Respuesta del registro sedimentario a la ciclicidad solar en el estrecho de Gerlache (península Antártica)

Abstract

The Gerlache Strait (Antarctic Peninsula) is a semi-enclosed basin that acts as a giant sedimentary trap collecting large amounts of material. Previous biogenic and glacial deposits are the main suppliers of sediments. The basin is also an area of high sea-surface productivity, mostly restricted to the summer months of December and January. In this study we present micropaleontological and geochemical data obtained from a set of four sediment cores obtained by the Spanish research vessel Hespérides during the Fruela-96 expedition. The cores were collected using a multiple corer allowing recovery of up to eight replicates, with core lengths ranging between 32 and 34 cm. The stratigraphic framework of the cores, based in 210Pb activity, shows that there has been a continuous sedimentation in the sites during the last 220 years BP. The diatom assemblage varies between absolute values of 0.9 to 240 x 108 valves/g of dry sediment. Chaetoceros RS are the main contributor showing values from 66 to 90 %. The Thalassiosira antarctica/ scotia group and Sea-ice taxa, mainly Fragilariopsis curta, are secondary contributors. The total abundance of diatoms and the content of biogenic silica are interpreted as paleoproductivity proxies. In this sense, a progressive reduction in paleoproductivity is observed towards the core top, with a sharp minimum around 100 yr B.P. Moreover an increase of Sea-ice Taxa is observed for the last 100 yr. These changes could be related to the onset of a neoglacial event during this period. In order to evaluate the cyclicity record, Spectral analyses (Multi-Tapered Method) were performed on different parameters (TOC, Opal, total diatom abundance, Sea-ice Taxa and T. antarctica). The time series study shows two main types of cyclicities, 80-90 and 20-30 years in two cores, G4 and G5, both recovered from central Gerlache Strait. This cyclicity seems to be in agreement with the Hale (22 years) and the Gleissberg (83 years) Solar Cycles. Both cycles are related to strong solar eruptive activity, which modulate the amplitude of the 11-year sunspot cycle (Schawe Cycle); this cycle was also recognised in our record