The Flow of Atlantic Water to the Nordic Seas and Arctic Ocean (original) (raw)

North Atlantic–Nordic Seas exchanges

Progress in Oceanography, 2000

The northeastern part of the North Atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes. The main reason for this is the large northward transport of heat that extends to high latitudes and crosses the Greenland-Scotland Ridge to enter the Nordic Seas and the Arctic. There the warm Atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge. In this paper, the state of knowledge on the exchanges especially across the eastern part of the Greenland-Scotland Ridge is reviewed based on results from the ICES NANSEN (North Atlantic-Norwegian Sea Exchanges) project, from the Nordic WOCE project and from other sources. The accumulated evidence allows us to describe the exchanges in fair detail; the origins of the waters, the patterns of their flow towards and over the ridge and their ultimate fate. There is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood. Quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established, and transport measurements of the Atlantic inflows to the Nordic Seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented. The deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water. The dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the Atlantic water inflow across the Greenland-Scotland Ridge, while wind stress seems to influence the characteristics and distribution of the Atlantic water north of the ridge.

Changes in Atlantic water properties: an important factor in the European Arctic marine climate

ICES Journal of Marine Science, 2012

Walczowski, W., Piechura, J., Goszczko, I., and Wieczorek, P. 2012. Changes in Atlantic water properties: an important factor in the European Arctic marine climate. – ICES Journal of Marine Science, 69: 864–869. The advection of warm Atlantic water (AW) through the Nordic Seas and its transformation (cooling and freshening) is one of the most important climatological processes in the region. Time-series of hydrographic observations in the northern Nordic Seas and the Fram Strait region are presented and analysed. Significant variability in the properties of AW has been observed in recent years. A 15-year time-series of summer observations indicate positive trends in salinity and temperature and two 5–6-year cycles. The northward advance of AW in 2006 was an unprecedented event. The position of the warm-water tongue shifted more than 350 km to the north, and temperatures in the West Spitsbergen Current reached the highest values ever recorded. These changes in AW temperature, heat co...

2000 years of North Atlantic-Arctic climate

Quaternary Science Reviews, 2019

The North Atlantic-Arctic boundary is highly variable due to the transports of heat and moisture through the Gulf Stream and polar jet stream. The North Atlantic storm track generally follows the Gulf Stream and terminates near southeast Greenland and Iceland as the Icelandic Low. The Icelandic Low is the main driver of the North Atlantic Oscillation, particularly during winter months as the baroclinic zone expands to lower latitudes, correlating with temperature and precipitation in many areas around the North Atlantic. Understanding how atmospheric circulation, temperature, and precipitation changes in this region is important to build robust projections of how these variables will change, especially under natural and anthropogenic forcings. Here, climate proxies correlating to the Icelandic Low, summer air temperature, and annual precipitation build an understanding of how these variables changed over the last 2000 years. Through the natural climate shifts of this period d Roman Warm Period, Dark Ages Cold Period, Medieval Climate Anomaly, and Little Ice Age d it is shown that storm frequency decreases as temperature increases and the Icelandic Low increases in pressure (i.e., becomes weaker). However, these climate changes are not simultaneous, and their amplitudes are not similar across the region. Keeping regionality rather than a pan-Arctic average better explains natural variability of each subregion and how each sub-region has evolved climatically due to anthropogenic forcings of greenhouse gases.

The role of the Atlantic Water in multidecadal ocean variability in the Nordic and Barents Seas

Progress in Oceanography, 2014

The focus of this work is on the temporal and spatial variability of the Atlantic Water (AW). We analyze the existing historic hydrographic data from the World Ocean Database to document the long-term variability of the AW throughflow across the Norwegian Sea to the western Barents Sea. Interannual-to-multidecadal variability of water temperature, salinity and density are analyzed along six composite sections crossing the AW flow and coastal currents at six selected locations. The stations are lined up from southwest to northeast -from the northern North Sea (69°N) throughout the Norwegian Sea to the Kola Section in the Barents Sea (33°30 0 E). The changing volume and characteristics of the AW throughflow dominate the hydrographic variability on decadal and longer time scales in the studied area. We examine the role of fluctuations of the volume of inflow versus the variable local factors, such as the air-sea interaction and mixing with the fresh coastal and cold Arctic waters, in controlling the long-term regional variability. It is shown that the volume of the AW, passing through the area and affecting the position of the outer edge of the warm and saline core, correlates well with temperature and salinity averaged over the central portions of the studied sections. The coastal flow (mostly associated with the Norwegian Coastal Current flowing over the continental shelf) is largely controlled by seasonal local heat and freshwater impacts. Temperature records at all six lines show a warming trend superimposed on a series of relatively warm and cold periods, which in most cases follow, with a delay of four to five years, the periods of relatively low and high North Atlantic Oscillation (NAO), and the periods of relatively high and low Atlantic Multidecadal Oscillation (AMO), respectively. In general, there is a relatively high correlation between the year-to-year changes of the NAO and AMO indices, which is to some extent reflected in the (delayed) AW temperature fluctuations. It takes about two years for freshening and salinification events and a much shorter time (of about a year or less) for cooling and warming episodes to propagate or spread across the region. This significant difference in the propagation rates of salinity and temperature anomalies is explained by the leading role of horizontal advection in the propagation of salinity anomalies, whereas temperature is also controlled by the competing air-sea interaction along the AW throughflow. Therefore, although a water parcel moves within the flow as a whole, the temperature, salinity and density anomalies split and propagate separately, with the temperature and density signals leading relative to the salinity signal. A new hydrographic index, coastal-to-offshore density step, is introduced to capture variability in the strength of the AW volume transport. This index shows the same cycles of variability as observed in temperature, NAO and AMO but without an obvious trend.

Warm Atlantic surface water inflow to the Nordic seas 34–10 calibrated ka BP

Paleoceanography, 2008

1] A number of short-lasting warm periods (interstadials) interrupted the otherwise cold climate of the last glacial period. These events are supposedly linked to the inflow of the warm Atlantic surface water to the Nordic seas. However, previous investigations of planktonic foraminifera from the Nordic seas have not been able to resolve any significant difference between the interstadials and intervening cold stadials, as the faunas are continuously dominated by the polar species Neogloboquadrina pachyderma s. Here we examine the planktonic foraminifera assemblages from a high-resolution core, LINK17, taken at 1500 m water depth off northern Scotland below the warmest part of the inflowing Atlantic water. The core comprises the time period 34-10 calibrated ka B.P., the coldest period of the last glaciation and the deglaciation. The results reveal a hitherto unknown faunistic variability indicating significant fluctuations in both surface water inflow and in summer sea surface temperatures. During the interstadials, relatively warm Atlantic surface water (4-7°C) flowed north into the eastern Norwegian Sea. During the stadials and Heinrich events the surface inflow stopped and the temperatures in the study area dropped to <2°C. The Last Glacial Maximum was nearly as warm as the interstadials, but the inflow was much more unstable. The data reveal two previously unrecognized warming events each lasting more than 1600 years and preceding Heinrich events HE3 and HE2, respectively. By destabilizing the ice sheets on the shelves the warmings may have played a crucial role for the development of Heinrich events HE2 and HE3.