Part IV referred to the 40% decline of Phytoplankton since 1950 and the 80% decline of Krill since 1970. Global warming and rising sea temperatures are almost always cited as the cause.

Human emissions of greenhouse gases – carbon dioxide, nitrous oxide, methane, and others – have increased global temperatures by around 1℃ since pre-industrial times from 10 m tons in 1760 to 200 million tons in the 1850s to 15 billion in the 1970s with current levels around 36 billion tons. We are producing more CO2 but converting less into O2. Why is that?

We have been told that the cause of the phytoplankton population decline is climate change. Phytoplankton is the primary source of oxygen, the primary sink for CO2, and the ocean’s primary food source. Phytoplankton exists from the surface of the ocean to 200 meters or deeper over most of the world oceans, which covers 70% of the Earth’s surface.

Scientists at MIT, Woods Hole Oceanographic Institution and elsewhere have found evidence that phytoplankton's productivity is declining steadily in the North Atlantic, one of the world's most productive marine basins. Researchers at Canada's Dalhousie University believe that rising sea temperatures are driving the decline. As surface water warms, it tends to form a distinct layer that does not mix well with cooler, nutrient-rich water below, depriving phytoplankton of some of the materials they need to turn CO2 and sunlight into energy.

This last sentence is very interesting. Is there an underlying reason that the scientists have not fully comprehended? Could it be there is a slightly obscure reason that led to climate change and the creation of a vicious circle?

Look at the dates referred to earlier; 1850’s, 1970’s

Whaling became increasingly important in the Industrial Revolution from 1760 to 1840. The depletion of some whale species was brought to the brink of extinction. By the 1960s, more efficient catch methods and giant factory ships made it obvious that whale hunting could not go unchecked and this led to the banning of whaling in many countries by 1969, and to a worldwide cessation of whaling as an industry in the late 1980s. In 1946, whaling nations formed the International Whaling Commission (IWC) and attempted to make the industry more sustainable through gradual rules, quotas, and size limits. In 1986, all IWC members agreed to a hunting moratorium to allow whale numbers to recover.

An estimated 2.9 million whales were killed between in less than 100 years. Around 300,000 dolphins and porpoises are killed each year as a result by-catch.

Whaling continues (and in some countries, this is purportedly for scientific reasons) but whale and dolphin meat is still freely available on supermarket shelves. Whale catches in 2018 were around 1,600 of the larger species (mainly Minke and Sei) by Japan, Norway, Greenland (Denmark), Iceland (146 Fin Whales), Russia, USA and Indonesia (20 Humpbacks). Canada, Iceland, Japan, Norway, Russia, South Korea, the United States and the Danish dependencies of the Faroe Islands and Greenland continue to hunt in the 21st century. Countries that support commercial whaling, notably Iceland, Japan, and Norway, wish to lift the IWC moratorium on certain whale stocks for hunting.

Norway's whaling kills more whales than any other country even though it is limited to the minke whale, which is killed using explosive grenade harpoons. It has no plans to slow down, despite the global moratorium on commercial whaling enacted by the IWC. Norwegian whalers hunted 332 whales in 2019. Whaling in Norway involves subsidised hunting of minke whales for use as animal and human food in Norway and for export to Japan.

Japan continued whaling for scientific research on population data. But in 2019 left the IWC and resumed commercial whaling. Dolphin and whale meat is on supermarket shelves in Japan. Since 1987, Japan has killed between 200 and 1,200 whales each year, saying this was to monitor stocks to establish sustainable quotas. A report sent to the IWC revealed Japanese hunters in their "third biological field survey" caught 333 minke whales in their 2017/2018 hunt in the Southern Ocean. Of the 333 minkes caught, 152 were male and 181 were female. Of these 122 were pregnant and 61 males and 53 females were juveniles. The damage caused by this alone has far-reaching implications on future stocks.

In 2019 the Icelandic government announced it will allow up to 2,000 whales to be killed in the next five years. A Ministry of Fisheries and Agriculture statement said a maximum of 209 fin whales and 217 minke whales can be killed each year between 2018 and 2025.

During the Faroe's traditional annual festival, up to 1,000 pilot whales are killed every year in the summer months. Both long and short-finned pilot whales swim close to the shore during migration. Fishermen surround the mammals in boats and dinghies, herding them towards the beach. Metal hooks are driven into the stranded mammals' blowholes before their spines are cut. Whole families are slaughtered, and some swim around in their family members' blood for hours. Although whale meat is eaten by the local people, some of the meat is left to rot.

While Japan, Norway, and Iceland get most of the heat for whaling, conservationists say South Korea engages in controversial whaling practices too. South Korean fishermen are known to take advantage of a loophole that allows them to legally sell whale meat from animals that are accidentally caught in fishing nets. Days before the 2016 Whale Festival in Ulsan, South Korea, authorities raided a cold storage unit and found more than 27 tons—about 40 whales’ worth—of Minke whale meat worth $3.4 million."Accidental ?"

Whaling in Russia is practised solely by the Chukotka peoples of the Russian far east, who take 136 grey whales yearly on an annual quota provided by the IWC and also take an occasional bowhead whale.

Small Cetaceans are also extensively hunted. By far, the world’s largest kill of small cetaceans is in Peru, where up to 15,000 dolphins are killed annually to be used as bait in shark fisheries (another endangered species with far-reaching implications). Other countries where direct takes of more than 1,000 individuals annually occur are Brazil, Canada, Greenland, Ghana, Guatemala, India, Indonesia, Japan, Madagascar, Malaysia, Nigeria, Republic of Korea, Solomon Islands, Sri Lanka, Venezuela, and Taiwan. Up to several hundred small cetaceans are hunted each year in Alaska, Cameroons, Colombia, Faroe Islands, Guinea Bissau, Kiribati, Myanmar, Pakistan, Philippines, Papua New Guinea, Senegal, St. Lucia, St. Vincent and the Grenadines, Vietnam, and Tanzania.

One could think that the reduction in numbers of whales (and dolphins) would increase the numbers of phytoplankton and krill. Phytoplankton being the food source for krill and krill being a primary food source for many cetaceans and other marine creatures upon which cetaceans feed. BUT phytoplankton levels declined by 40% since 1950 and krill have declined by 80% the 1970s. Climate change and rising sea temperatures were blamed for both.

As stated prior, the conversion of CO2 into O2 by photosynthesis in phytoplankton accounts for the production of 70% of the oxygen we breathe. It follows that if phytoplankton levels declined by 40% then conversion of CO2 into O2 would also decline and this alone could be the cause of rising sea temperatures/climate change?

My personal view is the root cause of the decline of phytoplankton (and krill) numbers is a direct result of whaling. This, in turn, leads to increasing sea temperatures/climate change. But how can that be? There are reasons that, in my opinion, are logical and should prompt further research.

PART VI - will look further into the comment from Canada's Dalhousie University about surface water not mixing well with cooler, nutrient-rich waters below, depriving phytoplankton of some of the materials they need to turn CO2 and sunlight into energy.