The Oceans: Past, Present and Future

Jess Spear

Paleooceanographer and organiser for RISE Ireland


“The mud! Ye gods, imagine a cart full of whitish mud, filled with minutest shells, poured all wet and sticky and slimy on to some clean planks” 

Lord George Campbell of the HMS Challenger


At approximately 6 o’clock in the morning on 23 March 1875, an Italian hemp rope bearing a lead weight at one end and carrying 2 glass thermometers was tossed into the ocean. The sailors and scientists of the Challenger Expedition watched as the rope descended, noting the white markings every 25 fathoms (150 feet or 45 meters) to indicate the ocean’s depth. Two hours later, and plunging more than 8 kilometers beneath the surface, the weighted rope touched bottom at the Mariana Trench.

This was but one of the remarkable discoveries made during the 41-month journey around the world. From just before Christmas 1872 to May 1876 six scientists and around 200 sailors traversed nearly 70,000 nautical miles, stopping at 360 “stations” to survey the life and conditions in our ocean basins. The Challenger Expedition discovered more than 4,700 new species, including critters inhabiting the deepest part of the ocean, which at the time was thought to be completely barren of life. It demonstrated the rich biodiversity of marine life and complex terrain, marking the beginning of oceanography, the study of the past, present, and future conditions of our ocean.

One hundred and forty years later, squished into a tiny submersible, Victor Vescovo made just the third trip ever to the Mariana Trench. Out of his 200mm-thick window, he eagerly scanned the seafloor, looking for new forms of life. What did he find? A plastic bag.

The deep past

Over millions of years, ocean basins and continents change shape, expand and contract as they glide around on plates atop the mantle of the earth. They collide to form supercontinents and mountain chains, and then break apart as new ocean basins are born and others melt back into the earth. The sand at the beach was once an old mountain. Remember that the next time you walk on a sandy beach, barefoot, feeling the ancient mountains in between each toe.

The Atlantic Ocean basin is getting bigger. As the seafloor spreads, magma from inside the earth’s mantle rises to the top and cools, forming a chain of oceanic mountains, the Mid-Atlantic Ridge. Meanwhile, the Pacific Ocean basin is shrinking as the Pacific plate is plunging beneath the Phillipine sea plate. It is this process that created the Mariana Trench.

As continental and oceanic plates danced around the surface, life arose – very likely from the ocean – and evolved, from single-celled organisms to multicellular, from drifting, swimming, hunting to crawling, running, hopping, socialising, flying and dam-building. And on one of the many branches of the tree of life came climbing, walking, thinking beings capable of developing theories and tools to then look back in time and uncover what was. Knowing what came before can help us understand what will be; and, since our planet is covered in ocean, knowing what happened in the ocean is a big part of understanding earth’s climate.

Alterations in climate, big and small, are recorded by the earth itself – in the bubbles captured in glaciers and ice sheets, in the width of tree rings, and in the shells of marine organisms. Indeed, while most people would be familiar with ice cores and tree rings, the unsung heroine of climate science is the mighty Foraminifera (usually called forams for short)

These unicellular organisms have existed for around 500 million years, and handy for us, they construct a shell that records the ocean conditions in which they lived. They can tell us about the water cycle (was there more or less rainfall compared to today), how much ice was on land during ice ages (and therefore the global sea level), and how hot or cold was the ocean temperature. We can even look at past seasonal changes in ocean temperature as some species only live during the winter or are most prevalent during the summer. After a very short life of weeks to a few months, their micro shells end up buried in the mud on the seafloor, and over hundreds to millions of years, bit by bit, these mini time capsules preserve a record of the ocean. Paleoceanographers (scientists studying the ancient ocean) collect cores of the seafloor, wash away the mud and examine the unearthed shells.

More than 2,000 sediment cores have been collected from all over the world. Each core is sampled in millimeter or centimeter sections from top to the bottom, with the top bearing the most recently deposited material and the bottom the oldest. The microshells are washed from each sample, identified under a microscope (using the thinnest paint brush one can find!) and then analysed for chemical changes linked to changes in the ocean.

Reading these time capsules reveals the emergence, evolution, and destruction of ocean habitat, the 50 million-year cooling of the planet, the growth and decay of major ice sheets synchronised to changes in earth’s orbit, and the recent warming of the earth by human activity. From such tiny shells we’ve uncovered earth’s dynamic past. We can see its long periods of relatively stable climate as well as sudden, sharp shifts that destroyed habitats and wiped out entire species.

Around fifty-six million years ago such an event occurred – the Paleocene-Eocene Thermal Maximum (PETM). A massive release of greenhouse gases into the atmosphere caused the earth to suddenly warm. (Sound familiar?) Over 10,000 years ocean surface temperature skyrocketed by as much as 8 degrees. Like today, a big chunk of the carbon dioxide and methane released was absorbed by the oceans, causing the ocean to become more acidic and hostile to shell-building organisms. Oxygen levels plummeted in the deep ocean, likely because ocean circulation reduced. The impact on life as far as we can discern was varied, but for deep-dwelling Foraminifera it was disastrous. Between 30-50% of all species perished. It took roughly 100,000 years for greenhouse gases to be drawn down out of the atmosphere – by reacting with carbonate sediments on the seafloor coupled with chemical weathering of granite rocks.

Understanding the past is key to the present. The history of the ocean is not yet fully known and likely can’t be. The earth is too dynamic, too quick to destroy the archives recorded in the rocks and shells. Dense oceanic plates slide beneath continental plates, melting ancient seafloor as new seafloor is created. (The oldest seafloor, in the eastern Mediterranean Sea is a mere 340 million years in age and is part of a dying ocean.)

Yet, what we have uncovered so far underscores the connection between air, sea, and land. A massive change in one will ripple out into the rest of the earth system, causing further perturbations and radically altering ecosystems. Though the earth was very different 56 million years ago – it was much hotter than today and there were no ice sheets – the implications for today’s global warming are clear.


As part of the Challenger Expedition’s mission, sediments from the top of the seafloor (and so relatively recently deposited) were collected and sifted for microfossils. The forams identified and saved for future research now provide us with a snapshot of the ocean’s history from which we can measure changes over the last 140 years. Similar to photos of mountain glaciers from the 1970s to today, we can compare the specimens and the physical data (that is, temperature and salinity) to today’s conditions and see the mark of global warming.

The ocean has absorbed 90% of all the heat trapped by the increase in greenhouse gases. Water can hold a lot of heat – we all know this from the hot water bottles warming our feet on winter nights.  On the one hand, its relatively high heat capacity means it can absorb large quantities of energy without its overall temperature going up, resulting in a smaller increase in air temperature than we’d have otherwise. On the other hand, that energy is absorbed by deadly storms and thrown back at us land-dwellers nonetheless. We can’t escape it.

At the same time, just like we saw in the PETM, the uptake of carbon dioxide in the oceans – like the fizzy bubbles in cold soft drinks or champagne – is also making them more acidic. In fact, 30% of all CO2 emissions have dissolved into the ocean. This is bad news for anything that makes a shell: corals, clams, oysters, pteropods, and Foraminifera. Indeed, present day Foraminifera shells are nearly 80% thinner than the Challenger Foraminifera. The ocean presently is 30% more acidic than 200 years ago.

However, we are pumping greenhouse gases into the atmosphere ten times faster than during the Paleocene-Eocene Thermal Maximum. The CO2 concentration is now higher than it has been in the last 3 million years. There is no analog in earth’s past for what’s happening now. Unless we immediately halt the emissions, going to net zero emissions, globally, within the next two decades, we can expect things to get much, much worse.

Foraminifera are not only used to uncover past changes in the ocean and earth’s climate. They are also used in oil exploration, helping petroleum companies understand the age and past environment of sedimentary rocks and target certain areas for drilling.

How ironic (and sad) that the fossils of these magnificently simple and elegant organisms are used to unearth the very substance that is now polluting the environment of their descendants. And obviously, not just the Foraminifera will feel the impact. The entire, complex and delicate marine ecosystem – from the pteropods at the “bottom” of the food chain to the coral reefs providing habitat to thousands of other species – will be impacted. To what extent we can’t yet say for certain. But it won’t be good.

It’s not just the heat-trapping gases. Plastics made from oil (which accounts for 6-8 percent of all oil consumption, globally) are spreading to every area of the planet, from microplastics carried by the wind to the tops of some of the highest mountains to the plastic bag “discovered” by Victor Vescovo at the bottom of the ocean.

Ever year anywhere from 5-12 million metric tons of plastic waste is dumped into the oceans. That’s the equivalent of a garbage truck every minute of every day. By about 2050 scientists predict the combined weight of plastic in the ocean will be larger than all the fish.

The waste is concentrated in the world’s 5 ocean gyres – massive ocean vortices caused by the effect of the earth’s rotation on ocean currents. Most people are familiar with the massive one in the North Pacific – the Great Pacific Garbage Patch – which covers an area the size of Russia.

Unfortunately, the plastic doesn’t just float around, benign to its surroundings. Marine mammals and birds, thinking it’s food, eat bunches of it and starve because it can’t be broken down and fills their stomachs so they can’t ingest actual food. It also gets entangled in coral reefs, blocking light and oxygen, and releasing harmful toxins, which then allows disease to set in and kill the coral.

Not just the marine animals and birds are ingesting plastics, we are too. If you regularly eat raw oysters, a nice bowl of steamed mussels or linguine vongole, you could be consuming up to 11,000 tiny pieces of plastic every year. What’s dumped into the ocean doesn’t stay in the ocean. Whether we realise it or not, we are connected.


The ocean remains largely unexplored – only 1% of the seafloor and around 5% of the water. Though, it’s not for lack of trying. The first thermometers attached to the rope sent down by the Challenger expedition came up broken due to the immense pressure (1,000 times heavier than air). In addition, frigid temperatures, lack of light, and all that water make data collection extremely challenging. Satellite observations, which can more easily capture data over time, revealing seasonal changes, average conditions, and what is or is not anomalous, are limited simply because water is not an easy veil to pierce. Still, what awe-inspiring wonders we have discovered.


When I was about ten years old, I found a box of shells my dad collected from scuba diving excursions in Florida. What creatures could make such beautiful and oddly shaped homes, I wondered. There was also a book he kept, Life in the Oceans, that I poured over, memorising the names of brilliantly coloured fish and wishing I could see them in real life. Around a decade later I sat in my college dorm room eagerly recording each episode of the BBC series Blue Planet so I could watch it again and again (this was clearly before everything and anything could be found online and on demand streaming!). The newest episodes, released in 2017, were the most popular show in Britain, and basically broke the internet in China from the sheer number of people downloading episodes.

David Attenborough, narrator of the Blue Planet series says

“Never before have we had such an awareness, never before have we had the power to do something. Surely we have a responsibility to care for our blue planet.” But the reality is that never before have people been so overwhelmed by the scale and magnitude of the problem, felt compelled and motivated to do something, but then simultaneously are provided with individual-focused solutions – stop using plastic straws and plastics – that aren’t really feasible with their busy lives and feel wholly inadequate.

How will refusing plastic straws prevent the big fishing industry from dumping their plastic nets, which make up nearly half of the plastic debris in the Great Pacific Garbage Patch? How do we stop the oil spills, the oil drilling, the overfishing, the chemical runoff from factory farms, commercial whale hunting, dredging (scraping the seafloor, destroying the ecosystem), and the greenhouse gases spewing into the air?  How do we stop all the destruction on land, too, which inevitably affects the ocean?

Even if we were successful in banning the use of all non-recyclable plastics in consumer products, which we should absolutely fight for, there would still be huge amounts of plastic still being dumped or lost in the ocean. Capitalist production would still reign supreme. The oceans would still be used as a dumping ground for pollution from the air and the land.

Let’s face it, what happens in the ocean, most of the time, is out of sight, out of mind. We can’t see the impact of ocean acidification or warming. Yes, you can read about it. You can see photos and hear reports from scientific studies warning of the dangers. But we will feel the impact of this destruction. We already are, really. We just haven’t yet connected the dots firmly in our minds.

With sea level rise, superstorms, mega droughts, crop failure, and mass species extinction nature is forcing us to see what capitalism denies, the interconnectedness of all life. And, that ours is an ocean planet. If we allow business-as-usual to continue on, the impact on us will become greater and more severe.

As Karl Marx put it in 1844, “Nature is our inorganic body, that is to say, nature in so far as it is not the human body. Humans live from nature . . . and we must maintain a continuing dialogue with it if we are not to die. To say that our physical and mental life is linked to nature simply means that nature is linked to itself, for humans are a part of nature.”

How can we stop the destruction? Let us start by taking all this in, from the history of our ocean told by the tiny Foraminifera, the discoveries of wondrous and spectacular marine life from the first oceanographic voyage by Challenger to today, to the knowledge that our society, as organised today under capitalism is “poking an angry beast”. Take it all in, and combine it with the other facts about life under capitalism – immense poverty, war, rampant inequality, racism, sexism, homophobia, and transphobia. All this needless suffering so the already monstrously rich can get richer. And then act. Act with an understanding that small tinkering here and there, that blames individuals while letting big business off the hook, isn’t going to work. The ocean will remind us of this if we dare ignore it. Act with confidence that the desire to protect our oceans (and ourselves) is clearly widespread.

Collectively, we can remake our world with the needs of people and nature at the heart of our economy. We don’t have to go on as is. Indeed we cannot go on as is. Let us reimagine a beautiful, socialist world on our magnificent blue planet and fight to make that a reality.


DisclaimerOpinions expressed in articles are the author’s and do not necessarily reflect the views of other members of the Global Ecosocialist Network

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Jess Spear
About Jess Spear 4 Articles
Paleoceanographer and National Organiser for RISE

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