Science Meetings

Contemporary Changes and Links Between Salinity and the Global Ocean Water Cycle
Vinogradova, N.T. and Ponte, R.M. (16-Dec-16)

To understand the ongoing alteration of the Earth’s water budget, it is essential to assess the variability of its oceanic constituent as this component supplies more than 75% of the evaporated and precipitated water in the global water cycle. Here we examine the change in the ocean water cycle and the ocean's response to such changes over the contemporary, well-observed period spanning the last two decades. In particular, we focus on recent changes in surface salinity and fluxes of freshwater within the atmosphere-ocean-land-ice system. Using a combination of historical observations and data-constrained ocean estimates we demonstrate that there have been persistent changes (defined as significant trends) in both salinity and the ocean water cycle in many ocean regions, including the subtropical gyres in both hemispheres, low latitudes of the tropical Pacific, the North Atlantic subpolar gyre and the Arctic Ocean. On average, the ocean water cycle has amplified by 5% since 1993, but strong regional variations exist, e.g., up to 11% intensification in the South Pacific contrasting with pattern weakening of -7% in the North Atlantic. An even larger spread in regional variations of the pattern amplification is visible in surface salinity records, ranging between +50% in the Southern Ocean to -40% in the North Atlantic, averaging to less than 1% over the globe. These findings imply a time of emergence of anthropogenic hydrological signals shorter in surface freshwater fluxes than in surface salinity, and point to the importance of ocean circulation and salt transports in shaping patterns of decadal change in surface salinity. The latter is discussed within a closed budget framework by examining the balance between the atmospheric freshwater fluxes and the ocean salt fluxes in regions of salinity extremes, such as salinity maxima in the subtropical gyres and salinity minima in the tropics and high latitudes.