Evidence of multidecadal salinity variability in the eastern tropical North Atlantic

Abstract

[1] Ocean circulation and global climate are strongly influenced by seawater density, which is itself controlled by salinity and temperature. Although adequate instrumental sea surface temperature (SST) records exist for most of the surface oceans over the past 100-150 years, records of salinity really only exist for the last 40-50 years. Here we show that longer proxy records from corals (Siderastrea radians) in the eastern tropical North Atlantic are dominated by multidecadal variations in salinity which are correlated with the relationship between SST and the North Atlantic Oscillation (NAO) over the course of the 20th century. The data reveal an increase in eastern tropical North Atlantic salinity of +0.5 practical salinity units (psu) between about 1950 and 1990. Rather than a monotonic secular increase, as indicated by some instrumental records, the preinstrumental coral proxy records presented here suggest that salinity in the tropical North Atlantic is periodic on a decadal to multidecadal scale.

Geochemistry-based coral palaeoclimate studies and the potential of ‘non-traditional’ (non-massive Porites) corals: Recent developments and future progression

“…However, variability between sampling transects within the same colony of Cape Verde S. radians was fairly high, although this may be an artefact of the sampling strategy utilised by Moses et al (2006a), wherein they were unable to restrict sampling to the 50 μm wide thecal wall. Despite these issues, Moses et al (2006b) were able to reconstruct a 0.1 increase in eastern tropical North Atlantic salinity from δ 18 O in S. radians from the Cape Verde Islands, similar to that observed in the instrumental record .…”

Calibration of stable oxygen isotopes in Siderastrea radians (Cnidaria:Scleractinia): Implications for slow‐growing corals

“…This is possible to explain because the seasonal SST signal is much greater than the difference in mean annual SST from one year to the next. The positive slope is likely caused by environmental factors that effect δ 18 O coral more than SST on an interannual basis [ Moses et al , 2006].…”

“…Unfortunately, there is no coherent record of SSS in the Cape Verde Islands. Considering the reported ability of Siderastrea to record salinity variations [ Guzmán and Tudhope , 1998; Swart et al , 1998], it is possible that even minimal interannual variability in the SSS, on the order of ±0.1–0.2 psu, could be corrupting the SST – δ 18 O relationship at the annual and interannual scales resulting in the apparent lack of correlation [ Moses et al , 2006].…”

Gulf Stream and ENSO Increase the Temperature Sensitivity of Atlantic Tropical Cyclones

“…Meandering of the Gulf Stream and variations in the northward transport of heat have been associated (Dijkstra and Ghil 2005) with 7.8-yr periodicity in the NAO; however, we find no coherence between TC and NAO. The Atlantic and Gulf Stream properties appear to have decadal to multidecadal periodicity (Dijkstra and Ghil 2005;Bryden et al 2005;Moses et al 2006). High-frequency atmospheric forcing can lead to a low-frequency response in the coupled atmosphere-ocean system; moreover, feedbacks between the ocean and atmosphere may act in concert to amplify perturbations (Dijkstra and Ghil 2005).…”