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Located at the same latitudes as the great deserts of Africa, the central North Atlantic is home to the saltiest waters in the open ocean.
Recent evidence shows that salinity in this area has been increasing in recent decades. The Salinity Processes in the Upper Ocean Regional
Study (SPURS) includes a series of expeditions to this "salt maximum" region, funded by NASA and international collaborators.
SPURS has employed a variety of tools - floats, gliders, drifters, moorings, ships, satellites, and
computer models - to help scientists understand the processes that are controlling upper-ocean salinity. Science objectives include
determining what processes maintain the salinity maximum and influence salinity variations over time, finding where the excess salt
goes, and examining the effects of salinity change on ocean circulation.
Like other ocean-observing satellite instruments, Aquarius detects surface seawater properties to depths of about 1 cm (~0.4 in). Given the dynamic nature of Earth's seas, it is important to link Aquarius's "skin" measurements with other observations of the upper ocean. A key advance in this effort is a special series of Argo profiling floats developed at the University of Washington, which are designed to acquire salinity and temperature in the upper 10 cm (~4 in) of the ocean. These enhanced floats help to "close the gap" between Aquarius and conventional Argo floats whose shallowest data are acquired at a depth of 3-5 m (~10-16 ft). Currently, only about 1% of more than 3,000 Argo floats in Earth's ocean have this enhanced capability. However, SPURS has demonstrated the promise of using Aquarius and Argo together to improve our knowledge of how freshwater cycles between the atmosphere and the ocean.
A key goal of the oceanographic community is to combine Aquarius measurements with European Space Agency's counterpart, the Soil Moisture and Ocean Salinity (SMOS) satellite to produce an even more accurate picture of ocean salinity. Launched in November 2009, SMOS satellite collects ocean salinity data at the same frequency as Aquarius, but uses a different technology: an interferometric technique in which the signal from many small antennas is used to achieve the resolution of a large antenna. Despite the difference in technology, SMOS data are very complementary to Aquarius data. In fact, early indications are that inter-comparison of results from these two satellites are crucial to better understanding the biases between ascending passes and descending passes seen in both missions, the cause of which may be geophysical in nature. Scientists representing both the Aquarius and SMOS Missions have concluded that providing observational-based measurements that are harmonized between Aquarius, SMOS, and in situ instruments will be the most help to the scientific community.
The Water Cycle
Several recent studies have suggested that seawater is becoming fresher in high latitudes and tropical areas dominated by rain, while in sub-tropical high evaporation regions, waters are getting saltier. Every seven days, Aquarius provides a new global map of salinity, delivering steady and reliable information about the vast ocean where about 86% of global evaporation and 78% of global precipitation occur. Aquarius's continuous coverage is allowing scientists to monitor variations in the water cycle and determine if it is indeed accelerating in response to climate change.
Climate Change Implications