Global Thermosteric Sea Level Research Articles

Global distribution of thermosteric contribution to sea level rising trend

The sea level derived from TOPEX/Poseidon (T/P) altimetry data shows prominent long term trend and inter-annual variability. The global mean sea level rising rate during 1993–2003 was 2.9 mm a−1. The T/P sea level trend maps the geographical variability. In the Northern Hemisphere (15°–64°N), the sea level rise is very fast at the mid-latitude (20°–40°N) but much slower at the high-latitude, for example, only 0.5 mm a−1 in the latitude band 40°–50°N. In the Southern Hemisphere, the sea level shows high rising rate both in mid-latitude and high-latitude areas, for example, 5.1 mm a−1 in the band 40°–50°S. The global thermosteric sea level (TSL) derived from Ishii temperature data was rising during 1993—2003 at a rate of 1.2 mm a−1 and accounted for more than 40% of the global T/P sea level rise. The contributions of the TSL distribution are not spatially uniform; for instance, the percentage is 67% for the Northern Hemisphere and only 29% for the Southern Hemisphere (15°–64°S) and the maximum thermosteric contribution appears in the Pacific Ocean, which contributes more than 60% of the global TSL. The sea level change trend in tropical ocean is mainly caused by the thermosteric effect, which is different from the case of seasonal variability in this area. The TSL variability dominates the T/P sea level rise in the North Atlantic, but it is small in other areas, and shows negative trend at the high-latitude area (40°–60°N, and 50°–60°S). The global TSL during 1945–2003 showed obvious rising trend with the rate of about 0.3 mm a−1 and striking inter-annual and decadal variability with period of 20 years. In the past 60 years, the Atlantic TSL was rising continuously and remarkably, contributing 38% to the global TSL rising. The TSL in the Pacific and Indian Ocean rose with significant inter-annual and decadal variability. The first EOF mode of the global TSL from Ishii temperature data was the ENSO mode in which the time series of the first mode showed steady rising trend. Among the three oceans, the first mode of the Pacific TSL presented the ENSO mode; there was relatively steady rising trend in the Atlantic Ocean, and no dominant mode in the Indian Ocean.