THE CHINESE DUST HYPOTHESIS
- Asian Soil Conservation and
Declining Productivity in the North Pacific
Are they linked? One of the ocean mysteries Planktos seeks to understand is the decline in productivity of the North Pacific that has been continuously documented for several decades. Don Schell is a researcher and director of the Institute of Marine Science at the University of Alaska - Fairbanks. He calculated ocean productivity by measuring the amount of carbon in the baleen of bowhead whales. The carbon comes from the whale's consumption of plankton. Bowhead whales add a layer of baleen each year, much like tree rings. Scientists can examine the layers of baleen and measure how ocean productivity has changed over time. Shell notes, "The record shows that from 1946 to 1963 everything went along fairly smoothly at a relatively high level of productivity. And then in the mid-60s it increased and peaked at around 1965, 1966. Then ocean plankton productivity began a steady decline and since the mid-1970s it has gone down and down and down. The last samples we have from 1994, 1995 and 1996 show the lowest primary productivity in the Bering Sea over this 50-year period." The story told in the baleen of bowhead whales is helping scientists explain the decline of species such as Steller sea lions, seabirds and fish that ultimately depend on plankton. Schell says the overall productivity of the North Pacific Ocean has declined some 40 percent. That means the ocean may not be able to support the variety of sea life that it once did.
(www.uaf.edu/seagrant/NewsMedia/98ASJ/08.17.98_SeaChanges.html) Over this same time frame something dramatic has also taken place in Asia where a rigorous soil conservation effort has been developing across the same time frame. Many people know the story of the America "Dust Bowl Days" which occurred in the early part of the twentieth century. In 1930 and 1931, the decade opened with unparalleled prosperity and growth. NATION'S BUSINESS magazine labeled the panhandles of Oklahoma and Texas as the most prosperous region. The Panhandle was a marked contrast to the long soup lines of the Eastern United States. Wheat was a boom commodity. The world needed it and was paying a good price for it. Using tractors, deep furrow plows, and combines purchased by most wheat farm owners after the phenomenal crop of 1926, farmers began plowing and planting wheat as never before. Their lands were replanted in wheat year after year without a thought about the damage that was being done. Millions of acres of great plains grasslands that should never have been touched swiftly fell to the plow. 
When drought hit in the mid-thirties, the pillaged soils dried to dust. When fierce winds followed, millions of tons of topsoil took to the skies creating the devastating "dust bowl years." The "Yearbook of Agriculture" for 1934 records, "Approximately 35 million acres of formerly cultivated land have essentially been destroyed for crop production. . . . 100 million acres now in crops have lost all or most of the topsoil; 125 million acres of land now in crops are rapidly losing topsoil. April 27 1935 - The US Congress declares soil erosion "a national menace" in an act establishing the Soil Conservation Service in the Department of Agriculture. Under the direction of Hugh H. Bennett, the SCS developed extensive conservation programs that retained topsoil and prevented irreparable damage to the land. Farming techniques such as strip cropping, terracing, crop rotation, contour plowing, and cover crops were advocated. Farmers were paid to practice soil-conserving farming techniques.
At a meeting in Pueblo, Colorado, in December of 1935 experts reported that 850,000,000 tons of topsoil had blown off the Southern Plains during the course of the year, and that if the drought continued, the total area affected would increase from 4,350,000 acres to 5,350,000 acres in the spring of 1936. Jump forward to post-revolution China in the last half of the twentieth century and the North Pacific Ocean eco-system. We now know that ocean productivity is tied to micronutrients, especially iron, that arrive in the open ocean primarily via dust that blows off of land. Most terrestrial dust contains between 1-3% iron oxides in the form of magnetite and hematite (aka iron ore when found in dense concentrations). The North Pacific depends heavily on dust from Asia especially western China and Mongolia for iron nutrients.
 | A dust storm that originated near the Mongolia-China border on April 10, 2001, made its way across the Pacific to the U.S., sprawling from Canada to the Southwest and as far east as the Great Lakes. The dust is see in the upper left quadrant of this Sea Wifs satellite image. |
The United Nations Environment Program has reported that China is now engaging in valuable and effective soil conservation practices meeting with much the same success as the US Soil Conservation Service. China has made great achievements in soil conservation in the past 50 years, bringing 780,000 square kilometers of soil erosion under control. The UNEP reports that in a recent 10-year period of conservation efforts (the 1980's) erosion has been brought under control in 2 million hectares, a third of the total affected area. Improved land productivity doubled the total grain output in these areas. The second phase of the program, covering 1993-2002, aimed to introduce higher quality and efficiency in crop production (NEPA, 1993). As a result of a serious effort by the Central Government of China, about 10% of the country’s desertified land has been rehabilitated in the last few decades and the deterioration of another 12 per cent has been halted in north China. About 444,000 hectares of severely degraded rangeland have been recovered and maintained. Up to 18.36 million hectares of land have been afforested in efforts aimed at combating desertification.
Today China's soil conservation efforts are saving some billions of tons of soil per year from being lost. Previously, a significant portion of this dust would have arrived in the world's oceans especially the North Pacific. An important research topic for Planktos is to find out whether this apparent correlation between the success of Chinese soil conservation and declining North Pacific Ocean productivity over matching time frames is a coincidence or causal relationship. The following chart shows a remarkable correlation between the spread of soil-protecting winter/spring wheat in China with the decline in N. Pacific ocean productivity. 
We know that the world's oceans and land areas are tightly tied together in many ways including the micronutrient regimes of the oceans. Dust and Ocean Forest Productivity The following extract shows where ocean productivity and iron dust fall coincide. Correlation Coefficients: Climatology of Dust Deposition and SeaWiFS Chlorophyll
 This map pinpoints possible iron-limited regions of the world's oceans by seeing which phytoplankton-rich areas are also areas that received iron from wind-blown dust. Areas with high levels of chlorophyll from phytoplankton and high levels of dust deposition (high correlation coefficients) are indicated in red. Dust deposition was calculated in a 3-year climatology model for the years 1996-1998. The chlorophyll measurements are from 1998 observations from the SeaWiFS (Sea-viewing Wide Field-of-view Sensor) instrument on the OrbView-2 satellite. Ref: "The Correlation Between Atmospheric Dust Deposition to the Surface Ocean and SeaWiFS Ocean Color: A Global Satellite-based Analysis," Erickson, D., et al.
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