Evaluation of Sub-Mesoscale Nutricline Variability on Pre-Conditioning the Extent of the Spring Bloom at the Bermuda Atlantic Time-Series

Horizontal supply of nutrients to the BATS (Bermuda Atlantic Time-Series Study) site via advective processes is poorly constrained due to a lack of extensive surveys over relevant time scales encompassing this dynamic mesoscale eddy-dominated region. High-resolution spatial process cruises aimed at capturing mesoscale eddy structure in the vicinity of BATS document extensive variability in upper ocean nutrient profiles over length scales of 20-40 km. Given this variability, we adopt a 3-dimensional synoptic strategy to estimate the horizontal nutrient transport to the local budgets at the BATS site. Five stations are sampled for dissolved nutrients (nitrate, nitrite, phosphate and silicate) from the surface ocean to a depth of 500 m in an 80 km wide grid with the BATS site at the centre. The survey is repeated monthly as part of the regular BATS cruises from the onset of destabilizing conditions in autumn through the spring bloom and initiation of the seasonal thermocline. Velocity fields are measured via shipboard ADCP observations and further supported with hindcast model data from a 1/12th degree global model to help derive the advective fluxes. In addition to estimating the advective contribution to the local budget, we develop short-term parameterizations for interpreting the nutrient relationship to biotic and abiotic processes and consider the extent to which density can be used as a proxy for individual nutrient concentrations that could be used to facilitate profiles based on modelled physical data. Finally, we assess the role of sub-mesoscale nutricline variability in supplying differential nutrient fluxes to the euphotic zone during the critical deep mixing periods as pre-conditioning for the spring bloom in the Sargasso Sea.