About every 14 years, a significant temperature change is observed in the ocean between Greenland and Svalbard. Why, you wonder? Well, the Gulf Stream transports warm water northwards and on a regular basis, the water is even warmer and saltier than normally. These variations are regular, but can we predict these changes reliably?

This question is what Helene R. Langehaug from the Nansen Center and several of her colleagues set out to answer in a new article. First though, a bit of background knowledge.

The Gulf Stream, the Atlantic water pathway, and unusual variations in temperature and salt content

The Gulf Stream is a current in the Atlantic, originating in the Gulf of Mexico. It transports warm surface water along the eastern coast of North America and towards Europe. But the Gulf Stream’s reach does not stop there – it extends northwards. This Atlantic water pathway transports warm water further northwards, up along the Norwegian Coast, and all the way into the waters between Greenland and Svalbard, leading into the Arctic Ocean. Observations have shown that the surface temperature and salt content of the water increases significantly on a regular basis along this pathway: About every 14 years, and such a variation can be traced all the way back to the Gulf Stream. It takes about 10 years for an anomaly to propagate from the south to the north. This was documented in a Nature Communications article from 2017 and was the basis for Helene R. Langehaug and her colleagues when they started their investigations.

A map of the Atlantic Ocean showing the Gulf Stream as pink arrow, and the Atlantic water pathway is indicated as red arrow. By Helene R. Langehaug.

Implications of higher water temperatures

The water temperature impacts the western European climate, fisheries in the Atlantic are affected by it, and the Arctic sea ice is influenced as well. So, being able to reliably predict these anomalies years and decades in advance is desirable. Researchers have developed computer programs that can predict the climate from years over decades to hundreds of years in advance. They are climate models that can be used to look forward in time, and even backward in time. The latter is useful for judging how well a model actually simulated real-world conditions at a given date and location in the past.

Can climate models properly predict the anomalies?

Helene R. Langehaug and her colleagues wanted to find out how good different climate models are at predicting when and where these anomalies occur along the Atlantic water pathway. They found that the climate models generally struggle to reliably reproduce anomalies that propagate along the Atlantic water pathway on longer timescales (beyond 1-2 years). The researchers hypothesise that the problem with predicting them lies within how the transport mechanisms are represented in the climate models, and that these are currently not properly resolved. Addressing this problem will likely improve how climate models can represent these anomalies, wandering along the Atlantic water pathway all the way to the Arctic Ocean. Achieving this, we can more reliably assess their impacts on our regional climate in (north-) western Europe.

Involved researchers and affiliations

Helene R. Langehaug from the Climate Dynamics and Prediction group at the Nansen Center led the study, her NERSC co-authors are François Counillon, Noel Keenlyside (also at the Geophysical Institute/University of Bergen), and Yiguo Wang. They collaborated with researchers from the University of Bergen, as well as researchers in Spain, Germany, the US, France, Denmark, and in Italy. The researchers at Norwegian Institutes are also affiliated with the Bjerknes Centre for Climate Research in Bergen. The study is a contribution to the EU project Blue-Action and the Bjerknes Climate Prediction Unit.

Publikasjon

Journal of Climate:
«Propagation of Thermohaline Anomalies and their predictive potential along the Atlantic water pathway»

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