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Marine Heatwaves Increasing in Intensity
Topic Started: 11 Apr 2018, 11:27 PM (86 Views)
skibboy
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Marine Heatwaves Increasing in Intensity

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BY MAREX 2018-04-10

An international study has demonstrated that marine heatwaves have increased globally over the past century in number, length and intensity as a direct result of warming oceans.

From 1925-2016, the researchers found the frequency of marine heatwaves had increased on average by 34 percent and the length of each heatwave had increased by 17 percent.

Combined, this led to a 54 percent increase in the number of marine heatwave days every year.

Heatwave frequency has increased for 97 percent of the global ocean surface, with the North Atlantic the only exception.

The study was co-authored by researchers from Australia's Centre of Excellence for Climate Extremes and Institute for Marine and Antarctic Studies (IMAS).

“Our research also found that from 1982 there was a noticeable acceleration of the trend in marine heatwaves,” said lead author Dr. Eric Oliver from Dalhousie University, Canada.
“While some of us may enjoy the warmer waters when we go swimming, these heatwaves have significant impacts on ecosystems, biodiversity, fisheries, tourism and aquaculture. There are often profound economic consequences that go hand in hand with these events.”

The researchers uses a definition of a marine heatwave that was recently agreed by an international working group.

In short, says Oliver, when daily ocean temperatures exceed a threshold for what is considered very warm at that time of year – technically, the 90th percentile, meaning it is only exceeded with a 10 percent chance – for at least five days, we call it a marine heatwave.

Marine heatwaves can be caused by a range of factors.

The most common drivers include ocean currents which can build up areas of warm water and air-sea heat flux, or warming through the ocean surface from the atmosphere.

Winds can enhance or suppress the warming in a marine heatwave, and climate modes like El Niño can change the likelihood of events occurring in certain regions.

Some recent examples of marine heatwaves include:

• In 2011, Western Australia saw a marine heatwave that shifted ecosystems from being dominated by kelp to being dominated by other seaweed.

That shift remained even after water temperatures returned to normal;

• In 2012, a marine heatwave in the Gulf of Maine led to an increase in lobsters but a crash in prices that seriously hurt the industry’s profits;

• Persistent warm water in the north Pacific from 2014-2016 led to fishery closures, mass strandings of marine mammals and harmful algal blooms along coastlines.

That heatwave even changed large-scale weather patterns in the Pacific Northwest;

• Tasmania’s intense marine heatwave in 2016 led to disease outbreaks and slowing in growth rates across aquaculture industries.

The researchers used a variety of observational datasets to reveal the trend of increasing marine heatwaves, combining satellite data with a range of century-long datasets taken from ships and various land-based measuring stations.

They then removed the influences of natural variability caused by the El Nino Southern Oscillation, the Pacific Decadal Oscillation and the Atlantic Multidecadal Oscillation to find the underlying trend.

“There was a clear relationship between the rise in global average sea-surface temperatures and the increase in marine heatwaves, much the same as we see increases in extreme heat events related to the increase in global average temperatures,” said IMAS co-author Professor Neil Holbrook.

The Intergovernmental Panel on Climate Change's fifth assessment report projects that the global ocean will continue to warm well into the 21st century.

The warming in the upper ocean is projected to be between 0.6°C and 2°C.

“With more than 90 percent of the heat from human caused global warming going into our oceans, it is likely marine heatwaves will continue to increase," says Holbrook.
"The next key stage for our research is to quantify exactly how much they may change. The results of these projections are likely to have significant implications for how our environment and economies adapt to this changing world.”

Source: Posted Image.com
Edited by skibboy, 11 Apr 2018, 11:28 PM.
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skibboy
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Climate change dials down Atlantic Ocean heating system

By Victoria Gill
Science correspondent, BBC News

7 hours ago

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The circulation system plays a "significant role" in regulating the Earth's climate by distributing heat around the globe

A significant shift in the system of ocean currents that helps keep parts of Europe warm could send temperatures in the UK lower, scientists have found.

They say the Atlantic Ocean circulation system is weaker now than it has been for more than 1,000 years - and has changed significantly in the past 150.

The study, in the journal Nature, says it may be a response to increased melting ice and is likely to continue.

Researchers say that could have an impact on Atlantic ecosystems.

Scientists involved in the Atlas project - the largest study of deep Atlantic ecosystems ever undertaken - say the impact will not be of the order played out in the 2004 Hollywood blockbuster The Day After Tomorrow.

But they say changes to the conveyor-belt-like system - also known as the Atlantic Meridional Overturning Circulation (Amoc) - could cool the North Atlantic and north-west Europe and transform some deep-ocean ecosystems.

That could also affect temperature-sensitive species like coral, and even Atlantic cod.

Posted Image
The Atlantic Meridional Overturning Circulation (Amoc) was the basis of the a 2004 science fiction blockbuster

Scientists believe the pattern is a response to fresh water from melting ice sheets being added to surface ocean water, meaning those surface waters "can't get very dense and sink".

"That puts a spanner in this whole system," lead researcher Dr David Thornalley, from University College London, explained.

The concept of this system "shutting down" was featured in The Day After Tomorrow.

"Obviously that was a sensationalised version," said Dr Thornally.

"But much of the underlying science was correct, and there would be significant changes to climate it if did undergo a catastrophic collapse - although the film made those effects much more catastrophic, and happening much more quickly - than would actually be the case."

Nonetheless, a change to the system could cool the North Atlantic and north-west Europe and transform some deep-ocean ecosystems.

That is why its measurement has been a key part of the Atlas project.

Scientists say understanding what is happening to Amoc will help them make much more accurate forecasts of our future climate.

Prof Murray Roberts, who co-ordinates the Atlas project at the University of Edinburgh, told BBC News: "The changes we're seeing now in deep Atlantic currents could have massive effects on ocean ecosystems.

"The deep Atlantic contains some of the world's oldest and most spectacular cold-water coral reef and deep-sea sponge grounds.

"These delicate ecosystems rely on ocean currents to supply their food and disperse their offspring. Ocean currents are like highways spreading larvae throughout the ocean and we know these ecosystems have been really sensitive to past changes in the Earth's climate."

To measure how the system has shifted over long timescales, researchers collected long cores of sediment from the sea floor.

The sediment was laid down by past ocean currents, so the size of the sediment grains in different layers provided a measure of the current's strength over time.

The results were also backed up by another study published in the same issue of Nature, led by researchers from the Potsdam Institute for Climate Impact Research in Germany.

This work looked at climate model data to confirm that sea-surface temperature patterns can be used as an indicator of Amoc's strength and revealing that it has been weakening even more rapidly since 1950 in response to recent global warming.

The scientists want to continue to study patterns in this crucial temperature-regulating system, to understand whether as ice sheets continue to melt, this could drive further slowdown - or even a shutdown of a system that regulates our climate.

Source: Posted Image.com
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