Estimating phytoplankton pigments in the changing Arctic Ocean

• Main Author: Liu, Yangyang
• Other Authors: Wolf-Gladrow, Dieter, Zielinski, Oliver
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Universität Bremen 2022
• Subjects: phytoplankton; pigments; ocean color; light absorption; photoprotection; 570; 570 Life sciences; biology; ddc:570; Arctic; Arctic Ocean; Climate change; Fram Strait; Phytoplankton; Sea ice
• Online Access: https://media.suub.uni-bremen.de/handle/elib/6052; https://doi.org/10.26092/elib/1657; https://nbn-resolving.org/urn:nbn:de:gbv:46-elib60521

Human-induced climate change is amplified in the Arctic. At the root of these amplifications are changes in air temperature and sea ice. The sea-ice cover is dramatically receding in the Arctic Ocean. In the study region of the thesis, the Fram Strait (the largest and only deep gateway to the Arctic Ocean) and its vicinity, changes have been observed in sea-ice conditions and water temperatures due to Arctic warming. This has consequences for phytoplankton. Phytoplankton are one of the main primary producers in the Arctic Ocean. Arctic warming induced alterations in light and nutrient regimes impact phytoplankton seasonality, biomass, community composition and distribution. Phytoplankton biomass and community composition are often indicated by their pigment composition and concentrations. To study the response of phytoplankton to the changing climate, this thesis aims to estimate phytoplankton pigments using observations from the shipboard underway flow-through AC-S spectrophotometer system and the Regulated Ecosystem model version 2 (REcoM2) (Hohn, 2008; Schartau et al., 2007) implemented with phytoplankton growth and photoinhibition models. In the first part of the thesis, an underway flow-through AC-S system was set up onboard R.V. Polarstern during two Fram Strait cruises, PS93.2 and PS99.2. Hyperspectral particulate absorption coefficient was derived from the underway AC-S measurements. Particulate absorption line height at 676 nm calculated from particulate absorption coefficient was empirically related to high performance liquid chromatography (HPLC) chlorophyll a (Chl a) concentrations for PS93.2 and PS99.2, respectively. Both relationships were applied to high frequency (4 Hz) AC-S data to estimate Chl a concentrations along the cruise tracks. In total, 24424 and 16110 Chl a data points were generated for PS93.2 and PS99.2, respectively. The reconstructed AC-S Chl a data sets were used to evaluate seven satellite Chl a algorithms. The number of AC-S-satellite match-ups is over one order of magnitude ...