CTD Data Research Articles

Antarctic Bottom Water Warming, Freshening, and Contraction in the Eastern Bellingshausen Basin

AbstractAntarctic Bottom Water has been warming in recent decades throughout most of the oceans and freshening in regions close to its Indian and Pacific sector sources. We assess warming rates on isobars in the eastern Pacific sector of the Southern Ocean using CTD data collected from shipboard surveys from the early 1990s through the late 2010s together with CTD data collected from Deep Argo floats deployed in the region in January 2023. We show cooling and freshening in the temperature‐salinity relation for water colder than ∼0.4°C. We further find a recent acceleration in the regional bottom water warming rate vertically averaged for pressures exceeding 3,700 dbar, with the 2017/18 to 2023/24 trend of 7.5 (±0.9) m°C yr−1 nearly triple the 1992/95 to 2023/24 trend of 2.8 (±0.2) m°C yr−1. The 0.2°C isotherm descent rate for these same time periods nearly quadruples from 7.8 to 28 m yr−1.

Underwater Acoustic Propagation using Monterey-Miami Parabolic Equation in Shallow Water Kayeli Bay Buru Distric

Indonesia's geographical position is an advantage compared to other countries, both in terms of geoeconomics, geopolitics and geostrategy. For this reason, it is necessary to develop and use acoustic methods to describe underwater features, carry out underwater communications or to measure oceanographic variables at sea. This research was intended to provide an analytical and visual graphical description with the aim that it can be used for various purposes both in the research, military and other marine fields, as well as to analyze the influence of sediment and different frequencies on acoustic propagation patterns in shallow waters of Kayeli Bay. This research was conducted using CTD data from Kayeli Bay, which is a body of water in Buru Regency, Maluku Province and is located between 3° 15' 55'' – 3° 22' 50" S and 127° 01'35" – 127° 01' 35 "E, using the Monterey-Miami parabolic equation method using 4 types of sediment and 3 different frequencies as model input. From the results of this research it can be concluded that the propagation of sound waves in shallow seas is greatly influenced by the type of sediment and frequenty used. Changes in acoustic impedance at the bottom of the water and within the water column can significantly influence the behavior of acoustic waves in shallow water environments, and accurate acoustic impedance data are critical for effective ray tracing modelling.

Vertical Mixing in The Onshore Region of The Northwestern Maluku Sea, Indonesia

Spatio-temporal dynamics of vertical mixing in the northwestern Maluku Sea were quantified using the Thorpe Method from archived CTD datasets collected during the expedition of Baruna Jaya VIII RCO-LIPI on November 12–13, 2000. The turbulent kinetic energy (TKE) dissipation rate and vertical eddy diffusivity values inspected the variability of mixing properties. Higher values for both parameters were found at the shallower bathymetry, which is less than 1000 m deep. This suggests that the water column is vertically unstable as a result of being often subjected to internal solitary wave (ISW) breaking events. The strong temporal variability observed from the density profile also indicated a strong impact on internal tide activity. There was temporal fluctuation of the TKE dissipation rate as well as vertical eddy diffusivity values following semidiurnal periodicity, with typical variability up to one order of magnitude for both the dissipation and diffusivity. The range of fluctuation is [6.8×10-8 ? 9.3×10-7] W kg-1 and [1.5×10-5 – 5.4×10-3] m2s-1, respectively in the upper 200 m depth. This water generated a high dissipation rate and vertical diffusivity when regularly exposed to internal solitary waves breaking from the Lifamatola Passage.Keywords: mixing properties, CTD data, turbulent kinetic energy, vertical eddy diffusivity

Multiple island effects shape oceanographic processes and zooplankton size spectra off an oceanic archipelago in the Tropical Atlantic

Pelagic ecosystems around tropical oceanic islands are considered oases of high plankton biomass in the middle of oligotrophic “blue deserts”. To understand the dynamics of such a pelagic ecosystem, we used CTD and ADCP data and zooplankton samples taken from the waters off the remote Fernando de Noronha Archipelago (FNA), Tropical Atlantic. We analyzed how the flow and island topography interactions influence the spatial variability of chlorophyll-a fluorescence and zooplankton abundance, biovolume, and normalized biovolume size spectra (NBSS). We used a 500-μm mesh bongo net to obtain plankton samples in July and August 2010 in areas upstream and downstream of FNA. Zooplankton samples were analyzed with a ZooScan device. Chlorophyll-a peaks and a rise in thermocline indicated a topographic uplift and turbulence downstream of the island, i.e., the “Island Mass Effect”. The NBSS presented a mean slope of −1.19 ± 0.28, and a mean intercept of 3.98 ± 0.87. There were no significant differences in NBSS slopes and intercepts between upstream and downstream areas. Nevertheless, zooplankton and decapod community structures were significantly different between areas: meroplanktonic communities showed higher abundances and biovolumes downstream (p < 0.05). Zoeae of stenopodid cleaner shrimps, anomuran and brachyuran crabs, and fish eggs were significantly more abundant downstream, indicating a “Larval Island Effect”. Distinct peaks in size spectra due to teleost eggs and decapod larvae, downstream of FNA, also indicated a Larval Island Effect. Upstream of the island, there was a higher abundance of gelatinous organisms, holoplanktonic decapods, and advanced stages of brachyuran crabs (“Upstream Island Effect”). Also, copepods, gelatinous organisms, large-sized “other crustaceans” (e.g., euphausiids, amphipods, stomatopod larvae, mysids, etc.), teleost eggs, and stenopodids caused abundance peaks in the size spectra upstream. Our study highlights the need for careful management and conservation of parental spawning stocks of fishes and macroinvertebrates surrounding tropical oceanic islands.

A study on the prediction model of water column sound absorption coefficients considering the characteristics of the East Sea of South Korea

East Sea of Korea has the deepest water depth among Korean seas, and the water column changes are distinct in space and time, resulting in a wide range of water column sound absorption coefficients. In this study, we calculate and analysis the spatiotemporal variation of water column sound absorption coefficient in the East Sea of Korea, which has unique oceanographic characteristics. Using extensive CTD data from the Korea Oceanographic Data Centre (KODC) from 1991 to 2021, we calculate the sound absorption coefficient using the widely applied Francois–Garrison model and reveal the unique absorption characteristics of the East Sea. The derived coefficients are then used to calibrate and improve past multibeam echosounder system (MBES) data, which suffered from incomplete water column information and arbitrary mean values. To facilitate the calculation and development of sound absorption coefficient, a MATLAB-based graphical user interface (GUI) was developed. The results of this study contribute to the calculation and inference of sound absorption coefficients along spatial and temporal dimensions of the water column in the East Sea and to the extraction of more accurate seafloor information from MBES data. This study developed the way for future research focusing on algorithmic advances and new methodologies for the calculation of sound absorption coefficients in the West and South Seas of Korea.

Identifying Probable Submarine Hydrothermal Spots in North Santorini Caldera Using the Generalized Moments Method

The presence of active hydrothermal vent fields near residential areas and their possible link to volcanic activity poses a potential hazard to the environment, society, and the economy. By capitalizing on Autonomous Underwater Vehicle sampling methodologies and applying the Generalized Moments Method model for geological and physical processes in these environments, we shed light on the underlying dynamics shaping the physicochemical characteristics of the vents. In this study, we focus on the Northern Caldera of Santorini and, more specifically, on the recorded CTD data (Conductivity, Temperature, Depth). The data sets were collected in 2017 in Santorini using an Autonomous Underwater Vehicle during the GEOMAR POS510 mission. Our research shows that the active vent field within the caldera probably follows a multifractal behavior and exhibits a weak memory effect. Depth Profiles and Time Series show similar behavior among conductivity and temperature. The variance and moments of both parameters underline the existence of two different mechanisms governing the behavior of the vent field. Finally, the structure function shows that changes in the time series are described by a Cauchy–Lorentz distribution.

Analysis of glider motion effect on the performance of pumped CTD: Implications for vehicle operation and data processing

With the expanding use of underwater gliders in marine observations, the quality of CTD data obtained by gliders has been of great concern over the past decades. However, current studies mainly focus on data correction methods and data quality control procedures, leaving some ambiguity regarding the influence of platform motion on the measurements of CTDs, especially for the pumped CTDs. In this study, we identified the effect of glider motion on CTD data obtained by the GPCTD through theoretical analysis and simulations, which was then validated by a field experiment. According to the results, it is recommended for underwater gliders to keep a slower platform speed and a relatively gentle operational attitude during observations. The new findings in this study are not only constructive for fine control of underwater gliders seeking to obtain high-quality CTD measurements, but also provide valuable guidance for the subsequent data processing.

СТРУКТУРА ВОД МОРЕЙ ДЕЙВИСА И МОУСОНА ПО ДАННЫМ ОКЕАНОГРАФИЧЕСКИХ ИССЛЕДОВАНИЙ, ВЫПОЛНЕННЫХ В ХОДЕ 67-й РАЭ

We present the results of oceanographic studies from 64 stations occupied on the slope and shelf in the Davis Sea and the Mawson Sea during the 67th Russian Antarctic Expedition (RAE) from the R/V “Akademik Fedorov” in January–February 2022. The analysis of unique highprecision CTD data and hydrochemical indicators, together with a comparison with the results of previous studies, allowed us to obtain valuable information about the interannual variability of thermohaline characteristics of Antarctic shelf water on the shelf in the central part of the Davis Sea, to determine the structure of water masses on the slope and shelf in the western part of the Davis Sea and the eastern part of the Mawson Sea. Cascading and dense Antarctic shelf water not been recorded during the research. The thermohaline characteristics of Antarctic shelf water recorded in the central part of the Davis Sea in 2001, 2017, 2021 and dense Antarctic shelf water presence in the basins in February 2022 suggest the participation of Davis Sea shelf water in the ventilation of deep waters and suggest an irregular nature of the source of Antarctic bottom waters in the Davis Sea.

An initial ecological characterization of mesopelagic fauna at Johnston Atoll and Musicians Seamounts

The mesopelagic region (200–1000 m) hosts a wide variety of organisms in a concentrated layer known as the deep scattering layer (DSL). Much of the mesopelagic region in the central North Pacific remains unexplored, limiting ecosystem considerations in fisheries management and other applications. The National Oceanic and Atmospheric Administration (NOAA) Office of Ocean Exploration and Research used NOAA Ship Okeanos Explorer to conduct two expeditions in the region, one to Johnston Atoll and the other to Musicians Seamounts. During these expeditions, a remotely operated vehicle collected video and CTD environmental data while the ship collected active acoustics. This project analyzed the video, CTD, and acoustic data to create an ecological characterization of the mesopelagic at Johnston Atoll and Musicians Seamounts. The initial characterization included a full inventory of mesopelagic fauna imaged, the relationship between the abundance of categorical groups (gelatinous, Chaetognatha, Crustacea, and fish) and the environmental variables of salinity, oxygen, and temperature, a comparison between the abundance of mesopelagic fauna below, within, and above the DSL, and a qualitative analysis of the spatial distribution of categorical groups. There was a significant negative relationship between the abundance of the gelatinous organisms and salinity and oxygen concentrations. Overall, there were more sightings per minute of all organisms combined below and within the DSL than above the DSL at Musicians Seamounts, while there was no difference in sightings per minute between the below, within, and above DSL groups at Johnston Atoll. Proportionally, there were more gelatinous organisms than any other single category (fish, Chaetognatha, and Crustacea) at all dive sites in the study. These initial characterizations strive to develop biodiversity concepts and the relationships between the environment and fauna. Progress in these areas can aid the management of marine national monuments and serve as a baseline for future ROV dives.

Karakteristik Fisik Perairan Selatan Kabupaten Kepulauan Tanimbar pada Musim Transisi II

This study investigated the characteristics of stratification and vertical stability of southern waters of Tanimbar Islands Regency. CTD Data from World Ocean Database 2018 especially November 1995 to represent second transitional season were utilized in this study. The CTD data were processed using Ocean Data View. This study showed that vertically the temperature of the surface layer ranged between 29 to 30 oC and the thickness of surface mixed layer was found to be 44 m. The thermocline layer has temperature ranging between 12 to 28 oC and a maximum depth of 306 m. Below thermocline layer temperature reduced to reach less than 7 oC (depth &gt; 500 m). On the halocline layer, a high saline water was found between 66 - 94 m depth and was located on the southern part between Barbar Islands and Tanimbar Islands. Water mass was found to be unstable in the mixing layer.

Estimation of Seawater Hydrophysical Characteristics from Thermistor Strings and CTD Data in the Sea of Japan Shelf Zone

The knowledge of salinity in a specific sea area with high accuracy is required to solve several acoustic and hydrophysical problems on the ocean shelf. Unlike temperature, which can be measured continuously for a long time, with, for example, thermistor strings (thermostrings), salinity values of required accuracy can be obtained only using CTD profiling. This is why methods of estimating salinity from temperature could be helpful. In this paper, the authors propose using the regression method for solving this type of problem and demonstrate the efficiency of this method using examples of temperature measurements from anchored thermostrings. For the correct construction of regressions, the authors analyzed the errors of CTD measurements and suggested a method for the dynamic correction of raw CTD data. From CTD profiling datasets of 12 years (2011–2022), after their dynamic correction, the authors obtained regression polynomial formulas for calculating salinity from temperature and studied data stability in space and time at the hydrophysical test site, located in the shelf zone of the Sea of Japan. The authors consider this method efficient and applicable in solving a variety of acoustic and hydrophysical problems.

АНАЛИЗ T, S-АНСАМБЛЕЙ АТЛАНТИЧЕСКОЙ ВОДНОЙ МАССЫ ЕВРАЗИЙСКОГО БАССЕЙНА АРКТИКИ С ПОМОЩЬЮ КЛАСТЕРНОГО МЕТОДА

Cluster analysis was performed using CTD data from transects across continental slope of the Eurasian Basin collected within the NABOS (Nansen and Amundsen Basins Observing System) project in 2002–2015. The most commonly used k-means clustering method was applied for calculations. Two cases were considered: division into two and three clusters. The identified clusters which united points on the θ, S-diagrams (θ, S are potential temperature and salinity, respectively) satisfactorily corresponded to the θ, S-values of the Fram and Barents branches of the Atlantic water. For each cluster the thermohaline characteristics of centroids (cluster centers) were calculated, that is, the average values at the same time of temperature, salinity and potential density of each water mass. The thermohaline characteristics of centroids, estimated from the available data obtained in different years of observation, were presented in θ, S-coordinates and θ, σ-coordinates (σ is potential density). Additionally, dependences of temperature, salinity, and potential density of centroids on the year of observation were analyzed. The final results made it possible to obtain estimates of the average thermohaline characteristics of Atlantic water in different years of observation and the variability of these estimates from year to year. In particular, it was found that the values of the average thermohaline characteristics of the AW indicated a strong warming and salinization of the AW in 2006–2009 (sections along 126° E), and the response to warming was observed in all AW clusters. An interpretation of the obtained results was given. Approaches to the choice of the most optimal method of cluster analysis were considered. The results of estimating the influence of temperature and salinity variability ranges in the analyzed CTD data on the accuracy of centroids evaluations were presented.

Mooring Service Cruise (MSC) 2022

The main objective of the cruise was to retrieve and deploy ocean moorings in the north-western Barents Sea and on the continental slope north of Kvitøya for the Nansen Legacy and A-TWAIN projects. A secondary objective was to perform hydrographic surveys in regions of Atlantic Water inflow and other regions of interest. In addition, the cruise aided other research groups by deployment and recovery of minor equipment at sites along the cruise trajectory.&#x0D; In general, mooring operations were conducted during day hours, while nights were used to collect CTD data along various transects. Mooring work was completed quickly, efficiently, and ahead of schedule. This left ample time for additional pre-planned hydrographic surveys after the mooring work was complete.&#x0D; The cruise departed from Longyearbyen in the afternoon on 02.10.2022. An IMR ARGO float was deployed north of Spitsbergen the day after. On the following day, the ship operated for three days in the area around the A-TWAIN mooring array on the continental slope north of Kvitøya. Here, four moorings were recovered, and four were deployed, and hydrographic transects (CTDs) were conducted across the Atlantic Water inflow current and across northern Kvitøya Trough.&#x0D; After transiting south from the A-TWAIN area on the evening of 06.10.2022, another transect was conducted at night across the southern outlet of Kvitøya Trough. Mooring work began the following morning at the Nansen Legacy M1 location in the north-western Barents Sea. Two moorings were recovered and redeployed. Afterwards, a cross-slope transect was conducted intersecting the M1 mooring location. In the following days, consecutive transects were conducted into the through extending from M1 to Hartogbukta, along the Storisstraumen glacier front, from Storisstraumen southeast across the ocean basin, and along the bathymetric saddle west of Kong Karls Land.&#x0D; During the transit back north and west, an additional brief transect was conducted outward from Wahlenbergfjorden into the Hinlopen Trough, to obtain data from a fjord with tidewater glaciers that are likely not influenced by Atlantic Water. On 10.10.2022 an NPI radio transmitter was retrieved from the island of Moffen by small boat. The ship then transited back to Longyearbyen, arriving in port on the evening of 11.10.2022.&#x0D; Overall, the cruise was highly successful. All planned operations were completed in good time, allowing room for extensive hydrographic surveying as well as two minor deployment and recovery operations for other research groups. The success was in part due to fair weather during the first five days of the cruise and completely sea ice-free seas throughout. This allowed mooring work to take place in favourable conditions in an area where operations are often hampered by wind, swell, and sea ice. However, we would also like to highlight the competence and professionalism of the crew of the Kronprins Haakon as a key factor in the success of the cruise. Cooperation and communication with crewmembers on deck and on the bridge were excellent throughout. In addition, the cruise participants efficiently completed all the planned objectives despite the small size of the team (7 team members).

Fine Structure of Vertical Density Distribution in the Black Sea and Its Relationship with Vertical Turbulent Exchange

This paper is concerned with the analysis of the long-term regular time series of current velocity and conductivity, temperature, and depth (CTD) profiles, measured with the moored autonomous profiler Aqualog over the upper part of the continental slope at a fixed geographical location in the Northeastern Black Sea. This study focuses on the fine structure of the density profiles to show that the fine-structure Cox number (C) is a power function of the Richardson number (Ri). A similar inverse power relationship with the same exponent was found earlier for the coefficient of vertical turbulent mass exchange (Kρ) and Ri. Based on those results, the analysis indicated a statistically significant correlation between C and Kρ, which suggests that the estimations of Kρ could be conducted from the CTD data only.

Extreme Upwelling Events in the Seas of the Alor Kecil, Alor Island, Indonesia

Upwelling is a process by which deep, colder, higher-nutrient waters are brought to the sea surface. In the tropics, an indicator that an upwelling event has occurred is lowering of sea surface temperatures (SSTs) to 25°–27°C from a mean of ~28°C. Based on more than one year of in situ data, we observed an unusual extreme upwelling event (EUE) when the near-surface temperature (NST) dropped by 10°C within one hour during the spring tide in Mulut Kumbang Strait of Alor Kecil. The extreme minimum NST during this EUE was ~12°C, and the upward displacement speed of the cold water was ~0.012 m s–1. The increase in salinity from ~30‰ to 34‰–36 ‰ during the decrease in NST indicates a deep source for the cold water mass . From bathymetry and CTD data, the source of the cold water mass was a deep basin (&gt;300 m) located at the southern part of Pantar Strait. In this basin, the temperature at 270 m depth can be as low as 8°C. We suggest that tidal sloshing (i.e., the back-and-forth movement of water) brings the cold water mass through a channel that connects this deep basin to Mulut Kumbang Strait. Interactions between semi-diurnal (M2, S2, and N2) tidal components strongly modulate the tidal signal with a period of nearly one month. That EUEs only occur from August to November also suggests a strong monsoonal influence. Because tides are predictable, we suggest that future EUEs are predictable.

On the Consistency of the Bottle and CTD Profile Data

Abstract Nansen bottle casts served as the main oceanographic instrumentation type for more than a century since the establishing of the technique in the late 1890s. Between the end of the 1960s and the end of the 1990s Nansen cast technique has been gradually replaced by electronic sensor profilers (CTD). Both instrumentation types are considered as the most accurate among other oceanographic instruments and are often used as the unbiased reference. We conducted a comprehensive investigation of the consistency of the temperature data from Nansen casts and CTD profilers analyzing the quasi-collocated bottle and CTD data between the 1960s and the 1990s when both instrumentation types overlap. We found that Nansen casts tend to overestimate the sample depth with reversing mercury-in-glass thermometer temperatures being on average slightly lower compared to CTD data. Respectively, depth and temperature corrections are provided. Further, we estimated the ocean heat content changes between 1955 and 1990 using (along with all other instrumentation types) corrected and uncorrected Nansen cast data. These calculations show that for the upper 2 km layer the global average warming trend for this time period increases from 0.20 ± 0.05 W m−2 for the uncorrected data to 0.28 ± 0.06 W m−2 for the corrected data at the 90% confidence level. Finally, we suggest that the Nansen bottle cast profiles be put into a separate instrumentation group within the World Ocean Database.

Efficient Underwater Sensor Data Recovery Method for Real-Time Communication Subsurface Mooring System

Marine submerged buoys can effectively obtain various parameters of seawater, which plays an important role in the research of marine physical phenomena, marine environmental changes, and climate change. However, traditional self-contained submerged buoys usually work underwater at a depth of about 100 m, and the observation data cannot be obtained before their recovery, which cannot satisfy the needs of real-time data acquisition for marine scientific research. To solve this problem, this paper proposes a real-time communication subsurface mooring system that consists of a satellite communication buoy (SCB), conductivity–temperature–depth sensors (CTD), and an inductive coupling mooring cable. The underwater inductive coupling link collects the data from the underwater sensors and transmit it to the SCB. Then, the data will be transmitted to the station receiver via satellite communication module integrated into the SCB. In order to ensure a high success rate of data recovery, the stress analysis and hydrodynamic simulation of the SCB were carried out in this paper. The results show that the SCB maintained a relatively stable attitude in the 3–4 sea state. The attitude data obtained from the subsequent sea trial was consistent with the simulation results, and the success rate of satellite communication during this period was more than 95%. In this paper, a modular embedded hardware circuit was designed to meet the functional requirements of the subsurface mooring system. An efficient data recovery strategy was also developed, which ensured that the average power consumption of the system was low and the success rate of data recovery is not less than 90% when operating in the severe sea state for a long time. The system underwent sea trials in the South China Sea for more than 3 months from the end of 2021 to the beginning of 2022. It transmitted more than 2034 sets of seawater profile temperature, salinity, and depth data in real-time, with a success rate of over 91% of the total sample data. The CTD data returned in real-time from our system is consistent with the data of the HYCOM and World Ocean Atlas (WOA), and a cyclonic mesoscale eddy was detected in the operation area.

Estimating the Ocean Interior from Satellite Observations in the Kerguelen Area (Southern Ocean): A Combined Investigation Using High-Resolution CTD Data from Animal-Borne Instruments

Abstract Observational surface data are utilized to reconstruct the subsurface density and geostrophic velocity fields via the “interior + surface quasigeostrophic” (isQG) method in a subdomain of the Antarctic Circumpolar Current (ACC). The input variables include the satellite-derived sea surface height (SSH), satellite-derived sea surface temperature (SST), satellite-derived or Argo-based sea surface salinity (SSS), and a monthly estimate of the stratification. The density reconstruction is assessed against a newly released high-resolution in situ dataset that is collected by a southern elephant seal. The results show that the observed mesoscale structures are reasonably reconstructed. In the Argo-SSS-based experiment, pattern correlations between the reconstructed and observed density mostly exceed 0.8 in the upper 300 m. Uncertainties in the SSS products notably influence the isQG performance, and the Argo-SSS-based experiment yields better density reconstruction than the satellite-SSS-based one. Through the two-dimensional (2D) omega equation, we further employ the isQG reconstructions to diagnose the upper-ocean vertical velocities (denoted wisQG2D), which are then compared against the seal-data-based 2D diagnosis of wseal. Notable discrepancies are found between wisQG2D and wseal, primarily because the density reconstruction does not capture the seal-observed smaller-scale signals. Within several subtransects, the Argo-SSS-based wisQG2D reasonably reproduce the spatial structures of wseal, but present smaller magnitude. We also apply the isQG reconstructions to the 3D omega equation, and the 3D diagnosis of wisQG3D is very different from wisQG2D, indicating the limitations of the 2D diagnostic equation. With reduced uncertainties in satellite-derived products in the future, we expect the isQG framework to achieve better subsurface estimations.

Chasing the offshore wind farm wind-wake-induced upwelling/downwelling dipole

The operational principle of offshore wind farms (OWF) is to extract kinetic energy from the atmosphere and convert it into electricity. Consequently, a region of reduced wind speed in the shadow zone of an OWF, the so-called wind-wake, is generated. As there is a horizontal wind speed deficit between the wind-wake and the undisturbed neighboring regions, the locally reduced surface stress results in an adjusted Ekman transport. Subsequently, the creation of a dipole pattern in sea surface elevation induces corresponding anomalies in the vertical water velocities. The dynamics of these OWF wind-wake induced upwelling/downwelling dipoles have been analyzed in earlier model studies, and strong impacts on stratified pelagic ecosystems have been predicted. Here we provide for the first time empirical evidence of the existence of such upwelling/downwelling dipoles. The data were obtained by towing a remotely operated vehicle (TRIAXUS ROTV) through leeward regions of operational OWFs in the summer stratified North Sea. The undulating TRIAXUS transects provided high-resolution CTD data which enabled the characterization of three different phases of the ephemeral life cycle of a wind-wake-induced upwelling/downwelling dipole: development, operation, and erosion. We identified two characteristic hydrographic signatures of OWF-induced dipoles: distinct changes in mixed layer depth and potential energy anomaly over a distance &amp;lt; 5 km and a diagonal excursion of the thermocline of ~10–14 m over a dipole dimension of ~10–12 km. Whether these anthropogenically induced abrupt changes are significantly different from the corridor of natural variability awaits further investigations.

TEMPERATURE AND SALINITY CHARACTERISTICS IN THE SOUTHERN SOUTH CHINA SEA AND STRAIT OF MALACCA

Temperature and salinity characteristics in the southern South China Sea and Strait of Malacca are investigated using CTD data and the global ocean model HYCOM. CTD data were obtained from cruises taken in March 2015, March 2019, and July-August 2019. The results showed that the average reading of temperature and salinity in the Strait of Malacca during March 2015 was 28.60±0.708 °C and 32.61±1.01 psu, respectively. The average readings during March 2019 were 29.31±1.593 °C and 32.38±0.884 psu, respectively. The average temperature and salinity in the Strait of Malacca during the August 2019 cruise were 29.63±0.701 °C and 32.52±0.553 psu, respectively. Meanwhile, in the southern South China Sea, the average readings in July 2019 were 28.98±0.310 °C and 33.07±0.126 psu and in August 2019 were 27.94±1.01 °C and 33.36±0.363 psu. Seasonal variations presented by the 15-years (1997-2012) HYCOM climatological model show that the sea surface temperature is warmer by approximately 1 - 2 °C during the southwest monsoon months (June-July-August) than during the northeast monsoon (December-January-February) in the southern South China Sea. The seasonal temperature variations in the Strait of Malacca are not significant except for the southern part. The sea surface salinity exhibits no clear seasonal cycle except for the coastal areas.