Moritz Zeising

The Fram Strait is the primary gateway between the North Atlantic and the Arctic Ocean, where ongoing Atlantification is reshaping hydrographic conditions and marine ecosystems. We applied ML-PhyTAO, a machine learning based retrieval model for Arctic phytoplankton functional types (PFTs), to generate a consistent 28-year (1998–2025) satellite record of total chlorophyll-a (TChla) and major PFT chlorophyll-a concentrations (Chla) in the Fram Strait. Trained with an extensive Arctic phytoplankton pigment dataset and ocean color and environmental products, the model provides robust performance for long-term analyses. Using a dynamic water mass classification based on sea surface temperature and sea ice fraction, the Fram Strait was partitioned into Atlantic Water (AW), Mixed Water (MW), and Polar Water (PW). Distinct seasonal cycles were observed among water masses, with later but more intense phytoplankton blooms in AW. Peak biomass timing advanced by 2–13 days decade⁻¹ for TChla, diatoms, and haptophytes in both AW and MW. Trend analyses revealed declining biomass primarily in MW and the AW–MW transition zone, while haptophytes and dinoflagellates increased within AW. Sea surface salinity, temperature, and sea ice fraction showed stronger and more spatially coherent relationships with PFT variability than modeled nutrient fields, indicating that Atlantification related hydrographic changes are driving shifts in phytoplankton phenology and community composition. This study highlights the unique value of long-term, consistent PFT observations for detecting climate-driven ecosystem change, linking hydrographic variability to community shifts, and supporting future ecosystem and biogeochemical assessments and modelling studies in the rapidly changing Arctic Ocean.

Marine combined carbohydrates in aerosol particles (CCHOaer) have the potential to influence cloud formation and properties, but it remains unclear to what extent they reach altitudes relevant for cloud processes. Balloon-borne measurements of major sea spray aerosol (SSA) constituents, including sodium (Naaer+) and CCHOaer, were conducted in autumn 2021 and spring 2022 in Ny-Ålesund (Svalbard). Total suspended particles were collected at 321–1112 m, covering both the marine boundary layer and the free troposphere, with Naaer+ ranging 23–850 ng m−3 and CCHOaer 3.8–274 ng m−3. The chemical composition of balloon-borne aerosol samples was compared with synchronized ground level measurements at the balloon's winch (Naaer+: 35–3710 ng m−3; CCHOaer: 1.9–194 ng m−3), and at the Old Pier (Naaer+: 140–1470 ng m−3; CCHOaer: 1.6–10.0 ng m−3), where freshly emitted SSA particles were sampled. Surface seawater from the Kongsfjorden was analyzed to evaluate the sea-air transfer of marine CCHO. Air mass histories, atmospheric mixing, and cloud conditions were evaluated for three selected cases to explain vertical concentration patterns. A strong correlation (R=0.78, p<0.001) between combined xylose (< 0.2–14.1 ng m−3) in CCHOaer and oxalateaer (< 1–67 ng m−3) across all altitudes, suggests either coproduction or a connection through atmospheric processing. These results provide a first comprehensive picture of how local primary sea-air transfer of marine combined carbohydrates, long-range transport, in-situ formation, and atmospheric processing together shape their distribution.

Marine carbohydrates are produced by a wide range of micro- and macroorganisms in seawater and are transferred to the atmosphere via sea spray aerosol (SSA). Recent laboratory and modelling studies suggest that these compounds can influence fog and cloud microphysics as ice nucleating particles. However, observational evidence from the atmosphere remains limited, as most field studies have relied on ship- or land-based filter samples, leaving their relevance for cloud processes at cloud-relevant altitudes largely unconstrained.Here, we present new measurements of marine carbohydrates and other SSA components at altitudes between 300 and 1200 m, obtained using a tethered helium balloon in Ny-Ålesund (Svalbard) during 2021-2022. These observations are compared with fresh SSA directly collected at the Kongsfjorden coast and with surface seawater samples to assess contributions beyond local ocean emissions. Our results highlight the key role of meteorological conditions in lifting and redistributing SSA constituents, including marine carbohydrates, to higher atmospheric layers. The study further examines potential additional sources and formation pathways, providing new insights into the atmospheric behaviour of marine carbohydrates and their implications for cloud microphysics.We gratefully acknowledge the funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Project Number 268020496—TRR 172, within the framework of the Transregional Collaborative Research Center “ArctiC Amplification: Climate Relevant Atmospheric and SurfaCe Processes, and Feedback Mechanisms (AC)3”

Primary marine organic aerosol (PMOA) constitutes an important fraction of the aerosol population over remote oceanic regions and plays a relevant role in aerosol–cloud–climate interactions. In the Arctic, ongoing sea-ice retreat and intensified summer ice loss are expected to enhance marine aerosol emissions. Here, we employ an extended version of the aerosol–climate model ECHAM6.3-HAM2.3 to examine the spatial distribution and long-term temporal evolution of PMOA emissions and transport in the Arctic for the period 1990–2019, accounting for changing climatic and sea-ice conditions. Marine biogeochemical fields are provided by the offline model FESOM2.1-REcoM3, from which three aerosol-relevant biomolecular species groups - polysaccharides (PCHO), amino acids (DCAA), and polar lipids (PL) - are represented. Their transfer from the ocean to the atmosphere is parameterized using OCEANFILMS, recently implemented in ECHAM6.3-HAM2.3 to enhance the marine emission scheme.The model results indicate that PMOA emission fluxes are primarily controlled by marine biological activity and sea-salt production, the latter mainly depending on near-surface winds. Biomolecular concentrations show limited variability in equatorial regions but pronounced seasonal cycles toward high latitudes. In seawater, PCHO dominates the simulated organic pool, followed by DCAA and PL. In contrast, PL contributes the largest fraction to aerosol-phase organic matter due to the comparatively strong air-seawater affinity of lipids. Arctic PMOA emissions and atmospheric transport peak between May and September, coinciding with the phytoplankton bloom and the seasonal sea-ice minimum. Substantial regional differences are evident in the timing of biomolecule production and aerosol emissions across the Arctic. Simulated PMOA seasonality agrees reasonably well with available ground-based observations, given the uncertainties in both measurements and model assumptions.Over the 30-year period, accumulated Arctic aerosol emissions and burdens increased by at least 7% and 4%, respectively, when comparing the first and second halves of the study period. Summer (June–August) trend analyses reveal a pronounced decline in sea ice that is associated with increasing concentrations of organic biomolecules in inner Arctic waters. Positive PMOA emission anomalies have become more frequent over the past 15 years, indicating a sustained upward trend. On average, PMOA production has increased by 0.8% per year since 1990, with changes varying among biomolecular groups and Arctic subregions.

We present an assessment of the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, in which we integrated state equations for dissolved acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP), as proposed by Engel et al. (2004), to explicitly describe these two organic carbon pools in the Arctic Ocean. PCHO is simulated as one fraction of the phytoplankton exudates, which can then aggregate to form larger particles, TEP. Since observational datasets on TEP are rare in time and space, we systematically assess the novel model implementation by stepwise discussing the essential components of the organic carbon cycle. Firstly, the simulated phytoplankton biomass yields good results when compared to in situ and remote-sensing products of total Chlorophyll a and particulate organic carbon. Secondly, we compare PCHO to observations in the Fram Strait, as an exemplary data-rich region, and to datasets in other regions of the Arctic Ocean. The model realistically reproduces a high phytoplankton exudation rate of PCHO under nutrient-depleted conditions. Thirdly, we assess simulated TEP concentrations by comparing them to in situ measurements from several campaigns to the Arctic Ocean. The simulation provides a first estimate of mean TEP concentrations of 200–400 µg C L⁻¹ on the continental shelves and 10–50 µg C L⁻¹ in the central basins (0–30 m depth range). Lastly, we put the model performance into a global context for TEP concentrations in the upper ocean layer. As such, the implementation of PCHO exudation, aggregation to TEP, and their remineralization processes into FESOM2.1–REcoM3 offers a reasonably good agreement with observations, on which further modeling work can build upon.

Marine combined carbohydrates in aerosol particles (CCHO_aer) have the potential to influence cloud formation and properties, but it remains unclear to what extent they reach altitudes relevant for cloud processes. Balloon-borne measurements of major sea spray aerosol (SSA) constituents, including sodium (Na⁺_aer) and CCHO_aer, were conducted in autumn 2021 and spring 2022 in Ny-Ålesund (Svalbard). Total suspended particles were collected at 321–1112 m, covering both the marine boundary layer and the free troposphere, with Na⁺_aer ranging 23–850 ng m^-3 and CCHO_aer 3.8–274 ng m^-3. The chemical composition of balloon-borne aerosol samples was compared with synchronized ground level measurements at the balloon's winch (Na⁺_aer: 35–3710 ng m^-3; CCHO_aer: 1.9–194 ng m^-3), and at the Old Pier (Na⁺_aer: 140–1470 ng m^-3; CCHO_aer: 1.6–10.0 ng m^-3), where freshly emitted SSA particles were sampled. Surface seawater from the Kongsfjorden was analyzed to evaluate the sea-air transfer of marine CCHO. Air mass histories, atmospheric mixing, and cloud conditions were evaluated for three selected cases to explain vertical concentration patterns. A strong correlation (R=0.78, p-3) in CCHO_aer and oxalate_aer (-3) across all altitudes, suggests either coproduction or a connection through atmospheric processing. These results provide a first comprehensive picture of local primary sea-air transfer of marine combined carbohydrates and highlight the roles of long-range transport, in-situ formation, and chemical aging in shaping their atmospheric distribution.

Marine combined carbohydrates in aerosol particles (CCHO_aer) have the potential to influence cloud formation and properties, but it remains unclear to what extent they reach altitudes relevant for cloud processes. Balloon-borne measurements of major sea spray aerosol (SSA) constituents, including sodium (Na⁺_aer) and CCHO_aer, were conducted in autumn 2021 and spring 2022 in Ny-Ålesund (Svalbard). Total suspended particles were collected at 321–1112 m, covering both the marine boundary layer and the free troposphere, with Na⁺_aer ranging 23–850 ng m^-3 and CCHO_aer 3.8–274 ng m^-3. The chemical composition of balloon-borne aerosol samples was compared with synchronized ground level measurements at the balloon's winch (Na⁺_aer: 35–3710 ng m^-3; CCHO_aer: 1.9–194 ng m^-3), and at the Old Pier (Na⁺_aer: 140–1470 ng m^-3; CCHO_aer: 1.6–10.0 ng m^-3), where freshly emitted SSA particles were sampled. Surface seawater from the Kongsfjorden was analyzed to evaluate the sea-air transfer of marine CCHO. Air mass histories, atmospheric mixing, and cloud conditions were evaluated for three selected cases to explain vertical concentration patterns. A strong correlation (R=0.78, p-3) in CCHO_aer and oxalate_aer (-3) across all altitudes, suggests either coproduction or a connection through atmospheric processing. These results provide a first comprehensive picture of local primary sea-air transfer of marine combined carbohydrates and highlight the roles of long-range transport, in-situ formation, and chemical aging in shaping their atmospheric distribution.

Marine combined carbohydrates in aerosol particles (CCHO_aer) have the potential to influence cloud formation and properties, but it remains unclear to what extent they reach altitudes relevant for cloud processes. Balloon-borne measurements of major sea spray aerosol (SSA) constituents, including sodium (Na⁺_aer) and CCHO_aer, were conducted in autumn 2021 and spring 2022 in Ny-Ålesund (Svalbard). Total suspended particles were collected at 321–1112 m, covering both the marine boundary layer and the free troposphere, with Na⁺_aer ranging 23–850 ng m^-3 and CCHO_aer 3.8–274 ng m^-3. The chemical composition of balloon-borne aerosol samples was compared with synchronized ground level measurements at the balloon's winch (Na⁺_aer: 35–3710 ng m^-3; CCHO_aer: 1.9–194 ng m^-3), and at the Old Pier (Na⁺_aer: 140–1470 ng m^-3; CCHO_aer: 1.6–10.0 ng m^-3), where freshly emitted SSA particles were sampled. Surface seawater from the Kongsfjorden was analyzed to evaluate the sea-air transfer of marine CCHO. Air mass histories, atmospheric mixing, and cloud conditions were evaluated for three selected cases to explain vertical concentration patterns. A strong correlation (R=0.78, p-3) in CCHO_aer and oxalate_aer (-3) across all altitudes, suggests either coproduction or a connection through atmospheric processing. These results provide a first comprehensive picture of local primary sea-air transfer of marine combined carbohydrates and highlight the roles of long-range transport, in-situ formation, and chemical aging in shaping their atmospheric distribution.

We present an assessment of the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, in which we integrated state equations for dissolved acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP), as proposed by Engel et al. (2004), to explicitly describe these two organic carbon pools in the Arctic Ocean. PCHO is simulated as one fraction of the phytoplankton exudates, which can then aggregate to form larger particles, TEP. Since observational datasets on TEP are rare in time and space, we systematically assess the novel model implementation by stepwise discussing the essential components of the organic carbon cycle. Firstly, the simulated phytoplankton biomass yields good results when compared to in situ and remote-sensing products of total Chlorophyll a and particulate organic carbon. Secondly, we compare PCHO to observations in the Fram Strait, as an exemplary data-rich region, and to datasets in other regions of the Arctic Ocean. The model realistically reproduces a high phytoplankton exudation rate of PCHO under nutrient-depleted conditions. Thirdly, we assess simulated TEP concentrations by comparing them to in situ measurements from several campaigns to the Arctic Ocean. The simulation provides a first estimate of mean TEP concentrations of 200–400 μg C L⁻¹ on the continental shelves and 10–50 μg C L⁻¹ in the central basins (0–30 m depth range). Lastly, we put the model performance into a global context for TEP concentrations in the upper ocean layer. As such, the implementation of PCHO exudation, aggregation to TEP, and their remineralization processes into FESOM2.1–REcoM3 offers a reasonably good agreement with observations, on which further modeling work can build upon.

We present an assessment of the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, in which we integrated state equations for dissolved acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP), as proposed by Engel et al. (2004), to explicitly describe these two organic carbon pools in the Arctic Ocean. PCHO is simulated as one fraction of the phytoplankton exudates, which can then aggregate to form larger particles, TEP. Since observational datasets on TEP are rare in time and space, we systematically assess the novel model implementation by stepwise discussing the essential components of the organic carbon cycle. Firstly, the simulated phytoplankton biomass yields good results when compared to in situ and remote-sensing products of total Chlorophyll a and particulate organic carbon. Secondly, we compare PCHO to observations in the Fram Strait, as an exemplary data-rich region, and to datasets in other regions of the Arctic Ocean. The model realistically reproduces a high phytoplankton exudation rate of PCHO under nutrient-depleted conditions. Thirdly, we assess simulated TEP concentrations by comparing them to in situ measurements from several campaigns to the Arctic Ocean. The simulation provides a first estimate of mean TEP concentrations of 200–400 μg C L⁻¹ on the continental shelves and 10–50 μg C L⁻¹ in the central basins (0–30 m depth range). Lastly, we put the model performance into a global context for TEP concentrations in the upper ocean layer. As such, the implementation of PCHO exudation, aggregation to TEP, and their remineralization processes into FESOM2.1–REcoM3 offers a reasonably good agreement with observations, on which further modeling work can build upon.