In recent years, the volume of freshwater run off flowing from the large rivers into the Arctic Ocean has increased. This is the result of warmer temperatures and more melting of land based ice. It may also be in part due to increase in precipitation in the Arctic. Additionally thinner and more mobile sea ice now exits the Arctic ocean in greater quantities than previously observed. All these processes impact the salinity of the north Atlantic ocean and may significantly effect the global ocean circulation system. Usually, the thermohaline circulation transports warm and salty water to the North Atlantic, where it becomes denser as it cools. As it gets denser, it sinks and finally flows southward in the depths of the ocean. In this way, warm water is transported northward, and cold water is exported southward. This is crucial to the movement of heat from the tropics to the high latitudes. As more fresh water is added, surface water's salinity decreases, lowering its density. Depending on where the additional fresh water accumulates this process may impact the formation and sinking of dense water masses at high latitudes in winter. This works against sinking, which is crucial to the ocean conveyor. In the worst case scenario, this process can significantly weaken or even shut off the ocean conveyor completely. It is thought that this happened 13 thousand years ago. In an event called the younger dryas, at this time gigantic amounts of fresh water were added to the North Atlantic Ocean from the margins of the melting Laurentide ice sheet that covered northern North America. This plunged the northern hemisphere Both ocean and land, back to ice age conditions for a period of about 1000 years. The slowing down, or shutting off of the ocean conveyor due to global warming, may paradoxically promote a cooling around the North Atlantic even while the rest of the Earth is rapidly warming. This potential outcome has been confirmed by climate models. However, a shut-down of the conveyor would also reduce the ocean's ability to take up carbon dioxide. This could, in the long term, leave more of this greenhouse gas in the atmosphere Leading to additional warming globally. The oceans take up significant amounts of CO2. One benefit of this is slowing the rate of increase of CO2 into the atmosphere due to the release of fossil fuel greenhouse gases since the Industrial Revolution. However, with the volume of human produced greenhouse gasses rising in the atmosphere, the ocean must take up more and more CO2. One problem with this is how carbon dioxide reacts when dissolved in ocean water. Using what you used in Lesson 2 Why might this be an issue? A, it leads to a decrease in ocean acidification. B, it leads to an increase in ocean acidification. C, it makes the oceans hotter, Due to CO2's radiative effect. D It leads to negative impacts on marine life, such as the ability for such life to build protective shells. Answer is B and D are correct, since the sun's incoming solar radiation does not significantly penetrate into the ocean. CO2 within the oceans cannot directly have a significant impact on it. We will examine these issues in the next section. Because the oceans represent a large reservoir of carbon compared to the atmosphere, they can have a dramatic impact on carbon dioxide in the atmosphere On the other hand, the algae that are floating in the surface ocean are also able to take up carbon dioxide from the atmosphere and use it for photosynthesis. Upon their death, many of these microorganisms, which have calcium carbonate shells. Sink down to the sea floor and are buried there. This means that carbon can essentially be buried in the ocean, and that the ocean can be a carbon sink through this biological pump. This significant oceanic uptake of CO2 has benefited humans since we began to release fossil fuel greenhouse gases into the atmosphere. During the Industrial Revolution. This is by limiting the amount of greenhouse warming that would otherwise have occurred. However, with the volume of human produced greenhouse gases rising in the atmosphere, the ocean must take up more and more CO2. One problem with this is how carbon dioxide reacts when dissolved in ocean water. When it is dissolved it forms a weak acid called carbonic acid, or H2CO3. This causes ocean water to be more acidic. More acidic ocean water will impact a vast majority of marine eco systems especially those organisms which build their shells out of calcium carbonate. Amongst these are very important species of marine eco systems including corals, Mollusks, such as mussels and clams, and perhaps most importantly, the basic food providers of the ocean ecosystem, plankton. Acidification of the ocean means these organisms are not able to build an sufficiently protective shell. This makes them susceptible to predation. As well this impacts their basic biological functions such as reproduction and feeding by damaging the base of the marine food chain and increasingly acidic ocean can greatly damage the marine ecosystem as a whole. This impacts all other species including humans that rely upon it. The melting of permafrost, the layer of permanent frozen soil and rock in the Arctic, is worrying for several reasons. Given that permafrost contains a pool of trapped carbon, which of the following statements are true? A, All the carbon stored in the world's permafrost will be released to the atmosphere. B) The Arctic permafrost carbon balance is known with certainty. C) Some of the carbon stored in the world's permafrost Will be released to the atmosphere. D) More abundant plant life, may draw down some of the permafrost carbon released to the atmosphere. More than one answer might be correct, so check all that you think apply. Answer C and D are both correct. Well some regions may lose their permafrost, others will retain theirs likely with the deeper active layer. Furthermore soils are important carbon throughout the world. For now the permafrost carbon balance is not known with certainty but it's the subject of on going study. One of the main concerns about the loss of permafrost is that permafrost contains a pool of trapped carbon stored for many thousands of years. The melting of permafrost risks exposing this carbon and eventually adding it the pool of green house gases in the atmosphere. Contributing to global warming. Permafrost covers about a quarter of the earth's surface. That is around 23 million square kilometers. Though it's typically less than one meter deep. It can reach thicknesses of at least one kilometer depending on the temperature of the air and soil. All of the world's permafrost, most of which is concentrated in Siberia, is estimated to hold a staggering 1,800 billion tons of carbon. This is three times the natural amount in the atmosphere. As of 2015 the outcome of the so called Arctic Carbon Balance is unclear. It has been suggested that if warming continues the Arctic could change from a carbon sink under natural conditions to a net carbon source. 2013 IPCC report states that Arctic permafrost has warmed up in most regions since the 1980s, with a maximum rise in temperatures of two to three degrees celsius. In the Russian arctic, permafrost has thinned and decreased in extent during each of the last three decades. If it remains frozen, arctic permafrost acts as a carbon sink. That is, more carbon is taken up from the atmosphere and used by vegetation in photosynthesis in the arctic summer then is released through decomposition and respiration. However, with increasing air and soil temperatures, permafrost thawing has become evident in many regions. As thawing progresses, permafrost dries out, and materials which have previously remained frozen, are decomposed through bacterial action. This in turn favors respiration and decomposition. These are mechanisms which change organic carbons, stored in permafrost, to the greenhouse gasses carbon dioxide and methane. How might climate warming lead to a positive feedback as permafrost is melted? A, warming promotes thawing of permafrost, which then leads to more greenhouse gases being released to the atmosphere, promoting warming. B, warming promotes thawing of permafrost, which then leads to more greenhouse gases being released to the atmosphere. Enhancing albedo and cooling. C, warming promotes thawing of permafrost, which then leads to less greenhouse gases being released to the atmosphere, promoting warming. D, warming promotes thawing of permafrost which then leads to less greenhouse gases being released to the atmosphere Enhancing albedo and cooling. Answer A is correct. A positive feedback is created where a potentially small initial change is enhanced. Climate warming promotes the thawing of permafrost, which then leads to enhanced greenhouse gas release into the atmosphere. Which in turn promotes climate warming. However a longer arctic growing season would promote additional plant photosynthesis and growth and remove some of this carbon from the atmosphere. So the total impact of melting permafrost may be less than some researchers predict. Permafrost is not just found on land, but also exists on the shallow continental shelves of the Arctic Ocean, such as those fringing the Russian coasts. Some of these regions contain methane hydrates. This is methane frozen into a matrix of ice. It is kept frozen and under pressure beneath the ocean floor. Any warming the occurs can make methane hydrate deposits unstable. This means that large amounts of methane could be rapidly released into the atmosphere. Per molecule, methane is 34 times more powerful than CO2 In terms of warming potential. it has been estimated that the Arctic as a whole has ten times more methane in the form of methane hydrates than the whole of the atmosphere. This is even with accounting for human produced methane. There is another problem with the melting of permafrost in the Arctic One that can profoundly effect Northern communities. Melting permafrost can cause the overlying soil layer to become detached and unstable. This soil is then free to move and can be washed away and transported into nearby water bodies, including streams, rivers and lakes. There it can deteriorate the water quality to the point that it becomes unusable for communities. With the decay of permafrost ground, community roads and infrastructure such as airport runways are also susceptible to damage due to instability. This leads to high repair and replacement costs And the need to build to different standards. As we have seen, some dramatic changes are forecasted for the physical environment of the Arctic. Both sea ice and permafrost show continuous trends in melting, and the Arctic may become seasonally ice free by the end of the century or sooner. On land permafrost is melting causing some dramatic effects, including the release of stored carbon into the atmosphere but also impacting people who live within the Arctic Circle. Before we continue, consider what we have discussed and see if you can identify how Arctic ecosystems might be impacted. Select the statements below that you believe would impact the Arctic ecosystems. A, loss of habitat. B, disruption of the food chain. C, altering the growing season. D, Opening the arctic to new invasive species from lower latitudes. More than one answer might be correct so check all that you think apply. If you selected all the statements you would be correct. However, the overall cost to the ecosystems in terms of the climate change is highly complex The repercussions of climate change are already impacting species, food webs, and ecological processes. Some species will likely derive some benefit from the shift to warming climate. For example, bowhead whales will be free to migrate across the Arctic Ocean, between Atlantic and Pacific populations. But these benefits need to be evaluated against the costs. Many species will not benefit. The Arctic is already opening up to new invasive species, which can sometimes out compete the existing Arctic species. Let's look at some of the factors that will impact the two Arctic species we discussed in lesson one. As we saw in lesson one, the polar bear is a marine mammal that is superbly adapted to the arctic environment. The polar bear is often seen as a symbol of the arctic, but due to its dependence on sea ice, it is also become a powerful symbol for arctic climate change. Polar bears spend most of their lives on sea ice. They need sea ice for virtually all their life's activities. This includes for food that is hunting seals, for breeding, for shelter and for traveling. The loss of sea ice in recent decades has meant that polar bears are quickly losing their habitat. Polar bears can and will go without food for several months during the summer. However, an increasingly short sea ice season, and a longer ice-free open water season, means that polar bears will have to go without food for longer. Which of the following do you think are likely to happen as a result of this longer starvation season for polar bears? A) Increased polar bear mortality. B) Increased polar bear conflicts with humans in Arctic communities. C, increased interactions between polar bears and brown or grizzly bears. D, increased foraging for alternative foods while on land. More than one answer might be correct, so check all that you think apply. Once again All answers are correct. All of these options are known outcomes of a longer on land season for polar bears. So what are the consequences of this change to the polar bear's ecosystem?
