Decadal Salinity Changes in the Oceanic Subtropical Gyres and Connection to Changes in the Global Water Cycle
There is evidence that the global water cycle has been undergoing an intensification over several decades as a response to increasing atmospheric temperatures, particularly in regions with skewed evaporation – precipitation (E-P) patterns such as the oceanic subtropical gyres. However, observation...
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| Format: | Text |
| Language: | English |
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Scholar Commons
2016
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| Online Access: | https://scholarcommons.sc.edu/etd/3886 https://scholarcommons.sc.edu/context/etd/article/4898/viewcontent/Melzer_sc_0202M_14695.pdf |
| Summary: | There is evidence that the global water cycle has been undergoing an intensification over several decades as a response to increasing atmospheric temperatures, particularly in regions with skewed evaporation – precipitation (E-P) patterns such as the oceanic subtropical gyres. However, observational data (rain gauges, etc.) can be quite sparse over such areas due to the inaccessibility of open ocean regions. This study utilizes in situ data, reanalysis, and model outputs to infer interannual to decadal scale trends in surface freshwater forcing within remote, evaporation-dominated subtropical regions of the ocean as they pertain to the past and present state of the global water cycle. Emphasized in this study is the importance of utilizing a wide range of ocean parameters to strengthen and validate the inferences made from any one proxy of a given parameter. A positive trend in sea surface salinity in the subtropical gyres revealed evidence for decadal intensification in the surface forcing of these regions. Zonal drift in the location of the salinity maximum of the south Pacific, north Atlantic, and south Indian regions implies a change in the mean near-surface currents responsible for advecting high salinity waters into the region. Additionally, a comparison of satellite, in situ, and model salinity datasets was conducted to highlight the potential applications of Aquarius and SMOS satellite-derived salinity products over oceanic regions of low observational density. Spatial and temporal salinity trends in the five subtropical gyre regions were also analyzed over the past six decades, with a focus on the subsurface salinity of the upper 1000 m of the ocean. Our results indicate an overall salinity increase within the mixed layer, and a salinity decrease at depths greater than 200m in the global subtropical gyres over 61 years. Our analysis of decadal variability of depth-integrated mixed layer fluxes into and out of the gyres reveals little change in the strength of the mean currents through this region ... |
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