The deglacial development of the Oxygen Minimum Zone in the Bering Sea: A study based on high-resolution laminated sediment records

• Main Author: Kühn, Hartmut
• Format: Thesis
• Language: unknown
• Published: http://www.suub.uni-bremen.de 2015
• Subjects: Bering Sea; NGRIP; North Atlantic; Alaska
• Online Access: https://epic.awi.de/id/eprint/42875/; https://epic.awi.de/id/eprint/42875/1/Kuehn_2015.pdf; https://hdl.handle.net/10013/epic.49415; https://hdl.handle.net/10013/epic.49415.d001

In the past decades several paleoceanographic studies found evidence for millennial scale climate variability during the late Pleistocene. While these climate fluctuations are well studied in the North Atlantic, the paleoceanographic history in the North Pacific is less well known. The last glacial termination is of special interest, as it represents the most recent transition from glacial to deglacoal conditions. In the North Pacific these changes led to a strengthening of the mid-depth oxygen minimum zone (OMZ) to anoxic bottom water conditions and the deposition of laminated sediments. The main objective of this thesis was to gain new insights into the deglacial mid-depth OMZ dynamics in the Bering Sea, using a suite of mid-depth, partly laminated sediment cores that were collected during R/V Sonne cruise SO202-INOPEX. It will be shown that during the Bølling–Allerød (BA) and early Holocene the Bering Sea OMZ strengthened to anoxic values of <0.1 ml/l, which led to the formation of laminations, and expanded vertically to water depths of >2100 m. Based on a correlation of 14C-dated, laminated sediment cores it is revealed that throughout the Bering Sea and the Gulf of Alaska the onset of deglacial anoxia at 14.6 ka and 11.7 ka was a synchronous event, while the disappearance of laminations was a diachronous process. A decadal-scale correlation of two 14C dated, layer counted sediment cores with seasonal resolution from the northeastern Bering Sea slope to the NGRIP δ18O record revealed, that (1) the formation of laminations was tightly coupled to warm phases of the B/A and the early Holocene, which implies an atmospheric teleconnection between the North Atlantic and Bering Sea, and (2) the presence of annually laminated sediments (varves). The established age model was partly independent from radiocarbon ages and allowed the calculation of surface reservoir ages, which are 770 yr, 910yr and 875 yr for the Holocene, Younger Dryas and B/A respectively. The anoxia were driven on millennial scales by ...