ALBERT

Description: This data is part of the BMBF project CUSCO (Coastal Upwelling Systems in a Changing Ocean). Here we report biogenic Silica concentrations in the watercolumn collected during a 35-day experiment, where we enclosed natural plankton communities in in-situ mesocosms off Peru. The experiment investigated the interactive effects of light and upwelling on the Humboldt upwelling ecosystem by mimicking a gradient of upwelling intensities (0%, 15%, 30%, 45% and 60%) under summer-time high light and winter-time low light. Integrated seawater samples from a depth between 0 and 10m were collected using a 5L Integrating Water sampler (IWS; Hydro-Bios, Kiel). Samples (0.15-1L) were filtered onto polycarbonate filters (0.65 µm pore size, Whatman). The filters were then dried in the oven at 60 °C for 24 hours and measured following a modified procedure by DeMaster (1981, doi:10.1016/0016-7037(81)90006-5). A standard water bath (Fisher Scientific Isotemp Water Bath, Thermo Fisher Scientific, Waltham, US) was used to digest BSi samples at 85°C. The BSi analysis was carried out with a 4.5-hour time course alkaline digestion (0.1N Na2CO3) to dissolve the BSi followed by a 48 hour HF acid digestion (2.0M) to release the remaining lithogenic silica (LSi). Spectrophotometric analysis of the solubilized silica was done using a Thermo Scientific Genesys 10 UV- VIS Spectrophotometer (Thermo Fisher Scientific, Waltham, US). Model I linear regression was performed to calculate the concentrations of BSi while accounting for the amount of LSi that leached out during the alkaline digestion. Due to restrictions caused by the COVID-19 pandemic BSi data is only available for day 1 until day 17 and for day 31 until day 35.