Abstract
Abstract. A two-dimensional reconstruction of past sea level is proposed at yearly interval over the period 1950–2003 using tide gauge records from 99 selected sites and 44-year long (1960–2003) 2°×2° sea level grids from the OPA/NEMO ocean general circulation model with data assimilation. We focus on the regional variability and do not attempt to compute the global mean trend. An Empirical Orthogonal Function decomposition of the reconstructed sea level grids over 1950–2003 displays leading modes that reflect two main components: (1) a long-term (multi-decadal), regionally variable signal and (2) an interannual, regionally variable signal dominated by the signature of El Nino-Southern Oscillation. Tests show that spatial trend patterns of the 54-year long reconstructed sea level significantly depend on the temporal length of the two-dimensional sea level signal used for the reconstruction (i.e., the length of the gridded OPA/NEMO sea level time series). On the other hand, interannual variability is well reconstructed, even when only ~10-years of model grids are used. The robustness of the results is assessed, leaving out successively each of the 99 tide gauges used for the reconstruction and comparing observed and reconstructed time series at the non considered tide gauge site. The reconstruction performs well at most tide gauges, especially at interannual frequency.
Highlights
Sea level is an indicator of climate change because it integrates the response of many components of the Earth sys-tem: the ocean and its interaction with the atmosphere, land ice, terrestrial waters
It has been shown that the main cause of regional variability in rates of sea level change is non uniform thermal expansion of the oceans (Cabanes et al, 2001), other processes may give rise to regional sea level trends
Account for the interannual/decadal variability associated with ENSO and other phenomena by coupled climate models is still imperfect insight into past regional variability over time spans longer than the altimetry record may be helpful to improve the climate models
Summary
For the last century, information about sea level is sparse and essentially based on tide gauge records along islands and continental coastlines. Previous studies used global sea level grids based on Topex/Poseidon satellite altimetry of limited (10 to 15 years) temporal coverage (e.g., Chambers et al, 2002; Church et al, 2004) or long but spatially inhomogeneous gridded time series of thermal expansion based on in situ hydrographic data (e.g., BN08). We use global dynamic heights grids from an Ocean General Circulation Model (OGCM), the OPA/NEMO model constrained by data assimilation (Madec et al, 1998). These model outputs, available over a 46-year time span (1960–2005), are combined with tide gauge records (that cover the period 1950– 2003). The resulting sea level reconstruction is presented below for the 1950–2003 time span
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