Siliceous productivity changes in Gulf of Ancud sediments (42°S, 72°W), southern Chile, over the last ~150 years

摘要

We evaluated changes in siliceous export production and the source of organic matter preserved in sediment core MD07-3109H recovered from the Gulf of Ancud, Chiloé Inner Sea (42°S, 72°W, water column depth: 328m), southern Chile. We analyzed the abundance of siliceous microfossils (diatoms, silicoflagellates, sponge spicules, Chrysophyte cysts, phytoliths), geochemical proxies (weight percent silicon %Si_(OPAL), organic carbon, total nitrogen, C/N molar), and sediment stable isotopes (δ~(13)C_(org), δ~(15)N). Chronology based on ~(210)Pb and ~(14)C provided an accumulated age of 144 years at the base of the core.Sediments of core MD07-3109H are predominantly marine in origin, averaging δ~(13)C_(org)=-20.75%±0.82, δ~(15)N=8.7±0.35%, and C/N=8.76±0.36. Marine diatoms compose 94% of the total assemblage of siliceous microfossils. Our record of productivity based on the mass accumulation rates of organic carbon, total nitrogen, Si_(OPAL), and total diatoms showed high values between 1863 and 1869 AD followed by a declining trend until 1921 AD, a transition period from 1921 to 1959 AD with fluctuating values, and a clear decreasing pattern from 1960 AD to the present. This marked reduction in productivity was associated with decreased precipitation and Puelo River streamflow (41°S), as well as a warmer and more stratified water column, especially since the 1980s.