Publication Date:
2022-06-17
Description:
We applied a 1-D plankton ecosystem-biogeochemical model to assess the impacts of
ocean alkalinity enhancement (OAE) on seasonal changes in biogeochemistry and
plankton dynamics. Depending on deployment scenarios, OAE should theoretically have
variable effects on pH and seawater pCO2, which might in turn affect (a) plankton growth
conditions and (b) the efficiency of carbon dioxide removal (CDR) via OAE. Thus, a major
focus of our work is how different magnitudes and temporal frequencies of OAE might affect seasonal response patterns of net primary productivity (NPP), ecosystem
functioning and biogeochemical cycling.
With our study we aimed at identifying a parameterization of how magnitude and
frequency of OAE affect net growth rates, so that these effects could be employed for
Earth System Modell applications. So far we learned that a meaningful response
parameterization has to resolve positive and negative anomalies that covary with
temporal shifts. As to the intricacy of the response patterns, the derivation of such
parameterization is work in progress. However, our study readily provides valuable
insights to how OAE can alter plankton dynamics and biogeochemistry. Our modelling
study first focuses at a local site where time series data are available (European Station
for Time series in the Ocean Canary Islands ESTOC), including measurements of pH,
concentrations of total alkalinity, dissolved inorganic carbon (DIC), chlorophyll-a and
dissolved inorganic nitrogen (DIN). These observational data were made available by
Andres Cianca (personal communication, PLOCAN, Spain), Melchor Gonzalez and
Magdalena Santana Casiano (personal communication, Universidad de Las Palmas de
Gran Canaria). The choice of this location was underpinned by the fact that the first OAE
mesocosm experiment was conducted on the Canary Island Gran Canaria, which will
facilitate synthesizing our modelling approach with experimental findings.
For our simulations at the ESTOC site in the Subtropical North Atlantic we found distinct,
non-linear responses of NPP to different temporal modes of alkalinity deployment. In
particular, phytoplankton bloom patterns displayed pronounced temporal phase shifts
and changes in their amplitude. Notably, our simulations suggest that OAE can have a
slightly stimulating effect on NPP, which is however variable, depending on the magnitude
of OAE and the temporal mode of alkalinity addition. Furthermore, we find that increasing
alkalinity perturbations can lead to a shift in phytoplankton community composition
(towards coccolithophores), which even persists after OAE has stopped. In terms of CDR,
we found that a decrease in efficiency with increasing magnitude of alkalinity addition, as
well as substantial differences related to the timing of addition.
Altogether, our results suggest that annual OAE during the right season (i.e. physical and
biological conditions), could be a reasonable compromise in terms of logistical feasibility,
efficiency of CDR and side-effects on marine biota.
With respect to transferability to global models, the complex, non-linear responses of
biological processes to OAE identified in our simulations do not allow for simple
parameterizations that can easily adapted. Dedicated future work is required to transfer
the observed responses at small spatiotemporal scales to the coarser resolution of global
models.
Type:
Report
,
NonPeerReviewed
,
info:eu-repo/semantics/book
Format:
text
Format:
text
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