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Biogeosciences An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Sep 2019

Submitted as: research article | 25 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Microstructure and composition of marine aggregates as co-determinants for vertical particulate organic carbon transfer in the global ocean

Joeran Maerz1, Katharina D. Six1, Irene Stemmler1, Soeren Ahmerkamp2, and Tatiana Ilyina1 Joeran Maerz et al.
  • 1Max Planck Institute for Meteorology (MPI-M), Hamburg, Germany
  • 2Max Planck Institute for Marine Microbiology (MPI-MM), Bremen, Germany

Abstract. Marine aggregates are the vector for biogenically bound carbon and nutrients from the euphotic zone to the interior of the oceans. To improve the representation of this biological carbon pump in the global biogeochemical HAMburg Ocean Carbon Cycle (HAMOCC) model, we implemented a novel Microstructure, Multiscale, Mechanistic, Marine Aggregates in the Global Ocean (M4AGO) sinking scheme. M4AGO explicitly represents the size, microstructure, heterogeneous composition, density, and porosity of aggregates, and ties ballasting mineral and particulate organic carbon (POC) fluxes together. Additionally, we incorporated temperature-dependent remineralization of POC. We compare M4AGO with the standard HAMOCC version, where POC fluxes follow a Martin curve approach with linearly increasing sinking velocity with depth, and temperature-independent remineralization. Minerals descend separately with a constant speed. In contrast to the standard HAMOCC, M4AGO reproduces the latitudinal pattern of POC transfer efficiency which has been recently constrained by Weber et al. (2016). High latitudes show transfer efficiencies of ≈ 0.25 ± 0.04 and the subtropical gyres show lower values of about 0.10 ± 0.03. In addition to temperature as a driving factor, diatom frustule size co-determines POC fluxes in silicifiers-dominated ocean regions while calcium carbonate enhances the aggregate excess density, and thus sinking velocity in subtropical gyres. In ocean standalone runs and rising carbon dioxide (CO2) without CO2 climate feedback, M4AGO alters the regional ocean-atmosphere CO2 fluxes compared to the standard model. M4AGO exhibits higher CO2 uptake in the Southern Ocean compared to the standard run while in subtropical gyres, less CO2 is taken up. Overall, the global oceanic CO2 uptake remains the same. With the explicit representation of measurable aggregate properties, M4AGO can serve as a testbed for evaluating the impact of aggregate-associated processes on global biogeochemical cycles, and, in particular, on the biological carbon pump.

Joeran Maerz et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Joeran Maerz et al.
Joeran Maerz et al.
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Short summary
Marine micro-algae bind carbon dioxide, CO2. During their decay, snowflake-like aggregates form that sink, remineralize and transport organically bound CO2 to depth, referred to as the biological carbon pump. In our model study, we elucidate how variable composition of aggregates impact on the global pattern of vertical carbon fluxes. Our mechanistic model approach advances the representation of the global biological carbon pump and promotes its more realistic projection under climate change.
Marine micro-algae bind carbon dioxide, CO2. During their decay, snowflake-like aggregates form...