The Oceans Won’t Suffocate!

harbor fish kill

 

What’s Natural?

Published in Pacifica Tribune August 12, 2020

 

The Oceans Won’t Suffocate!

 

There is a saying in the journalistic community: ‘Bad news is  good news! Good news is no news!” Bad news sells papers. It’s internet click-bait. So, we’re bombarded with a disproportionate amount of fearful news. Unfortunately, scientific journals also succumb to the same profit incentives. Indeed, pictures of thousands of suffocated fish floating belly-up is very disturbing. However, media outlets amplified our fears with headlines like “A Horrifying New Study Found that the Ocean is on its Way to Suffocating by 2030”. Only slightly less sensational, the Smithsonian promoted one of their researchers articles as “Why Our Oceans Are Starting to Suffocate”, while the NY Times suggests “World’s Oceans Are Losing Oxygen Rapidly”.

 

 

Changing oxygen concentrations is determined by the balance between oxygen addition versus consumption. Oxygen is only added at the surface, via diffusion from the atmosphere or via photosynthesis.  The chemical wizardry of photosynthesis uses sunlight to break apart water molecules and generate new oxygen while creating organic matter. Although this organic matter forms the base of the ocean food web, its digestion and decay consumes oxygen.  Paradoxically, wherever the surface ocean food web is most bountiful, the waters below lose the most oxygen.

 

To analyze natural- versus human-caused losses of oxygen, we must consider how the supply of nutrients for photosynthesis differs between the open ocean and coastal oceans. In the open ocean digestion and decay of sinking organic matter consumes oxygen and releases nutrients  to be recycled. Those nutrients must then be upwelled from dark subsurface waters back into sunlit waters.

 

In contrast, the supply of nutrients to coastal waters is greatly affected by river discharge. In the early 20^th century, chemists learned to convert atmospheric nitrogen into biologically useful nitrogen fertilizer. Starting around 1950, agriculture doubled, then tripled their use of synthesized fertilizer. While greatly benefitting  human food supplies, increased fertilizer use coincided with decreasing coastal oxygen.

 

Coastal populations and sewage also increased. Sewage and fertilizer run-off combined to stimulate coastal algal blooms that produced excessive organic matter which sank to shallow (< 100 meters) ocean floors, where its decay consumed bottom water oxygen. Along the Texas-Louisiana coast, the term “dead zone” was first used by shrimp fishermen to describe the resulting seasonal disappearance of shrimp and other invertebrates from the ocean floor.

 

The good news is people are now preventing and restoring dead zones. Sewage treatment plants extract solids and recycle it as fertilizer and farmers are engaging in more judicious use of fertilizers.

 

In contrast, the open ocean contains natural, permanent “oxygen minimum zones” (OMZ) at depths between about 200 and 800 meters. OMZs are maintained by the constant supply of sinking organic matter but OMZ size fluctuates. While some researchers blame global warming for any OMZ expansion, the evidence points to natural climate change that affects upwelling and ocean circulation.  

 

 

 

For example, in the eastern Pacific natural El Nino events reduce photosynthesis which decreases the supply of organic matter. Less decay causes OMZ’s oxygen to increase. Conversely during a La Nina, enhanced upwelling stimulates photosynthesis and organic matter production. Increased decay then expands the area of depleted oxygen.  Similarly, during the Little Ice Age, upwelling and photosynthesis off the coast of Peru was reduced and oxygen increased. Since the mid 1800s, upwelling has increased and Peru boasts one of the world’s largest fisheries. However, the increase in decaying organic matter has steadily consumed oxygen, and Peru’s expanding OMZ is also the world’s largest.

 

 

 

Open ocean OMZs are ancient, allowing a highly diverse ecosystem to evolve and adapt to the low oxygen environment.  A great diversity of jellyfish, squid, krill, sea snails, and other invertebrates inhabit the OMZs. Sperm whales (i.e. Moby Dick) evolved to hunt abundant squid at those depths. Researchers estimate that 95% of the global ocean fish mass inhabits OMZ depths. Most of these abundant organisms migrate nightly to feed in surface waters, then during the day migrate back to depths where they digest their food, further reducing the oxygen.

 

Finally, the claim that global warming is causing OMZ’s to expand and oceans to suffocate is largely based on simplistic physics that less oxygen will dissolve from the atmosphere into warmer waters. Although that is true, the scientific consensus still finds most of the oceans’ surface is supersaturated with oxygen. That’s because warmer waters also stimulate photosynthesis and produce more oxygen. Some researchers found photosynthesis could contribute 2.4 times more new oxygen than is absorbed from the atmosphere.  Accordingly, scientists estimate  50% - 80% of the earth’s oxygen is produced by ocean plankton. Based on natural ocean dynamics and its historical changes, we can breathe easy. Global warming is not suffocating our oceans!

 

 

Jim Steele is director emeritus of the Sierra Nevada Field Campus, SFSU and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism.

 

Contact: naturalclimatechange@earthlink.net

 

 

 

  

Turtle-paced Recoveries

 

Green Turtle

Published in the Pacifica Tribune July 28, 2020

What’s Natural?

Turtle-paced Recoveries

Many humans are working hard to prevent any further extinctions of our plants and animals and with growing success. Pelicans are increasing and no longer endangered. Humpback whales are increasing at a rate of 12% per year. Mountain lions and bald eagles are increasingly abundant. In 1982 the California Condor had dwindled to just 25 individuals. A captive breeding program began and today there are about 325 individuals and condors are expanding back into their historical range. This summer, condors were seen in Sequoia National Park for the first time in 50 years.

Over-harvesting, loss of habitat and introduced species are the main causes of endangered species. The green sea turtle, prized for its meat and eggs, was seriously over-harvested and endangered. Their numbers continued to fall as beach resorts disturbed their traditional nesting sites. Many others were killed as by-catch in fishing nets. But several new studies report seeing an uptick in green turtles around the world. One of the world’s largest nesting rookeries, Raine Island off northeastern Australia, just experienced the most abundant nesting season as ~64,000 breeding turtles have arrived. What is the reason for these higher numbers?

Green Turtles nesting on Raine Island

There is a degree of certainty conservation efforts have been effective. Many countries have banned harvesting eggs or turtles for meat, although poaching remains a threat. Fishermen have developed Turtle Exclusion Devices that prevent turtles from being captured in their nets.  Still, it is extremely difficult to reliably measure the success of sea turtle conservation.

Green turtles feed primarily on low-calorie sea grass. The good news is sea grass thrives under higher concentrations of CO2. However, that diet limits turtle growth and it takes 10 to 25 years before turtles reach sexual maturity. So, even if today’s conservation efforts are successful, we won’t see today’s benefits for at least another 10 years when hatchlings return to their birth sites as breeding females.

Despite increasing populations, some researchers have been needlessly gripped by a global warming fear. Like several reptiles, a turtle’s gender is determined by the temperature of the incubating egg. Eggs at the top of a nest are warmed the most and become females. Just a 4° F cooler temperature will create males. Furthermore, sex ratio of turtles from nests along the northern Great Barrier Reef have averaged 88% to 99% females, while populations from the cooler southern Great Barrier Reef average about 66% female. So the fear is, if the earth warms only females will be born and the population goes extinct. But gender determination by temperature is not a fragile system.

Turtles evolved during the age of dinosaurs over 250 million years ago when global temperatures were much warmer. Palm trees grew along the coast of Antarctica and crocodiles roamed the Greenland coast 55 million years ago. Since then temperatures cooled and ice ages ensued, yet turtles did not become all males. Nonetheless, cooler temperatures are an immediate threat. Along the USA’s east coast, many turtles travel northward as waters warm with summer heat. But if they do not return south in time, autumn’s cooler temperatures paralyze them, stranding hundreds on east coast beaches. (Again, humans help out by flying rescued turtles back to warmer waters).

During the Holocene Optimum 6000 to 9000 years ago, temperatures were bout 1.8° F warmer than today without causing extinctions. In 1957, the Whittaker brothers petitioned Australia’s Queensland government to commercially harvest female turtles on Raine Island. They cited surveys that found over 99% of the turtles were female. That high percentage of females has remained despite 60 years of climate change and Raine island remains one of the world’s most abundant nesting sites.

There are good scientific reasons why 99% females are beneficial. Only female turtles go on shore to nest. Males remain offshore mating with every available female. One male fertilizes several females. On shore females suffer more mortality. They come ashore in the evening to avoid the deadly effects of the sun. If they do not return to the sea by early morning, they often die of heat exhaustion. Some females get disoriented or fall into pits, becoming stranded in the midday sun. Some flip over on uneven ground and cannot right themselves. On crowded beaches, some females become so exhausted from jostling with other females they return to the ocean without laying their eggs.

Nesting turtles can flip and die

Females may lay 2 to 5 clutches, each with 100 eggs, during the breeding season. This greatly depletes their energy. So, females only breed every 3 to 5 years, allowing time to replenish their body condition. Finally, it is estimated only 1 of every 1000 successfully hatched turtle ever survives to maturity. So the high percentage of females is certainly not a sign of impending global warming doom. It is an ancient breeding system that maximizes egg production and ensures the species’ survival.

Hatchling Ridley Turtles