AUB-EN — AUB English Entrance Examination

Practice session

Read the following academic passage, then answer the question. --- PASSAGE 1 — Physical Sciences & Paleoclimatology Ice cores extracted from continental ice sheets in Greenland and Antarctica provide some of the most continuous, high-resolution archives of Earth's past climate. As snow accumulates and undergoes densification into firn and glacial ice, ambient atmospheric gases and atmospheric particulates become trapped in discrete stratigraphical layers. Paleoclimatologists quantify stable isotope ratios—principally the ratio of oxygen-18 to oxygen-16 (^18O/^16O)—preserved within the water molecules of the frozen matrix. Because water molecules containing the lighter oxygen-16 isotope evaporate more readily and condense less readily than those with heavier oxygen-18, the isotopic composition of precipitation directly reflects the ambient condensation temperature at the time of snowfall. Lower ratios of ^18O to ^16O indicate cooler atmospheric conditions, whereas elevated ratios signal warmer intervals. Concurrently, microscopic bubbles of fossil air sealed hermetically within the recrystallized ice matrix offer empirical measurements of greenhouse gas concentrations, including carbon dioxide and methane, spanning several glacial-interglacial cycles. By cross-calibrating isotopic thermometry with greenhouse gas concentrations and microparticle deposition rates, researchers have overturned long-held assumptions regarding the pace of global climatic shifts. Rather than exhibiting solely gradual, millennia-long transitions driven by orbital Milankovitch variations, the paleoclimate record preserves episodes of startlingly abrupt change. The most celebrated of these abrupt disruptions is the Younger Dryas cold reversal, which commenced approximately 12,900 years before the present. Emerging abruptly toward the close of the last deglaciation, the Younger Dryas plunged the North Atlantic region back into near-glacial cold within a matter of decades, or possibly years. Paleoceanographic proxies indicate that this sudden thermal deterioration was triggered by a massive outburst of continental meltwater from proglacial Lake Agassiz into the North Atlantic Ocean. The sudden inundation of buoyant freshwater sharply curtailed the Atlantic Meridional Overturning Circulation (AMOC) by preventing surface waters from becoming sufficiently dense and saline to sink. Consequently, the northward transport of tropical heat was abruptly attenuated, inducing severe hemispheric cooling and reorganizing global atmospheric precipitation patterns before the system re-equilibrated roughly 1,150 years later. --- Which of the following best states the primary purpose of the passage?

Loading your practice session…