Abstract
2D sea level trend and variability fields of the Baltic Sea were reconstructed based on statistical modeling of monthly tide gauge observations, and model reanalysis as a reference. The reconstruction included both absolute and relative sea level in 11 km resolution over the period 1900-2014. The reconstructed monthly sea level had an average correlation of 96% and root mean square error of 3.8 cm with 56 tide gauges which are independent of the statistical model. The statistical reconstruction of sea level was based on multiple linear regression and took land deformation information into account. An assessment of the quality of an open ocean altimetry product (ESA Sea Level CCI ECV, hereafter “the CCI”) in this regional sea was performed by validating the variability against the reconstruction as an independent source of sea level information. The validation allowed determining how close to the coast the CCI can be considered reliable. The CCI matched reconstructed sea level variability with correlation above 90% and RMS difference below 6 cm in the southern and open part of the Baltic Proper. However, areas with seasonal sea ice and areas of high natural variability need special treatment. The reconstructed relative sea level change, which is important for coastal communities, was dominated by isostatic land movements. This pattern was confirmed by independent observations and the values were provided along the entire coastline of the Baltic Sea. The area averaged absolute sea level rise for the Baltic Sea was 1.3 ± 0.3 mm/yr for the 20th century, which was slightly below the global mean for the same period. Considering the relative shortness of the satellite era, natural variability made trend estimation sensitive to the selected data period, but the linear trends derived from the reconstruction (3.4 ± 0.7 mm/yr for 1993-2014) fitted with those of the CCI (4.0 ± 1.4 mm/yr for 1993-2015) and with global mean estimates within the limits of uncertainty.
Highlights
Considering ongoing climate change, adequate quantification of the global pattern of sea level change is of crucial importance to helping societies cope with its adverse impact on the future (IPCC, 2013)
This section first introduces the tide gauge, reanalysis model and satellite data used, the methods and data used for land movement correction, and the method used for the statistical sea level reconstruction (Figure 1)
The results presented in this paper demonstrate that the satellite altimetry observations can provide valuable information in the coastal sea for studying the long term linear sea level trends, and the two estimates of sea level trends agreed within the uncertainty limits
Summary
Considering ongoing climate change, adequate quantification of the global pattern of sea level change is of crucial importance to helping societies cope with its adverse impact on the future (IPCC, 2013). As the sea surface topography may dynamically vary in time and space in intricate patterns, the impact of climate change and of sea level change occur differently in various areas. Baltic 2D Sea Level Reconstruction on Earth (Milne et al, 2009). A problem in quantification of general sea level trends is that traditional, tide gauge-based estimation of relative sea level (RSL) change is dependent on local, spatially varying land surface movements (SantamaríaGómez et al, 2017). Their removal, on the other hand, requires the use of a truly fixed (geocentric) reference network. Recent development in Global Isostatic Adjustment (GIA) modeling (e.g., Spada, 2017; Simon et al, 2018; Vestøl et al, 2019), use of satellite altimetry (e.g., Nerem et al, 2018) and sea surface reconstructions (Meier et al, 2004; Madsen et al, 2015) have contributed to overcoming the abovementioned problems
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