A hemispheric circulation asymmetry during Late Tertiar

Abstract

ZusammenfassungNach zahlreichen Befunden des Deep Sea Drilling Projekts hatte der antarktische Eisdora im mittleren Mioz~in (14~12 Ma, 1 Ma = 10 ~ Jahre) etwa das bisherige Volumen erreicht, im Messinian (6--5 Ma) sogar ein noch gr613eres (Kennett, Frakes). Im Gegensatz hierzu bildete sicb --yon Gebirgsvereisungen abgesehen --die erste grol3r~iumige Vergletschernng auf den Nordkontinenten erst vor fund 8 Ma, darnach das arktisdae Treibeis, das wahrscheinlich mehr als 20 Interglaziale tiberlebt hat, mindestens seit den letzten 700 000 Jahren. W/ihrend einer Periode yon fund 10 Ma war also Ost-Antarktika hoch vereist, w~ihrend der arktische Ozean praktisch eisfrei blieb.Dieser asymmetrische Zustand wird mit der heute geringeren Asymmetrie yon Atmosph/ire und Ozean verglichen: eine unipolare mit der heute bipolaren Polvereisung. Der meteorologische ~quator muB damals im Jahresmittel in rund 10 ~ (gegeniiber 6 ~ heute) gelegen haben. Die Terme des W~irmehaushalts werden verglichen ffir einen vereisten Kontinent und einen eisbedeckten Ozean im Polargebiet. Die Verlagerungen der planetarischen Klimagtirtel werden (vorliiufig) abgesch/itzt; sie stimmen gut iiberein mit einer einfachen Formel fiir die Breitenlage des subtropischen Hochdruckgtirtels, die auch die heutigen jahreszeitlichen Verlagernngen auf beiden Halbkugeln gut reproduziert. AbschlieBend wird die Rolle des /iquatorialen Aufquellens im Ozean --das mit einer Zirkulationsasymmetrie gekoppelt ist --umrissen.Diese Asymmetrien kSnnen eine hSchst aktuelle Bedeutung erlangen, wenn die erwartete Zunahme des COe-Gehalts der Atmosph~ire einen eisfreien arktischen Ozean wiederherstellen sollte. AbstractRecent data obtained within the Deep Sea Drilling Project (Legs 28, 29, 85, 36) in the southern oceans revealed that the formation of Antarctic sea-ice started 88 m. y. b. p. ago at the begin of the Oligocene. The Antarctic ice-cap reached nearly its present volume during the Middle Miocene (14--12 m. y. b. p.) and a volume greater than the present during the Messinian (6--5 m. y, b. p.). Apart from local mountain glaciations, the first large-scale glaciation of the northern continents was developed about 3 m. y. b. p. followed by the formation of the Arctic sea-ice, which has probably survived more than 20 fully developed interglacials, certainly during the last 0.7 m.y. This evolution indicates a period of about 10 m.y. during which East Antarctica was highly glaciated, while the Arctic Ocean was essentially ice-flee.This asymmetric pattern is compared with the present asymmetry (unipolar versus bipolar glaciation); the annually averaged position of the '"meteorological equator" had then displaced from about Lat. 6 ~ to-day to about 10 ~ Some estimates of the heat budget terms in polar latitudes at a glaciated continent and at an ice-covered ocean are given. A preliminary review of paleoclimatic data reveals significant shifts of the position of the climatic belts at both hemispheres. These shifts coincide rather well with an extrapolation of the actual seasonal var...

Grain-Size Record of Ocean Current Winnowing in Oligocene to Pleistocene Ooze, Broken Ridge, Southeastern Indian Ocean

“…These data are also consistent with the information presented by Rea and Bloomstine (1985), Leinen (1979), andMiller et al (1987) that atmospheric and oceanic surface circulation increased about 10 Ma and not at about 13 Ma. The apparent lag between the isotopic indication of Northern Hemisphere ice buildup and the intensification of Southern Hemisphere sea-surface circulation is consistent with the observation made first by Flohn (1981) that the hemispheres may be somewhat independent in their circulatory behavior; a cooling at one pole and concomitant increase in the temperature gradient of that hemisphere need not serve to increase the circulation energy of the other. Indications of the intensity of Southern Hemisphere atmospheric circulation do not appear to reflect any changes associated with the onset of Northern Hemisphere glaciation (Rea, 1989).…”

Climate: Is the past the key to the future?

“…Will the earth remain in an interglacial in its ''icehouse'' state, return to a full glacial, or shift back to its long-term preferred ''greenhouse'' state? Another possibility was suggested by Flohn (1981). He noted Fig.…”

On the Origin of the Surface Air Temperature Difference between the Hemispheres in Earth's Present-Day Climate

“…The marked difference between surface temperatures in the Antarctic and the Arctic was discussed as an additional factor in the asymmetry between Earth's hemispheres in the following decades (e.g., Flohn 1981). The differences between Earth's polar regions are mainly due to geography: while the Arctic comprises a partly icecovered ocean surrounded by continents, its southern equivalent consists of the continent of Antarctica, which is continuously covered by ice and surrounded by open ocean.…”