Ocean circulation plays a critical role in Earth’s climate system, influencing the distribution of heat, carbon, nutrients, and energy across the planet. To understand these complex processes, scientists need accurate measurements that directly reflect ocean dynamics. This is where instruments such as Lagrangian drifters and floats come into play. Lagrangian drifters are tracking devices that follow the movement of water masses on the ocean surface to collect data on surface current patterns, temperature, and other dynamics. They use GPS technology or other satellite systems to provide real-time position and environmental data. Since their introduction in the 1980s, drifters have become a key tool for understanding the interaction between wind and ocean surface currents, as well as the transport of pollutants or organic matter in the ocean. Floats, on the other hand, are instruments designed to move vertically through the water column, collecting vital information on temperature, salinity, and pressure. One of their greatest innovations is the Argo program, a global network of thousands of automated floats that provide consistent, high-quality oceanographic data. Floats have revolutionized our understanding of deep-sea temperature variability, the ocean’s role in absorbing heat, and the relationship between the ocean and the atmosphere. Both drifters and floats use Lagrangian motion, which means that these instruments move with the water mass. This approach differs from the Eulerian method, which observes currents from a fixed point such as a buoy station. By using the Lagrangian method, scientists can directly follow the path of the water’s movement, providing deeper insights into ocean dynamics, especially at time and space scales that are difficult to reach with other methods. Throughout this article, we will explore how these instruments have helped shape modern research in the field of ocean circulation, as well as their potential to expand our insight into the ocean in the context of climate change and sustainability.
Lagrangian drifters and floats are advanced oceanographic instruments designed to study ocean dynamics using a water mass motion-based approach. Drifters are tracking devices that follow ocean currents at the surface. They typically consist of a buoy floating on the ocean surface, equipped with a Global Positioning System (GPS) or satellite tracking device, and sensors to measure environmental parameters such as sea surface temperature, salinity, and current speed and direction. Drifters are often designed with a submerged section below the surface to minimize the influence of wind and waves and thus more accurately represent the motion of water masses. They are widely used to study ocean current patterns, sediment transport, contaminant distribution, and other processes in the surface layer of the ocean. Floats, on the other hand, are instruments that move vertically in the water column, allowing data to be collected at different depths in the ocean. Modern floats, such as those used in the Argo program, are equipped with pumps that regulate their density and buoyancy, allowing them to rise and fall automatically in the water column. In its operational cycle, the float typically spends time at a certain depth (e.g., 1,000 meters) and then rises to the surface to transmit the collected data to a satellite. These floats measure parameters such as temperature, salinity, and pressure at various depths, which are important for understanding the stratification of water masses, the movement of deep ocean currents, and the physical processes that influence global climate. The main advantage of these two tools is their ability to provide real-time data with very large geographic coverage. Their Lagrangian method – which directly follows the movement of water – opens new perspectives in understanding ocean dynamics compared to traditional methods that only observe currents from fixed points. The combination of drifters and floats allows not only surface monitoring but also exploration of deeper ocean conditions, making it an invaluable tool for a wide range of applications, from scientific research to mitigating the effects of climate change.
The following is an explanation of the main components or parts of Lagrangian drifters and floats, along with their functions:
A.) Lagrangian Drifters
Drifters are designed to passively track sea surface currents by following the motion of the water mass. The main components include:
- Main Buoy; The part that floats on the ocean surface. It is generally equipped with electronics for communication and measurement, and is covered with materials that are resistant to marine environments such as UV, saltwater, and waves.
- Environmental Sensors; Measure parameters such as sea surface temperature (SST), salinity, atmospheric pressure and other environmental data. These sensors are important for providing oceanographic data used in climate and ocean current models
- Drogue (Sea Anchor); A structure designed to stabilize a drifter and ensure that it follows the motion of the current, rather than the wind or waves. The drogue is usually made of durable fabric and is connected to the buoy via a rope or cable.
- GPS or Satellite Tracker Unit; Provides real-time position data so that the drifter’s movements can be tracked with high accuracy. These systems often use satellites such as Argos or Iridium.
- Battery; The main power source for electronic devices. Batteries are usually lithium-based with high endurance to ensure operation for months to years.
- Antenna; Used for communication with satellites, enabling the transmission of data and location.
B.) Floats
Floats are more complex instruments as they are capable of moving vertically within the water column. Its main components include:
- Main Buoy; The part that provides buoyancy, often cylindrical to minimize water resistance. Made of lightweight, pressure-resistant materials, such as titanium or composite plastic.
- Buoyancy Pump; A mechanism that controls changes in the volume of water entering or leaving the float’s internal reservoir, allowing it to rise or fall in the water column.
- Profile Sensors; Includes sensors to measure temperature, salinity, pressure and dissolved oxygen. Some advanced floats are also equipped with biogeochemical sensors to measure chlorophyll, pH, or carbon dioxide.
- Satellite Communication Unit; Allows the float to transmit data to the processing center via satellite, such as Argos or Iridium.
- Battery and Energy System; Typically uses lithium batteries that are designed to withstand the high pressures of the ocean depths and have an operational life of several years.
- Pressure Resistant Framework; Protects electronic and mechanical components from the extreme pressures of the deep, often made from materials such as titanium.
- Antenna; Located at the top of the float and only comes to the surface when the float is transmitting data.
How Lagrangian Drifters and Floats Work
A.) Lagrangian Drifters
- Deployment; The Drifters are deployed into the ocean from a research vessel or aircraft. The deployment site is usually determined by the research area, such as major ocean currents, offshore waters, or areas with specific oceanographic phenomena.
- Floating on the surface; Once deployed, the drifter floats on the ocean surface, following the movement of surface currents. The drogue section (if any) ensures that the drifter is not affected by wind or waves, so that it moves only with the ocean currents.
- Data Collection; Sensors on the drifter begin to measure environmental parameters such as sea surface temperature, salinity, air pressure, or waves. Data is collected continuously or at specified intervals, depending on the settings.
- Data Transmission; Position information (from GPS) and measurement data are transmitted via satellite (such as Argos or Iridium) to a data center. This data is then analyzed to understand the dynamics of surface currents.
- Passive and automatic; Once released, the drifter continues to move with the ocean’s surface currents without human intervention.
B.) Floats
- Deployment; The float is released from the research vessel into the ocean at a predetermined location. It will automatically sink to a certain depth (usually around 1,000 meters).
- Drifting at depth; The float remains at a given depth for several days (typically 9-10 days), following the movement of deep ocean currents.
- Vertical profile; At the end of the drifting period, the float descends to a depth of about 2,000 meters and then slowly rises to the surface. During the ascent, the float measures parameters such as temperature, salinity, and pressure in different layers of water.
- Data Transmission; Upon reaching the surface, the float transmits the collected data via satellite to global data centers, such as the Argo Global Data Assembly Center.
- Cycle Repetition; Floats automatically repeat this cycle until battery power is exhausted, typically up to 4-5 years.
Lagrangian Drifters and Floats Advantages and Disadvantages
Lagrangian drifters and floats, though distinct in design and purpose, are often used together in oceanographic research to provide a comprehensive understanding of ocean circulation. Here’s a combined breakdown of their Advantages and Disadvantages
Advantages:
- Comprehensive ocean monitoring; Ideal for studying surface currents and dynamics, providing real-time data on ocean circulation and environmental conditions such as sea surface temperature and salinity. Best suited for subsurface profiling, providing detailed vertical profiles of ocean properties (temperature, salinity, pressure) from the surface down to 2,000 metres, making them critical for studying ocean stratification and vertical mixing. Together, they provide a complete view of both surface and subsurface ocean dynamics, allowing researchers to study the full range of ocean circulation patterns.
- Global coverage and scalability; Floats are often deployed in large numbers, allowing for broad spatial coverage of ocean currents in different regions. Floats, particularly those in the Argo programme, provide global coverage with a network of over 3,000 floats operating worldwide. The global data from these instruments contribute to the understanding of large-scale ocean and climate systems, such as the El Niño phenomenon and the deep ocean circulation.
- Autonomous and long-term operation; Both instruments are designed to operate autonomously for long periods of time (typically up to a year for drifters and 4-5 years for floats) without the need for constant human intervention, making them ideal for long-term monitoring. Their low-maintenance design means they can operate in remote, hard-to-reach areas, such as the deep ocean, and continue to collect data without frequent retrieval.
- Cost-effective ocean data collection; Compared to traditional research methods, such as using large vessels, drifters and floats are more cost-effective for collecting large-scale, real-time ocean data. This makes them an attractive option for routine oceanographic surveys over long periods and large areas.
- Supporting climate change research; Both instruments are essential for studying the role of the ocean in global climate systems, providing critical data on heat storage, carbon sequestration and ocean circulation, all of which are affected by climate change. Their data support climate models and help scientists monitor ocean changes such as global warming, sea level rise and ocean acidification.
Disadvantages:
- Data transmission and gaps; They rely on satellite communications, which can be interrupted by technical problems, poor satellite coverage or environmental obstructions. Data transmission is periodic rather than continuous, leading to potential data gaps. Similarly, swimmers rely on satellite communication, which can sometimes be affected by weather conditions, satellite failure or coverage limitations. In remote areas, the lack of immediate communication can cause delays in data retrieval.
- Limited horizontal and vertical coverage; Drifters are primarily surface-based, tracking horizontal currents but not providing data below the surface. This means they cannot study deeper ocean processes such as vertical mixing or thermohaline circulation. Floats, while capable of collecting valuable data at depth, do not measure horizontal currents and are limited to vertical profiling at specific locations, thus lacking data on large-scale horizontal ocean motion or surface dynamics.
- Battery and lifetime limitations; Drifters generally have a short lifetime (months to a year) due to battery limitations, limiting their ability to provide continuous data over long periods of time. Floats, although designed for long term use (4-5 years), have a finite battery life and will eventually need to be retrieved or replaced at the end of their operational life.
- Susceptibility to environmental factors; Their movement can be affected by external factors such as strong winds, waves or storms, potentially causing them to deviate from their intended tracking path. This can reduce the accuracy of the data. Floats are subject to biofouling (accumulation of marine organisms on sensors), which can affect sensor readings over time and reduce the accuracy of measurements.
- Deployment costs and logistics; Floats, particularly those used in global oceanographic networks such as Argo, require careful planning and significant resources for deployment, including sensor costs, global tracking and maintenance. Drifters, while less expensive than floats, still require resources for deployment and ongoing monitoring. If not properly managed, they can be lost or fail to transmit useful data.
