Testing the D/H ratio of alkenones and palmitic acid as salinity proxies in the Amazon Plume

Autor(es)

Haeggi, C. ^[1] ; Chiessi, C. M. ^[2] ; Schefuss, E. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Bremen, Ctr Marine Environm Sci, MARUM, D-28359 Bremen - Germany

^[2] Univ Sao Paulo, Sch Arts Sci & Humanities, Sao Paulo - Brazil

• Tipo de documento: Artigo Científico
• Fonte: BIOGEOSCIENCES; v. 12, n. 23, p. 7239-7249, 2015.
• Citações Web of Science: 6

Resumo

The stable hydrogen isotope composition of lipid biomarkers, such as alkenones, is a promising new tool for the improvement of palaeosalinity reconstructions. Laboratory studies confirmed the correlation between lipid biomarker delta D composition (delta D-Lipid), water delta D composition (delta D-H2O) and salinity; yet there is limited insight into the applicability of this proxy in oceanic environments. To fill this gap, we test the use of the delta D composition of alkenones (delta D-C37) and palmitic acid (delta D-PA) as salinity proxies using samples of surface suspended material along the distinct salinity gradient induced by the Amazon Plume. Our results indicate a positive correlation between salinity and delta D-H2O, while the relationship between delta D-H2O and delta D-Lipid is more complex: delta D-PA correlates strongly with delta D-H2O (r(2) = 0.81) and shows a salinity-dependent isotopic fractionation factor. delta D-C37 only correlates with delta D-H2O in a small number (n = 8) of samples with alkenone concentrations > 10 ng L-1, while there is no correlation if all samples are taken into account. These findings are mirrored by alkenone-based temperature reconstructions, which are inaccurate for samples with low alkenone concentrations. Deviations in delta D-C37 and temperature are likely to be caused by limited haptophyte algae growth due to low salinity and light limitation imposed by the Amazon Plume. Our study confirms the applicability of delta D-Lipid as a salinity proxy in oceanic environments. But it raises a note of caution concerning regions where low alkenone production can be expected due to low salinity and light limitation, for instance, under strong riverine discharge. (AU)

• Processo FAPESP: 12/17517-3 - Resposta da porção oeste do Oceano Atlântico às mudanças na circulação meridional do Atlântico: variabilidade milenar a sazonal
• Beneficiário: Cristiano Mazur Chiessi
• Modalidade de apoio: Auxílio à Pesquisa - Programa de Pesquisa sobre Mudanças Climáticas Globais - Jovens Pesquisadores