Ocean Water Modifies and Influences

¶ … Ocean Water Modifies and Influences Solar Radiation Spectra

There are a multitude of complex factors that influence the absorption of solar radiation by ocean water, including two very specific laws involving the amount of light transmitted through a liquid. The Beer and Lambert laws govern the transmission of solar spectra in ocean water, but beyond these laws, other factors also play a role in the way the radiation is influenced and absorbed (Stramski and Woz'niak, 2005). The role of suspended particulate matter and the composition of this matter also have much to do with absorption, and can be traced to differing patterns of distribution and diffusion. The seasonal variations and cycles that occur within the ocean are poorly-understood, especially when it comes to solar radiation and light diffusion and backscattering. These effects, as far as natural phenomena are concerned, are well understood. The factors influencing them are not.

The types of this particulate matter are many, and their roles are just now being understood and fit into the complex picture that makes up the ocean's solar radiation and light absorption abilities. Organic particulates like phytoplankton as well as man-made pollutants, colloids, and minerals all have specific effects on ocean water when it comes into contact with solar radiation (Stramski and Woz'niak, 2005). The overly-simplified understanding of how the size, shape, and composition of these particulates can influence the way in which they both behave and change the dynamic of sea water is starting to be more clearly understood and represented within the scientific community. Ocean water has much more dynamic and complex optical qualities than previously understood. The purity and general health of the ocean in specific sample regions can also be determined based upon the diffusion levels of the water itself (Stramski, Boss, Bogucki, and Voss, 2004). This is not to say that the water, as an inorganic compound controls the health of the ocean, but the presence of certain organisms, namely algae at specific depths and temperatures, helps to estimate the environmental costs of man-made and in-organic pollutants.

Satellite Data and Research

Over the past 20 years, scientists have used satellites to help measure the way that light and solar radiation is diffused in ocean water. Making certain distinctions between the ways that particle size and depth affect this diffusion, scientists have been able to observe and predict the diffusion levels using imagery from outer space. According to the satellite data, ocean water that is found primarily in tidal mixed shelf seas as well as estuaries, the scattering of light based on the color of the water and the particles suspended within it is rather uniform and predictable (Stramski, Boss, Bogucki, and Voss, 2004). The levels of particulates as well as the sizes involved also suggest that a seasonal cycle occurs relative to the changing of the turbidity and tides. This comes into play with the diffusion of solar spectra because as the particles become smaller in size, in periods of higher turbidity, the diffusion occurs at deeper levels. This result has more to do with the dispersion of particulates and their sizes over the seasons. The local knowledge of turbulence in the water can also help improve satellite estimations of light and radiation diffusion because as the seasonally adjusted turbidity changes, so does the light reflected back to the satellites (Lahet, F. And D. Stramski. 2010). This data shows that the solar radiation is reflected by the ocean water differently during different seasons and weather patterns. It is important to note that other specifics like the location and tidal activity surrounding the specified area is also important in measuring this diffusion.

Backscattering and "Missing" Light Diffusion

Historically, the idea that certain elements in the water can scatter and diffuse light in different ways, according to different and often seasonal conditions has been surrounded by mystery. The concept itself has enjoyed much scientific acceptance, but the way in which light is diffused has recently become quite interesting since satellites and scientists now have the ability to much more accurately measure this phenomenon. In the past, scientists believed that phytoplankton and other organic compounds and elements were responsible for up to 80% of the light backscatter and diffusion in the ocean. Scientific studies seemed to support this idea, which was interesting given the seasonal nature of these phytoplankton blooms. But in recent years, as the role of pollutants such as man-made particulate matter has come under scrutiny, scientists are beginning to see that both the seasonality of these blooms as well as other organic and non-organic compounds have more of a role to play than the seasonal compounds often do, and on a larger scale.

Because of the substantial variety of compounds in the water, there have recently been studies conducted that show these compounds diffuse and backscatter light in different ways and to different extents than previously understood. It appears that the small-size, non-living particles have more of a backscattering effect on the incoming light and solar radiation than the organic ones, according to one study (Stramski, Boss, Bogucki, and Voss, 2004). This means that both the organic and man-made particulates that are currently in the ocean are beginning to affect the way that the ocean's engine- sunlight and solar radiation, behaves both at the surface and at certain depths. It is interesting to note that while the previously-adopted scenario of phytoplankton creating up to 80% of the backscattering was relatively accurate, at certain times in the year, it is becoming more and more evident that the effects of particulates is largely dependant on the depth, consistency, and seasonality of the water and its contents.

The role that phytoplankton play in diffusion is well-understood. However, up until recently, it wasn't well documented that this role, though rather large, was only taking place in certain specific time periods. The rest of the year, other particulates were backscattering the light and diffusing the solar radiation (Dera, J., S. Sagan, and D. Stramski. 1993). This shows a certain balance that has been disrupted within the ocean itself. Other conditions like air bubbles in the water near the shore that are added as waves break as well as tidal variations and shallow seas help to make up for the effects of non-bloom times for the phytoplankton. Scientists are beginning to develop a much clearer and much more complex picture of how the seas scatter, diffuse, and absorb light, depending on the conditions and particulates involved. Stramski, Boss, Bogucki, and Voss (2004) make a great point when they conclude that in the past, the study of how sunlight and radiation affect the ocean has been grossly oversimplified and poorly-understood. The true processes that affect ocean cycles and functions are much more complex than previously believed.

Minerals, Colloidal Compounds, and Absorption

The concentration of minerals within seawater also greatly affects the absorption of light and the way solar radiation is diffused. Interestingly enough, according to Babin and Stramski (2004), iron (Fe) is a major influence on the way solar radiation is absorbed and processed within ocean water. It is not necessarily the presence of pure iron compounds, or the singular presence of the element itself, rather it is the combination of iron and other elements, in pure and crystal form, that tends to affect ocean water and solar radiation diffusion the most. The study suggests that areas of the ocean that have higher levels of both pure iron hydroxide as well as this element mixed with other compounds tend to absorb UV radiation at much higher levels. However, this does not translate to a greater ability to absorb light from the visible spectrum. Regardless of the visible light anomaly, the ocean's ability to absorb solar radiation and UV has a massive effect on the sea life and livability of that part of the ocean.

Using scientific evidence, it is possible to map out the portions of the ocean that have higher than average iron and iron hydroxide compounds suspended in the water. These areas tend to be concentrated within certain geothermal and geologic features (Stramski, D., S.B. Wo-niak, and P.J. Flatau. 2004). Another area where these compounds are concentrated in is mineral rich surface soil areas on the coasts near the equator and other significant landscape features (Babin and Stramski, 2004). The ocean water and solar radiation absorption associated with these areas helps to explain how different parts of the ocean, with seemingly similar depths and organic compounds, absorb light and radiation differently. This is significant because it shows the further complexity of the ocean's water and compound composition and how this complexity is both barely understood and able to influence the life within the areas of the ocean it exists in. Interestingly enough, these compounds range in size from one nanometer to one micrometer, the latter being the single most abundant particle size in the ocean. The larger colloids play a huge role in diffusion while the smaller particulate play a role in backscattering.

Depending on the concentrations of each particle size, their influence can vary. The larger particles can influence the absorption rates of solar energy by a factor of three over particulates such as phytoplankton and minerals (Stramski and Woz'niak, 2005). This means that a small concentration of these particles can do a lot for the absorption rates of the water they are suspended in. The smaller particles can also have this effect, but their concentrations need to be proportionately higher to exact this same influence. The smaller particles are more influential as far as backscattering is concerned, and represent a massive shift in the way that scientists think about light diffusion and backscattering within the ocean. Previously, scientists thought that only the larger of these particles combined with other particulates were responsible for most of the solar radiation absorption (Bricaud, a., Morel, a. And Prieur, L., 1981). Now scientists understand that in shallow, mineral-rich waters, even a small presence of these tiniest of colloids will change the way in which ocean water reacts to sun light.

Colloidal compounds, which make up the abundance of the suspended compound matter within ocean water, are understood to have a great affect on the absorption of solar radiation and light. The presence of these particles does vary seasonally as well as regionally, with the vast majority of the concentration occurring near the equator during the summer and winter months (Stramski and Woz'niak, 2005). This shows the further vulnerability of the scientific models to seasonal variations and cycles. While the depths at which these particulates exist, as well as the forced changes to the ocean water's composition through environmental and man-made influences has a significant effect on the existence of these particulates, the ocean's own, natural cycles and variations tend to play a larger role in the dynamics of these substances.

The "Clearest" Natural Waters: Some Characteristics and Anomalies

The clearest, must pure natural ocean water has some very interesting characteristics and commonalities around the world, wherever it is found. In one study involving the optical backscattering and diffusion qualities of ocean waters, scientists took samples from several locations in the southeast Pacific. These locations had some very interesting commonalities, yet they were far enough away from each other to not be dismissed or regarded as anomalies. Scientists found that the clearest waters, regardless of the mineral and organic compounds associated with the sample areas, were found at a very specific depth. This, according to the scientists, has a little to do with salinity and a lot to do with the water pressures and solubility of some of the important, diffusion and backscattering-influencing particles (Twardowski, M.S., H. Claustre, S.A. Freeman, D. Stramski, and Y. Huot., 2007). This means that the ocean has a natural symbiosis that exists at a specific depth, and that if small changes to the particulate concentrations at these levels are made, the results could be quite striking.

The depths at which these samples yielded the highest levels of purity were between 300 and 350 m, and the locations ranged from 23.5 degrees S, 118 degrees W. To 26 degrees S, 114 degrees W, where total backscattering at 650 nm was not distinguishable from pure seawater (Twardowski, M.S., H. Claustre, S.A. Freeman, D. Stramski, and Y. Huot., 2007). Within this area, the commonalities in the sea water were striking, and also resulted in other scientific discoveries. The study suggests that these waters all had similar mineral and diffusion characteristics, stating that, "The particulate backscattering ratio typically ranged between 0.4% and 0.6% at 650 nm through the majority of the central gyre from the surface to _210 m, indicative of "soft" water-filled particles with low bulk refractive index." (Twardowski, M.S., H. Claustre, S.A. Freeman, D. Stramski, and Y. Huot., 2007). This is significant because it shows that the ocean water, within these sample areas, had purity commonalities and anomalies that do not exist anywhere else in surrounding areas.

The presence of the single-celled algae coccolithophorid created some very specific purity and diffusion properties within these sample areas, suggesting that the ocean's natural balance of this organic compound is essential in maintaining water purity and specific optical quality within these regions. Interestingly, the Twardowski, M.S., H. Claustre, S.A. Freeman, D. Stramski, and Y. Huot study states, "showed a distinct secondary deeper layer centered at 230m that was absent in particulate attenuation sample data. The particulate backscattering ratio was significantly higher in this layer than in the rest of the water column, reaching 1.2% in some locations. This high relative backscattering, along with the pigment composition and ecological niche of this layer, appear to be consistent with the coccolithophorid concentrations." (Twardowski, M.S., H. Claustre, S.A. Freeman, D. Stramski, and Y. Huot., 2007). This shows that ocean water particulate matter, purity, and diffusion properties are very fragile, and this complex balance as it is disrupted at these levels, creates a very specific and strong influence on these characteristics.