User:Alyssa Schultz/Climate change and ecosystems

Ocean acidification
Ocean acidification poses a severe threat to the earth's natural process of regulating atmospheric CO2 levels. Atmospheric CO2 emissions have increased by almost 50% from preindustrial levels of 280 ppm (part per million) to nearly 420 ppm today. Due to high proportion of Earth that oceans represent and the buffering capacity of seawater for CO2, ocean absorbs up to 25% of atmospheric carbon dioxide, lessening the effects of climate change. Oceanic uptake of CO2 decreases with increasing atmospheric CO2 concentrations as the buffering capacity becomes reduced. As atmospheric CO2 is mixed in with seawater it forms carbonic acid, which then dissociates into free hydrogen ions (H+), bicarbonate (HCO3-), and carbonate ions (CO32-). As H+ ions increase, so does the ocean's acidity, decreasing its ph by up to 0.1 per 100 ppm of atmospheric CO2. Following gas exchange with the atmosphere, CO2 becomes aqueous and mixes in with the surface layers of the ocean as dissolve inorganic carbon (DIC) before being transported by ocean currents to deeper waters. Ocean pH has already decreased from 8.2 to 8.1 since preindustrial levels and is expected to continue decreasing with time. The increase of ocean acidity also decelerates the rate of calcification in salt water, leading to slower growing reefs which supports approximately 25% of marine life. As seen with the great barrier reef, the increase in ocean acidity in not only killing the coral, but also the wildly diverse population of marine inhabitants which coral reefs support.

Dissolved oxygen
Another issue faced by increasing global temperatures is the decrease of the ocean's ability to dissolve oxygen, one with potentially more severe consequences than other repercussions of global warming. Ocean depths between 100 meters and 1,000 meters are known as "oceanic mid zones" and host a plethora of biologically diverse species, one of which being zooplankton. Zooplankton feed on smaller organisms such as phytoplankton, which are an integral part of the marine food web. Phytoplankton perform photosynthesis, receiving energy from light, and provide sustenance and energy for the larger zooplankton, which provide sustenance and energy for the even larger fish, and so on up the food chain. The increase in oceanic temperatures lowers the ocean's ability to retain oxygen generated from phytoplankton, and therefore reduces the amount of bioavailable oxygen that fish and other various marine wildlife rely on for their survival. This creates marine dead zones, and the phenomenon has already generated multiple marine dead zones around the world, as marine currents effectively "trap" the deoxygenated water.

Algal blooms
Climate change and a warming ocean can increase the frequency and the magnitude of algal bloom. There is evidence that harmful algal blooms have increased in recent decades, resulting in impacts ranging from public health, tourism, aquaculture, fisheries, to ecosystem Such events may result in changes in temperature, stratification, light, ocean acidification, increased nutrients, and grazing. As climate change continues, harmful algal blooms will likely exhibit spatial and temporal shifts under future conditions. Spatially, species may experience range expansion, contraction, or latitudinal shifts, while temporally, the seasonal windows of growth may expand or shorten. In 2019, the biggest Sargassum bloom ever seen created a crisis in the Tourism industry in North America. The event was probably caused by Climate Change and Fertilizers. Several Caribbean countries, even considered declaring a state of emergency due to the impact on tourism. The bloom can benefit the marine life, but, can also block the sunlight necessary for it.

Impact on calcifying organisms
Marine calcifying organisms use CO32- ions to form their shells and reefs. As ocean acidification continues, calcium carbonate (CaCO3) saturation states, a measure of CO32- in seawater are lowered, inhibiting calcifying organisms from building their shells and structures. Increased anthropogenic CO2 invasion into the ocean results in fewer carbonate ions for shell and reef-forming organisms due to an increase in H+ ions, resulting in fewer and smaller calcifying organisms.

Impact on phytoplankton
Phytoplankton are vital to Earth systems forming the base of nearly every marine food web, as well as producing nearly 50% of oxygen in the atmosphere. Critical for global ecosystem functioning and services, phytoplankton are vary with environmental parameters such as, temperature, water column mixing, nutrients, sunlight, and consumption by grazers. Climate change results in fluctuations and modification of these parameters, which in turn may impact phytoplankton community composition, structure, and annual and seasonal dynamics. These impacts then affect the entire marine system. Satellite measurement and chlorophyll observations show decline in the number of phytoplankton, microorganisms that produce half of the earth's oxygen, absorb half of the world carbon dioxide and serve foundation of the entire marine food chain. The decline is probably linked to climate change. However, there are some measurements that show increases in the number of phytoplankton.

Coral bleaching
The warming ocean surface waters can lead to bleaching of the corals which can cause serious damage and/or coral death. Coral bleaching occurs when. In the Great Barrier Reef, before 1998 there were no such events. The first event happened in 1998 and after it they begun to occur more and more frequently so in the years 2016 - 2020 there were 3 of them.

Combined impact
Eventually the planet could warm to such a degree that the ocean's ability to dissolve oxygen would no longer exist, resulting in a worldwide dead zone. Dead zones, in combination with ocean acidification, may usher in an era where marine life in most forms would cease to exist, resulting in a sharp decline in the amount of oxygen generated through photosynthesis in surface waters. This disruption to the food chain will cascade upward, thinning out populations of primary consumers, secondary consumers, tertiary consumers, etc., as primary consumers being the initial victims of these phenomenon.