DATE2022-06-22 10:23:04
TITLEClimate variations in the Mediterranean Sea during the last 21,000 years: insights into biogeochemical implications with a regional ocean model
AUTHORSKatharina D. Six (1) ,Uwe Mikolajewicz (1)
  1. 1) Max Planck Insititute For Meteorology, Hamburg (Germany)
ABSTRACTSapropels in the eastern Mediterranean Sea (MedSea) during the early Holocene are the most pronounced signal of changes in biogeochemistry over the last deglaciation. The building and preservation forces of these organic-rich layers are not yet fully understood. In addition, the nutrient distribution for the entire MedSea at the onset of deglaction is poorly constrainted. We perform simulations with a regional general ocean circulation model including biogeochemistry in the water column and sediments over the last 21,000 years. Atmospheric forcing fields, river discharge and oceanic boundary conditions at the western model domain are adapted from transient simulations with an Earth System Model. We find a more sluggish zonal overturning circulation in the MedSea during the Last glacial maximum (LGM). Colder temperatures lead to a lower basin-wide evaporation rate. In combination with a shallow sill depth at the Strait of Gibraltar, the baroclinic water exchange with the North Atlantic reduces by about 35% compared to present day. Enhanced river discharge during the LGM supplies more nutrients to the basin, but the overall net primary production decreases due to circulation changes and an increased remineralisation length scale. LGM nutrient concentrations below 200 m are more than twice as high as today. Elevated nutrient concentrations at depth are present until 6000-8000 years BP and could play an essential role on the temporal variability of biogeochemistry over the simulated deglaciation.