2000 H 2 16 O10 HD 16 O10 H 2 18 O ice land Latitude increasing ice land 1000 H 2 16 O7 HD 16 O7 H 2 18 O 1000 H 2 16 O 3 HD 16 O 3 H 2 18 O 2000 H 2 16 O10 HD 16 O10 H 2 18 O Latitude increasing 500 H 2 16 O 1 HD 16 O 1 H 2 18 O 1500 H 2 16 O9 HD 16 O9 H 2 18 O 1000 H 2 16 O 3 HD 16 O 3 H 2 18 O 1000 H 2 16 O7 HD 16 O7 H 2 18 O Latitude increasing ice land 300 H 2 16 O 0 HD 16 O 0 H 2 18 O 1700 H 2 16 O10 HD 16 O10 H 2 18 O 500 H 2 16 O 1 HD 16 O 1 H 2 18 O 1500 H 2 16 O9 HD 16 O9 H 2 18 O Latitude increasing ice land 300 H 2 16 O 0 HD 16 O 0 H 2 18 O 1700 H 2 16 O10 HD 16 O10 H 2 18 O ice land Latitude increasing 300 H 2 16 O ice land Latitude increasing 1700 H 2 16 O10 HD 16 O10 H 2 18 O 18 O of ice decreasing 18 O of sea-water increasing C. Oxygen Isotope stratigraphy 1. The overwhelming conclusion from the studies, which have been made of both planktic and benthic species, is that similar isotopic variations are recorded in all areas. Because of the relatively short mixing time, these nearly synchronous variations enable correlations to be made between cores that may be thousands of kilometer apart. 2. Warmer periods (interglacials and interstadials) are assigned odd numbers (the present interglacial being number 1) and colder (glacial) periods are assigned even numbers. 3. The change in benthic 18 O commonly recorded between stage 5e and 5d is so large and so rapid that it is almost impossible to account for it only in terms of ice-sheet growth. It seems likely that at least part of this change reflects a rapid temperature decline (of 1.5 C) in abyssal water temperature. Subsequent changes in 18 O (in stage 5c to 1) were then primarily the result of changing ice volume on the continent. 4. It should be emphasized that the isotopic signals in ocean cores contain both a temperature and an ice-volume component, which may not be synchronous. (Shackleton & Opdyke 1976) (Prell et al. 1986) D. 18 O / Ice volume / Sea-level changes 1. Milankovitch hypotheses(1941) Glaciations in the past were principally a function of variations in the Earths orbital parameters, and the resulting redistribution of solar radiation reaching the earth. An important signal which has been inspected for a relationship between orbital perturbations and climatic change is the marine core 18 O record, which reflects changes in continental ice volume (principally Northern Hemisphere). (a) Emiliani(1955, 1966) 18 O maxima in Caribbean and equatorial Atlantic cores closely matched summer isolation minima at 65 N, which was the latitude that Milankovitch had considered critical for the growth of continental ice sheets. (b) Broecker and Van Donk(1970) They suggested revisions of Emilianis timescale, but still concluded that insolation changes were a primary factor in continental glaciation. (c) Broecker et al. 1968, Mesolella et al. 1969, Veeh & Chappell 1970 Dates of coral terrace formation, indicative of a former higher sea level (lower global ice volume), were shown to be closely related to times of insolation maxima. (d) Hays et al.(1976) Three parameters were studied: 18 O value in the foram G.bulloides (an index of global, but primarily Northern Hemisphere, ice volume); summer sea-surface temperature (T s ) derived from radiolaria-based transfer functions (an index of sub-Antarctic temperatures); and abundance variations of the radiolaria C.davisiana (an index of Antarctic surface water structure). These proxy records were concentrated at frequencies corresponding closely to those expected from an orbital forcing function(~100kyrs, 40-43kyrs, and kyrs). 2. Chappell & Shackleton(1986) (a) formal assumption: the deep ocean, at least in the Pacific, is so cold that its temperature may be regarded as constant. (b) V19-30 vs. Huon Pennisula, New Guinea: a discrepancy has been noted. (c) the final time-scale of V19-30 is developed by tuning the initial record on the basis of its relationship to orbital precession, obliquity and eccentricity functions. (d) oxygen isotope studies clearly associate reef VIIa (the older) with substage 5e. (e) Before 130kyr the sea-level curve derived from marine terraces is subject to larger uncertainties because both the assigned ages and assumed uplift rates become less secure. (f) Within the past 130kyr the greatest uncertainty relates to the reef IVb-IIIa area where the isotopic record shows little structure. (g) By plotting sea-level against 18 O, they found a cluster of points around zero sea level and +3.4 corresponding to full interglacial stage 1 and substage 5e. (h) A more probable explanation is that this isotopic shift results from a temperature effect on the isotopic composition of the benthic foraminifera analysed. (i) They conclude that deep waters in the Pacific Ocean were ~1.5 C cooler in glacial and interstadial times than in the short (~10kyr duration) interglacials of substage 5e and the present. 3. Mechanisms of glaciation and deglaciation: the oceanic evidence Ruddinman and McIntyre(1981): Ice sheet growth is favored when Northern Hemisphere summer insolation levels are low (due to orbital factors) but oceanic temperatures at high latitudes are warm, providing an abundant moisture source adjacent to the relatively cool continents. Strong thermal contrasts at the continental margin help steer depressions towards the developing ice sheets, thereby increasing the local accumulation rate. (a) Heinrich events are attributed to instabilities in the ice sheets once they have grown to continental dimensions, resulting in iceberg discharge. (b) Heinrich events raises global sea level by 10-15m (c) There must be strong and swift interactions between the major ice sheets in both hemisphere, in which the collapse of one ice sheet raises sea level sufficiently to destabilize those margins of the others where ice advanced onto the shelves. 4. A longer Perspective: the Entire Brunhes (a) Oxygen isotope values for interglacial extremes are then compared with the Stage 1. (b) The extremes of Stage 1, 5e, 9, 11 are significantly lighter than Stage 7, 13, 15,17 and 19. During these interglacials either some northern hemisphere ice must have remained, or ocean deep water must have been colder than they are today. (c) Although the planktonic values are more scattered, the values for interglacial Stage 7, 13, 15, 17 and 19 are indeed systematically more positive than the extreme values for Stages 1, 5, 9, and 11. This in turns suggests that on slowly uplifting coastlines where should be marked gap between the Stage 11 and the much older Stage 23. (d) Sachs(1973) suggested that this was substantially the warmest interglacial in the last million years. In DSDP Site 552A in the North Atlantic, Stage 11 is represented by the thickest section of nannofossil ooze with the least ice-rafted contribution of any of the interglacials in the last 2.5Ma. (e) Comparing each glacial extreme, without doubt Stages 12 and 16 were more extreme than Stage 2. Stage 6 perhaps marginally more extreme. Stage 10 was perhaps marginally less extreme than Stage 2. Stages 4, 8, 14, and 18 were significantly less important. (f) Amongst the planktonic data sets no consistent pattern emerges. This is not surprising, since temperature variations must have played a part for many of the cores.