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Multidecadal Increase in Plastic Particles in Coastal Ocean Sediments

September 4, 2019

We analyzed coastal sediments of the Santa Barbara Basin, California, for historical changes in microplastic deposition using a box core that spanned 1834–2009. The sediment was visually sorted for plastic, and a subset was confirmed as plastic polymers via FTIR (Fourier transform infrared) spectroscopy. After correcting for contamination introduced during sample processing, we found an exponential increase in plastic deposition from 1945 to 2009 with a doubling time of 15 years. This increase correlated closely with worldwide plastic production and southern California coastal population increases over the same period. Increased plastic loading in sediments has unknown consequences for deposit-feeding benthic organisms. This increase in plastic deposition in the post–World War II years can be used as a geological proxy for the Great Acceleration of the Anthropocene in the sedimentary record.

Climate-driven oscillation of phosphorus and iron limitation in the North Pacific Subtropical Gyre

June 10, 2019

The supply of nutrients is a fundamental regulator of ocean productivity and carbon sequestration. Nutrient sources, sinks, residence times, and elemental ratios vary over broad scales, including those resulting from climate-driven changes in upper water column stratification, advection, and the deposition of atmospheric dust. These changes can alter the proximate elemental control of ecosystem productivity with cascading ecological effects and impacts on carbon sequestration. Here, we report multidecadal observations revealing that the ecosystem in the eastern region of the North Pacific Subtropical Gyre (NPSG) oscillates on subdecadal scales between inorganic phosphorus (Pi) sufficiency and limitation, when Pi concentration in surface waters decreases below 50–60 nmol⋅kg−1. In situ observations and model simulations suggest that sea-level pressure changes over the northwest Pacific may induce basin-scale variations in the atmospheric transport and deposition of Asian dust-associated iron (Fe), causing the eastern portion of the NPSG ecosystem to shift between states of Fe and Pi limitation. Our results highlight the critical need to include both atmospheric and ocean circulation variability when modeling the response of open ocean pelagic ecosystems under future climate change scenarios.

The Little Ice Age and 20th-century deep Pacific cooling

January 4, 2019

Proxy records show that before the onset of modern anthropogenic warming, globally coherent cooling occurred from the Medieval Warm Period to the Little Ice Age. The long memory of the ocean suggests that these historical surface anomalies are associated with ongoing deep-ocean temperature adjustments. Combining an ocean model with modern and paleoceanographic data leads to a prediction that the deep Pacific is still adjusting to the cooling going into the Little Ice Age, whereas temperature trends in the surface ocean and deep Atlantic reflect modern warming. This prediction is corroborated by temperature changes identified between the HMS Challenger expedition of the 1870s and modern hydrography. The implied heat loss in the deep ocean since 1750 CE offsets one-fourth of the global heat gain in the upper ocean.

Global Integrated Drought Monitoring and Prediction System (GIDMaPS)

January 1, 2019

The Global Integrated Drought Monitoring and Prediction System (GIDMaPS) is a drought monitoring and prediction system that provides near real-time drought information based on multiple drought indicators and input data sets.

Admitting Students to Selective Education Programs: Merit, Profiling, and Affirmative Action

June 1, 2015

For decades, colleges and universities have struggled to increase participation of minority anddisadvantaged students. Urban school districts confront a parallel challenge; minority and disadvantaged students are underrepresented in selective programs that use merit-based admission. In their referral and admission policies to such selective programs, school districts may potentially set different admission thresholds based on income and race (affirmative action), and they may potentially take account of differences in achievement relative to ability across race and income groups (profiling). We develop an econometric model that provides a unified treatment of affirmative action and profiling. Implementing the model for an urban district, we find profiling by race and income, and affirmative action for low-income students. Counterfactual analysis reveals that these policies achieve more than 80% of African American enrollment that could be attained by race-based affirmative action.