While welcoming the June 1, 2006, publication in “Nature” of three papers (refs. 1,2,3) revealing the sedimentary evidence of an early Tertiary ice free Arctic Ocean I wondered why science writers fail to mention the data which indicate that summer ice free oceanic conditions also existed in the far north within the last ~ 10,000 years of the Holocene period? This would add perspective for those who seem to worry that such a near-future event, driven by 20th & 21st century gas emissions, would be unprecedented in geologically recent times, and these data might modulate the current concern about polar bear extirpation, since Ursus maritimus survived such ice loss just a few millennia ago.
I write as a long-term student of paleo-environmental change in the arctic, and needless to say I have no connection whatsoever with funding or influence by the hydrocarbon industry. I am sympathetic to the plight of the southernmost population of polar bears in Hudson Bay, but note that they have demonstrated a remarkable ability in the late Quaternary period to evolve from the brown bear species to the fully maritime modern ‘ice bear’ and to survive many climatic changes.
I recall that in 1966 the Rand Corporation published the “Proceedings of the Symposium on the Arctic Heat Budget and Atmospheric Circulation” (ed. J.O. Fletcher) in which the Russian climatologist Dr. M. I. Budyko wrote the introductory paper “Polar Ice and Climate” (pp. 5 – 21, cf. page 12). Dr. Budyko calculated that a mean summer increase of Arctic Ocean air temperature of 4 degrees Celsius for a period of a few years to a few decades would cause loss of the summertime ice cover (the ‘ice pack’).
In 1967 (refs. 4 & 5) I published initial palynological studies of the history of the Canadian Boreal forest – tundra ecotone which suggested that the arctic tree-line had moved northwards 350 to 400 km beyond its modern position (extending soils evidence collected by Irving and Larsen, in Bryson et al. 1965, ref. 6) during the mid-Holocene warm period, the Hypsithermal. The climatic control of the modern arctic tree-line indicated that prolonged summer temperature anomalies of ~ + 3 to 4 C were necessary for this gigantic northward shift of the tree-line, thus fulfilling Budyko’s temperature requirement for the melting of Arctic Ocean summer ice pack. A more extensive peat stratigraphic and palynological study (Nichols, 1975, ref. 7) confirmed and extended the study throughout much of the Canadian Northwest Territories of Keewatin and Mackenzie, with a paleo-temperature graph based on fossil pollen and peat and timber macrofossil analyses. This solidified the concept of a +3.5 to 4 degree (+/- 0.5) C summer warming, compared to modern values, for the Hypsithermal episode 3500 BP back at least to 7000 before present, again suggesting that by Budyko’s (1966) calculations there should have been widespread summer loss of Arctic Ocean pack ice. By this time J.C. Ritchie and F. K. Hare (1971, ref.8) had also reported timber macrofossils from the far northwest of Canada’s tundra from even earlier in the Hypsithermal.
The first proof of the pudding came with Bent Fredskild’s 1969 (ref. 9) publication of pollen diagrams from the polar desert of Pearyland in northeast Greenland, taken from near the 200 km long Independence Fiord, frozen (in the 1960’s) all year round. Dr. Fredskild notes (ref. 9, page 580) that the first hint of ice free Arctic Ocean came from sub-fossil timbers incorporated in isostatically uplifted beach sediments and paleo-eskimo fire pits or hearths at 4500 BP. The timbers presumably came down the great Siberian rivers (Ob, Yenisei, Lena, etc. and the Mackenzie River in northwest Canada) and floated throughout the summer ice free Arctic Ocean, to be buried in shoreline deposits which later became raised beaches. Dr. Fredskild reported that charred driftwood from these sources were found in every Independence-1 hearth, primarily from 4000 to 3600 BP. The youngest dating on charred driftwood was 2700 BP, and he remarked that the polar basin and fiords became permanently frozen ca. 2500 years ago, with no further driftwood in the fiord beaches after that time. Bearing in mind the current concern about ecosystem effects from an ice free ocean, the palynological data recorded a more vegetated environment with sedges, grasses and arctic (dwarf) willows, allowing grazing by musk-ox, and occupation by quasi-Inuit peoples who hunted those and other animals, facilitated by a milder and moister summer climate. From slides which Dr. Fredskild gave me, it seems that the present day polar desert, with a plant cover of perhaps only 5 – 10%, might have resembled the present day mostly vegetated ‘high arctic’ ecosystems in southern Greenland and northern mainland Canada, during the ice- free episode.
There are several additional reports within the last decade which I think confirm the above hypothesis of Holocene summers episodically free of Arctic Ocean pack-ice, and their summaries are available from the Net:
Arthur Dyke, James Hooper and James Savelle (1996) published “A history of sea ice in the Canadian Arctic Archipelago based on postglacial remains of the bowhead whale (Balaena mysticetus)” in Arctic, vol. 49 (3), pp.235- 255. A very large number of radiocarbon dates on whale bones showed that both early and mid Holocene times experienced pack-ice free conditions, with an episode from 5000 to 3000 years BP demonstrating whale populations beyond recent historical limits, and a reportedly more complex history of ice formation and melting than revealed in other proxy data.
J.Knies, Nowaczyk, N., Muller, C., Vogt, C., and R. Stein, (2000), “A multiproxy approach to reconstruct the environmental changes along the Eurasian continental margin over the last 150000 years” in Marine Geology, vol. 163, # 1, pp. 317-344. “Sustained periods of open water were largely restricted to substages 5.5, 5.1, and the Holocene as indicated by distinct carbonate dissolution and higher accumulation of marine organic matter.”
J-C Duplessy, E. Ivanova, I. Murdmaa, M. Paterne, and L. Labeyrie, ( 2001): “Holocene paleoceanography of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean” in “Boreas” vol. 30, # 1, pp. 2 – 16. Marine sediment cores representing the entire Holocene yielded foraminifera which showed that a temperature optimum (the early Hypsithermal) developed between 7800 and 6800 BP, registering prolonged seasonal (summer) ice free conditions, and progressing to 3700 BP with temperatures similar to those of today, after which a relatively abrupt cooling occurred. The authors note that foram assemblage changes were linked to alterations in the flow of Atlantic waters and the oceanic conveyor belt.
References not fully cited in the text:
1: Kathryn Moran et al. (2006) “The Cenozoic paleoenvironment of the Arctic Ocean”, Nature, vol. 441, pp. 601 – 605.
2: Henk Brinkhuis et al. (2006) “Episodic fresh surface waters in the Eocene Arctic Ocean” Nature 441 pp.606 – 609.
3: Appy Sluijs et al. (2006) “Subtropical Arctic Ocean temperatures during the Palaeocene/Eocene thermal maximum”, Nature 441, pp. 610 -613.
4: Harvey Nichols (1967a) “The post-glacial history of vegetation and climate at Ennadai Lake, Keewatin, and Lynn Lake, Manitoba (Canada)”, Eiszeitalter und Gegenwart, vol. 18, pp. 176 – 197.
5: H. Nichols (1967b) “Pollen diagrams from sub-arctic central Canada”, Science 155, 1665 – 1668.
6: Reid A. Bryson, Irving W. N. and J.A. Larsen, (1965), “Radiocarbon and soils evidence of former forest in the southern Canadian tundra”, Science, 147, 46 – 48.
7: H. Nichols (1975): “Palynological and paleoclimatic study of the late Quaternary displacement of the Boreal Forest – tundra ecotone in Keewatin and Mackenzie, N.W.T., Canada. INSTAAR University of Colorado Occasional Paper # 15, pp. 87.
8: J.C Ritchie and F. K. Hare (1971) “Late-Quaternary vegetation and climate near the arctic tree-line of northwestern North America”, Quaternary Research, vol. 1, #3, pp. 331 – 342.
9: Bent Fredskild (1969) “A postglacial standard pollendiagram fromPearyland, North Greenland”, Pollen et Spores, vol.XI, # 3, pp. 573 -584.
Harvey Nichols, Ph.D.
Professor of Biology