Increasing concentrations of carbon dioxide (CO2) in the atmosphere are making the oceans more acidic—in other words, lowering the pH...
GMAT Multi Source Reasoning : (MSR) Questions
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.
OWNING THE DATASET
Understanding Source A: Text Source - Scientific Report on Ocean Acidification
| 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." |
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| "Worldwide, the average pH of the upper ocean—the top 1,000 m—has declined 0.12, to 8.1, between 1750 and 2010." |
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| "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" |
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| "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." |
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| "Research suggests that a 0.3 decline in pH reduces phytoplankton iron consumption by about 15 percent" |
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| "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.
Understanding Source B: Chart - Ocean CO2 and pH Measurements (1985-2005)
Chart Analysis:
- What it shows: Scatter plot displaying two measurements from the upper ocean over 20 years - CO2 concentration (in pCO2 units) and pH levels
- Key patterns observed:
- Red dots/line: CO2 concentration increases from ~320 to ~380 pCO2
- Blue dots/line: pH decreases from ~8.14 to ~8.08
- Both trends show consistent patterns despite individual measurement variability
- Inference: The inverse relationship is clear - as CO2 goes up, pH goes down (ocean becomes more acidic)
- Inference: Natural variability exists in measurements, but overall trends are unmistakable
- Linkage to Source A: This chart provides real-world evidence for Source A's claim that "CO2 increases cause ocean acidification" - we can actually see it happening in the data
- Linkage to Source A: The pH drop shown here (~0.06 units over 20 years) is part of the 0.12 unit decline Source A mentions from 1750-2010
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.
Understanding Source C: Chart - Long-term pH Change Projections by Depth
Chart Analysis:
- What it shows: Contour plot showing pH changes (ΔpH) from pre-1750 baseline across different ocean depths and time periods (past to year 3000)
- Key patterns observed:
- Surface waters (0-1km) show the darkest shading = most severe pH changes
- pH changes penetrate deeper over time (contour lines slope downward)
- Most dramatic changes occur between 2000-2300
- Maximum change shown reaches -0.8 pH units at surface
- Inference: Acidification starts at the surface and gradually works its way down to deeper waters
- Inference: The rate of change accelerates dramatically in the near future before eventually stabilizing
- Linkage to Source A: This visualization confirms Source A's statement that "deep ocean acidification occurs more slowly" - we can see the delayed response at depth
- Linkage to Source A: The projected surface pH changes align with Source A's prediction of pH dropping to 7.8-7.7 by 2100
- Linkage to Source B: While Source B showed the beginning of this trend (1985-2005), Source C reveals it's just the start of much larger changes to come
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.
Overall Summary
The three sources together reveal that ocean acidification from atmospheric CO2 is:
- Already measurably occurring, with pH dropping 0.12 units since 1750
- Accelerating rapidly, with projected drops 5-6 times larger than recent measurements
- Most severe in the upper ocean where critical organisms like phytoplankton live
- Following predictable patterns where surface waters acidify first and most severely
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).
Question Analysis
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:
- Projections based on current trends continuing
- Long-term ecological and chemical impacts
- Classification requirements for each statement
Connecting to Our Analysis
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.
Extracting Relevant Findings
The evaluation process involves comparing each statement to established trends and documented scientific findings. Current scientific consensus shows:
- Increasing atmospheric CO2 lowers ocean pH
- Acidification reduces phytoplankton iron absorption by approximately 15%
- Past ocean acidification events correlated with marine extinctions
Statements consistent with these patterns should be labeled 'Projected', while those contradicting established trends should be 'Not projected'.
Individual Statement Evaluations
Statement 1 Evaluation
Statement: Decreased iron absorption by phytoplankton leads to increased extinctions of sea life
- Evidence: Matches source data stating acidification reduces iron absorption and past acidification events caused extinctions
- Baseline Comparison: Current trends show reduced iron absorption with acidification and related extinctions
- Analysis: This represents a direct consequence of acidification effects on marine ecosystems
- Conclusion: PROJECTED
Statement 2 Evaluation
Statement: Increased iron absorption by phytoplankton contributes to decreased oceanic CO2 concentrations
- Evidence: Contradicts source data which states acidification makes iron absorption harder, not easier
- Baseline Comparison: Current trends show reduced, not increased, iron absorption due to acidification
- Analysis: This statement opposes the established acidification effect on phytoplankton
- Conclusion: NOT PROJECTED
Statement 3 Evaluation
Statement: Increased atmospheric CO2 concentrations contribute to decreased ocean water pH
- Evidence: Supported by all sources describing how CO2 increase lowers ocean pH
- Baseline Comparison: Current trends confirm inverse relationship between CO2 and pH
- Analysis: This represents a fundamental and well-established mechanism of ocean acidification
- Conclusion: PROJECTED
Systematic Checking
Verification of assessments through cross-referencing all source materials and known scientific principles related to ocean acidification confirms:
- Statement 1 aligns with acidification-driven reduction in phytoplankton iron absorption and historical correlations with extinctions
- Statement 2 contradicts the observed acidification impact on iron absorption by phytoplankton
- Statement 3 directly reflects the well-documented effect of increasing atmospheric CO2 leading to lower ocean pH
Final Answer
- Statement 1: Projected
- Statement 2: Not Projected
- Statement 3: 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