In chapter 5 the combined evidence of pollen analysis and 4C dates resulted in a time scale for climatic fluctuations in North-west Europe during the early part of the Last Glacial. It remains to be discussed whether these fluctuations formed part of a global pattern of changing climatic conditions.
Changes in climate have been observed in such diverse features as pollen distri-bution preserved in sediments, continental loess deposits, the oxygen isotopic com-position of glacier ice, variations in the faunal assemblages and the oxygen isotopic composition of carbonate skeletons in deep-sea sediments, and coral terraces. We will compare the climatic information f r o m the different sources, and the time scales separately.
Climatic information was obtained f r o m :
(i) The variations in oxygen isotopic composition of ice cores extracted f r o m the Greenland and Antarctic ice cap (Dansgaard et al., 1 9 7 1 ; Johnsen et al., 1972). The heavy isotopic molecule H2 0 more easily condenses f r o m water vapour. The precipitation at higher latitudes shows therefore a
deple-18
t i o n in O, which increases w i t h decreasing temperature,
(ii) The varying composition of the pollen rain at the sites described in chapter 5, at Grande Pile, Southern Vosges, France (Woillard, 1975), in Macedonia, Northern Greece (Wijmstra, 1969) and in the Fuquene area in Colombia (Van Geel and Van der Hammen, 1973).
(iii) Advances and retreats of the ice cap as evidenced by tills, meltwater and lake deposits in the Great Lakes — St. Lawrence region (Dreimanis and Karrow,
1972).
(iv) The sedimentary record preserved in loess deposits in continental areas which were not glaciated, e.g. Central Europe (Kukla, 1970). The soils reflect the former existence of relatively warmer climatic conditions, whereas loess deposits reflect the cold periods,
(v) Palaeo sea levels obtained f r o m old shore lines visible in regions of tectonic
uplift like Barbados (Mesolella et al., 1969; James et al., 1971) and New Guinea (Bloom et al., 1974). The formation of an ice cap on the con-tinents leads to a drop in sea level. Contrarily a high sea level indicates reduced ice volume related to a relatively warmer climate,
(vi) The variations in the oxygen isotopic composition of the carbonate of fossil shells of foraminifera obtained from deep-sea cores from the Caribbean (Emiliani, 1966; Emiliani et al., 1975), the Pacific (Shackleton and Opdyke, 1973), the southern Indian Ocean (Hays et al., 1976) and other localities. The
18
O content of the shell carbonate reflects the oxygen isotopic composition
18
and the temperature of the water in which it was deposited. The O content of the oceans increases when a large amount of isotopically light water is fixed in an ice cap on the continents. A lower water temperature also favours
18
the concentration of O in carbonate, precipitated from the ocean.
(vii) The faunal assemblages found in deep-sea cores, e.g. from the Caribbean (Emiliani et al., 1975), the southern Indian Ocean (Hays et al., 1976) and the North Atlantic (Sancetta et al., 1973). The faunal assemblages of foraminifera and radiolaria may reflect the sea water temperature (Imbrie and Kipp,
1971).
(viii) The varying calcium carbonate content of the sediment in deep-sea cores, e.g. from the eastern equatorial Atlantic (Hays and Peruzza, 1972). The carbonate content of the sediment is determined by the production of organic carbonate and the rate of dissolution of the shells. Both are influ-enced by temperature.
The climatic patterns obtained from the sources mentioned above show different detail. The 0 / O changes in ice cores provide the most detailed information.
Also the pollen record may reflect climatic fluctuations in considerable detail. The information from loesses and sea levels is less detailed since here the difference between extremes of warm and cold is detected rather than the complete temper-ature development. The interpretation of the scattered data is difficult. Generally the deep-sea records lack information on short term climatic fluctuations due to the buffering capacity of the oceans and the mixing of the upper layer of sediment on the ocean floor. It provides, however, a well documented and consistent record of long term variations.
The patterns of climatic fluctuations obtained with different techniques and from largely different localities show a striking similarity. This suggests that we are dealing with global climatic fluctuations. It should therefore be possible to syn-chronize the different climate curves.
There are three independent dating methods that have provided dates for the climatic record of the last interglacial—glacial cycle.
The younger part (less than 20 000 years) of all time scales w i t h the exception of (i) has been based on radiocarbon dates.
Time scales for the methods of continental climatic measurement (ii), (iii) and (iv) summarized above were obtained f r o m C dates up t o the age limit of this dating method, formerly about 50 000, presently at about 75 000 years BP. A few enrichment dates obtained before 1967 were used in the 60 000 year range by Dreimanis and Karrow (1972). If a longer time scale of (ii) and (iii) is given, it is based on extrapolation and/or correlation w i t h high palaeo sea levels reflected by dated coral terraces on Barbados (v) and w i t h the generalized O deep-sea record.
For (iv) also interpolation between 0 and the Brunhes/Matuyama palaeomagnetic boundary (established by potassium-argon dating at about 700 000 years BP) is used.
Palaeo sea levels (v) were dated on basis of the disequilibrium activities of the decay products of 2 3 5U and 2 3 8U , especially 2 3 0T h and 2 3 1P a , that are incorporated in corals. Based on this technique Mesolella et al. (1969) have concluded t o three relatively high sea levels at Barbados about 85 000, 105 000 and 125 000 years BP.
James et al. (1971) reported an additional high sea level terrace dated w i t h
2 3 0T h /2 3 1P a at about 60 000 years BP. On the Huon peninsula of New Guinea, Bloom et al. (1974) dated a series of 6, partly m u l t i p l e , coral terraces which have originated in the same period.
The disequilibrium decay series technique has been applied also to some of the deep-sea cores (Rona and Emiliani, 1969; Broecker and Van Donk, 1970). Because generally only carbonate is available for C dating this method cannot be used beyond about 20 000 years BP. Shackleton and Opdyke (1973) obtained a time scale by interpolation between the palaeomagnetic Brunhes/Matuyama boundary (K-Ar dated at about 700 000 years BP) and 0. For most of the cores, however, a time scale has been derived f r o m a correlation w i t h the dated Barbados high sea levels or with dated cores.
We will make a detailed comparison of our chronology w i t h that obtained on the Camp Century ice core (Dansgaard et al., 1971), w i t h the t w o generalized versions of the deep-sea chronology (Emiliani and Shackleton, 1974) and w i t h the New Guinea high sea levels (Bloom et al., 1974) (fig. 6.1).
The radiocarbon chronology has been the subject of this thesis and needs not t o be discussed here. In section 3.1 we estimated that the uncertainty of the method in the age range of 50 000 t o 75 000 years BP is almost certainly less than 10%
(corresponding to a factor 2 in natural C activity).
The younger part of the Camp Century ice core time scale (0—12 000 years BP) was obtained by matching the periodicity of the fluctuations in the ice of 5 , the relative difference in oxygen isotopic composition between a sample and the
stand-CD O
NORTH-WEST EUROPE 5 10 15 20 °C
CAMP CENTURY
*18(
D E E P - S E A
20000 YEARS
B.P
80000-
120000-®
ALLER0D B0LLING
DENEKAMP
HENGELO
MOERSHOOFD
ODDERADE BR0RUP AMERSFOORT
45 -40 -35 -30 6 'aO ( 7 „ ) 61H0(%o) 0 -1.8 -120
NEW GUINEA REEF
-40 sea level (m) 0
BRADTVILLE TILL"
ODDERADE ST P I E R R E ™ " ^ BR0RUP BECANCOUR T I L L - ^A M E R SF O O R T
BARBADOS
©
GROOTES 1977 DANSGAARD et al. 1971 EMILIANI - SHACKLETON 1974
100000
- V I ID
BLOOM et a l . 1974
Fig 6 . 1 . Comparison of climatic chronologies for the last interglacial—glacial cycle.
A — pollen record in North-west Europe, dated with 1 4C .
B — 8*° record of the Camp Century ice core (Greenland), time scale based on constant periodicity of 6 '8 variations, C — generalized 61° deep-sea record, time scale based on 2 3 0T n/ 2 3 1
palaeomagnetic boundary at about 700 000 years BP; Emiliani, —
Pa dates and interpolation between 0 and the Brunhes/Matuyama
• Shackleton,