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Sea turtle coming to the surface of the ocean

Blue Planet II

Sir David Attenborough presents Blue Planet II.

About the programme

A generation on from the BBC Natural History Unit’s series The Blue Planet, Blue Planet II, presented by Sir David Attenborough, uses breakthroughs in marine science and cutting-edge technology to explore new worlds and reveal the very latest discoveries. This landmark seven-part series will bring viewers face to face with unexpected new landscapes and introduce compelling contemporary stories from our ocean.

Read more about the series on the BBC's programme pages , or explore the oceans in more detail below.

Thetitle screen for Blue Planet 2. It simultaneously shows a seal mid-swim in a lush underwater environment, with small fish in the background and, above this, what appears to be a walrus, sat on a floating block of ice

Copyright: The BBC

Terminus of Kangerlugssuup Sermerssua glacier in west Greenland. At the edge of an expansive glacier, its melting is evident as a pool has formed

Blue Planet II's message to humanity

Alongside the stunning photography and amazing stories, there's a serious warning in Blue Planet II that deserves our attention, say Miranda Dyson and Phil Sexton.

As expected, the first episode of Sir David Attenborough’s Blue Planet II has been greeted with rapturous applause. But alongside the gasps of delight at the beauty of the natural world, the programme came with an urgent message for viewers which we can no longer afford to ignore.

Produced by the BBC’s Natural History Unit  in partnership with the Open University, and narrated by the world’s favourite natural historian, the series revisits The Blue Planet after a gap of 16 years.

The series does what the BBC’s Natural History Unit does best – films the natural world in a fresh and compelling way using the latest technology. Blue Planet II allows the audience to get up close and personal to an array of extraordinary creatures that depend on and harness Earth’s vast oceans for their survival.

From the depths of the abyss where sunlight is absent and the pressure immense, to the wild rapidly changing coast, viewers are introduced to a variety of habitats and privy to remarkable behaviours, some of which have never been filmed before.

An ocean-going journey

By revealing the awe-inspiring nature of the oceans in a way the audience can connect with emotionally, Blue Planet II raises critical awareness of the immediate threats facing our oceans and underscores what we stand to lose by ignoring them.

The series is based around five ocean habitats, exploring the world of the animals that live there and the threats they face. There are many filming firsts: the ingenious tusk fish which uses rocks as an anvil to smash clam shells; co-operative hunting between bottlenose dolphins and false killer whales ; as well as a giant trevally  fish that hunts terns by plucking them out of the air. All that and sealions hunting as a co-ordinated pack, driving 60kg tuna into the shallows; as well as coral grouper and reef octopus hunting together and communicating using gestures – a behaviour usually associated with apes.

There are also behaviours that are new to science, such as an octopus that covers itself with shells to create a suit of armour to deter predators and female cuttlefish that flash a white stripe to indicate to amorous males an unwillingness to mate. Some of these uncovered behaviours demonstrate an intelligence that has been vastly underestimated.

As academic consultants on the series, we were captivated by the footage that leads viewers into this largely unexplored world from the perspective of the creatures that live there, capturing fascinating behaviour in exquisite detail.

But working on it also made us acutely aware how much humans and the planet stand to lose if we fail to recognise and acknowledge the negative impact we are having on the oceans. And it is this awareness which makes the timing of Blue Planet II so important. By revealing the awe-inspiring nature of the oceans in a way the audience can connect with emotionally, Blue Planet II raises critical awareness of the immediate threats facing our oceans and underscores what we stand to lose by ignoring them.


The cost of global warming and pollution

An industrial unit of grey buildings and tall chimneys releases fumes into the surrounding nature

Scientific research now overwhelmingly demonstrates that the ocean is changing. Sea surface temperatures have increased , levels of dissolved oxygen are declining , sea water has become more acidic  and food supplies have declined . The consequences are uncertain in their details but the rapidity and breadth of changes means that they will be profound.

Recent research  suggests that more than half the world’s oceans could suffer these multiple effects of rising carbon dioxide level over the next 15 years. By mid-century it is possible that more than 80% of oceans could be affected, forcing its inhabitants to migrate, adapt, or in some cases, face extinction.

It’s happening already. Huge swaths of coral reefs around the world have bleached  in recent years, and two-thirds of Australia’s Great Barrier Reef is affected  by coral bleaching. Seagrass meadows, kelp beds and mangrove forests are some of the most productive habitats on earth, storing vast amounts of carbon – but are also some of the most threatened. In 2015 and 2016 the worst instance of mangrove forest die-off  ever recorded occurred off the Australian coast.


Plastic debris floats on the open water - including bottles, packaging and even a shoe

And that is not all. The oceans are facing a major threat from pollution – by 2050 it is predicted  that without significant action there will be more plastic in the oceans than fish. It is estimated that between four and 12 metric tons of plastic makes its way into the oceans each year.

Nearly 700 marine species have been found entangled in plastic, and an increasing number – from microscopic plankton to whales – ingest it, compromising their ability to digest food, maintain body condition and give birth to healthy young. Persistent organic pollutants have been found  10km down in the Mariana trench , and are ingested by organisms that live there.

This is the more serious message that the series addresses alongside its spellbinding footage, particularly in the final episode that explores the struggle many species experience in the face of environmental change caused by humans.


A large  grey fishing vessel sits on the water while seagulls fly overhead

But, there is also a message of hope. Now we understand more fully the consequences of our actions we can act to stop or at least slow them. Some of the initiatives aimed at mitigating the damage humans have inflicted are highlighted in the final episode.

For example, overfishing in the 1950s resulted in the collapse of Norway’s herring stock, but better regulation and scientific monitoring has led to a spectacular recovery in numbers. Today, there is enough herring for both humans and the hundreds of humpback whales and orcas that feed on them. Ultimately though, keeping our oceans healthy and functioning properly will require bold leadership, motivation and coordinated effort on a global scale.

As Sir David Attenborough succinctly puts it: “For the first time in 500 million years, one species has the future in its hands.”

This article was originally published on The Conversation . Read the original article .


The life of almost all marine animals relies on the 'polar pumps' caused by rising and falling water. Philip Sexton explains how they work.

Episode 2 of Blue Planet II is centred around ‘The Deep’, a largely unknown world of brutal cold and utter darkness. The waters that fill the deep ocean form in restricted small areas of the ocean near the Poles, where surface waters become dense enough (via cooling and higher salinity) to sink into the abyss. These sinking waters thereby form the downwelling limbs of the deep ocean circulation system that flows throughout the ocean interior. The sinking happens in specific, restricted areas of the polar North Atlantic and the Southern Ocean. The deep water that is formed in the polar North Atlantic is referred to as North Atlantic Deep Water (NADW) whereas that in the Southern Ocean is referred to as Antarctic Bottom Water (AABW). These water masses are commonly distinguished by their contrasting temperatures and salinities, as you can see from the figure below of the distribution of salinity throughout the Atlantic Ocean.

A graph illustrating seawater salinity across various ocean water sources

The sinking of these polar surface waters into the abyss is essential for almost all marine animals, because these freshly formed deep waters are responsible for supplying the abyss with the oxygen required for animals to breathe. Without this regular re-supply of oxygen, the ocean interior would quickly become oxygen deficient (or even anoxic), posing a major threat to most marine life.

Deep water produced in the North Atlantic (NADW) is somewhat warmer and somewhat saltier than that produced in the Southern Ocean (AABW). Warmth reduces water density and salt increases it. So it appears that in the modern ocean, there must be a fine balance in the temperatures and salinities of the high latitude North Atlantic and Southern Ocean source waters that hence allow both NADW and AABW to occupy the modern abyss (but with NADW filling slightly more of the ocean interior than AABW, and thus being slightly denser than AABW).

With ongoing global warming it is predicted that upper ocean waters of both of these polar regions will become less dense (more ‘buoyant’) and thus less likely to sink, thereby weakening or collapsing the polar pumps that re-supply oxygen to the abyss. This increased surface buoyancy will arise from the warming of surface waters in a warmer climate, and from a stronger hydrological cycle and ice sheet melting, both of which serve to lower the salinity (and thus density too) of polar surface waters.

A low angle shot from the water of the sun hovering low over the sea.

Sunlight powered food: key for life on Earth

One chemical process, with energy from sun, is responsible for nearly all life on Earth. Pallavi Anand explains why that is the case.

Blue Planet II has shown many sequences of the bounty of life in our oceans: the feasting Mobular rays sequence (episode 1); a plankton bloom causing a “Manta cyclone” (episode 3); a shark finding the perfect location at Darwin’s arch to give birth because of the abundant food supply (episode 4); the plankton bloom in the seasonal seas (episode 5), and so on.

The main reason for all of these amazing sights are microscopic algae: phytoplankton. Phytoplankton bloom by utilising available nutrients and harnessing the energy from sunlight. The sunlight powers the process by which organisms and plants use the inorganic form of carbon (carbon dioxide), water and other dissolved nutrients in seawater to form organic compounds (such as lipids (a type of fat), proteins and sugars),  they produce oxygen as a by-product. The whole process is called photosynthesis and it happens in terrestrial plants too. This marine photosynthesis forms the basis for nearly all marine food chains and it is called primary production. Primary producers include marine algae (such as phytoplankton, a kelp forest), sea grasses and bacteria (such as blue green algae).

Plankton blooms from the topics to the poles depend on the availability of sunlight and nutrients

Moderate Resolution Imaging Spectroradiometer (MODIS) image showing phytoplankton bloom off the coast of France (bottom right) and the UK (top right). Image courtesy, Jeff Schmaltz, NASA.

There are two physical limitations for oceanic primary productivity: sunlight and nutrients. In the tropical region, even though sunlight is available year around, primary productivity is limited due to a lack of nutrients in the surface waters. As soon as all the available essential nutrients for growth have been utilised in the surface ocean, the plankton bloom ceases. These waters are vertically stable (we say stratified) because solar heating warms the sea surface and this prevents further supply of nutrients from deeper waters, unless there is mixing by eddies, turbulence and storms that can break this barrier.

In contrast, the polar regions have nutrients in plenty due to stronger winds mixing the waters, but sunlight is limited to the summer. This summer warmth also releases nutrients from melting sea ice so polar waters produce some of the largest seasonal plankton blooms.

In temperate latitudes, the primary productivity peaks twice: in the spring, and in the autumn when there is sufficient sunlight and nutrients.

This general pattern of global primary productivity can be supplemented with additional short-lived (for days or weeks) plankton blooms caused by storms and hurricanes supplying essential nutrients into the surface waters.


Marine photosynthesis also regulates atmospheric carbon dioxide

One-third of the carbon dioxide emitted by burning fossil fuels is captured by marine photosynthesis.

One-third of the carbon dioxide emitted by burning fossil fuels is captured by marine photosynthesis. The captured carbon, organic and inorganic (in calcifying plankton) along with nitrogen, phosphorous and other chemicals (bounded in the organic matter produced from photosynthesis), from the surface ocean is vertically transported. Most of the organic matter decays and components are recycled as subsurface nutrients, which can become available through mixing into the surface waters for more primary production. A small proportion reaches the deep providing food for the benthic organisms in the abyss, and an even smaller proportion gets buried in the sediments locking carbon away for millions of years. Although small, the latter is responsible for regulating the climate on Earth.

Additionally, a by-product of marine photosynthesis provides us with oxygen, a vital ingredient for sustaining majority of life forms on Earth. The marine photosynthesis accounts for approximately half of the oxygen produced on Earth and the other half comes from all the terrestrial plants combined.


The future of phytoplankton growth

The rising sea surface temperatures causing stratification, variable nutrient availability and changing seawater chemistry is likely to impact the growth of primary producers. Some research shows that the warming oceans will slow down the phytoplankton growth, and some computer models present unexpected results in the Southern Ocean, indicating primary productivity increasing in some regions and decreasing in others. We do need more observational data to fully understand the future of phytoplankton productivity in rapidly changing oceans.

If you would like to learn more about our oceans, the physical and chemical properties of seawater, the causes for the variability in seawater properties and ocean circulation, see our courses S206 Environmental Science and S309 Earth processes.


Meet the Experts

Dr Miranda DysonSenior Lecturer in Biology - School of Environment, Earth & Ecosystem SciencesVIEW FULL PROFILE
Dr Miranda DysonSenior Lecturer in Biology - School of Environment, Earth & Ecosystem Sciences

I am a Behavioural Ecologist and my primary interest lies with animal communication and sexual selection. Much of my research has focused on vocal communication with an emphasis on behavioural investigations of intraspecific female mate choice in anuran amphibians.

 I also have an interest in  fiddler crab reproductive behaviour and mate choice, the mating behaviour and male parental care in giant water bugs and duetting in birds. My current research interests include the relationship between bumblebees and snakeshead fritillaries on floodplain meadows. 

A photograph of Dr Philip Sexton
Philip SextonSenior LecturerVIEW FULL PROFILE
A photograph of Dr Philip Sexton
Philip SextonSenior Lecturer

I am a palaeoceanographer and foraminiferal micropalaeontologist. My research focuses on using the superb archive of marine plankton microfossils (foraminifera) contained in deep-seafloor sediments to tackle questions about how carbon cycles through the oceans, how oceans operated in past warm climates, and the role of climatic change in structuring ocean ecosystems and evolution. The foraminifer microfossil record is unparalleled, on land and sea, in its temporal resolution, continuity, chronological precision, spatial coverage, and ease with which biotic time series and palaeo-environmental reconstructions can be integrated. My work spans the disparate fields of the palaeoceanography of the very warm Eocene and the cold Pleistocene epochs, but with a unifying emphasis on understanding links between climatic variability, carbon cycling, and the biosphere in both end-member climate states.

A photograph of Dr Pallavi Anand
Pallavi AnandSenior Lecturer, Faculty of Science, Technology, Engineering & MathematicsVIEW FULL PROFILE
A photograph of Dr Pallavi Anand
Pallavi AnandSenior Lecturer, Faculty of Science, Technology, Engineering & Mathematics

Pallavi is an ocean biogeochemist in the School of Environment Earth and Ecosystem Sciences in the STEM faculty at the Open University. She also has a role of postgraduate research administration in the STEM faculty as a Deputy Associate Dean of postgraduate research (DAD-PGR). She has been invited to serve on various national/international external committees: Diversity Equity and Inclusion (DEI) of the European Association of Geochemistry and Geochemical Society (2020), the editorial board of Paleocenography and Paleoclimatology (2021) and Peer review group (panel C) of UK's National Environmental Isotope Facilities (2021).  

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