The Salinity Fingerprint
Salinity is the saltiness or dissolved salt content (such as sodium chloride, magnesium and calcium sulfates, and bicarbonates) of a body of water. Salinity is an ecological factor of considerable importance, influencing the types of organisms that live in a body of water. As well, salinity influences the kinds of plants that will grow either in a water body, or on land fed by a water (or by a groundwater). For ages salinity was mostly affected by slow geologic type processes. The ocean's salinity field is driven primarily by evaporation, precipitation, and river discharge, all key elements of the Earth's hydrological cycle. Observations show the salinity field has been changing in recent decades but more rapidly than expected and by mad made effects.
The saltiness, or salinity, of the oceans is controlled by how much water is entering the oceans from rivers and rain versus how much is evaporating. This is the water cycle or the continuous movement of water on, above and below the surface of the Earth. The water moves from one reservoir to another, such as from river to ocean, or from the ocean to the atmosphere, by the physical processes of evaporation, condensation, precipitation, infiltration, runoff, and subsurface flow.
The more sunshine and heat there is, the more water can evaporate, leaving the salts behind in higher concentrations in some places. Over time, those changes spread out as water moves, changing the salinity profiles of the oceans.
Oceanographers from Scripps Institution of Oceanography and Lawrence Livermore National Laboratory fingerprinted salinity changes from 1955 to 2004 from 60 degrees south latitude to 60 degrees north latitude and down to the depth of 700 meters in the Atlantic, Pacific and Indian oceans.
The ocean data was compared to 11,000 years of ocean data generated by simulations from 20 of the latest global climate models. When they did that they found that the changes seen in the oceans matched those that would be expected from human forcing of the climate. When they combined temperature changes with the salinity, the human imprint is even clearer.
"These results add to the evidence that human forcing of the climate is already taking place, and already changing the climate in ways that will have a profound impact on people throughout the world in coming decades," the oceanographers conclude.
The key points from their report are:
1. Climate change has altered the salinity field of the world's oceans.
2. Changes match model predictions over the top 125 meters.
3. The human effect signal is even stronger when salinity is taken jointly with temperature.
For further information see Fingerprint.
Salinity image via Wikipedia.