Halosteric Sea Level Changes during the Argo Era

Authors:

Gongjie Wang¹, Lijing Cheng^2,*, Timothy Boyer³ and Chongyin Li^1,4

¹Institute of Meteorology and Oceanography, National University of Defense Technology, Nanjing 210001,China; wanggj_9015@sina.com (G.W.); lcy@lasg.iap.ac.cn (C.L.)

²International Center for Climate and Environment Sciences, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

³NOAA/United States National Centers for Environmental Information (NCEI), Silver Spring, MD 20910, USA;  tim.boyer@noaa.gov

⁴State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

* Correspondence: chenglij@mail.iap.ac.cn

Abstract:

In addition to the sea level (SL) change, or anomaly (SLA), due to ocean thermal expansion, total steric SLA (SSLA, all change to the existing volume of ocean water) is also affected by ocean salinity variation. Less attention, however, has been paid to this halosteric effect, due to the global dominance of thermosteric SLA (TSLA) and the scarcity of salinity measurements. Here, we analyze halosteric SLA (HSLA) since 2005, when Argo data reached near-global ocean coverage, based on several observational products. We find that, on global average, the halosteric component contributes negatively by ~5.8% to SSLA during the 2005–2015 period, and reveals a modest correlation (~0.38) with ENSO on the inter-annual scale. Vertically, the global ocean was saltier in the upper 200-m and fresher within 200 to 600-m since 2005, while the change below 600-m was not significantly different from zero. The upper 200-m changes dominate the HSLA, suggesting the importance of surface fresh water flux forcing; meanwhile, the ocean dynamic might also play a role. The inconsistent pattern of salinity trend between upper 200-m and 200 to 600-m implies the importance of ocean dynamics. Our analysis suggests that local salinity changes cannot be neglected, and can even play a more important role in SSLA than the thermosteric component in some regions, such as the Tropical/North Pacific Ocean, the Southern Ocean, and the North Atlantic Ocean. This study highlights the need to better reconstruct historical salinity datasets, to better monitor the past SSLA changes. Also, it is important to understand the mechanisms (ocean dynamics vs. surface flux) related to regional ocean salinity changes.

Key words:

sea level; halosteric; Argo; thermosteric; salinity; climate change

Citation:

Gongjie Wang, Lijing Cheng, Timothy Boyer and Chongyin Li, Halosteric Sea Level Changes during the Argo Era, Water, 2017, 9, 484; doi:10.3390/w9070484