For more than forty years, ICES Working Group on Ocean Hydrography (WGOH) have carried out analyses of multiple time-series to give an overview of the state of the environment in the North Atlantic: climate headlines, the North Atlantic atmosphere, summary of upper ocean conditions, and detailed area descriptions for the upper and lower oceans.
The highlights for 2018 have just been released by WGOH.
In 2016, freshening of the upper ocean (0–1000m depth) was observed in the eastern subpolar North Atlantic. This decrease in salinity has since expanded northwards into the Nordic seas, influencing the Greenland Sea and northern Norwegian Sea to Fram Strait, as well as the southern reaches of the Barents Sea. Freshening is also observed spreading westward into the Irminger Sea and eastward into the North Sea.
Throughout the subpolar region, freshening is accompanied by moderate cooling at just a few sites, indicating that the large changes in salinity are dissociated from changes in temperature.
Freshening of central waters in the northeast Subtropical Gyre and intergyre region (Bay of Biscay, West Iberia, Gulf of Cadiz, and Canaries) was enhanced and extended deeper into the water column. In contrast to northern regions, temperatures here decreased in concert with freshening, thereby conserving water mass properties.
Coupled with atmospheric conditions, sea surface temperatures (SST) exhibited a tri-pole pattern, with warm conditions in both the subtropical and Nordic seas regions and cooler conditions in the subpolar region. A cold anomaly observed in the surface and upper ocean of the central subpolar North Atlantic intensified and expanded after weakening in 2017.
The Scotian and Northeast US shelves were warmer than normal, accompanied by notable freshening at several sites.
Extremely warm temperatures were observed near the surface in spring–summer across the Baltic Sea and the North Sea (> 1.5˚C than normal), with less pronounced warming observed from Biscay to Ireland (0.5–+1.0 ˚C).
The North Atlantic Oscillation (NAO) index is a measure of the difference 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. The index is a simple indicator of the relative strength of these two pressure systems and of the strength and direction of westerly winds and storm tracks across the North Atlantic that they help govern. Following a run of four consecutive winters with strong positive index, the winter North Atlantic Oscillation (NAO) index was near neutral, meaning that it alone cannot explain anomalies in ocean conditions at the start of 2018.
The Azores High–Iceland Low systems had little influence in the winter anomaly pattern of sea level pressure in 2018. Instead, a low-pressure anomaly centred over northern France, and a large-scale high-pressure anomaly was split to the northeast and southwest of Iceland across the Nordic seas, Northwest Atlantic, and Labrador Sea.
North-westerly wind anomalies between Cape Farewell and Iberia and north-easterly wind anomalies from northern Norway to Rockall contributed to cold conditions across Europe's Atlantic coast from Gibraltar to Tromsø.
Air temperatures were cold over the Subpolar Gyre, including over the Irminger Sea and Iceland Basin. Warmer-than-average conditions were evident in the Greenland Sea, Barents Sea and west of the Azores towards Nova Scotia spreading northwards into the western Labrador Sea.
The Barents Sea experienced notably stronger winds than average across the rest of 2018, part of a pattern of strong winds stretching from the western Sub Polar Gyre through the Norwegian Sea, affecting a number of scientific cruises in the region.
The sea-level pressure (SLP) pattern for December 2018–March 2019 suggests that the NAO winter index will again be weakly positive and near-neutral. In contrast to winter 2017/2018, high pressure across western Europe through to Iceland led to warm conditions in Europe and cold air temperatures south of Newfoundland.
Wind speeds were generally lower than average in winter 2018/2019, particularly so east of Newfoundland, south of Cape Farewell, and in a band stretching across the Nordic Seas from Scoresby Sund in Greenland to the North Cape of Norway.
Experimental forecasts from the US (seasonal periods: NOAA Climate PredictionCenter - The North American Multi-Model Ensemble) and the UK (1–5 years: Met Office Decadal forecast January 2019) suggest a warmer outlook for the Subpolar Gyre region more typical of the long-term average (1981–2010).
WGOH's findings form the basis of the annual ICES Report on Ocean Climate (IROC). The data are available to visualize and download. Through their assessment of trends in ocean climate, WGOH improve our understanding of the oceanography of the North Atlantic. As this
understanding advances and evolves, so does our
capacity to report and advise on the status of the
marine environment and to measure, describe, and
manage human interactions with the sea.
A pod of pilot whales surround the deployment of a CTD. Photo: David Herbert.