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Charting the current climate

With the recent publication of the ICES Report on Ocean Climate (IROC) 2015, we take a look at some of the key trends highlighted in the document.
Published: 4 November 2016
​​​​​​​​A fountain of knowledge

While a vast quantity of fisheries and biological data is handled and stored ICES, there is also a wealth of information relating to the physical environment harnessed from across the organization's area. Each year this encyclopaedia of knowledge is compiled by the Working Group on Oceanic Hydrography, which sources it from various experts and institutions over decades of observations. The resulting publication, the ICES Report on Ocean Climate (IROC), uses the longest time-series of data to give the best possible overview of oceanic change.

This year's IRO​​C​, published in September and part of the Cooperative Research Report (CRR) series, provides the latest information on the state of North Atlantic and Nordic seas in 2015, mainly at the ocean's surface and the upper thousand metres of water, but also in places at its depths. Although the document largely focuses on measurements of temperature and salinity, datasets on parameters such as sea level pressure, air temperature, and ice cover are also included. 

Much of the data that form the bedrock of the report can also be visualized and downloaded through an interactive online application, which hosts aggregated data from all of the points across the ICES area.

​​From the air...                                                                           

Throughout 2015, the temperature of the air over the sea region containing the Subpolar Gyre were noted to be lower than usual. This dip was particularly pronounced in winter, for the gyre as well as for Northeast America, Labrador, and West Greenland. Despite the lower-than-usual winter air readings over the North American continent though, the waters of the Northeast US continental shelf remained warmer than average.

Over the Northwest Atlantic, air temperatures were ​especially cold during the first half of the year. At the end of the year, however, above average air temperatures were observed over the European continent stretching from the coast of the Iberian Peninsula in the south to Svalbard in the north.

Over the Nordic seas, Scandinavia, and central and eastern Europe, winter air temperatures were higher than usual.

...to the water

At the sea surface, temperatures in the North and Baltic seas as well as along the Norwegian coast were recorded at higher-than-normal levels, with the exception of summer. South of Iceland and in the southern part of the Nordic seas were lower, with the Iceland Basin displaying its lowest temperature measurements since 1996. Another standout cold zone was near the 50°N latitude in the central North Atlantic. This anomaly lasted throughout the year, expanding to influence other areas covered by the time-series.

Fresh 

Another important variable in the seas and oceans is the composition of salt and fresh water, consistencies of which can differ depending on the layer of water. The IROC takes this into account through monitoring of the ocean's upper layers. Freshening, the greater presence of fresh water, had occurred in these layers in the the Irminger Sea, Iceland Basin, and Hatton-Rockall Basin as well as in adjacent parts of the Nordic seas following periods of high salinity between 2009 and 2011. Freshening was also noted in the Bay of Biscay, continuing and strengthening the trend first seen in 2014.

Sea ice, meanwhile, was at a record low in the Baltic Sea, whilst in the Barents Sea the peak extent of ice formation was reached in February, two months earlier than usual.

Cold spots

One weather occurrence also charted in the IROC is the North Atlantic Oscillation (NAO). The condition describes fluctuations in the atmospheric pressure at sea level between the Icelandic low, a centre of low pressure, and the Azores high, an area of high pressure, both of which feed into the NAO as it governs the strength and direction of westerly winds and storm tracks across the North Atlantic. An index is kept of this phenomenon, which, in 2015, was at its highest positive (+3.56) since 1995 and the fourth strongest in the last 110 years.

"The cold anomaly centered near 50°N in the central North Atlantic (termed "the cold blob" by the media) was in the IROC ​2013/2014 mentioned as a feature that did not influence the borders of the ocean, where in-situ sampling mainly takes place. In the 2015 report we are able to follow the evolution of the cold anomaly: it has now expanded and its influence is visible in temperature time series from the North Atlantic and southern Norwegian Sea," explained IROC editor and WGOH co-chair Karin Larsen.

The IROC also gives an initial assessment of the North Atlantic atmosphere in winter 2015/2016. Here, the sea level pressure pattern indicated a positive but weaker NAO index than in 2014 and 2015. ​​​

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​The Norwegian research vessel Lance picking up readings in the Fram Strait in 2007; photo: Agnieszka Beszczynska-Möller

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Charting the current climate

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