PhD project(2015-) Yangyang Liu funded by the China Scholarship Council (CSC)

Phytoplankton, the main primary producers at the base of marine food web, have distinctive impacts on the changes of Arctic climate system. The Arctic region is warming at rates double than the global average, coinciding with persistent sea ice decline [1]. Seasonal sea ice cover retreat favors phytoplankton bloom development and the extension of phytoplankton growing season, increasing annual mean phytoplankton biomass and production [2,3]. This increase, in turn, is expected to further warm the ocean surface layer by absorbing more solar radiation and triggering additional positive feedbacks, which could amplify Arctic warming by 20% [2]. Meanwhile, together with ice algae, the increasing phytoplankton stocks generate more dimethylsulphide, a trace gas that provides 80% of global biogenic atmospheric sulphur [4]. When released to the atmosphere, dimethylsulphide, via formation of sulphate aerosol, cool the Arctic atmospheric temperature by dispersing solar radiation [5-7]. The shipboard underway spectrophotometry represents a promising in situ observation technique of phytoplankton biomass and functional types. It utilizes a WET Labs AC-S hyperspectral spectrophotometer (or its former alternative, the 9-wavelength resolved AC-9) that is operated in flow-through mode to derive particulate absorption coefficients (ap) [8-19]. Chl-a, the proxy of phytoplankton biomass, together with phytoplankton functional types, are then derived from ap.

First results for the project have been published in Liu et al. (2018) show the capability of obtaining highly resolved surface Chl-a and phytoplankton functional types (PFT) using shipboard underway AC-S flow-through system in the Fram Strait. These quality-controlled datasets are finally used to validate the quality of the Chl-a datasets of several satellite sensors and assess various satellite Chl-a algorithms and numerical model outputs of PFT.

Publication within PhD thesis:


Liu. Y., Roettgers R., Ramírez-Pérez M., Dinter T., Steinmetz F., Noethig E.-M., Hellmann S., Wiegmann S., Bracher A. (in press 22 Jan 2018) Underway spectrophotometry in the Fram Strait (European Arctic Ocean): a highly resolved chlorophyll a data source for complementing satellite ocean color. Optics Express


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Figure 1. Comparison between Chl-a data obtained from underway AC-S flow-through system and HPLC measurements during the Fram Strait cruises PS93.2 and PS99.2.