Diagenetic control of nitrogen isotope ratios in Holocene sapropels and recent sediments from the Eastern Mediterranean Sea

[摘要] The enhanced accumulation of organic matter in Eastern Mediterraneansapropels and their unusually low δ¹⁵N values have beenattributed to either enhanced nutrient availability which led to elevatedprimary production and carbon sequestration or to enhanced organic matterpreservation under anoxic conditions. In order to evaluate these twohypothesis we have determined Ba/Al ratios, amino acid composition, N andorganic C concentrations and δ¹⁵N in sinking particles, surfacesediments, eight spatially distributed core records of the youngest sapropelS1 (10–6 ka) and older sapropels (S5, S6) from two locations. These datasuggest that (i) temporal and spatial variations in δ¹⁵N ofsedimentary N are driven by different degrees of diagenesis at differentsites rather than by changes in N-sources or primary productivity and (ii)present day TOC export production would suffice to create a sapropel like S1under conditions of deep-water anoxia. This implies that both enhanced TOCaccumulation and δ¹⁵N depletion in sapropels were due to the absence ofoxygen in deep waters. Thus preservation plays a major role for theaccumulation of organic-rich sediments casting doubt on the need of enhancedprimary production for sapropel formation.

[学科分类] 地球化学与岩石