Biogeochemical processes controlling oxygen and carbon isotopes of diatom silica in Late Glacial to Holocene lacustrine rhythmites

Abstract

Biogeochemical cycles and sedimentary records in lakes are related to climate controls on hydrology and catchment processes. Changes in the isotopic composition of the diatom frustules (δ 18 O diatom and δ 13 C diatom ) in lacustrine sediments can be used to reconstruct palaeoclimatic and palaeoenvironmental changes. The Lago Chungará (Andean Altiplano, 18°15′S, 69°10′W, 4520 masl) diatomaceous laminated sediments are made up of white and green multiannual rhythmites. White laminae were formed during short-term diatom superblooms, and are composed almost exclusively of large-sized Cyclostephanos andinus. These diatoms bloom during mixing events when recycled nutrients from the bottom waters are brought to the surface and/or when nutrients are introduced from the catchment during periods of strong runoff. Conversely, the green laminae are thought to have been deposited over several years and are composed of a mixture of diatoms (mainly smaller valves of C. andinus and Discostella stelligera) and organic matter. These green laminae reflect the lake's hydrological recovery from a status favouring the diatom super-blooms (white laminae) towards baseline conditions. δ 18 O diatom and δ 13 C diatom from 11,990 to 11,530 cal years BP allow us to reconstruct shifts in the precipitation/evaporation ratio and changes in the lake water dissolved carbon concentration, respectively. δ 18 O diatom values indicate that white laminae formation occurred mainly during low lake level stages, whereas green laminae formation generally occurred during high lake level stages. The isotope and chronostratigraphical data together suggest that white laminae deposition is caused by extraordinary environmental events. El Niño-Southern Oscillation and changes in solar activity are the most likely climate forcing mechanisms that could trigger such events, favouring hydrological changes at interannual-to-decadal scale. This study demonstrates the potential for laminated lake sediments to document extreme pluriannual events.

Evolution of the Lake Titicaca basin and its diatom flora over the last ~370,000years

“…C. andinus was first described from Lake Titicaca and was originally thought to be endemic to the basin. Subsequently, it has been reported from other Andean fossil locations and in one contemporary site Ekdahl et al, 2008;Hernandez et al, 2011). These data suggest that the taxon occurs outside the Lake Titicaca basin, although its distribution appears to be restricted to the tropical Andes.…”

Climatic and lacustrine morphometric controls of diatom paleoproductivity in a tropical Andean lake

“…There is a former appreciable knowledge of the main changes that occurred in the lake since the Late Glacial based on multiproxy evidence. These included sedimentary facies characterization (Sáez et al, 2007), isotopic composition of bulk organic matter (δ 13 C org , δ 15 N org ; Pueyo et al, 2011), carbonates (δ 18 O carbonate , δ 13 C carbonate ; Pueyo et al, 2011), and diatom frustules (δ 18 O diat , δ 13 C diat ; Hernández et al, 2008Hernández et al, , 2010Hernández et al, , 2011Hernández et al, , 2013, as well as a moisture balance reconstruction based on magnetic susceptibility, X-ray Fluorescence (XRF), X-ray Diffraction (XRD), Total Carbon and Total Organic Carbon (TC and TOC),…”

The last glacial maximum and late glacial environmental and climate dynamics in the Baikal region inferred from an oxygen isotope record of lacustrine diatom silica

“…In the past decade researchers have paid special attention to investigating past climate changes and factors leading to switches between glacial and interglacial conditions. Numerous studies have shown the transition from cold and dry glacial to warm and wet interglacial climate led to major environmental alterations in the terrestrial part of lake catchments and in aquatic ecosystems (Morley et al, 2005;Stebich et al, 2009;Müller et al, 2010;Hernandez et al, 2011;Cook et al, 2012;Zhao et al, 2013).…”