

Remote sensing and in situ platform based study on impact of Bay of Bengal cyclones (Phailin, Helen, Lehar, and Madi) on ocean chlorophyll and associated physical parameters

Impact of four major cyclones: Phailin, Helen, Lehar, and Madi have been studied in terms of changes in ocean productivity utilizing Indian satellite Oceansat-2 ocean color monitor and MODIS-Aqua data during October–December 2013. The 8-day and monthly composite chlorophyll images have been generated owing to the pre-, during, and post-stages of four cyclones; out of which, three were very severe cyclonic storms and the Helen was severe cyclonic storm. The chlorophyll concentration increased two- to threefolds due to the aftereffect of cyclone in the coastal water, and the concentration was very high (around 2–3 mg/m3). To understand the possible links of cyclones to cooling and upwelling, MODIS-Aqua sea surface temperature (SST) images have been processed. The SST images have shown the cooling effect near the cyclone track pass, over Bay of Bengal. The cooling was observed by 2–3 degree Celsius during the above cyclones. To understand the in situ surface water and water column salinity and temperature variability, the Argo float data are plotted and interpreted. The surface contour shows the lowering of salinity and temperature with effects of cyclones. In addition, the Argo depth profile data have shown possible mixed layer deepening in few profiles around halocline and thermocline depths. This study will be useful for mapping potential fishing zone, ocean biogeochemistry and other useful applications and research.

Evaluation of spatial distribution of turbulent mixing in the central Pacific

A long-term mean turbulent mixing in the depth range of 200–1000 m produced by breaking of internal waves across the middle and low latitudes (40°S–40°N) of the Pacific between 160°W and 140°W is examined by applying fine-scale parameterization depending on strain variance to 8-year (2005–2012) Argo float data. Results show that elevated turbulent dissipation rate (e) is related to significant topographic regions, along the equator, and on the northern side of 20°N spanning to 24°N throughout the depth range. Two patterns of latitudinal variations of e and the corresponding diffusivity (Kρ) for different depth ranges are confirmed: One is for 200–450 m with significant larger e and Kρ, and the maximum values are obtained between 4°N and 6°N, where eddy kinetic energy also reaches its maximum; The other is for 350–1000 m with smaller e and Kρ, and the maximum values are obtained near the equator, and between 18°S and 12°S in the southern hemisphere, 20°N and 22°N in the northern hemisphere. Most elevated turbulent dissipation in the depth range of 350–1000 m relates to rough bottom roughness (correlation coefficient = 0.63), excluding the equatorial area. In the temporal mean field, energy flux from surface wind stress to inertial motions is not significant enough to account for the relatively intensified turbulent mixing in the upper layer.

Salinification in the South China Sea Since Late 2012: A Reversal of the Freshening Since the 1990s

AbstractSalinification has occurred in the South China Sea from late 2012 to the present, as shown by satellite Aquarius/Soil Moisture Active Passive data and Argo float data. This salinification follows a 20 year freshening trend that started in 1993. The salinification signal is strongest near the surface and extends downward under the seasonal thermocline to a depth of 150 m. The salinification occurs when the phase of the Pacific Decadal Oscillation switches from negative to positive. Diagnosis of the salinity budget suggests that an increasing net surface freshwater loss and the horizontal salt advection through the Luzon Strait driven by the South China Sea throughflow contributed to this ongoing salinification. In particular, a decrease in precipitation and enhanced Luzon Strait transport dominated the current intense salinification. Of particular interest is whether this salinification will continue until it reaches the previous maximum recorded in 1992.

Use of bio-optical profiling float data in validation of ocean colour satellite products in a remote ocean region

Utility of data from autonomous profiling floats for the validation of satellite ocean colour products from current satellite ocean colour sensors was assessed using radiometric and chlorophyll a fluorescence data from biogeochemical profiling floats (BGC-Argo) deployed in the subtropical gyre of the Indian Ocean. One of the floats was equipped with downward irradiance and upwelling radiance sensors, allowing the remote sensing reflectance, Rrs, to be determined. Comparisons between satellite and in situ Rrs indicated good agreement for the shorter wavelengths, but weak relationships for both satellites for the 555 nm channel, and showed that radiometers deployed on multipurpose, off-the-shelf BGC-Argo floats can provide validation-quality measurements. About 300 chlorophyll a concentration match-ups were achieved within 18 months, which increased the number of validation data points available for the Indian Ocean as a whole by a factor of ~4 from the previous historical record. Generally, the satellite data agreed with the float-derived chlorophyll concentration within the uncertainty of ±35%, for the band-difference (OCI) and band-ratio (OC3) algorithms, but not for a semianalytical ocean colour model (GSM) that exhibited significantly higher chlorophyll values (>100% mean difference). Our results indicate that autonomous float-based measurements provide substantial potential for improving regional validation of satellite ocean colour products in remote areas.

Properties, formation, and dissipation of the North Pacific Eastern Subtropical Mode Water and its impact on interannual spiciness anomalies

The properties, formation, and dissipation of the North Pacific Eastern Subtropical Mode Water (ESTMW), their interannual variability, and impact on spiciness anomalies in the upper permanent pycnocline were investigated using Argo profiling float data in 2005–2015. The core temperature and salinity of ESTMWs were horizontally compensated to a constant density, and core potential density concentrates in a range of 24.5–25.2 kg m−3 with two distinct peaks. ESTMWs showed different spatial distribution and persistence for its core potential density. Denser ESTMWs with a potential density of 24.9–25.2 kg m−3 were formed in winter mixed layer depth maximum centered at 30°N, 140°W and lighter ESTMWs of 24.5–24.9 kg m−3 were formed south and east of it. After formation through shoaling of the winter mixed layer, the former persisted until the following autumn and a small part of it subducted in winter, while the latter dissipated in summer. The formation region of ESTMW corresponded to the summer sea surface density maximum resulting from its poleward sea surface salinity front. Sea surface density maximum maintains weak stratification during summer, preconditioning the deepening of the winter mixed layer and hence the formation of ESTMWs. A relationship between the ESTMW formation region and the summer sea surface density maximum was also found in the North Atlantic and the South Pacific, implying the importance of sea surface salinity fronts and the associated summer sea surface density maximum to ESTMW formation. Interannual variations of ESTMW reflected that of the winter mixed layer in its formation region, and the thickness of ESTMW was related to the Pacific decadal oscillation. ESTMW contributed to the occurrence of spice injection and affected spiciness anomalies in the upper permanent pycnocline through its formation and dissipation.

Upper ocean response to the passage of two sequential typhoons

Two sequential typhoons, separated by five days, Chan-hom and Nangka in the summer of 2015, provided a unique opportunity to study the oceanic response and cold wake evolution. The upper ocean response to the passage of these two typhoons was investigated using multi-satellite, Argo float data and HYCOM global model output. The sea surface cooling (SSC) induced by Chan-hom was gradually enhanced along its track when the storm was intensified while moving over the ocean with shallow mixed layer. The location of maximum cooling of sea surface was determined by the storm's translation speed as well as pre-typhoon oceanic conditions. As a fast-moving storm, Chan-hom induced significant SSC on the right side of its track. Localized maximum cooling patches are found over a cyclonic eddy (CE). An analysis of data from Argo floats near the track of Chan-hom demonstrated that the mixed layer temperature (MLT) and mixed layer depth (MLD) had more variabilities on the right side than those on the left side of Chan-hom's track, while mixed layer salinity (MLS) response was different from those of MLT and MLD with an increase in salinity to the right side and a decrease in salinity to the left side of the track. Subsequently, because of the remnant effect of Chan-hom, the strong upwelling induced by Typhoon Nangka, the pre-existing CE as well as a slow translation speed (<2ms−1) of the storm, the most significant SSC (~ 6°C) was observed over the CE region in the wake of the storm. Further, Nangka experienced a rapid weakening suggesting immediate negative feedback from the intensified SSC occurred in the CE region. After these two typhoons, the CE was enhanced and the sea surface height of eddy core was depressed by 10cm. It took more than one month for SSC to restore to its pre-typhoon conditions, with the anomalous geostrophic current advection playing an important role in the process. The enhancement of chlorophyll-a concentrations was also noticed at both the CE region and close to Chan-hom's track.