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SMAP and CalCOFI Observe Freshening During the 2014-2016 Northeast Pacific Warm Event
[12-Feb-2018] Gomez-Valdes, J. and Vazquez, J.
Presented at the 2018 Ocean Sciences Meeting
Data from NASA's Soil Moisture Active Passive Mission (SMAP) and from the California Cooperative Oceanic Fisheries Investigations (CalCOFI) were used to examine the freshening that occurred during the Northeast Pacific Warming of 2014-2016. Overall the freshening was found to be related to the warming and the weakening of coastal upwelling.
To first determine the feasibility of using SMAP data, direct comparisons were done with salinity from the CalCOFI data at one meter depth. During 2015 SMAP was saltier than CalCOFI by 0.5 PSU, but biases were reduced to < 0.1 PSU during 2016. South of 33°N, and within 100 km of the coast, SMAP was fresher in 2015 by almost 0.2 PSU. CalCOFI showed freshening of 0.1 PSU. North of 33°N SMAP and CalCOFI saw significant freshening in 2016, SMAP by 0.4 PSU and CalCOFI by 0.2 PSU. Both showed maximum freshening in April of 2016. To study the time evolution of the oceanographic fields in the CalCOFI region, the interannual variability during 2003-2017 of the temperature and salinity anomalies were examined along the 90, 83.3, and 76.7 CalCOFI lines at 1 meter and at 100 meters depth. Overall, the range of salinity anomalies was greater during 2015 than during 2016. At CalCOFI line 90, freshening was seen more pronounced in 2015, along with positive SST anomalies of 4 degrees Celsius at 1 m depth. At CalCOFI line 76.7 (North) freshening increased in 2016 with negative SSS anomalies of 0.4 PSU at 1 m depth. The area of the negative SSS anomalies was more extensive, both temporally and spatially, at 100 m depth than at 1 m depth. Overall, SMAP and CalCOFI showed significant freshening in coastal regions, with more pronounced freshening North of 35°N in 2016. The analysis of the spatiotemporal variation of the 25.0 kg/m3 isopycnal surface from CalCOFI revealed the impact of the 2014 - 2016 warming. Freshening in the region was most likely due to the warming event and the influence of the 2014-2016 El Niño events. Differences between SMAP and CalCOFI are consistent with the increased stratification in 2015 observed in the deepening of the 25.0 kg/m3 isopycnal surface and in the T-S diagrams from CalCOFI. Results are encouraging for applying SMAP data to understanding salinity processes in coastal and upwelling regions at the interannual to climate scales.

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