SURATLANT: a 1993–2017 surface sampling in the central part of the North Atlantic subpolar gyre

Abstract

This paper presents the SURATLANT data set (SURveillance ATLANTique). It consists of individual data of temperature, salinity, parameters of the carbonate system, nutrients, and water stable isotopes (δ18O and δD) collected mostly from ships of opportunity since 1993 along transects between Iceland and Newfoundland (https://doi.org/10.17882/54517). We discuss how the data are validated and qualified, their accuracy, and the overall characteristics of the data set. The data are used to reconstruct seasonal cycles and interannual anomalies, in particular of sea surface salinity (SSS); inorganic nutrients; dissolved inorganic carbon (DIC); and its isotopic composition δ13CDIC, total alkalinity (At), and water isotope concentrations. Derived parameters such as fCO2 and pH are also estimated. The relation between salinity and At is estimated from these data to investigate the possibility to replace missing At when estimating other parameters of the carbonate system. When examining the average seasonal cycle in the deep ocean, in both these data with other climatologies, we find a period of small seasonal change between January and late April. On the Newfoundland shelf and continental slope, changes related with spring stratification and blooms occur earlier. The data were collected in a period of multi-decennial variability associated with the Atlantic multi-decadal variability with warming between 1994 and 2004–2007, and with the recent cooling having peaked in 2014–2016. We also observe strong salinification in 2004–2009 and fresher waters in 1994–1995 as well as since 2010 south of 54° N and in 2016–2017 north of 54° N. Indication of multi-decadal variability is also suggested by other variables, such as phosphate or DIC, but cannot be well resolved seasonally with the discrete sampling and in the presence of interannual variability. As a whole, over the 24 years, the ocean fCO2 trend (+1.9 µatm yr−1) is close to the atmospheric trend and associated with an increase in DIC (+0.77 µmol kg−1 yr−1). The data also revealed a canonical pH decrease of −0.0021 yr−1. There is also a decrease in δ13CDIC between 2005 and 2017 (in winter, −0.014 ‰ yr−1, but larger in summer, −0.042 ‰ yr−1), suggesting a significant anthropogenic carbon signal at play together with other processes (mixing, biological activity).