Sea surface microlayer
Encyclopedia
The sea surface microlayer (SML) is the top 1000 micrometers (or 1 millimeter) of the ocean surface. It is the boundary layer where all exchange occurs between the atmosphere
and the ocean
. The chemical, physical, and biological properties of the SML differ greatly from the sub-surface water just a few centimeters beneath.
are highly enriched in the SML interface. Most of these come from biota
in the sub-surface waters, which decay and become transported to the surface, though other sources exist also such as atmospheric deposition, coastal runoff, and anthropogenic nutrification. The relative concentration of these compounds is dependent on the nutrient sources as well as climate
conditions such as wind speed and precipitation
. These organic compounds on the surface create a "film," referred to as a "slick" when visible, which affects the physical and optical properties of the interface. These films occur because of the hydrophobic tendencies of many organic compounds, which causes them to protrude into the air-interface. The existence of organic compounds, or "surfactants" on the ocean surface impedes wave formation for low wind speeds. For increasing concentrations of "surfactant" there is an increasing critical wind speed necessary to create ocean waves. Increased levels of organic compounds at the surface also hinders air-sea gas exchange at low wind speeds. One way in which particulates and organic compounds on the surface are transported into the atmosphere is the process called "bubble bursting". Bubbles generate the major portion of marine aerosols. They can be dispersed to heights of several meters, picking up whatever particles latch on to their surface. However, the major supplier of materials comes from the SML.
, viruses, toxic metals and organic pollutants as compared to the sub-surface water. These materials can be transferred from the sea-surface to the atmosphere in the form of wind-generated aqueous aerosols due to their high vapor tension and a process known as volatilisation
. When airborne, these microbes can be transported long distances to coastal regions. If they hit land they can have detrimental effects on animals, vegetation and human health. Marine aerosols that contain viruses can travel hundreds of kilometers from their source and remain in liquid form as long as the humidity is high enough (over 70%). These aerosols are able to remain suspended in the atmosphere for about 31 days. Evidence suggests that bacteria can remain viable after being transported inland through aerosols. Some reached as far as 200 meters at 30 meters above sea level. A month long study done by scientists in the Tyrrhenian Sea
in 1999 revealed that signals of pollution from chemicals of petrogenic origin in the harbor of Livorno
was the result of chemicals found in the SML. It was also noted that the process which transfers this material to the atmosphere causes further enrichment in both bacteria and viruses in comparison to either the SML or sub-surface waters (up to three orders of magnitude in some locations).
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
and the ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
. The chemical, physical, and biological properties of the SML differ greatly from the sub-surface water just a few centimeters beneath.
Overview of Properties
Organic compounds such as amino acids, carbohydrates, fatty acids, and phenolsPhenols
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group...
are highly enriched in the SML interface. Most of these come from biota
Biota (ecology)
Biota are the total collection of organisms of a geographic region or a time period, from local geographic scales and instantaneous temporal scales all the way up to whole-planet and whole-timescale spatiotemporal scales. The biota of the Earth lives in the biosphere.-See...
in the sub-surface waters, which decay and become transported to the surface, though other sources exist also such as atmospheric deposition, coastal runoff, and anthropogenic nutrification. The relative concentration of these compounds is dependent on the nutrient sources as well as climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
conditions such as wind speed and precipitation
Precipitation (meteorology)
In meteorology, precipitation In meteorology, precipitation In meteorology, precipitation (also known as one of the classes of hydrometeors, which are atmospheric water phenomena is any product of the condensation of atmospheric water vapor that falls under gravity. The main forms of precipitation...
. These organic compounds on the surface create a "film," referred to as a "slick" when visible, which affects the physical and optical properties of the interface. These films occur because of the hydrophobic tendencies of many organic compounds, which causes them to protrude into the air-interface. The existence of organic compounds, or "surfactants" on the ocean surface impedes wave formation for low wind speeds. For increasing concentrations of "surfactant" there is an increasing critical wind speed necessary to create ocean waves. Increased levels of organic compounds at the surface also hinders air-sea gas exchange at low wind speeds. One way in which particulates and organic compounds on the surface are transported into the atmosphere is the process called "bubble bursting". Bubbles generate the major portion of marine aerosols. They can be dispersed to heights of several meters, picking up whatever particles latch on to their surface. However, the major supplier of materials comes from the SML.
Health and Environment
Extensive research has shown that the SML contains elevated concentration of bacteriaBacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
, viruses, toxic metals and organic pollutants as compared to the sub-surface water. These materials can be transferred from the sea-surface to the atmosphere in the form of wind-generated aqueous aerosols due to their high vapor tension and a process known as volatilisation
Volatilisation
Volatilization is the process whereby a dissolved sample is vaporised. In atomic spectroscopy this is usually a two step process. The analyte is turned into small droplets in a nebuliser which are entrained in a gas flow which is in turn volatilised in a high temperature flame in the case of AAS or...
. When airborne, these microbes can be transported long distances to coastal regions. If they hit land they can have detrimental effects on animals, vegetation and human health. Marine aerosols that contain viruses can travel hundreds of kilometers from their source and remain in liquid form as long as the humidity is high enough (over 70%). These aerosols are able to remain suspended in the atmosphere for about 31 days. Evidence suggests that bacteria can remain viable after being transported inland through aerosols. Some reached as far as 200 meters at 30 meters above sea level. A month long study done by scientists in the Tyrrhenian Sea
Tyrrhenian Sea
The Tyrrhenian Sea is part of the Mediterranean Sea off the western coast of Italy.-Geography:The sea is bounded by Corsica and Sardinia , Tuscany, Lazio, Campania, Basilicata and Calabria and Sicily ....
in 1999 revealed that signals of pollution from chemicals of petrogenic origin in the harbor of Livorno
Livorno
Livorno , traditionally Leghorn , is a port city on the Tyrrhenian Sea on the western edge of Tuscany, Italy. It is the capital of the Province of Livorno, having a population of approximately 160,000 residents in 2009.- History :...
was the result of chemicals found in the SML. It was also noted that the process which transfers this material to the atmosphere causes further enrichment in both bacteria and viruses in comparison to either the SML or sub-surface waters (up to three orders of magnitude in some locations).