| Summary: | An investigation involving stable oxygen and carbon isotopes on core Ml5612 from the Mid-Atlantic Ridge (445N, 26°W) shows that distinct negative δIRO anomalies punctuate the plank tonic isotope records and correlate with the ice-raftcd detritus (IRD) events. Within most IRD layers, detntal carbonate contributes between 1 and 13% and supports the contention that the layers are the southern equivalents of the northern North Atlantic Ocean's Heinnch events Anomalies are strongest for the Neogloboquadrina pachyderma (sinistral coiling) isotope record. Systematic changes in the δIRO offset between Globigerina bulloides and Globorotalia inflata signify variations in the mid-latitude thermocline structure. In conjunction with negative benthic δIRC anomalies, the data document a stronger contribution of an IRO-depleted, nutrient-rich water mass during the Heinrich events. The δIRC amplitude of >l% between 25 and 57 ka indicates changes between northern-source (North Atlantic Deep Water) and southern-source (Antarctic Bottom Water) water masses at this site. The Heinrich layers in the mid-latitude core arc correlative with those from a core off Portugal. This synchronicity may have resulted from common changes in a North Atlantic thermohaline switch. RÉSUMÉ Une étude touchanl les isotopes lourds d'oxyéene ct de carbone du noyau M156I2 dc la ride médio-allantique (44=nord. 26° ouest) révéle que des anomalies negatives distinctes de δIRO ponctuent les enregistrements d'isotopes planctoniques et les rapprochent avec des phenomènes d'alimcntation en débris glaciels. La contribution du carbonate délrilique varie entre 1 et 13% a l'inteneur de la majorité des couches de débris glaciels, ce qui conforte la théorie que les couches constituent les équivalents méndionaux des phènoménes de Heinrich septentnonaux de I'Atlantique ...
|
|---|