Enhanced Arctic Stratification during Mid Pliocene Warm Period
This study proposes that the water column stratification strengthens at the Yermak Plateau during warmer periods of MPWP and weakened during colder periods based on the relative nutrient utilization at the surface. The relative nutrient utilization is reconstructed using nitrogen isotope (δ15N) of sedimentary organic matter (SOM), where we have also checked for the provenance and the burial diagenesis. The sediment core is collected during ODP expedition 151 from Hole 910C, Yermak Plateau, Arctic Ocean. The water column depth at the study site is 556.4 m. We have measured the δ15N values of SOM to reconstruct the relative nutrient utilization. The CaCO3 %, Mass accumulation rate of CaCO3 (MAR), and Ba/Al are used to reconstruct the surface water productivity. The carbon isotope (δ13C) and the elemental concentration (total organic carbon (TOC) and total nitrogen (TN)) of SOM are measured to determine the provenance and diagenetic alteration at the study site. The provenance of the organic matter is determined from δ13C versus C/N ratio. While, the diagenetic alteration is observed from the cross plot between δ15N vs TOC, TN, and C/N. From this data set, we found that the origin of the organic matter is mostly from the marine environment with a negligible diagenetic alteration. The high δ15N values with high productivity indicate the maximum consumption of nutrients during the interglacial periods, which suggests that the limited nutrient supply to the surface could be due to the strong stratification. Whereas during the colder period the low δ15N values with low productivity indicate low relative nutrient utilization and it implies the repletion of nutrient at the surface with new nitrate could be due to the weak stratification. This study finds that the strong stratification during the warmer period at the Yermak Plateau could be due to the freshening of the surface layer via more sea ice melt, river runoff and, net precipitation. The weak stratification during the colder period could be due to the lowering of salinity gradient due to brine rejection during sea ice formation.