Carbonate preservation history in the Peru Basin: Paleoceanographic implications

Abstract

We studied preservation/dissolution cycles and paleoproductivity in eight sediment cores from the Peru Basin south of the highly productive surface waters of the eastern equatorial Pacific. Stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy. Sediment cores which span the last 8 m.y., were retrieved during cruise 79 with RV SONNE close to the carbonate compensation depth (CCD). In general, sediments show Pacific‐type carbonate cycles. We interpret a pronounced carbonate peak between 6 and 7 Ma as the result of a western and northern extension of the highly productive Peru Current. Decreased carbonate contents from the late Miocene to the late Pliocene might be associated with a slow contraction of the latitudinal extent of the high‐productivity belt north of the study areas. During the Pliocene, carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets, which should have been associated with pulsations of the Antarctic ice cap. An abrupt collapse of the carbonate system occurred at 2.4 Ma. Higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation. During the Quaternary, carbonate fluxes are high during glacials and low during interglacials. Large amplitude variations with long broad minima and maxima, associated with small migrations of the lysocline and the CCD (< 200 m), are indicative of the preservation/dissolution history in the Peru Basin. During the early Pleistocene, climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record. During the last 800 kyr, variability in the carbonate record was dominated by the 100 kyr eccentricity cycle. Fluxes of biogenic material (calcium carbonate, organic carbon, opal, and barium) were greatest during glacials, which imply higher productivity and export production of the Peru Current during cold climatic periods. Dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate. After the Mid‐Brunhes Event (400 ka), we observe a plateaulike shift to enhanced dissolution and to intensified productivity.

Variaciones del sistema de surgencia de Punta Angamos (23 S) y la Zona de Mínimo Oxígeno durante el pasado reciente: Una aproximación desde el registro sedimentario de la Bahía Mejillones del Sur

“…Bajo situaciones muy especiales, los sedimentos marinos pueden constituirse en un importante registro de condiciones oceanográficas pasadas que permiten, por una parte, trabajar con una alta resolución temporal (en casos muy excepcionales, en forma anual), y por otra, abarcar un largo intervalo de tiempo. Estudios en esta dirección han sido desarrollados en sistemas de surgencia de distintas partes del mundo (Lange et al 1990, Divakar et al 1992, Farrel et al 1995, Weber et al 1995, Martínez et al 1996, Von Road et al 1999.…”

Biogeochemical Regeneration of a Nodule Mining Disturbance Site: Trace Metals, DOC and Amino Acids in Deep-Sea Sediments and Pore Waters

“…Predominantly, siliceous and calcareous muds and oozes make up the sediments in this region (Weber et al, 1995). For detailed site description of the DISCOL area and the disturbance experiment carried out in 1989 please refer to Thiel and Schriever (1990); Boetius (2015); Greinert (2015).…”

Insolation dependence of the southeastern subtropical Pacific sea surface temperature over the last 400 kyrs

“…Unfortunately, the extremely low sedimentation rates and poor carbonate preservation in this area (most of the southeastern Pacific sea floor is deeper than 4000 meters, the approximate present carbonate compensation depth [Weber et al, 1995] problems. In this sense, the present work is devoted to study a core located in the Nazca Ridge at 3120 m water depth and therefore above the present depth of the lysocline.…”