The ocean mass emphasizes the interannual variations of sea level difference in super El Niño events, and its relation to land water storage variations

Abstract:

Global mean sea level (GMSL) variations are closely linked to the anthropogenic impacts and natural climate variability, such as the El Niño Southern Oscillation (ENSO). ENSO is an unignorable contributor to interannual variations of GMSL. Observed records show that the GMSL peak during the 2015–2016 El Niño event (8.40 mm) is approximately 100% higher than that of the 1997–1998 case (3.59 mm), in which the ENSO strengths were similar, and the reason of such differences remains elusive. Here, we use multiple sources of observational data from satellite altimetry, satellite gravity (Gravity Recovery and Climate Experiment, GRACE), in-situ ocean floats (Argo), and reanalysis data from Estimating the Circulation and Climate of the Ocean (ECCO) to demonstrate that the barystatic (ocean mass) and steric (ocean density) ocean states have specific temporal characteristics during the two ENSO events. We found that the disparity in GMSL changes can be attributed to the difference in barystatic response to El Niño events. Compared to the shorter 1997–1998 event, the prolonged El Niño since late 2014 affords a more extended period to accumulate ocean mass. The variations in precipitation and evaporation during 2014–2016 were more substantial than that during the 1996–1998 event. These results indicate that the duration, not the magnitude, of the El Niño event, might play more critical roles in the GMSL response. The barystatic effect dominates the interannual GMSL variation, which underscores the role of water mass transition in different reservoirs on Earth. This study also implies the essential role of land hydrological processes in GMSL changes.