Week 9 Flashcards
How do phytoplankton act as indicators of global change?
Phytoplankton are sensitive to environmental and climate oscillations (e.g., ENSO), making them key indicators of global change.
How has oceanic primary production changed over geological time?
Primary production has evolved with major shifts in primary producer groups, ocean chemistry, and atmospheric oxygen levels. Most carbon fixation has occurred in the ocean.
What is the ‘glacial iron hypothesis’?
Increased atmospheric dust during glacial periods led to higher iron inputs to the ocean, enhancing phytoplankton productivity. This correlated with lower atmospheric CO₂, increased export production, and reduced surface nitrate during glacial periods.
What evidence supports the glacial iron hypothesis?
Paleo-studies link iron fluxes to CO₂ and climate changes during glacial cycles. Increased organic material in sediments during cold periods. Decreased residual nitrate in surface waters during cold periods.
How does ENSO influence oceanic primary production?
El Niño: Deepened thermocline reduces nutrient upwelling, lowering productivity in the eastern Pacific. La Niña: Shoaled thermocline enhances nutrient supply, increasing productivity.
What changes in NPP are observed during ENSO events?
Net Primary Production (NPP) decreases during El Niño due to stratification and nutrient limitation, while La Niña enhances new production and export.
How does iron limitation vary with ENSO?
Fe limitation intensifies during some ENSO events, though models poorly predict these patterns.
What are the main anthropogenic drivers of change in ocean production?
Increased temperature. Decreased pH (ocean acidification). Altered nutrient inputs (e.g., coastal eutrophication, atmospheric nitrogen deposition).
How does ocean acidification affect phytoplankton?
Calcifying organisms like coccolithophores are most affected. Impacts vary widely between taxa and experiments, with both positive and negative effects on growth observed.
What is the impact of anthropogenic nutrient inputs on the ocean?
Coastal eutrophication increases local productivity. Atmospheric deposition of nitrogen is approaching natural nitrogen fixation rates, altering open ocean nutrient cycles.
How is ocean stratification expected to change in the future?
Increased stratification due to warming will reduce nutrient supply to surface waters, particularly in low latitudes, decreasing primary and export production.
What do models predict about future ocean productivity?
Most models forecast declines in low-latitude production due to stratification. Predictions for high latitudes are more variable, with some models suggesting increases in productivity.
Are oceanic ‘deserts’ expanding?
Satellite data suggest an increase in low-latitude oligotrophic regions, though longer time series are needed to confirm this trend.
What challenges exist in detecting anthropogenic changes in ocean production?
Long-term, consistent monitoring is required to distinguish anthropogenic signals from natural variability.
What evidence exists for recent changes in ocean production?
Boyce et al. (2010) suggest a global decline of ~1% per year in phytoplankton biomass. This finding is controversial and requires further validation.
How can time-series stations like BATS and HOT contribute to our understanding?
These stations provide long-term data on environmental forcing and primary production, crucial for detecting trends and variability.
What are the physical characteristics of ENSO events?
El Niño: Warmer eastern Pacific surface temperatures, deeper thermocline, increased stratification, reduced nutrient upwelling.
La Niña: Cooler eastern Pacific surface temperatures, shallower thermocline, increased nutrient upwelling.
How do anthropogenic nutrient inputs vary regionally?
Coastal eutrophication dominates in nearshore systems.
Dust and nitrogen deposition vary widely and are uncertain in magnitude for open ocean regions.
Why was the Boyce et al. (2010) study controversial?
Critics questioned the methods and dataset consistency, suggesting potential biases in the reported decline of phytoplankton biomass.
What challenges exist in predicting high-latitude productivity?
High-latitude systems exhibit greater variability in predictions due to complex feedbacks in circulation, nutrient supply, and ice cover changes.
How might ocean circulation and nutrient distribution change by 2300?
Models predict large-scale reorganizations of circulation, altering nutrient distributions and productivity, particularly in upwelling regions.
