17-Sep-2019: Rising temperatures in Indian Ocean can boost Atlantic’s ocean currents
While greenhouse warming caused by human activity is heating up the Indian oceans, it is likely to boost a key system of currents in the Atlantic Ocean, that plays a key role in determining the weather across the world.
Atlantic meridional overturning circulation (AMOC) — which is sometimes referred to as the “Atlantic conveyor belt” — is one of the Earth’s largest water circulation systems where ocean currents move warm, salty water from the tropics to regions further north, such as western Europe and sends colder water south.
It aids in distributing heat and energy around the earth, as the warm water it carries releases heat into the atmosphere, and in absorbing and storing atmospheric carbon.
For thousands of years, AMOC has remained stable, but since the past 15 years, it has been weakening — a development that could have dramatic consequences for Europe and other parts of the Atlantic rim. Researchers have found that rising temperatures in the Indian Ocean can help boost the AMOC and delay slow down.
Warming in the Indian Ocean generates additional precipitation, which, in turn, draws more air from other parts of the world, including the Atlantic. The higher level of precipitation in the Indian Ocean will reduce precipitation in the Atlantic and increase salinity in the waters.
This saline water in the Atlantic, as it comes north via AMOC, will get cold much quicker than usual and sink faster, acting “as a jump start for AMOC, intensifying the circulation”. However, scientists don't know for how long this enhanced warming in Indian Ocean will continue. If other tropical oceans’ warming, especially the Pacific's, catches up with the Indian Ocean, the advantage for AMOC will stop.
Moreover, it isn't clear whether slowdown of AMOC is caused by global warming alone or it is a short-term anomaly related to natural ocean variability. There is a need to understand the importance of AMOC stability.
AMOC last witnessed a slowdown 15,000 to 17,000 years ago. It caused harsh winters in Europe, with more storms or a drier Sahel in Africa due to the downward shift of the tropical rain belt.
The mere possibility that the AMOC could collapse should be a strong reason for concern in an era when human activity is forcing significant changes to the Earth’s systems. Warming of the Indian Ocean is considered one of the most robust aspects of global warming.
1-Sep-2019: Influence of Southern Ocean on global climate control
Scientists have made a new discovery challenging the previous understanding of the link between the Southern Ocean and the atmospheric carbon dioxide levels. The study shows that, contrary to existing assumptions, biological processes far out at sea are the most important factors determining how the ocean absorbs carbon dioxide.
Carbon dioxide is absorbed in the surface oceans and stored in the deep seas, gradually, over a timescale of 100s to 1,000s years.
The Southern Ocean plays a critical role in how the carbon dioxide is taken out of the atmosphere, and knowing how it functions helps scientists understand this mechanism’s role during dramatic climate transitions in the past, such as the ice ages, and better predict the current and future climate change.
Whether carbon is released into the atmosphere or trapped in the deep ocean, is crucially determined by the transformation of the water from light to dense which is in turn caused by cooling at the ocean’s surface.
So researchers from the University of Southampton with British Antarctic Survey, University of East Anglia and the Alfred Wegener Institute in Germany, studied the ocean circulation and carbon concentration of the Weddell Gyre — a region lying east of the Antarctic Peninsula.
The team studied data collected as part of the ANDREX project (Antarctic Deep water Rates of Export) which measured the physical, biological, and chemical properties of the waters in the gyre between 2008 and 2010.
The data considered in this study showed unambiguously that, in the Weddell Gyre, the dominant process enabling the uptake of carbon dioxide from the atmosphere and its removal to the deep ocean included the role of phytoplanktons.
The researchers reasoned that as phytoplankton in the centre of the gyre grow and sink, they remove carbon from the surface of the ocean, causing an uptake of carbon dioxide from the atmosphere - a process known as the ‘biological carbon pump’.
From this, the team showed that the dominant factor driving the uptake of carbon from the atmosphere to the ocean was not related to dense water formation in the shallow seas close to Antarctica, but rather to biological processes further out in the sea.
The findings are important both for our understanding of climate transitions in the past, such as the ice ages, as well as our projections of future climate change. It will also help to shift the focus of future research towards the critical processes taking place in the Antarctic Gyres, rather than the historical focus on the shelf-sea regions.
18-Aug-2019: Iceland holds funeral for first glacier lost to climate change
Iceland has marked its first-ever loss of a glacier to climate change as scientists warn that hundreds of other ice sheets on the subarctic island risk the same fate.
As the world recently marked the warmest July ever on record, a bronze plaque was mounted on a bare rock in a ceremony on the barren terrain once covered by the Okjökull glacier in western Iceland.
Around 100 people walked up the mountain for the ceremony, including Iceland’s prime minister, Katrín Jakobsdóttir, the former UN human rights commissioner Mary Robinson, and local researchers and colleagues from the United States who pioneered the commemoration project.
The plaque bears the inscription “A letter to the future”, and is intended to raise awareness about the decline of glaciers and the effects of climate change. It is also labelled “415 ppm CO2”, referring to the record level of carbon dioxide measured in the atmosphere last May.
Iceland loses about 11bn tonnes of ice per year, and scientists fear all of the island’s 400-plus glaciers will be gone by 2200. Glaciers cover about 11% of the country’s surface.
Glaciologists stripped Okjökull of its glacier status in 2014, a first for Iceland. In 1890, the glacier ice covered 16 sq km (6.2 square miles) but by 2012 it measured just 0.7 sq km, according to a report from the University of Iceland in 2017.