|Black & White Edition in
Arctic Heats Up.
Spitsbergen 1919 to 1939
|Colored Edition in Europe
How Spitsbergen Heats the World
The Arctic Warming 1919-1939
|ISBN: 978-1-4401-4087-7||ISBN 978-3-8370-9524-1|
|Ca.116 pages and 100 b/w figures. More details in right column.||Ca. 116 pages and 100 color figures. Details see column.|
Regional impact of the Spitsbergen warming
A. Introduction to When & Where
Being impressed by the big warming at Spitsbergen is one thing, another one, to make sense of it by putting the sudden temperature increase in winter 1918/19 in a perspective. How was the event recorded in other locations of the wider region? At what time could a commencement of the warming be observed, was it before Spitsbergen or after Spitsbergen; was it more pronounced or less pronounced, and how long did it last, two decades unit 1940 as in Spitsbergen or ended the warming up trend earlier? In so far this chapter can be called a fact finding mission. It aims at preparing the basis required to discuss matters of correlation and causation. After all, the heat that increased the temperatures in the Artic region must have been generated either locally or somewhere else. If generated outside the Polar Circle, it should be possible to identify the generating source and the path of transport either through the atmosphere of the ocean system.
When discussing "the nature of polar forcing" (Zakharov, 1997), the author stressed that the feature of climate change spatial structure in the 20th Century is most well pronounced in the northernmost part of the Atlantic and in the adjacent Arctic regions, which supports the idea that obviously, the atmosphere thermal regime is in some way connected with the ocean. To support this idea, as we will do in the next chapter, a broader picture on facts and information portraying the Spitsbergen event is required.
B. The regional feature with four sea water bodies
The availability of large water-bodies so high in the Northern Hemisphere are the ultimate "blueprint" for the Northern Hemisphere climate, which needs to be recognised in the first place. However such plain statement cannot explain the "climate revolution" in the region in the early 20th Century. Calling this initial event "Arctic Warming" might even be misleading, if the warming commenced primarily over the northern part of the North Atlantic, and even more precisely, in the Spitsbergen region. On the other hand all ocean space and seas within the Arctic Circle are relevant for the arctic weather and arctic climate, although on a very different scale due to size, depths, sea ice, freshwater, sun-less periods, and sea currents, to mention only few decisive factors. In order to detect the time and source of the sudden start of the Arctic Warming one must have a look at each of the specific sea areas in question. This needs to be kept in mind that the "explosion" of air temperatures at the Spitsbergen archipelago at 80o North during winter 1918/19, must have been generated by "something".
Although no option, including an internal atmospheric process, should be excluded, the most likely source is the sea area between the direction 135o (SE) and 270o (West) of Spitsbergen, which is usually sea ice-free throughout the year and belongs to the Barents Sea, the Norwegian Sea and the Greenland Sea. The source of the warming was presumably due to either internal processes within the water bodies, or influenced by more warm water coming from the Atlantic Gulf current, or both. The latter came with the Norwegian Current and West Spitsbergen Current, formed by water flowing from the Gulf Current after it had passed the Iceland - Faroe â€“ Scotland line, enhanced by North Sea water, and continental run off rain and melt water. However, once the warm Atlantic water has passed the north of the Scottish Hebrides and Faroe, and travelling northwards, things tend to complicate.
a) Arctic Ocean
Due to the size of the Arctic Ocean, which is much larger than the Northern North Atlantic, and due to its considerable depths of more than 3000 metres, one would assume that its immediate impact on the weather should succeed by far the influence of the Northern North Atlantic. That is not the case. At least during the winter periods in the early 20th Century the Arctic Ocean was permanently covered by sea ice, which diminishes any heat release from the sea in the atmosphere to a small factor, thus making this huge water body "continental", characterized by cold and stable weather conditions, and clear skies. However the sea ice is not very thick, and not always unbroken, so that an interchange is not completely excluded. According to Aagaard (Aagaard, 1982) it seems possible that two-third of the oceanic flux should be accomplished by the Atlantic water of the West Spitsbergen Current.
The feature of the Arctic Ocean is very complex and only few aspects can be mentioned. Above the very cold and saline bottom water is a layer of "Atlantic Water", which occupies the depth range between ca. 150m and
|Deviation from mean 1921-1930, air pressure (left), air temperature (right)|
900m that is superseded by the "Arctic Surface Water" in the range from the sea surface to a depth of 150/200m and temperatures close to the freezing point (between -1.5oC and -1.9oC). In this layer the salinity depends strongly on the degree of the sea ice processing, freezing or melting, ranging from about 28 to 33.5%. These conditions represent in the Arctic a relatively warm ocean surface water layer which has an influence on the regional air temperatures.
Despite the fact that the water
body of Arctic Oceans is based on many complex features, and highly
influenced by internal transformation, e.g. sea ice freezing and melting,
and external influences, e.g. fresh water from rivers, there is not
one aspect from which a sudden warming could have been generated. None
of the seas in question can be excluded with such unequivocal certainty
from the list of potential contributor for the early Arctic Warming
as the Arctic Ocean.
This assertion is addressing only the sudden warming in the late 1910s. The huge water body in an extreme harsh environment will transfer any internal changes ultimately to the atmosphere, presumably with considerable time lags.
One needs only to consider the water renewal time for the Arctic Bottom water, which is a couple of dozen years in the Amundsen- and Nansen-Basin but more than 500 years in the Canada- and Makarov-Basin.
Due to the long internal processing most recent dramatic arctic warming and sea ice melting may have been caused by warm Atlantic water that arrived many decades ago. In order to find out, it would primarily require establishing what and why the Spitsbergen warming occurred in the first place, as it constitutes the early Arctic Warming from 1918 to 1940.
b) Greenland Sea
A significant climatic impact is due to the southward flowing East Greenland Current (EGC) which constitutes the major outflow route of Arctic water into the Atlantic. The pathway to the south of Greenland is due to the season covered with sea ice. The water temperature is below -1oC, and due to ice melting of low salinity of about 30-33%. Some of it is diverted just north of Denmark Strait and northeast of Iceland into the East Iceland Current, which before reaching the latitude if Iceland towards the Norwegian Sea as part of the formation process of Arctic Bottom Water. The remainder pass the Denmark Strait, gets partly mixed with the Irminger Current and in this combination flow around the southern tip of Greenland, Kapp Farvel, into the West Greenland Current. Cold sea surface temperature of the EGC is associated with negative anomalies of surface air temperatures with an amplitude of 2o near Greenland declining to several tenth of a degree over north-western Europe (Delworth, 1997). In the west of Spitsbergen, the seawater has a temperature of 5oC and a salinity of 34.90-35.00 mg.
A significant part of the warm Atlantic Gulf water that has reached Spitsbergen "turns left" in the south-western direction, at the position of 75-77o North, and flows either as Greenland current down to Newfoundland and back in the Atlantic, or goes down into the huge Greenland Sea Basin with depths of 2,000 metres (max. ca. 3,500 m), or circles for some time at the sea surface water layer or in sub surface layers. At the surface the water forms a layer of 100-200m, which reflects the depth of summer water heating. Within the annual cycle, these water body experience considerable deviation of temperature (4oC) and salinity (1.2%).
Although the Greenland Sea represents a huge water body, the option for being a serious contributor to the extreme warming event in winter 1918/19 is remote. The West Greenland Current is colder and less salty than the Atlantic water of the Spitsbergen Current, and the current is to a considerable extent covered with sea ice during the winter season, but only partly in summer. Concerning this investigation the Greenland Sea matter gets "hot" if one looks at the EGC and whether the current had been getting more than usual portion of warm Atlantic water that made the temperatures exploding at Spitsbergen around winter 1918/19. Did the thus warmed up EGC current brought a warming to Greenland's coast in the East and the West of the island? We will discuss this aspect later, while mentioning already now, that Greenland had experienced warmer sea water and warmer air during the time period in question, but later and only temporarily (Bjerkness, 1959).
c) Norwegian Sea
The Norwegian Sea Basin is up to ca. 3,000 metres deep, with a mean depth of 1740 m. The sea is separated from the Arctic Ocean by a ridge of about 600 metres under the sea surface. This allows huge water exchange from north to south and vice versa. A key role for the moderate temperature conditions in the region derives from huge warm water supply by a branch of the Atlantic Gulf currents which is "pushed down" to lower depths after passing by the Shetland Islands, Faroe Island and Iceland ridge, travelling North about 500 m below the sea surface. On the first stretch parallel the coast line of Norway, the warm Atlantic water is called Norwegian Current, which is to be kept separate from the Norwegian Coastal Current, but once it has reached the latitude of the North Cap the major part continues as West Spitsbergen Current (WSC) towards the Fram Strait in the West of Spitsbergen, and a small part goes eastwards in the Barents Sea. Due to its high northern location, size and volume, the Norwegian Sea has a lot of facets that are too complex for being presented in few words.
If for example the wind would not mix a low saline sea surface, due to rain fall, with saltier water from lower sea levels, the sea ice would presumably reach Iceland, Scotland and the North Sea at least every winter season. That would even happen when the most unique feature, the West Spitsbergen Current, would pass the Norwegian Sea as usually, but latest demonstrate its impact on the Arctic climatology as soon as the current has arrived in the West of Spitsbergen. This is of foremost interest, and any other details concerning the Norwegian Sea will be mentioned if deemed helpful.
As already mentioned, the WSC is the major source of heat and salt for the Arctic Ocean. The Current cools dramatically downstream, although the warmest water can be frequently observed 100-200m below the surface moves via the currents towards the basin of the Arctic Ocean. For the last distance over ca. 1000 km, Lofoten to Spitsbergen the travel time is about 5 weeks, which means the average speed is 0.30 to 0.35ms-1 Actually, due to the high salinity of the warm Atlantic water and the cooling process, the water becomes very dense and "falls" over a ridge (with a depth of 600 m below sea level) in the Arctic Basin. Before the Spitsbergen current reaches the ridge, at about 80o North, the water, has a depth of 20 metres, a salinity of about 35 per mile, and a temperature > 3o up to 7oC.
But also the basin of the Norwegian Sea is a reservoir for warm Gulf water, reaching depths of 800 metres. Status and dynamics of the Norwegian Sea is also strongly influenced by other factors, particularly wind, rain, melt water, and the low saline water form the North Sea. Any increase in temperature, or enlargement of the "warm water part", or "change of dynamics", would quickly be reflected in temperatures in Europe or elsewhere in the Northern Hemisphere.
|Warm Atlantic water form the Gulf Current flow over the Iceland-Faroe Ridge in the Norwegian Sea|
|High saline Atlantic water enter the Norwegian Sea|
d) Barents Sea
The Barents Sea is a shallow shelf sea with an average depth of 230m, and a maximum depth of below 500m. There are three main types of water mass; warm, salty Atlantic water (temperature >3oC), cold Arctic water, less salty (< 0oC), and warm coastal water, less salty than the Arctic water (>3oC).
Generally speaking, the warm Atlantic water "disappears" in the East of the North Cape. In the northern part polar water flows from Northeast to Southwest and partly joins the Spitsbergen Current in the south of Spitsbergen and Bear Island. The North Cape Current, and its subsequent currents, which supply the eastern part of the Barents Sea with Atlantic water, may have contributed to the warming in the long run, under the condition that a permanent inflow of warm Atlantic water is guaranteed. Actually the whole water body of the Barents Sea is replaced within a 3-4 year period. The Barents Sea itself is not able to sustain a longer warming period due to limited heat storage.
With regard to the Spitsbergen, it has already be mentioned that the air temperatures in North Norway have increased only modestly since 1920 (Manley; 1944). Neither Vardo (close to the North Cape), nor any Russian Station reported any exceptional winter temperature rise. On a 10-year mean basis (1911/20 and 1921/30), a significant increase of 6oC was observed at Franz-Joseph Land (Kirch, 1966), whereby the highest water temperatures in the top 200 m of the Barents Sea at 70-72oN; 33oE, north of the Kola Peninsula, shall have been reached during the period 1935-39 (Lamb, 1980). That all confirms a slow process but hardly any facts that the Barents Sea had significantly generated a temperature jump in its southern part (North Cape), or in the eastern part (Kola Peninsula).
The observed warming at Franz-Joseph-Land can also be hardly connected to the sea, which is partly supplied via the North Cape current and subsequent currents along the Kola Peninsula. In addition the Barents Sea between Spitsbergen (East) and Franz-Joseph-Land (West) is not very deep and is governed by very cold currents flowing southwest towards South Spitsbergen and the Bear Island. (See also next section).
According to Wagner (Wagner, 1940), the mean surface-water temperatures in the Barents Sea, the deviations from the means during the months July to September, was -0.7oC during 1912-1918, against + 1.1oC during the following years 1919-1928, as indicated in the table:
|1914 = -0.3oC||1915 = + 0.7oC||1916 = -1.1oC||1917 = -1.5oC||1918 = -1.6oC|
|1919 = +0.6oC||1920 = +2.2oC||1921 = +1.0oC||1922 = +1.9oC||1923= +1.0oC|
Wagner's additional observations ascertain a "rise" of 2-3oC, at water depths of 100 and 200 m, during the last 30 years (1895 and 1927). However, a general observation of "over 30 years" is of little help in this case, presumably also his general assessment that the Barents Sea ice border retreated significantly since 1919, even though it is undisputed that the retreat occurred gradually over a two-decade period (Kirch, 1966).
There are no significant indications that the Barents Sea contributed significantly in the early stage of the Arctic warming. The presumably most relevant aspect is that no particular strong winter warming had been observed at the southern parts of the Barents Sea, albeit a trend change was observed since 1919. The question would remain, whether the trend change had been caused by higher temperatures in the North, or alone by the Barents Sea, or was due to changes over the European Continent, or had been a combination of all three factors. But this does not need to be answered here.
The brief overview on the possible potential of the most relevant sea areas for the early Arctic Warming could show that two, out of the discussed four areas, can be excluded with high certainty as serious contributor, namely the Arctic Ocean and the Greenland Sea, and with less certainty the Barents Sea. The highest potential by far has the northern part of the Norwegian Sea and the Spitsbergen Current. This preliminarily assessment shall be verified with further information in the next section.
28 Here meant as area between: Greenland, Iceland, Scotland, Norway, and Spitsbergen.
29 Transport estimates are 5 Sv (5 x 106 m3 s-1) for the East Greenland Current and 8-11 Sv (8-11 x 106 m3 s-1) for the Irminger Current. The combined flow continues around the southern tip of Greenland into the West Greenland Current.
30 The Labrador Current originates from East Greenland Current, continues as West Greenland Current (NW), than as Baffin Island Current (SW), and subsequently the Labrador Current (SW), which transports cold Arctic and sub-polar water south along the Atlantic Canadian coast to the Grand Banks (Newfoundland) where it divides, the East branch joining the North Atlantic Current and the West branch flowing into the Gulf of St. Lawrence. The International Ice Patrol had first quantitatively studied the Labrador Current in 1937.