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.
Ocean water coming from similar depths as the samples taken from the southeast Pacific show other specificities as well. Mainly, scientists are learning that levels of single-cell algae in warmer waters, and the depths at which these animals thrive and are concentrated is an excellent indicator of water purity and ocean health (Twardowski, M.S., H. Claustre, S.A. Freeman, D. Stramski, and Y. Huot., 2007). The areas of the ocean in these regions that are most polluted show a significant absence of this and other algae, signaling that these organisms act as "canaries in the coal mine," whereas mineral and non-organic particulate levels, having an equally as large influence on sea water diffusion, do not vary with the specific health and purity of the ocean water.
Other Diffusion Modifiers
Besides the diffusion modifiers existing in suspended form, both organic and in-organic, there are other ways in which solar spectra gets diffused and backscattered in ocean water. These methods are not completely understood, and scientists are just beginning to use the most up-to-date technology to quantify their effects. One of these modifiers is gas bubbles in the water itself (Lahet, F. And D. Stramski. 2010). This occurs most often where waves break in shallow water, but it can also happen as gasses escape from organisms and as rainfall affects the ocean's surface. These bubbles and surface anomalies are largely determined by the frequency and concentration of the bubbles, but certain areas in the ocean have more of a tendency to modify sunlight in these ways (Piskozub, J., D. Stramski, E. Terrill, and W.K. Melville. 2009). This means areas that are subject to massive tidal shifts and breaking waves are susceptible to sunlight reaching greater depths and having more influence as radiation.
While these modifiers are typically concentrated along coastlines, regions of the ocean that are affected by weather patterns, specifically larger amounts of rain and wind are also greatly affected (Piskozub, J., D. Stramski, E. Terrill, and W.K. Melville. 2009). The fragile and extremely complex picture that scientists are forming relative to how the ocean water acts to modify solar radiation spectra, relative to its contents, location, depth, and outside modifiers presents quite a daunting reality of these natural processes. These modifiers also interact with the above mentioned modifiers in ways that are little-known, and unpredictable. Certainly there will be thousands of future studies that help to explore these possibilities and potential for environmental influence.
To summarize, ocean water and solar radiation spectra are influenced by myriad factors. This is not to say that scientists will never have a firm grasp on the larger picture, but evidence is emerging that the complexities associated with just one of these diffusion modifiers is quite striking. The particulates suspended in ocean water, be they organic, in-organic, colloids, or algae, all have a role to play on the way in which light interacts with the water. The regional and seasonal considerations of the ocean water columns are also worth noting, since these factors can affect they way in which the environment itself interacts with the water, specifically the surface. Scientists are certainly better able to predict the purity, health, and backscatter capabilities of specific regions and portions of the globe's oceans, and will be able to use this data and these understandings in the future to build more accurate models of how humans have impacted the ocean and the environment as a whole.
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