Impact of Lagrangian Sea Surface Temperature Variability on Southern Ocean Phytoplankton Community Growth Rates. Issue 8 (23rd August 2021)

• Record Type: Journal Article
• Authors: Zaiss, Jessica; Boyd, Philip W.; Doney, Scott C.; Havenhand, Jon N.; Levine, Naomi M.
• Is Part Of: Global biogeochemical cycles. Volume 35:Issue 8(2021)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2021-08-23
• Subjects: phytoplankton growth -- SST variability -- Q10 -- Southern Ocean; Biogeochemical cycles -- Periodicals; Electronic journals; 577.1405
• DOI: 10.1029/2020GB006880
• Languages: English
• ISSNs: 0886-6236

Abstract

Abstract: Ocean phytoplankton play a critical role in the global carbon cycle, contributing ∼50% of global photosynthesis. As planktonic organisms, phytoplankton encounter significant environmental variability as they are advected throughout the ocean. How this variability impacts phytoplankton growth rates and population dynamics remains unclear. Here, we systematically investigated the impact of different rates and magnitudes of sea surface temperature (SST) variability on phytoplankton community growth rates using surface drifter observations from the Southern Ocean (>30°S) and a phenotype‐based ecosystem model. Short‐term SST variability (<7 days) had a minimal impact on phytoplankton community growth rates. Moderate SST changes of 3–4°C over 7–45 days produced a large time lag between the temperature change and the biological response. The impact of SST variability on community growth rates was nonlinear and a function of the rate and magnitude of change. Additionally, the nature of variability generated in a Lagrangian reference frame (following trajectories of surface water parcels) was larger than that within an Eulerian reference frame (fixed point), which initiated different phytoplankton responses between the two reference frames. Finally, we found that these dynamics were not captured by the Eppley growth model commonly used in global biogeochemical models and resulted in an overestimation of community growth rates, particularly in dynamic, strong frontal regions of the Southern Ocean. This work demonstrates that the timescale for environmental selection (community replacement) is a critical factor in determining community composition and takes a first step towards including the impact of variability and biological response times into biogeochemical models. Plain Language Summary: Ocean phytoplankton are fundamental to the global carbon cycle. However, it remains unclear how environmental variability impacts phytoplankton growth, and thus, the global carbon cycle. Phytoplankton encounter environmental variability (e.g., sea surface temperature [SST] changes) as they are transported throughout the oceans by surface currents. Here, we quantified this variability (i.e., in a Lagrangian reference frame) using surface drifters and investigated the impact of this variability on phytoplankton community growth rates using an ecosystem model. We also compared the Lagrangian SST to the SST variability of a fixed point (e.g., a buoy) where ocean currents flow past (i.e., the Eulerian reference frame) using high‐resolution satellite data. We found larger SST changes in the Lagrangian than in the Eulerian reference frame and discovered that this difference impacted phytoplankton community structure and growth rates. The impact of SST variability was not captured by the growth model that is typically used by global biogeochemical models. Our results provide an important extension on the classic principle that "everything is everywhere: but the environment selects" (Hutchinson, 1961, https://doi.org/10.1086/282171 ). Even when "everything is everywhere", we show that the timescale for environmental selection (community replacement) is a critical factor in determining community composition. Key Points: Sea surface temperature (SST) variability differs between the Lagrangian and Eulerian reference frames SST variability on timescales of days to weeks encountered by advecting phytoplankton decreases phytoplankton community growth rates The commonly used Eppley curve or Q10 growth models do not capture the effects of SST variability on phytoplankton growth