Biological carbon pump is the process of converting and exporting atmospheric carbon to different oceanic depths via different pathways. Its efficiency is a function of vertical velocity, biomass decay rate, fragmentation rate, ocean temperature and others. Recently, gelatinous zooplankton (GZ) has been proposed as one of the potential missing links to the global carbon export due to its fast sinking speed. In this study we refine the current work on GZ with a physical model for the mass dependent vertical sinking velocity. We therefore construct a coupled model between sinking and microbial decay of GZ. Furthermore, we propose a possible improvement in microbial decay modeling, where the GZ biomass rate is a function of its area rather than mass. We solve these models inside our newly developed $\textit{python}$ environment $\texttt{CarbonDrift}$, which is an extension of the Lagrangian tracking library $\texttt{OpenDrift}$. Using initial mass data from Ref. [1] and decay rate to temperature dependencies from Ref. [2], we re-estimate global GZ biomass export to be between (3.83 - 4.50)PgCY$^{-1}$, (1.53 - 2.20)PgCY$^{-1}$ and (0.77-1.53)PgCY$^{-1}$ at depths of 100 m, 1000 m and at the seafloor, respectively. The former represents (38-45)%, while the latter represents (39-77)% of global particulate carbon (POC) export estimates. Furthermore, we find, that the additional consideration of horizontal advection does not visibly change the mass estimates. Lastly, we discuss the effects of different temperature fields on the model outcome. We find that marine heatwaves accelerate GZ decay and subsequently slow their sinking velocity, which leads to an inhibition of carbon export of up to some 10% locally. This difference, however, can reduce the global carbon export only up to 5%. In contrast, model projections at the end of the 21$^{\mathrm{st}}$ century suggest a major decrease in carbon export of up to 20% globally.
|
