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Author Topic: AN INTERHEMISPHERIC TRANSECT  (Read 560 times)
Adam Hawthorne
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Posts: 4250

« on: July 15, 2007, 03:51:25 am »


The short background presented above shows that increased understanding of the climatic relationships and mechanisms between the two hemispheres during events of global as well as regional climate change, are necessary to understand underlying processes behind climate variability of both glacial and interglacial scenarios. We therefore propose to start an Atlantic palaeoclimatic project focused on: 1) the last glacial-interglacial period, 2) interhemispheric comparisons and correlations, and 3) direct comparisons between marine and atmospherically influenced climate records.

                      We believe that these aims can be best achieved by analysing environmental/climatic variables, mainly from lacustrine records and peat bogs, as well as glacial records, on islands along a north-south transect in the Atlantic Ocean.


Parts of, or complete late-glacial and Holocene palaeoclimatic reconstructions, mainly based on lake and peat deposits, and geomorphic features, do already exist or are under progress from eastern Greenland (70-730N), Iceland (c. 660N), the Faroe Islands (620N), and southernmost Greenland (600N), and the principal investigator (PI) together with some of the project members are responsible or co-responsible for several of these studies (see PI`s CV and ref. list), as well as for similar studies around the Antarctic Peninsula (CV and ref. list). The transect is therefore tightly anchored in the north as well as in the very south. Furthermore, O. Ingolfsson plans to anchor the transect in the very north, Svalbard, in a future application.

The Azores

This island group of 2335 km2 is situated at the Azores High, in the central part of the N Atlantic (c. 380N), and consists of 9 islands, of which eight are of volcanic origin. Annual temperatures vary between 12-260C, with a fairly humid climate. Lakes of different types, but usually of volcanic origin, occur on all islands. The first attempts to retrieve cores from some of these were made in 1965. Samples were collected from five lakes and four samples were 14C dated, with an oldest age of 3.9 14C ka BP at a sediment depth of 150 cm in a crater lake on São Miguel (Fries, 1968). This was, however, not the deepest retrieved sediment. In the mid-90`s B. Ammann and H. E. Wright cored the same lake and the corer stopped in fairly coarse material at about 4.0 14C ka BP (Ammann & Wright; pers. comm.). Sediment slumping and related processes are possibly big problems in some of these steep-sided crater lakes, and may explain the difficulties to penetrate older sediments. No stratigraphic details have come out from those studies. However, the PI visited the two larger islands São Miguel and Terceira in January 1999 and found that there is a larger potential for lake corings in some non-crater lake basins as well as in some older, less steep craters. Fries (1968) also indicated more than 20 "promising" lakes on six of the islands, incl. information on size, altitude and often also water depths. Furthermore, the summit on the island of Pico, surrounded by some very promising lake basins, is situated at 2351 m.a.s.l. and is completely snow-covered in winter. This summit area has most likely been glaciated, and may thus hold glacigenic deposits.

Logistics: regular flights from Lisboa and good infrastructure on and between the islands.

St. Helena

In contrast to Cape Verde and Ascension, the climate of the island of St. Helena (120 km2) at 160S, situated between the Intratropical Convergence zone and the South Atlantic High (SAH), is humid enough for the formation of peaty and muddy deposits in some of the valleys on the northern part of the island. At least 5 m thick “mud” deposits in Fisher`s Valley as well as some thick open peat exposures in Rupert`s Valley have been reported to us (Q. Cronk; pers. comm.). At the arrival of the first (Portugese) settlers in 1504 the island was to a large extent covered by lush vegetation, with at least 50 endemic species, but the southern part was, and still is, desert-like. This also shows that the local climate is sensitive for changes in atmospheric circulation, i.e. the position of the southeast trade wind. The highest point on St. Helena reaches 820 m.a.s.l. and the most promising areas for organic rich Quaternary deposits are situated in some of the deeper valleys around 500 m.a.s.l., where also the richest vegetation of bushes and semi-tropical trees can be found. Mean summer temperatures vary from 320 (at sea level) and 210C, and winter temperatures vary between 26-150C, but with 50 lower temperatures in the central hills. Precipitation varies between 150-1000 mm/year, depending on altitude.

Logistics: regular connecton with Cardiff, Tenerife or Cape Town by the ship RMS St. Helena. Good infrastructure on the island with its 6000 inhabitants.

Tristan de Cunha and Nightingale Island

The Tristan de Cunha Island Group is situated at 370S, where Tristan de Cunha (78 km2) is the largest island with 300 inhabitants. It is built up around an impressive volcano, reaching 2060 m.a.s.l., which is snow-covered in winter. Annual temperatures vary between 4-260C in this southern part of the SAH, and precipitation is up to 1700 mm/yr. Areas below the volcano, situated at 600-900 m.a.s.l., are covered by thick peat deposits, e.g. at Soggy Plains in the south, where Hafsten (1960) reports at least 3.75 m peat, but peat bogs also occur close to the settlement of Edinburgh, e.g. at Jenny`s Waterun (Hafsten 1960). Furthermore, three smaller lakes, The Ponds, occur on the northeastern part of the island, only some 4 km ESE of Edin­burgh, and a small lake region is also found on Nightingale Island, where Hafsten (1951) pollen analysed a 3.5 m thick undated core, showing some very significant pollen stratigraphic changes. Furthermore, Wace and Dickson (1965) and Preece et al. (1986) report 14C ages of 8.3, 10.8, 11.3, 39.2, and >40 ka BP from lake sediments and peat on Tristan and Inaccessible Island. In contrast to the latter, Nightingale Island, which is extensively covered by peat, is fairly accessible with smaller paths around the island (B. Baldwin, Tristan de Cunha manager; pers. comm.). Altogether this shows that there is a good potential for studies of both peat and lake sediments, as well as possible glacigenic deposits from past glacial activity on Tristan de Cunha.

Logistics: Tristan de Cunha is connected with Cape Town and St. Helena by RMS St. Helena. Bad infra-structure (apart from two guest bungalows and roads stretching a few kms from Edinburgh) necessitates travel by foot and by local boat to a few landing places. Nightingale I is reachable from Tristan and we are able to rent some of the many huts on the island, owned by Tristanians (B. Baldwin; pers, comm.).

Gough Island

Gough Island (50 km2), which has a meteorological station with a staff of 7 people, is situated at 400S, 350 km SSE of Tristan de Cunha, in the “Roaring Fourties”, at the border between the SAH and the southern westerlies. The island`s climate is sensitive to Polar Front changes. Annual precipitation is >2500 mm and mean annual temperature at sea level is 110C, with extremes between -30 and 250C. Its highest peak reaches 910 m.a.s.l. and the island has a rugged, “wild” topography, bounded by 150-300 m high cliffs. The volcanic activity ceased long time ago and the landscape is main­ly shaped by erosion. The forest zone extends up to 300 m.a.s.l. According to the survey map of Heaney and Holdgate (1957) at least six small lakes occur on the island, of which five are situated on the Tarn Moss plateau 3-5 km from the only harbouring place (Quest Bay), and can be reached through the island`s largest valley, The Glen. Flatter areas inside and above the coastal cliffs at 600-700 m.a.s.l. are covered by thick peat deposits. At least 4.5 m thick peat was penetrated on the Albatross Plain (Hafsten 1960) and a 14C dating at 2.15 m resulted in an age of 4.7 14C ka BP. Furthermore, Bennett et al. (1989) pollen analysed and dated well-bedded organic-rich sediments at the meteorologi­cal station­. The age of the bottom-most retrieved sediments at 2.9 m was >43.000 14C years old, overlain by a hiatus. However, the total thickness of these deposits were estimated to 9.1 m. Studies of other Quaternary deposits were not carried out during the different Gough Island expeditions, but photographs of the landscape morphology together with the presence of snow on the higher parts of the island in winter, show that the higher areas may have been influenced by glacier activity. In general, the previous studies from Tristan, Nightingale and Gough I did not result in any stratigraphic details, but they clearly point out the potential of these island records.

Logistics: Some boat connections with S Africa and possibilities for hiring local boats on Tristan. Bad infrastructure (apart from the meteorological station) will necessitate boat travel to Quest Bay (see above) and travel by foot.

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