The phenology of the spring phytoplankton bloom in the North Atlantic does not trend with temperature

Authors: FRIEDLAND, KEVIN - Southwest Fisheries Science Center; NIELSEN, JENS - University Of Washington; RECORD, NICHOLAS - Bigelow Laboratory For Ocean Sciences; BRADY, DAMIEN - University Of Maine; MORROW, CLAY - Us Forest Service (FS)

Submitted to: Elementa: Science of the Anthropocene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2023
Publication Date: 3/13/2024
Citation: Friedland, K.D., Nielsen, J.M., Record, N.R., Brady, D.C., Morrow, C.J. 2024. The phenology of the spring phytoplankton bloom in the North Atlantic does not trend with temperature. Elementa: Science of the Anthropocene. 12(1). Article 00111. https://doi.org/10.1525/elementa.2023.00111.
DOI: https://doi.org/10.1525/elementa.2023.00111

Interpretive Summary: Climate change is anticipated to affect phytoplankton bloom dynamics, making recent observations important for future predictions. In the North Atlantic, sea surface temperatures (SST) have risen by 0.27°C per decade, yet the timing of spring blooms has largely remained stable, with only minor changes in specific areas. This study analyzed ocean color data from 1998 to 2022, finding no significant trends in bloom timing or duration across most of the region. Despite warmer temperatures, some continental shelf seas have experienced a decline in bloom productivity, suggesting that increased winter temperatures may negatively impact bloom magnitude and intensity. The consistent availability of vernal light may explain why spring bloom phenology has remained resistant to climate change. Overall, while future climate change may not significantly alter the timing of spring blooms, it could substantially affect phytoplankton production. This research highlights the complex interactions between temperature and bloom dynamics, indicating that different phytoplankton taxa may respond variably to warming condition.

Technical Abstract: Climate change is anticipated to alter the phenology of phytoplankton blooms in the ocean, making their recent dynamics of interest to inform models of future ocean states. We characterized temperature change in the North Atlantic using metrics that track the patterns of sea surface water temperature (SST) defined by quantiles. To complement these thermal indicators, we estimated a thermal phenology index in the form of the date of the spring transition, taken as the date that temperature achieved the long-term mean at a specific location. We then used ocean color data (1998–2022) and characterized spring bloom phenology using change point methods to derive bloom initiation, duration, magnitude, and intensity. The North Atlantic has warmed over recent decades, averaging a rate of increase of 0.27C decade1, yet throughout most of the basin, spring transition timing has remained constant, with the exception of small areas with either delayed or advanced transitions. There were no clear trends in bloom start or duration in the North Atlantic, indicating that spring bloom phenology was independent of climate-driven temperature change. Bloom magnitude and intensity trended downward in some North Atlantic continental shelf seas, indicating that increased temperatures may have had negative effects on overall bloom productivity.