Climate Change Affects Marine Environment
The ocean has a natural ability to buffer the atmosphere and the ocean surface is in a state of equilibrium with the atmosphere with respect to CO2 and heat. As concentrations of either increase in the atmosphere, they increase in the ocean as well. These increases change the physical and chemical properties of the ocean and affect several oceanic processes.
The most significant impact of global warming on marine environment is due to the melting of mountain and continental glaciers. Ice melting causes slow down and/or shut down of thermohaline circulation, and makes hypoxic environment for the first time, then makes anoxic with time. This can cause decreasing biodiversity, and finally makes global extinction of animals and plants. Furthermore, global warming causes sea-level rise, soil erosion and changes in calcium carbonate compensation depth (CCD). These changes also can make marine ecosystem unstable. If we emit carbon dioxide at a current rate, the global mean temperature will rise at least 6°C at the end of this century, as predicted by IPCC (Intergovernmental Panel on Climate Change). In this case, the ocean waters become acidic and anoxic, and the thermohaline circulation will be halted, and marine ecosystems collapsed.
Hypoxia or oxygen depletion is one of the most acute symptoms of eutrophication. The other is harmful algal blooms, and all things together can destroy aquatic life in affected areas.
The rise in eutrophic and hypoxic events has been attributed to the rapid increase in intensive agricultural practices, industrial activities, and population growth which together have increased nitrogen and phosphorus flows in the environment. The Millenium Ecosystem Assessment (MA) found that human activities have resulted in the near doubling of nitrogen and tripling of phosphorus flows to the environment when compared to natural values.
Before nutrients—nitrogen in particular—are delivered to coastal ecosystems, they pass through a variety of terrestrial and freshwater ecosystems, causing other environmental problems such as freshwater quality impairments, acid rain, the formation of greenhouse gases, shifts in community food webs, and a loss of biodiversity.
Once nutrients reach coastal systems, they can trigger a number of responses within the ecosystem. The initial impacts of nutrient increases are the excessive growth of phytoplankton, microalgae (e.g., epiphytes and microphytes), and macroalgae (i.e., seaweed). These, in turn, can lead to other impacts such as: loss of subaquatic vegetation, change in species composition, coral reef damage, low dissolved oxygen, and the formation of dead zones (oxygen-depleted waters) that can lead to ecosystem collapse.
Ocean warming and sea level rises
 | Ocean warming has several consequences. A well-known example is sea-level rise. As water warms, it expands, and the ocean surface rises. Currently, most of the excess heat in the ocean, and the associated thermal expansion, is in a surface layer only a few hundred meters deep (Domingues et al. 2008). Over time, this heat will diffuse downward to greater depths, increasing expansion and triggering further changes in sea level. Additional sea-level rise is caused by the melting of inland glaciers and continental ice sheets including those resting on Greenland and Antarctica. Recent studies conclude that mean sea-level rise of 0.5m-0.8m over 1990 levels by 2100 is likely and that a rise of more than one meter in that time is possible (Rahmstorf 2007;Pfeffer et al. 2008, Richardson et al. 2009). A change this significant causes storm surges and flooding to be more dangerous and to occur more regularly (McMullen and Jabbour 2009). |
Ocean acidification and its impact on ocean noise
Ocean Acidification
A decrease in the pH of sea water due to the uptake of anthropogenic carbon dioxide (IPCC)
Writing in the Journal of the Acoustical Society of America, Reeder and Chiu (2010) say "it has been reported that, given a 0.3 reduction in pH, from 8.1 to 7.8, a reduction in the acoustic absorption at low frequencies could result, suggesting a significant increase in ocean noise," while more recently, "it has been suggested that low-frequency sound will travel farther due to the ocean pH reduction expected by 2050," and most recently, it has been suggested that "in an ocean more transparent to sound, the resultant changes in propagation range will be noticeable in the operation of scientific, commercial and naval applications that are based on ocean acoustics." But in a world where new bad consequences of earth's rising atmospheric CO2concentration are invented almost daily, one has to ask oneself: Is this really so? And, fortunately, Reeder and Chiu did just that ... and much, much more. They reviewed "the fundamental principles of acoustic transmission loss in the ocean and how the multiple transmission loss mechanisms impact ocean noise levels within the context of changing ocean pH," after which they conducted "an analytical analysis involving physical and empirical models of all relevant transmission loss mechanisms," focusing on "three ocean acoustic environments ... to elucidate the expected change in ocean noise level from sources at the surface as a function of frequency: shallow water, the acoustic surface duct and the deep ocean."
So what did they find? The two researchers in the Department of Oceanography of the Naval Postgraduate School in Monterey California (USA) found that for even a large reduction in ocean pH from 8.1 to 7.4, there was "no observable change in ocean noise in the shallow water and surface duct environments for all frequencies -- two environments which host a large portion of the marine mammal population." They also found "a negligible change in ocean noise level in the deep water environment for all frequencies ... which also provides an upper bound to the maximum expected increase in ocean noise level due to the fact that it does not fully account for the range-dependent water column sound speed, bottom topography and distributed sources."
Putting their results into the context of average background ocean noise levels as represented by Wenz (1962) curves, they found "a statistically insignificant change compared to the inherent variability of ocean noise associated with shipping and surface-generated mechanisms." Thus, "after 250 years," as they describe it, "there would still be no significant modifications to the Wenz curves," which suggests to us that all's well that ends well. Hear ye, hear ye!
