PAR and Turbidity
PAR (photosynthetically
active radiation) and turbidity data were measured year-round with a
sampling frequency of 1hz (1sec-1) in the framework of
the AWIPEV-COSYNA underwater observatory in Ny Ålesund (UMT 8763953°N,
433992°E, for map see Figure 2). For a detailed description of the
AWIPEV-COSYNA underwater observatory see Fischer et al. (2017) and
Fischer et al. (2020). Briefly, the system comprises a land-based
FerryBox system equipped with various hydrographic sensors receiving
water from a remote-controlled underwater pump station at 11m water
depth. Additionally, a cable connected (fibre-optic and 240 V power)
underwater node system comprises a fixed sensor carrier at 11m water
depth (+/- tide) as well as a vertical profiling sensor elevator to the
surface. For the here presented analysis, PAR and turbidity data from a
CTD (Sea & Sun 90, installed in June 2012) and a PAR sensor (Sea-Bird
ECO-PAR, installed in September 2016) mounted at a vertical profiling
sensor elevator were used. The profiling sensor elevator performs one
full vertical profile from about 11 m to 1 m water depth (+/- tide)
every day. After that daily profile, the vertical profiling unit is
randomly positioned in one of the five depth strata 9, 7, 5, 3 and 1 m
below the water surface for 24h in a way that each depth stratum is
sampled once a week. Turbidity was measured in formazine turbidity unit
(FTU) and PAR in µmol m-2 s-1. All
sensors are maintained regularly in a one-year interval. Data gaps due
to system maintenance or a sensor failure were compensated by averaging
all measurements within the 24h period to a single 24h mean value and
subsequently averaging these daily means over one week. Weeks when no
PAR and turbidity data were available at all were excluded and Appendix
2 shows the real number of available data weeks for all years. The focus
of the present study is PAR and turbidity during the macroalgal growth
season in the polar summer and therefore only data from week 8 in March
to week 44 in October were included in further analysis.