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Evaluating the Role of Seasonal Freshwater Flux Variability on the Anomalous 2016 Seasonal Freshening of Ocean Surface water in the SPURS-2 Region
[24-May-17] Paget, A., Edson, J., and Clayson, C.A.
Presented at the Global Ocean Salinity and the Water Cycle Workshop
The upper ocean waters in the SPURS-2 region undergo an annual cycle of seasonal freshening. From 2011 through 2015, the annual range of these variations was from 33 to 35 PSU; however, during 2016 the range extended from 31 to 34 PSU. In particular, the October and November of 2016 are fresher than the previous years, and, even more striking, the salinity values during that period are nearly 1 PSU fresher than the previous years. This freshening is confirmed by Argo floats, the SPURS-2 Buoy, and SMAP observations. The goal of this work is to understand the reasons for this increased freshening in 2016.

Contributing factors to the variations in the salinity come from precipitation, evaporation, mixing, and advection. The role of each of these contributing factors in this event are discussed, using a combination of satellite, reanalysis, and in situ data. Sea surface salinity (SSS) observations from satellites are available from Aquarius, SMAP, and SMOS. The NASA Aquarius/SAC-D mission was developed with the goal of measuring sea surface salinity (SSS) with the Aquarius instrument on the SAC-D satellite observatory platform. Aquarius launched in 2011 and provided data from August 2011 – May 2015 (shown from 2013). The Aquarius L3 data are a weekly SSS product on a 0.25° x 0.25° grid and are available from NASA JPL PO.DAAC. Satellite-based SSS observations are also produced by the NASA Soil Moisture Active Passive (SMAP) instruments with data as an 8-day running mean of SSS starting in April 2015 on a 0.25° x 0.25° grid and are available from NASA JPL PO.DAAC. The European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) provides SSS observations starting in January 2010.

In situ data comes from the Argo floats and from the SPURS-2 Buoy. The Argo float data comes as a 10-day value for the mixed layer salinity gridded globally and are available from the Japan Argo Delayed-mode Data Base (Argo JAMSTEC, JAMSTEC.GO.JP/ARGO). For this analysis, periods without Argo floats near the SPURS-2 Buoy location are 2-D linearly interpolated from the surrounding Argo observations for the same date. The Argo data record covers the entire time period of available satellite observations. The SPURS-2 Buoy, located at 10 N, 125 W, provides a full suite of in situ observations of the ocean surface and near surface including SSS. Hourly values of SSS from the SPURS-2 Buoy are analyzed in this record starting late August 2016.

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