Abstract
AbstractArctic sea surface height (SSH) is poorly observed by radar altimeters due to the poor coverage of the polar oceans provided by conventional altimeter missions and because large areas are perpetually covered by sea ice, requiring specialized data processing. We utilize SSH estimates from both the ice‐covered and ice‐free ocean to present monthly estimates of Arctic Dynamic Ocean Topography (DOT) from radar altimetry south of 81.5°N and combine this with GRACE ocean mass to estimate steric height. Our SSH and steric height estimates show good agreement with tide gauge records and geopotential height derived from Ice‐Tethered Profilers. The large seasonal cycle of Arctic SSH (amplitude ∼5 cm) is dominated by seasonal steric height variation associated with seasonal freshwater fluxes, and peaks in October–November. Overall, the annual mean steric height increased by 2.2 ± 1.4 cm between 2003 and 2012 before falling to circa 2003 levels between 2012 and 2014 due to large reductions on the Siberian shelf seas. The total secular change in SSH between 2003 and 2014 is then dominated by a 2.1 ± 0.7 cm increase in ocean mass. We estimate that by 2010, the Beaufort Gyre had accumulated 4600 km3 of freshwater relative to the 2003–2006 mean. Doming of Arctic DOT in the Beaufort Sea is revealed by Empirical Orthogonal Function analysis to be concurrent with regional reductions in the Siberian Arctic. We estimate that the Siberian shelf seas lost ∼180 km3 of freshwater between 2003 and 2014, associated with an increase in annual mean salinity of 0.15 psu yr−1. Finally, ocean storage flux estimates from altimetry agree well with high‐resolution model results, demonstrating the potential for altimetry to elucidate the Arctic hydrological cycle.
Highlights
The Arctic is experiencing some of the most rapid climatic changes on Earth [IPCC, 2013] including the reduction of sea ice extent [e.g., Stroeve et al, 2012] and the emergence of Arctic amplification [e.g., Serreze et al, 2009; Serreze and Barry, 2011]
The interannual variability of the steric height seasonal cycle is smaller than our monthly steric height uncertainty estimate, suggesting that our uncertainty estimate is probably quite conservative. This complements the findings of Volkov and Landerer [2013] that nonseasonal Sea surface height (SSH) fluctuations at monthly time scales are due to ocean mass changes driven by atmospheric forcing; we find that steric height variations account for the largest part of the Arctic SSH seasonal cycle
Between 2012 and 2014, the steric height dropped back to circa 2003 levels. To investigate whether this is caused by redistribution of freshwater back to the central Arctic basin, we examined the change in steric height from 2012 to 2014, utilizing the synoptic coverage provided by CryoSat-2 (Figure 10)
Summary
The Arctic is experiencing some of the most rapid climatic changes on Earth [IPCC, 2013] including the reduction of sea ice extent [e.g., Stroeve et al, 2012] and the emergence of Arctic amplification [e.g., Serreze et al, 2009; Serreze and Barry, 2011]. Proshutinsky et al [2004] have used tide gauges to estimate secular sea level change in the Siberian Arctic of 1.85 mm/yr between 1954 and 1989, and Richter et al [2012] estimate trends of 1.3–2.3 mm/yr along the Norwegian coast between 1960 and 2010. Conventional processing of satellite radar altimetry breaks down in the presence of sea ice, meaning that SSH in large areas of the Arctic and adjacent seas is not routinely monitored. This has meant that conventional altimeter studies of Arctic SSH have been limited to the open ocean [e.g., Prandi et al, 2012]
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