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Increasing concentrations of carbon dioxide (CO2) in the atmosphere are making the oceans more acidic—in other words, lowering the pH of ocean water. Worldwide, the average pH of the upper ocean—the top 1,000 m—has declined 0.12, to 8.1, between 1750 and 2010. If humans continue to emit greenhouse gases at current rates, atmospheric CO2 concentrations will reach 500 parts per million (ppm) by 2050 and 800 ppm by 2100, by which time the pH of the upper ocean could drop to 7.8 or 7.7. The deep ocean—below 4,000 m—had a pH of 8.2 in 2010. At that depth, acidity is relatively stable and not expected to increase as quickly, as is shown in the graph labeled Long-Term Graph.
The base of the ocean food web is phytoplankton, which, like plants, use sunlight for photosynthesis and thus can live only in the upper ocean. For many types of phytoplankton, acidification makes it harder to absorb iron, a vital nutrient. Research suggests that a 0.3 decline in pH reduces phytoplankton iron consumption by about 15 percent, slowing photosynthesis and impacting growth and reproduction. Comparable changes in the past correlated with massive extinctions of sea life.
Assuming that current trends will continue, for each of the following, select Projected if it is a long-term projection of the information provided, and otherwise select Not projected.
Decreased iron absorption by phytoplankton will contribute to increased extinctions of sea life.
Increased iron absorption by phytoplankton will contribute to decreased oceanic CO2 concentrations.
Increased atmospheric CO2 concentrations will contribute to decreased ocean water pH
| Information from Dataset | Analysis |
|---|---|
| "Increasing concentrations of carbon dioxide (CO2) in the atmosphere are making the oceans more acidic—in other words, lowering the pH of ocean water." |
|
| "Worldwide, the average pH of the upper ocean—the top 1,000 m—has declined 0.12, to 8.1, between 1750 and 2010." |
|
| "If humans continue to emit greenhouse gases at current rates, atmospheric CO2 concentrations will reach 500 parts per million (ppm) by 2050 and 800 ppm by 2100" |
|
| "by which time the pH of the upper ocean could drop to 7.8 or 7.7" |
|
| "The deep ocean—below 4,000 m—had a pH of 8.2 in 2010. At that depth, acidity is relatively stable and not expected to increase as quickly" |
|
| "The base of the ocean food web is phytoplankton, which, like plants, use sunlight for photosynthesis and thus can live only in the upper ocean." |
|
| "Research suggests that a 0.3 decline in pH reduces phytoplankton iron consumption by about 15 percent" |
|
| "Comparable changes in the past correlated with massive extinctions of sea life." |
|
Summary: This source explains how atmospheric CO2 is acidifying the oceans, with the upper ocean pH already dropping 0.12 units since 1750 and potentially dropping another 0.3-0.4 units by 2100, threatening phytoplankton and the entire marine food web.
Summary: Source B visually confirms Source A's explanation by showing actual measurements of increasing ocean CO2 and decreasing pH from 1985-2005, demonstrating that acidification is actively occurring and measurable.
Summary: Source C provides the big picture, showing how the acidification documented in Source B and explained in Source A will progress over centuries, with surface waters experiencing the most severe changes while deeper waters respond more slowly.
The three sources together reveal that ocean acidification from atmospheric CO2 is:
This combination of past changes comparable to extinction events and future projections showing dramatic acceleration presents a dire warning for marine ecosystems, particularly since the biological impact zone (where phytoplankton live) coincides exactly with the chemical impact zone (where acidification is worst).
For each statement about ocean acidification effects, we need to determine if it represents a logical projection based on current trends shown in the data. Each statement must be evaluated as either 'Projected' or 'Not projected' based on:
The ocean acidification data and analysis provide comprehensive information on pH trends, atmospheric CO2 impact on ocean acidity, and phytoplankton iron absorption effects, which relate directly to the statements under evaluation. All required information to classify the statements is contained in the available analysis.
The evaluation process involves comparing each statement to established trends and documented scientific findings. Current scientific consensus shows:
Statements consistent with these patterns should be labeled 'Projected', while those contradicting established trends should be 'Not projected'.
Statement: Decreased iron absorption by phytoplankton leads to increased extinctions of sea life
Statement: Increased iron absorption by phytoplankton contributes to decreased oceanic CO2 concentrations
Statement: Increased atmospheric CO2 concentrations contribute to decreased ocean water pH
Verification of assessments through cross-referencing all source materials and known scientific principles related to ocean acidification confirms:
Decreased iron absorption by phytoplankton will contribute to increased extinctions of sea life.
Increased iron absorption by phytoplankton will contribute to decreased oceanic CO2 concentrations.
Increased atmospheric CO2 concentrations will contribute to decreased ocean water pH