North Atlantic evidence of orbital to millennial-scale climate variability during the Mid-Pleistocene transition
Abstract
Oceanic sediments recovered from the Bermuda Rise (North-western Atlantic) have been investigated to document changes in the oceanic circulation patterns and their relationship with the long term and millennial scale climate variability, between the top of the Jaramillo and the Brunhes/Matuyama reversal boundary (from approximately 1020 to 738 ka BP). This period represents a significant interval of climate change because it encompasses the Middle Pleistocene climatic transition, when a global climatic system dominated by 41 thousand year cyclicity (orbital obliquity) was replaced by the more recent "ice age" regime dominated by 100 thousand year cyclicity (orbital eccentricity). ODP Site 1063, located on the sediment drift which comprises the northeast Bermuda Rise (33^o41'N, 57^o36'W), lies at 4584 m water depth within the mixing zone between North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW), in an ideal position to record distinctive changes in the AABW/Lower NADW front. Oxygen and carbon isotope records from benthic and planktonic foraminifera, together with the ice-rafted detritus occurrence, indicate that millennial-scale climate instability occurred during the Middle Pleistocene. These oscillations suggest high-frequency climate variability analogous to that associated with MIS 3 Heinrich events. The benthic carbon isotope record shows that the deep North Atlantic experienced millennial-scale changes in ventilation throughout the time interval analysed: rapid and distinctive events of reduced ventilation (inferred from low benthic δ13C) occurred during both glacial and interglacial conditions, confirming that interglacial periods are not necessarily times of stable thermohaline circulation. Taking into account that Site 1063 is located at a sensitive depth to monitor the influence of AABW, the benthic carbon isotope signal has been compared with existing datasets from other areas (DSDP Sites 552, 607 and ODP Site 677), This comparison demonstrates that the relative strength of AABW production varied through time, similarly to that of NADW. This consideration implies that inter-ocean carbon isotopic gradients are not to be interpreted simply as variations in the production rate of NADW, but should be viewed within a broader context in which the two different source components of deep water undergo dramatic changes in their circulation regime through time.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....7429F