Dyaserobic Conditions During Heinrich Events: Evidence From Organic Matter And Phosphorus Data

Organic carbon, total nitrogen and phosphorus phases concentrations and stable isotope ratios (13C, 15N) of fine (< 50 μm) size fractions of deep-sea sediments from the central north Atlantic were employed to identify changes in detrital supply and bottom water conditions during Heinrich events 1-5 (past 50 kaBP). Prominent Heinrich layers are composed of more refractory organic matter originating from soil and lithic sources (low 13C, varying 15N and TOC/TN values), contrasting sharply with that of ambient glacial sediments composed of vaying mixtures of marine and terrestrial sources (high 13C and 15N values). The distribution of P phases in Heinrich layers reflects: 1) enhanced detrital P supply linked to glacially eroded supply of soils and basement rock detritus; 2) in -situ limitation of authigenic and Fe-bound P formation indicating suboxi c/anoxic conditions in the sediment. The overall results suggest that during the phases of massive iceberg discharges corresponding to prominent Heinrich events, very-low bottom water oxygen levels were attained.