2000 H216O 10 HD16O 10 H2

18O

ice

land

Latitude increasing

ice

land1000 H2

16O 7 HD16O 7 H218O

1000 H216O

3 HD16O

3 H218O

2000 H216O 10 HD16O 10 H2

18O

Latitude increasing

500 H216O

1 HD16O

1 H218O

1500 H216O 9 HD16O 9 H2

18O

1000 H216O

3 HD16O

3 H218O

1000 H216O 7 HD16O 7 H2

18O

Latitude increasing

ice

land

300 H216O

0 HD16O

0 H218O

1700 H216O 10 HD16O 10 H2

18O

500 H216O

1 HD16O

1 H218O

1500 H216O 9 HD16O 9 H2

18O

Latitude increasing

ice

land

300 H216O

0 HD16O

0 H218O

1700 H216O 10 HD16O 10 H2

18O

ice

land

Latitude increasing

300 H216O

ice

land

Latitude increasing

1700 H216O 10 HD16O 10 H2

18O

18O of ice decreasing

18O 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 18O 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 ≥1.5C) in abyssal

water temperature. Subsequent changes in 18O (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. 18O / Ice volume / Sea-level changes

1. Milankovitch hypotheses(1941)

Glaciations in the past were principally a function of

variations in the Earth’s 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 18O record, which reflects

changes in continental ice volume (principally Northern

Hemisphere).

(a) Emiliani(1955, 1966)

18O maxima in Caribbean and equatorial Atlantic

cores closely matched summer isolation minima at 65N,

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 Emiliani’s 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: 18O value in the foram

G.bulloides (an index of global, but primarily Northern

Hemisphere, ice volume); summer sea-surface

temperature (Ts) 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 19.5-24kyrs).

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 18O, 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 ~1.5C 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.