Volume 13, issue 17 | Copyright
Biogeosciences, 13, 4959-4973, 2016
https://doi.org/10.5194/bg-13-4959-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 08 Sep 2016

Research article | 08 Sep 2016

Spring blooms in the Baltic Sea have weakened but lengthened from 2000 to 2014

Philipp M. M. Groetsch1,2, Stefan G. H. Simis3,4, Marieke A. Eleveld5,1, and Steef W. M. Peters2 Philipp M. M. Groetsch et al.
  • 1Institute for Environmental Studies (IVM), De Boelelaan 1087, 1081 HV Amsterdam, the Netherlands
  • 2Water Insight, Marijkeweg 22, 6709 PG Wageningen, the Netherlands
  • 3Plymouth Marine Laboratory, Prospect Place, The Hoe, Plymouth, PL1 3DH, UK
  • 4Finnish Environment Institute SYKE, Erik Palménin Aukio 1, 00560 Helsinki, Finland
  • 5Deltares, P.O. Box 177, 2600 MH Delft, the Netherlands

Abstract. Phytoplankton spring bloom phenology was derived from a 15-year time series (2000–2014) of ship-of-opportunity chlorophyll a fluorescence observations collected in the Baltic Sea through the Alg@line network. Decadal trends were analysed against inter-annual variability in bloom timing and intensity, and environmental drivers (nutrient concentration, temperature, radiation level, wind speed).

Spring blooms developed from the south to the north, with the first blooms peaking mid-March in the Bay of Mecklenburg and the latest bloom peaks occurring mid-April in the Gulf of Finland. Bloom duration was similar between sea areas (43 ± 2 day), except for shorter bloom duration in the Bay of Mecklenburg (36 ± 11 day). Variability in bloom timing increased towards the south. Bloom peak chlorophyll a concentrations were highest (and most variable) in the Gulf of Finland (20.2 ± 5.7mgm−3) and the Bay of Mecklenburg (12.3 ± 5.2mgm−3).

Bloom peak chlorophyll a concentration showed a negative trend of −0.31 ± 0.10mgm−3yr−1. Trend-agnostic distribution-based (Weibull-type) bloom metrics showed a positive trend in bloom duration of 1.04 ± 0.20dayyr−1, which was not found with any of the threshold-based metrics. The Weibull bloom metric results were considered representative in the presence of bloom intensity trends.

Bloom intensity was mainly determined by winter nutrient concentration, while bloom timing and duration co-varied with meteorological conditions. Longer blooms corresponded to higher water temperature, more intense solar radiation, and lower wind speed. It is concluded that nutrient reduction efforts led to decreasing bloom intensity, while changes in Baltic Sea environmental conditions associated with global change corresponded to a lengthening spring bloom period.

Download & links
Publications Copernicus
Download
Short summary
Phytoplankton spring bloom phenology was derived from a 15-year time series (2000–2014) of ship-of-opportunity chlorophyll a fluorescence observations in the Baltic Sea. Bloom peak concentrations have declined over the study period, while bloom duration has increased. It is concluded that nutrient reduction efforts led to decreasing bloom intensity, while changes in Baltic Sea environmental conditions associated with global change corresponded to a lengthening spring bloom period.
Phytoplankton spring bloom phenology was derived from a 15-year time series (2000–2014) of...
Citation
Share