Abstract
Instrumental data evidence an accelerating freshwater release from Arctic sea ice export and the Greenland Ice Sheet over the past three decades causing cooling and freshening in the subpolar North Atlantic region. However, evaluating the observed acceleration on a historical oceanic and climatic perspective remains challenging given the short available instrumental time series. Here we provide a marine perspective on the freshwater releases to the ocean since 1850 as reflected in the northern limb of the Subpolar Gyre. Our reconstructions suggest that the recent acceleration tracks back to the 1940s/50s and is unprecedented since 1850. The melting, initiated by the 1920s natural rise in solar irradiance, accelerated in response to a combined effect of natural and anthropogenic forcing factors. We find that Greenland’s freshwater discharge has contributed to a nutrient-driven fertilization of the upper ocean and consequently increased the marine primary productivity since the 1940s/50s.
Highlights
MethodsThe marine sediment core GS15-198-33 was collected by the R/V ‘G.O. Sars’ in 2015 at 66°37.53′N, 20°51.16′W from 361 m water depth offshore western North Iceland
Despite the negative trend in solar irradiance forcing since the 2000s (Fig. 3c), the northern hemisphere has experienced significant climatic warming (Supplementary Fig. 5e) and ice sheet melting, and drift/sea ice retreat continued at an unprecedented rate similar to carbon emissions (Fig. 3d) and the global sea-level rise[8]
Our combined analyses of historical and proxy data provide evidence that this surface water freshening in the subpolar North Atlantic started already back in the 1940s/50s, and is part of a longer-term process
Summary
The marine sediment core GS15-198-33 was collected by the R/V ‘G.O. Sars’ in 2015 at 66°37.53′N, 20°51.16′W from 361 m water depth offshore western North Iceland. Core GS15-198-33 has been collected from a well-known high accumulation area on the shelf that was previously sampled in 1999 by the R/V ‘Marion Dufresne’ (core MD99-2269)[25]. The sediment core was sampled continuously at 1 cm resolution (1 cm thick sediment slices)
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