Ocean Heating and Acidification: Difference between revisions

Revision as of 08:41, 30 September 2020

Increasing ocean stratification over the past half-century

28 September 2020 Guancheng Li, Lijing Cheng, Jiang Zhu, Kevin E. Trenberth, Michael E. Mann & John P. Abraham <embed>https://www.nature.com/articles/s41558-020-00918-2</embed>

Seawater generally forms stratified layers with lighter waters near the surface and denser waters at greater depth. This stable configuration acts as a barrier to water mixing that impacts the efficiency of vertical exchanges of heat, carbon, oxygen and other constituents. Previous quantification of stratification change has been limited to simple differencing of surface and 200-m depth changes and has neglected the spatial complexity of ocean density change. Here, we quantify changes in ocean stratification down to depths of 2,000 m using the squared buoyancy frequency N2 and newly available ocean temperature/salinity observations. We find that stratification globally has increased by a substantial 5.3% [5.0%, 5.8%] in recent decades (1960–2018) (the confidence interval is 5–95%); a rate of 0.90% per decade. Most of the increase (~71%) occurred in the upper 200 m of the ocean and resulted largely (>90%) from temperature changes, although salinity changes play an important role locally.

Ocean carbon uptake widely underestimated

Previous estimates of the movement of carbon (known as "flux") between the atmosphere and oceans have not accounted for temperature differences at the water's surface and a few metres below.
The new study, led by the University of Exeter, includes this—and finds significantly higher net flux of carbon into the oceans.
It calculates CO2 fluxes from 1992 to 2018, finding up to twice as much net flux in certain times and locations, compared to uncorrected models.

Harmful algae blooms in Arabian Sea linked to Himalayas melting

As snow and ice melt in the Himalayan mountains, the winter winds that blow down from them are becoming warmer and more humid, the researchers say. This alters the currents of the Arabian Sea and distribution of nutrients – and in turn the marine food chain, with fish struggling in the new conditions. This is happening at a much faster rate than that predicted by global models, the study says.

Climate velocity reveals increasing exposure of deep-ocean biodiversity to future warming

Moreover, projected climate velocities in the future (2050–2100) are faster for all depth layers, except at the surface, under the most aggressive GHG mitigation pathway considered (representative concentration pathway, RCP 2.6). This suggests that while mitigation could limit climate change threats for surface biodiversity, deep-ocean biodiversity faces an unavoidable escalation in climate velocities, most prominently in the mesopelagic (200–1,000 m). To optimize opportunities for climate adaptation among deep-ocean communities, future open-ocean protected areas must be designed to retain species moving at different speeds at different depths under climate change while managing non-climate threats, such as fishing and mining.

Ocean Discovery Complicates Plans to Slash Climate Pollution

Bloomberg News 6/05/20

Oceans have absorbed almost 40% of carbon dioxide humanity has emitted from fossil fuels since 1750, considerably slowing global temperature rise, but the forces that govern how much CO₂ disappears into the deep every year are unknown. The early 1990s saw a jump in this sponge-like capacity, followed by a significant slowdown until 2001, raising concerns that the ocean may not be able to help us out forever.

Global Temperature Anomalies from 1880 to 2018

2018 Fourth Warmest Year in Continuing Warming Trend, According to NASA, NOAA

Earth's global surface temperatures in 2018 were the fourth warmest since 1880, according to independent analyses by NASA and the National Oceanic and Atmospheric Administration (NOAA).

Global temperatures in 2018 were 1.5 degrees Fahrenheit (0.83 degrees Celsius) warmer than the 1951 to 1980 mean, according to scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York. Globally, 2018's temperatures rank behind those of 2016, 2017 and 2015. The past five years are, collectively, the warmest years in the modern record.

“2018 is yet again an extremely warm year on top of a long-term global warming trend,” said GISS Director Gavin Schmidt.

Oceans losing oxygen at unprecedented rate, experts warn

Oxygen in the oceans is being lost at an unprecedented rate, with “dead zones” proliferating and hundreds more areas showing oxygen dangerously depleted, as a result of the climate emergency and intensive farming, experts have warned.

Sharks, tuna, marlin and other large fish species were at particular risk, scientists said, with many vital ecosystems in danger of collapse. Dead zones – where oxygen is effectively absent – have quadrupled in extent in the last half-century, and there are also at least 700 areas where oxygen is at dangerously low levels, up from 45 when research was undertaken in the 1960s.

The world’s oceans are already being overfished, and assailed by a rising tide of plastic waste, as well as other pollutants. Seas are about 26% more acidic than in pre-industrial times because of absorbing the excess carbon dioxide in the atmosphere, according to the Intergovernmental Panel on Climate Change, with damaging impacts on shellfish in particular.

Why is an ocean current critical to world weather losing steam? Scientists search the Arctic for answers.

Fram Strait and the waters to the south, in the Greenland, Norwegian, and Irminger seas, make up the control room of a global “conveyor belt” of currents that stretches the length of the planet. Only in this region and one other, in the Antarctic, does water at the sea surface become heavy enough—dense with cold and salt—to sink all the way to the seafloor and race downhill along the deepening ocean bottom. That sinking powers the conveyor, known as the Atlantic meridional overturning circulation, or AMOC—which in turn regulates temperatures and weather around the world.

A new report warns that the AMOC is one of nine critical climate systems that greenhouse-gas-fueled warming is actively pushing toward a tipping point. Crossing that threshold in one of these systems could trigger rapid and irreversible changes that drive other systems over the edge—leading to a global tipping cascade with catastrophic consequences for the planet. The analysis, released last week in Nature by an international group of leading climate scientists, says the tipping point risks are greater than most of us realize.

The AMOC conveyor belt may already be showing signs of sputtering as a result. A network of ocean probes across the mid-Atlantic, between the Bahamas and Africa, has recorded a 15 percent drop in the current’s flow over the past decade. A recent modeling study suggests that the slowdown began a half-century ago as planet-warming carbon emissions started to soar.

Ocean Acidification's impact on oysters and other shellfish

HARI SREENIVASAN: But there's trouble in the water. The ocean's pH, which measures the level of acidity of a liquid, shows the water is becoming acidified. Most growers like the Wysockis can only farm oysters if they can buy oyster larvae, also called oyster seed, from hatcheries. But a few years ago, the larvae suddenly began dying by the billions. The culprit? The seawater pumped into the hatcheries is so corrosive that it eats away the young oyster shells before they can form.

Acid oceans are shrinking plankton, fuelling faster climate change

In our study we discovered increased seawater acidity reduced Antarctic phytoplanktons’ ability to build strong cell walls, making them smaller and less effective at storing carbon. At current rates of seawater acidification, we could see this effect before the end of the century.

Global alteration of ocean ecosystem functioning due to increasing human CO2 emissions

Ocean warming and acidification have received increasing focus as global change stressors, but marine species will also be impacted in their performance by other emerging stressors such as changes in sea surface height, UV, underwater irradiance, water salinity, and seawater oxygen content (7). Hypoxic zones are becoming widespread in oceanic as well as shelf environments because of climate change and local stressors such as eutrophication (37). Many species will be challenged by the interactive effects of ocean warming, acidification, and deoxygenation, but at present, hardly any (multistressors) studies exist to evaluate the effects of hypoxia on marine species and ecosystems (8, 38). For some species, there are opportunities to move to deeper waters or extend their ranges to higher latitudes, but not all species will be able to keep up with the pace of climate change, leading to alterations in current species distributions (39, 40). Moreover, species that have fewer generations (e.g., k strategists with greater longevity and later maturation) have fewer opportunities to adapt to rapidly changing conditions forecast for the next ∼85 y. Unless longer-lived species relocate to climate refugia

A study of 632 published experiments of the world’s oceans, from tropical to arctic waters, spanning coral reefs and the open seas, found that climate change is whittling away the diversity and abundance of marine species.
The paper, published in the Proceedings of the National Academy of Sciences, found there was “limited scope” for animals to deal with warming waters and acidification, with very few species escaping the negative impact of increasing carbon dioxide dissolution in the oceans.

Phytoplankton Population Drops 40 Percent Since 1950

Researchers at Canada's Dalhousie University say the global population of phytoplankton has fallen about 40 percent since 1950. That translates to an annual drop of about 1 percent of the average plankton population between 1899 and 2008.
The scientists believe that rising sea surface temperatures are to blame.
"It's very disturbing to think about the potential implications of a century-long decline of the base of the food chain," said lead author Daniel Boyce, a marine ecologist.

Critical Ocean Organisms Are Disappearing

Science Mag 7/28/2019

he number of marine phytoplankton, the microscopic organisms that gobble greenhouse gases and directly or indirectly feed every animal in the ocean, has been declining by about 1% of the global average per year, according to a new study. If the trend continues, it could decimate ocean food chains and accelerate global warming.

Icebergs delay Southern Hemisphere future warming, study shows

Science Daily 8/12/2019

Future warming can accelerate the disintegration of the West Antarctic ice sheet. A large fraction of the ice will enter the Southern Ocean in form of icebergs, which melt and provide a cooling and freshening effect to the warmer and denser ocean water. This process will increase the formation of sea-ice and shift winds and ocean currents. The overall effect is a slowdown in the magnitude of human-induced Southern Hemispheric warming and sea-level rise, according to a new study.

Pacific Ocean's effect on Arctic warming

Science Daily 4/08/2019

The Arctic is experiencing larger and more rapid increases in temperature from global warming more than any other region, with sea-ice declining faster than predicted. This effect, known as Arctic amplification, is a well-established response that involves many positive feedback mechanisms in polar regions. Q7 What has not been well understood is how sea-surface temperature patterns and oceanic heat flow from Earth's different regions, including the temperate latitudes, affect these polar feedbacks. This new research suggests that the importance of changes occurring in the Pacific may have a stronger impact on Arctic climate than previously recognized.

Marine heatwaves kill coral instantly

Increasingly frequent marine heatwaves can lead to the almost instant death of corals, scientists working on the Great Barrier Reef have found. Scientists studying coral after a heat event discovered that extreme temperature rises decayed reefs much more rapidly than previously thought.

Rapid Coral Decay Is Associated with Marine Heatwave Mortality Events on Reefs

Severe marine heatwaves have recently become a common feature of global ocean conditions due to a rapidly changing climate [1, 2]. These increasingly severe thermal conditions are causing an unprecedented increase in the frequency and severity of mortality events in marine ecosystems, including on coral reefs [3]. The degradation of coral reefs will result in the collapse of ecosystem services that sustain over half a billion people globally [4, 5]. Here, we show that marine heatwave events on coral reefs are biologically distinct to how coral bleaching has been understood to date, in that heatwave conditions result in an immediate heat-induced mortality of the coral colony, rapid coral skeletal dissolution, and the loss of the three-dimensional reef structure.

Heatwaves 'cook' Great Barrier Reef corals

In surveying the 3,863 individual reefs that make up the system off Australia's north-east coast, scientists found that 29% of communities were affected. In some cases up to 90% of coral died, in a process known as bleaching.
This occurs when the stress of elevated temperatures causes a breakdown of the coral's symbiotic relationship with its algae, which provide the coral with energy to survive, and give the reef its distinctive colours.

Coral reefs head for 'knock-out punch'

A study of 100 reefs, published in Science Magazine, shows the interval between bleaching events in recent decades has shortened dramatically. It has gone from once every 25-30 years in the early 1980s to an average of just once every six years today.Bleaching is caused by anomalously warm water, which prompts coral polyps to eject their symbiotic algae.This drains the corals of their colour and is fatal unless conditions are reversed in a reasonably short time. But even if temperatures fall back quickly, it can still take many years for damaged reefs to fully recover.

Record Warm Water Likely Gave Kuskokwim Salmon Heart Attacks

KYUK 7/12/2019

Earlier this week, water temperatures near Bethel broke into the lower 70s, marking the highest river temperature that’s ever been recorded in early July. This spell was part of a heat wave that shot thermometers to their highest point ever in towns across Alaska.
During this time, residents along the lower Kuskokwim River from Tuntutuliak to Akiak reported dead salmon floating downstream. Salmon don’t function well past 70 degrees, and the water had pushed just above that limit.

Climate Change is Weakening an Ocean Current

Both studies found that melting ice from Greenland has spilled huge quantities of freshwater into the North Atlantic, diluting the dense salinity of North Atlantic currents and weakening the AMOC by 15 percent. However, the results disagree on when the changes started.
For decades, scientists have worried that human-caused global warming could weaken this system and drastically alter weather patterns. It’s an idea best known from the scientifically and cinematically awful 2004 film The Day After Tomorrow.

Heatwaves sweeping oceans ‘like wildfires’, scientists reveal

The number of heatwaves affecting the planet’s oceans has increased sharply, scientists have revealed, killing swathes of sea-life like “wildfires that take out huge areas of forest”.
The damage caused in these hotspots is also harmful for humanity, which relies on the oceans for oxygen, food, storm protection and the removal of climate-warming carbon dioxide the atmosphere, they say.

Historical photographs revisited: A case study for dating and characterizing recent loss of coral cover on the inshore Great Barrier Reef

Monitoring programs within the Great Barrier Reef World Heritage Area (GBRWHA) have recently revealed dramatic losses in coral cover on the mid-shelf and offshore reefs1. Declining water quality as a result of rapid coastal development since European settlement (c.1850) in conjunction with crown-of-thorns starfish outbreaks and coral bleaching, is believed to have also resulted in a decline in coral cover and changes in community composition on inshore reefs2,3,4,5. This rather austere outlook is further exacerbated by the Great Barrier Reef (GBR) contentiously being argued as not the best managed reef in the world, with delays in water quality improvement programs and the threat of increased port development along the Queensland coastline6,7. The seriousness of the current state of the GBR has manifested in its potential delisting from World Heritage to World Heritage in Danger by the United Nations Educational, Scientific and Cultural Organisation (UNESCO).

Ocean acidification is already harming the Great Barrier Reef’s growth

It was clear from our results that reef calcification was around 7% higher under pre-industrial conditions than those experienced today.
Our work provides the first strong evidence from experiments on a natural ecosystem that ocean acidification is already causing reefs to grow more slowly than they did 100 years ago. Ocean acidification is already taking its toll on coral reef communities. This is no longer a fear for the future; it is the reality of today.

1 Climate velocity reveals increasing exposure of deep-ocean biodiversity to future warming 2 Ocean Discovery Complicates Plans to Slash Climate Pollution 3 Global Temperature Anomalies from 1880 to 2018 4 Oceans losing oxygen at unprecedented rate, experts warn 5 Why is an ocean current critical to world weather losing steam? Scientists search the Arctic for answers. 6 Ocean Acidification's impact on oysters and other shellfish 7 Acid oceans are shrinking plankton, fuelling faster climate change 8 Global alteration of ocean ecosystem functioning due to increasing human CO2 emissions 9 Phytoplankton Population Drops 40 Percent Since 1950 10 Critical Ocean Organisms Are Disappearing 11 Icebergs delay Southern Hemisphere future warming, study shows 12 Pacific Ocean's effect on Arctic warming 13 Marine heatwaves kill coral instantly 14 Rapid Coral Decay Is Associated with Marine Heatwave Mortality Events on Reefs 15 Heatwaves 'cook' Great Barrier Reef corals 16 Coral reefs head for 'knock-out punch' 17 Record Warm Water Likely Gave Kuskokwim Salmon Heart Attacks 18 Climate Change is Weakening an Ocean Current 19 Heatwaves sweeping oceans ‘like wildfires’, scientists reveal 20 Historical photographs revisited: A case study for dating and characterizing recent loss of coral cover on the inshore Great Barrier Reef 21 Ocean acidification is already harming the Great Barrier Reef’s growth