The Surface of the Ocean
Author
Sara Mielish
The ocean covers over 70% of Earth’s surface, yet we know remarkably little about it. What we do know is that its surface controls more of our climate, weather, and ecosystems than most people realize. Two measurements, temperature and salinity, tell us much of what we need to know.
Sea surface temperature (SST) is important to understand because it impacts different weather systems, influences climate patterns, affects the health of marine ecosystems, and is an important factor in climate change tracking.
Weather events like hurricanes, storms, and even cyclones are fueled by warm waters, which is why these patterns are more commonly found in areas of lower latitude, because they use the warmer water to start. These weather events are commonly found in the summer months because the more direct sunlight warms the ocean even more, fueling these systems to not only start but develop into more dangerous, bigger systems.
Sea surface temperature is one of the major driving forces of large-scale climate patterns like El Niño and La Niña. During El Niño, trade winds weaken and sometimes reverse, causing warm water to travel closer to the Western coast of the Americas; this also stops coastal upwelling, which introduces cold water to the surface of the water, leading to much warmer waters. During La Niña, trade winds strengthen and cause warm water to travel to the west and focus more on the coast of Asia.
Just like on land, the ocean can experience heatwaves. These heatwaves can cause habitat loss, widespread coral bleaching, and more stress and damage to different ecosystems. Immobile organisms like coral, algae, and sponges are more at risk for these events.
Water has a much higher heat capacity than land; thus, the ocean doesn’t experience large temperature changes as we do on land. So scientists closely monitor the temperature of the ocean to hopefully predict and understand many of the impacts discussed above.
Similar to on land, the ocean’s surface temperature changes across latitudes. Closer to the equator, you will find higher temperatures and lower temperatures towards the poles. The tilt of the Earth creates this effect. While the ocean doesn’t have as large temperature differences as we do on land, the temperature still changes seasonally. As seen in this line graph there is an almost 40°C change in temperature between the equator and the poles.
Another measure of the ocean surface is salinity. Salinity is the concentration of salts and minerals in water. Salinity impacts ocean circulation, the water cycle, marine life, and carbon uptake.
The circulation of water in the ocean drives deep water currents that allow nutrients to move throughout different depths of the ocean. The more salty the water, the more dense it is, and thus more dense water sinks, which is downwelling; as the water moves in currents to warmer areas, the water comes back to the surface in upwelling.
Salinity will fluctuate based on evaporation and precipitation, so measuring salt concentration is a good indicator of the water cycle and climate patterns. Higher salinity levels may indicate more evaporation, which could indicate warmer weather and more direct sunlight. Lower salinity levels may indicate more precipitation, so either more rain, which indicates a rainy season, or more ice melting at the poles, which is an indication of warmer weather.
Salinity impacts the buoyancy and metabolism of many marine organisms. The higher the salinity, the denser the water. The denser the water, the greater the buoyant force is exerted. This leads to fish and other marine organisms floating more easily, which allows them to expend less energy.
The makeup of the dissolved salts in the oceans impacts the ocean’s ability to absorb carbon dioxide. When salinity is high, it takes up more space, which limits the amount of room carbon dioxide has to be absorbed in the ocean. Higher salinity forces more carbon dioxide to stay in the atmosphere, which can be very dangerous.