Oxygen Isotope Content Research Articles

Planktonic foraminiferal and oxygen isotopic stratigraphy and paleoclimatology of Norwegian Sea deep‐sea cores

BOREAS Kellogg, T. B., Duplessy, J. C. & Shackleton, N. J. 1978 03 01: Planktonic foraminiferal and oxygen isotopic stratigraphy and paleoclimatology of Norwegian Sea deep‐sea cores. Boreas. Vol. 7, pp. 61–73. Oslo. ISSN 0300–9483.Three Norwegian Sea deep‐sea cores, which penetrate to sediments at least 200,000 years old, were analyzed for oxygen isotope content, total calcium carbonate, and planktonic foraminifera. The oxygen isotopic stratigraphy was used to refine the time control for paleoclimatic and paleo‐oceanographic events previously described for the region. Two pulses of relatively warm subpolar water entered the region between 124,000 B.P. and 115,000 B.P. (the last interglacial), and since about 13,000 B.P. The remaining portion of the last 150,000 years was characterized by extensive ice cover. The magnitude of the change in isotopic composition between peak glacial and peak interglacial conditions is larger than can be explained by the changing isotopic content of the oceans alone suggesting that large temperature and salinity effects are recorded in isotope curves from Norwegian Sea isotope curves. The magnitude of the isotopic change from substage 5e to 5d (greater than 1%) is attributed to a combination of changing oceanic isotopic composition combined with a large temperature effect due to a sudden sea‐surface temperature decrease of about 6oC. The persistence of heavy isotope values throughout substages 5d through 5a may be related to the sea‐ice cover which prevented dilution of the isotopically heavy waters by isotopically light run‐off. Sedimentation rates calculated for each of the isotope stages show large changes from one stage to another with some tendency for odd numbered stages to have higher rates.

Distribution, stratigraphic position and age of ash layer “L”, in the Panama Basin region

Deep-sea sediments in the Panama Basin-Carnegie Ridge area contain biogenic material, detrital carbonate, mineral clay and volcanic ash layers. Ash layer “L” of Bowles et al. (1973) is correlated mineralogically and by the physical property of glass shards through sixteen cores. Isopachs and grain-size analyses of the ash layer indicate that it originated in Colombia or Ecuador, and was carried by easterly winds. The distribution of the ash and of mica percentage in the ash form a W-shaped pattern opening towards the west. This suggests that two branches of the Cromwell current, one moving along the equator and one along 3°S, had a significant influence on the distribution of the ash. CaCO 3 content has been measured down thirteen cores and oxygen isotope content of benthonic Foraminifera obtained in two. Two cores penetrate the Stylatractus universus extinction datum. Ash “L” fell 230,000 years ago during the cold substage 7b of isotope stage 7. Deposition rates vary between 2.5 and 6 cm/1000 yr and show no relationship with bottom topography or proximity to land.

Low-O 18 basalts from Iceland

The volcanic rocks of Iceland are anomalous in their oxygen isotope content. Recent tholeiitic and transitional alkali basalts from Iceland range in (δO 18 from 1·8 to 5δ7%. Most of the tholeiitic basalts and their phenocrysts are at least 1% lower in δO 18 than unaltered basalts from other oceanic islands or oceanic ridges. The Icelandic basalts that resemble ridge basalts in δO 18 also resemble them in major element chemistry. δO 18 values of alkali olivine basalts are closest to those of other oceanic islands. Secondary alteration processes have lowered as well as raised the δO 18 values of some Icelandic rocks, but such surface mechanisms cannot account for the distribution of oxygen isotopes in the Recent basalts of Iceland. Three mechanisms that could give rise to the low-O 18 magmas are (1) exchange of oxygen between magma and low-O 18 hydrothermally altered rock, (2) exchange with low-O 18 meteoric water, or (3) an exceptional mantle under Iceland. None of the above models can satisfactorily account for all the observations.

Untersuchungen zur Frühontogenie vonNautilus pompilius (Linné)

A series of initial shells ofNautilus pompilius was investigated for morphologic and isotopic evidence of the early ontogenetic development. Shell morphologic features, such as curvature of early shell, cancellate sculpture, suture and grouping of septa, as well as very early shell injuries, color banding and shell/egg dimensions, seem to indicate an interpretation of early ontogeny differing from that which is now generally accepted. The O18/O16 and C13/C12 ratios in the early shell and septa of twoNautilus specimens are given. Changes in the carbon isotope content are tentatively correlated with the end of the embryonic period and with environmental changes. Variations in the oxygen isotope content are in part ascribed to migrations from warm to cooler water after a certain stage of development. The size of the body chamber of the young animals can be determined by comparison of the isotope contents in outer shell and septa. Existing ideas concerning early ontogeny ofNautilus are critically discussed.

Isotopic Evidence on the Early Life History of Nautilus pompilius (Linné)

The ratios of oxygen-18 to oxygen-16 and of carbon-13 to carbon-12 in the early shell and septa of two Nautilus specimens are interpreted for the early ontogeny of the animals. Changes in the carbon isotope content are tentatively correlated with the end of the embryonic period and with environmental changes. Variations in the oxygen isotope content are in part ascribed to migrations from warm to cooler water after a certain stage of development. The size of the body chamber of the young animals can be determined by comparison of the isotope contents in outer shell and septa.