Publication Date:
2024-01-22
Description:
Benthic foraminiferal assemblages were studied at core S075-26KL from the Portuguese continental margin at 1100 m waterdepth. Special interest was laid on faunal fluctuations during Heinrich- events I and II. They were studied with high resulution to describe the fluctuations of oxygen and nutrient content and the influence of MOW during the episodes of enhanced ice rafting. The high percentages of Cibicidoides ssp. and Quinqueloculina seminula indicate high fluxes of nutrient and high oxygen levels durig Heinrich- event II. The oxygen content decreases immediately after this event. The beginning of the last glacial maximum is characterized by high abundances of Globobulimina affinis and Melonis barleeanum. Uvigerina peregrina parva is also frequent. It is concluded that upwelling had a great influence during this period, leading to high concentracions of nutrients and thus to a lower content of oxygen at intermediate waterdepth. During the further course of the last glacial maximum, high oxygen levels and a low flux of nutrients are indicated by high abundances of Cibicidoides ssp. and a decrease in G. affinis. This trend reverses, however, towards the beginning of Termination I. A peak of U. peregrina parva is found in Heinrich- layer I. The maximal abundance of G. affinis is recognized 10 cm below the center of this layer. This maximum is also linked to Heinrich-event I since this species lives deeply endobenthic. Heinrich-event I is thus characterized by oxygen depletion and a high flux of nutrients. These conditions were not continuous. Smaller peaks of Cibicidoides wuellerstorfi and Q. seminula represent at least one shorter event of enhanced bottom current and higher values of oxygen during early Heinrich- event I. Subsequent to Heinrich- event I, Cibicidoides pseudoungerianus and Planulina ariminensis show maximal abundances. The bottom water is characterized by a high oxygen content, low nutrient values and an enhanced bottom current. This change slowly inverts during the Holocene, leading to lower values for oxygen and higher nutrient levels in the late Holocene. The bottom current intensity also decreases. The intensity of the Mediterranean Outflow (MOW) in this area was described by using the frequency of elevated epibenthic Foraminifera as proxy for bottom current strenght. A maximal intensity of the MOW is recognized for the last glacial maximum and the late Termiation I. The influence of the MOW was stronger during Heinrich- event II than in the Holocene. It reached present-day values during Heinrich-event I.
Type:
Thesis
,
NonPeerReviewed
Format:
text
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