問題詳情

(41-45)Since long before the beginning of the Industrial Age,oceans were effectively absorbing carbon dioxide. Recentstudies show that in addition to rising sea levels and a 0.5degree Fahrenheit increase in ocean surface temperature,excess Carbon dioxide in the atmosphere is increasing oceanpH levels, a process known as ocean acidification. This changein chemistry appears to be affecting the ability of somemollusks and other marine organisms to build calciferousshells, and threatens to shift the ranges of marine organismsand alter entire food webs in ways not yet fully understood.Several species of marine birds that depend on Californiahabitats—including already endangered breeding populationsof ashy storm-petrels, Craveri’s murrelets and black-ventedshearwaters—are expected to experience declines as risingsea levels inundate the rocky areas where they breed on andnear the coast. In addition, critical foraging for at least 70 birdspecies could be disrupted by the effects of rising seatemperatures on the food chain.Corals, calcareous phytoplankton, mussels, snails, seaurchins and other marine organisms use calcium andcarbonate in seawater to construct their calcium carbonateshells or skeletons. As the pH decreases, carbonate becomesless available, which makes it more difficult for organisms tosecrete Calcium carbonate to form their skeletal material. Foranimals in general, including invertebrates and some fish,carbon dioxide accumulation and lowered pH may result inacidosis, or a buildup of carbonic acid in the organism's bodyfluids. This can lead to lowered immune response, metabolicdepression, behavioral depression affecting physical activityand reproduction, and asphyxiation. Since the oceans havenever experienced such a rapid acidification, it is not clear ifecosystems have the ability to adapt to these changes. Effectsof ocean acidification on organisms and ecosystems are stillpoorly understood. Over the last few years, research hasintensified significantly to fill the many knowledge gaps.Nearly 500 million people depend on healthy coral reefsfor sustenance, coastal protection, renewable resources, andtourism, with an estimated 30 million of the world's poorestpeople depending entirely on the reefs for food. Coral reefsface two challenges from increasing atmospheric carbondioxide. First, higher carbon dioxide concentrations in theatmosphere are linked to warmer global temperatures, whichin turn lead to warmer water temperatures. Corals are verysensitive to temperature change: a 1–2º Celsius change in localtemperature above their normal summer maximum can leadto a phenomenon called ‘bleaching’, whereby the corals expeltheir vital algal symbionts (algae which live in the cells of thecoral), leaving the coral tissues translucent.In 1998, a single bleaching event led to the loss of almost20% of the world’s living coral. Corals can recover from theseevents but repeated episodes are likely to weaken the coralecosystem, making them more susceptible to disease andcausing a loss of biodiversity. The second challenge faced bycorals is the increasing acidity of the water caused by highercarbon dioxide concentrations. Lowered calcification ratesaffect the reef’s ability to grow its carbonate skeleton, leadingto slower growth of the reef and a more fragile structuralsupport, which makes it more vulnerable to erosion.By the middle of this century, the estimated reduction incalcification rates may lead to more reef area erosion than canbe rebuilt through new calcification.
41.Which of the following aspects does NOT correspond tothe definition of “acidification”?
(A)A change in chemistry.
(B)An ability to affect marine organisms.
(C)A cycle of nature.
(D)A threat for the food web.

參考答案

答案：C
難度：簡單0.75
統計：A(5),B(3),C(24),D(0),E(0)

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