By Dahr Jamail / Al Jazeera

A drumbeat of recent scientific studies emphasises an increasingly alarming convergence of crises for Earth’s oceans.

The amount of plastic floating in the Pacific Gyre – a massive swirling vortex of rubbish – has increased 100-fold in the past four decades, phytoplankton counts are dropping, over-fishing is causing dramatic decreases in fish populations, decreasing ocean salinity is intensifying weather extremes, and warming oceans are speeding up Antarctic melting.

One warning of humanity’s increasingly deleterious impact on the oceans came from prominent marine biologist Jeremy Jackson of the Scripps Institute of Oceanography.

In a 2008 article published in Proceedings of the National Academy of Sciences, Jackson warned that, without profound and prompt changes in human behaviour, we will cause a “mass extinction in the oceans with unknown ecological and evolutionary consequences”.

The statement might sound extreme, until one considers what science journalist Alanna Mitchell has written about the oceans: “Every tear you cry … ends up back in the ocean system. Every third molecule of carbon dioxide you exhale is absorbed into the ocean. Every second breath you take comes from the oxygen produced by plankton.”

These and other issues will be discussed at the Rio 20 United Nations Conference on Sustainability, which will be held between June 20 and 22 in Rio de Janeiro, Brazil.

But marine biologists, oceanographers, and others who study the seas are telling Al Jazeera of the deepening impact humans are having on the oceans, and, from what they are saying, now is the time to listen.

Plastic, plastic everywhere…

The most obvious impact humans are having on the world’s oceans is pollution. Though it can take myriad forms, pollution is now most shockingly evident in the seas in the form of giant, swirling gyres of plastic.

Scientists recently investigated the North Pacific Subtropical Gyre, known as the “Great Pacific Garbage Patch”, and found an “alarming amount” of refuse, much of it comprising individual pieces of very small size. The eastern section of the spiralling mass, between Hawaii and California, is estimated to be around twice the size of Texas, and is having ecosystem-wide impacts, according to their study released May 8.

Miriam Goldstein, a graduate student researcher at Scripps Institution of Oceanography at University of California San Diego, and the lead author of the study, told Al Jazeera that by adding this amount of plastic to the oceans, humans could be causing large-scale change to the ocean’s ecological system.

“We found eggs on the pieces of plastic, and these were sea-skater [insect] eggs,” Goldstein said. “Sea skaters naturally occur in the gyre and are known to lay their eggs on floating objects. So we found that the amount of eggs being laid had increased with the amount of plastic.”

Goldstein is also concerned by the findings because, “Our work shows there could be potential effects to the ocean ecosystem that we can’t expect or predict. There are five subtropical gyres, one in each ocean basin, and they are natural currents. They are vast areas of the oceans; together they comprise the majority of the area of the oceans. So altering them on a large scale could have unexpected results on all kinds of things.”

The study shows how an increase in pollution, in this case an immense amount of plastic, may have dire consequences for animals across the entire marine food web.

This Scripps study follows another report by colleagues at the institution that showed nine per cent of the fish collected during the trip to study the gyre had plastic waste in their stomachs.

Published in Marine Ecology Progress Series, that study estimated that fish at intermediate ocean depths in the North Pacific Ocean could be ingesting plastic at the staggering  rate of 12,000 to 24,000 tonnes per year.

Dr Wallace J Nichols, a research associate at the California Academy of Sciences, told Al Jazeera he finds plastic on every beach he visits across the globe, and added, “Probably every sea turtle on the planet interacts with plastic at some point in its life.”

Jo Royle, a trans-ocean skipper and ocean advocate, has seen the same.

“For 13 years I’ve been crossing oceans,” she told Al Jazeera. “I’ve seen plastic on the coastline of Antarctica, and over the years we’ve noticed plastic becoming more of an issue on remote islands. Over the last seven years we’ve seen it increase dramatically. I can’t remember the last time I’ve been on a beach and not seen plastic.”

Biological oceanographer Dr Debora Iglesias-Rodriguez, with the National Oceanography Centre at Britain’s University of Southampton, is also concerned.

“Marine pollution is a big issue,” she told Al Jazeera. “There is this idea that oceans have unlimited inertia, but nano-particles of plastic getting into marine animals and the food chain are affecting fish fertility rates, and this affects food security and coastal populations. Pollution is having a huge impact on the oceans, and is urgent and needs to be dealt with.”

Dead zones

Another phenomenon afflicting Earth’s oceans are “dead zones”.

While these can be formed by natural causes, climate change, along with human activities and industrial waste, have greatly aggravated the situation.

The US National Oceanographic and Atmospheric Administration released a study showing that rising global temperatures cause oceans to warm, which translates into a decreased capacity to hold oxygen.

The excessive use by industrial agriculture of chemical fertilisers containing phosphorus and nitrogen is the other key factor, since these chemicals encourage the increased development of algae – starving other marine life of oxygen.

The world’s second-largest and most heavily studied human-caused coastal dead zone is in the Gulf of Mexico, a zone caused by massive amounts of the aforementioned chemicals, along with other sources of nitrogen from animal feed, sewage treatment plants, and urban runoff from the Mississippi River flowing into the Gulf.

“All this pollution flows down and in the summer causes huge algae blooms,” Matt Rota, Science and Water Policy Director for the Gulf Restoration Network, told Al Jazeera. “These algae then die and sink to the bottom, where bacteria eat them and deplete the water of oxygen. And the water can’t mix to get more oxygen into it, so sea life suffocates and dies if it’s unable to swim away.”

The Gulf of Mexico dead zone varies in size and shape, but has been steadily increasing in size since it was first measured at 9,774 sq km in 1985. It forms annually at the mouth of the Mississippi River, and spans an area that encompasses the entire coast of Louisiana, and over to Texas.

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