Milankovitch cycles and paleoceanographic evolution within sediments from ODP Sites 980 and 983 of the North Atlantic Ocean

摘要

Sediments from Ocean Drilling Program (ODP) Sites 980 and 983 in the North Atlantic Ocean were analyzed to obtain evidence of long-range Milankovitch cycles and to examine the cycles' effect on the paleoceanographic evolution of the North Atlantic Ocean. Wide cyclic variations in total organic carbon and biogenic carbonate occur throughout the columns at both sites and provide distinctive characteristics of both sediment groups. Spectral modeling of these variations shows typical 100-ka cyclic variations in both the total organic carbon (TOC) and carbonate records at Site 980, although this 100-ka Milankovitch frequency occurs only in the upper, ≈472,5 ka, section of the core. In Site 983, only 400-ka cycle in carbonate is observed but the 100-ka cycle in TOC and carbonate is absent. The terrigenous content, expressed in terms of K, Al, Ti, and Th, also shows strong 100-ka and 400-ka cyclic variations at Site 983. The earth's eccentricity as expressed 100-ka and 400-ka cycles, and no appearance of obliquity (41-ka) and precession (23-ka) are important characteristics of North Atlantic Ocean sediments. Milankovitch pulse differences in carbonate, TOC at the two sites likely arise from the evolution of paleocean-ography. The dilution of carbonate fractions by terrigenous materials (indicated by the cyclical behavior of trace elements) at Site 983 is one of plausible explanation. Climatic warming over the last 600 ka probably caused the differences in the sedimentary cycles at the two sites; induced meltwater discharge is recorded in the terrigenous record, and changes in the oceanic circulation system are related to major glacial-interglacial climatic episodes that probably underlie the differences in the cyclical records.