What percentage of Earth's surface do the oceans cover?
71%.
What is the ocean's average salinity?
About 34.5 g/kg.
What causes surface salinity to rise through evaporation?
Evaporation removes freshwater and concentrates dissolved salts.
What freshwater additions lower surface salinity?
Precipitation, river discharge, and melting ice.
Through which pathways do dissolved elements enter the ocean?
Continental waters, volcanoes, and hydrothermalism.
Which dissolved elements have different oceanic origins?
Sodium and chlorine.
What characterizes the mixed layer in density, salinity, and temperature?
It is a surface layer homogeneous in density, salinity, and temperature.
What defines a thermocline, and what forms can it take?
It is a zone of rapid temperature transition between surface and deep waters, and may be permanent or seasonal.
How does stratification affect vertical mixing at low latitudes and at the poles?
Strong low-latitude stratification prevents vertical mixing, while weak polar temperature contrasts permit it.
What drives thermohaline circulation, also called meridional overturning circulation?
Ocean-water density differences caused by temperature and salinity.
What happens to currents during thermohaline circulation?
They sink into the deep ocean and later return to the surface.
What forms when dense North Atlantic water sinks to 2,000–4,000 m?
North Atlantic Deep Water.
What conditions make North Atlantic water dense enough to sink?
Cooling and/or increasing salinity.
What do sea-level pressure gradients created by Ekman transport drive?
Currents.
What defines dynamic topography?
The difference between sea level and the geoid.
What can dynamic topography be used to calculate?
Current speed.
What causes equatorial surface-current divergence and upwelling?
Converging trade winds associated with the intertropical convergence zone.
What causes downwelling at the centers of subtropical gyres?
Ekman transport causes water to converge beneath atmospheric high-pressure regions.
How many anticyclonic subtropical and cyclonic subpolar gyres comprise surface circulation?
Five anticyclonic subtropical gyres and four cyclonic subpolar gyres.
What distinctive currents occur in subtropical gyres?
Intense western boundary currents.
How many subpolar gyres are sites of deep dense-water formation?
Three.
Where does photosynthesis occur in the ocean?
Only at the ocean surface.
At what depths does ocean respiration occur?
At the surface and at depth.
What share of world fisheries comes from eastern-boundary upwelling zones?
Approximately 17%.
What share of ocean surface area do eastern-boundary upwelling zones cover?
Approximately 0.02%.
According to IPCC AR6 WG1 (2021), what share of excess energy has the ocean absorbed since 1970?
91%.
According to IPCC AR6 WG1 (2021), what explains the ocean’s absorption of excess energy since 1970?
Greenhouse gases prevent the excess energy from escaping at the top of the atmosphere.
What share of sea-level rise comes from ocean thermal expansion?
Approximately 50%.
What is the ocean's average depth?
3,700 m.
What is the ocean's average temperature?
About 3.0 °C.
Which freshwater sources lower local surface salinity?
The Amazon, Congo, major Asian rivers entering the Bay of Bengal, Siberian rivers, and melting ice.
Where does rainfall reach its maximum, and where is precipitation weak?
Rainfall peaks in the intertropical convergence zone; precipitation is weak under five atmospheric anticyclones.
What formula defines the density anomaly, , of seawater?
, where is seawater mass density in kg/m³.
What is the mass density range of ocean seawater?
1,024–1,027 kg/m³.
At what depths does the largest temperature variation occur in the permanent thermocline?
Between 200 and 1,000 m.
How does the Northern Hemisphere mixed layer differ between August and March?
It is shallow in August and deep in March.
What surface density corresponds to high temperature and precipitation?
Low surface density.
What forms when dense Southern Ocean water sinks deeper than 4,000 m?
Antarctic Bottom Water.
What timescale characterizes the schematized journey of thermohaline circulation?
Millennia.
How deep does wind directly affect surface currents?
Approximately the upper 50–100 m.
How does the Coriolis force change toward the equator?
It decreases and becomes zero at the equator.
Where did simulated and tracked debris accumulate over six years?
In the central North and South Pacific, North and South Atlantic, and Indian Ocean gyres.
What limits temperate phytoplankton blooms first as seasons change?
Light.
What limits temperate phytoplankton blooms later as seasons change?
Nutrients.
Where do eastern-boundary subtropical-gyre upwellings occur?
Off the Canaries and Mauritania, Benguela, California, and Peru–Chile.
What current is associated with the Peru–Chile upwelling?
The Humboldt Current.
What formula expresses net surface freshwater loss?
In the classical Ekman model, what sets surface current direction relative to the wind?
Approximately 45° from the wind direction.
What does the classical Ekman model produce through friction and the Coriolis effect?
An Ekman spiral and transport.
What share of anthropogenic CO₂ emissions did the ocean absorb during 2011–2020?
Approximately 25%.
How much carbon did the ocean absorb annually during 2011–2020?
Approximately 2.9 GtC per year.
Which dissolved elements do biology and sedimentation, hydrothermalism, and evaporites remove, respectively?
SiO2 and CaCO3; S and Mg; NaCl, MgSO4, and KCl, respectively.
Answer 20 questions on Ocean Dynamics and Climate.
1. Approximately what fraction of Earth's surface is covered by the oceans?
2. What is the ocean's average salinity?
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