Seasonal variability in the abundance and stable carbon-isotopic composition of lipid biomarkers in suspended particulate matter from a stratified equatorial lake (Lake Chala, Kenya/Tanzania): Implications for the sedimentary record. (15th July 2018)

• Record Type: Journal Article
• Authors: van Bree, L.G.J.; Peterse, F.; van der Meer, M.T.J.; Middelburg, J.J.; Negash, A.M.D.; De Crop, W.; Cocquyt, C.; Wieringa, J.J.; Verschuren, D.; Sinninghe Damsté, J.S.
• Is Part Of: Quaternary science reviews. Volume 192(2018)
• Page Start: 208
• Page End: 224
• Publication Date: 2018-07-15
• Subjects: East Africa -- Aquatic biomarkers -- Organic geochemistry -- Stable isotopes -- Paleolimnology -- Paleoclimatology; Geology, Stratigraphic -- Quaternary -- Periodicals; Stratigraphie -- Quaternaire -- Périodiques; 551.79
• DOI: 10.1016/j.quascirev.2018.05.023
• Languages: English
• ISSNs: 0277-3791

Abstract

Abstract: We studied the distribution and stable carbon-isotopic (δ 13 C) composition of various lipid biomarkers in suspended particulate matter (SPM) from the water column of Lake Chala, a permanently stratified crater lake in equatorial East Africa, to evaluate their capacity to reflect seasonality in water-column processes and associated changes in the lake's phytoplankton community. This lake has large seasonal variation in water-column dynamics (stratified during wet seasons and mixing during dry seasons) with associated phytoplankton succession. We analyzed lipid biomarkers in SPM collected monthly at 5 depths (0–80 m) from September 2013 to January 2015. Seasonal variation in total phytoplankton biovolume is strongly reflected in the concentration of phytadienes, a derivative of the general photosynthetic pigment chlorophyll. The wax and wane of several specific biomarker lipids between June and December 2014 reflect pronounced phytoplankton succession after deep mixing, starting with a long and sustained chlorophyte bloom (reflected by C23:1, C25:1 and C27:1 n -alkenes, and C21 and C23 n -alkanes), followed by a peak in diatoms between July and October (loliolide and isololiolide), and then eustigmatophytes (C30 and C32 1, 15 diols) once stratification resumes in October. Peak abundance of the C19:1 n -alkene during shallow mixing of the water column in January–February 2014 can be tentatively linked to the seasonal distribution of cyanobacteria. The concentration, seasonal variability, and low δ 13 C values of the C28 fatty acid in the SPM suggest that this biomarker is produced in the water column of Lake Chala instead of having the typically assumed vascular plant origin. The δ 13 C signature of particulate carbon and all aquatic biomarkers become increasingly more negative (by up to 16‰) during mixing-induced episodes of high productivity, whereas enrichment would be expected during such blooms. This reversed fractionation may be attributed to chemically enhanced diffusion, which generates depleted HCO3 − under high pH (>9) conditions, as occur in the epilimnion of Lake Chala during periods of high productivity. The influence of this process can potentially explain previously observed 13 C-depleted carbon signatures in the paleorecord of Lake Chala, and should be considered prior to paleorecord interpretation of organic-matter δ 13 C values derived (partially) from aquatic organisms in high-pH, i.e. alkaline, lakes. Highlights: Seasonal mixing of Lake Chala's water column is related to climate. Phytoplankton dynamics is reflected by stable carbon isotopes and lipid biomarkers. Aquatic lipids dominate biomarker composition of suspended matter in Lake Challa. The C28 fatty acid is primarily produced in the water column of Lake Challa. Remarkably low biomarker δ 13 C values are potentially induced by high lake-water pH.