Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - WhiteShift (A calcifying phytoplankter’s response to climate change and its role in sinking carbon in the Subarctic Ocean using spaceborne and in situ observations and ecological modelling)

Teaser

Anthropogenic carbon dioxide emissions are skyrocketing, resulting in ocean warming and acidification. Yet we are only beginning to understand how this human footprint impacts phytoplankton and associated sinking carbon fluxes to the deep ocean. WhiteShift addresses these...

Summary

Anthropogenic carbon dioxide emissions are skyrocketing, resulting in ocean warming and acidification. Yet we are only beginning to understand how this human footprint impacts phytoplankton and associated sinking carbon fluxes to the deep ocean. WhiteShift addresses these questions for a marine calcifying phytoplankton species, Emiliania huxleyi, in one of the most climate sensitive regions, the Subarctic Ocean. The first objective of WhiteShift is to investigate the impact of a changing ocean on the spatiotemporal distribution of the species by a novel integrative approach connecting long-term optical satellite observations with fundamental ecological theory. The second objective is to examine if the enormous amounts of calcite produced by this species ballast organic carbon using optical technology on autonomous profiling floats (Biogeochemical-Argo floats). Thus, WhiteShift targets two scientific objectives: (1) Response of E.huxleyi to climate change, and (2) Impact of E. huxleyi on sinking carbon flux to the deep ocean.

Work performed

To address the response of E. huxleyi to ocean warming and changing water masses, I have prepared and validated a long-term satellite dataset of E. huxleyi blooms in the Barents Sea, an Arctic shelf sea, which connects the Atlantic with the Arctic Ocean. I found striking and fast-paced changes in the distribution pattern of blooms of Emiliania huxleyi, a marine calcifying phytoplankton species typically associated with temperate waters. Over the last three decades, blooms of this species have shifted poleward at rates up to 56 km per year and thereby testify to one of the most rapid poleward expansions of marine organisms reported so far. The observed biogeographic shift is attributed to climate change-induced increases in the inflow and warming of Atlantic waters into the Arctic Ocean. I further showed that E. huxleyi calcite concentration was modulated by strong seasonal cycles of temperature, light and mixed layer depth.

To examine if the enormous amounts of calcite produced by E. huxleyi blooms ballast organic carbon I used optical measurements of particle backscatter, chlorophyll-a fluorescence and beam attenuation on Biogeochemical-Argo profiling floats. My results show the feasibility of identifying E. huxleyi blooms and quantifying associated calcite concentration from optical measurements on floats, consistent with results from an optical model for E. huxleyi that I set up. Results obtained from a Biogeochemical-Argo float that sampled sinking carbon particles associated with three distinct phytoplankton blooms of calcifying and non-calcifying phytoplankton suggests that E. huxleyi blooms promote deeper carbon fluxes compared to carbon fluxes associated with blooms from non-calcifying phytoplankton. These observations are thus the first high-resolution observations of the calcite ballast effect in the ocean.

Final results

Within the ocean colour community there is a strong interest in remote sensing of phytoplankton species or functional groups, which will become possible with future hyperspectral ocean colour satellites. The Whiteshift project may serve as a precursor for studies targeting the impact of climate change on phytoplankton using remote sensing, allowing us to maximally prepare for the coming decade when ocean colour satellite time series of phytoplankton biomass will become long enough.

Biological carbon fluxes are chronically under-sampled leading to large uncertainties in estimates of biological carbon export and sequestration. In the same way as Argo floats have revolutionized our understanding of global ocean circulation, Biogeochemical-Argo floats allow a quantum leap in understanding the ocean’s carbon cycle. WhiteShift contributes to this effort through (1) the development of optical approaches to identify calcifying phytoplankton blooms and quantify associated calcite concentration which are directly transportable to the global fleet of Biogeochemical-Argo floats thanks to uniform float-wide optical technology, (2) examining the widely debated calcite ballast hypothesis; an old hypothesis which has now been tested with new in situ technology for the first time. The resulting parameterizations of calcite ballasting are highly relevant to the carbon cycle modelling community and may facilitate improved predictions of climate models at space and time scales useful to decision-making.

Website & more info

More info: https://grietneukermans.weebly.com/.