Deep-sea sediments and global change: Research frontiers and challenges

doi:10.13745/j.esf.sf.2022.6.28

Abstract

Abstract:

Present-day oceans are experiencing the effects of global change such as warming and acidification caused by human activities. Deep-sea sediments store a detailed archive of past global changes driven by nature during Earth’s evolution. By exploring today’s and past global change processes, we can reveal the characteristics and laws of global change and provide a basis for predicting future changes. The outstanding research progresses made in recent years were the discovery in the deep-sea of a variety of analogous scenarios that humans, when choosing future greenhouse gas emission trajectories, can reference to for evaluating future changes—their processes and consequences —in the Earth system. Among such scenarios, millennium-scale climate events, represented by the Dansgaard-Oeschger oscillation, and decadal-scale climate events, represented by the El Nino-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO), are the closest rapid climate change analogues to today’s global warming. The Earth system is currently at the beginning of a “Hothouse Earth” emission trajectory. If the system passes the “tipping points”, it will follow an irreversible path to a “Hothouse Earth” state; whereas an alternative path may lead to a “Stabilized Earth” state. Analogous scenarios in the deep-sea sedimentary archive can provide societies with valuable information in choosing future emission trajectories. The major challenges for researchers are to fully understand the mechanisms of the key processes of global change. Taking the example of ocean warming and acidification’s influence on diatom and coccolithophore functioning as marine biological pump. The conventional knowledge has suggested that acidification is beneficial to diatom formation; but recent mesocosm experiments have found that global diatom output is significantly reduced. Likewise, the suggestion that acidification leads to calcification crisis in marine life has also been proven wrong, as recent black shale studies of Mesozoic oceanic anoxic events showed that calcium carbonate output from coccolithophores increased significantly during ocean acidification. The above examples demonstrate that conventional knowledges of the key processes of global change are under serious challenge.

Key words: deep-sea sediments, global change, ocean warming, ocean acidification, rapid climate change, tipping points

CLC Number:

LIU Zhifei, CHEN Jianfang, SHI Xuefa. Deep-sea sediments and global change: Research frontiers and challenges[J]. Earth Science Frontiers, 2022, 29(4): 1-9.

Figures/Tables 8

Fig.1 Distribution of deep-sea regions on the Earth’s surface (modified from [5]) showing outlined areas (red line) with water depths exceeding 2000

Fig.2 Comparison between a Cretaceous oceanic anoxic event (A) and present Anthropocene ocean warming andacidification scenarios (B). Adapted from [6].

Fig.3 Evolution of atmospheric CO2 recorded in deep-sea sediments over the past 55 Ma (left) and predicted atmospheric CO2 scenarios up to the year 2300 (right). Adapted from [6,17-18].

Fig.4 Planktonic foraminiferal oxygen isotope and bioturbation index of Late Quaternary at ODP Hole 893A, Santa Barbara Basin, East Pacific. Adapted from [24].

Fig.5 Comparison of modern annual average sea surface temperature (A) with sea surface temperature during the January 1998 El Niño event (B) and Pliocene annual average sea surface temperature (C). Adapted from [20,28].

Fig.6 Variation of global silicic acid distribution influenced by ocean acidification. Adapted from [35].

Fig.7 Schematic diagram illustrating changes of phytoplankton export and formation of nannofossil imprints through an oceanic anoxic event. Adapted from [37].

Fig.8 Potential trajectories of the Earth system development in the Anthropocene. Adapted from [6,39].

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