Seaweed

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Seaweed

Seaweed Informal group of macroscopic marine algae
Fucus serratus
Scientific classification
Domain:	Eukaryota
Seaweeds can be found in the following groups
Chlorophyta (green algae) Phaeophyceae (brown algae) Phaeothamniophyceae Chrysophyceae (gold algae) Cyanobacteria Rhodophyta (red algae)

Ascophyllum nodosum exposed to the sun in Nova Scotia, Canada

Dead man's fingers (Codium fragile) off the Massachusetts coast in the United States

The top of a kelp forest in Otago, New Zealand

Seaweed, or macroalgae, refers to thousands of species of macroscopic, multicellular, marine algae. The term includes some types of Rhodophyta (red), Phaeophyta (brown) and Chlorophyta (green) macroalgae. Seaweed species such as kelps provide essential nursery habitat for fisheries and other marine species and thus protect food sources; other species, such as planktonic algae, play a vital role in capturing carbon and producing at least 50% of Earth's oxygen.

Natural seaweed ecosystems are sometimes under threat from human activity. For example, mechanical dredging of kelp destroys the resource and dependent fisheries. Other forces also threaten some seaweed ecosystems; for example, a wasting disease in predators of purple urchins has led to an urchin population surge which has destroyed large kelp forest regions off the coast of California.

Humans have a long history of cultivating seaweeds for their uses. In recent years, seaweed farming has become a global agricultural practice, providing food, source material for various chemical uses (such as carrageenan), cattle feeds and fertilizers. Due to their importance in marine ecologies and for absorbing carbon dioxide, recent attention has been on cultivating seaweeds as a potential climate change mitigation strategy for biosequestration of carbon dioxide, alongside other benefits like nutrient pollution reduction, increased habitat for coastal aquatic species, and reducing local ocean acidification. The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic.

Taxonomy

"Seaweed" lacks a formal definition, but seaweed generally lives in the ocean and is visible to the naked eye. The term refers to both flowering plants submerged in the ocean, like eelgrass, as well as larger marine algae. Generally, it is one of several groups of multicellular algae; red, green and brown. They lack one common multicellular ancestor, forming a polyphyletic group. In addition, blue-green algae (Cyanobacteria) are occasionally considered in seaweed literature.

The number of seaweed species is still a topic of discussed among scientists, but it is most likely that there are several thousand species of seaweed.

Genera

Claudea elegans tetrasporangia

The following table lists a very few example genera of seaweed.

Genus		Algae Phylum	Remarks
Caulerpa		Green	Submerged.
Fucus		Brown	In intertidal zones on rocky shores.
Gracilaria		Red	Cultivated for food.
Laminaria		Brown	Also known as kelp 8–30 m under water and cultivated for food.
Macrocystis		Brown	Giant kelp forming floating canopies.
Monostroma		Green
Porphyra		Red	Intertidal zones in temperate climate and cultivated for food.
Sargassum		Brown	Pelagic especially in the Sargasso Sea.

Anatomy

Seaweed's appearance resembles non-woody terrestrial plants. Its anatomy includes:

• Thallus: algal body
  • Lamina or blade: flattened structure that is somewhat leaf-like
    • Sorus: spore cluster
    • pneumatocyst, air bladder: a flotation-assisting organ on the blade
    • Kelp, float: a flotation-assisting organ between the lamina and stipe
  • Stipe: stem-like structure, may be absent
  • Holdfast: basal structure providing attachment to a substrate
    • Haptera: finger-like extension of the holdfast that anchors to a benthic substrate

The stipe and blade are collectively known as the frond.

Ecology

Seaweed covers this rocky seabed on the east coast of Australia

Two environmental requirements dominate seaweed ecology. These are seawater (or at least brackish water) and light sufficient to support photosynthesis. Another common requirement is an attachment point, and therefore seaweed most commonly inhabits the littoral zone (nearshore waters) and within that zone, on rocky shores more than on sand or shingle. In addition, there are few genera (e.g., Sargassum and Gracilaria) which do not live attached to the sea floor, but float freely.

Seaweed occupies various ecological niches. At the surface, they are only wetted by the tops of sea spray, while some species may attach to a substrate several meters deep. In some areas, littoral seaweed colonies can extend miles out to sea. The deepest living seaweed are some species of red algae. Others have adapted to live in tidal rock pools. In this habitat, seaweed must withstand rapidly changing temperature and salinity and occasional drying.

Macroalgae and macroalgal detritus have also been shown to be an important food source for benthic organisms, because macroalgae shed old fronds. These macroalgal fronds tend to be utilized by benthos in the intertidal zone close to the shore. Alternatively, pneumatocysts (gas filled "bubbles") can keep the macroalgae thallus afloat; fronds are transported by wind and currents from the coast into the deep ocean. It has been shown that benthic organisms also at several 100 m tend to utilize these macroalgae remnants.

As macroalgae takes up carbon dioxide and releases oxygen in the photosynthesis, macroalgae fronds can also contribute to carbon sequestration in the ocean, when the macroalgal fronds drift offshore into the deep ocean basins and sink to the sea floor without being remineralized by organisms. The importance of this process for the Blue Carbon storage is currently a topic of discussion among scientists.

Biogeographic expansion

Nowadays a number of vectors - e.g., transport on ship hulls, exchanges among shellfish farmers, global warming, opening of trans-oceanic canals - all combine to enhance the transfer of exotic seaweeds to new environments. Since the piercing of the Suez Canal, the situation is particularly acute in the Mediterranean Sea, a 'marine biodiversity hotspot' that now registers over 120 newly introduced seaweed species -the largest number in the world.

Production

As of 2019, 35,818,961 tonnes were produced, of which 97.38% were produced in Asian countries.

Seaweed production

Country	tonns per year, cultured and wild
China	20,351,442
Indonesia	9,962,900
South Korea	1,821,475
Philippines	1,500,326
North Korea	603,000
Chile	427,508
Japan	412,300
Malaysia	188,110
Norway	163,197
United Republic of Tanzania	106,069

Farming

Seaweed farming or kelp farming is the practice of cultivating and harvesting seaweed. In its simplest form farmers gather from natural beds, while at the other extreme farmers fully control the crop's life cycle.

The seven most cultivated taxa are Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., Saccharina japonica, Undaria pinnatifida, Pyropia spp., and Sargassum fusiforme. Eucheuma and K. alvarezii are attractive for carrageenan (a gelling agent); Gracilaria is farmed for agar; the rest are eaten after limited processing. Seaweeds are different from mangroves and seagrasses, as they are photosynthetic algal organisms and are non-flowering.

The largest seaweed-producing countries as of 2022 are China (58.62%) and Indonesia (28.6%); followed by South Korea (5.09%) and the Philippines (4.19%). Other notable producers include North Korea (1.6%), Japan (1.15%), Malaysia (0.53%), Zanzibar (Tanzania, 0.5%), and Chile (0.3%). Seaweed farming has frequently been developed to improve economic conditions and to reduce fishing pressure.

The Food and Agriculture Organization (FAO), reported that world production in 2019 was over 35 million tonnes. North America produced some 23,000 tonnes of wet seaweed. Alaska, Maine, France, and Norway each more than doubled their seaweed production since 2018. As of 2019, seaweed represented 30% of marine aquaculture.

Seaweed farming is a carbon negative crop, with a high potential for climate change mitigation. The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic. World Wildlife Fund, Oceans 2050, and The Nature Conservancy publicly support expanded seaweed cultivation.

Uses

Further information: Seaweed farming § Uses

Seaweed has a variety of uses, for which it is farmed or foraged.

Food

Main article: Edible seaweed

Seaweed is consumed across the world, particularly in East Asia, e.g., Japan, China, Korea, Taiwan and Southeast Asia, e.g. Brunei, Singapore, Thailand, Burma, Cambodia, Vietnam, Indonesia, the Philippines, and Malaysia, as well as in South Africa, Belize, Peru, Chile, the Canadian Maritimes, Scandinavia, South West England, Ireland, Wales, Hawaii and California, and Scotland.

Gim (김, Korea), nori (海苔, Japan) and zicai (紫菜, China) are sheets of dried Porphyra used in soups, sushi or onigiri (rice balls). Gamet in the Philippines, from dried Pyropia, is also used as a flavoring ingredient for soups, salads and omelettes. Chondrus crispus ('Irish moss' or carrageenan moss) is used in food additives, along with Kappaphycus and Gigartinoid seaweed. Porphyra is used in Wales to make laverbread (sometimes with oat flour). In northern Belize, seaweed is mixed with milk, nutmeg, cinnamon and vanilla to make "dulce" ("sweet").

Alginate, agar and carrageenan are gelatinous seaweed products collectively known as hydrocolloids or phycocolloids. Hydrocolloids are food additives. The food industry exploits their gelling, water-retention, emulsifying and other physical properties. Agar is used in foods such as confectionery, meat and poultry products, desserts and beverages and moulded foods. Carrageenan is used in salad dressings and sauces, dietetic foods, and as a preservative in meat and fish, dairy items and baked goods.

Seaweeds are used as animal feeds. They have long been grazed by sheep, horses and cattle in Northern Europe, even though their nutritional benefits are questionable. Their protein content is low and their heavy metal content is high, especially for arsenic and iodine, which are respectively toxic and nutritious.

They are valued for fish production. Adding seaweed to livestock feed can substantially reduce methane emissions from cattle, but only from their feedlot emissions. As of 2021, feedlot emissions account for 11% of overall emissions from cattle. 

Medicine and herbs

See also: Fucoidan

Seaweed-covered rocks in the United Kingdom

Seaweed on rocks on Long Island

Alginates are used in wound dressings (see alginate dressing), and dental moulds. In microbiology, agar is used as a culture medium. Carrageenans, alginates and agaroses, with other macroalgal polysaccharides, have biomedicine applications. Delisea pulchra may interfere with bacterial colonization. Sulfated saccharides from red and green algae inhibit some DNA and RNA-enveloped viruses.

Seaweed extract is used in some diet pills. Other seaweed pills exploit the same effect as gastric banding, expanding in the stomach to make the stomach feel more full.

Climate change mitigation

Further information: Carbon sequestration and blue carbon

Seaweed cultivation in the open ocean can act as a form of carbon sequestration to mitigate climate change. Studies have reported that nearshore seaweed forests constitute a source of blue carbon, as seaweed detritus is carried into the middle and deep ocean thereby sequestering carbon. Macrocystis pyrifera (also known as giant kelp) sequesters carbon faster than any other species. It can reach 60 m in length and grow as rapidly as 50 cm a day. According to one study, covering 9% of the world’s oceans with kelp forests could produce “sufficient biomethane to replace all of today’s needs in fossil fuel energy, while removing 53 billion tons of CO2 per year from the atmosphere, restoring pre-industrial levels”.

Other uses

See also: Seaweed fertilizer and Seaweed fuel

Other seaweed may be used as fertilizer, compost for landscaping, or to combat beach erosion through burial in beach dunes.

Seaweed is under consideration as a potential source of bioethanol.

Seaweed is lifted out of the top of an algae scrubber/cultivator, to be discarded or used as food, fertilizer, or skin care

Alginates are used in industrial products such as paper coatings, adhesives, dyes, gels, explosives and in processes such as paper sizing, textile printing, hydro-mulching and drilling. Seaweed is an ingredient in toothpaste, cosmetics and paints. Seaweed is used for the production of bio yarn (a textile).

Several of these resources can be obtained from seaweed through biorefining.

Seaweed collecting is the process of collecting, drying and pressing seaweed. It was a popular pastime in the Victorian era and remains a hobby today. In some emerging countries, seaweed is harvested daily to support communities.

Women in Tanzania grow "Mwani" (seaweed in Swahili). The farms are made up of little sticks in neat rows in the warm, shallow water. Once they harvest the seaweed, it is used for many purposes: food, cosmetics, fabric, etc.

Seaweed is sometimes used to build roofs on houses on Læsø in Denmark

• 
  Onigiri and wakame miso soup, Japan
   
• 
  Laverbread and toast
   
• 
  Small plots being used to farm seaweed in Indonesia, with each rectangle belonging to a different family

Health risks

Rotting seaweed is a potent source of hydrogen sulfide, a highly toxic gas, and has been implicated in some incidents of apparent hydrogen-sulphide poisoning. It can cause vomiting and diarrhea.

The so-called "stinging seaweed" Microcoleus lyngbyaceus is a filamentous cyanobacteria which contains toxins including lyngbyatoxin-a and debromoaplysiatoxin. Direct skin contact can cause seaweed dermatitis characterized by painful, burning lesions that last for days.

Threats

Bacterial disease ice-ice infects Kappaphycus (red seaweed), turning its branches white. The disease caused heavy crop losses in the Philippines, Tanzania and Mozambique.

Sea urchin barrens have replaced kelp forests in multiple areas. They are "almost immune to starvation". Lifespans can exceed 50 years. When stressed by hunger, their jaws and teeth enlarge, and they form "fronts" and hunt for food collectively

Special Report on the Ocean and Cryosphere in a Changing Climate

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Special_Report_on_the_Ocean_and_Cryosphere_in_a_Changing_Climate

 

Intergovernmental Panel on
Climate Change

IPCC Assessment Reports

IPCC Special Reports

UNFCCC WMO UNEP

Cover of IPCC SROCC

The United Nations' Intergovernmental Panel on Climate Change's (IPCC) Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC) is a report about the effects of climate change on the world's seas, sea ice, icecaps and glaciers. It was approved at the IPCC's 51st Session (IPCC-51) in September 2019 in Monaco. The SROCC's approved Summary for Policymakers (SPM) was released on 25 September 2019. The 1,300-page report by 104 authors and editors representing 36 countries referred to 6,981 publications. The report is the third in the series of three Special Reports in the current Sixth Assessment Report (AR6) cycle, which began in 2015 and will be completed in 2022. The first was the Special Report on Global Warming of 1.5 °C, while the second was the Special Report on Climate Change and Land (SRCCL), also known as the "Special Report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems", which was released on 7 August 2019.

Main statements

SROCC summary for policymakers

"This highlights the urgency of prioritising timely, ambitious, coordinated and enduring action."

SRCCL summary for policymakers (SPM)

In its Summary for Policymakers (SPM), the report said that, since 1970, the "global ocean has warmed unabated" and "has taken up more than 90% of the excess heat in the climate system." The rate of ocean warming has "more than doubled" since 1993. Marine heatwaves are increasing in intensity and since 1982, they have "very likely doubled in frequency". Surface acidification has increased as the oceans absorb more CO₂. Ocean deoxygenation "has occurred from the surface to 1,000 m (3,300 ft)."

Rising sea levels

Main article: Sea level rise

Global mean sea levels (GMSL) rose by 3.66 mm (0.144 in) per year which is "2.5 times faster than the rate from 1900 to 1990". At the rate of acceleration, it "could reach around 30 cm (12 in) to 60 cm (24 in) by 2100 even if greenhouse gas emissions are sharply reduced and global warming is limited to well below 2 °C, but around 60 cm (24 in) to 110 cm (43 in) if emissions continue to increase strongly. In their summary of the SROCC, Carbon Brief said that rate of rising sea levels is "unprecedented" over the past century. Worst-case projections are higher than thought and a 2 metres (6.6 ft) rise by 2100 "cannot be ruled out", if greenhouse gas emissions continue to increase strongly."

Ocean deoxygenation

Main article: Ocean deoxygenation

The viability of species is being disrupted throughout the ocean food web due to changes in ocean chemistry. As the ocean warms, mixing between water layers decreases, resulting in less oxygen and nutrients being available for marine life.

Meridional overturning circulation in the Atlantic

Main article: Atlantic meridional overturning circulation

Chapter 6 which deals with ..., Atlantic meridional overturning circulation (AMOC) "will very likely weaken over the 21st century" but it is unlikely that AMOC will collapse. A weakening of AMOC would result in "a decrease in marine productivity in the North Atlantic, more winter storms in Europe, a reduction in Sahelian and South Asian summer rainfall, a decrease in the number of tropical cyclones in the Atlantic, and an increase in regional sea-level around the Atlantic especially along the northeast coast of North America." Carbon Brief described AMOC as "the system of currents in the Atlantic Ocean that brings warm water up to Europe from the tropics. It is driven by the formation of North Atlantic Deep Water – the sinking of cold, salty water in the high latitudes of the North Atlantic."

Melting glaciers

Main article: Retreat of glaciers since 1850

There has been an acceleration of glaciers melting in Greenland and Antarctica as well as in mountain glaciers around the world, from 2006 to 2015. This now represents a loss of 720 billion tons (653 billion metric tons) of ice a year.

Carbon Brief said that the melting of Greenland's ice sheets is "unprecedented in at least 350 years." The combined melting of Antarctic and Greenland ice sheets has contributed "700% more to sea levels" than in the 1990s.

Arctic sea ice decline

Main article: Arctic sea ice decline

The Arctic Ocean could be ice free in September "one year in three" if global warming continues to rise to 2 °C. Prior to industrialization, it was only "once in every hundred years".

Global marine animal biomass and fish catch decline

"Since about 1950 many marine species across various groups have undergone shifts in geographical range and seasonal activities in response to ocean warming, sea ice change and biogeochemical changes, such as oxygen loss, to their habitats."

SRCCL summary for policymakers (SPM)

In "Chapter 5: Changing Ocean, Marine Ecosystems, and Dependent Communities", the authors warn that marine organisms are being affected by ocean warming with direct impacts on human communities, fisheries, and food production. The Times said that it is likely that there will be a 15% decrease in the number of marine animals and a decrease of 21% to 24% in the "catches by fisheries in general" by the end of the 21st century because of climate change.

Decline of snow and lake ice cover

In "Chapter 3: Polar Regions", the authors reported that there has been a decline of snow and lake ice cover. From 1967 to 2018, the extent of snow in June decreased at a rate of "13.4 ± 5.4% per decade".

Thawing permafrost

Future climate-induced changes to permafrost "will drive habitat and biome shifts, with associated changes in the ranges and abundance of ecologically-important species." As permafrost soil melts, there is a possibility that carbon will be unleashed. The permafrost soil carbon pool is much "larger than carbon stored in plant biomass". "Expert assessment and laboratory soil incubation studies suggest that substantial quantities of C (tens to hundreds Pg C) could potentially be transferred from the permafrost carbon pool into the atmosphere under the Representative Concentration Pathway (RCP) 8.5" projection.

Low-lying islands and coasts

In the final section on low-lying islands and coasts (LLIC), the report says that cities and megacities—including New York City, Tokyo, Jakarta, Mumbai, Shanghai, Lagos And Cairo—are "at serious risk from climate-related ocean and cryosphere changes." If emissions remain high, some low-lying islands are likely to become "uninhabitable" by the end of the 21st century. Low lying areas including islands and the Low Elevation Coastal Zone were estimated have approximately 625 million people living in them based on 2000 estimates, with most in "non-developed contexts."

Reactions

The New York Times headlined their 25 September article with "We're All in Big Trouble". According to the Times, "Sea levels are rising at an ever-faster rate as ice and snow shrink, and oceans are getting more acidic and losing oxygen." The article cited Princeton University's Michael Oppenheimer, who was one of the report's lead authors who said that, "The oceans and the icy parts of the world are in big trouble, and that means we're all in big trouble, too. The changes are accelerating." IPCC Working Group I Co-Chair, Valérie Masson-Delmotte, was quoted as saying in Monaco, that "Climate change is already irreversible. Due to the heat uptake in the ocean, we can't go back."

The BBC headline referred to a red alert on the Blue Planet.

The Economist said that the "world's oceans are getting warmer, stormier and more acidic. They are becoming less productive as the ecosystems within them collapse. Melting glaciers and ice sheets are causing sea levels to rise, increasing the risk of inundation and devastation to hundreds of millions of people living in coastal areas."

PBS NewsHour cited National Oceanic and Atmospheric Administration's (NOAA) Ko Barrett, who is also a vice chair of IPCC, saying, "Taken together, these changes show that the world's ocean and cryosphere have been taking the heat for climate change for decades. The consequences for nature are sweeping and severe."

The Atlantic called it a blockbuster report.

National Geographic said that according to the report, "These challenges are only going to get worse unless countries make lightning-fast moves to eliminate greenhouse gas emissions... But strong, decisive action could still forestall or evade some of the worst impacts."

Ocean deoxygenation

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Ocean_deoxygenation

Global map of low and declining oxygen levels in coastal waters (mainly due to eutrophication) and in the open ocean (due to climate change). The map indicates coastal sites where oxygen levels have declined to less than 2 mg/L (red dots), as well as expanding ocean oxygen minimum zones at 300 metres (blue shaded regions).

Ocean deoxygenation is the reduction of the oxygen content in different parts of the ocean due to human activities. It occurs firstly in coastal zones where eutrophication has driven some quite rapid (in a few decades) declines in oxygen to very low levels. This type of ocean deoxygenation is also called "dead zones". Secondly, there is now an ongoing reduction in oxygen levels in the open ocean: naturally occurring low oxygen areas (so called oxygen minimum zones (OMZs)) are now expanding slowly. This expansion is happening as a consequence of human caused climate change. The resulting decrease in oxygen content of the oceans poses a threat to marine life, as well as to people who depend on marine life for nutrition or livelihood. Ocean deoxygenation poses implications for ocean productivity, nutrient cycling, carbon cycling, and marine habitats.

Ocean warming exacerbates ocean deoxygenation and further stresses marine organisms, reducing nutrient availability by increasing ocean stratification through density and solubility effects while at the same time increasing metabolic demand. The rising temperatures in the oceans cause a reduced solubility of oxygen in the water, which can explain about 50% of oxygen loss in the upper level of the ocean (>1000 m). Warmer ocean water holds less oxygen and is more buoyant than cooler water. This leads to reduced mixing of oxygenated water near the surface with deeper water, which naturally contains less oxygen. Warmer water also raises oxygen demand from living organisms; as a result, less oxygen is available for marine life.

Studies have shown that oceans have already lost 1-2% of their oxygen since the middle of the 20th century, and model simulations predict a decline of up to 7% in the global ocean O₂ content over the next hundred years. The decline of oxygen is projected to continue for a thousand years or more.

Terminology

The term ocean deoxygenation has been used increasingly by international scientific bodies because it captures the decreasing trend of the world ocean's oxygen inventory. Oceanographers and others have discussed what phrase best describes the phenomenon to non-specialists. Among the options considered have been ocean suffocation, ocean oxygen deprivation, decline in ocean oxygen, marine deoxygenation, ocean oxygen depletion and ocean hypoxia.

Types and mechanisms

There are two types of ocean deoxygenation, taking place in two different zones and having different causes: the reduction of oxygen in coastal zones versus in the open ocean as well as deep ocean (oxygen minimum zones). These are coupled but different.

Coastal zones

Red circles show the location and size of many dead zones (in 2008). Black dots show dead zones of unknown size. The size and number of marine dead zones—areas where the deep water is so low in dissolved oxygen that sea creatures cannot survive (except for some specialized bacteria)—have grown in the past half-century.

Coastal regions, such as the Baltic Sea, the northern Gulf of Mexico, and the Chesapeake Bay, as well as large enclosed water bodies like Lake Erie, have been affected by deoxygenation due to eutrophication. Excess nutrients are input into these systems by rivers, ultimately from urban and agricultural runoff and exacerbated by deforestation. These nutrients lead to high productivity that produces organic material that sinks to the bottom and is respired. The respiration of that organic material uses up the oxygen and causes hypoxia or anoxia.

Open and deep ocean zones (oxygen minimum zones)

Further information: Effects of climate change on oceans, Ocean stratification, and Ocean heat content

In the open ocean there are natural low oxygen areas and these are expanding slowly. These oceanic oxygen minimum zones (OMZ) generally occur in the middle depths of the ocean, from 100 – 1000 m deep. They are natural phenomena that result from respiration of sinking organic material produced in the surface ocean. However, as the oxygen content of the ocean decreases, oxygen minimum zones are expanding both vertically and horizontally. In these low oxygen areas the water circulation is slow. This stability means it is easier to see quite small changes in oxygen, such as a decline of 1-2%. In many of these areas, this decline does not mean these low oxygen regions become uninhabitable for fish and other marine life but over many decades may do, particularly in the Pacific and Indian Ocean.

Oxygen is input into the ocean at the surface, through the processes of photosynthesis by phytoplankton and mixing with the atmosphere. Organisms, both microbial and multicellular, use oxygen in respiration throughout the entire depth of the ocean, so when the supply of oxygen from the surface is less than the utilization of oxygen in deep water, oxygen loss occurs.

This phenomenon is natural, but is exacerbated with increased stratification and increasing ocean temperature. Stratification occurs when water masses with different properties, primarily temperature and salinity, are layered, with lower density water on top of higher density water. The larger the differences in the properties between layers, the less mixing occurs between the layers. Stratification is increased when the temperature of the surface ocean or the amount of freshwater input into the ocean from rivers and ice melt increases, enhancing ocean deoxygenation by reducing supply. Another factor that can reduce supply is the solubility of oxygen. As temperature and salinity increase, the solubility of oxygen decreases, meaning that less oxygen can be dissolved into water as it warms and becomes more salty.

Role of climate change

While oxygen minimum zones (OMZs) occur naturally, they can be exacerbated by human impacts like climate change and land-based pollution from agriculture and sewage. The prediction of current climate models and climate change scenarios is that substantial warming and loss of oxygen throughout the majority of the upper ocean will occur. Global warming increases ocean temperatures, especially in shallow coastal areas. When the water temperature increases, its ability to hold oxygen decreases, leading to oxygen concentrations going down in the water. This compounds the effects of eutrophication in coastal zones described above.

Open ocean areas with no oxygen have grown more than 1.7 million square miles in the last 50 years, and coastal waters have seen a tenfold increase in low-oxygen areas in the same time.

Measurement of dissolved oxygen in coastal and open ocean waters for the past 50 years has revealed a marked decline in oxygen content. This decline is associated with expanding spatial extent, expanding vertical extent, and prolonged duration of oxygen-poor conditions in all regions of the global oceans. Examinations of the spatial extent of OMZs in the past through paleoceanographical methods clearly shows that the spatial extent of OMZs has expanded through time, and this expansion is coupled to ocean warming and reduced ventilation of thermocline waters.

Research has attempted to model potential changes to OMZs as a result of rising global temperatures and human impact. This is challenging due to the many factors that could contribute to changes in OMZs. The factors used for modeling change in OMZs are numerous, and in some cases hard to measure or quantify. Some of the processes being studied are changes in oxygen gas solubility as a result of rising ocean temperatures, as well as changes in the amount of respiration and photosynthesis occurring around OMZs. Many studies have concluded that OMZs are expanding in multiple locations, but fluctuations of modern OMZs are still not fully understood. Existing Earth system models project considerable reductions in oxygen and other physical-chemical variables in the ocean due to climate change, with potential ramifications for ecosystems and humans.

The global decrease in oceanic oxygen content is statistically significant and emerging beyond the envelope of natural fluctuations. This trend of oxygen loss is accelerating, with widespread and obvious losses occurring after the 1980s. The rate and total content of oxygen loss varies by region, with the North Pacific emerging as a particular hotspot of deoxygenation due to the increased amount of time since its deep waters were last ventilated (see thermohaline circulation) and related high apparent oxygen utilization (AOU). Estimates of total oxygen loss in the global ocean range from 119 to 680 T mol decade⁻¹ since the 1950s. These estimates represent 2% of the global ocean oxygen inventory.

Melting of gas hydrates in bottom layers of water may result in the release of more methane from sediments and subsequent consumption of oxygen by aerobic respiration of methane to carbon dioxide. Another effect of climate change on oceans that causes ocean deoxygenation is circulation changes. As the ocean warms from the surface, stratification is expected to increase, which shows a tendency for slowing down ocean circulation, which then increases ocean deoxygenation.

Estimates for the future

The results from mathematical models show that global ocean oxygen loss rates will continue to accelerate up to 125 T mol year⁻¹ by 2100 due to persistent warming, a reduction in ventilation of deeper waters, increased biological oxygen demand, and the associated expansion of OMZs into shallower areas.

Variations

Expanding oxygen minimum zones (OMZ)

Several areas of the open ocean have naturally low oxygen concentration due to biological oxygen consumption that cannot be supported by the rate of oxygen input to the area from physical transport, air-sea mixing, or photosynthesis. These areas are called oxygen minimum zones (OMZs), and there is a wide variety of open ocean systems that experience these naturally low oxygen conditions, such as upwelling zones, deep basins of enclosed seas, and the cores of some mode-water eddies.

Ocean deoxygenation has led to suboxic, hypoxic, and anoxic conditions in both coastal waters and the open ocean. Since 1950, more than 500 sites in coastal waters have reported oxygen concentrations below 2 mg liter⁻¹, which is generally accepted as the threshold of hypoxic conditions.

The extent of OMZs has expanded in tropical oceans during the past half century.

Oxygen-poor waters of coastal and open ocean systems have largely been studied in isolation of each other, with researchers focusing on eutrophication-induced hypoxia in coastal waters and naturally occurring (without apparent direct input of anthropogenic nutrients) open ocean OMZs. However, coastal and open ocean oxygen-poor waters are highly interconnected and therefore both have seen an increase in the intensity, spatial extent, and temporal extent of deoxygenated conditions.

Drivers of hypoxia and ocean acidification intensification in upwelling shelf systems. Equatorward winds drive the upwelling of low dissolved oxygen (DO), high nutrient, and high dissolved inorganic carbon (DIC) water from above the oxygen minimum zone. Cross-shelf gradients in productivity and bottom water residence times drive the strength of DO (DIC) decrease (increase) as water transits across a productive continental shelf.

The spatial extent of deoxygenated conditions can vary widely. In coastal waters, regions with deoxygenated conditions can extend from less than one to many thousands of square kilometers. Open ocean OMZs exist in all ocean basins and have similar variation in spatial extent; an estimated 8% of global ocean volume is within OMZs. The largest OMZ is in the eastern tropical north Pacific and comprises 41% of this global volume, and the smallest OMZ is found in the eastern tropical North Atlantic and makes up only 5% of the global OMZ volume.

Vertical extent of low oxygen conditions

The vertical extent of low oxygen conditions is also variable, and areas of persistent low oxygen have annual variation in the upper and lower limits of oxygen-poor waters. Typically, OMZs are expected to occur at depths of about 200 to 1,000 meters. The upper limit of OMZs is characterized by a strong and rapid gradient in oxygenation, called the oxycline. The depth of the oxycline varies between OMZs, and is mainly affected by physical processes such as air-sea fluxes and vertical movement in the thermocline depth. The lower limit of OMZs is associated with the reduction in biological oxygen consumption, as the majority of organic matter is consumed and respired in the top 1,000 m of the vertical water column. Shallower coastal systems may see oxygen-poor waters extend to bottom waters, leading to negative effects on benthic communities.

Many persistent OMZs have increased in thickness over the last five decades. This happened because the upper limit of the OMZ became shallower and also because the OMZ expanded downward.

Variations in temporal duration

The temporal duration of oxygen-poor conditions can vary on seasonal, annual, or multi-decadal scales. Hypoxic conditions in coastal systems like the Gulf of Mexico are usually tied to discharges of rivers, thermohaline stratification of the water column, wind-driven forcing, and continental shelf circulation patterns. As such, there are seasonal and annual patterns in the initiation, persistence, and break down of intensely hypoxic conditions. Oxygen concentrations in open oceans and the margins between coastal areas and the open ocean may see variation in intensity, spatial extent, and temporal extent from multi-decadal oscillations in climatic conditions.

Coastal regions have also seen expanded spatial extent and temporal duration due to increased anthropogenic nutrient input and changes in regional circulation. Areas that have not previously experienced low oxygen conditions, like the coastal shelf of Oregon on the West coast of the United States, have recently and abruptly developed seasonal hypoxia.

Impacts

Further information: Effects of climate change on oceans

Ocean deoxygenation poses implications for ocean productivity, nutrient cycling, carbon cycling, and marine habitats. Studies have shown that oceans have already lost 1-2% of their oxygen since the middle of the 20th century, and model simulations predict a decline of up to 7% in the global ocean O₂ content over the next hundred years. The decline of oxygen is projected to continue for a thousand years or more.

The viability of species is being disrupted throughout the ocean food web due to changes in ocean chemistry. As the ocean warms, mixing between water layers decreases, resulting in less oxygen and nutrients being available for marine life.

Ocean deoxygenation is an additional stressor on marine life. Ocean deoxygenation results in the expansion of oxygen minimum zones in the oceans . Along with this ocean deoxygenation is caused by an imbalance of sources and sinks of oxygen in dissolved water. The change has been fairly rapid and poses a threat to fish and other types of marine life, as well as to people who depend on marine life for nutrition or livelihood. Ocean deoxygenation poses implications for ocean productivity, nutrient cycling, carbon cycling, and marine habitats.

As low oxygen zones expand vertically nearer to the surface, they can affect coastal upwelling systems such as the California Current on the coast of Oregon (US). These upwelling systems are driven by seasonal winds that force the surface waters near the coast to move offshore, which pulls deeper water up along the continental shelf. As the depth of the deoxygenated deeper water becomes shallower, more of the deoxygenated water can reach the continental shelf, causing coastal hypoxia and fish kills. Impacts of massive fish kills on the aquaculture industry are projected to be profound.

Marine organisms and biodiversity

Short term effects can be seen in acutely fatal circumstances, but other sublethal consequences can include impaired reproductive ability, reduced growth, and increase in diseased population. These can be attributed to the co-stressor effect. When an organism is already stressed, for example getting less oxygen than it would prefer, it does not do as well in other areas of its existence like reproduction, growth, and warding off disease. Additionally, warmer water not only holds less oxygen, but it also causes marine organisms to have higher metabolic rates, resulting in them using up available oxygen more quickly, lowering the oxygen concentration in the water even more and compounding the effects seen. Finally, for some organisms, habitat reduction will be a problem. Habitable zones in the water column are expected to compress and habitable seasons are expected to be shortened. If the water an organism's regular habitat sits in has oxygen concentrations lower than it can tolerate, it will not want to live there anymore. This leads to changed migration patterns as well as changed or reduced habitat area.

Long term effects can be seen on a broader scale of changes in biodiversity and food web makeup. Due to habitat change of many organisms, predator-prey relationships will be altered. For example, when squeezed into a smaller well-oxygenated area, predator-prey encounter rates will increase, causing an increase in predation, potentially putting strain on the prey population. Additionally, diversity of ecosystems in general is expected to decrease due to decrease in oxygen concentrations.

Effects on fisheries

See also: Microbiology of oxygen minimum zones and Human impact on marine life

Vertical expansion of tropical OMZs has reduced the area between the OMZ and surface. This means that many species that live near the surface, such as fish, could be affected periodically. Ongoing research is investigating how OMZ expansion affects food webs in these areas. Studies on OMZ expansion in the tropical Pacific and Atlantic have observed negative effects on fish populations and commercial fisheries that likely occurred from reduced habitat when the OMZ moved to a shallower depth.

A fish's behavior in response to ocean deoxygenation is based upon their tolerance to oxygen poor conditions. Species with low anoxic tolerance tend to undergo habitat compression in response to the expansion of OMZs. Fish species with a low tolerance for low oxygen conditions may move to live nearer the ocean surface where oxygen concentration will usually be higher. Biological responses to habitat compression can be varied. Some species of billfish, predatory pelagic predators such as sailfish and marlin, that have undergone habitat compression actually have increased growth since their prey, smaller pelagic fish, experienced the same habitat compression, resulting in increased prey vulnerability to billfishes. Fish with tolerance to anoxic conditions, such as jumbo squid and lanternfish, can remain active in anoxic environments at a reduced level, which can improve their survival by increasing avoidance of anoxia intolerant predators and have increased access to resources that their anoxia intolerant competitors cannot.

The relationship between zooplankton and low oxygen zones is complex and varies by species and life stage. Some gelatinous zooplankton reduce their growth rates when exposed to hypoxia while others utilize this habitat to forage on high prey concentrations with their growth rates unaffected. The ability of some gelatinous zooplankton to tolerate hypoxia may be attributed to the ability to store oxygen in intragel regions. The movements of zooplankton as a result of ocean deoxygenation can affect fisheries, global nitrogen cycling, and trophic relationships. These changes have the potential to have large economic and environmental consequences through overfishing or collapsed food webs.

Free Ocean CO2 Enrichment

From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Free_Ocean_CO2_Enrichment

Free Ocean CO₂ Enrichment (FOCE) is a technology facilitating studies of the consequences of ocean acidification for marine organisms and communities by enabling the precise control of CO₂ enrichment within in situ, partially open, experimental enclosures. Current FOCE systems control experimental CO₂ perturbations by real-time monitoring of differences in seawater pH between treatment (i.e. high-CO₂) and control (i.e. ambient) seawater within experimental enclosures.

Overview

In situ, controlled perturbation experiments, often conducted over weeks to months, can provide inference concerning the response of natural communities to ocean acidification that is difficult or impossible to derive from laboratory experiments. Studies conducted in situ can include the effects of potentially important factors such as natural variation in planktonic food resources, larval abundance, changes in predators or competitors, as well as oceanographic conditions (e.g. changes in upwelling intensity). Drawing on the experience of Free Air CO₂ Enrichment (FACE) experiments used to investigate the response of terrestrial plant communities to rising atmospheric CO₂ levels, the scientific community has developed an analogous approach, Free Ocean CO₂ Enrichment (FOCE) experiments, for studying marine communities, and to complement a range of experimental methods and technologies for ocean acidification studies research. FOCE was first proposed and implemented by researchers at the Monterey Bay Aquarium Research Institute (MBARI).

Purpose

As studies of the consequences of ocean acidification for marine organisms and ecosystems expanded rapidly over the past decade, the methods employed to evaluate the effects of expected future changes in ocean chemistry have become more sophisticated. Initial studies frequently involved measurements of the survival or physiological response of individuals of marine species to large changes in pCO2 or pH, while held in small containers under laboratory conditions. This approach increased the level of understanding of the effects of these environmental changes on individual species but provided little information concerning the response of natural assemblages of interacting species, in which the direct impacts of ocean acidification as well as their cascading indirect consequences (e.g. changes in the intensity of interaction strengths among predators or competitors) may be evident. Pelagic mesocosm experiments that examined the response of natural plankton communities to controlled pH perturbations helped move methods of ocean acidification research toward more comprehensive studies of whole communities and embedded processes under mostly natural conditions. The FOCE approach represents an analogous advance for benthic assemblages, by allowing examination of the direct effects of acidification on particular species, but also potential changes in interactions among species. Moreover, FOCE methods provide precise control of pH, while allowing many other parameters to vary naturally. Like mesocosm studies, FOCE methods exploit the advantages of studying a natural community under mostly natural ranges of environmental variability.

Methods

The key elements of any FOCE experimental units are perspex, partially open, chambers, a CO₂ mixing system, sensors to continuously monitor ambient and chamber pH, and a control loop to regulate the addition of gases or liquids to each experimental chamber.

The carbonate chemistry of seawater can be manipulated using different approaches to mimic future conditions. It is possible to directly inject gases (pure CO₂ or CO₂-enriched air) but this is more difficult than delivering water to achieve precise pH control. Current FOCE systems lower pH using metered addition of CO₂-enriched seawater into the experimental chambers. pH is controlled as a constant pH offset relative to ambient values, maintaining natural variability, or as a constant value.

Other approaches have been used to manipulate the seawater carbonate chemistry in the field. In pelagic mesocosm experiments, the carbonate chemistry is generally altered at the beginning of the experiment and subsequently drifts as a function of biological processes and air-sea gas transfer. CO₂ bubbling in open water has also been used. This approach does not enable precise control of the carbonate chemistry because it does not include a device to ensure full equilibration of added CO₂ in seawater and its precise control. There are no experimental chambers to regulate water flow, and thus allows for natural near-bottom flow conditions, but it generates highly variable pH under variable current speed or direction. This approach is therefore more similar to natural CO₂ vents than to FOCE systems. This approach can be useful when organisms can not be enclosed in chambers and when they inhabit environments such as estuaries where pCO2 levels are naturally hyper-variable. The approach has inherent limitations but may allow greater replication, at lower cost.

Current users of FOCE systems have organized to release guidelines and best practices information for future users. Furthermore, the Monterey Bay Aquarium Research Institute will release an open source package to transfer FOCE technology to interested researchers (xFOCE). This package will comprise all engineering information required to develop cost effective FOCE systems.

Future development of FOCE systems will include the study of the combined effects of ocean acidification and other environmental factors such as temperature or the concentration of dissolved oxygen.

Current FOCE Projects

Deep FOCE (dpFOCE)

A FOCE system for studies of deep-sea benthic communities (designated dp-FOCE) was developed by Monterey Bay Aquarium Research Institute. The dpFOCE project, deployed at a depth of 900 m, was attached to the MARS cabled seafloor observatory in Monterey Bay, central California. The system used a flume concept for maintaining greater control over the experimental volume while still maintaining access to natural seafloor sediments and suspended particulate material. Time-delay wings attached to either end of the dpFOCE chamber allow for tidally driven changes in near-bottom currents, and provide sufficient time for full hydration of the injected CO₂ enriched seawater before entering into the experiment chamber. Fans are integrated into the dpFOCE design to control flow rates through the experimental chamber and to simulate typical local-scale flow conditions. Multiple sensors (pH, CTD, ADV, and ADCP) used in conjunction with the fans and the enriched seawater injection system allow the control loop software to achieve the desired pH offset. dpFOCE connects to shore via the MARS cabled observatory, which provides power and data bandwidth. Enriched CO₂ seawater is produced from liquid CO₂ held in a small container near the dpFOCE chamber; seawater flowing slowly over the top of the liquid CO₂ dissolves some of the liquid CO₂ producing a CO₂-rich dissolution plume used for injection into the dpFOCE chamber. The dpFOCE system operated over 17 months and verified the effectiveness of the design hardware and software.

Coral Prototype FOCE (cpFOCE)

The cpFOCE uses replicate experimental flumes to enclose sections of a coral reef and dose them with CO₂-enriched seawater using peristaltic pumps with computer controlled feedback loop to maintain a specified pH offset from ambient conditions. A cpFOCE chamber has forward and rear flow conditioners on either end to accommodate bidirectional ocean currents. The openings are placed parallel to the dominant axis of tidal currents over the reef flat, and the chamber is anchored with sand stakes. The flow conditioners are attached to maximize turbulence and provide passive mixing of the CO₂ enriched seawater. Four of the tubes in the flow conditioners furthest from the chamber have small holes along their length through which low pH water is pumped to dispense it evenly along the entire width and height of the conditioner. The flow conditioners are also painted white to minimize heating and algal growth. The cpFOCE system was deployed at Heron Island (Great Barrier Reef) to investigate the response of coral communities to ocean acidification.

European FOCE (eFOCE)

The European FOCE (eFOCE) comprises two open-top chambers (control and experimental) as well as a surface buoy housing the electronics and pumps to produce CO₂-enriched water. The system is powered by solar and wind energy. Data packets are wirelessly sent to the nearby laboratory and can be monitored on the internet. The eFOCE system is currently deployed in the bay of Villefranche-sur-mer (France) at about 12 m depth and 300 m offshore. The eFOCE project has been developed to investigate the long-term effects of acidification on benthic marine communities of the North West Mediterranean Sea, especially Posidonia seagrass beds. Over a 3-year period, the aim of the project is to develop relatively long (> 6 month) experiments.

Shallow Water FOCE (swFOCE)

In collaboration with Hopkins Marine Station and the Center for Ocean Solutions, Monterey Bay Aquarium Research Institute is developing a swFOCE system to examine the effects of ocean acidification on shallow subtidal communities in central California. swFOCE will use a shore side station for the control system and production of CO₂ enriched seawater, and will also use and will use an existing cabled observational and research platform to connect the swFOCE node. Two swFOCE chambers will be installed initially at a depth of 15 m, approximately 250 m offshore. The nearby node of the cabled observatorynode, has instruments to monitor local currents, temperature, pH, and O2 in real-time, as a cabled observatory platform for scientific research.

Antarctic FOCE (AntFOCE)

The first polar FOCE (antFOCE) experiment was awarded funding in November 2012, followed by design and concept studies initiated in 2013. Installation and initial science experiments are planned for 2014. antFOCE is a collaborative effort between the University of Tasmania, Australian Antarctic Division, Antarctic Climate & Ecosystems Cooperative Research Centre, Monterey Bay Aquarium Research Institute and specialist ocean acidification policy advisors from the International Ocean Acidification Reference Users Group (IOA-RUG). The IOA-RUG will take the lead in communicating the outcomes of the FOCE experiment to global climate and ocean policy related organizations.