Book contents
- Frontmatter
- Dedication
- Epigraph
- Contents
- Foreword and Preface
- Preface
- Summary of the first global integrated marine assessment
- The context of the assessment
- Assessment of Major Ecosystem Services from the Marine Environment (Other than Provisioning Services)
- Chapter 3 Scientific Understanding of Ecosystem Services
- Chapter 4 The Ocean's Role in the Hydrological Cycle
- Chapter 5 Sea-Air Interactions
- Chapter 6 Primary Production, Cycling of Nutrients, Surface Layer and Plankton
- Chapter 7 Calcium Carbonate Production and Contribution to Coastal Sediments
- Chapter 8 Aesthetic, Cultural, Religious and Spiritual Ecosystem Services Derived from the Marine Environment
- Chapter 9 Conclusions on Major Ecosystem Services Other than Provisioning Services
- Assessment of the Cross-cutting Issues: Food Security and Food Safety
- Assessment of Other Human Activities and the Marine Environment
- Assessment of Marine Biological Diversity and Habitats
- Section A Overview of Marine Biological Diversity
- Chapter 36 Overview of Marine Biological Diversity
- Section B Marine Ecosystems, Species and Habitats Scientifically Identified as Threatened, Declining or Otherwise in need of Special Attention or Protection
- I Marine Species
- II Marine Ecosystems and Habitats
- Section C Environmental, economic and/or social aspects of the conservation of marine species and habitats and capacity-building needs
- Overall Assessment
- Annexes
- References
Chapter 4 - The Ocean's Role in the Hydrological Cycle
from Assessment of Major Ecosystem Services from the Marine Environment (Other than Provisioning Services)
Published online by Cambridge University Press: 18 May 2017
- Frontmatter
- Dedication
- Epigraph
- Contents
- Foreword and Preface
- Preface
- Summary of the first global integrated marine assessment
- The context of the assessment
- Assessment of Major Ecosystem Services from the Marine Environment (Other than Provisioning Services)
- Chapter 3 Scientific Understanding of Ecosystem Services
- Chapter 4 The Ocean's Role in the Hydrological Cycle
- Chapter 5 Sea-Air Interactions
- Chapter 6 Primary Production, Cycling of Nutrients, Surface Layer and Plankton
- Chapter 7 Calcium Carbonate Production and Contribution to Coastal Sediments
- Chapter 8 Aesthetic, Cultural, Religious and Spiritual Ecosystem Services Derived from the Marine Environment
- Chapter 9 Conclusions on Major Ecosystem Services Other than Provisioning Services
- Assessment of the Cross-cutting Issues: Food Security and Food Safety
- Assessment of Other Human Activities and the Marine Environment
- Assessment of Marine Biological Diversity and Habitats
- Section A Overview of Marine Biological Diversity
- Chapter 36 Overview of Marine Biological Diversity
- Section B Marine Ecosystems, Species and Habitats Scientifically Identified as Threatened, Declining or Otherwise in need of Special Attention or Protection
- I Marine Species
- II Marine Ecosystems and Habitats
- Section C Environmental, economic and/or social aspects of the conservation of marine species and habitats and capacity-building needs
- Overall Assessment
- Annexes
- References
Summary
The interactions between the seawater and freshwater segments of the hydrological cycle
The global ocean covers 71 per cent of the Earth's surface, and contains 97 per cent of all the surface water on Earth (Costello et al., 2010). Freshwater fluxes into the ocean include: direct runoff from continental rivers and lakes; seepage from groundwater; runoff, submarine melting and iceberg calving from the polar ice sheets; melting of sea ice; and direct precipitation that is mostly rainfall but also includes snowfall. Evaporation removes freshwater from the ocean. Of these processes, evaporation, precipitation and runoff are the most significant at the present time.
Using current best estimates, 85 per cent of surface evaporation and 77 per cent of surface rainfall occur over the oceans (Trenberth et al., 2007; Schanze et al., 2010). Consequently, the ocean dominates the global hydrological cycle. Water leaving the ocean by evaporation condenses in the atmosphere and falls as precipitation, completing the cycle. Hydrological processes can also vary in time, and these temporal variations can manifest themselves as changes in global sea level if the net freshwater content of the ocean is altered.
Precipitation results from the condensation of atmospheric water vapour, and is the single largest source of freshwater entering the ocean (∼530,000 km3/yr). The source of water vapour is surface evaporation, which has a maximum over the subtropical oceans in the trade wind regions (Yu, 2007). The equatorward trade winds carry the water vapour evaporated in the subtropics to the Intertropical Convergence Zone (ITCZ) near the equator, where the intense surface heating by the sun causes the warm moist air to rise, producing frequent convective thunderstorms and copious rain (Xie and Arkin, 1997). The high rainfall and the high temperature support and affect life in the tropical rainforest (Malhi and Wright, 2011).
Evaporation is enhanced as global mean temperature rises (Yu, 2007). The water-holding capacity of the atmosphere increases by 7 per cent for every degree Celsius of warming, as per the Clausius-Clapeyron relationship. The increased atmospheric moisture content causes precipitation events to change in intensity, frequency, and duration (Trenberth, 1999) and causes the global precipitation to increase by 2-3 per cent for every degree Celsius of warming (Held and Soden, 2006).
- Type
- Chapter
- Information
- The First Global Integrated Marine AssessmentWorld Ocean Assessment I, pp. 91 - 104Publisher: Cambridge University PressPrint publication year: 2017
References
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