Salinity refers to the saltiness or the amount of salt dissolved in a body of water, specifically saline water. It is typically measured in grams per liter (g/L) or grams per kilogram (g/kg) of water. This measurement helps quantify how much dissolved salt is present in water, which is crucial for understanding aquatic environments.

How is salinity typically measured in terms of units?

Salinity is commonly measured in grams per liter (g/L) or grams per kilogram (g/kg) of water. The latter unit is dimensionless and equivalent to parts per thousand (‰). These units provide a standardized way to express the concentration of dissolved salts in water.

Why is salinity considered an important factor in the chemistry and biology of natural waters?

Salinity is a crucial factor because it significantly influences the chemical properties of natural waters and affects biological processes within them. It also acts as a thermodynamic state variable, alongside temperature and pressure, that governs physical characteristics like water density and heat capacity. Understanding these influences is vital for comprehending phenomena such as ocean currents and heat exchange between water bodies and the atmosphere.

What is a contour line of constant salinity called?

A contour line representing constant salinity is known as an isohaline, or sometimes an iso-hale. Similar to contour lines on a map showing constant elevation, isohalines visually represent areas of equal salt concentration in water.

What are the conceptual and technical challenges in defining salinity?

Conceptually, salinity is the quantity of dissolved salt content. However, technically, it is challenging to define and measure precisely because natural waters contain a complex mixture of dissolved substances, not all of which are simple salts, and their chemical forms can change with temperature and pressure. This complexity means that precise measurement requires careful consideration of various factors and standardized methods.

What types of compounds are considered salts in the context of water salinity?

In the context of water salinity, salts are compounds like sodium chloride, magnesium sulfate, potassium nitrate, and sodium bicarbonate, which dissolve into ions in water. These dissolved salts are the primary contributors to the salty taste and chemical properties associated with saline water.

Chlorinity is a measure that refers to the concentration of dissolved chloride ions in water. Historically, it was sometimes used as a proxy for total salinity. While related to salinity, chlorinity specifically measures only one type of ion, whereas salinity encompasses all dissolved salts.

How is dissolved matter operationally defined for salinity measurement?

Operationally, dissolved matter is defined as that which can pass through a very fine filter, historically with a pore size of 0.45 micrometers, though more recently often 0.2 micrometers. This filtration method provides a consistent way to separate dissolved substances from suspended particles in water samples.

What is the typical mass salinity of seawater?

Seawater typically has a mass salinity of around 35 grams per kilogram (g/kg). This value is a widely recognized average for the salt content in the world's oceans.

How does salinity typically vary near coasts where rivers enter the ocean?

Salinity values are typically lower near coasts where rivers enter the ocean, due to the influx of freshwater diluting the saltwater. This mixing zone creates a gradient of salinity from the freshwater source to the open ocean.

What is the typical range of salinities found in rivers and lakes?

Rivers and lakes can exhibit a wide range of salinities, generally from less than 0.01 g/kg to a few grams per kilogram. This variability highlights that freshwater bodies are not always completely devoid of dissolved salts.

What is the salinity of the Dead Sea?

The Dead Sea has a very high salinity, exceeding 200 grams per kilogram (g/kg). Its extreme saltiness makes it significantly denser than typical seawater and supports unique life forms.

What is the typical Total Dissolved Solids (TDS) concentration in precipitation?

Precipitation, such as rain or snow, typically has a Total Dissolved Solids (TDS) concentration of 20 milligrams per liter (mg/kg) or less. This indicates that precipitation is generally very low in dissolved substances compared to other water bodies.

Why is precision in salinity measurements important for physical oceanographers?

Precision in salinity measurements is crucial for physical oceanographers, especially those working in the abyssal ocean, to ensure the intercomparability of data collected by different researchers at different times. Accurate and consistent data is essential for understanding complex oceanographic processes and global climate patterns.

What is used by oceanographers to standardize their salinity measurements for high precision?

Oceanographers use a bottled seawater product known as IAPSO Standard Seawater to standardize their measurements, ensuring the necessary precision for their research. This standard reference material allows for calibration and comparison of salinity data across different studies and instruments.

What are the major ions usually considered when calculating solution salinity in natural waters?

For many purposes, the calculation of solution salinity in natural waters is limited to a set of eight major ions. These major ions are the most abundant dissolved chemical species and significantly contribute to the overall salt content.

Are dissolved gases like oxygen and nitrogen typically included in descriptions of salinity?

No, the concentrations of dissolved gases like oxygen and nitrogen are not usually included when describing salinity. Salinity primarily focuses on dissolved salts and ions, not dissolved atmospheric gases.

How was seawater salinity primarily measured before the 1980s?

Before the 1980s, seawater salinity was primarily measured using titration-based techniques. These chemical analysis methods were the standard for determining salt concentrations in water for many decades.

What does the suffix "psu" or "PSU" denote, and what is its formal status?

The suffix "psu" or "PSU" denotes practical salinity unit and is sometimes added to measurement values from the PSS-78 scale. However, its addition as a unit is formally incorrect and strongly discouraged. This indicates a nuance in scientific notation where "psu" is often used for convenience but lacks formal unit status.

What new standard for seawater properties was introduced in 2010, and what did it advocate?

In 2010, the "thermodynamic equation of seawater 2010" (TEOS-10) was introduced, advocating for absolute salinity as a replacement for practical salinity and conservative temperature as a replacement for potential temperature. TEOS-10 represents a significant update in the scientific definition and calculation of seawater properties, aiming for greater accuracy and consistency.

How are absolute salinities on the TEOS-10 scale expressed?

Absolute salinities on the TEOS-10 scale are expressed as a mass fraction, measured in grams per kilogram of solution. This provides a more direct and physically meaningful measure of salinity compared to previous scales.

How has human-caused climate change affected ocean salinity since the 1950s?

Since the 1950s, human-caused climate change has contributed to observed changes in both surface and subsurface ocean salinity. This indicates a direct link between global warming and alterations in the salt content of the oceans.

What are the projections for surface salinity changes throughout the 21st century?

Projections for the 21st century indicate that ocean regions with lower salinity are expected to become even fresher, while regions with higher salinity will likely become saltier. This phenomenon, often referred to as "salinity contrast intensification," is a predicted consequence of ongoing climate change.

How does salinity distribution contribute to shaping oceanic circulation?

Salinity distribution is a key factor in shaping oceanic circulation by influencing water density. Variations in salinity, along with temperature, cause differences in buoyancy, which drive the sinking and rising of water masses. This process is fundamental to the large-scale movement of water throughout the world's oceans, often referred to as thermohaline circulation.

In what units do limnologists and chemists often define salinity for lakes and rivers?

Limnologists and chemists often define salinity in terms of the mass of salt per unit volume, typically expressed in milligrams per liter (mg/L) or grams per liter (g/L). This approach is practical for studying freshwater systems where concentrations are generally lower than in marine environments.

What is often used by limnologists as a proxy for salinity in lakes and rivers?

Limnologists frequently use electrical conductivity, sometimes referred to as "reference conductivity," as a proxy to estimate salinity in lakes and rivers. Electrical conductivity is a relatively easy and quick measurement that correlates well with the amount of dissolved ions in water.

What is the typical specific conductivity range for river or lake water with a salinity of 70 mg/L at 25°C?

River or lake water with a salinity of approximately 70 mg/L typically exhibits a specific conductivity between 80 and 130 µS/cm at 25°C. This provides a practical reference point for correlating conductivity measurements with salinity levels in freshwater environments.

What other physical measurement is sometimes used to estimate salinities, particularly in highly saline lakes?

Direct density measurements are sometimes used to estimate salinities, particularly in highly saline lakes where traditional methods might be less practical. The density of water is directly influenced by the amount of dissolved salts it contains.

What are "marine waters" also referred to as?

Marine waters, which are waters of the ocean, are also referred to as euhaline seas. This term specifically denotes the typical salinity range found in oceanic environments.

What is the typical salinity range for euhaline seas?

The salinity of euhaline seas typically ranges from 30 to 35 parts per thousand (‰). This is the standard salinity range associated with the open ocean.

What is the salinity range for brackish seas or waters?

Brackish seas or waters have salinities in the range of 0.5 to 29 parts per thousand (‰). Brackish water represents an intermediate salinity level, often found where freshwater rivers meet saltwater oceans.

What is the salinity range for metahaline seas?

Metahaline seas have salinities ranging from 36 to 40 parts per thousand (‰). This category represents waters that are slightly saltier than typical euhaline seas.

What does the term "homoiohaline" mean in the context of salinity?

In the context of water bodies, "homoiohaline" describes environments where the salinity does not vary significantly over time, remaining essentially constant. This implies a stable salinity condition, common in large, open bodies of water.

What is the defining characteristic of "poikilohaline" environments?

The defining characteristic of poikilohaline environments is that their salinity varies significantly over time, often on a seasonal basis, within a biologically meaningful range. These are bodies of water with fluctuating salt concentrations, which can pose challenges for the organisms living within them.

What is the term for highly saline water from which salts crystallize or are about to?

Highly saline water, from which salts are crystallizing or are on the verge of crystallizing, is referred to as brine. Brine represents the most concentrated form of saline water, often found in evaporating basins or specific geological formations.

Why is salinity considered an important ecological factor?

Salinity is an important ecological factor because it directly influences the types of organisms that can live in a body of water and affects the kinds of plants that can grow in or near water sources. This means that the salt concentration is a primary determinant of the biodiversity and vegetation found in aquatic and riparian ecosystems.

What is a plant adapted to saline conditions called?

A plant that is adapted to survive in saline conditions is known as a halophyte. Halophytes have specialized mechanisms to tolerate or thrive in environments with high salt concentrations.

What are organisms that can live in very salty conditions specifically classified as?

Organisms, primarily bacteria, that can survive in very salty conditions are specifically classified as halophiles. Halophiles are a type of extremophile organism adapted to high-salt environments.

What term describes an organism that can withstand a wide range of salinities?

An organism capable of tolerating a broad spectrum of salinity levels is described as euryhaline. Euryhaline species are adaptable to different aquatic environments, from freshwater to saltwater.

Why is salt content an important factor in water use, particularly for potability and irrigation?

Salt content is important for water use because it affects the water's potability (suitability for drinking) and its suitability for irrigation, as high salinity can harm crops and affect soil quality. Managing salinity is crucial for ensuring safe drinking water supplies and maintaining agricultural productivity.

What common substances have been observed to increase salinity in lakes and rivers in the United States?

Common road salt and other salt-based de-icers used in runoff have been observed to increase salinity levels in lakes and rivers in the United States. This highlights an environmental impact of winter road maintenance practices on freshwater ecosystems.

How does the degree of salinity in oceans drive the world's ocean circulation?

The degree of salinity in oceans drives circulation by influencing water density; changes in salinity, along with temperature, alter buoyancy, causing water masses to sink or rise. This density-driven movement is a fundamental mechanism of global ocean currents.

What is the relationship between changes in ocean salinity and carbon dioxide solubility?

Changes in ocean salinity are thought to contribute to global changes in carbon dioxide levels because more saline waters are less soluble to carbon dioxide. This suggests a feedback loop where ocean salinity affects the ocean's capacity to absorb atmospheric CO2.

What is a possible cause of reduced ocean circulation during glacial periods related to ocean stratification?

During glacial periods, the hydrography could lead to stratified oceans, making it more difficult for water to subduct through the thermohaline circulation, potentially causing reduced circulation. Ocean stratification refers to the layering of water masses with different densities, which can impede vertical mixing.

How have changes in ocean circulation affected salinity in the subpolar North Atlantic between 1990 and 2010?

Between 1990 and 2010, increased contributions of Greenland meltwater in the subpolar North Atlantic were counteracted by increased northward transport of salty Atlantic waters, influencing salinity levels. This illustrates the complex interplay between freshwater input, ocean currents, and salinity in a specific region.

What has caused North Atlantic waters to become fresher since the mid-2010s?

North Atlantic waters have become fresher since the mid-2010s primarily due to increased contributions of meltwater from Greenland. This indicates a recent shift in the factors influencing salinity in this region, likely linked to accelerated ice melt.

What are some related topics concerning the desalination of water?

Related topics concerning desalination include the desalination of water itself, soil salinity control, and the Sodium Adsorption Ratio (SAR). These topics are all concerned with managing or removing salt from water or soil.

What is a device used for measuring salinity?

A device used for measuring salinity is called a salinometer. Salinometers are instruments specifically designed to determine the salt concentration in water.

What are some biological contexts related to salinity in organisms, particularly human health?

Biological contexts related to salinity include electrolytes, fluid balance, hypernatremia, hyponatremia, and salt poisoning, particularly concerning human health. These terms relate to how salt balance within the body affects physiological functions and health.

What are the terms for fish that can tolerate different salinity ranges?

Fish that can tolerate only a narrow range of salinities are called stenohaline, while those that can tolerate a wide range are called euryhaline. This classification highlights the different physiological adaptations fish have developed for various aquatic environments.

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Definitions

Conceptual Understanding

Salinity refers to the measure of dissolved salts within a body of water, commonly termed saline water. It is typically quantified in grams per liter (g/L) or grams per kilogram (g/kg), with the latter serving as a dimensionless value equivalent to parts per thousand (‰). This parameter is fundamental to understanding the chemical properties of natural waters and influences biological processes within them. Furthermore, salinity acts as a thermodynamic state variable, which, alongside temperature and pressure, dictates crucial physical characteristics such as water density and heat capacity, thereby impacting ocean currents and atmospheric heat exchange.

Operational Measurement

While conceptually straightforward, the precise definition and measurement of salinity present technical challenges. Operationally, dissolved matter is defined as that which can pass through a fine filter, historically 0.45 μm, but more recently 0.2 μm. Salinity can be expressed as a mass fraction—the mass of dissolved material relative to the total mass of the solution. Seawater typically exhibits a mass salinity of approximately 35 g/kg, though values near coastal riverine inputs are often lower. Freshwater bodies display a wide range, from less than 0.01 g/kg to several g/kg, with exceptions like the Dead Sea exceeding 200 g/kg.

Precision in Oceanography

For physical oceanographers, particularly those studying the abyssal ocean, achieving high precision and inter-comparability in salinity measurements is paramount, often requiring accuracy to five significant digits. To meet these stringent requirements, oceanographers utilize standardized reference materials like the International Association for the Physical Sciences of the Oceans (IAPSO) standard seawater. This ensures consistency across different researchers and measurement periods.

Composition

Elemental and Molecular Forms

Natural waters contain a complex mixture of dissolved substances originating from various sources, not all of which are simple salts. These substances exist in different molecular and ionic forms, whose chemical properties can be influenced by temperature and pressure. Measuring these constituents with high accuracy and performing complete chemical analyses for every sample is often impractical.

Major and Minor Ions

For practical purposes, salinity is often related to the sum of masses of a specific subset of dissolved chemical constituents, referred to as 'solution salinity'. In most natural waters, the inorganic composition is dominated by eight major ions. For seawater analyses requiring the highest precision, seven minor ions are also included. While these ions constitute the bulk of dissolved matter, exceptions exist in certain environments like pit lakes or hydrothermal springs.

Gases and Other Dissolved Matter

Dissolved gases such as oxygen and nitrogen are typically not included in salinity calculations. However, carbon dioxide, which dissolves and partially converts into carbonates and bicarbonates, is often considered. Silicon, present as silicic acid, may also be included in salinity/density relationship studies, particularly within the typical pH range of natural waters.

Seawater Salinity

Historical Measurement Techniques

Historically, salinity in seawater was primarily determined using titration methods. Titration with silver nitrate allowed for the quantification of halide ions (chlorine and bromine), yielding a value known as chlorinity. This chlorinity value was then multiplied by a conversion factor to estimate the total salt content, resulting in 'Knudsen salinities' expressed in parts per thousand (ppt or ‰).

Practical Salinity Scale (PSS-78)

The advent of electrical conductivity measurements led to the development of the Practical Salinity Scale 1978 (PSS-78). This scale relates salinity to the electrical conductivity of seawater. Salinities measured using PSS-78 are technically dimensionless, though the suffix 'psu' or 'PSU' (practical salinity unit) is sometimes appended. However, the formal addition of 'PSU' as a unit is discouraged.

TEOS-10 Standard

Introduced in 2010, the International Thermodynamic Equation of Seawater 2010 (TEOS-10) represents a significant advancement. It advocates for 'Absolute Salinity' as a replacement for practical salinity and introduces 'Conservative Temperature'. Absolute salinity is expressed as a mass fraction (g/kg) and is determined by combining conductivity measurements with additional data that accounts for regional variations in seawater composition, or through direct density measurements. A typical seawater sample with a chlorinity of 19.37 ‰ corresponds to a Knudsen salinity of 35.00 ‰, a PSS-78 practical salinity of approximately 35.0, and a TEOS-10 absolute salinity of about 35.2 g/kg.

Lakes and Rivers

Freshwater Definitions

In limnology and chemistry, salinity is often defined by the mass of salt per unit volume, typically expressed in milligrams per liter (mg/L) or grams per liter (g/L). This value is generally accurate at a reference temperature, as solution volume varies with temperature. These measurements usually have an accuracy of about 1%.

Conductivity as a Proxy

Limnologists frequently employ electrical conductivity (EC) as a proxy for salinity, often referred to as 'reference conductivity'. This measurement can be corrected for temperature effects and is usually reported in units of μS/cm. A river or lake water with a salinity of approximately 70 mg/L typically exhibits a specific conductivity between 80 and 130 μS/cm at 25 °C, though the exact ratio depends on the specific ions present. Conductivity typically changes by about 2% per degree Celsius.

Density Measurements

Direct density measurements are also utilized to estimate salinities, particularly in highly saline lakes. Sometimes, density at a specific temperature serves as a salinity proxy. In other cases, empirical salinity/density relationships, developed for a particular water body, are applied to estimate salinity from measured density values.

Classification

Salinity Levels

Water bodies are classified based on their salinity content, with distinct categories reflecting the concentration of dissolved salts:

Water Salinity
Fresh Water	Brackish Water	Saline Water	Brine
< 0.05%	0.05 – 3%	3 – 5%	> 5%
< 0.5 ‰	0.5 – 30 ‰	30 – 50 ‰	> 50 ‰

Marine and Thalassic Waters

Marine waters, synonymous with euhaline seas, typically exhibit salinities ranging from 30 to 35 ‰. Brackish seas or waters fall within the 0.5 to 29 ‰ range, while metahaline seas have salinities between 36 and 40 ‰. These are considered thalassic, meaning their salinity originates from the ocean. Homoiohaline environments maintain relatively constant salinity over time.

Poikilohaline Variability

In contrast, poikilohaline environments are characterized by significant seasonal or temporal variations in salinity, which are biologically meaningful. These salinities can range widely, from 0.5 ‰ to over 300 ‰. Highly saline water from which salts are crystallizing (or are about to) is specifically termed brine.

Environmental Considerations

Ecological Impact

Salinity is a critical ecological factor, profoundly influencing the types of organisms that can inhabit aquatic environments. It dictates the suitability of water for plant life, both within water bodies and on adjacent land irrigated by them. Plants adapted to saline conditions are known as halophytes, with specific types like glasswort and saltwort being tolerant of residual sodium carbonate salinity. Organisms capable of thriving in highly saline conditions are classified as extremophiles, specifically halophiles.

Water Use and Pollution

The removal of salts from water is an expensive process, making salinity a key consideration for water potability and suitability for irrigation. Increases in salinity have been observed in lakes and rivers, often attributed to the runoff of road salts and other de-icing agents. These increases can have significant impacts on freshwater ecosystems.

Ocean Circulation and Climate

Ocean salinity plays a pivotal role in driving global ocean circulation through the thermohaline circulation. Variations in salinity, along with temperature, alter water density, leading to the sinking and rising of water masses. Changes in ocean salinity are also linked to atmospheric carbon dioxide levels, as saltier waters exhibit lower solubility for CO2. Recent decades have seen complex changes in North Atlantic salinity, influenced by factors such as Greenland meltwater flux and shifts in ocean currents, highlighting the interconnectedness of climate and oceanographic processes.

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References

World Ocean Atlas 2009. nodc.noaa.gov

Unesco (1981). The Practical Salinity Scale 1978 and the International Equation of State of Seawater 1980. Tech. Pap. Mar. Sci., 36

Unesco (1981). Background papers and supporting data on the Practical Salinity Scale 1978. Tech. Pap. Mar. Sci., 37

Venice system (1959). The final resolution of the symposium on the classification of brackish waters. Archo Oceanogr. Limnol., 11 (suppl): 243â248.

A full list of references for this article are available at the Salinity Wikipedia page

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This page has been generated by an Artificial Intelligence and is intended for informational and educational purposes exclusively. The content is derived from a snapshot of publicly available data and may not be entirely accurate, comprehensive, or current.

This is not professional scientific or environmental advice. The information provided herein is not a substitute for expert consultation in fields such as oceanography, environmental science, or water resource management. Always consult with qualified professionals for specific applications and refer to official scientific documentation for critical data.

The creators of this page assume no responsibility for any errors or omissions, or for any actions taken based on the information presented.

The Salinity Spectrum

💡 Dive in with Flashcard Learning! 💡

Definitions ℹ️

🧪 Conceptual Understanding

📏 Operational Measurement

🔬 Precision in Oceanography

Composition 🧪

⚛️ Elemental and Molecular Forms

⚖️ Major and Minor Ions

💨 Gases and Other Dissolved Matter

Seawater Salinity 🌊

📜 Historical Measurement Techniques

⚡ Practical Salinity Scale (PSS-78)

💡 TEOS-10 Standard

Lakes and Rivers 🏞️

💧 Freshwater Definitions

🔌 Conductivity as a Proxy

⚖️ Density Measurements

Classification 📊

📊 Salinity Levels

🌊 Marine and Thalassic Waters

⏳ Poikilohaline Variability

Environmental Considerations 🌍

🌱 Ecological Impact

🏭 Water Use and Pollution

🔄 Ocean Circulation and Climate

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Disclaimer ⚠️

📜 Important Notice

Dive in with Flashcard Learning!

Definitions

Conceptual Understanding

Operational Measurement

Precision in Oceanography

Composition

Elemental and Molecular Forms

Major and Minor Ions

Gases and Other Dissolved Matter

Seawater Salinity

Historical Measurement Techniques

Practical Salinity Scale (PSS-78)

TEOS-10 Standard

Lakes and Rivers

Freshwater Definitions

Conductivity as a Proxy

Density Measurements

Classification

Salinity Levels

Marine and Thalassic Waters

Poikilohaline Variability

Environmental Considerations

Ecological Impact

Water Use and Pollution

Ocean Circulation and Climate

Teacher's Corner

True or False?

Test Your Knowledge!

Gamer's Corner

Discover other topics to study!

References

Feedback & Support

Disclaimer

Important Notice